Evaluation of N-acetylcysteine and glutathione as quenching agents for the analysis of halogenated disinfection by-products.

Disinfection by-products (DBPs), formed from the reactions of disinfectants with natural organic matter and halides in drinking water, were considered to be cytotoxic and genotoxic, and might trigger various cancers. The relatively low concentration of DBPs in finished water (low µg/L or even ng/L levels) and the interference from water matrix inhibited in situ determination of DBPs. Moreover, the further formation and degradation of DBPs by disinfectants during the holding time (several hours to several days) from sample collection to analysis could adversely affect the determination of DBPs. To obtain accurate, precise and reliable data of DBP occurrence and formation, robust and reliable sample preservation is indispensable. However, the commonly used quenching agents (e.g., sodium sulfite, sodium thiosulfate, and ascorbic acid) for sample preservation can decompose reactive DBPs by reductive dehalogenation. This study evaluated the performance of N-acetylcysteine (NAC) and glutathione (GSH) as quenching agents for the analysis of halogenated DBPs by investigating the stoichiometry of the disinfectant-quenching agent reaction, the formation of DBPs during chlor(am)ination of NAC or GSH, and the effects of NAC or GSH on the stability of 18 individual DBPs and total organic halogen (TOX). Based on the results of this study, NAC and GSH were considered to be ideal quenching agents for the analysis of most DBPs and TOX, except halonitromethanes.

Plasma metabolomics study reveals the critical metabolic signatures for benzene-induced hematotoxicity.

Metabolomics has been used to explore the molecular mechanism and screen biomarkers. However, the critical metabolic signatures associated with benzene-induced hematotoxicity remain elusive. Here, we performed a plasma metabolomics study in 86 benzene-exposed workers and 76 healthy controls, followed by a validation analysis in mice, to investigate the dynamical change of the metabolic profile. We found that 8 fatty acids were significantly altered in both benzene-exposed worker and benzene-exposed animal models. These metabolites were significantly associated with S-phenylmercapturic acid and WBC, and they mediated the benzene-induced WBC decline. Furthermore, in vivo results confirm that fatty acid levels were dynamically altered, characterized by a decrease at 15 days and then sharp increases at 30 and 45 days. Following these identified fatty acids, the potential metabolic pathways were investigated. Fatty acids, as precursors for fatty acid oxidation, may disturb the balance of fatty acid biosynthesis and degradation. Our results reveal that fatty acid metabolism was strongly reprogrammed after benzene exposure. This abnormal change of fatty acids might be the key metabolic signature associated with benzene-induced hematotoxicity.

Psychosocial impairment following mild blast-induced traumatic brain injury in rats.

Traumatic brain injury (TBI) is associated with increased risk for mental health disorders, impacting post-injury quality of life and societal reintegration. TBI is also associated with deficits in psychosocial processing, defined as the cognitive integration of social and emotional behaviors, however little is known about how these deficits manifest and their contributions to post-TBI mental health. In this pre-clinical investigation using rats, a single mild blast TBI (mbTBI) induced impairment of psychosocial processing in the absence of confounding physical polytrauma, post-injury motor deficits, affective abnormalities, or deficits in non-social behavior. Impairment severity correlated with acute upregulations of a known oxidative stress metabolite, 3-hydroxypropylmercapturic acid (3-HPMA), in urine. Resting state fMRI alterations in the acute post-injury period implicated key brain regions known to regulate psychosocial behavior, including orbitofrontal cortex (OFC), which is congruent with our previous report of elevated acrolein, a marker of neurotrauma and 3-HPMA precursor, in this region following mbTBI. OFC of mbTBI-exposed rats demonstrated elevated mRNA expression of metabotropic glutamate receptors 1 and 5 (mGluR1/5) and injection of mGluR1/5-selective agonist in OFC of uninjured rats approximated mbTBI-induced psychosocial processing impairment, demonstrating a novel role for OFC in this psychosocial behavior. Furthermore, OFC may serve as a hotspot for TBI-induced disruption of psychosocial processing and subsequent mental health disorders.

