Analytical Methods

Published by Royal Society of Chemistry
Online ISSN: 1759-9679
Publications
Article
A new analytical method was developed and validated for the rapid determination of phencyclidine (PCP) in human blood and serum. Rapid chromatographic separation decreased the analysis time relative to standard gas chromatography (GC)-based methodologies. The method involved the use of solid-phase extraction for sample preparation and cleanup followed by liquid chromatography tandem spectrometric (LC-MS/MS) analysis and an electrospray-ionization (ESI) interface. PCP was quantified using multiple-reaction-monitoring with deuterium labeled PCP (PCP-d(5)) as an internal standard. The method was validated for accuracy, precision, linearity, and recovery. The method was accurate with error <14% and precision with coefficient of variation (CV) <5.0%. The assay was linear over the entire range of calibration standards (r(2) > 0.997). The recovery of PCP after solid-phase extraction was greater than 90% with the lower limit of detection (LLOD) for PCP in 500 µl of human serum after solid-phase extraction at 0.06 ng ml(-1). This method was used to determine the levels of PCP in postmortem human blood samples. The LLOD in blood was 1 ng ml(-1). Blood PCP concentrations were also determined separately using GC and flame ionization detection (FID). Blood calibration standards and serum calibration standards yielded similar concentrations when used to quantitate authentic human blood samples that tested positive for PCP under the GC-FID method. Extraction of PCP from serum required fewer steps and therefore could be used as a calibration matrix in place of blood. The LC-MS/MS methodology shown here was higher throughput compared with GC-based methods because of very short chromatographic run times. This was accomplished without sacrificing analytical sensitivity.
 
Article
Acetonitrile is a choice of solvent for almost all chromatographic separations. In recent years, researchers around the globe have faced an acetonitrile shortage that affected routine analytical operations. Researchers have tried to counter this shortage by applying many innovative solutions, including using ultra performance liquid chromatography (UPLC) columns that are shorter and smaller in diameter than traditional high performance liquid chromatography (HPLC) columns, thus significantly decreasing the volume of eluent required. Although utilizing UPLC in place of HPLC can alleviate the solvent demand to some extent, acetonitrile is generally thought of as the solvent of choice due to its versatility. In the following communication, we describe an alternative eluent system that uses isopropanol in place of acetonitrile as an organic modifier for routine chromatographic separations. We report here the development of an isopropanol based UPLC protocol for G5 PAMAM dendrimer based conjugates that was transferred to semi-preparative applications.
 
Article
Methods to determine neurochemical concentrations in small samples of tissue are needed to map interactions among neurotransmitters. In particular, correlating physiological measurements of neurotransmitter release and the tissue content in a small region would be valuable. HPLC is the standard method for tissue content analysis but it requires microliter samples and the detector often varies by the class of compound being quantified; thus detecting molecules from different classes can be difficult. In this paper, we develop capillary electrophoresis with fast-scan cyclic voltammetry detection (CE-FSCV) for analysis of dopamine, serotonin, and adenosine content in tissue punches from rat brain slices. Using field-amplified sample stacking, the limit of detection was 5 nM for dopamine, 10 nM for serotonin, and 50 nM for adenosine. Neurotransmitters could be measured from a tissue punch as small as 7 µg (7 nL) of tissue, three orders of magnitude smaller than a typical HPLC sample. Tissue content analysis of punches in successive slices through the striatum revealed higher dopamine but lower adenosine content in the anterior striatum. Stimulated dopamine release was measured in a brain slice, then a tissue punch collected from the recording region. Dopamine content and release had a correlation coefficient of 0.71, which indicates much of the variance in stimulated release is due to variance in tissue content. CE-FSCV should facilitate measurements of tissue content in nanoliter samples, leading to a better understanding of how diseases or drugs affect dopamine, serotonin, and adenosine content.
 
Article
Macroscopic assays that are traditionally used to investigate the adhesion behaviour of microbial cells provide averaged information obtained on large populations of cells and do not measure the fundamental forces driving single-cell adhesion. Here, we use single-cell force spectroscopy (SCFS) to quantify the specific and non-specific forces engaged in the adhesion of the human fungal pathogen Candida albicans. Saccharomyces cerevisiae cells expressing the C. albicans adhesion protein Als5p were attached on atomic force microscopy tipless cantilevers using a bioinspired polydopamine wet polymer, and force-distance curves were recorded between the obtained cell probes and various solid surfaces. Force signatures obtained on hydrophobic substrates exhibited large adhesion forces (1.25 ± 0.2 nN) with extended rupture lengths (up to 400 nm), attributed to the binding and stretching of the hydrophobic tandem repeats of Als5p. Data collected on fibronectin (Fn) -coated substrates featured strong adhesion forces (2.8 ± 0.6 nN), reflecting specific binding between Fn and the N-terminal immunoglobulin-like regions of Als5p, followed by weakly adhesive macromolecular bonds. Both hydrophobic and Fn adhesion forces increased with contact time, emphasizing the important role that time plays in strengthening adhesion. Our SCFS methodology provides a versatile platform in biomedicine for understanding the fundamental forces driving adhesion and biofilm formation in fungal pathogens.
 
Schematic of the SERCA activity assay based on TR-FRET detection of ADP.
(A) ATP and ADP titrations in assay buffer 2 with 63 nM tracer and 4 nM ADP antibody. (B) FRET signal differences between ATP and ADP under the same adenosine concentrations. Each point is the average FRET value of three parallel samples. Error bars represent standard deviation.
(A) FRET signals at different ATP to ADP ratios. The total concentration of adenosine in each sample was 2 μM. Detection mixture contained 4 nM ADP antibody and 63 nM ADP tracer. (B) Calibration curves showing FRET signals at different ATP to ADP ratios. Curves with black symbols and lines were obtained with different starting ATP concentrations in the absence of Ca 2+ ; curves with colored symbols and lines were obtained with varying concentrations of Ca 2+ in the presence of 4 μM ATP. Each point is the average FRET value of three replicate samples. Error bars represent standard deviation.
(A) SERCA titration curves in C 12 E 8 . Reactions were quenched at 5 min and 18 min. (B) Normalized SERCA activity curve in C 12 E 8 . (C) SERCA titration curves in reconstituted lipids. Reactions were quenched at 5 min and 20 min. (D) Normalized SERCA and SERCA +PLN activity curves in reconstituted lipids. Each data point shows the average FRET value of three parallel samples, and error bars represent standard deviation.
Article
Various isoforms of sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA) regulate Ca(2+) homeostatic balance in both the heart (SERCA2a) and skeletal muscle (SERCA1a). Ca(2+) plays a key role in these tissues as an intracellular signal that controls contractility. Due to its key role in the contractility cycle, SERCA is emerging as a promising pharmacological target to modulate heart muscle function. SERCA function is regulated by its endogenous inhibitor phospholamban (PLN). Upon binding, PLN decreases SERCA's apparent affinity for Ca(2+). Therefore the interaction between PLN and SERCA has an important role in determining both physiological and pathological conditions. Quantifying the inhibitory potency of PLN is of great importance in understanding the pathophysiology of heart muscle. Traditionally, SERCA activity assays have been performed using a PK/LDH-coupled enzyme reaction, which suffers from limited sensitivity. We have developed a new SERCA activity assay based on the direct detection of the product ADP via time resolved FRET (TR-FRET). Under optimized conditions, our assay reduced the amount of SERCA required to perform the assay 1,000-fold. Inter-day reproducibility was shown to be excellent for SERCA preparations in either detergent (C12E8) or reconstituted lipids. The inhibitory effect of PLN on SERCA measured under the low-concentration conditions of our assay allowed us to more accurately investigate the binding between PLN and SERCA. Significant inhibitory effects of PLN were observed even at mid-nanomolar concentrations significantly lower than previous Kd estimates for the SERCA-PLN complex.
 
