Vapor Generation Atomic Fluorescence Spectrometry Research Articles

Application of flow injection–green chemical vapor generation–atomic fluorescence spectrometry to ultrasensitive mercury speciation analysis of water and biological samples

A simple, non-chromatographic and green method based on flow injection UV photochemical or ultrasonic vapor generation atomic fluorescence spectrometry (AFS) was developed for the determination and speciation analysis of mercury. Mercury cold vapor (Hg0) was generated by using only formic acid and UV or ultrasonic irradiation, and was subsequently detected by AFS. Both mercury (Hg2+) and methyl mercury (MeHg) can be converted to Hg0 for the determination of total mercury with UV irradiation, while only Hg2+ can be reduced to Hg0 with ultrasonic irradiation, thus determining only Hg2+. Then, the concentration of MeHg can be calculated by subtracting the Hg2+ concentration from the total mercury concentration. The optimal conditions for the best cold vapor generation efficiencies are discussed in detail, together with interference from transition metals. This new speciation analysis not only provides high sensitivity for the determination of mercury species but further eliminates the use of toxic reducing reagents and avoids potential destruction of analyte species that occur in chromatographic separation. Moreover, a simpler and less toxic Hg2+ standard series can be used for the calibration of both Hg2+ and MeHg. The limit of detection is 0.005 or 0.01μgL−1 for total mercury with the UV or inorganic mercury with the ultrasonic irradiation, respectively. This method was successfully applied to ultrasensitive mercury speciation analysis of water and biological samples.

Label-Free and Separation-Free Atomic Fluorescence Spectrometry-Based Bioassay: Sensitive Determination of Single-Strand DNA, Protein, and Double-Strand DNA.

Based on selective and sensitive determination of Hg(2+) released from mercury complex by cold vapor generation (CVG) atomic fluorescence spectrometry (AFS) using SnCl2 as a reductant, a novel label-free and separation-free strategy was proposed for DNA and protein bioassay. To construct the DNA bioassay platform, an Hg(2+)-mediated molecular beacon (hairpin) without labeling but possessing several thymine (T) bases at both ends was employed as the probe. It is well-known that Hg(2+) could trigger the formation of the hairpin structure through T-Hg(2+)-T connection. In the presence of a specific target, the hairpin structure could be broken and the captured Hg(2+) was released. Interestingly, it was found that SnCl2 could selectively reduce only free Hg(2+) to Hg(0) vapor in the presence of T-Hg(2+)-T complex, which could be separated from sample matrices for sensitive AFS detection. Three different types of analyte, namely, single-strand DNA (ssDNA), protein, and double-strand DNA (dsDNA), were investigated as the target analytes. Under the optimized conditions, this bioassay provided high sensitivity for ssDNA, protein, and dsDNA determination with the limits of detection as low as 0.2, 0.08, and 0.3 nM and the linear dynamic ranges of 10-150, 5-175, and 1-250 nM, respectively. The analytical performance for these analytes compares favorably with those by previously reported methods, demonstrating the potential usefulness and versatility of this new AFS-based bioassay. Moreover, the bioassay retains advantages of simplicity, cost-effectiveness, and sensitivity compared to most of the conventional methods.

Ovalbumin labeling with p-hydroxymercurybenzoate: The effect of different denaturing agents and the kinetics of reaction

The aim of our study was to investigate how denaturing agents commonly used in protein analysis influence the labeling between a reactive molecule and proteins. For this reason, we investigated the labeling of ovalbumin (OVA) as a globular model protein with p-hydroxymercurybenzoate (pHMB) in its native state (phosphate buffer solution) and in different denaturing conditions (8molL−1 urea, 3molL−1 guanidinium thiocyanate, 6molL−1 guanidinium chloride, 0.2% sodium dodecyl sulfate, and 20% methanol). In addition to chemical denaturation, thermal denaturation was also tested. The protein was pre-column simultaneously denatured and derivatized, and the pHMB-labeled denatured OVA complexes were analyzed by size exclusion chromatography (SEC) coupled online with chemical vapor generation–atomic fluorescence spectrometry (CVG–AFS). The number of –SH groups titrated greatly depends on the protein structure in solution. Indeed, we found that, depending on the adopted denaturing conditions, OVA gave different aggregate species that influence the complexation process. The results were compared with those obtained by a common alternative procedure for the titration of –SH groups that employs monobromobimane (mBBr) as tagging molecule and molecular fluorescence spectroscopy as detection technique.We also investigated the labeling kinetics for denatured OVA and pHMB, finding that the 4 thiolic groups of OVA have a very different reactivity toward mercury labeling, in agreement with previous studies.