Fabrication of a "Selenium Signature" Chemical Probe-Modified Paper Substrate for Simultaneous and Efficient Determination of Biothiols by Paper Spray Mass Spectrometry.

Significant efforts have been made to develop robust and reliable methods for simultaneous biothiols determination in different matrices, but there still exist the problems such as easy oxidation, tedious derivatization, and difficulty in discrimination, which brings unsatisfactory results in their accuracy and fast quantification in biological samples. To overcome these problems, a simultaneous biothiols detection method combining a "selenium signature" chemical probe and paper spray mass spectrometry (PS-MS) was proposed. In the strategy, the modified-paper substrate is used to enhance the analytical performance. Chemical probe Ebselen-NH2 that has a specific response to biothiols was designed and covalently fixed on the surface of an oxidized paper substrate. By the identification of derivatized product with distinctive selenium isotope distribution and employment of the optimized PS-MS method, qualitative and quantitative analysis of five biothiols including glutathione (GSH), cysteine (Cys), cysteinylglycine (CysGly), N-acetylcysteine (Nac), and homocysteine (Hcy) were realized. Biothiols in plasma and cell lysates were measured with satisfactory results. The established method not only provides a novel protocol for simultaneous determination of biothiols, but also is helpful for understanding the biological and clinical roles played by these bioactive small molecules.

Prospective randomized multicentre comparison on sibling oocytes comparing G-Series media system with antioxidants versus standard G-Series media system.

RESEARCH QUESTION: Does the inclusion of three antioxidants (A3), acetyl-l-carnitine (ALC), N-acetyl-l-cysteine (NAC) and alpha-lipoic acid (ALA) improve human embryo development and pregnancy potential? DESIGN: Prospective randomized multicentre comparison of sibling oocytes. A total of 1563 metaphase II oocytes from 133 patients in two IVF centres. Day 3 embryo and day 5/6 blastocyst quality were assessed. Good embryo quality on day 3 was defined as 8 to 10 cells with even cells and low fragmentation; good quality blastocysts as 3BB or greater. Clinical outcome was assessed on transfers of fresh or vitrified-warmed blastocyst on day 5. RESULTS: Of the two-pronuclei, 40.7% (G-Series) and 50.2% (G-Series with A3 group) resulted in good quality embryos on day 3 (P < 0.05). The implantation rate by fetal sac was 39.2% and 50.6%, and by fetal heartbeat was 37.8% and 47.1% for the G-Series and G-Series with A3 group, respectively. When stratified by female patient age, patients 35-40 years had an implantation rate by fetal sac and heart of 23.5% in the G-Series compared with 57.5% (P < 0.05) and 50.0% (P < 0.05) in the A3 group. The ongoing pregnancies in patients 35-40 years were significantly higher in the A3 group (50%) compared with the control (25.8%) (P < 0.05). CONCLUSIONS: The presence of antioxidants during IVF and embryo culture for patients 35-40 years resulted in a significant increase in implantation and pregnancy rate. Supplementation of antioxidants to IVF and culture media may therefore improve the viability of human embryos in assisted reproductive technologies, plausibly through the reduction of oxidative stress.

Global Profiling of Toxicologically Relevant Metabolites in Urine: Case Study of Reactive Aldehydes.

