The Analyst

Published by Royal Society of Chemistry
Online ISSN: 1364-5528
Publications
Article
The purpose of this paper is to develop a sensitive and low-cost colorimetric method for detection of melamine using simple circuitry. The stable p-nitroaniline-modified silver nanoparticles (Ag NPs) were synthesized by a zero-length covalent coupling chemistry, which showed sensitivity and selectivity towards melamine. The melamine induces the aggregation of nanoparticles due to electron donor-acceptor interaction between melamine and p-nitroaniline at the Ag NP interface, resulting in a shift in the surface plasmon band and a consequent color change of the Ag NPs from yellow to blue. The color change was monitored using UV-vis spectrophotometry. More importantly, this optical method was successfully utilized to a practical infant formula sample. As low as 0.1 ppm melamine in infant formula could be distinguished upon a color change of solution in two minutes.
 
Article
The roles of CdS nanocrystals (quantum dots) stabilized by oleic acid ligands in toluene were investigated in the 1,1'-oxalyldiimidazole chemiluminescence (ODI-CL) reaction generated under various environmental conditions. CdS excited by high-energy intermediates formed in ODI-CL reaction emitted dim CL. Also, CdS acted as a catalyst to enhance the yield of high-energy intermediates, capable of transferring energy to fluorescent molecules, in aqueous ODI-CL reactions, whereas it acted as a strong quencher, capable of inhibiting the CL emission of excited fluorescent molecules, in non-aqueous ODI-CL reactions. Based on the role of CdS in the aqueous ODI-CL reaction, the limit of detection (LOD = signal/noise = 3, 0.1 μM) determined to quantify glucose using aqueous ODI-CL reaction in the presence of 2.75 μM CdS was four times lower than that in the absence of CdS. The range of recovery determined in the aqueous ODI-CL reaction in the presence of CdS was 91.7-104%. We expect that the aqueous ODI-CL reaction in the presence of CdS can be applied as a highly sensitive sensor in various research fields such as bioanalytical chemistry, environmental engineering, homeland security, and toxicology.
 
Article
A novel competitive 1,1'-oxalyldiimidazole (ODI) chemiluminescent enzyme immunoassay (CLEIA) was developed as a method for rapid and simple screening of melamine in milk. Fat existing in milk acts as an inhibitor in the competitive binding interaction of melamine and anti-melamine in the presence of melamine-conjugated horseradish peroxidase. Thus, the calibration curve and sensitivity of competitive ODI CLEIA for the quantification of melamine in fat free milk were wider and better than those in milk containing fat. However, a centrifuge is not a good method for removing the inhibitor because a portion of the melamine is also removed with the fat. The incubation time (20 min) for the competitive binding interaction of anti-melamine and melamine in 20% milk diluted with PBS buffer of pH 7.4 was longer than that (10 min) in 100% milk even though the sensitivity of the former was better than latter. The limit of detection (1.12 ppb) determined in rapid ODI CLEIA (dynamic range: 3.8-125 ppb) for the quantification of melamine in 20% milk not containing fat was lower than those (6.3 and 9.0 ppb) calculated in relatively time-consuming luminol CLEIA and enzyme-linked immunosorbent assay (ELISA). Also, we expect that ODI-CLEIA (dynamic range: 62.5-2000 ppb) capable of directly quantifying melamine in 100% milk without any pretreatment can be applied as a new and simple method for rapid screening of melamine in milk.
 
Article
Solvent and pH effects on fast and ultrasensitive 1,1'-oxalyldi(4-methyl)imidazole chemiluminescence (OD4MI-CL) were studied. The influences of these two factors on the complex OD4MI-CL reaction are discussed within a conceptual prototype for developing aqueous and non-aqueous capillary electrophoresis (ACE and NACE) devices with OD4MI-CL detection. The reaction channel length and OD4MI yield from the reaction between bis(2,4,6-trichlorophenyl) oxalate (TCPO) and 4-methylimidazole in the channel will be influenced by pH, water volume fraction, and cosolvent properties of the solution. Optimum OD4MI-CL efficiency is observed at pH 6.5 when 1-propanol, which has a low dielectric constant (epsilon = 20.8), is used as the NACE solvent in the separation channel. Water (epsilon = 80.1), the solvent in the ACE separation channel, acts similarly to a high dielectric constant organic solvent in NACE because the disadvantages normally associated with TCPO-CL reactions in water disappear due to the faster OD4MI-CL reaction versus OD4MI decomposition in aqueous solution. Therefore, it is expected that the OD4MI-CL detection system can be used in both NACE and ACE devices without requiring detector modifications. We also conclude that OD4MI-CL detection in NACE and ACE devices will be much more sensitive than the TCPO-CL detection used in current NACE devices.
 