Concentration and distribution of mercury in drainage catchment sediment and alluvial soil of China

The China Geochemical Baselines (CGB) project provides nation-wide catchment sediment/alluvial soil geochemical baseline data for 76 elements including Hg from 3382 top (0–25cm) and 3380 deep sediment/alluvial soil samples (under a depth of 100cm) at 3382 sampling sites, corresponding to a sampling density of about 1 site per 3000km2. Mercury was determined by cold vapour generation atomic fluorescence spectrometry (AFS) under strict quality control using field duplicates, standard reference materials and analytical replicate samples. The 25th percentile is at 13 and 11μg/kg in top and deep sediment/alluvial soil samples, respectively; these concentrations are close to the crustal abundance in China. The median Hg value is at 26 and 18μg/kg in top and deep sediment/alluvial soil samples, respectively; the 75th percentile is 56μg/kg in top and 36μg/kg in deep sediment/alluvial soil samples. Mercury concentrations at the 50th (26μgHg/kg) and 75th (56μgHg/kg) percentiles exhibit systematic enrichment in the near-surface material. The Hg distribution maps show distinct increasing trends from northern to southern and from western to eastern China, which are primarily related to the distribution of parent rocks, including rocks associated with mineral resources of Hg, Sb, Au, As, Pb–Zn, and climate, resulting in different soil types, as well as to population density with accompanying industrial development. Anomalous Hg concentrations in top sediment/alluvial soil samples above the 85th percentile (87μg/kg) occur mainly in south and south-west and sparsely in north and east China; they most likely have a dual origin, natural and human-induced, with the latter having a greater contribution because of the intense industrial activities, and particularly mercury emissions from Hg, Sb, As, Au, Pb–Zn mining, coal combustion, and production of batteries, fluorescent lamps, thermometers and cement. The spatial distribution map of Hg ratios of top to deep sediment/alluvial soil samples displays higher values, suggesting that top samples are most likely polluted from human activities in the highly populated urban areas of eastern China. About 6.86% and 3.52% of top and deep sediment/alluvial soil samples, respectively, have Hg concentrations higher than the soil contamination limit of 150μg/kg set by the National Environmental Standards for Heavy Metals of the People's Republic of China.

Magnetic solid-phase extraction combined with in situ slurry cold vapor generation atomic fluorescence spectrometry for preconcentration and determination of ultratrace mercury

A magnetic SPE method combined with CVG-AFS for the determination of Hg2+is established.

Microwave Photochemical Reactor for the Online Oxidative Decomposition of p-Hydroxymercurybenzoate (pHMB)-Tagged Proteins and Their Determination by Cold Vapor Generation-Atomic Fluorescence Detection

A novel method is presented for the characterization and determination of thiolic proteins. After the labeling with p-hydroxymercurybenzoate, the pHMB-labeled proteins underwent on-line oxidation with a novel microwave (MW)/UV photochemical reactor, followed by cold vapor generation-atomic fluorescence spectrometry (CVG-AFS) detection. The MW/UV process led to the conversion of pHMB to Hg(II) with a yield of 89.0 ± 0.5% without using chemical oxidizing reagents and avoiding the use of toxic carcinogenic compounds. Hg(II) was reduced to Hg(0) in a knotted reaction coil with NaBH4 solution, stripped from the solution by an argon flow and detected. The chromatographic method for labeled thiolic peptides was linear in the 0.2-100 μmol L(-1) range, with a LOD as mercury of 57 nmol L(-1). This system has proven to be a useful interface for liquid chromatography coupled with CVG-AFS in the determination and characterization of thiolic proteins. This method has been applied to the determination of thiolic peptides after tryptic digestion of serum albumins from different species (human, bovine, rat, horse, and sheep).

