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Investigation of amperometric detection of phosphate Application in seawater and cyanobacterial biofilm samples
Abstract
Detection of phosphate using amperometry was investigated. The phosphomolybdate complex, formed by addition of nitric acid, ammonium molybdate and phosphate, was reduced at a carbon paste electrode polarised at +0.3V (versus Ag/AgCl). The major characteristics observed were simplicity of the equipment, a limited consumption of reagents and a low detection limit (0.3mumoll(-1)), with a linear range between 1 and 20mumoll(-1). The interference of silicate was completely eliminated using an appropriate concentration of nitric acid and ammonium molybdate. The amperometric detection of orthophosphate in seawater using the batch injection analysis (BIA) technique was reported. Moreover, a carbon paste microelectrode was constructed. Its use allows the analysis of small volume of samples with little dilution in supporting electrolyte. This method was applied to the determination of orthophosphate in cyanobacterial biofilms collected from Roman catacombs. There was a good statistical correlation between results obtained with the proposed method and the standard spectrophotometric method.
... For environmental monitoring of phosphate in highly saline waters, a number of researchers have turned their attention to development of amperometric sensor systems. Quintana and coworkers showed that phosphate can be detected amperometrically in seawater down to 0.3 mM levels (Quintana et al., 2004). This relies on the formation of a phosphomolybdate complex which is reduced at a carbon paste electrode held at þ0.3 V with respect to an Ag/AgCl reference electrode (Fig. 4A). ...
... Illustration of chemical sensors for phosphate detection in aquatic medium. (A) Schematic of the carbon paste microelectrode assembled in a glass capillary tube, adapted from(Quintana et al., 2004) with permission. (B) Schematic representation of the apparatus for continuous flow phosphate analysis, adapted from(Talarico et al., 2015) with permission. ...
Aquatic chemical sensors have experienced rapid development in recent years largely due to advances in the fields of nanotechnology. Accurate in situ monitoring of nutrients is fundamental to understanding the biogeochemistry of aquatic ecosystems and is necessary for the sustainable utilization of water resources. Although many sensor technologies can achieve nM detection levels, quality assurance and reliability for long-term sensing in complex environments is still lacking. Furthermore, some sensors suffer from sensitivity to high background ion concentration. This review aims to address these challenges by highlighting recent improvements in aquatic chemical sensors to monitor nitrate (NO3⁻), nitrite (NO2⁻), ammonium (NH4⁺), and phosphate (PO4³⁻) ion concentrations in water. The review critically analyses and compares the performance of these chemical sensors with a particular emphasis on their capability for long-term in situ water monitoring. We also provide an overview on some crucial problems significantly affecting the analytical performance of the sensors. Finally, this review details some recommendations and future directions for improving sensing accuracy and robustness.
... In rivers, orthophosphate concentrations vary greatly from 0.02 to 1 mg L −1 . (Quintana et al. 2004;Warwick, Guerreiro, and Soares 2013). In natural and waste waters orthophosphate concentration varies from 0.2 to 10 mg L −1 , while in soil it varies from 0.2 to 50 mg kg −1 (Warwick, Guerreiro, and Soares 2013). ...
... Although this improvement is promising, further investigation is still needed to lower the limit of quantification by a further order of magnitude (to ca. 0.01 ppm) for accurate monitoring of orthophosphate levels in natural waters that are not yet subject to eutrophication (Quintana et al. 2004;UK Environmental Agency 2012;Warwick, Guerreiro, and Soares 2013). ...
A phosphate-sensitive cobalt electrode was evaluated in detecting orthophosphate ions ( ) in ammonium lactate-acetic acid soil extracts. The dependence of the mixed potential of a cobalt electrode on concentration was investigated via potentiometry. The mechanism of detection is based on the consumption of a surface cobalt (II) oxide layer to form (Co3(PO4)2), which leads to a concentration-dependent shift of the mixed potential. Two reference electrodes were evaluated: Ag/AgCl (3 M) KCl and a platinum (Pt) wire. A linear response was observed using both reference electrodes. However, application of a Pt wire quasireference electrode increased the linear dynamic response range of the detector from 10–10³ mg L⁻¹ or 10⁻⁴–10⁻¹ M (Ag/AgCl (3 M) KCl) to 0.1–10⁵ mg L⁻¹ or 10⁻⁶–10¹ M. In addition, the response time using the Pt wire was less than 5 minutes compared to a minimum of 10 minutes using Ag/AgCl (3 M) KCl. There was close agreement between the response of the phosphate-sensitive cobalt electrode with a standard colorimetric method. As dissolved organic substances can potentially interfere with electrochemical techniques, an investigation into the use of a nonpolar resin for decolorization and removal of organic matter in soil extracts was carried out and successfully employed. The phosphate-sensitive cobalt electrode was found to be a fast method for the analysis of soil extracts with high sensitivity and selectivity. It has the potential to be developed into a sensor for the in situ measurement of phosphate in various environmental matrices.
... As an alternative to spectrophotometry, methods based on electrochemistry have also been proposed. Amperometric procedures have been reported for the determination of phosphate as phosphomolybdate complex [38][39][40]. Phosphate has been also determined by using voltammetric methods with carbon paste electrode [41], gold microdisk electrode [42] and glassy carbon electrode [43]. Different modifications were proposed to increase the sensitivity or eliminate the interferences from other coexisting molecules. ...
... Different modifications were proposed to increase the sensitivity or eliminate the interferences from other coexisting molecules. Applications of these methods are proposed but only [30] a few of them were used for natural analysis of water in laboratory conditions [39,40,44]. In spite of many advantages of voltammetric or amperometric methods, some serious problems may appear. ...
Phosphorus is an important macronutrient and the accurate determination of phosphorous species (namely phosphate) in environmental matrices such as natural waters and soils is essential for understanding the biogeochemical cycling of this element, studying its role in ecosystem health and monitoring the compliance with legislation. This paper is focused on phosphate determination in seawater. Thus, the sources, occurrence and importance of phosphate together with several aspects regarding the analysis and terminology used in the determination of this element in the ocean are briefly described. Existing and future in situ analytical techniques for the determination of phosphate in seawater are presented. Today’s in situ phosphate monitoring is dominated by different spectrophotometrical analyzers. Thus, a description of the basis, advantages and disadvantages of the different existing analyzers is provided. It seems that these techniques may be replaced in the near future by electrochemical sensors which provide excellent possibilities for phosphate determination with high precision, long lifetime, low detection limit and good reproducibility. Additionally, electrochemistry allows going further in miniaturization, provides a decrease in energy requirements and avoidance of additional reagents. Recently developed electrochemical methods for phosphate determination will lead to the first in situ autonomous sensor (ANESIS) which will fulfill all these expectations.
... It is usually present in the form of the orthophosphates (H 2 PO 4 − and HPO 4 2− ) in the range 0.01 -3 ppm in soil extracts. In rivers, the range is typically 0.02 -1 ppm, and in natural and waste waters 0.2 -10 ppm [47]. The Murphy and Riley molybdenum blue colourimetric method [48] based on the reduced phosphor-molybdenum blue complex is typically used to quantify soluble reactive phosphate because of its low limit of detection (LOD) (≤ 0.01 ppm), yet this is unsuitable for in-field testing over long time periods. ...
... Meanwhile, the reduction peaks observed around 0.3 and 0.13 V are likely due to the electrochemical reduction of Mo (VI) to Mo (IV) and Mo (IV) to Mo(II), respectively. 31,32 The mechanism of the electrochemical reduction reaction could be understood from eq 5 below, where the P−Mo complex formed in acidic media (eq 1) is reduced to mixed molybdenum oxidation states by gaining electrons in a multielectron process (eq 5). 33 The reduced Mo in the complex oxidizes back by losing electrons, giving rise to the oxidation peaks. ...
... Currentbased (amperometric) sensors that can detect phosphate in the submicromolar range require enzymes that can cause stability problems in environmental conditions [6]. Meanwhile, potentiometric sensors have a slightly better linear range than amperometric sensors [7][8][9]. Potentiometric sensors are widely used because their detection is quite fast, the instrument is simple and the manufacturing process is easy. Among potentiometric sensors, cobalt electrodes are very popular because they have several advantages such as no additional reagents, fast detection and easy miniaturization. ...
... To measure the ionic concentration of soil nutrients, several electrical and mechanical techniques, including spectroscopic, calorimetric [29], potentiometric, micro-and nanomechanical sensors, and electrochemical sensors, have been developed [28,[19][20][21][22][23]. Ion-selective electrodes are the earliest direct electrochemical detection available sensing techniques [30], which comprise the following division: coated wire electrodes, carbon paste electrodes [31], plant tissue electrodes [32], heterogeneous membrane electrodes, solid-state 1474 Page 2 of 12 J Mater Sci: Mater Electron (2023) 34:1474 membrane electrodes [33,34], liquid membrane electrodes, and redox exchange electrodes. It is the recent approach for sensing macronutrients and has the advantage of being far more portable and affordable to create than previously described sensing techniques [30,35,36]. ...