Article
In the present work, for the first time, investigation of the initial fast step of reaction between 1,1,1-trichloro-3-methyl-3-phospholene (TCMP) and methanol was studied under a dry inert atmosphere by a newly constructed CSF apparatus by means of a further development in the configuration of the previous stopped-flow spectrophotometer (SFS). Hence, it was necessary to make many changes to the stopped-flow apparatus: replacement of the spectrophotometer amplifier with a conductance amplifier and the use of a conductivity cell to replace the optical one. The conductivity cell was made of polyethylene capillary tube (1 mm internal diameter; i.d.) and its inside dimensions were 1 mm i.d. × 3 mm long. Two tube electrodes which are made of stainless steel (0.8 mm i.d. × 14 mm long) were fixed at opposite ends of the observation cell and their outer surfaces were connected to the conductivity bridge amplifier by the two lead wires. The mixer was a 3-way Teflon valve and the distance between the mixer and the end of the observation cell was 30 mm. For each run, at least 24 µL of solution was required for a typical trace with a dead time of about 5 ms. Because of the extreme sensitivity of TCMP to moisture, the stopped-flow (CSF) apparatus was used inside a glove bag under a dry nitrogen atmosphere. Kinetic parameters for pseudo first-order reaction involving k(obs) = 30 s(-1) at 22 °C and activation energy E(a) = 13.55 KJ mol(-1) were successfully calculated for the initial fast step of the reaction between TCMP and methanol at 22 °C.
 
Article
A simple and accurate spectrophotometric method is proposed for the determination of tannins in tea and beer samples based on the reduction of iron(III) to iron(II) by tannins at 80 degrees C for 20 min. The iron(II) was then reacted with 1,10-phenanthroline at pH 4.4 to form a coloured complex. Background correction could be effected by precipitating the tannins in the sample solution twice with gelatin and kaolin. Absorbance measurements were made at 540 nm and the calibration graph was linear from 0 to 5.5 micrograms ml-1 of tannic acid with a slope of 0.213 A p.p.m.-1. The precision for the determination of tannins in a tea sample containing 9.45% of tannins was 1.8%. Most of the ingredients commonly found in tea and beer samples do not interfere with the determination. Several tea and beer samples were analysed for their tannin content using the proposed method.
 
Imprinted and blank polymers prepared in this study 
Schematic diagram of flow injection chemiluminescent system. P = peristaltic pump; PMT = photomultiplier tube. 
Schematic representation of the molecular imprinting process and the principle of the molecular recognition chemiluminescent reaction. (a) Decomposition of hydrogen peroxide with phen-Cu(II)-VPy complex as catalyst; (b) superoxide radical ion attack on phen molecule of copper complex; (c) phen molecule destruction, chemiluminescence emission and recognition cavity remaining; and (d) accepting a new phen molecule into the recognition cavity. 
Baselines of H 2 O 2 carrier solution flowing through newly prepared sensors and typical CL profiles for phen determination. Signals (a)-(c) are the baseline profiles of sensors prepared from polymers P(blank), P(phenCu-VPy) and P(phen-Co-VPy), respectively. Signal (d) is the CL profile of phen injected into the carrier after the baseline became stable. Conditions for (d): flow rate of 0.1 mol dm 23 H 2 O 2 carrier solution 1.5 ml min 21 and sampling volume 50 ml. Phen sampling solution was injected into the carrier after the sensor showed a stable baseline. 
Scheme 1 Chemiluminescent reaction between 1,10-phenanthroline and superoxide radical anion. 
Article
A functional polymer for the catalysis of the chemiluminescent reaction and molecular recognition ability of 1,10-phenanthroline was prepared based on the molecular imprinting method. The structural and catalytic roles of transition metal ion interactions were applied in the material design. A ternary complex, 4-vinylpyridine-Cu(II)-1,10-phenanthroline (2:1:1), was synthesized and used as a functional monomer. The ligand 1,10-phenanthroline in the ternary complex was the template used to form the molecularly imprinted polymer. Another monomer, styrene, and the cross-linking reagent divinylbenzene were copolymerized with the ternary complex. The polymer containing the ternary complex is an efficient catalyst for the decomposition of hydrogen peroxide. During the hydrogen peroxide decomposition, superoxide radical ion is formed, which reacts with 1,10-phenanthroline and gives a chemiluminescent emission. The 1,10-phenanthroline was destroyed during the chemiluminescent reaction, leaving a cavity and copper binding sites for another 1,10-phenanthroline molecule. The prepared polymer particles were packed into a glass tube and developed as a molecular recognition chemiluminescent flow-through sensor for 1,10-phenanthroline. The sensitivity and selectivity of the sensor were tested.
 
Article
To improve the electrocatalytic activities of carbon nanotubes (CNT) towards the oxidation of nicotinamide adenine dinucleotide (NADH), we derive them with a redox mediator, 1,10-phenanthroline-5,6-dione (PD), by the noncovalent functionalization method. The redox carbon nanotubes (PD/CNT/GC) show excellent electrocatalytic activities towards the oxidation of NADH (catalytic reaction rate constant, k(h) = 7.26 × 10(3) M(-1) s(-1)), so the determination of NADH can be achieved with a high sensitivity of 8.77 μA mM(-1) under the potential of 0.0 V with minimal interference. We also develop an amperometric ethanol biosensor by integration of alcohol dehydrogenase (ADH) within the redox carbon nanotubes (PD/CNT/GC). The ethanol biosensor exhibits a wide linear range up to 7 mM with a lower detection limit of 0.30 mM as well as a high sensitivity of 10.85 nA mM(-1).
 
Article
A method for the determination of iron(II) in water in the presence of iron(III) with 1,10-phenanthroline is described, in which the interfering effect of iron(III) ions is suppressed by masking with complexones. In the absence of a chelating agent for iron(III) the colour intensity of samples being analysed is unstable, owing to redox processes induced by the effect of 1,10-phenanthroline on the iron(II)-iron(III) system, causing reduction of iron(III) and formation of the corresponding coloured iron(II) chelate compound in a stoicheiometrically proportional concentration. The advantages of complexones, especially nitrilotriacetic acid, over other chelating agents are discussed.
 