Determination of thiomersal by flow injection coupled with microwave-assisted photochemical online oxidative decomposition of organic mercury and cold vapor atomic fluorescence spectroscopy

We developed a flow injection (FI) method for the determination of thiomersal (sodium ethylmercurithiosalicylate, C9H9HgNaO2S) based on the UV/microwave (MW) photochemical, online oxidation of organic mercury, followed by cold vapor generation atomic fluorescence spectrometry (CVG-AFS) detection. Thiomersal was quantitatively converted in the MW/UV process to Hg(II), with a yield of 97±3%. This reaction was followed by the reduction of Hg(II) to Hg(0) performed in a knotted reaction coil with NaBH4 solution, and AFS detection in an Ar/H2 miniaturized flame. The method was linear in the 0.01–2μgmL−1 range, with a LOD of 0.003μgmL−1. This method has been applied to the determination of thiomersal in ophthalmic solutions, with recoveries ranging between 97% and 101%. We found a mercury concentration in commercial ophthalmic solutions ranging between 7.5 and 59.0μgmL−1.

Preconcentration and in-situ photoreduction of trace selenium using TiO2 nanoparticles, followed by its determination by slurry photochemical vapor generation atomic fluorescence spectrometry

We have developed a method for the determination of trace levels of total selenium in water samples. It integrates preconcentration, in-situ photoreduction and slurry photochemical vapor generation using TiO2 nanoparticles, and the determination of total selenium by AFS. The Se(IV) and Se(VI) species were adsorbed on a slurry of TiO2 nanoparticles which then were exposed to UV irradiation in the presence of formic acid to form volatile selenium species. The detection limits were improved 17-fold compared to hydride generation and 56-fold compared to photochemical vapor generation, both without any preconcentration. No significant difference was found in the limits of detection (LODs) for Se(IV) and Se(VI). The LOD is as low as 0.8 ng L−1, the precision is better than 4.5 % (at a level of 0.1 μg L−1 of selenium). The method gave good recoveries when applied to the determination of total selenium in a certified tissue reference material (DORM-3) and in spiked drinking water and wastewater samples containing high concentrations of transition and noble metal ions. It also excels by very low LODs, a significant enhancement of sample throughput, reduced reagent consumption and sample loss, and minimal interference by transition and noble metal ions.

Ultraviolet vapor generation atomic fluorescence spectrometric determination of mercury in natural water with enrichment by on-line solid phase extraction

A novel method, which coupled an on-line solid phase extraction (SPE) enrichment with ultraviolet vapor generation (UVG) atomic fluorescence spectrometry (AFS), was developed to improve the sensitivity of mercury determination and to remove the interference of some anion and organics to UVG of mercury. A high mercury retention efficiency and maximum exclusion of inorganic and organic matrix in water samples were achieved by using C18 SPE mini cartridge modified with sodium diethyldithiocarbamate (DDTC). Fast and efficient elution from the cartridge was found by using l-cysteine mixing solution. Furthermore, through the investigation of different UV reactor designs, the most important factor was the structure of the reactor (which corresponded roughly to the photon flux) wherein the tubing was sintered into the UV lamp to give the highest UV generation efficiency. The second factor was the materials of the tubing (which roughly corresponded to the working wavelength). Synthetic quartz, characterized by the highest transparency at 185nm, attained the highest UVG efficiency, suggesting that the most favorable wavelength for UVG was 185nm. Under optimum conditions, the achievable detection limit (3σ) with sample loadings of 10.0mL was 0.03ngL−1 and 0.08ngL−1 with different manifolds, respectively. The method was successfully applied to the determination of Hg in tap water, river water and lake water samples.