A solid-contact ion-selective electrode (ISE) was fabricated using zinc oxide/reduced graphene oxide (ZnO/rGO) nanocomposites as an intermediate layer between glassy carbon electrode (GCE) and ionophore. The resulting solid contact acts as an ion-to-electron transducer in potassium ion-selective electrode (K⁺-ISE) containing valinomycin as ionophore. The new transducing layer was characterized by using scanning electron microscopy (SEM), X-ray diffraction analysis, and cyclic voltammetry (CV) techniques. Hexagonal wurtzite phase of ZnO was revealed from diffraction analysis and the SEM images showed the formation of one-dimensional nanorods with hexagonal top surfaces. Validation of the sensing material was carried out using CV studies and the experimental studies showed that ZnO/rGO has a strong capability to function as a solid contact in the fabrication of K⁺-ISEs. Valinomycin-based ISE developed using ZnO/rGO showed a high sensitivity of 9.95 µA (µM)⁻¹ cm− 2 with a faster response time of ~ 2 s and limit of detection (LOD) of 0.956 mM. Interference studies, reproducibility, and long-term stability of the sensing material toward K⁺ detection were assessed and the results showed that the ZnO/rGO redox capacitance is favorable for solid contact as K⁺-ISE for real-time application in soil analysis.
... The formation of phosphomolybdate complexes requires acidic conditions which is not suitable for in-field monitoring. Sensors based on carbon and carbon-based nanomaterials were used in flow sensor formats, and these sensors generally required external reagent mixing [69,72]. A study proposed a glassy carbon electrode modified with ammonium 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 A c c e p t e d M a n u s c r i p t 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 A c c e p t e d M a n u s c r i p t ...
Phosphorus is required for plants and humans to survive because it is needed for cell signaling, skeletal integrity, energy storage, and metabolism. Phosphorus measurements are performed using colorimetric and electrochemical methods. Colorimetry is the most accepted method for commercial devices while electrochemical systems are still in the research phase. Here we provide the first comprehensive review of solid-state sensors for phosphate monitoring. The review focuses on solid state reagent storage for colorimetric sensors and different materials used in solid state electrochemical sensors. The electrochemical sensors are further classified into three groups: potentiometric, amperometric, and voltammetric. All sensors are evaluated based on parameters such as measurement range, limit of detection (LOD), working pH, and response time. Finally, we discuss limitations of the current sensors and future directions for the development of these sensors.
... Therefore, electrochemical methods provide a promising method for sensitive and on-site determination of phosphate in turbid coastal waters. To date, electrochemical methods have been widely applied to determine phosphate concentration in various water matrices, including mineral water (Talarico et al., 2015a), river water (Talarico et al., 2015b), canal water (Kolliopoulos et al., 2015), and seawater (Jonca et al., 2011(Jonca et al., , 2013Quintana et al., 2004), as shown in Table S1. However, the majority of researches have focused on the use of electrochemical methods for the determination of dissolved phosphate in water samples prefiltered through 0.45 µm membranes. ...
Phosphate is considered to be an important biogenic element and responsible for eutrophication in aquatic ecosystems, existing in both dissolved and absorbed forms. Due to the complex matrix of coastal seawater, a high sensitivity and anti-interference method for phosphate detection is required for environmental protection. In this study, a novel electrochemical method was proposed based on reduced graphene oxide-ordered mesoporous carbon screen-printed electrode (rGO-OMC/SPE) analysis, allowing sensitivity and reliable determination of phosphate in turbid coastal waters. Combining the good absorption capacity of OMC with the excellent electroconductivity of rGO, the fabricated electrode exhibits improved signal responses, enhanced by up to 43-fold. The platform was evaluated using turbidity interference test with good recovery percentages comprised between 96% and 105% in different phosphate concentration, and salinity interference test between 92% and 105%, respectively. A linear range from 0.2 to 150 μM phosphate was achieved, with a detection limit of 0.05 μM (s/n = 3). The fabricated platform was successfully used for on-site analysis of phosphate in turbid coastal waters. This reliable and effective method for the analysis of phosphate in turbid coastal waters allows for sensitivity and anti-interference determination, while also representing a significant step towards comprehensive and convenient analysis of phosphorus species.
... 26,27 Several analytical techniques have been utilized for the detection of phosphate ions and different phosphate containing compounds. 25,26 Such techniques vary from conventional absorption 28 and NMR ( 1 H and 31 P) spectroscopy 29 and electrochemical studies [30][31][32] (cyclic and square-wave voltammetry) to surface-based methods 26,33 (electron microscopy including SEM and TEM) to X-ray diffraction methods 34 ( powder and single crystal) to isothermal titration calorimetry (ITC), which provides quantitative information including enthalpy, entropy and free energy values for a binding event. 26,35 However, many such techniques suffer from various disadvantages including detailed instrumentation, sample preparation, only provisions for the solid-sample analysis and the requirement of dried samples that may not correctly represent the actual solutionbased species. ...
This review article presents a variety of luminescent chemosensors for the selective detection of assorted biologically relevant phosphates (phosphate ion, pyrophosphate ion and AMP, ADP and ATP) via the "Turn-On"emission mechanism. The focus has been placed to understand the design aspects, chemical structures and luminescence properties including binding constants, detection limits and lifetime parameters of the chemosensors and their emission enhancement based detection mechanism. The article concludes by addressing various future prospects both for the biological and the environmental challenges in front of the scientific community to develop intelligent chemosensors not only for detection purposes but also for remediation processes. This journal is
... Alternatively, again PMo12 chemistry [7,8] is capitalized to optimize electrochemical sensors. Phosphate, reacting with molybdate in acidic medium, forms PMo12, that can be determined by amperometric and voltammetric methods measuring currents of reduction and/or oxidation [15,16]. A non-conventional, autonomous and reagent-less device based on Mo-metal electrode was optimised by Jonca et al. [17]. ...
Inorganic phosphorous (as phosphate (PO4³⁻), is one of the essential nutrients for all living forms, either terrestrial or marine. In oligotrophic seawaters, this macronutrient is limited (10⁻⁹ M) and its ratio with other elements (nitrogen or carbon) is denoting the health state of the marine environment; a small variation of its concentration can produce eutrophication. The gold standard method used for PO4³⁻ detection is based on colorimetric detection of phosphomolybdate. The colored complex is obtained by mixing water-soluble molybdenum salts (Mo(VI)) and reducing agents in acid media, along with the sample containing PO4³⁻. Moreover, the kinetic of complex formation is slow, about 1 hour is generally required for color to develop, exposing the assay to the drawbacks of interferences as those from silica. The detection is preferably performed in a controlled environment (i.e. in a laboratory) because several chemicals and steps of preparations are required as well as the optical instrumentation is not intended for in-field use.
Electrochemical sensors offer portability and simplicity making them a practical option for on-site detection applications. To gain an analytical alternative in measuring low quantities of PO4³⁻ (10⁻⁹ M), and overcome some of the drawbacks from the classical approaches, we optimized a new easy way to produce a plastic electrode decorated with an alkyl Mo-polyoxometalate (Mo8O26⁴⁻), that is soluble in organic solvents. This tetra-butyl-ammonium octamolybdate powder, [N (C4H9)4]4 Mo8O26, purposely synthetized was identified with FTIR, Raman, MS methods, and the electroactivity and reactivity with PO4³⁻ was confirmed in solution with cyclic voltammetry (CV). When the Mo-decorated electrode was in contact with PO4³⁻, an electroactive phosphomolybdate aggregate formed at the electrode surface that was electrochemically detectable with square wave voltammetry (SWV). A remarkably low detection limit of 6.1 nM, to PO4³⁻, as well as good stability and selectivity were obtained also in real samples. In fact, PO4³⁻ was measured in saline simulated and real seawater samples at nM concentrations in less than 5 min. The current work provides a new alternative to the current standard colorimetric methods to detect low phosphate concentrations, showing the potential to be used for oligotrophic seawater nutrient monitoring applications.
... The targeted range chosen is 1.63-132. 8 μmol L − 1 and shows two linear behaviours with silicate concentration on Fig. 3. Calibration's slope changings have also been observed in the literature, as well as saturation of the signal at higher silicate or phosphate concentrations, using electroanalytical [37,[45][46][47][48] or colorimetric detections [29,49]. ...
An autonomous electrochemical sensor suitable for in situ silicate detection and monitoring in marine environments, is presented without any use of liquid reagent. This paper shows silicate sensor characteristics and figures of merit using optimized chemical and electrochemical parameters. Under controlled laboratory conditions in a 40 L tank, good calibration between 1.63 and 132.8 µmol L⁻¹ was obtained. The limit of detection and the limit of quantification obtained are respectively LOD = 0.32 µmol L⁻¹ and LOQ = 1.08 µmol L⁻¹. No bias was found while analysing Certified Reference Material (CRM) solutions i.e. natural seawaters samples with different salinities and nutrients compositions. Repeatability test showed very good reproducibility of the measurement with low overall uncertainty, cumulating systematic error and reproducibility error, of 2.4%. Accuracies obtained with the Silicate sensor are higher than 97.4%, 95.3% for the smallest concentration tested, under LOQ. Spike and recovery tests were conducted with two different CRM concentrations and showed 97.9-100.1% recovery, indicating no matrix influence in the determination of silicate concentration using electrochemical sensor and its calibration process (realised with artificial seawater solutions). In situ deployment of silicate electrochemical sensor was realized in the Thau lagoon (Mediterranean Sea) at 1.6 meters depth. A good agreement between the results obtained with the sensor compared to reference colorimetric measurements made at the Marine Station of Sète (France) validates sensor’s performances.