Among the numerous unknown metabolites representative of our exposure, focusing on toxic compounds should provide more relevant data to link exposure and health. For that purpose, we developed and applied a global method using data independent acquisition (DIA) in mass spectrometry to profile specifically electrophilic compounds originating metabolites. These compounds are most of the time toxic, due to their chemical reactivity toward nucleophilic sites present in biomacromolecules. The main line of cellular defense against these electrophilic molecules is conjugation to glutathione, then metabolization into mercapturic acid conjugates (MACs). Interestingly, MACs display a characteristic neutral loss in MS/MS experiments that makes it possible to detect all the metabolites displaying this characteristic loss, thanks to the DIA mode, and therefore to highlight the corresponding reactive metabolites. As a proof of concept, our workflow was applied to the toxicological issue of the oxidation of dietary polyunsaturated fatty acids, leading in particular to the formation of toxic alkenals, which lead to MACs upon glutathione conjugation and metabolization. By this way, dozens of MACs were detected and identified. Interestingly, multivariate statistical analyses carried out only on extracted HRMS signals of MACs yield a better characterization of the studied groups compared to results obtained from a classic untargeted metabolomics approach.

S-Nitroso-N-acetylcysteine (NAC-SNO) as an Antioxidant in Cured Meat and Stomach Medium.

The stability of lipids in meat products depends on the initial concentration of hydroperoxides, the catalytic involvement of metal ions and myoglobin, endogenous antioxidants, and biological and technological factors. Ground meat was treated with additives, sealed in vacuum bags, heated to 75 °C, and stored opened to air at 4 °C. S-Nitroso-N-acetylcysteine (NAC-SNO) at concentration like nitrite used by the industry prevents lipid peroxidation in the product, even after storage for 1 month at 4 °C. The same simulated treatments at different concentrations of both compounds show that NAC-SNO acts as an antioxidant ∼4-fold better than nitrite at pH 6.2 or 3.0. Ascorbic acid significantly improves nitrite antioxidant effect. NAC-SNO was found to prevent, much better than nitrite, accumulation of reactive aldehydes and hydroxynonenal protein modification. In condition like those used by the industry for meat products processing, NAC-SNO acts better than nitrite to provide antioxidant protection without the side effect of N-nitrosation, oxidation, and the loss of nutrient generated by nitrite.

An ultra-high-performance liquid chromatography tandem mass spectrometry method for oxidative stress biomarker analysis in wastewater.

Reported herein is the development of an analytical method for the detection of four oxidative stress biomarkers in wastewater using ultra-high-performance liquid chromatography coupled with tandem mass spectrometry (UHPLC-MS/MS) and solid phase extraction (SPE). The following four biomarkers of oxidative stress and lipid peroxidation have been investigated: hydroxynonenal-mercapturic acid (HNE-MA), 8-iso-prostglandin F2beta (8-iso-PGF2ß), 8-nitroguanine (8-NO2Gua) and 8-hydroxy-2-deoxyguanosine (8-OHdG). The method showed very good performance: accuracy (> 87%), precision (> 90%), method quantification limits (1.3-3.0 ng L-1) and biomarker stability in wastewater in the case of HNE-MA, 8-OHdG and 8-iso-PGF2ß. In contrast, 8-NO2Gua was found to be less stable in wastewater, which affected its method performance: accuracy (> 63%), precision (> 91%) and method quantification limits (85.3 ng L-1). Application of the developed method resulted in, for the first time, HNE-MA being successfully observed and quantified within wastewater over a study period of a week (displayed average daily loads per capita of 48.9 ± 4.1 mg/1000/people/day). 8-iso-PGF2ß was detected with good intensity but could not be quantified due to co-elution with other isomers. 8-OHdG was detected, albeit at < MQL. This study demonstrates the potential for expanding on the possible endogenous biomarkers of health used in urban water fingerprinting to aid in measuring health in near-real time on a community-wide scale.

Microchip Isotachophoresis: Analysis of Pharmaceuticals.