Article
We describe a versatile approach for functionalizing core-shell Ag@SiO2 nanoparticles for live-cell imaging. The approach uses physical adsorption and does not need covalent linkage to synthesize antibody-based labels. The surface orientation is not controlled in this approach, but the signal enhancement is strong and consistent. Antibodies were then attached using a non-covalent process that takes advantage of biotin-avidin affinity. Metal-enhanced nanoparticles doped with rhodamine B were used as the luminescent reporter. The enhancement of rhodamine B was between 2.7-6.8 times. We demonstrated labeling of CD19+ Ramos B lymphocytes and CD4+ HuT 78 T lymphocytes using anti-CD19 and anti-CD4 nanocomposite labels, respectively. This physical adsorption process can accommodate a variety of fluorophore types, and has broad potential in bioanalytical and biosensing applications.
 
Article
Plant cell and tissue cultures are a scalable and controllable alternative to whole plants for obtaining natural products of medical relevance. Cultures can be optimized for high yields of desired metabolites using rapid profiling assays such as HPLC. We describe an approach to establishing a rapid assay for profiling cell culture expression systems using a novel microscale LC-UV-MS-NMR platform, designed to acquire both MS and NMR each at their optimal sensitivity, by using nanosplitter MS from 4 mm analytical HPLC columns, and offline microdroplet NMR. The approach is demonstrated in the analysis of elicited Eschscholzia californica cell cultures induced with purified yeast extract to produce benzophenanthridine alkaloids. Preliminary HPLC-UV provides an overview of the changes in the production of alkaloids with time after elicitation. At the time point corresponding to the production of the most alkaloids, the integrated LC-MS-microcoil NMR platform is used for structural identification of extracted alkaloids. Eight benzophenanthridine alkaloids were identified at the sub-microgram level. This paper demonstrates the utility of the nanosplitter LC-MS/microdroplet NMR platform when establishing cell culture expression systems.
 
(A) Photo and (B) schematic of an extraction spray ionization source for MS analysis. (C) MS/MS spectrum obtained using a TSQ for 10 ng mL À1 amitriptyline in blood, dried sample prepared with 0.2 mL blood, and 10 mL methanol for extraction and spray solvent. (D) Photos of paper substrates with dried blood samples before and after the extraction spray process using different solvents. 
Limits of detection (LODs) of chemicals in various matrices using the extraction spray method 
Ion chronograms recorded with SRM transition m/z 399 to m/z 283 for sunitinib using (a) a TSQ and (b) QTRAP 4000 using paper spray (blue) and extraction spray (red), 200 ng mL À1 sunitinib in blood, 1 and 0.2 mL used for preparing dried samples for paper spray and extraction spray, respectively; 10 mL methanol used as an extraction/spray solvent. (c) Calibration curve for analysis of amitriptyline in blood samples using extraction spray, MRM transition m/z 277 to 223 for amitriptyline and m/z 283 to 223 for internal standard amitriptyline-d6 (200 ng mL À1 ), 0.2 mL blood used for DBS, and 10 mL methanol for extraction and spray. 
MS and MS/MS spectra (insets) obtained using a QTRAP 4000 for (a) nicotine in blood, (b) methamphetamine in blood, (c) methamphetamine in urine, (d) clenbuterol in pork homogenate, (e) atrazine in river water, and (f) thiabendazole in orange homogenate. The m/z values marked for the precursor and the fragment peaks of the analytes in the MS/MS spectra. 0.5 mL sample was used to prepare each dried sample, and 10 mL methanol and 2 kV for extraction nanoESI. 
Article
Direct mass spectrometry analysis of untreated samples of volumes as low as 0.2 µL were achieved using fast extraction and nanoESI (electrospray ionization) in a combined fashion. The analytes in dried samples on paper substrates were extracted by organic solvent in a nanoESI tube and ionized with a high voltage applied for generating a spray. The ionization source produced stable signals for different atmospheric pressure interfaces of triple quadrupole instruments. Analysis time more than 20 minutes were available with 10 µL solvent consumed for the entire analysis process. The performance in qualitative and quantitative analysis was characterized with a wide variety of samples. Limits of detection as low as 0.1 ng/mL (corresponding to an absolute amount of 0.05 pg) were obtained for analysis of atrazine in river water, thiabendazole in orange homogenate, and methamphetamine in blood.
 
Article
Cell membranes are made up of a mixture of glycerolipids, sphingolipids, gangliosides and cholesterol. Lipids play important roles in a cell's life. However many of their functions have still to be discovered. In the present work, we describe an efficient, easy and rapid methodology to accurately localize phosphatidylcholines and sphingomyelins from a single coronal rat brain section in the cerebrum area. Matrix assisted laser desorption/ionization (MALDI) mass spectrometry was used to profile and image lipids. The best resolved structure was 25-50 μm in the hippocampus.
 
Article
The low abundance of angiotensin peptides in biological tissues such as the kidney cortex, adipose tissue, urine and plasma makes their detection and quantification a challenge. A few available methods used to quantify these peptides involve lengthy processes of sample preparation and are hardly quantitative. Here, we report a mass spectrometry approach for quantifying angiotensin peptides [Ang II, Ang-(1-7)] in the kidney cortex, epididymal white adipose tissue (eWAT), urine and plasma of male mice. Tissue homogenates, urine and plasma samples were solid-phase extracted with C18 Sep-Pak cartridges and eluted off proteinaceous compounds. These extracted peptide samples were separated on C18 column with a linear acetonitrile gradient and detected by Q-ToF mass analyzer in ESI+-MS ion mode based on their retention time, accurate mass measurement of peptides, the isotope pattern of doubly charged molecular ion, and quantitation of peak area (or ion count) when referencing to the angiotensin peptide standards. The lower limit of quantitation for each angiotensin peptide was 10 pgmg(-1) with the percent recovery at 100.6%. The intra-batch precision for Ang-(1-7) and Ang II were 24.0 and 12.7%, accuracy 84.0-123.0% and 100.2-116.0% respectively. Using this method, we determined the levels of Ang II and Ang-(1-7) in the kidney cortex, eWAT, urine and plasma. Quantification of angiotensin peptides could help target subtle therapeutics changes against pathophysiological conditions such as obesity, kidney disease and hypertension.
 
Article
Discovery-based proteomic studies aim to answer important biological questions by identifying as many proteins as possible. In order to accomplish this lofty goal, an effort must be placed on determining an optimal workflow that maximizes protein identifications. In this study, we compare protein extraction, digestion and fractionation methods for bottom-up proteomics using a human colon cancer cell line as our model system. Four different buffers for protein extraction, two digestion approaches, as well as three sample fractionation methods were evaluated in order to determine an accessible workflow that gives maximal protein identifications. Samples comparing these workflows were analyzed via UPLC paired with tandem MS on a Q-Exactive mass spectrometer. Our goal is to determine an optimal workflow to enable users to maximize protein identifications. Our results show that an increased number of confident protein identifications are attained with a filter-aided digestion approach as compared to an in-solution digestion. Overall SDS-PAGE fractionation leads to higher numbers of identifications than SCX SpinTip and reverse phased cartridge platforms. The novel aspect of this work is the comparison of two readily available, offline platforms for fractionation in reference to a traditional technique, SDS-PAGE.
 