Article
A new fluorescence reagent, 2-methylbenzo[b][1,10]phenanthrolin-7(12H)-one (mBPO), synthesized in our laboratory was used as the probe for protein and its interaction with Bovine Serum Albumin (BSA) was investigated in detail in this paper. It was found that BSA had the ability to quench the fluorescence of mBPO at 411 nm (λ(ex) = 286 nm), and the quenched intensity of fluorescence was proportional to the concentration of BSA. Based on this fact, mBPO has been used as a fluorescence probe for the detection of BSA. Under the optimal conditions, the calibration graph is linear up to 0.5 mg L(-1) for BSA and the limit of detection (LOD) was 0.06 mg L(-1). The regression equation is y = 1048.8x + 7.2093 with R(2) = 0.9913. The mechanism for the interaction of mBPO with BSA was also studied, while the binding constant and the number of binding sites were calculated. According to the thermodynamics parameter, the binding mode between mBPO and BSA was deduced. The results suggested the interaction between mBPO and BSA to be hydrophobic force in nature. It also proved that the fluorescence quenching reaction was affected by the tryptophan residue of BSA. For there are two tryptophan (Trp) residues, in site 134 and site 212 of BSA, and mBPO maybe has interaction with them respectively.
 
Article
An atomic-absorption spectrometric method for the determination of trace amounts of copper in solution with 1,2-naphthoquinone thiosemicarbazone is described. This compound reacts with copper in a weakly acidic medium to produce a complex that can be extracted into isobutyl methyl ketone. The atomic absorption of the organic phase is measured at 324.8 nm. The sensitivity of the method is 0.6 ng ml-1 for 1% absorption in aqueous solution and the presence of several milligrams of 55 foreign ions is tolerated. The method has been applied successfully to the analysis of waters, foods and analytical reagents.
 
Article
Methods are described for the determination of the nitrate esters, ethylene glycol dinitrate, propylene glycol 1,2-dinitrate, ethylene glycol mononitrate, propylene glycol 1-mononitrate and propylene glycol 2-mononitrate, in blood. These esters can be removed efficiently from blood by extraction with diethyl ether, and determination of the dinitrates can be carried out colorimetrically, after alkaline hydrolysis, by a diazotisation and coupling reaction. As the mononitrates are not determined by this procedure, they do not interfere with the determination of the corresponding dinitrate. Gas chromatography, with the electron-capture detector, provides a sensitive method for detecting and measuring the mononitrates, with adequate separation from the parent dinitrate, and the latter can also be determined by this method as an alternative to the colorimetric procedure. For both methods the effect of possible interferences is investigated, and the efficiency of recovery from blood over the range 0 to 25 µg of ester is reported.
 
Article
The derivatization of amphetamine and methamphetamine with 1,2-naphthoquinone-4-sulfonate (NQS) into solid-phase extraction cartridges (C18) is described. Optimum conditions were the use of carbonate-hydrogencarbonate buffer of pH 10, a 10 min reaction time at 25 degrees C and an NQS concentration of 9.6 x 10(-3) M. The accuracy and the precision of the method were tested. The results obtained with the proposed liquid-solid procedure were compared with those obtained with a traditional liquid-liquid extraction with hexane-ethyl acetate. The procedure was used to measure amphetamine in pharmaceutical and urine samples.
 
Article
Selenium(IV) reacts with 1,2-diamino-4-nitrobenzene to form 5-nitropiazselenol, which is detected by means of a gas chromatograph equipped with an electron-capture detector. Trace amounts of selenium(VI) and total selenium in milk, milk products and albumin were determined by this method with a practical detection limit of 0.005 µg. The amount of selenium(VI) found in milk was about 60% of the total selenium content.
 
Article
A sensitive extraction-spectrophotometric method for the determination of iron has been developed. Iron(II) forms a complex cation with 3-(2-pyridyl)-5,6-diphenyl-1,2,4-triazine (PDT) in aqueous solution and may be extracted into 1,2-dichloroethane (DCE) with tetrabromophenolphthalein ethyl ester (TBPE) as an ion pair at pH 5–7.5. The maximum absorbance of the extracted species occurs at 610 nm. The calibration graph is rectilinear over the range 0–0.25 p.p.m. of iron(II) and the apparent molar absorptivity of the ion-association complex is 1.9 × 105 l mol–1 cm–1. The extracted species has a molar ratio of Fe(II): PDT : TBPE = 1:3:2. The method has been applied to the determination of iron in various sera and also to river and well waters.
 
Article
We report the first use of 3-amino-5-mercapto-1,2,4-triazole (AMT) to construct a surface-enhanced Raman scattering (SERS) based pH nano- and microsensor, utilizing silver nanoparticles. We optimize the procedure of homogenous attachment of colloidal silver to micrometer-sized silica beads via an aminosilane linker. Such micro-carriers are potential optically trappable SERS microprobes. It is demonstrated that the SERS spectrum of AMT is strongly dependent on the pH of the surroundings, as the transformation between two different adsorption modes, upright (A form) and lying flat (B form) orientation, is provoked by pH variation. The possibility of tuning the nanosensor working range by changing the concentration of AMT in the surrounding solution is demonstrated. A strong correlation between the pH response of the nanosensor and the AMT concentration in solution is found to be controlled by the interactions between the surface and solution molecules. In the absence of the AMT monomer, the performance of both the nano- and microsensor is shifted substantially to the strongly acidic pH range, from 1.5 to 2.5 and from 1.0 to 2.0, respectively, which is quite unique even for SERS-based sensors.
 
