Atomic Fluorescence Spectrometry Detection Research Articles

Homogeneous catalysis for photochemical vapor generation for speciation of inorganic selenium by high performance liquid chromatography-atomic fluorescence spectrometry

A simple, sensitive and cost-effective homogeneous catalysis photochemical vapor generation (PVG) system for HPLC separation and atomic fluorescence spectrometry detection was reported herein for the speciation analysis of trace Se(iv) and Se(vi).

Simultaneous and highly sensitive determination of selenium and tellurium species in environmental samples by on-line ionic liquid based in-situ solvent formation microextraction with hydride generation atomic fluorescence spectrometry detection

A novel on-line preconcentration and speciation analysis method for the simultaneous determination of inorganic Se and Te species is presented in this work. The methodology is based on the on-line formation of a hydrophobic ionic liquid (IL) directly in the liquid sample stream of a flow injection system, thus achieving an efficient and rapid extraction of the analytes complexed with ammonium pyrrolidine dithiocarbamate into the finely dispersed extractant droplets, that were then retained in a column filled with cotton. A full study of the chemical and hydrodynamical parameters was developed, including the right selection of the IL used as extractant and its concentration, pH, complexing reagent, sample and ion-exchange reagent volumes and column design. Additionally, a miniaturized external hydride generator was adapted to the spectrometer in order to increase the sensitivity of the atomic fluorescence measurements using only 250 μL of 5 mol L−1 HNO3 in methanol as eluent. The analytical figures of merit obtained for 15 mL of sample included sensitivity enhancement factors of 71, 70, 49 and 40 for Te(IV), Te(VI), Se(IV) and Se(VI), respectively, and limits of detection of 1.8 ng L−1 for both Te species, 2.6 ng L−1 for Se(IV) and 3.2 ng L−1 for Se(VI). After optimization, the method was successfully applied for the analysis of environmental samples: soils and sediments, as well as sea, river, underground and tap water.

Determination of arsenic species compound in blood by high performance liquid chromatographyatomic fluorescence spectrometry

Objective: To establish a method for determination of arsenic species in blood with high performance liquid chromatography-atomic fluorescence spectrometry (HPLC-AFS) . Methods: The effect of mobile phase about chromatography separation and sample pretreatment conditions and atomic fluorescence spectrometry detection parameters has been optimized to reliably measure the following four kinds of species arsenic compound including arsenic[As (III) ]、dimethylarsinic acid (DMA) 、monomethylarsonic acid (MMA) and arsenate[As (V) ] in acute intoxication human blood. The method of technical standard about within-run, between-run and recoveries of standard were optimized. Results: The method showed As (III) linear relationship was 2.63-100.00 μg/L, The detection limit was 2.63 μg/L. The relative coefficient (r) was 0.9999; DMA linear relationship was 3.21-100.00 μg/L, The detection limit was 3.21 μg/L. The r was 0.9992; MMA linear relationship was 3.41-100.00 μg/L, The detection limit was 3.41 μg/L. The r was 0.9998; As (V) linear relationship was 3.90-100.00 μg/L, The detection limit was 3.90 μg/L. The r was 0.9996. The average recovery of four species arsenic in tested samples ranged from 91.3%-99.8% with the relative standard deviation (RSD) from 2.39% to 4.05%. The within-run and between-run relative standard deviations (RSD) of repetitive measurement at 10.00, 40.00, 80.00 μg/L concentration levels were 1.99%-4.59% and 2.72%-4.53%. Conclusion: This method is low detection limit, good accurate and high sensitivity, proposed method had been applied to the analysis of arsenic species in blood samples those who acute intoxication or poisoning diagnosis.

Hybrid ionic liquid-3D graphene-Ni foam for on-line preconcentration and separation of Hg species in water with atomic fluorescence spectrometry detection

A preconcentration method based on a novel hybrid sorption nanomaterial consisting in a 3D graphene-Ni foam functionalized with an ionic liquid (IL) was developed for Hg species determination. The capability of different phosphonium-ionic liquids (PILs) to functionalize the hybrid material and form ion-pairs with Hg(II) chlorocomplex was evaluated. A comparative study with PILs containing the trihexyl(tetradecyl)phosphonium cation but different anions (dicyanamide and decanoate) and trihexyl(tetradecyl)phosphonium chloride was performed. Inorganic Hg (InHg) species was selectively retained forming a chlorocomplex (HgCl42−) followed by its retention in a column filled with the IL-3D graphene-Ni foam material implemented in an on-line micro solid phase extraction system (μSPE). The elution of Hg from the column was performed with SnCl2, which was also used as reducing agent for subsequent detection by cold vapor generation atomic fluorescence spectrometry (CV-AFS). Organic mercury species (OrgHg) were not retained on the sorption material of the column. The effect of several parameters determining the efficiency of the preconcentration and detection system (sample loading and elution flow rate, sample volume, instrumental conditions, etc.) was investigated. A sensitivity enhancement factor (EF) of 180 was achieved for InHg. The detection limit obtained after the preconcentration of 100 mL of sample was 3.6 ng L−1 of InHg. The relative standard deviation (RSD) was 4.1% (at 1 μg L−1 InHg and n = 10) calculated from the peak height of the absorbance signals (Gaussian form and reproducible peaks). This work reports the first application of the IL-3D graphene-Ni foam in an on-line μSPE preconcentration system for the speciation analysis of Hg in mineral, tap, and river water samples.