Article
Exposure to high inorganic arsenic concentrations in drinking water has been related to detrimental health effects, including cancers and possibly cardiovascular disease, in many epidemiological studies. Recent studies suggest that arsenic might elicit some of its toxic effects also at lower concentrations. The Strong Heart Study, a large epidemiological study of cardiovascular disease in American Indian communities, collected urine samples and performed medical examinations on 4,549 participants over a 10-year period beginning in 1989. We used anion-exchange HPLC/ICPMS to determine concentrations of arsenic species (methylarsonate, dimethylarsinate and arsenate) in 5,095 urine samples from the Strong Heart Study. We repeated the chromatography on a portion of the urine sample that had been oxidised, by addition of H(2)O(2), to provide additional information on the presence of As(III) species and thio-arsenicals, and by difference, of arsenobetaine and other non-retained cations. Total concentrations for As, Cd, Mo, Pb, Sb, Se, U, W, and Zn were also determined in the urine samples by ICPMS. The dataset will be used to evaluate the relationships between the concentrations of urinary arsenic species and selected metals with various cardiometabolic health endpoints. We present and discuss the analytical protocol put in place to produce this large and valuable dataset.
 
Article
The aim of this study was to identify a plasma biomarker of exposure to pyrethroid insecticides. A major metabolite, 3-phenoxybenzoic acid (3-PBA), can be detected in urine but urinary 3-PBA cannot be used to assess the active dose. The 3-PBA-adduct represents a much more persistent class of biomarkers than metabolites excreted into urine, having half lives up to several weeks or months. We developed an enzyme-linked immunosorbent assay (ELISA) for total 3-PBA including adduct formed after alkaline hydrolysis, liquid-liquid extraction (LLE) and solid phase extraction (SPE) of the sample. The developed ELISA had an IC50 value of 26.7 ng/mL. The intra- and inter-assay coefficients of variation (%CV) were lower than 5% and were within the optimum condition variance (OCV) range. The LLE cleanup technique satisfactorily eliminated the matrix effect from plasma samples before SPE and ELISA analysis yielding good recoveries (85.9-99.4%) with a limit of quantitation (LOQ, 5 ng/mL) that was 30- to 47-fold more sensitive than previous studies. Moreover, the developed method could separate more than 80% of 3-PBA from adduct form. The method was successfully applied to the detection of the target in real samples obtained from consumers (n=50) and farmers (n=50). To our knowledge, this is the first ELISA method for detecting 3-PBA in human plasma and applied to a field study.
 
Article
An automated system for methyl Hg analysis by purge and trap gas chromatography (GC) was evaluated, with comparison of several different instrument configurations including chromatography columns (packed column or capillary), detector (atomic fluorescence, AFS, or inductively coupled plasma mass spectrometry, ICP-MS, using quadrupole and sector field ICP- MS instruments). Method detection limits (MDL) of 0.042 pg and 0.030 pg for CH(3)Hg(+) were achieved with the automated Hg analysis system configured with AFS and ICPMS detection, respectively. Capillary GC with temperature programming was effective in improving resolution and decreasing retention times of heavier Hg species (in this case C(3)H(7)Hg(+)) although carryover between samples was increased. With capillary GC, the MDL for CH(3)Hg(+) was 0.25 pg for AFS detection and 0.060 pg for ICP-MS detection. The automated system was demonstrated to have high throughput (72 samples analyzed in 8 hours) requiring considerably less analyst time than the manual method for methyl mercury analysis described in EPA 1630.
 
Retention time standards are required for unambiguous peak assignment in the quantitation of LPA species during reverse phase HPLC ESI MS/MS analysis. An internal standard mixture of commercially available LPA standards produced distinct MRM chromatograms for 14:0 LPA, 16:0 LPA, 17:0 LPA, 18:1 LPA, 18:0 LPA and 20:4 LPA. Insets: LLOQ chromatograms for the respective LPA species.  
The method of detection for LPA species shows a linear response in the range from 10 fmol to 1 pmol for LPA standards. An internal standard mixture of 14:0 LPA, 16:0 LPA, 17:0 LPA, 18:0 LPA and 20:4 LPA was made in concentrations varying from 10 fmol/inject to 1 pmol/injection. (A) The results were plotted as signal response (area under the peak) versus amount standard in fmol/injection. Data are the average of four separate sample injections ? SEM. (B) The results were plotted as log10 of signal response (area under the peak) versus log10 fmol of standard per injection in a log-log plot. Data are the average of 35 four separate sample injections ? SEM.  
Article
Lysophosphatidic acid (LPA) is a bioactive lipid with a plethora of biological functions including roles in cell survival, proliferation, and migration. Although high-performance liquid chromatography electrospray ionization tandem mass spectrometry (HPLC ESI-MS/MS) technology has been used to measure the levels of LPA in human blood, serum and plasma, current methods cannot readily detect the minute levels of LPA from cell culture. In this study, a modified HPLC ESI-MS/MS method with enhanced sensitivity was developed, which allows accurate measurements of LPA levels with a limit of quantitation at approximately 10 femtomoles. The method was validated by quantitation of LPA levels in the media of previously characterized cell lines ectopically expressing autotaxin. Specifically, autotaxin overexpression induced an increase in the 16:0, 18:2, 18:1, 18:0, and 20:4 subspecies of LPA, but not the 22:6 LPA subspecies. Lastly, this HPLC ESI-MS/MS method was cross-validated via biological assays previously utilized to assay LPA levels. Hence, this HPLC ESI-MS/MS method will allow researchers to measure in vitro LPA levels and also distinguish between specific LPA subspecies for the delineation of individual biological mechanisms.
 
Article
A facile method for quantifying the concentration of the powerful and widely available hallucinogen salvinorin A (a selective kappa opioid agonist) from non-human primate cerebrospinal fluid (CSF) and human plasma has been developed using liquid chromatography-tandem mass spectrometry (LC-MS/MS) in positive electrospray ionization (ESI) mode. With CSF solid phase extraction can be avoided completely by simply diluting each sample to 10 % (v/v) acetonitrile, 1 % (v/v) formic acid and injecting under high aqueous conditions for analyte focusing. Extensive plasma sample preparation was investigated including protein precipitation, SPE column selection, and plasma particulate removal. Human plasma samples were centrifuged at 21,000 × gravity for 4 minutes to obtain clear particulate-free plasma, from which 300 μl was spiked with internal standard and loaded onto a C18 SPE column with a 100 mg mL(-1) loading capacity. Guard columns (C18, hand packed 1 mm × 20 mm) were exchanged after backpressure increased above 4600psi, about 250 injections. A shallow acetonitrile/water gradient was used, 29 to 33% CH3CN over 8 minutes to elute salvinorin A. Reduction of chemical noise was achieved using tandem mass spectrometry with multiple reaction monitoring while sensitivity increases were observed using a 50 μL injection volume onto a small bore analytical column (C18, 1 mm ID × 50 mm) thus increasing peak concentration. Limits of quantification were found to be 0.0125 ng mL(-1) (CSF) and 0.05 ng mL(-1) (plasma) with interday precision and accuracy below 1.7 % and 9.42 % (CSF) and 3.47 % and 12.37 % (plasma) respectively. This method was used to determine the concentration of salvinorin A from an in vivo Rhesus monkey study and a trial of healthy human research participants, using behaviorally active doses.
 
Article
Nanostructure-initiator mass spectrometry (NIMS) is a recently developed matrix-free laser desorption/ionization technique that has shown promise for peptide analyses. It is also useful in mass spectrometric imaging (MSI) studies of small molecule drugs, metabolites, and lipids, minimizing analyte diffusion caused by matrix application. In this study, NIMS and matrix-assisted laser desorption/ionization (MALDI) MSI of a crustacean model organism Cancer borealis brain were compared. MALDI was found to perform better than NIMS in these neuropeptide imaging experiments. Twelve neuropeptides were identified in MALDI MSI experiments whereas none were identified in NIMS MSI experiments. In addition, lipid profiles were compared using each ionization method. Both techniques provided similar lipid profiles in the m/z range 700 - 900.
 