Determination of Mercury (Hg) in Sediment by a Sequential Injection (SI) System With Cold Vapor Generation Atomic Fluorescence Spectrometry (CVAFS) Detection After a Rapid and Mild Microwave-Assisted Digestion

A simple and rapid method has been developed for the determination of total Hg in drainage sediment. The method is performed by using a sequential injection (SI) system with cold vapor generation atomic fluorescence spectrometry (CVAFS) after a closed microwave assisted digestion. Digestion was carried out at a temperature of 140°C for 5 minutes using a mixture of 10% HCl + 50% HNO3 +40% H2O as digestion acid media. Stability experiment revealed that the extracted samples were stable in 24 hours. The SI–CVAFS system was well optimized. At optimized conditions, the detection limit of the method was 0.5 ng/g−1. Relative standard deviation (RSD) for the complete procedure by the analysis of the 10 digestions was 3.7%. The method was validated against 3 drainage sediment certified reference materials: GSD-2, GSD-9, and GSD-10 and successfully applied to the determination of Hg in the sediment of Pi River, China.

Advanced oxidation using Fe3O4 magnetic nanoparticles and its application in mercury speciation analysis by high performance liquid chromatography-cold vapor generation atomic fluorescence spectrometry

A novel, green and efficient post-column oxidation method using Fe(3)O(4) magnetic nanoparticles (MNPs) was developed to on-line convert hydride generation/cold vapor generation (HG/CV) inactive species to their active species without microwave/UV irradiation. It was applied to high performance liquid chromatography HG/CV atomic fluorescence spectrometry (HPLC-HG/CV-AFS) to enable sensitive speciation analysis of both HG/CV inactive and active species. Inorganic mercury (Hg(2+)), methylmercury (MeHg), ethylmercury (EtHg) and phenylmercury (PhHg) were selected as model compounds to validate the methodology. Separation of these mercury species was accomplished on a RP-C18 column with a mixture of acetonitrile and water (10 : 90) at pH 6.8 containing 0.12% (m/v) L-cysteine as the mobile phase. In the presence of 0.6% (v/v) H(2)O(2), on-line conversion of the organomercury species eluted from the HPLC column to Hg(2+) was obtained using the advanced oxidation method at pH 2.0. Optimum conditions for the separation, oxidation and cold vapor generation were carefully investigated. The limits of detection (LODs) were 0.7, 1.1, 0.8 and 0.9 μg L(-1) (as Hg) for Hg(2+), MeHg, EtHg and PhHg, respectively, corresponding to 14, 22, 16 and 18 pg absolute detection limits for Hg(2+), MeHg, EtHg and PhHg by using a 20 μL sample loop, which are comparable to or better than those previously reported. National Research Council Canada DORM-2 fish muscle tissue and several real water samples were analyzed to validate the accuracy of the proposed method.

Evaluation of different extraction procedures for determination of organic Mercury species in petroleum by high performance liquid chromatography coupled with cold vapor atomic fluorescence spectrometry

An extraction procedure for extracting organic mercury species including methylmercury (MeHg) and ethylmercury (EtHg) from petroleum samples was developed. Three extraction methods (shaking, ultrasonic and microwave assisted extraction) using different extraction solvents (TMAH, KOH/CH3OH, HCl and acidic CuSO4/KBr) were investigated by comparing the extraction efficiency of the organic mercury species. Microwave assisted extraction at 60W for 5min using TMAH (tetramethylammonium hydroxide, 25%, m/v) provided the most satisfactory extraction efficiency for MeHg and EtHg in petroleum at 86.7%±3.4% and 70.6%±5.9%, respectively. Speciation analysis of mercury was done by on-line coupling of high performance liquid chromatography with cold vapor generation atomic fluorescence spectrometry (HPLC-CV-AFS). The proposed method was successfully applied to analyze several crude oil and light oil samples. The concentrations of MeHg ranged from under detection limit to 0.515ngg−1, whereas EtHg was not detected in the samples. This method can be a very useful tool in evaluating the risk of mercury emissions from petroleum.