Microchip isotachophoresis (µITP) is a miniaturized version of conventional isotachophoresis (ITP) characterized by low sample and buffer consumption and reduced waste production. µITP with universal conductivity detection is suitable for quantitative analysis of relatively simplified samples that contain analyte(s) at relatively high concentration, e.g., pharmaceutical preparations. Here we describe in detail a principle of µITP in terms of reaching highly precise results. A practical use of µITP is shown on the analyses of various pharmaceutical preparations for content of major constituents including active pharmaceutical ingredients as well as pharmaceutical counterions. The pharmaceuticals are treated only minimally prior to the ITP run on a microchip with coupled channels and sample injection channel with 0.9 µL volume. Developed method is suitable for rapid (analysis time up to 10 min), precise (less than 1% RSD of analyte zone length), and accurate (recovery of 98-101%) determination of major pharmaceutical ingredients using a method of internal standard for data evaluation.

Simultaneous determination of total homocysteine, cysteine, glutathione, and N-acetylcysteine in brain homogenates by HPLC.

We have developed a simple, fast, accurate, and cheap method for the simultaneous determination of total cysteine, homocysteine, glutathione, and N-acetylcysteine in brain homogenates based on the reduction of disulfide bonds by tris(2-carboxyethyl) phosphine, pre-column derivatization of free thiol groups with 2-chloro-1-methylquinolinium tetrafluoroborate followed by ion-pair reversed-phase high-performance liquid chromatography separation with ultraviolet detection. The separation of thiol derivatives was achieved in 10 min. Linearity was observed in the range of 10-300, 0.7-10, 2-30, and 3-20 µmol/L homogenate with a limit of detection of 3.7, 0.2, 0.8, and 1.2 µmol/L homogenate for cysteine, homocysteine, glutathione, and N-acetylcysteine, respectively. The precision, calculated as relative standard deviation, was in the range of 1.21-4.77, 1.53-14.35, 0.47-1.92, and 1.61-8.95% for cysteine, homocysteine, glutathione, and N-acetylcysteine, respectively. The presented method was successfully applied to the selective determination of total amino thiols in pig brain tissue samples.

Fast and reliable BIA/amperometric quantification of acetylcysteine using a nanostructured double hydroxide sensor.

This study reports the preparation and characterization of nickel/lead hydroxide nanoparticles used to construct electrochemical sensors, which were investigated for amperometric quantification of N-acetylcysteine (NAC). The newly synthesised material presents good uniformity, with the lead (II) ions homogenously incorporated into the alpha nickel hydroxide crystal structure, confirmed by X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy analyses. Films of nanoparticles (3 nm in size) were prepared on conductive fluorine-doped tin oxide-coated glass slides and used connected to a specially built batch injection analysis (BIA) cell with a capacity of only 4 mL and the electrode positioned in the bottom. To attain optimal analytical performance, the main parameters for BIA measurements (volume injected, different velocities of injection and best distance of the pipette from the electrode) were evaluated, as was the working potential, to determine the optimal conditions. Linear responses were obtained for the concentration range from 20 to 220 µmol L-1, and the limits of detection (3σ/slope) and quantification (10σ/slope) were calculated as 0.23 µmol L-1 and 0.70 µmol L-1, respectively. The new NAC sensor does not exhibit a memory effect and has enormous potential utility in the quantitative determination of N-acetylcysteine in drugs. The results of the analysis of NAC obtained using BIA presented good concordance with those obtained by chromatography. The analytical frequency attained using BIA (120 analysis h-1) compares very favourably with the one obtained using chromatography (6 analysis h-1).

The determination of pharmaceutically active thiols using hydrophilic interaction chromatography followed postcolumn derivatization with o-phthaldialdehyde and fluorescence detection.