Microscopic images of normal and different tumour subtypes of the brain. Haematoxylin and eosin (H&E) staining of normal brain (Nor) tissue is shown in (A); low-grade tumours like meningioma (Men) in (B); Glioma WHO grade II or low-grade astrocytoma (LA) in (C); high-grade tumours like Glioma WHO grade III or anaplastic astrocytoma (AA) in (D); Glioma WHO grade IV or glioblastoma multiforme (GBM) in (E); and, metastatic brain tumours (Mets, primary colon cancer) in (F). Scale bar = 50 −… m.
Article
The most common initial treatment received by patients with a brain tumour is surgical removal of the growth. Precise histopathological diagnosis of brain tumours is to some extent subjective. Furthermore, currently available diagnostic imaging techniques to delineate the excision border during cytoreductive surgery lack the required spatial precision to aid surgeons. We set out to determine whether infrared (IR) and/or Raman spectroscopy combined with multivariate analysis could be applied to discriminate between normal brain tissue and different tumour types (meningioma, glioma and brain metastasis) based on the unique spectral "fingerprints" of their biochemical composition. Formalin-fixed paraffin-embedded tissue blocks of normal brain and different brain tumours were de-waxed, mounted on low-E slides and desiccated before being analyzed using attenuated total reflection Fourier-transform IR (ATR-FTIR) and Raman spectroscopy. ATR-FTIR spectroscopy showed a clear segregation between normal and different tumour subtypes. Discrimination of tumour classes was also apparent with Raman spectroscopy. Further analysis of spectral data revealed changes in brain biochemical structure associated with different tumours. Decreased tentatively-assigned lipid-to-protein ratio was associated with increased tumour progression. Alteration in cholesterol esters-to-phenylalanine ratio was evident in grade IV glioma and metastatic tumours. The current study indicates that IR and/or Raman spectroscopy have the potential to provide a novel diagnostic approach in the accurate diagnosis of brain tumours and have potential for application in intra-operative diagnosis.
 
Temperature-time program for dry ashing of milk samples in muffle furnace 
ICP-MS (Elan 6100) instrument operation parameters 
Comparison of Pb recoveries and reproducibility for the three sample digestion methods 
-time program for nitric acid digestion of milk samples in high-pressure high temperature asher 
Article
Measurement of lead in breast milk is an important public health consideration and can be technically quite challenging. The reliable and accurate determination of trace lead in human breast milk is difficult for several reasons including: potential for contamination during sample collection, storage, and analysis; complexities related to the high fat content of human milk; and poor analytic sensitivity at low concentrations. Breast milk lead levels from previous published studies should therefore be reviewed with caution. Due to the difficulty in identifying a method that would successfully digest samples with 100% efficiency, we evaluated three different digestion procedures including: (1) dry ashing in a muffle furnace, (2) microwave oven digestion, and (3) digestion in high pressure asher. High temperature, high pressure asher digestion was selected as the procedure of choice for the breast milk samples. Trace lead analysis was performed using isotope dilution (ID) inductively coupled plasma mass spectrometry (ICP-MS). Measured lead concentrations in breast milk samples (n = 200) from Mexico ranged from 0.2 to 6.7 ng ml(-1). The precision for these measurements ranged from 0.27-7.8% RSD. Use of strict contamination control techniques and of a very powerful digestion procedure, along with an ID-ICP-MS method for lead determination, enables us to measure trace lead levels as low as 0.2 ng ml(-1) in milk (instrument detection limit = 0.01 ng ml(-1)).
 
Article
In this paper, an approach to fabricate epoxy or polystyrene microdevices with encapsulated tubing and electrodes is described. Key features of this approach include a fixed alignment between the fluidic tubing and electrodes, the ability to polish the device when desired, and the low dead volume nature of the fluidic interconnects. It is shown that a variety of tubing can be encapsulated with this approach, including fused silica capillary, polyetheretherketone (PEEK), and perfluoroalkoxy (PFA), with the resulting tubing/microchip interface not leading to significant band broadening or plug dilution. The applicability of the devices with embedded tubing is demonstrated by integrating several off-chip analytical methods to the microchip. This includes droplet transfer, droplet desegmentation, and microchip-based flow injection analysis. Off-chip generated droplets can be transferred to the microchip with minimal coalescence, while flow injection studies showed improved peak shape and sensitivity when compared to the use of fluidic interconnects with an appreciable dead volume. Importantly, it is shown that this low dead volume approach can be extended to also enable the integration of conventional capillary electrophoresis (CE) with electrochemical detection. This is accomplished by embedding fused silica capillary along with palladium (for grounding the electrophoresis voltage) and platinum (for detection) electrodes. With this approach, up to 128,000 theoretical plates for dopamine was possible. In all cases, the tubing and electrodes are housed in a rigid base; this results in extremely robust devices that will be of interest to researchers wanting to develop microchips for use by non-experts.
 
Information related to the mineralogy and location sites of soil samples collected from the Atacama Desert
E ff ect of the concentration of 18-crown-6 on the separation of the selected cations at 100 m mol L À 1 each. Conditions : 30 mmol L À 1 MES and 30 mmol 
E ff ect of the injection time on the signal magnitude. Hydrodynamic injections were performed applying vacuum ( $ 70 kPa) on the SW reservoir for the selected times. Migration order is as shown in previous fi gures. 
Article
Compared to conventional bench-top instruments, microfluidic devices possess advantageous characteristics including great portability potential, reduced analysis time (minutes), and relatively inexpensive production, putting them on the forefront of modern analytical chemistry. Fabrication of these devices, however, often involves polymeric materials with less-than-ideal surface properties, specific instrumentation, and cumbersome fabrication procedures. In order to overcome such drawbacks, a new hybrid platform is proposed. The platform is centered on the use of 5 interconnecting microfluidic components that serve as the injector or reservoirs. These plastic units are interconnected using standard capillary tubing, enabling in-channel detection by a wide variety of standard techniques, including capacitively-coupled contactless conductivity detection (C(4)D). Due to the minimum impact on the separation efficiency, the plastic microfluidic components used for the experiments discussed herein were fabricated using an inexpensive engraving tool and standard Plexiglas. The presented approach (named 5(2)-platform) offers a previously unseen versatility: enabling the assembly of the platform within minutes using capillary tubing that differs in length, diameter, or material. The advantages of the proposed design are demonstrated by performing the analysis of inorganic cations by capillary electrophoresis on soil samples from the Atacama Desert.
 
Article
Many new and exciting portable HIV viral load testing technologies are emerging for use in global medicine. While the potential to provide fast, isothermal, and quantitative molecular diagnostic information to clinicians in the field will soon be a reality, many of these technologies lack a robust front end for sample clean up and nucleic acid preparation. Such a technology would enable many different downstream molecular assays. Here, we present a portable system for centrifuge-free room temperature nucleic acid extraction from small volumes of whole blood (70 µL), using only thermally stable reagents compatible with storage and transport in low resource settings. Quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) analysis of simulated samples demonstrate a lower limit of detection of 1000 copies/ml, with the ability to detect differences in viral load across four orders of magnitude. The system can also be used to store extracted RNA on detachable cartridges for up to one week at ambient temperature, and can be operated using only hand generated air pressure.
 