Determination of Hg, As, Pb, and Cd in Orchard Soils by Sequential Injection Vapor Generation Atomic Fluorescence Spectrometry

An analytical procedure was developed for determination of Hg, As, Pb, and Cd in soil samples using sequential injection vapor generation atomic fluorescence spectrometry (SI-VG-AFS) with sample preparation by microwave digestion system. The effects of analytical conditions on the fluorescence intensity were investigated and optimized. Under the optimized condition, the detection limits of the method were 5, 68, 40, and 3 ng L−1 for Hg, As, Pb, and Cd, respectively. The accuracy of method was verified by the determination of the certified reference soil, and the recoveries for Hg, As, Pb, and Cd were in the range of 98.7–106.1%. The proposed method has been successfully applied to determine the heavy metals in navel orange orchard soils in Ganzhou, and the environmental quality of the orchard soils was assessed based on the content of the heavy metals. According to the second criterion of environmental quality standard for soils, Pb content in all soil samples collected from the orchards of 18 districts were within safe limits, but a few orchards were slightly contaminated with Hg, As, and Cd. Comparison of heavy metal mean concentrations with the safe limits of environmental quality standard for soils, the quality of Ganzhou navel orange orchard soils were in line with the request of the green food production base.

Determination of Methylmercury and Inorganic Mercury in Sediments by High Performance Liquid Chromatography Hyphenated to Cold Vapor Generation Atomic Fluorescence Spectrometry Following a Microwave-Assisted Extraction

A high performance liquid chromatography(HPLC) coupled with cold vapor generation atomic fluorescence spectrometry method(CVAFS) has been developed for the separation and determination of methylmercury(MeHg+) and inorganic mercury(Hg2+) in sediment samples.The previous extraction of samples was carried out at a temperature of 80 ℃ for 8 min by using 0.1%(V/V) 2-mercaptoethanol as the extractant.The separation and determination of mercury species were achieved by direct injecting the extractant to HPLC-CVAFS system.Under the optimized conditions,the limit of detection was 0.58 ng/g for MeHg+ and 0.48 ng/g for Hg2+.The average recoveries were 96.2% and 95.8% for MeHg+ and Hg2+,respectively,by spiking three concentration levels of mercury species into samples.The proposed method was validated for the determination of certified reference material IAEA-405 and ERM-CC580,and the analytical results were in good agreement with the certified values.The proposed method was simple,rapid,accurate,no interference and suitable for the determination of methylmercury and inorganic mercury in sediment samples.

Antibody-biotemplated HgS nanoparticles: Extremely sensitive labels for atomic fluorescence spectrometric immunoassay

In this work, antibody goat anti-human IgG as a scaffold was employed for the synthesis and biofunctionalization of HgS nanoparticles (NPs) via a facile one-pot process. After a complete sandwich-type immunoreaction among primary antibody, human IgG and secondary antibody labeled with HgS NPs, a large number of mercury ions released from captured HgS NPs dissolution were quantitatively detected by chemical vapor generation atomic fluorescence spectrometry (CVG-AFS). Taking advantage of the signal amplification property of HgS NPs and the high sensitivity of CVG-AFS, the assay detected human IgG with a limit of detection (S/N = 3) of 0.6 ng mL(-1) (4.0 fmol mL(-1) or 0.4 fmol) and the response was linear over a dynamic range from 1.0 to 5.0 × 10(4) ng mL(-1) with a correlation coefficient of 0.996. A relative standard deviation (RSD) of 1.0 × 10(2) ng mL(-1) human IgG was 1.5% for within-batch (intra-assay) and 4.5% for between-batch (inter-assay). Other proteins, such as goat anti-rabbit IgG, goat anti-human IgG, rabbit anti-human IgG, carcinoembryonic (CEA), α-fetoprotein (AFP), human serum albumin (HSA) and bovine serum albumin (BSA) did not significantly interfere with the assay for human IgG. The analytical result of HgS NPs with AFS-based immunoassay technology for the quantification of human IgG in human serum from patients is in good agreement with the result obtained by conventional immunoturbidimetric method. The consequence shows that the novel immunosensor possessed satisfactory precision, extremely high sensitivity, high selectivity and could be applied for the quantification analysis of real samples.