A rapid, precise and specific hydrophilic interaction chromatography (HILIC) combined with postcolumn derivatization using o-phthaldialdehyde and fluorescence detection was developed and validated for the determination of selected pharmaceutically active thiols. The analysis was carried out on a Diol HILIC column using a mobile phase consisting of acetonitrile and solution of 10 mmol/L citric acid adjusted with 1-propylamine to pH 5.5 in ratio 75:25 (v/v) for separation of cysteine and homocysteine and in ratio 85:15 (v/v) for separation of N-acetyl-l-cysteine and captopril. The postcolumn derivatization reaction was performed at room temperature using reagent (5 mmol/L OPA in 0.05 mol/L 4- (2-hydroxyethyl) piperazine-1-ethanesulfonic acid at pH 7) delivered at the flow rate of 0.3 mL/min. Fluorescence detection was carried out at excitation and emission wavelength of 345 nm and 450 nm, respectively. The effect of chromatographic conditions including acetonitrile content, salt concentration in the mobile phase and mobile phase pH on the retention of tested thiols was investigated. The postcolumn reaction conditions such as reaction temperature, derivatization reagent flow rate, o-phthaldialdehyde concentration and derivatization reagent pH were deeply studied. The developed method was validated in terms of linearity, accuracy, precision and selectivity according to the International Conference on Harmonisation guidelines. The HILIC method was successfully applied for the analysis of commercially available samples of pharmaceutically active thiols such as captopril, N-acetyl-l-cysteine (NAC) and cysteine.

Correlation between benzene and testosterone in workers exposed to urban pollution.

AIM: Many studies have examined the effects of benzene on testosterone. The purpose of this study was to evaluate the possible correlation between the blood levels of benzene and the levels of testosterone. MATERIALS AND METHODS: The study involved a group of 148 subjects. For every worker have been made out a blood sample for the evaluation of benzene and testosterone levels and an urine analysis for the evaluation of the levels of trans, trans-muconic acid and S-phenylmercapturic acid. We estimated the Pearson correlation coefficient between the variables in the sample and the urinary metabolites, age, length of service, gender, BMI. For the analysis of the major confounding factors it was performed a multiple linear regression. RESULTS: The Pearson correlation coefficiet showed: 1. a significant inverse correlation between the S-phenyl mercapturic acid and free testosterone; 2. a significant direct correlation between trans-trans muconic acid and BMI. After dividing the sample according to the median of blood benzene (161.0 ng / L), Pearson correlation coefficient showed a significant inverse correlation between the S-phenyl mercapturic acid and free testosterone in the group with values below this median. CONCLUSIONS: Our results, to be considered preliminary, suggest that occupational exposure to low levels of benzene, present in urban pollution, affect the blood levels of testosterone. These results need to be confirmed in future studies, with the eventual possibility of including more specific fertility tests.

Application of novel Ni(II) complex and ZrO2 nanoparticle as mediators for electrocatalytic determination of N-acetylcysteine in drug samples.

The electrooxidation of N-acetylcysteine (N-AC) was studied by a novel Ni(II) complex modified ZrO2 nanoparticle carbon paste electrode [Ni(II)/ZrO2/NPs/CPE] using voltammetric methods. The results showed that Ni(II)/ZrO2/NPs/CPE had high electrocatalytic activity for the electrooxidation of N-AC in aqueous buffer solution (pH = 7.0). The electrocatalytic oxidation peak currents increase linearly with N-AC concentrations over the concentration ranges of 0.05-600µM using square wave voltammetric methods. The detection limit for N-AC was equal to 0.009µM. The catalytic reaction rate constant, kh, was calculated (7.01 × 102 M-1 s-1) using the chronoamperometry method. Finally, Ni(II)/ZrO2/NPs/CPE was also examined as an ultrasensitive electrochemical sensor for the determination of N-AC in real samples such as tablet and urine.

Non-parametric estimation of low-concentration benzene metabolism.