Article
We report the validation of a reversed-phase gradient HPLC method allowing simultaneous quantification of retinol, retinyl esters, tocopherols and selected carotenoids in lung, liver and plasma of mouse, rat and guinea pig (gp) using a diode array detector. A significant species difference was observed regarding the distribution of retinol and retinyl esters. The levels of total retinol in lung, liver and plasma were in the following order: mouse > rat > gp; rat >mouse > gp; and gp > rat > mouse, respectively. Furthermore, comparison studies revealed similarities between the vitamin A profiles of human and gp lung samples.
 
Article
In this work, a polystyrene (PS)-polydimethylsiloxane (PDMS) hybrid device was developed to enable the integration of cell culture with analysis by microchip electrophoresis and electrochemical detection. It is shown that this approach combines the fundamental advantages of PDMS devices (the ability to integrate pumps and valves) and PS devices (the ability to permanently embed fluidic tubing and electrodes). The embedded fused-silica capillary enables high temporal resolution measurements from off-chip cell culture dishes and the embedded electrodes provide close to real-time analysis of small molecule neurotransmitters. A novel surface treatment for improved (reversible) adhesion between PS and PDMS is described using a chlorotrimethylsilane stamping method. It is demonstrated that a Pd decoupler is efficient at handling the high current (and cathodic hydrogen production) resulting from use of high ionic strength buffers needed for cellular analysis; thus allowing an electrophoretic separation and in-channel detection. The separation of norepinephrine (NE) and dopamine (DA) in highly conductive biological buffers was optimized using a mixed surfactant system. This PS-PDMS hybrid device integrates multiple processes including continuous sampling from a cell culture dish, on-chip pump and valving technologies, microchip electrophoresis, and electrochemical detection to monitor neurotransmitter release from PC 12 cells.
 
Article
The binding of drugs with serum proteins and binding agents such as human serum albumin, α1-acid glycoprotein, and lipoproteins is an important process in determining the activity and fate of many pharmaceuticals in the body. A variety of techniques have been used to study drug interactions with serum proteins, but there is still a need for faster or better methods for such work. High-performance liquid chromatography (HPLC) is one tool that has been utilized in many formats for these types of measurements. Advantages of using HPLC for this application include its speed and precision, its ability to be automated, its good limits of detection, and its compatibility with a wide range of assay formats and detectors. This review will discuss various approaches in which HPLC can be employed for the study of drug-protein interactions. These techniques include the use of soluble proteins in zonal elution and frontal analysis methods or vacancy techniques such as the Hummel-Dreyer method. Zonal elution and frontal analysis methods that make use of immobilized proteins and high-performance affinity chromatography will also be presented. A variety of applications will be examined, ranging from the determination of free drug fractions to the measurement of the strength or rate of a drug-protein interaction. Newer developments that will be discussed include recent work in the creation of novel mathematical approaches for HPLC studies of drug-protein binding, the use of HPLC methods for the high-throughput screening of drug-protein binding, and the creation and use of affinity monoliths or affinity microcolumns for examining drug-protein systems.
 
Article
High-throughput analyses of a large number of samples for pharmacokinetic (PK) studies are essential in drug development. Analysis of drug candidates from blood using LC-ESI-MS generally requires separation of the plasma fraction followed by various offline sample preparation procedures. This step is a bottleneck that impedes throughput. In order to overcome this difficulty and accelerate analysis in PK and other studies, we developed an approach allowing the direct analysis of low volumes of whole blood (10 μL) after dilution and centrifugation. Samples were injected in an online-SPE-LC-ESI-MS/MS setup allowing a total run time of only 126 s for a full gradient separation. Analytes were extracted from the matrix within 30 s by turbulent flow chromatography. Subsequently, a full gradient separation was carried out within 1.5 minutes on a 50 × 2.1 mm (1.7 μm) RP-18 column and the analytes were sensitively detected by ESI-MS/MS in SRM mode. The performance of this new ultra fast online SPE-LC-ESI-MS/MS approach was demonstrated by the analysis of diclofenac (DCF), a widely used anti-inflammatory drug. DCF eluted at stable retention times (±0.33%) with narrow peak width (FWHM 3.3 ± 0.15 s). The method displays excellent analytical performance, with a limit of detection of 6 fmol on column, a linear range of over four orders of magnitude and a negligible carry over of 0.12 ± 0.03% for DCF. The PK profile of DCF administered by topical and intraperitoneal routes in rats and by oral route in one human volunteer is investigated using this method. Finally, general applicability of the approach for drugs is demonstrated by analysis of rofecoxib and several inhibitors of the soluble epoxide hydrolase. This new method requires only readily available, off the shelf standard LC instrumentation, and is compliant with the requirements of green analytical chemistry.
 
UPLC-MS MRM chromatograms showing the retention times of the three human urinary microbial co-metabolites multiple transitions. (Figure 1A) Analytes and 2 H internal standards detected in ESI(+) mode, (Figure 1B) analytes and 2 H internal standards detected in ESI(À) mode. The x-axis shows the time in minutes and the y-axis the relative response (0-100%). 
Article
The role of the gut microbiome in human health, and non-invasive measurement of gut dysbiosis are of increasing clinical interest. New high-throughput methods are required for the rapid measurement of gut microbial metabolites and to establish reference ranges in human populations. We used ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) -- positive and negative electrospray ionization modes, multiple reaction monitoring transitions -- to simultaneously measure three urinary metabolites (phenylacetylglutamine, 4-cresyl sulphate and hippurate) that are potential biomarkers of gut function, among multi-ethnic US men and women aged 40-59 from the INTERMAP epidemiologic study (n = 2000, two timed 24-hr urine collections/person). Metabolite concentrations were quantified via stable isotope labeled internal standards. The assay was linear in the ranges 1ng/mL (lower limit of quantification) to 1000ng/mL (phenylacetylglutamine and 4-cresyl sulfate) and 3ng/mL to 3000ng/mL (hippurate). These quantitative data provide new urinary reference ranges for population-based human samples: mean (standard deviation) 24-hr urinary excretion for phenylacetylglutamine was: 1283.0 (751.7) μmol/24-hr (men), 1145.9 (635.5) μmol/24-hr (women); for 4-cresyl sulphate, 1002.5 (737.1) μmol/24-hr (men), 1031.8 (687.9) μmol/24-hr (women); for hippurate, 6284.6 (4008.1) μmol/24-hr (men), 4793.0 (3293.3) μmol/24-hr (women). Metabolic profiling by UPLC-MS/MS in a large sample of free-living individuals has provided new data on urinary reference ranges for three urinary microbial co-metabolites, and demonstrates the applicability of this approach to epidemiological investigations.
 
EI-mass spectra of AEP-2-nonanone adducts: (A) Z-isomer, (B) E-isomer. Adducts were obtained by derivatization of turmeric root extract using AEP-33 and AEP-34 in a 1 : 1 ratio. 
Article
We describe an isotope coding strategy that enables simultaneous GC-MS analysis of multiple samples for substrate identification and quantification. The method relies on direct measurement of isotopic ethyl carbenium ions serving as mass spectral tags in a zone of minimal interference (ZMI) at m/z 31-37. Sample aldehyde and ketone mixtures were reacted with isotopic 2-aminooxyethyl propionates to illustrate the method, which determined the relative abundance of the mixed compounds with an average 95% accuracy. ZMI reporter ion detection also enables chemoselective substrate profiling and absolute quantification, as demonstrated using a biologically derived sample.
 