... The use of Amperometric sensors, that measure the current produced by the target analyte at an electrode with a constant voltage, has also been investigated widely (Beer et al., 1996(Beer et al., , 1997 showing some selectivity for dihydrogen phosphate and orthophosphate. Some involved measuring the reduction of the ammonium phosphomolybdate complex formed in the standard phosphomolybdate reaction (Quintana et al., 2004;Udnan et al., 2005) or anodic oxidation of molybdenum (Jonca et al., 2011), while others involved the use of electrodes embedded with ammonium molybdate (Berchmans et al., 2011). Others involved the use of phosphate sensitive enzyme electrodes, designed for potential environmental applications, and are able to detect orthophosphates down to 3 µg/L (Midgley, 1986;Engblom, 1998;Villalba et al., 2009;Rahman et al., 2006). ...
Phosphate detection in the environment (especially, water bodies) is very essential in view of its consequent pollution effects on eutrophication. Continuous monitoring of phosphate concentration (and phosphorus compounds in general) in water samples has been based on phosphomolybdenum blue formation coupled with spectrophotometric detection. Continuous flow injection analyses (FIA) are well known to present numerous advantages over batch methods. Furthermore, the development of on-chip micro-channel analytical (μFIA) systems begun and have gained much attention within the last two decades in view of the striking advantages over conventional FIA techniques. This paper reviews published information on detection of phosphomolybdenum blue in conventional systems as well as on micro-chip. It reports on the challenges encountered (interference from other complex anions), the achievements made so far (intereference removal by electrokinetic separation) and what the future holds (simultaneous determination).
... Since molybdenum-based substances selectively form electrochemical active complexes with phosphate ions, they have been used for the detection of phosphate in the literature (Quintana et al. 2004;Jo nca et al. 2011;Kolliopoulos, Kampouris, and Banks 2015;Cinti et al. 2016;Arvas et al. 2018Arvas et al. , 2019. However, only one species of the phosphate was detected in these studies. ...
... Therefore, sensitive and selective detection of phosphate content in water samples are required. So far, a number of methods have been developed for the determination of phosphate ion, including electrochemical methods [6][7][8], colorimetry [9], chemiluminescence [10], plasma mass spectrometry [11] and bio-sensing approaches with amperometric [12] or fluorescence [13] detection modes. Some of these methods also involve expensive equipments and need complicated procedure. ...
A new sensing solution for the colorimetric determination of PO4³⁻ in drinking water samples was developed. The sensing solution composed of silver nanorods in the absence of PO4³⁻ ions. Mixing the sensing solution and high concentration of PO4³⁻ the growth and formation of silver nanorods are suppressed, and the colour of the solution was changed from wine colour to yellow. The wavelength shift of the sensing solution in the presence and absence of PO4³⁻ was monitored for PO4³⁻ quantification. Colorimetric determination of PO4³⁻ revealed the limit of detection (LOD) of 0.076 μM and 0.12 μM in the absence and presence of all interferences, respectively.
... Since phosphate plays an important role in the soil and groundwater sediments both for uranium and living organisms as well as to ensure consistent water quality, the phosphate concentration should be quantified and monitored in order to deploy the right quantity for remediation. Throughout the years, these factors encouraged the scientists to investigate methods for phosphate detection [22][23][24][25][26][27][28][29]. Up to now, several sensor technologies for monitoring phosphate species have been implemented. ...
... CalvoQuintana et al. [52] in the potential range of 0.5 to 0 V versuss SCE. Although, this region is referred as uncomplicated amperometric analysis region, it is mentioned that the peak at lower potential is difficult to reproduce due to apparent adsorption [53]. ...
In this study, simple and a rapid solvent extraction method is investigated to recover Mo(VI) from simulated HLLW. The (NH 4) 6 Mo 7 O 24 ·4H 2 O dissolved in 3 M HNO 3 was treated with ascorbic acid and KSCN to form orange red colored Mo(V)-SCN. Reduction of Mo(VI) was confirmed by cyclic voltammetry. The freshly formed complex was completely extracted to ethyl acetate layer. The organic solvent could be recovered using rotary evaporator. The Mo-complex disproportionated gradually to form a yellow solid, Mo(OH) 2 (SCN) 3 ·6H 2 O, which forms MoO 3 @ 400 °C. The solid product was characterized by XRD, FT-IR, EDX, TG-DSC and SQUID measurements. Graphic abstract KSCN 10 mM Mo(VI) in 3 M HNO 3 AA Mo(OH) 2 (SCN) 3 6H 2 O Extracted to Ethyl acetate phase After 5 min Evaporation to dryness MoO 3 400 0 C
... CalvoQuintana et al. [52] in the potential range of 0.5 to 0 V versuss SCE. Although, this region is referred as uncomplicated amperometric analysis region, it is mentioned that the peak at lower potential is difficult to reproduce due to apparent adsorption [53]. ...
In this study, simple and a rapid solvent extraction method is investigated to recover Mo(VI) from simulated HLLW. The (NH4)6Mo7O24·4H2O dissolved in 3 M HNO3 was treated with ascorbic acid and KSCN to form orange red colored Mo(V)-SCN. Reduction of Mo(VI) was confirmed by cyclic voltammetry. The freshly formed complex was completely extracted to ethyl acetate layer. The organic solvent could be recovered using rotary evaporator. The Mo-complex disproportionated gradually to form a yellow solid, Mo(OH)2(SCN)3·6H2O, which forms MoO3 @ 400 °C. The solid product was characterized by XRD, FT-IR, EDX, TG–DSC and SQUID measurements.
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... However, they resulted in a decrease of the response to AA and UA of ca. 30%, and thus, recovery studies were employed with the standard addition method [30]. The interference effect of other urinary compounds such as glucose (1 mM), urea (50 mM), creatinine (1 mM), and oxalates (1 mM) was also examined with measurements at mixed solutions containing 1 mM AA and 0.1 mM UA. Taking as criterion a ±10% error in the peak current magnitude, none of the examined compounds interfered. ...
Graphite screen-printed electrodes (SPEs) were modified with gold nanoparticles (AuNPs) produced by electric spark discharge between the SPE and a gold-silicon eutectic alloy (eAu/Si) tip electrode, under atmospheric conditions at 1.2 kV DC using a fully automated procedure. The automation was based on a 3D positioning device, which allowed to precisely adjust the sparking distance and to achieve regular spacing of a predetermined number of sparks across the surface of SPEs (d = 3 mm) by controlling the movement of the eAu/Si tip. Moreover, the effect of voltage-time characteristics of the produced discharges on the morphological and electroanalytical properties of the sparked-modified SPEs was investigated by setting the values of capacitors in the high voltage multiplier cascade, and at the power supply output. It is shown that under specific variables the underlying carbon layer is not appreciably damaged by the spark discharges and does not contribute to electrochemical responses of sparked SPEs, i.e., the active electrode surface has been entirely covered by AuNPs. Sparked surfaces were extensively characterized by scanning electron microscopy and various electrochemical techniques, while the electroanalytical utility of eAu/Si-sparked SPE was investigated with ascorbic acid as a pilot analyte. Advanced electrocatalytic activity is documented by an extreme shift of ascorbate oxidation overpotential (E p = 89 mV at eAu/Si-sparked SPE) with respect to both bare SPE (E p = 503 mV) and bulk gold electrode (E p = 358 mV). Simultaneous differential pulse voltammetric sensing of ascorbic and uric acids in human urine is also demonstrated.
... Carbon paste electrode 29 Amperometric 10 −6 -2 × 10 −4 3 × 10 −7 Glassy carbon electrode 30 Amperometric 7.9 × 10 −7 -3.15 × 10 −5 7.9 × 10 −7 1:12 phosphomolybdic film modified glassy carbon electrode 31 Cyclic Volta-mmetry 7 × 10 −6 -8 × 10 −5 8.7 × 10 −7 Screen-printed electrode modified with carbon black nanoparticles 32 Amperometric 5 × 10 −6 -10 −4 1 × 10 −7 Molybdenum-based electrode 21 Potentimetric 10 −5 -10 −1 1.9 × 10 −6 Cobalt-based electrode 7 Potentimetric 10 −5 -10 −2 5 × 10 −6 Tungsten-based electrode (this study) Potentimetric 10 −6 -10 −1 4.1 × 10 −7 ...