Two apparently contradictory findings in the literature on low-dose human metabolism of benzene are as follows. First, metabolism is approximately linear at low concentrations, e.g., below 10 ppm. This is consistent with decades of quantitative modeling of benzene pharmacokinetics and dose-dependent metabolism. Second, measured benzene exposure and metabolite concentrations for occupationally exposed benzene workers in Tianjin, China show that dose-specific metabolism (DSM) ratios of metabolite concentrations per ppm of benzene in air decrease steadily with benzene concentration, with the steepest decreases below 3 ppm. This has been interpreted as indicating that metabolism at low concentrations of benzene is highly nonlinear. We reexamine the data using non-parametric methods. Our main conclusion is that both findings are correct; they are not contradictory. Low-concentration metabolism can be linear, with metabolite concentrations proportional to benzene concentrations in air, and yet DSM ratios can still decrease with benzene concentrations. This is because a ratio of random variables can be negatively correlated with its own denominator even if the mean of the numerator is proportional to the denominator. Interpreting DSM ratios that decrease with air benzene concentrations as evidence of nonlinear metabolism is therefore unwarranted when plots of metabolite concentrations against benzene ppm in air show approximately straight-line relationships between them, as in the Tianjin data. Thus, an apparent contradiction that has fueled heated discussions in the recent literature can be resolved by recognizing that highly nonlinear, decreasing DSM ratios are consistent with linear metabolism.

Evidence for non-linear metabolism at low benzene exposures? A reanalysis of data.

The presence of a high-affinity metabolic pathway for low level benzene exposures of less than one part per million (ppm) has been proposed although a pathway has not been identified. The variation of metabolite molar fractions with increasing air benzene concentrations was suggested as evidence of significantly more efficient benzene metabolism at concentrations <0.1 ppm The evidence for this pathway is predicated on a rich data set from a study of Chinese shoe workers exposed to a wide range of benzene concentrations (not just "low level"). In this work we undertake a further independent re-analysis of this data with a focus on the evidence for an increase in the rate of metabolism of benzene exposures of less than 1 ppm. The analysis dataset consisted of measurements of benzene and toluene from personal air samplers, and measurements of unmetabolised benzene and toluene and five metabolites (phenol hydroquinone, catechol, trans, trans-muconic acid and s-phenylmercapturic acid) from post-shift urine samples for 213 workers with an occupational exposure to benzene (and toluene) and 139 controls. Measurements from control subjects were used to estimate metabolite concentrations resulting from non-occupational sources, including environmental sources of benzene. Data from occupationally exposed subjects were used to estimate metabolite concentrations as a function of benzene exposure. Correction for background (environmental exposure) sources of metabolites was achieved through a comparison of geometric means in occupationally exposed and control populations. The molar fractions of the five metabolites as a function of benzene exposure were computed. A supra-linear relationship between metabolite concentrations and benzene exposure was observed over the range 0.1-10 ppm benzene, however over the range benzene exposures of between 0.1 and 1 ppm only a modest departure from linearity was observed. The molar fractions estimated in this work were near constant over the range 0.1-10 ppm. No evidence of high affinity metabolism at these low level exposures was observed. Our reanalysis brings in to question the appropriateness of the dataset for commenting on low dose exposures and the use of a purely statistical approach to the analysis.

[Biomarkers of internal exposure to toxicologically relevant contaminants in food]. / Biomarker der internen Exposition gegenüber toxikologisch relevanten Kontaminanten in Lebensmitteln.

The assessment of health risks resulting from the intake of genotoxic carcinogens in food depends essentially on a valid exposure assessment. The reliability of the external exposure estimation is restricted by various factors, e. g. inaccurate data from dietary protocols and variations of food contaminant contents. As an alternative, the individual internal exposure to genotoxic substances may be described by specific biomarkers in different matrices. For example, mercapturic acids formed after glutathione conjugation of electrophilic metabolites can be detected in the urine. This typically reflects the exposure to the parent compound over a period of one to two days. The determination of adducts in the blood proteins serum albumin (SA) and hemoglobin (Hb) allows for conclusions to be drawn about the external exposure within the last three weeks (SA) or within the last four months (Hb). Protein adducts are used routinely in occupational medicine as biomarkers of internal exposure to substances in the ambient air of the workplace. The availability of increasingly sensitive analytical techniques also makes it possible to detect numerous adducts in proteins from human blood samples that are formed after the continuous intake of very small doses of toxic substances from foods. Here, we present the current state of science exemplified by protein adducts of the food contaminants acrylamide, aflatoxin B1 and glycidol. The biomarker can be used in the future to investigate previously unknown relationships between internal exposure and disease incidences.