Article
This work demonstrates that recordable compact discs (CDs) that contain gold as a reflective layer can be used as an electrode substrate for microchip-based analysis systems. A fabrication procedure that enables the reproducible patterning of multiple electrodes has been developed. It is shown that the microelectrodes can be integrated within a PDMS-based fluidic network and used for amperometric detection of electroactive analytes at both single and dual microelectrodes. A detailed comparison is made between the CD-based patterned electrodes and electrodes made by the traditional method of sputtering gold and titanium adhesion layers onto a glass substrate. It is also shown that mercury can be electrodeposited onto a CD-based microelectrode and the amalgam electrode used to selectively detect thiols. Finally, it is demonstrated that a decoupler for microchip-based electrophoresis can be made by electrodepositing palladium onto a gold electrode and a separate downstream gold working electrode can be used for amperometric detection. These CD-based patterned electrodes are attractive alternatives for situations where device cost is of a concern or sputtering facilities are unavailable.
 
Schematic illustration of target protein–MNP based affinity extraction coupled with ESI-MS/MS for identification of enzyme inhibitors in complex matrices. 
In vitro tests on inhibitory activity
Chemical structures of ellagic acid (compound 1), gallagic acid (compound 2), punicalin (compound 3), and punicalagin (compound 4). 
Article
Target protein - magnetic nanoparticle (MNP) conjugates, i.e. α-glucosidase-MNP and protein tyrosine phosphatase 1B (PTP1B)-MNP, were prepared and evaluated for the first time for affinity extraction of the enzyme inhibitors from herbal extracts. Four ligands extracted from granati pericarpium were identified by ESI-MS analysis. In vitro tests indicated that they inhibited both α-glucosidase and PTP1B, two important target proteins for diabetic treatment.
 
Article
The feasibility of using EDXRF for a rapid quantitative analysis of gold in tumor tissue has been investigated. The protocol described here demonstrates that sample biopsies can be analyzed in as little as 8 hours, with minimal sample preparation. Samples were prepared by drying a 35 μL aliquot of tissue dissolved in KOH in a standard EDXRF cup on a Prolene® support, producing a thin sample. Calibration curves of XRF peak intensity (CPS/mA) to the gold concentration (0-50 PPM) were prepared for liver, tumor, and a mix of tissue types. A linear regression demonstrated an R(2) correlation of 0.93. Analysis of experimental samples showed that gold accumulation in tumors (5.8-41.3 PPM) was in agreement with previous studies, where samples were processed using INAA or ICP-MS. This report provides guidance for elemental analysis of gold in tissue in a shorter time span, showing potential for its use in a clinical setting.
 
Article
A novel ZrO2 nanoparticles-modified carbon paste electrode (ZONMCPE) was fabricated and used to study the electrooxidation of norepinephrine (NE), acetaminophen (AC), folic acid (FA) and their mixtures by electrochemical methods. Using differential pulse voltammetry (DPV), a highly selective and simultaneous determination of NE, AC and FA has been explored at the modified electrode. Differential pulse voltammetry peak currents of NE, AC and FA increased linearly with their concentrations at the ranges of 1.0 × 10−7–2.0 × 10−3 M, 1.0 × 10−6–2.5 × 10−3 M and 2.0 × 10−5–2.5 × 10−3 M, respectively and the detection limits for NE, AC and FA were 8.95 × 10−8, 9.12 × 10−7and 9.86 × 10−6 M, respectively. The modified electrode displayed strong function for resolving the overlapping voltammetric responses of NE, AC and FA into three well-defined voltammetric peaks. In the mixture containing NE, AC and FA, the three compounds can well separate from each other with potential differences of 220, 290 and 510 mV between NE–AC, AC–FA and NE–FA, respectively, which was large enough to determine NE, AC and FA individually and simultaneously.
 
Article
The differential pulse adsorptive stripping voltammetric behavior of selenium (IV)–p-aminobenzene sulfonic acid–cetyltrimethylammonium bromide system at a bismuth-coated glassy carbon electrode (BiFE) has been investigated. A well-defined and sensitive stripping peak of the selenium (IV)–p-aminobenzene sulfonic acid complex was observed at −0.76 V (vs. SCE) in a 0.15 mol/L acetate solution (pH 2.9) at a deposition potential of −0.40 V (for 120 s). The linear range was 2–30 μg/L and the detection limit for an accumulation time of 300 s was 0.1 μg/L. This method was applied to determine the trace amount of selenium in the samples.
 
Article
A new method for the detection of latent fingermarks on thermal paper by dry contact with 1,2-indanedione, which reacts with the amino acids present to give coloured, photo luminescent prints is described. The simple and reliable method is based on contact between the thermal paper sample and reagent impregnated treatment papers. Different treatment paper reagent formulations and treatment times were investigated. The conditions which provided the best performance used treatment papers prepared from an acid-free fluorous solution containing 1,2-indanedione and zinc chloride, with a contact time of 48 h. The dry contact approach was compared to current methods used by law enforcement agencies within Australia and was found to give similar or better performance.
 
PLE conditions during cleaning and extraction 
Ratios (%) between the PAH concentration values obtained by Soxhlet extraction with 10% diethyl ether in hexane (set as 100%) and by PLE with hexane (extraction conditions reported in Table 1). The error bars in the graph represent the standard deviation.
Article
The aim of the present study was to develop a pressurized liquid extraction (PLE) method as an alternative to the relatively time consuming Soxhlet extraction procedure described in the United States Environmental Protection Agency (US EPA) method TO-13A for the extraction of PAHs adsorbed onto polyurethane foam plugs (PUFs). For this purpose PUF air samples were collected and split into two parts: one part extracted using PLE and the other one using Soxhlet extraction. Comparable PAH concentrations were obtained upon analysis of the extracts showing that the PLE method developed in this work is a more convenient choice than the commonly used Soxhlet extraction technique proposed by US EPA for the determination of PAHs in air samples. In fact, the developed PLE method required shorter assay times (minutes versus hours), less solvent consumption and simpler operational methods. The exhaustiveness of the developed PLE method was evaluated using repeat static extraction cycles, demonstrating an extraction efficiency for the PAHs of greater than 99 %. The PLE method was then applied to diesel exhaust and wood smoke PUF samples showing an extraction efficiency for the PAHs of greater than 93 % and 96 %, respectively. Furthermore, a PLE method for PUF cleaning was developed as well and employed as an alternative to Soxhlet extraction. The PLE methods developed for cleaning and extracting PUFs presented in this work are suitable to be used in mutagenicity studies using the Ames Salmonella assay as no mutagenicity was found in the PLE generated blanks.
 
Chemical structures of 17 compounds and naringin (IS).
MRM chromatograms of 17 compounds assayed along with IS and the total ion chromatogram (TIC) of S. glabra . (a) The MRM chromatograms of 17 compounds; (b) protocatechuic acid ( 1 ); (c) 3- O -ca ff eoylquinic acid ( 2 ), 5- O -ca ff eoyl quinic acid ( 4 ) and 4- O -ca ff eoylquinic acid ( 6 ); (d) eleutheroside B 1 (3); (e): fraxin ( 5 ); (f) ca ff eic acid ( 7 ); (g) isofraxidin ( 8 ); (h) neoastilbin ( 9 ), astilbin ( 10 ), neoisoastilbin ( 12 ) and isoastilbin ( 13 ); (i) rosmarinic acid-4- O - b - D -glucoside ( 11 ); (j) rosmarinic acid ( 14 ); (k) quercetin-3- O - b - D -glucuronide ( 15 ); (l) quercitrin ( 16 ); (m) chlor- 
Precision, repeatability and stability of the 17 constituents assayed
Recoveries of the 17 determined constituents
Article
A high performance liquid chromatography with electrospray tandem mass spectrometry (HPLC-ESI-MS/MS) method has been developed to quantify 17 bioactive compounds in Sarcandra glabra and its preparations simultaneously. These constituents including flavones, coumarins, caffeoyl derivatives and sesquiterpenoids, were detected by ESI- ionization method and quantified by multiple reaction monitor (MRM). All 17 constituents were separated and determined within 17 minutes. The linear regressions were acquired with r2 > 0.9990, respectively. The precision was evaluated by intra- and inter-day tests, and relative standard deviation (R.S.D.) values were reported within the range of 0.86–2.29%, 1.16–4.83% and 0.87–4.94%, 0.69–4.92% for mixed standard solutions and extract solutions, respectively. The recovery studies for the assayed constituents were observed over the range of 80.20–119.68%. It demonstrated that the method developed was successfully applied for quantification of 17 main constituents, which provided a new basis for overall assessment on quality of S. glabra and its preparations.
 