We describe a novel, tungsten-based potentiometric electrode for measuring phosphate (HPO42-) concentration in aqueous solutions. The Nernst-like potential response of this sensor is linear in a concentration range between 1.0×10 −6 and 1.0×10 −1 M, with a slope of −29.9 ± 0.2 mV/decade (at a pH of 10). The sensor has a response time of <1min and is capable of being used for more than eight weeks without maintenance and change in slope. It combines the advantages of good reproducibility, excellent selectivity and fast response time. Therefore, it can potentially be applied for in situ monitoring of phosphate concentration in surface and in interstitial waters under a wide range of environmental conditions.
... The procedure showed good repeatability (RSD < 4 %) and low limit of detection (10 mmol L À1 ). Quintana et al. [76] developed a CPE modified with phosphomolybdate complex for amperometric detection of phosphate in seawater and cyanobacterial biofilm samples. The LOD and linear range of this sensor were estimated as 0.3 mmol L À1 and 1 to 20 mmol L À1 , respectively. ...
Since the development of batch-injection analysis (BIA) in 1990, the technique has been constantly upgraded, especially for electrochemical systems, including the creation of novel cell designs and association with new accessories to cover a wide range of applications. BIA systems have provided faster, portable, and more precise analyses. In addition, application of new materials as working electrodes provide improvement on sensitivity and selectivity, resulting in unique advantages for such analytical systems. This review focuses on the most recent advances of BIA systems, including the evolution of designs and materials used to construct BIA cells, with special emphasis to novel materials applied for improved electrochemical sensing. Modified electrodes with inorganic and organic nanomaterials on different substrates, including disposable platforms (screen-printed electrodes and paper-based devices) are highlighted. Boron-doped diamond electrodes (BDDE), carbon-nanotube and graphene-modified electrodes have been combined with BIA systems for a wide range of applications that demand on-site analyses.
... The LOD of the sensor is 4 mM with a wide linear range up to 300 mM. Electrochemical sensors detected phosphates ions by quantifying the anodic oxidation of molybdenum 213 or reducing the phosphomolybdate complex 214,215 have also been reported. These indirect voltammetric methods usually require reagents and have a working range between 0.02 to 1 mg L −1 . ...
Nutrients such as nitrogen and phosphorus are key indexes in evaluating water eutrophication. Electronic sensors, i.e., potentiometric sensors, voltammetric sensors, and field-effect transistor (FET) sensors, that rely on electrical signals (e.g., potential, current and resistance) have shown unique properties and capabilities in detecting nutrients. Compared with conventional methods, these electronic sensors enable a rapid and low-level detection of nitrogen salts and phosphates in water. Over the past decades various sensor designs and sensing elements have been studied and reported. With the development of nanomaterials, the performance of electronic sensors has been further improved, presenting tremendous opportunities for detecting nutrients and other water contaminants. This review article will introduce the recent progress of electronic sensors in detecting nitrogen salts and phosphates, and will discuss current limitations and future directions for these sensors.
... Pathogenic bacteria could be detected using affinity-based biosensors [5], electrochemical [6], affinity-based magnetic nanoparticle [7][8][9][10][11] and others [12][13][14][15][16][17]. These techniques could be classified to biosensor technique for whole-cell or techniques that detect or biosensing a target analyte inside the cell [18]. The first strategy is difficult as it required detection of large size species (micrometer scale) than typical molecular analytes such as cell biomolecules including protein, DNA, RNA and others. ...
Selective biosensing of Staphylococcus aureus (S. aureus) using chitosan modified quantum dots (CTS@CdS QDs) in the presence of hydrogen peroxide is reported. The method is based on the intrinsic positive catalase activity of S. aureus. CTS@CdS quantum dots provide high dispersion in aqueous media with high fluorescence emission. Staphylococcus aureus causes a selective quenching of the fluorescence emission of CTS@CdS QDs in the presence of H2O2 compared to other pathogens such as Escherichia coli and Pseudomonas aeruginosa. The intrinsic enzymatic character of S. aureus (catalase positive) offers selective and fast biosensing. The present method is highly selective for positive catalase species and requires no expensive reagents such as antibodies, aptamers or microbeads. It could be extended for other species that are positive catalase.
... mM PO 4 3− in adult human serum [3]. Various detection strategies for phosphate have been developed, which include phosphate ion selective electrodes, amperometry, chromatography, flurometry, colorimetry, spectroscopy and enzymatic biosensors [4][5][6][7][8][9][10][11][12][13][14][15][16][17]. Most manual and automated methods of phosphorus determination are based on the reaction of phosphate with an acidified molybdate reagent to yield phosphomolybdate heteropolyacid. ...
... Several electroanalytical tools have been reported in literature, exploiting different techniques and electrodes such as amperometric multienzymatic sensors [12], ion selective and membrane enzyme-based electrodes [13], plant tissue electrodes [14], carbon paste electrodes [15], gold rotating disk electrodes [16], cobalt wire electrodes [17], cobalt phthalocyanine-modified screen-printed electrodes [18]. However, the colorimetric method developed by Murphy and Riley [19] remains the most used, and the only one recommended by the Environmental Protection Agency (EPA). ...
... The phosphate concentration will be proportional to the absorbance measured at 831 nm [13]. An amperometric measurement of phosphate in seawater and cyanobacterial biofilm samples has been developed by our group through batch analysis technique [14]. The method, based on the amperometric reduction of phosphomolybdate at a carbon paste electrode (CP) polarised at +300 mV (versus Ag/AgCl), allowed to overcome the problem arisen from the chemical reduction by means of ascorbic acid used in the colorimetric reaction. ...
The final aim of this work is the realization of an automatic system based on amperometric measurements able to detect the phosphate in absence of the operator, thus in remote mode control, using automatic valves leaded by a software. The SPEs (screen-printed electrodes) thank to their small size and long term stability, can be easily embedded in a flow system for continuous in situ analysis. Gold nanoparticles (AuNPs), carbon black (CB) and both of them have been used to obtain 'composite' (CB/AuNPs) for modifying the SPEs. The different types of sensor (SPE-AuNPs, SPE-CB and SPE-CB/AuNPs), obtained by drop casting technique, were challenged towards phosphate in order to investigate the electrochemical performances. The optimization of the operative parameters for the phosphate detection has been carried out first via batch measurements and in the second step, the flow system has been assembled and re-optimized. The amperometric method developed in this work is able to detect phosphate in a linear range from 20 to 80 μM with detection limit equal to 6 μM (calculated as 3σ/ slope). Moreover, the system was challenged toward tap, river and lake water samples and compared to the colorimetric reference method; a good concordance of the results confirmed that the method is able to detect phosphate also in a complex matrix such as River water.
... As an alternative to spectrophotometry, methods based on electrochemistry have also been proposed. Amperometric procedures have been reported for the determination of phosphate as phosphomolybdate complex (Fogg and Bsebsu, 1981;Harden and Nonidez, 1984;Quintana, 2004). Phosphate has been also determined by using voltammetric methods with carbon paste electrode (Guanghan et al., 1999), gold microdisk electrode (Carpenter et al., 1997) and glassy carbon electrode (Matsunaga et al., 1986). ...
Developing new sensors for improving our understanding of the coupled biogeochemical cycles constitutes an immense challenge. Electrochemistry provides promising reagentless methods by going further in miniaturization, decreasing the response time and energy requirements and thus increasing our observing capacities in the ocean. This study is focused on phosphate and oxygen, two key compounds of the marine ecosystems. Improvement of the amperometric STOX sensor for ultra-low oxygen detection in seawater is presented. The improvement was achieved by changing sensor construction and preliminary studies showed higher sensitivity and faster response time. A novel electrochemical method for phosphate detection was developed. The method is based on anodic oxidation of molybdenum in seawater in order to form the phosphomolybdic complex, electrochemically detectable by means of amperometry or voltammetry. Thanks to special construction of an electrochemical cell including specific membrane technology, the method does not require addition of reagents and is free from silicate interferences. The method was tested during Pelagico 1011- 12-BIC OLAYA cruise offshore Peru in 2010. The Peruvian water masses analysis was also performed using data collected during this cruise
Stably retaining the water-soluble molybdate within electrodes is of great significance in phosphate analysis. This study fabricated an [Omim]6Mo7O24 carbon paste electrode (OCPE), which was able to effectively retain molybdate in the aqueous solution. The electrochemistry of phosphate at the surface of the OCPE was studied using cyclic voltammetry (CV). The voltammograms showed three reversible redox peaks corresponding to the redox of Mo(VI/V) as well as several irreversible peaks involving the formation of hydrogen molybdenum bronze. The currents of all three reversible redox peaks linearly varied versus phosphate concentrations in 0.1 mol·L−1 H2SO4-KCl. After optimizing the mass ratio of the [Omim]6Mo7O24 and carbon powder, peak C6 shows a wide linear range (1.0 × 10–2–1.0 × 10–7 mol·L−1; R2 = 0.9970) with a sensitivity of 5.3 (± 0.1) μA/μM. The limit of detection (LOD = 3σ/s) was 8.5 × 10–8 mol·L−1. Interferences from common anions, silicate, and glyphosate on phosphate analysis were also investigated. The proposed sensing method was successfully applied to the determination of phosphate in tap water, whose results were verified with ion chromatography (IC).