Determination of Diclofenac and N-Acetylcysteine by an Optimized Luminescence Method Using CdS Quantum Dots as Sensitizers.

A simple, sensitive and selective chemiluminescence method is proposed for the determination of Acetylcysteine and Diclofenac in pharmaceutical samples. The method is based on the measuring light intensity of NaHCO3-H2O2 @ CdS chemiluminescence system in the absence and presence of Acetylcysteine and Diclofenac. It was found that the intensity of chemiluminescence is increased by addition of acetylcysteine while the light intensity is decreased with increasing diclofenac concentration. The CdS quantum dots nanoparticles were characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), UV-Vis spectrophotometry and Fluorescence spectroscopy. The optimum conditions for maximizing the CL emission intensity were studied by means of a Box-Behnken experimental design combined with response surface modeling (RSM) and quadratic programming. Under the optimal conditions, results for measurement of diclofenac was found as follows: linear range 1 × 10-5 - 1 × 10-9 Molar with R2 = 0.98, limit of detection 5 × 10-10 Molar and relative standard deviation of 2.4% for diclofenac; and for N-acetylcysteine was : linear range 1 × 10-6 - 1 × 10-9 Molar, the limit of detection 5 × 10-10 Molar, and the relative standard deviation of 3.4%.

Distribution, enrichment, and source identification of selected heavy metals in surface sediments of the Siran River, Mansehra, Pakistan.

To assess the trace metal pollution in the Siran River, sediments were collected from 12 sites, from the left and right banks of the river in 2013. The concentrations, accumulation, distribution pattern, and pollution status of heavy metals in sediments were investigated using geoaccumulation index (I geo) and enrichment factor (EF). The toxic risk of heavy metals was assessed using interim sediment quality guidelines (ISQGs), portable effect level (PEL), threshold effect level (TEL), and toxic effect threshold (TET). I geo and EF values showed that sediments were loaded with Ni, Cd, Pb, and Co and no obvious variations were found among the left and right banks of the river. The EF and I geo values were found in order of Co > Pb > Ni > As > Cd > Cu > Zn > Fe and Cd > Co > Pb > Ni > As > Fe > Zn > Cu > Mn, respectively. Furthermore, multivariate statistical analysis like inter-metal correlation, cluster analysis (CA), and principal component analysis (PCA) results revealed that geogenic and anthropogenic activities were major sources of sediment contamination in the study area. These results indicated that more attention should be paid to the inner loads of sediment in order to achieve improvements in reservoir water quality after the control of external pollution.

Simultaneous assessment of endogenous thiol compounds by LC-MS/MS.

Biological thiol compounds are very important molecules that participate in various physiological events. Alteration in levels of endogenous thiols has been suggested as a biomarker of early stage of pathological changes. We reported a chemical derivatization- and LC-MS/MS-based approach to simultaneously determine thiol compounds including glutathione (GSH), cysteine (Cys), N-acetyl cysteine (NAC), homocysteine (Hcy), and cysteinylglycine (CysGly) in biological samples. Thiol-containing samples were derivatized with monobromobimane (mBrB) at room temperature, followed by LC-MS/MS analysis. Assessment of the analytes with baseline separation was completed within 10min, using a gradient elution on a C18 reversed-phase column. Excellent linearity was observed for all analytes over their concentration ranges of 1-400µM. The lowest limits of detection (S/N=3) in a range from 0.31fmol (for NAC) to 4.98fmol (for CysGly) were achieved. The results indicate that this approach was sensitive, selective, and well suited for high-throughput quantitative determination of the biological thiols.