Article
Metal–organic frameworks (MOFs), a novel class of hybrid inorganic–organic materials, possess high surface area, good thermal stability and selectivity, and thus have great potential for use as sorbent materials. MOF-177 is attractive for its large pores, high adsorptivity and selectivity, which has rarely been used in analytical science. Herein a facile magnetization of MOF-177 for rapid magnetic solid phase extraction of phenols from environmental water samples was studied, with analysis using gas chromatography-mass spectrometry. The magnetization of MOF-177 microcrystals as well as solid-phase extraction (SPE) of phenols was achieved simultaneously by mixing MOF-177 and Fe3O4@SiO2 microparticles in the water sample under sonication. Under the optimized conditions, the developed method showed good linearity within the range of 1–200 μg L−1, low detection limits (16.8–208.3 ng L−1) and quantitation limits (56.0–694.2 ng L−1). The recoveries are between 83.3 and 108.7% with the spiked level of 25 μg L−1. The results demonstrated that the Fe3O4@SiO2–MOF-177 magnetic microspheres are promising sorbents in the MSPE field in environmental samples.
 
Article
Required routine monitoring of endocrine disrupting compounds in real samples demands for cost-effective, selective and sensitive detection methods. Layered tungsten disulfide (WS2) nanosheet is a kind of two-dimensional covalent-network solid material with remarkable structural and electronic properties that attract increasing interest in recent years. In this work, the WS2 nanosheets are prepared by a one-step sonication-assisted exfoliation method and characterized using X-ray powder diffraction, scanning electron microscopy and transmission electron microscopy. A novel aptamer-based label-free electrochemical biosensor for 17β-estradiol is fabricated with the aptamers immobilized on the WS2 nanosheets/Au nanoparticels modified glassy carbon electrode through Au-S interaction. After blocked with bovine serum albumin, the aptamer probe is then bound with the addition of 17β-estradiol to form the estradiol/aptamer complex on the electrode surface, which leads to a significantly decrease of peak current. The change in the peak current has a good linear relationship with 17β-estradiol concentration in the range of 1.0×10-11 to 5.0×10-9 M, with a detection limit of 2.0×10-12 M (3σ/S). The aptamer sensor exhibits high sensitivity and remarkable reproducible analytical performance, and has been successfully applied for the determination of 17β-estradiol in serum and water samples with recoveries of 96.0-104.2%. The layered WS2 nanosheet/Au nanoparticles film thus acts as an efficient platform for assembling of bio-probes, and will be extended to other analytes such as protein, DNA and RNA electrochemical biosensing.
 
Article
The CP4 EPSPS gene is widely used in herbicide-tolerant crops/plants all over the world. In this study, a sensitive liquid chromatography tandem mass spectrometry (LC-MS/MS) method has been developed and validated to quantify the amount of CP4 EPSPS expression in Nicotiana tabacum leaves. The quantification of protein was used to measure the unique peptides of the CP4 EPSPS protein. Two peptides unique to CP4 EPSPS were synthesized and labelled in H218O to give 18O stable isotope labelled peptides which served as internal standards. The validated method resulted in good specificity and linearity. The intra- and inter-day precisions and accuracy for all samples were satisfactory. The results demonstrated that the novel method was sensitive and selective to quantify CP4 EPSPS in the crude extract without time-consuming pre-separation or purification procedures.
 
Typical GC-MS chromatograms from the FFA analysis of mice adipose tissues from the (A) control group, (B) low dosage group and (C) high dosage group. The peak assignments are: (1) L -serine; (2) 
Differential metabolites detected in adipose tissues of high dose TCDD-exposed mice by metabolomic analysis based on GC-MS
The score plot from partial least-squares-discriminant analysis classifying the high dosage group (8 – 14), low dosage group (15 – 21) and control group (1 – 7). 
Box plot of metabolites of (A) myristic acid and (B) stearic acid in control, low dosage and high dosage groups. 
Contribution for one group to another group of (A) low-control and (B) high-control.
Article
Dioxin exposure tends to accumulate in adipose tissue and alters metabolism in mammals. In this study, gas chromatography coupled with mass spectrometry (GC-MS) in conjunction with multivariate statistical analysis was applied to profile small molecular metabolites in adipose tissue of aryl hydrocarbon receptor (AhR)-high affinity wild-type C57BL/6J mice exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Partial least squares discriminant analysis model was also constructed to map the discrimination between TCDD dosages and control group. As a result, a total of 16 differential metabolites were identified in high-dose TCDD group compared to control group, and 12 free fatty acids (FFAs) were highlighted among them. Both saturated and unsaturated FFA levels were significantly elevated in adipose tissues of TCDD-exposed mice. This promising tool for global characterization highlights FFAs which could be served as indicators for understanding the toxic responses to TCDD exposure in a dose-dependent manner. The data indicated that the use of GC-MS coupled with multivariate statistical analysis could provide new insight for fatty acid biosynthesis on AhR activation with TCDD exposure in wild-type mice.
 
Article
In this work, Fe3O4@Ag2Se/Ag nanocomposites were fabricated on a self-cleaning and recyclable surface-enhanced Raman scattering (SERS) substrate via a simple and ingenious precipitation shift reaction. The superparamagnetic property of Fe3O4 facilitates the efficient purification of products with the assistance of an external magnetic field. The as-prepared substrates have excellent stability and show no significant loss after six recycles for the photodegradation of rhodamine B (RhB). The unique Raman enhancement effect of Fe3O4@Ag2Se/Ag substrates indicates that RhB can be detected at a concentration as low as 1 × 10−8 M. Furthermore, the experimental results also suggest that these nanocomposites may be promising multifunctional SERS substrate candidates for environmental monitoring, cleaning and so on.
 
Article
In this paper, a simple and sensitive ECL sensor based on mesoporous silica (mSiO2) nanospheres was constructed for the quantitative detection of matrine (MT). Electrochemical and ECL behaviors were investigated with Ru(bpy)32+/mSiO2/Nafion modified electrodes and the sensor was used for detection of matrine under Ru(bpy)32+/tripropylamine (TPA) system. The influence of pH and scan rate was studied. Under optimum conditions the experimental results indicated that the sensor had excellent ECL efficiency and showed a good response to the concentration of MT with a linear range from 1.5×10-6 M to 2.0×10-3 M. The lowest detection limit was 0.5 μM with a relative standard deviation 5.47%. This constructed ECL sensor could be applicable for real sample analysis.
 