Article
High-performance liquid chromatographic methods have been developed for the determination of ampicillin (ABPC), amoxicillin (AMPC) and ciclacillin (ACPC) in serum and urine. The methods involve acetylation of these aminopenicillins with acetic anhydride in aqueous solutions (pH 9.0) at ambient temperature for 3 min followed by reaction with 2 M 1,2,4-triazole and 10–3M mercury(II) chloride in solution (pH 9.0) at 60 °C for 10 min. The resulting products were separated on a C18 column following stabilisation in an eluent containing sodium thiosulphate. They were detected at 328 nm for ABPC and AMPC and 327 nm for ACPC.
 
Article
Liquid and poly(vinyl chloride) membrane electrodes that are highly selective and sensitive to benzene-1,2,4-tricarboxylic acid (trimellitic acid) were developed. Both electrodes exhibit a linear response in the range 10–1–10–5M over the pH range 6–9 with a near-Nernstian slope of 27–28 mV per concentration decade at 25 °C. As little as 1 mg ml–1 of trimellitic acid can be measured directly with an average recovery of 98.7%(standard deviation 1.8%) and without interference from many organic acids and inorganic anions.
 
Article
A high-performance liquid chromatographic method has been developed for the assays of carbenicillin (CBPC), ticarcillin (TIPC) and sulbenicillin (SBPC) in serum and urine. These penicillins were reacted with 2 M 1,2,4-triazole and 10–3M mercury(II) chloride in solution (pH 9.0) at 60 °C for 10 min. The resulting products were separated on a C18 column using a mobile phase containing tetrabutylammonium bromide and sodium thiosulphate, and were detected at between 327 and 331 nm. The method has been applied to the assays of these penicillins in serum and urine samples, which were ultra-filtered with a YMT membrane, or filtered with an acrylate copolymer membrane. The procedure permits the accurate determination of penicillin concentrations in serum down to 0.05 µg ml–1 for SBPC and 0.1 µg ml–1 for CBPC and TIPC, and is specific to intact penicillins without interference from corresponding penicilloic acids.
 
RIA dose-response plot for 1,25-(OH) 2-D 3 .
Article
This paper describes the development and preliminary testing of a competitive surface-enhanced Raman scattering (SERS) immunoassay for calcitriol, the 1,25-dihydroxy metabolite (1,25-(OH)(2)-D(3)) of vitamin D(3). Deficiencies in 1,25-(OH)(2)-D have been linked to renal disease, while elevations are linked to hypercalcemia. Thus, there has been a sharp increase in the clinical demand for measurements of this metabolite. The work herein extends the many attributes of SERS-based sandwich immunoassays that have been exploited extensively in the detection of large biolytes (e.g., DNA, proteins, viruses, and microorganisms) into a competitive immunoassay for the low level determination of a small biolyte, 1,25-(OH)(2)-D(3) (M(w) = 416 g mol(-1)). The assay uses surface modified gold nanoparticles as SERS labels, and has a dynamic range of 10-200 pg mL(-1) and a limit of detection of 8.4 ± 1.8 pg mL(-1). These analytical performance metrics match those of tests for 1,25-(OH)(2)-D(3) that rely on radio- or enzyme-labels, while using a much smaller sample volume and eliminating the disposal of radioactive wastes. Moreover, the SERS-based data from pooled-patient sera show strong agreement with that from radioimmunoassays. The merits and potential utility of this new assay are briefly discussed.
 
Article
2-Nitro-5,6-dimethylindane-1,3-dione is a new orally active anti-asthmatic drug and is administered in the form of the monohydrate sodium salt. It possesses three electro-reducible groups, namely the two carbonyl and the nitro group, the reduction of which are pH dependent. The best defined waves for analytical purposes are those produced by the 4e reduction of the nitro group in acidic media, which, when combined with the fact that the known breakdown products and impurities do not contain this electro-active group, endows a polarographic method for the assay of this drug in raw materials and formulations with enhanced selectivity.
 
Article
The presence of various BHC isomers in the human organism has received relatively little attention, and studies were often restricted to only one BHC isomer. A previously described one-step extraction and clean-up procedure before gas-liquid chromatographic determination of organochlorine pesticide residues in human blood has now been applied to various organs and depot fat. The identification of the BHC isomers was performed by gas-liquid chromatography with several stationary liquid phases. 2,2-Dimethylpropane-1,3-diol succinate was found to be the most satisfactory stationary liquid phase for the present purpose, as it gave distinctly separated peaks and characteristic relative retention times.
 
Article
The electrooxidation of dopamine (DA), uric acid (UA) and their mixture on a gold electrode modified by a self-assembled monolayer of 2-(3,4-dihydroxyphenyl)-1,3-dithialone has been studied by cyclic voltammetry (CV), chronoamperometry and differential pulse voltammetry (DPV). CV was used to investigate the redox properties of the modified electrode at various scan rates and the apparent charge transfer rate constant (k(s)), and transfer coefficient (α) were calculated. The mediated oxidation of DA at the modified electrode under the optimum condition (pH = 7.0) in CV occurs at a potential about 220 mV less positive than that of the unmodified gold electrode. The values of electron transfer coefficients (α), catalytic rate constant (k) and diffusion coefficient (D) were calculated for DA, using electrochemical methods. DPV exhibited a linear dynamic range over the concentration range of 0.2-250.0 μM and a detection limit (3σ) of 0.07 μM for DA. The modified electrode was used for simultaneous determination of DA and UA by DPV. The results showed that the electrode is highly efficient for the catalytic electrooxidation of DA and UA, leading to a remarkable peak resolution (~350 mV) for two compounds. The electrode was used for the determination of DA in an injection sample.
 