In this paper, a novel Schiff base ligand NaHL (NaHL = sodium (S,E)-2-((4-chloro-2-hydroxybenzylidene) amino) propanoate) was designed and synthesized, and three novel complexes with Zn(ii) were obtained by a solvent evaporation technique. Single crystal X-ray diffraction indicated that [Zn(L)(H2O)]n1 and [Zn(L)(H2O)]n2 were one-dimensional coordination polymers (CPs) with a helix structure, while [Zn2(L)2(bipy)] 3 was a two-dimensional CP with the participation of an auxiliary ligand. Fluorescence spectra exhibited that 1 and 2 had good fluorescence properties in both solution and solid states, but 3 was basically quenched due to the addition of ancillary ligands in the solid state. Density functional theory (DFT) calculations have been performed to further reveal the intrinsic fluorescence properties and mechanisms of 1 and 2, which demonstrated the chelate fluorescence enhancement effect (CHEF). Moreover, 1 and 2 show selective recognition of NH4⁺ and HPO4²⁻ accompanied by an efficient fluorescence “turn off” phenomenon, and a series of related experiments demonstrate that 1 and 2 were fully quenched through the removal of Zn²⁺ from the complex and the protonation of the ligand.
Today, easy availability and efficient detection assays in low-resource settings are mandatory. Therefore, a smartphone-assisted paper-based detection strategy using eosin Y (EY)-embed ZIF-8 nanocomposite for phosphate (Pi), neutral red (NR) and heparin (HP) on site testing was fabricated. After adding the targets in a specific order, the prepared strips produced brilliant color transitions (astonishing colors, ranging from pistachio to bright yellow for Pi, from bright yellow to jacinth for NR and from jacinth to light orange for HP). These variation on tonality can be evaluated by the smartphone-based readout device (Color Assist App) through the ratio change of B/(R + G + B), which exhibits superior performance of on-site detection in wastewater, including high sensitivity (LOD is 0.015, 0.031 and 0.014 mM for Pi, NR and HP, respectively), ultra-fast response time and excellent selectivity. This strips and smartphone dual-mode monitoring strategy may offer a convenient idea to identify Pi, NR and HP, with great prospects for environmental wastewater applications. Additionally, the probe was enabled for bioimaging of Pi, NR and HP in living cells. Finally, the related anti-counterfeiting fluorescent ink of probe was proposed on schedule.
This work designed ammonium heptamolybdate (AHM) preloaded on a polyaniline (PANI)/coconut shell-derived carbon (CC)/poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF) composite flexible film electrode. The as-prepared novel [email protected]/CC/PVDF composite film electrode allowed to the selective and sensitive determination of phosphate in river water samples. The optimized [email protected]/CC/PVDF film delivered excellent ionic conductivity (6.58 × 10⁻⁵ S cm⁻¹). The analysis of the flexible composite matrix film confirmed the presence of three AHM redox couples, and their formal potential, peak potential difference, and surface coverage (τ) were calculated. The [email protected]/CC/PVDF film comprised an excellent microenvironment for phosphate (H2PO4⁻) detection, while the resulting electroactive phosphomolybdic complex species were stabilized by the composite matrix. The product of phosphomolybdic complex was electrochemically reduced at +0.25 V vs. saturated calomel electrode (SCE). The Keggin-type phosphomolybdic complex on the composite film was ex-situ examined by elemental mapping, X-ray diffraction pattern and X-ray photoelectron spectroscopy. From the spectroscopic studies individual composite materials interaction with molybdate mechanism provided. The [email protected]/CC/PVDF film electrode revealed a good phosphate detection concentration range of 10 – 114 µM, and it exhibited a low detection limit (0.6 µM). Besides, [email protected]/CC/PVDF was used to analyze a tap and river water sample and validated the obtained data through the spectrophotometric method which yielded an excellent recovery range (101.3% – 113.3%).
Determination of phosphate ions in aqueous solutions attracts a great deal of interest in the areas of environment, medicine, and agriculture. As phosphoric acid is a poly basic acid, the different forms of existence at different pH result in direct determination facing a big challenge. Herein, we reported a potentiometric phosphate ion sensor based on a surface-modified tungsten electrode. Pure tungsten was electrodeposited at a constant potential of 0.2 V versus Ag|AgCl in Na2HPO4. WO3 and H3O40PW12·xH2O were electrodeposited on the surface of the tungsten electrode. The modified tungsten electrode was used as a working electrode in a two-electrode system to detect the concentration of phosphate ions in aqueous solutions. The detection limit of the modified tungsten electrode for phosphate ions is 10–6 M from pH 7 to pH 8 and 10–5 M from pH 9 to pH 10. It has good selectivity to other common anions. The long-term monitoring experiment showed that the potential fluctuation was less than ±3 mV in 24 h. Compared to conventional determination methods, the current phosphate ion sensor showed a close value in a real sample. The mechanism of phosphate ion response was investigated in detail. This sensor possesses advantages of simple manufacture, low cost, a wide pH range for detecting, and good selectivity.
Monitoring the spatio-temporal distribution and concentration changes of nutrients in marine environments is significant for the protection of marine ecosystems. Electrochemical technologies are ideal candidates for marine nutrient monitoring systems with the advantage of miniaturization, low reagent consumption, and easy combination with automation devices. This review assesses nutrient determination (including nitrate, nitrite, ammonium, phosphate, and silicate) using electrochemical technologies, focusing on methods for analysis of coastal, estuarine and marine water, or with specific salinity effects. The research principles, laboratory methodology and in situ application of devices are summarized. In particular, this review focuses on the response mechanism, sensitivity and detection limit of the reported sensors, with reports on in situ instruments also reviewed. Overall, this review summarizes the advances in knowledge in terms of the modes of action of devices and deployment strategies, identifying the current limitations and future challenges for the electrochemical detection of nutrients in marine environments.
In this paper, ultrasensitive electrochemical determination of phosphate in water is achieved by hydrophilic TiO2 modified glassy carbon electrodes for the first time. Differential pulse voltammetry (DPV) method is proposed to measure phosphate in water as pulse techniques offer higher sensitivity compared with conventional cyclic voltammetry (CV) method. Hydrophilic TiO2 films were obtained upon ultraviolet (UV) illumination after TiO2 precursor emulsions coatting on the surfaces of glassy carbon electrodes, and used for phosphate determination. Contact angle measuremment (around 23.4°) proved the good hydrophily of the TiO2 modified surface upon UV illumination. A detection limit of 0. 1 μg L-1 is obtained , and a linear reationship (R2=0.99) between phosphate concentration (ranging from 0.1 μg L-1 to 1 μg L-1 ) and the peak current was observed.
A method based on Digital Image Analysis (DIA) is described to quantify pH and phosphates simultaneously in eye drops for the treatment of glaucoma and dry eye syndrome. In this work, images acquired with a smartphone were used. For phosphate determination, the colorimetric reaction that uses ammonium molybdate and antimony potassium tartrate was used. The formed blue complex was quantified using the R channel of the RGB color space. The pH was measured using bromothymol blue indicator, which gives a color between yellow and blue. The information of the pH measurement was extracted from histograms of the pictures and a PLS model was performed to quantify the values. All solutions were placed in microtitration wells in which less than 400 μL of sample are necessary and up to 92 samples can be measured in a single image.
The method shows good linearity (R²= 0.9962) for phosphates between 5.0·10⁻⁶ and 3.0·10⁻⁵ mol L⁻¹. Inter and intra-day precision were less than %12.8 (RSD) and LOD and LOQ were between 1.8·10⁻⁶ mol L⁻¹and 5.6·10⁻⁶ mol L⁻¹respectively. For pH, the color change of the indicator gives good results between 4.99 and 9.02 values. The RMSEC and REMSEP values of the PLS models were between 0.103 and 0.462 respectively with four components. Inter and intraday precision were less than %12.2 in terms of RSD. Phosphates and pH were determined simultaneously in different eye drops and the results were validated using reference method such as potentiometry (pHmeter) and ion chromatography.
A novel type of electrochemical sensor for detection of phosphate in water environment was developed by combining the interfacial barrier of p-n junction with the adsorption of phosphate. The electrochemical response was produced by the induced change of the barrier height, which was only caused by the specific adsorption of phosphate. Two linear concentration ranges (0 - 0.045 mg·L-1 and 0.045 - 0.090 mg·L-1) with two sensitivities (4.98 µA·(µg·L-1)-1 and 1.28 µA·(µg·L-1)-1) were found. The good performance made the sensor meet the requirements of the World Health Organization for drinking water (1 mg·L-1 of phosphate) well. It is an approach to develop electrochemical sensors by employing the interfacial barrier effects on electrochemistry.