Flow injection-chemical vapor generation atomic fluorescence spectrometry hyphenated system for organic mercury determination: A step forward

Monomethylmercury and ethylmercury were determined on line using flow injection-chemical vapor generation atomic fluorescence spectrometry without neither requiring a pre-treatment with chemical oxidants, nor UV/MW additional post column interface, nor organic solvents, nor complexing agents, such as cysteine. Inorganic mercury, monomethylmercury and ethylmercury were detected by atomic fluorescence spectrometry in an Ar/H 2 miniaturized flame after sodium borohydride reduction to Hg 0, monomethylmercury hydride and ethylmercury hydride, respectively. The effect of mercury complexing agent such as cysteine, ethylendiaminotetracetic acid and HCl with respect to water and Ar/H 2 microflame was investigated. The behavior of inorganic mercury, monomethylmercury and ethylmercury and their cysteine-complexes was also studied by continuous flow-chemical vapor generation atomic fluorescence spectrometry in order to characterize the reduction reaction with tetrahydroborate. When complexed with cysteine, inorganic mercury, monomethylmercury and ethylmercury cannot be separately quantified varying tetrahydroborate concentration due to a lack of selectivity, and their speciation requires a pre-separation stage (e.g. a chromatographic separation). If not complexed with cysteine, monomethylmercury and ethylmercury cannot be separated, as well, but their sum can be quantified separately with respect to inorganic mercury choosing a suitable concentration of tetrahydroborate (e.g. 10 − 5 mol L − 1 ), thus allowing the organic/inorganic mercury speciation. The detection limits of the flow injection-chemical vapor generation atomic fluorescence spectrometry method were about 45 nmol L − 1 (as mercury) for all the species considered, a relative standard deviation ranging between 1.8 and 2.9% and a linear dynamic range between 0.1 and 5 μmol L − 1 were obtained. Recoveries of monomethylmercury and ethylmercury with respect to inorganic mercury were never less than 91%. Flow injection-chemical vapor generation atomic fluorescence spectrometry method was validated by analyzing the TORT-1 certificate reference material, which contains only monomethylmercury, and obtaining 83 ± 5% of monomethylmercury recovered, respectively. This method was also applied to the determination of monomethylmercury in saliva samples.

Mercury speciation with l-cysteine functionalized cellulose fibre as adsorbent by atomic fluorescence spectrometry

The functionalization of cellulose fibre by grafting L-cysteine on the surface (Cys-fibre) significantly improves the sorption capacity toward mercury and methyl-mercury. The Cys-fibre is used to pack a mini-column for on-line separation and preconcentration of mercury species in a sequential injection system. The retained mercury and methyl-mercury could readily be recovered by a mixture of L-cysteine and nitric acid. The inorganic mercury is selectively quantified using the cold atomization mode with vapor generation atomic fluorescence spectrometry. The total amount of mercury is determined by adopting the flame/heat atomization mode, and thus the concentration of methyl-mercury is achieved by the difference. When 1000 μL of sample solution is processed followed by elution with 100 μL of eluent, detection limits of 1 ng L−1 (3σ, n = 9) for inorganic mercury and 3 ng L−1 (3σ, n = 9) for methyl-mercury are obtained within linear ranges of 0.01–0.7 μg L−1Hg2+ and 0.03–2.0 μg L−1MeHg, respectively. The precisions for Hg2+ and MeHg of 1.5% RSD (n = 11) and 2.6% RSD (n = 9) are recorded at 0.1 μg L−1 and 1.0 μg L−1, respectively. The procedure has been validated by analyzing mercury in certified reference material of BCR176 and a cosmetic sample. Speciation of mercury and methyl-mercury in a series of water samples and the extracts of cosmetic and seaweed samples are performed, and favorable spiking recoveries have been demonstrated.