Article
The static headspace gas chromatographic technique can be conveniently employed to check the presence and amount of the odorous side-products, 2-R-1,3-dioxanes (R = H, CH3, C2H5, i-C3H7, n-C3H7), directly from the wastewaters flowing from the reactors during the synthesis of polyester resins. By the optimisation of a simple and direct analytical method, the amounts of these compounds may be continuously monitored and controlled. This method is characterized by good repeatability (3-4%) and does not seem to suffer from matrix effects. The detection limits for the determination of the five dioxanes fall in the range 400-700 micrograms dm-3 (alpha = beta = 0.05).
 
Article
A new micro-procedure for the quick regiospecific analysis of triacylglycerols (TAG) with a 1,3-specific lipase, Lipozyme IM 20 (produced from strains of Muccor miehei) is described. After dissolution of triacylglycerols in butan-1-ol or butan-2-ol 250 mg of Lipozyme IM 20 were added and the whole mixture was agitated. This operation was repeated 5-10 times and the esterified fatty acids in the form of butyl esters (FABE) were dissolved in pentane and washed with water. The pentane layer was dried over sodium sulfate and the solvent was removed under vacuum to a constant weight. The residue was analysed using GC-MS. The same triacylglycerols were converted to fatty acid methyl esters (FAME). The FAME were analysed by gas chromatography (GC).
 
Article
An atomic-absorption spectrometric method for the determination of trace amounts of copper(I) after adsorption of tis 2,4,6-tri(2-pyridyl)-1,3,5-triazine tetraphenylborate ion-associated complex on microcrystalline naphthalene has been developed. This ion-associated complex is adsorbed on microcrystalline naphthalene in the pH range 2.2–8.0 by shaking for a few seconds. The solid mass so formed is separated by filtration, dissolved in dimethylformamide and the absorbance is measured at 324.7 nm. Beer's law is obeyed in the concentration range 5.0–95.0 µg of copper in 10 ml of the dimethylformamide solution. Ten replicate determinations on a sample containing 40 µg of copper gave a mean absorbance of 0.225 with a standard deviation of 0.0018 and a relative standard deviation of 0.82%. The sensitivity for 1% absorption and the detection limit are 0.075 µg ml–1 and 0.018 µg ml–1, respectively. The method has been successfully applied to the determination of copper in some standard reference materials and biological samples.
 
Article
The present paper reports on the first preparation of 2,4,6-tris(2-pyridyl)-1,3,5-triazine nanobelts (TPTNBs) by adjusting the pH value of the solution and the subsequent synthesis of Ag nanoparticle (AgNP)-decorated TPTNBs (AgNP-TPTNBs) by mixing an aqueous AgNO(3) solution with preformed TPTNBs without use of any external reducing agent. It is found that the resultant AgNP-TPTNBs exhibit notable catalytic performance for H(2)O(2) reduction. A glucose biosensor was fabricated by immobilizing glucose oxidase (GOD) onto a AgNP-TPTNBs-modified glassy carbon electrode (GCE) for glucose detection. The constructed glucose sensor has a wide linear response range from 3 mM to 20 mM (r: 0.999) with a detection limit of 190 μM. It is further shown that this glucose biosensor can be used for glucose detection in human blood serum.
 