Article
The coordination compound of Ru(II) with three 2,2’-bipyridine ligands possesses a potent photosensitization capacity for electron- and energy-transfer processes. In combination with salts of peroxydisulfate acid as sacrificial electron acceptors, Ru(bpy)32+ is widely used for photocatalytic oxidative transformations in organic synthesis and water splitting. The drawback of this system is that bipyridine degrades in the resulting strongly oxidative conditions, the concentration of Ru(bpy)32+ diminishes, and the photocatalytic reaction eventually stops. A commonly employed assay for the determination of the Ru(bpy)32+, UV-Vis spectroscopy, has low selectivity and does not distinguish between the intact complex and its decayed forms. Here, we report a matrix assisted laser desorption/ionisation mass spectrometric method for quantitative analysis of Ru(bpy)32+ in photochemical reaction mixtures. The developed method was successfully used for the determination of intact Ru(bpy)32+ during the course of the water photooxidation reaction. The significant difference between the results of MALDI MS and UV-Vis analyses was observed.
 
Article
We present a 3D darkfield imaging method for tracking AuNPs. With this approach, we recorded the entire transmembrane process of cell-penetrating peptide (CPP) modified AuNPs from the plasma membrane surface to deep inside the cell.
 
Article
A novel chemically modified electrode is constructed based on a multi-walled carbon nanotube (MWCNT), nickel hydroxide nanoparticle (NHNP) and Mobil catalytic material number 41 (MCM-41) composite modified glassy carbon electrode (MWCNTs–NHNPs–MCM-41/GCE). It is demonstrated that the sensor can be used successfully for the simultaneous determination of levodopa (LD), paracetamol (PAR) and tryptophan (TRY). The measurements were carried out by the application of differential pulse voltammetry (DPV), cyclic voltammetry (CV) and chronoamperometry (CA) methods. Under the optimum conditions the electrode provides linear response versus concentration with detection limits of 0.15 μM for LD, 0.01 μM for PAR and 0.11 μM for TRY using the DPV method.
 
Article
Genkwa flos, a traditional Chinese medicine, displays severe hepatotoxicity when it is excessively or chronically used in its raw form. It has been proven that the chloroform extracts within Genkwa flos are responsible for its hepatotoxicity. Note that the vinegar process procedure may weaken the toxicity and enhance the therapeutic effects. This study was conducted to investigate a quality control method of the chloroform extracts of Genkwa flos and to identify the potential hepatotoxic ingredients using HL-7702 cells. A LC-MS method was developed and fully validated to simultaneously determine three flavonoids (apigenin, genkwanin and hydroxygenkwanin), three lignans (syringaresinol, medioresinol and matairesinol) and two diterpene esters (yuanhuacine and genkwadaphnin) in the chloroform extracts. With satisfactory linearity, precision, repeatability, stability and recovery, the developed method was then applied to compare the content changes of the eight compounds in raw and processed herbs. After processing, the content of flavonoids increased, the lignans did not obviously change, while the diterpene esters decreased. Compared with the blank control group, the HL-7702 cells treated with the two diterpene esters exhibited obvious morphology change, viability decrease and increase in the level of hepatic marker enzymes in cell culture supernatant. The study showed a comprehensive quantitative method to simultaneously determine eight compounds of the chloroform extracts from Genkwa flos, and they indicated that yuanhuacine and genkwadaphnin could be two of the potential hepatotoxic substances of the herb.
 
Article
This study proposed a fast, simple and sensitive ultra-high-pressure liquid chromatography-tandem mass spectrometry (UPLC-MS/MS)-based method for the detection of abamectin in edible oils. An effective one-step process of extraction and cleanup of abamectin from edible oils was achieved with the use of a humic acid-bonded silica (HAS) based solid phase extraction (SPE), providing good cleanup performance and satisfactory recovery of abamectin. The effects of experimental variables, such as the amount of sorbents, loading, washing and eluting solvents, and the flow rates of sampling and eluting have been studied in detail. Under the optimized conditions, the method validation was performed in terms of linearity, recovery and precision. Good linearity was obtained for abamectin with R2 0.9996. The limit of detection (LOD) was found to be 0.16 μg/kg. The method recoveries of abamectin spiked at three concentration levels in a blank sample were from 91.7% to 101.8%, with inter- and intra-day relative standard deviations (RSDs) less than 7.0%.
 
Article
Sulfide sulfur is an important indicator of environmental monitoring and anaerobic bioengineering, has attracted increasing attention due to its significance in the anaerobic biotreatment process and high toxicity to human and aquatic microorganisms. A detection system was designed for rapid and accurate determination of sulfide sulfur in anaerobic system by gas-phase molecular absorption spectrometry (GPMAS). Based on the maximum absorption of hydrogen sulfide (H2S) at 202.6 nm, the calibration curve between sulfide content and absorbance was obtained, which was used to calculate the sulfide concentration in samples. The simulated samples of landfill leachate were detected after anaerobic reaction. A new method for removal of the effects of interference ions on determination of sulfide in the fermentation broth was proposed. The results showed that the method gave satisfactory precision and recovery. The detection limit of H2S in biogas is 5.1×10-3 mg L-1, the quantification limit is 1.7×10-2 mg L-1; the detection limit of S2- in fermentation broth is 1.2×10-2 mg L-1, the quantification limit is 4.1×10-2 mg L-1 while the detection limit of acid volatile sulfide (AVS) in fermentation residue is 2.7×10-2 mg g-1(dry sample) and the quantification limit is 8.9×10-2 mg g-1(dry sample). This indicates that the proposed method is suitable for determination of sulfide sulfur derived from anaerobic system.
 
Article
A homogeneous label free colorimetric sensing strategy for bleomycin (BLM) assay was developed on the basis of BLM enhanced Fe(II)-H2O2-ABTS reaction. Fe(II) exhibits a catalytic effect on H2O2-mediated oxidation of ABTS by Fenton chemistry. BLM•Fe(II) complex possessed a much higher catalytic ability than Fe(II) probably due to the further formation of more active “activated oxo-iron-bleomycin complex”. The present method was convenient without any complicated chemical synthesis, modification, or tedious experimental procedures. And the analysis results can be seen with the naked eye and monitored by UV-vis spectra. The peak absorbance exhibits a linear relationship with BLM concentrations from 25 nM to 1 μM and a detection limit of 16 nM can be achieved. The designed colorimetric strategy may provide a promising alternative for the BLM detection in clinical samples.
 
Article
This study aimed to investigate the application of the near infrared spectroscopy (NIRS) and multivariate calibration methods for direct determination of tannin content in the Acacia mearnsii bark, in order to improve control during the tannin content extraction process. For this purpose, 89 bark samples were collected in the industrial plant of an extractive tannin industry. The spectra in the near infrared were acquired using a FT-NIR spectrometer with an integrating sphere, an Indium-Gallium-Arsenic detector in the range of 7,500 to 4,000 cm-1, resolution of 16 cm-1 and 23 scans divided in two different ways: a) in natura samples (no sample processing); and, b) dried and milled samples. The partial least squares models (PLS) were developed and different strategies were investigated during the infrared spectra preprocessing. The results of the prediction were compared to the ones obtained through the reference methodology (NBR 11131), showing values for the root mean square error of prediction (RMSEP) between 2.11 and 2.42% for the dried and milled bark samples, and 2.31 and 2.54% for the in natura samples. These results show that NIRS combined with multivariate calibration methods may be used for direct determination of tannin content in Acacia mearnsii bark. Low need of sample preparation, short analysis time, no reagent consumption and, consequently, no waste generation are the main characteristics of the proposed method
 
Top-cited authors
Rasmus Bro
  • University of Copenhagen
Craig E Banks
  • Manchester Metropolitan University
Kathleen Murphy
  • Chalmers University of Technology
Daniel Graeber
  • Helmholtz-Zentrum für Umweltforschung
Colin Andrew Stedmon
  • Technical University of Denmark