Environmental pollution has always been a global concern, e.g. water eutrophication caused by the high concentrations of phosphorous. It is especially important to detect harmful substances conveniently, quickly and accurately. This study reports a free-standing electrode composed of Ni foam (NF) and in situ grown nanoflakes and nanoflower-like Ni hydrated hydroxide (NHH) on the NF surface (NHH/NF) by a one-step hydrothermal method for phosphate detection. The NHH/NF electrode was directly applied as a binder-free and conductive agent-free working electrode in a three electrode system and showed a wide linear detection range of 10-50,000 μM, high sensitivities of 210 and 87 μA mM-1 cm-2 for the phosphate concentration ranges of 10-14,000 and 14,000-50,000 μM, respectively, and a fast response time of 6 s for phosphate detection in a NaOH solution (pH≈11). The nanostructure of the NHH layer not only provided a large surface area and rapid electron transfer but also protected the NF substrate from being degraded by the electrolyte and interfering species, thereby achieving good stability and selectivity. In addition, for artificial and real wastewater detection, the good recover ability presented here improves the prospects of developing a cost-effective, simple, and accurate sensor for phosphate detection.
Biofilms affect many industries and our daily lives. Their formation and growth processes have common essential factors, but some of their components differ from one environment to another. Biofilms have a negative side in that they cause many problems. However, on a positive note, they provide benefits if used properly and effectively. Therefore, it is very important to be able to control biofilm formation and growth. In this chapter, we describe future trends for the research and applications of biofilms and the types of results that we can expect.
Molybdenum blue was electrodeposited on a pencil graphite electrode (PGE) with cyclic voltammetry and used for detection of phosphate for the first time in the literature. The surface of the modified electrode was coated with polyvinyl chloride to improve the stability of the electrode. Prepared electrodes were characterized by electrochemical and microscopic methods. Parameters affecting the analytical response of the electrode in differential pulse voltammetry such as concentration of supporting electrolyte, immersion time, operation temperature and thickness of film were optimized before the analysis of a soil sample containing phosphate. The prepared electrode exhibited high sensitivity for phosphate. Limit of detection (LOD) and limit of quantification (LOQ) were determined as 2.19×10-8 M (S/N=3) and 7.30x10-8 M (S/N=10), respectively. Quantification of phosphate in soil samples was confirmed by spectroscopic analysis.
Phosphate is not only an important indicator for aquatic ecosystems, but also plays vital roles in biosystems. A new strategy for ultrasensitive and selective detection of phosphate is fabricated based on a new insight found in this paper, which a lower concentration of surfactant sodium dodecylbenzenesulfonate (SDBS) can greatly induce fluorescence resonance energy transfer (FRET) from ciprofloxacin (CIP) to Eu3+ in the CIP-Eu3+ complex. Surfactant SDBS does not act as a sensitizer for enhancing the fluorescence intensity of the system, while acts as a sensitizer of FRET and make the native fluorescence of CIP quenched completely (switch off). Eu3+ ions can coordinate with the oxygen-donor atoms of phosphate, which weakens FRET from CIP to Eu3+ and results in the fluorescence recovery of CIP (turn on). The multi-complex of the CIP-Eu3+-phosphate has more sensitive fluorescent response than that of the reported coordination nanoparticle-based fluorescent probes. The LOD (S/N=3) of this sensing system can attain 4.3 nM. The possible interferential substances existed in environmental samples, such as 17 common metal ions, 11 anions and fulvic acid investigated do not interfere with the phosphate detection. This sensing system has been successfully applied for the phosphate detection in environmental samples such as wastewater, surface water and atmospheric particulates. This work not only develops a fluorescent probe for the phosphate detection, but also provides a new strategy for designing fluorescent probes based on FRET or coordination nanoparticle-based.
Determination of phosphate ion (PO4³⁻) is important in biomedical and environmental arrays because its controlling concentrations are associated with different pathologies or the quality of water. Herein, we report a new type of photoluminescence (PL) probe for highly selective detection of PO4³⁻ based on a single-layered graphene quantum dots chelating with aluminium ions (s-GQDs-Al³⁺) system. The PL of s-GQDs can be enhanced by Al³⁺ through the aggregation-induced emission enhancement (AIEE) effect. With the addition of PO4³⁻, the PL of the s-GQDs-Al³⁺ system is faded away because PO4³⁻ has stronger coordination with Al³⁺ which results in the elimination of AIEE effect and the decrease in the PL intensity of the s-GQDs-Al³⁺ system. Therefore, the s-GQDs-Al³⁺ system can behave as an on-off type PL probe for PO4³⁻ detection. It is found that the PL intensity ratio (I/I0) of s-GQDs in the presence of Al³⁺ at 463 nm is proportional to the concentration of PO4³⁻ in the range of 0.25–7.5 μM with the limit of detection as low as 0.1 μM. This selective assay has a great application prospect in the complex matrixes owing to its simplicity and specificity for PO4³⁻ detection.
Using Zn(2+)-BPMP or Cu(2+)-BPMP as a receptor and o-mercaptophenol as an indicator, potentiometric sensing of aqueous phosphate by competition assays was achieved. With attractive features of portability, low cost and resistance to interference from turbidity and color, this sensor was successfully used for phosphate detection in biological and water samples.
In this chapter, electrochemical sensors and biosensors for the analysis of inorganic nonmetallic analytes, comprising selected inorganic anions, such as nitrate, nitrite, sulfate, cyanide, and hydroxyl, cations (H+, NH4+, N2H5+), and inorganic molecules (O2, H2O2, and common toxic gases like H2S, SO2, NOX, and Cl2) of environmental importance are presented. Additionally, some other species from the individual categories will be shortly presented throughout the text in an effort to cover briefly most analytes which deserve some attention with respect to their environmental occurrence and possible impact on the biosphere.
The aim of this paper is to introduce a virtual special issue that reviews the development of analytical approaches to the determination of phosphorus species in natural waters. The focus is on sampling and sample treatment, analytical methods and quality assurance of the data. The export of phosphorus from anthropogenic activities (from diffuse and point sources) can result in increased primary production and eutrophication, and potentially the seasonal development of toxic algal blooms, which can significantly impact on water quality. Therefore the quantification of phosphorus species in natural waters provides important baseline data for studying aquatic phosphorus biogeochemistry, assessing ecosystem health and monitoring compliance with legislation.
Molybdenum oxide (MoOx) is a well-studied transition-metal semiconductor material, and has a wider band gap than MoS2 which makes it become a promising versatile probe in a variety of fields, such as gas sensor, catalysis, energy storage ect. However, few MoOx nanomaterials possessing photoluminescence have been reported until now, not to mention the application as photoluminescent probes. Herein, a one-pot method is developed for facile synthesis of highly photoluminescent MoOx quantum dots (MoOx QDs) in which commercial molybdenum disulfide powder and hydrogen peroxide (H2O2) are involved as the precursor and oxidant, respectively. Compared with current synthesis methods, the proposed one has the advantages of rapid, one-pot, easily prepared, environment friendly as well as strong photoluminescence. The obtained MoOx QDs is further utilized as an efficient photoluminescent probe, and a new off-on sensor has been constructed for phosphate (Pi) determination in complicated lake water samples, attributed to the fact that the binding affinity of Eu3+ ions to the oxygen atoms from Pi is much higher than that from the surface of MoOx QDs. Under the optimal conditions, a good linear relationship was found between the enhanced photoluminescence intensity and Pi concentration in the range of 0.1–160.0 μM with the detection limit of 56 nM (3σ/k). The first application of the photoluminescent MoOx nanomaterials for ion photochemical sensing will open the gate of employing MoOx nanomaterials as versatile probes in a variety of fields, such as chemi-/bio-sensor, cell imaging, biomedical and so on.
Abstract Herein, the facile method with high selectivity for phosphate ion (Pi) sensing using novel Type-II core/shell Mn: ZnTe/ZnSe quantum dots (QDs) was reported. This was the first time that Mn: ZnTe/ZnSe QDs with highlighted optical properties were used for sensing. The water-soluble Mn: ZnTe/ZnSe QDs with a high quantum yield of 7% were synthesized by aqueous synthetic method. Compared with traditional ZnSe QDs or Mn: ZnSe QDs, the smaller effective band gap, longer wavelength and lower ionization potential (high valence band edge) for effective hole localization made Type-II core/shell Mn: ZnTe/ZnSe QDs to be stable and had high photoluminescence (PL). Only Mg2+ was found to be able to enhance Mn: ZnTe/ZnSe QDs PL selectively. The mechanism of fluorescence enhancement was attributed to the passivated surface nonradiative relaxation centers of Mn: ZnTe/ZnSe QDs. In the presence of Pi anion, the PL intensity got quenched due to the aggregation species of QDs via electrostatic attraction between Pi and Mg2+ on the surface of Mn: ZnTe/ZnSe QDs. Therefore, the quenching effect can be used to detect Pi selectively. The PL was observed to be linearly proportional to the Pi analyte concentration in the range from 0.67 to 50.0 μmol/L, with a detection limit of 0.2 μmol/L (S/N=3). The novel "on-off" fluorescence nanosensor for Pi detection was sensitive and convenient in the real analysis application. The reported analytical method of Mn: ZnTe/ZnSe QDs is highly sensitive and selective, which can corroborate the extension of its usages in chemo/ biosensing and bioimaging.