(A) Effect of Coumarin 6 on the aggregation pattern of BCA. BCA was aggregated in the presence of 250, 500, 750 and 1000 nM of Coumarin 6 as described in the text. 100% aggregation refers to the value of the starting protein in the absence of any dye. (B) Fluorescence intensity of Coumarin 6 (C) and DPH (:) in the presence of aggregated BCA (17.2 mM). Emission intensities of Coumarin 6 (,) and DPH (>) in the presence of native BCA are shown. Emission intensities of Coumarin 6 (O) and DPH (B) in the presence of 3.4 mM of BCA aggregates are also shown. In both cases, excitation slit width was kept at 5 nm and emission slit width was kept at 7.5 nm. The emission intensities of Coumarin 6 (Â) and DPH (*) alone are shown for comparison. (C) Representative fluorescence emission spectra of 400 nM Coumarin 6 in the absence (spectrum I) and presence (spectrum II) of BCA aggregates showing blue shift in the latter case. (D) Effect of DPH on the aggregation pattern of BCA. BCA was aggregated in the presence of 5, 100 and 500 nM of DPH as described in the text. 100% aggregation refers to the value of the starting protein in the absence of any dye. All experiments were carried out in triplicate and means of individual sets are shown.  
Fluorescence intensities of Coumarin 6 (curve I) and DPH (curve II) in the presence of aggregated a-synuclein. The emission intensities of the two dyes were monitored at 507 nm and 423 nm, respectively, after exciting the samples at 450 nm and 360 nm. Inset shows the change in fluorescence intensity of thioflavin T with time in the presence of a-synuclein at 482 nm. Excitation and emission slit widths were 5 nm and 10 nm, respectively.  
Characterization of BCA aggregates formed by thermal inactivation of the enzyme. Electrophoresis of aggregated BCA was carried out on (A) non-denaturing and (B) denaturing polyacrylamide gels. (A) Native gel electrophoresis of the samples was carried out on 8% crosslinked gel. Lane 1: native BCA; lane 2: BCA aggregate under nonreducing conditions; lane 3: BCA aggregate under reducing conditions; lane 4: BCA aggregate with 6 M urea. (B) SDS (denaturing) gel electrophoresis of the samples was carried out on a 12% cross-linked gel. Lane 1: native BCA; lane 2: BCA aggregate under non-reducing conditions ; lane 3: BCA aggregate under reducing conditions. Gels were stained by silver staining. (C) Fluorescence of the hydrophobic dye ANS was measured alone (empty bars) and in the presence of thermally aggregated BCA (filled bars). (D) Effect of ANS on the aggregation pattern of BCA. BCA was aggregated in the presence of 10 mM (black) and 100 mM (grey) of ANS as described in the text. White bar represents aggregation of BCA in the absence of any dye. Excitation of the samples was carried out at 350 nm and the emission intensity was recorded at 461 nm. The excitation slit width was kept at 5 nm and the emission slit width was kept at 7.5 nm. All experiments were carried out in triplicate and means of individual sets are shown.  
Article
We report the use of Coumarin 6 and 1,6-diphenyl-1,3,5-hexatriene (DPH) for the identification of protein aggregates for the first time. The two dyes can be used at very low (nanomolar) concentrations and do not interfere with the aggregation process, as is reported for other commonly used fluorescent protein probes. In the presence of protein aggregates, their quantum yields are significantly high. DPH is able to recognize both amorphous and fibrillar aggregates but cannot distinguish between them. Coumarin 6 can distinguish between both types of aggregates. It also exhibits the characteristic sigmoidal curve of amyloid formation, with higher sensitivity for detection of fibrillation than the conventionally used Thioflavin T.
 
Article
A high-pressure liquid chromatographic method has been developed in order to determine low levels of a new triazine herbicide, 2-(1-cyano-1-methylethyl-amino)-4-ethylamino-6-methylthio-1, 3, 5-triazine (cyanatryn), in water. The herbicide was extracted from water with dichloromethane. The recoveries were between 88 and 101 per cent. for concentrations of herbicide ranging from 0·005 to 0·1 p.p.m. in three sources of water.
 
Article
Hexahydro-1,3,5-tris(2-hydroxyethyl)-s-triazine is a widely used biocide in metalworking fluids that resists direct quantification in many analytical methods due to instability. It can be detected in electrospray-mass spectrometry (ES-MS) due to the formation of a charged and relatively stable adduct with the sodium ion. This adduct produces a distinct ion spectrum via collision-induced fragmentation, which should promote specific detection of the analyte in complex matrices. ES-MS detection of the analyte added to, or already present in, metalworking fluid samples at microg mL(-1) levels is demonstrated. Parameters affecting the formation and detection of the sodium adduct, including choice of solvent, alkalinity, and sodium ion level are explored. Linearity of response in flow injection mode is demonstrated.
 
Article
Thiosemicarbazones, thiosemicarbazides, thioureas and also isothiocyanates are made to react with 2,3-dichloro-1,4-naphthoquinone in an ethanolic medium and on rendering the mixtures alkaline with ethanolic ammonia solution, a red to violet colour is developed with absorption maxima between 500 and 570 nm. The reaction forms the basis of a spot test for these compounds.
 
Article
As one vital member among the family of phosphates, guanosine triphosphate (GTP) not only plays a very important role in many critical biological processes but also closely associates with definite pathological states. Based on the ratiometric fluorescence response of the zinc complex of 1,4-bis(imidazol-1-ylmethyl) benzene (bix) in this contribution, a highly selective recognition of GTP has been successfully developed. The fluorescence of bix-Zn(ii) at 289 nm decreased in the presence of GTP with the appearance of one new emission band at 341 nm, resulting in ratiometric fluorescence changes with the concentration of GTP. With that, ratiometric fluorescence recognition for GTP could be effectively established, and so GTP could be successfully discriminated from other structurally similar anions, including ATP and PPi. Furthermore, bix-Zn(ii) also has a ratiometric fluorescence response to DNA sequences containing guanine.
 
Article
During the positive-ion mode electrospray ionization mass spectrometry analysis of 1,4-diphenyl-3-benzoyl-1,4-dihydropyridines with methanol as the solvent, the major ion generated is one mass unit lower than the analyte, which can be rationalized as the oxidative aromatization of 1,4-dihydropyridines to pyridine cations.
 
Article
A method for the determination of emissions in workroom air as a result of the thermal degradation of polyester coating powders is described. The method is based on the determination of certain marker compounds only. Polyester coating powders were degraded thermally in laboratory experiments and 1,4-dicyanobenzene was chosen as the marker compound. An air sampling method and a high-performance liquid chromatographic method for the determination of the marker compound are proposed. The detection limit for a 48-I air sample was 0.4 microgram m-3.
 