Microwave-Assisted Photochemical Reactor for the Online Oxidative Decomposition and Determination of p-Hydroxymercurybenzoate and Its Thiolic Complexes by Cold Vapor Generation Atomic Fluorescence Detection

We developed a photochemical method for the online oxidation of p-hydroxymercurybenzoate (PHMB), an organic mercury species widely used for mercaptan and thiolic compound labeling. The method is based on a fully integrated online UV/microwave (MW) photochemical reactor for the digestion of PHMB, followed by cold vapor generation atomic fluorescence spectrometry (CVG-AFS) detection. The MW/UV process led to the quantitative conversion of PHMB and thiol-PHMB complexes to Hg(II), with a yield between 91% and 98%, without using chemical oxidizing reagents and avoiding the use of toxic carcinogenic compounds. This reaction was followed by the reduction of Hg(II) to Hg(0), performed in a knitted reaction coil with NaBH(4) solution, and AFS detection in an Ar/H(2) miniaturized flame. The low MW power applied (18 W) allowed us to keep constant the temperature of the photochemical reactor (21 ± 1 °C), using a flowing water bath. This avoided peak widening due to diffusion processes generally occurring at high temperatures and in the additional cooling coil. This method has been applied to the determination of thiols in human plasma, blood, and wine.

Direct determination of mercury in white vinegar by matrix assisted photochemical vapor generation atomic fluorescence spectrometry detection

This paper proposes the use of photochemical vapor generation with acetic acid as sample introduction for the direct determination of ultra-trace mercury in white vinegars by atomic fluorescence spectrometry. Under ultraviolet irradiation, the sample matrix (acetic acid) can reduce mercury ion to atomic mercury Hg 0, which is swept by argon gas into an atomic fluorescence spectrometer for subsequent analytical measurements. The effects of several factors such as the concentration of acetic acid, irradiation time, the flow rate of the carrier gas and matrix effects were discussed and optimized to give detection limits of 0.08 ng mL − 1 for mercury. Using the experimental conditions established during the optimization (3% v/v acetic acid, 30 s irradiation time and 20 W mercury lamp), the precision levels, expressed as relative standard deviation, were 4.6% (one day) and 7.8% (inter-day) for mercury ( n = 9). Addition/recovery tests for evaluation of the accuracy were in the range of 92–98% for mercury. The method was also validated by analysis of vinegar samples without detectable amount of Hg spiked with aqueous standard reference materials (GBW(E) 080392 and GBW(E) 080393). The results were also compared with those obtained by acid digestion procedure and determination of mercury by ICP-MS. There was no significant difference between the results obtained by the two methods based on a t-test (at 95% confidence level).

Determination of S-nitrosoglutathione in plasma: Comparison of two methods

In this work we compared the results of the GSNO determination in human plasma by two independent methods. The first method is based on the pre-column derivatization of GSNO thiolic part by p-hydroxymercury benzoate (PHMB) and followed by the determination of GS-PHMB product by reversed phase chromatography coupled to chemical vapour generation atomic fluorescence spectrometry (RPC-CVGAFS). The second method is based on RPC separation of GSNO from interfering compounds and the post-column, on-line enzymatic hydrolysis of GSNO by commercial gamma-glutamyl transferase (GGT) and fluorescence detection. Endogenous GSNO was determined only in plasma from blood sampled by syringe (not by Vacutainers) and ranged between 157 and 257nM on the basis of RPC-CVGAFS method, and between 90 and 225nM by RPC-FD method. There was a good correlation between the two methods (slope=1.06+/-0.09, R(2)=0.9543). RPC-CVGAFS method based on PHMB derivatization determined a GSNO concentration 60+/-20nM in excess with respect to RPC-FD method. Sampling issues connected with common blood sampling procedures like venipuncture and sampling in syringe or Vacutainers still introduce in GSNO analysis unknown factors, which require further investigations.