Biofilm-forming cyanobacteria are widespread inhabitants of exposed stones in archaeological and historical sites and caves. Outdoors, these phototrophic biofilms are adapted to all types of stress imposed by growth at the air-rock interface and have developed the capacity to tolerate excess solar radiation, extreme temperatures and desiccation at different latitudes. Indoors, the typology of the cave or the characteristics of confined environments strongly selects the microbial community according to light availability and air humidity. Interactions of cyanobacteria with rocky substrata serving as the source of mineral nutrients are based on the adhesion mechanisms and metabolic processes that allow the development of these biofilms. Both types of subaerial phototrophic community include cyanobacteria that support associated populations of heterotrophic populations of mostly very specialized species. The distribution of particular cyanobacterial taxa on monuments in urban or agricultural areas is related mostly to climatic conditions and the position and orientation of the hard surface with respect to water availability and air circulation. The chapter provides an overview of the more recent studies on free-living subaerophytic cyanobacteria causing discolouration and erosion of lithic faces. Emphasis is on the biodeterioration of artworks due to physical and chemical processes caused by the growth of epilithic and endolithic organisms. The methods used for studying cyanobacterial communities on rocks and buildings of historic and artistic value are summarized, with the focus on conservation issues. Study techniques which are non-invasive of the underlying substrata are essential and it is important to identify the biodeteriogens responsible for the damage.
The accelerated eutrophication of most freshwaters is limited by P inputs. Nonpoint sources of P in agricultural runoff now contribute a greater portion of freshwater inputs, due to easier identification and recent control of point sources. Although P management is an integral part of profitable agrisystems, continued inputs of fertilizer and manure P in excess of crop requirements have led to a build-up of soil P levels, which are of environmental rather than agronomic concern, particularly in areas of intensive crop and livestock production. Thus, the main issues facing the establishment of economically and environmentally sound P management systems are the identification of soil P levels that are of environmental concern; targeting specific controls for different water quality objectives within watersheds; and balancing economic with environmental values. In developing effective options, we have brought together agricultural and limnological expertise to prioritize watershed management practices and remedial strategies to mitigate nonpoint-source impacts of agricultural P. Options include runoff and erosion control and P-source management, based on eutrophic rather than agronomic considerations. Current soil test P methods may screen soils on which the aquatic bioavailability of P should be estimated. Landowner options to more efficiently utilize manure P include basing application rates on soil vulnerability to P loss in runoff, manure analysis, and programs encouraging manure movement to a greater hectareage. Targeting source areas may be achieved by use of indices to rank soil vulnerability to P loss in runoff and lake sensitivity to P inputs.
The determination of mercury(II) ions at the trace level by inhibition of the invertase enzyme-catalysed hydrolysis of sucrose into glucose and fructose coupled to electrochemical batch injection analysis was investigated using two approaches. In the first, the glucose produced was detected by injection of 100 microliters samples into the batch injection cell containing a platinum electrode modified by immobilised glucose oxidase. In the second, the glucose and fructose present in injected samples were oxidised directly at a copper-modified glassy carbon electrode. The experimental parameters were optimised and the degree of enzyme inhibition by mercury(II) ions under both conditions was measured. Mercury concentrations in the ng ml-1 range were determined by these two techniques with low sample and reagent consumption. Comparison is made between the two methods and perspectives as a screening test for field application are indicated.
An on-line flow-injection system for the determination of total phosphorus in waters and wastewaters is described. Digestion was performed using a UV photoreactor and a thermal digestion unit connected in series. The orthophosphate formed was detected as phosphomolybdenum blue after on-line filtration. Reagent and digestion conditions required to give optimal oxidation and hydrolysis of organic and condensed model compounds are reported. The flow-injection method gave complete recovery for all the model organic P compounds tested, and >85% recovery for condensed phosphates. When the proposed method was applied to a series of wastewater samples, the results obtained were in close agreement with those from a conventional batch digestion method. The technique was rapid (8 samples h−1 4 replicates), with a linear range of interest for wastewaters 0–18 mgPl−1 and a detection limit of 0.15 mgPl−1.
Orthophosphate in turbid natural waters exists in dissolved and adsorbed forms. Phosphate adsorbed on suspended matter in turbid waters is difficult to determine spectrophotometrically. In the voltammetric method, the peak current is related to the reoxidation of the molybdophosphate complex at a glassy-carbon electrode. This allows the determination of dissolved and adsorbed phosphate at micromolar levels in natural waters, especially turbid waters, with good precision and accuracy.
Anionic detergents have been shown to lower markedly the differential-pulse voltammetric peak currents obtained for 12-molybdophosphate and 12-molybdosilicate in aqueous solutions, but when ethanol - water or acetone - water (1 + 1 V/V) solutions are used there is no interference. Static differential-pulse voltammetric and flow-injection voltammetric procedures have been developed for the determination of total phosphate (involving hydrolysis of polyphosphates) and soluble silicate in commercial washing powders using these partly aqueous conditions. The effect of increasing ethanol and acetone concentrations on the differential-pulse voltammograms has been studied.
The redox behaviour of molybdovanadophosphate at a glassy carbon electrode is described and a procedure is given for the voltammetric determination of phosphate as molybdovanadophosphate at a glassy carbon electrode in a static system. Procedures are also given for the voltammetric flow injection determination of phosphate, silicate, arsenate and germanate by the injection of heteropolyacids pre-formed in various aqueous, aqueous acetone and aqueous ethanolic reagents into eluents consisting of the reagent blank. This procedure effectively eliminates the background signal of the blank and allows precise determinations to be made. Plots of electrode potential against the current obtained are given. Silicate and phosphate can be determined at 10-7 and 10-6 M levels, respectively. Arsenate has only been determined at the 10-5 M level, and the precise determination of germanate is difficult owing to adsorption at the glassy carbon electrode.
The alteration and weathering of stone is basically determined by natural and anthropogenic impacts influencing various physical, chemical and biological damage factors at the object site. Whether as direct or catalytically enhancing factor, the biodeterioration of stone is coupled with nearly all environmentally induced degradation processes: the presence of the one makes deterioration by the other all the more effective. The bioreceptivity of stone is described by its structure and chemical composition, while the intensity of the microbial contamination is determined by the referring climatic conditions and the anthropogenic euthrophication of the atmosphere. The microflora improves the nutrient and moisture-restricted growth conditions on building stones by the formation of surface-covering biofilms. Besides the aesthetical impairment caused by the coloured biopatina, the biofouling effect promotes even “abiotic” deterioration processes due to the alteration of the material structure as well as their thermo-hygric properties; in addition, mechanical pressure due to the shrinking and swelling of the colloidal biofilms might cause a further weakening of the mineral lattice. Acidolytic and oxido-reductive biocorrosion processes complete the biodeteriorating attack of stone acting as a preliminary precursor for the latter formation of detrimental crusts. Suitable and reliable methods for the detection of biodeterioration processes are available, but only the interdisciplinary diagnosis and evaluation of the entire decay process of stone allows the formulation of adaequate countermeasure strategies. In case the significance of biodeterioration impacts is proven, the possible effects of the microbial contamination on cleaning procedures, protective treatments as well as biocidal applications has to be considered. This paper will give a comprehensive overview to the biodeterioration of stone and stresses the practical relevance for the conservation.
The performance of the recently developed batch injection analysis (BIA) technique was investigated with regard to the behaviour of enzyme-immobilized electrodes. Glucose oxidase and xanthine oxidase sensors were prepared by casting the enzyme-immobilized membranes on the electrode surface. The measurements are based on the amperometric detection of the product of the enzymatic reaction: hydrogen peroxide at +650 mV vs. Ag/AgCl (GOx) or the reduced form of methylene blue at +50 mV vs. Ag/AgCl (XOD). The enzyme glutamate dehydrogenase was incorporated in the carbon paste and the direct and phenazine methosulphate-mediated detection of NADH was followed at the enzyme electrode. The major characteristics observed were simplicity of the equipment, a high sampling rate and limited consumption of the carrier, i.e., reagents such as the mediator and cofactor. The repeatability of the manual injection of the sample was shown to be the critical step in the BIA mode. A new BIA cell design, allowing semi-continuous solution draining, is reported.
Phosphate can be determined precisely as molybdophosphate by flow injection analysis using a glassy carbon electrode as a voltammetric detector. The sample solution (25 µl, 1 × 10–6–5 × 10–4M in phosphate) is injected into an eluent which is 2%m/V in ammonium molybdate and 0.6%V/V in concentrated sulphuric acid. Molybdophosphate, which is determined by reduction at the glassy carbon electrode, is fully formed when a 3-m delay coil (0.58 mm i.d.) is incorporated before the detector and a flow-rate of 4 ml min–1 is used.