Article
Monolithic capillary columns were prepared by thermally initiated free radical copolymerization of N-vinylcarbazole (NVC) and 1,4-divinylbenzene (DVB) within the confines of 200 and 100 μm i.d. fused silica capillaries. The reaction was carried out under the influence of inert micro-(toluene) and macroporogen (1-decanol) and α,α'-azoisobutyronitrile (AIBN) as a free radical initiator. The material proved high mechanical stability applying water and acetonitrile as mobile phases. The morphological and porous properties were studied by scanning electron microscopy (SEM), nitrogen sorption (BET) and mercury intrusion porosimetry (MIP). The homogeneity of the copolymerization process was confirmed by elemental analysis and monomer conversion measurements. The newly developed NVC/DVB monolithic supports showed high separation efficiency towards biomolecules, applying reversed-phase (RP) and ion-pair reversed-phase (IP-RP) separation modes, which is exemplified by the separations of peptides, proteins and oligonucleotides. Furthermore the maximum loading capacity was evaluated. The chromatographic performance under isocratic elution was determined in terms of theoretical plate number and plate height, where up to 41 000 plates per column and a minimum plate height value of 1.7 μm were achieved, applying oligonucleotide separations. In gradient elution mode, peak capacities of 96 and 127 were achieved within a gradient time window of 60 min for protein and oligonucleotide separations, respectively. The material proved to have high permeability, good repeatability of the fabrication process and high surface areas in the range of 120-160 m(2) g(-1).
 
Article
A kinetic-spectrophotometric method is proposed for the determination of HCHO based on its “catalytic” property to oxidise N,N-dimethylphenylenediamine (DMPDA) by H2O2. The sensitivity at optimum conditions with this method is 1.3-fold greater than the corresponding oxidation of p-phenylenediamine (PDA). The condensation reaction step leading to the Bandrowski Base is much slower with DMPDA than with the PDA oxidation process. Other analytical parameters remain virtually unchanged and the detection limit lies in the range of a few p.p.m. However, the N,N,N′,N′-tetramethyl-1,4-phenylenediamine is not oxidised by H2O2 even in the presence of HCHO.
 
Article
The electrochemical reduction of four 1,4-thienodiazepines at a rotating disc glassy carbon electrode has been investigated and reduction mechanisms are proposed. The method has been satisfactorily applied to the determination of a 1,4-thienodiazepine in pharmaceutical formulations with coefficients of variation of 1–3%.
 
Article
Differential pulse anodic stripping voltammetry (DPASV) coupled with redox-magnetohydrodynamics (MHD) is used to enhance the anodic stripping voltammetry (ASV) response using a mercury thin film-glassy carbon electrode. The sensitivity increased to at least a factor of two (at 1.2 T) and is facilitated by using 20.0 mmol L(-1) 1,4-benzoquinone as an alternative pumping species to enhance ASV by redox-MHD. The MHD force formed by the cross-product of ion flux with magnetic field induces solution convection during the deposition step, enhancing mass transport of the analytes to the electrode surface and increasing their preconcentrated quantity in the mercury thin film. Therefore, larger ASV peaks and improved sensitivities are obtained, compared with analyses performed without a magnet. The influence of pH, 1,4-benzoquinone concentration, accumulation potential, and time are also investigated. Detection limits of 0.05, 0.09 and 2.2 ng mL(-1) Cd(II), Pb(II) and Zn(II) were established with an accumulation time of 65 s. The method is used for the analysis of Cd(II), Pb(II) and Zn(II) in different water samples, certified reference materials, and saliva samples with satisfactory results.
 
Article
The volatile and polar solvent 1,4-dioxane has recently been reported as a contaminant of ground and surface waters, establishing the need to determine this substance in drinking water. This investigation established that 1,4-dioxane can be determined in water by various techniques including direct aqueous injection (DAI) gas chromatography (GC) and purge and trap GC-mass spectrometry (MS). Purge and trap GC-MS is limited by 1,4-dioxane's poor purge efficiency, resulting in detection limits up to 100 times greater than the efficiently purged volatile organic compounds. To attain the sensitivity required for drinking water monitoring, a method based on continuous liquid-liquid extraction with dichloromethane was developed. Isotope dilution was more accurate and reproducible than quantification with external standards, and the improvement in precision led to a lower method detection limit, 0.2 microgram L-1, using a quadrupole ion trap instrument in the electron ionization mode. Isotope dilution accuracy approached 100% in ppb determinations. Isotopic dilution quantification was also possible using a non-selective GC detector owing to the high efficiency of capillary GC columns that resolve the deuterium-labeled solvent from the natural isotopes.
 
Article
4-Acetylaminobenzaldehyde thiosemicarbazone (thiacetazone) is made to react with 2,3-dichloro-1,4-naphthoquinone in an ethanolic medium. When the mixture is rendered alkaline with ammonia a purple product with an absorption maximum at 560 nm is obtained. A method based on this reaction is described for the quantitative determination of micro-scale amounts of thiacetazone. The procedure is applied to its determination in tablets. The results are compared with those obtained by the official method.
 
Article
A rapid high-performance liquid chromatographic procedure has been developed for the assay of 1,4-dioxane in cosmetic products. After solid-phase extraction, using Bond Elut CN and Bond Elut C18 cartridges, samples were analysed directly on a LiChrospher CH-8 reversed-phase column with spectrophotometric detection at 200 nm and acetonitrile - water as eluent. Recovery of 1,4-dioxane from different cosmetic matrices was between 81.5 and 90.1% in the 30-90 microgram g(-1) range. The minimum quantifiable amount was 6.5 microgram g(-1). The method is simple, reproducible and specific and is suitable for routine analyses of commercial cosmetics.
 
Article
The new cyclic polyazacycloalkane 1.4,8,11-tetra(n-octyl)-1,4,8,11-tetraazacyclotetradecane (L1) was synthesised and the copper(II) complex [Cu(L1)]2+ characterised. Different electrodes were prepared using the [Cu(L1)]2+ complex as ionophore, PVC as plastic matrix and o-nitrophenyl octyl ether (NPOE), bis(2-ethylhexyl) sebacate (BEHS) or dibutyl phthalate (DBP) as plasticizers. The electrode containing DBP showed a Nernstian response over a wide pH range and a fast response time (ca. 3 s) whereas NPOE and BEHS gave near-Nernstian slopes. Selectivity coefficients for the different anions with respect to perchlorate were calculated. The response of the electrodes basically followed the Hofmeister sequence, suggesting that interaction of the ionophore with the anions is via electrostatic forces rather than due to anion coordination to the axial sites of the square-planar [Cu(L1)]2+ complex.
 
Article
An inductively coupled plasma atomic emission spectrometric method for the determination of trace amounts of cadmium after extraction of the metal into isobutyl methyl ketone containing 1,5-bis(di-2-pyridylmethylene) thiocarbonohydrazide is described. The optimum extraction conditions were evaluated from a critical study of the effects of pH, concentration of extractant, shaking time and ionic strength. The detection limit for cadmium is 0.1 ng ml-1 and the calibration is linear from 0.2 to 140 ng ml-1. The relative standard deviation for ten replicate measurements is 2.9% for 2 ng ml-1 of cadmium. Results from the analysis of some certified biological reference materials are given.
 
Deflection of silicon cantilevers coated with a self-assembled monolayer of 1,6-hexanedithiol on the gold surfaces as a function of the change in concentration of CH 3 Hg + in deionized water. A binding constant of 3 6 10 212 M 21 was obtained using a Langmuir model based non-linear curve fitting method (solid line), which is in the range of 10 212 – 10 213 at pH = 7.0 reported by Hintelmann et al. 14  
Article
1,6-Hexanedithiol monolayer acts as an unusually specific recognition agent for CH3Hg+ when the microcantilever is used as the transducer; the mechanism of the sensor is discussed.
 
Article
The stabilization of the isocyanate (NCO) groups during workplace sampling is necessary for their subsequent laboratory analysis. Most derivatization reagents are secondary amines. By carrying out a test in which two secondary amines are added to an isocyanate, the relative rates of these reactions can be evaluated. This evaluation is known for a monoisocyanate, phenylisocyanate (PHI), but is being developed for diisocyanates. This study deals with the relative reactivity (RR) of four diisocyanates: hexamethylene 1,6-diisocyanate (HDI), 4,4'-methylenebis(phenyl isocyanate) (MDI), and the ortho and para isomers of toluene diisocyanate (TDI) in addition to PHI, with four secondary amines: 1-(2-methoxyphenyl)piperazine (MOPIP), 9-(N-methylaminomethyl)anthracene (MAMA), 1-(9-anthracenylmethyl)piperazine (MAP), and dibutylamine (DBA). These competitive derivatization reactions are studied in three reaction solvents, namely acetonitrile, toluene, and acetonitrile doped with water (1% v/v). The results show that the order of reactivity, which doesn't change with the isocyanate as well as with the solvent used, is the following: DBA > MAP > MOPIP > MAMA. The relative difference in reactivity is a function of both the isocyanate and the solvent used. Hindered aromatic diisocyanates (TDI and MDI) show a greater difference in reactivity with the derivatization agents. These differences in reactivity are also modified by the solvent used. For example, larger differences are observed in acetonitrile than in toluene, but the introduction of water to acetonitrile, which does not affect the reaction yield, makes these differences smaller.
 
Article
In this study three different types of samplers for the determination of 1,6-hexamethylene diisocyanate in air were compared. The experimental set up was a simulation of real life conditions with spray painting operations performed inside a commercial, full sized, spray box. The sampling methods were 1-(2-methoxyphenyl)-piperazine impregnated on glass fibre filter, and the same reagent in impinger, and also dibutylamine in impinger. All analyses were performed by LC-MS-MS. The determined concentrations varied between 20 and 90 microg m(-3) with relative standard deviations from 7 to 17% for each method. No significant difference was found between the three methods using ANOVA with a significance level of alpha = 0.05.
 
Article
N-Allyl-4-(N-2'-hydroxyethyl)amino-1,8-naphthalimide (AHEAN), a naphthalimide derivative, was synthesized as a new fluorophore for optical chemical sensor preparation. To prevent leakage of the fluorophore, AHEAN was photo-copolymerized with 2-hydroxypropyl methacrylate on a glass surface treated with a silanizing agent. An optical chemical sensor based on AHEAN can be utilized for nitrofurantoin assay based on fluorescence quenching. The sensor shows sufficient repeatability, selectivity and a fast response of less than 30 s. Nitrofurantoin can be determined in the range between 1.00 x 10(-6) and 1.00 x 10(-3) mol l(-1) with a detection limit of 4.8 x 10(-7) mol l(-1). Most commonly co-existing drug substances and ions do not interfere with the nitrofurantoin assay. The sensor was applied to the analysis of pharmaceutical and urine samples.
 
Top-cited authors
Michael Thompson
  • Birkbeck, University of London
James Darwin Thomas
  • Reef Foundation, Inc.
Craig E Banks
  • Manchester Metropolitan University
Edward Cocking
  • University of Nottingham
Hugh J Byrne
  • Technological University Dublin - City Campus