The dominant algae colonizing hypogean sites are usually epilithic cyanophytes which are often associated with chlorophytes and diatoms, and sometimes mosses. High relative humidity and extremely low photon fluxes characterize the environment in which a prevalence of shade-adapted species is supposed. The interactions with the substrate and the light adaptation of the algae encountered is discussed also in relation to biodeterioration processes. The taxa occurring in hypogea are reported in comparison with cave vegetation. The phototrophic communities support the growth of abundant bacterial populations.
A new, highly sensitive enzyme sensor was developed for the determination of inorganic phosphate using maltose phosphorylase, acid phosphatase, glucose oxidase and mutarotase. The combination of the first two enzymes generates two glucose molecules per reaction cycle and recycles one molecule of phosphate. Finally, the oxidation of glucose is catalysed by mutarotase and glucose oxidase. The four enzymes were coimmobilized on a regenerated cellulose membrane which was mounted on the tip of a platinum amperometric electrode for the detection of enzymatically formed hydrogen peroxide. Thus, a detection limit of 10(-8) M was obtained and the sensor response was linear in the range 0.1-1 mu M, which is relevant for the monitoring of water pollution.
A simple flow injecton system for determination of orthophosphate is described. The system utilizes a commercially available thin-layer amperometric detector for measurement of 12-molybdophosphoric acid reduction currents in an aqueous solvent system 0.10 F nitric acid, 1.95 × 10-3 M sodium molybdate, and 30% (v/v) methanol. The system is capable of analysis of 70 samples per hour at a flow rate of 2.2 mL/min. The linear dynamic range extends to a concentration of 5.0 × 10-5 M and the detection limit at a signal to noise level of 2:1 is 2 × 10-3 M orthophosphate. The relative standard deviation of the technique at the 1.0 × 10-6 M orthophosphate level is 2.6%.
Amperometric methods using microdisk electrodes and based on the formation of electroactive molybdophosphate and molybdosilicate complexes are described for the determination in water samples of phosphate and silicate. It is demonstrated that it is possible to devise conditions for the analysis of 1—100 μM phosphate or silicate in the presence of a large excess of the other. It is also possible to determine both phosphate and silicate in a single analysis provided they are present in not too dissimilar concentrations.
The voltammetry of the molybdosilicate and molybdophosphate complexes, formed by the addition of hexafluorosilicate and phosphate to anacidic sodium molybdate solution, have been defined at gold microdisk electrodes. It is shown that the reaction conditions influence both the kinetics of formation of the complexes and their voltammetry. It is possible to find conditions where the steady state amperometric response of the Au microdisk electrodes allows a rapid and convenient method for the determination of silicate and phosphate at concentrations in the range 1–1000 μM.
In this work the development of a pyruvate oxidase-based phosphate biosensor is illustrated. The use of polyelectrolyte stabilized recombinant pyruvate oxidase in conjunction with a porous conductive carbon results in the development of a simple, reproducible and stable phosphate biosensor. The polyelectrolyte diethylaminoethyl-dextran or DNA was used as the enzyme stabilizer, and the resulting enzyme–polyelectrolyte complexes were physically adsorbed into the transducer, a highly porous and conductive carbon electrode, for the construction of the biosensor. The optimized biosensor exhibits high operational (67% remaining activity after 220 h) and storage (49% remaining activity after 24 weeks) stability, and very good sensor-to-sensor reproducibility. The optimized phosphate biosensor was used for the measurement of the phosphate ion activity in serum.
This paper presents a spectrophotometric sequential injection (SI) determination of phosphate and silicate in environmental samples and cell cultivation medium using the molybdenum blue reaction. The interference of silicate in the determination of phosphate was eliminated by using a reagent composed of 5 mmol l−1 ammonium molybdate in 0.2 mol l−1 nitric acid, containing 0.25% (w/v) oxalic acid to avoid the formation of molybdosilicic acid. The interference of phosphate in the determination of silicate was avoided adding a 10% (w/v) oxalic acid solution to the reaction zone where the molybdophosphoric and molybdosilicic acids were previously formed, in order to destroy the molybdophosphoric acid. To perform this task in the single line SI system, obtaining a total sample and reagent zones penetration, it was used as a combination of sandwiching the sample zone between reagent zones and flow reversal through an auxiliary reaction coil. The method has a phosphate sampling frequency of 75 h−1, with a linear dynamic range between 0.2 and 7 mg l−1 and a detection limit of 0.1 mg l−1 PO43=P. For silicate, the sampling frequency is 40 h−1 with a linear dynamic range between 5 and 50 mg l−1 and a limit of detection of 1 mg l−1 SiO32=Si.
The development of a reagentless phosphate biosensor with potential applications in continuous monitoring of environmental samples is described. The sensor is based on a biorecognition sequence of three enzymes: phosphorylase A, phosphoglucomutase and glucose 6-phosphate dehydrogenase. The incorporation of these enzymes, the substrate glycogen, the cofactor NAD+, and Os(1,10-phenanthroline-5,6-dione)2Cl2 mediator in a carbon paste electrode covered with in situ formed hydrogels was the fundamental base for the development of an amperometric enzyme electrode for the detection of inorganic phosphate. A study of the effects on the response of enzymatic biosensor response were carried out with dialysis membrane-covered glassy carbon electrodes, achieving a maximum current density of 2 μA cm−2, a detection limit of 6 μM of phosphate with an extended linear dynamic range up to 2 mM, and sensitivity in the linear region of 4.5 μA cm−2 mM−1 with a useful pH operational range between 6.5 and 7.5. The preliminary results with carbon paste phosphate electrodes showed a maximum current density of 30 μA cm−2, a detection limit of 2 mM of phosphate with linearity up to 250 mM, and sensitivity in the linear region of 0.1 μA cm−2 mM−1.
The application of batch injection analysis to the determination of trace metals in samples of volume ≤ 100 μl by square wave anodic stripping voltammetry has been investigated in detail, using a programmable electronic micropipette. The in situ formation of a mercury film on a glassy carbon electrode substrate, the influence of preconcentration time, injection rate and injected volume of analyte ions have been studied and optimised procedures are recommended. Results for zinc, cadmium, lead and copper are presented, with particular emphasis on lead and cadmium, and nanomolar detection limits corresponding to sub-picomole quantities found. Comparison is made with flow-injection analysis and with experiments at wall-jet electrodes in continuous flow.
A highly sensitive enzyme electrode was designed for the assay of phosphate ions. For this purpose, a bienzyme membrane with co-immobilized nucleoside phosphorylase and xanthine oxidase was used with a platinum amperometric electrode for the detection of enzymatically generated hydrogen peroxide. A detection limit of 10−7 M was obtained and phosphate assays could be easily performed in the range 0.1–10 μM, which is of interest in the control of water pollution.
Specific reaction conditions for automated continuous flow analysis of phosphate are optimized in regard to minimizing coating and silicate interference, while maintaining high sensitivity. Use of Sb in the reagent increases sensitivity and yields absorbances with little temperature dependence. Coating can be minimized by using a final solution at a pH>0.5. At final pH of 0.78 there is maximum interference from silicate in the sample. We recommend therefore as an optimal reaction condition with minimal silicate interference, the use of Sb, a final solution pH of 1.00, room temperature for the reaction and a [H(+)]/[Mo] ratio of 70. An equation is provided to correct silicate interference in high precision phosphate determination.
A 1:12 phosphomolybdic anion film modified carbon paste electrode (PMo(12) electrode) is prepared by electrochemical deposition and its application is studied by cyclic voltammetry. The film modified electrode can adsorb PMo(12) selectively and thus be used for the determination of trace phosphorus. In a solution containing 2 mug ml(-1) phosphorus, the relative standard deviation is 4.69% (n=4), the peak height also varies linearly with the concentration of phosphorus over the range 0.4-25 mug ml(-1), and the detection limit is 0.04 mug ml(-1). The method is convenient and rapid. It has been used for the determination of inorganic phosphorus in phytic acid directly with satisfactory results.
A bienzymatic sensor for the determination of phosphate was constructed by coimmobilization of xanthine oxidase (EC 1.2.3.22) and nucleoside phosphorylase (EC 2.4.2.1) on a polycarbonate membrane mounted on the tips of amperometric hydrogen peroxide and oxygen electrodes. The sensor response was linear to phosphate concentrations in the range 10-250 microM.
This paper reports on the development and characterization of Prussian Blue-modified carbon paste electrodes. New methods of matrix modification with Prussian Blue are reported. Two different carbon pastes have been prepared, using mineral oil or solid paraffin, thus obtaining different types of sensors whose behavior toward the electrochemical reduction of hydrogen peroxide has been fully characterized. Results obtained with Prussian Blue-modified electrodes showed a long operational lifetime, an excellent stability in a wide range of pH (3-9), a high sensitivity, and a fast response time. In addition, the coupling of solid carbon paste modified with Prussian Blue and the enzymes glucose oxidase and choline oxidase led to the assembling of biosensors that showed an optimum working range at alkaline pH.
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