Ultra-trace tellurium preconcentration and speciation analysis in environmental samples with a novel magnetic polymeric ionic liquid nanocomposite and magnetic dispersive micro-solid phase extraction with flow-injection hydride generation atomic fluorescence spectrometry detection

A highly efficient magnetic dispersive micro-solid phase extraction (M-D-μSPE) method was developed for Te preconcentration and speciation analysis in different environmental samples. A novel magnetic polymeric ionic liquid nanocomposite synthesized based on the Radziszewski reaction was applied for the selective retention of Te(IV) species, followed by elution with 5 mol L−1 HCl and determination by flow-injection hydride generation atomic fluorescence spectrometry. Te(VI) was selectively determined by difference between total Te and Te(IV) after a pre-reduction step. Studies on the sorption capacity of the nanocomposite were performed, while several parameters concerning the retention, separation and elution were optimized. A 100% retention efficiency and a sensitivity enhancement factor of 67 were achieved. Limits of detection of 1.9 ng L−1 and 3.7 ng L−1, and standard deviations of 4.3% and 5.1% were obtained for Te(IV) and Te(VI). A gas-liquid separator with a low dead volume was used for reduced dispersion of the flow injection signals and additional sensitivity enhancement. Finally, the feasibility of the proposed M-D-μSPE method for Te speciation was demonstrated by the analysis of several environmental samples, such as tap, rain, river and underground waters, soils and sediments, with excellent recovery results in spiked samples.

Dielectric barrier discharge induced atomization of gaseous methylethylmercury after NaBEt4 derivatization with purge and trap preconcentration for methylmercury determination in seawater by GC-AFS

A novel method suitable for methylmercury (CH3Hg) analysis in seawater by gas chromatography (GC)-atomic fluorescence spectrometry (AFS) based on dielectric barrier discharge (DBD) induced atomization of gaseous methylethylmercury (CH3HgC2H5) after sodium tetraethylborate (NaBEt4) derivatization with purge and trap preconcentration was developed in this work. In the proposed method, with NaBEt4 used as derivatization reagent, the nonvolatile CH3Hg could be converted to the gaseous CH3HgC2H5 and trapped in a quartz tube with Tenax sorbent for preconcentration. A DBD atomizer was employed for the atomization of CH3HgC2H5 to Hg0 between the GC separation and AFS detection instead of the conventional thermal decomposition atomizer, which had not been reported before. The DBD atomizer not only produces a comparable atomization efficiency for CH3HgC2H5 to the thermal decomposition atomizer, but also can be operated at room temperature with low power consumption (5 W). The effects of DBD input discharge voltage, DBD discharge distance, N2 gas purge time, and thermal desorption time on CH3Hg determination were evaluated. The method provided good reproducibility (RSD, 2.0%) and low detection limits of CH3Hg (LOD, 0.0008 ng L−1). The proposed method was validated by the analysis of a certified reference material (GBW08675) and successfully applied to the determination of CH3Hg in sub ng L−1 level in different seawater samples.

An inter-laboratory comparison of different analytical methods for the determination of monomethylmercury in various soil and sediment samples: A platform for method improvement

An inter-laboratory study was conducted to compare results from different analytical methods for monomethylmercury (MeHg) concentrations in 17 soil and sediment samples. The samples were collected from mercury-contaminated areas, including Minamata Bay and Kagoshima Bay in Japan, the Idrija mercury mine in Slovenia, and an artisanal small-scale gold mining area in Indonesia. The Hg in these samples comes from several different sources: industrial waste from an acetaldehyde production facility, volcanic activity, Hg mining activity, and artisanal and small-scale gold mining activity (ASGM). MeHg concentrations in all the samples were measured in four separate laboratories, using three different determination methods: Kagoshima University (Japan), using high-performance liquid chromatography–chemiluminescence detection (HPLC-CL); National Institute for Minamata Disease (Japan), using gas chromatography–electron capture detection; and Metropolitan Council Environmental Services (USA) and Jozef Stefan Institute (Slovenia), both using alkylation-gas chromatography–atomic fluorescence spectrometry detection. The methods gave comparable MeHg results for most of the samples tested, but for some samples, the results exhibited significant variability depending on the method used. The HPLC-CL method performed poorly when applied to samples with elevated sulfur concentrations, producing MeHg concentrations that were much lower than those from the other methods. Additional analytical work demonstrated the elimination of this sulfur interference when the method was modified to bind sulfur prior to the analytical step by using Hg2+ as a masking agent. These results demonstrate the value of laboratory intercomparison exercises in contributing to the improvement of analytical methods.

A comparative evaluation of different ionic liquids for arsenic species separation and determination in wine varietals by liquid chromatography – hydride generation atomic fluorescence spectrometry

The application of different ionic liquids (ILs) as modifiers for chromatographic separation and determination of arsenite [As(III)], arsenate [As(V)], dimethylarsonic acid (DMA) and monomethylarsonic acid (MMA) species in wine samples, by reversed-phase high performance liquid chromatography coupled to hydride generation atomic fluorescence spectrometry detection (RP-HPLC-HG-AFS) was studied in this work. Several factors influencing the chromatographic separation of the As species, such as pH of the mobile phase, buffer solution concentration, buffer type, IL concentration and length of alkyl groups in ILs were evaluated. The complete separation of As species was achieved using a C18 column in isocratic mode with a mobile phase composed of 0.5% (v/v) 1-octyl-3-methylimidazolium chloride ([C8mim]Cl) and 5% (v/v) methanol at pH 8.5. A multivariate methodology was used to optimize the variables involved in AFS detection of As species after they were separated by HPLC. The ILs showed remarkable performance for the separation of As species, which was obtained within 18min with a resolution higher than 0.83. The limits of detection for As(III), As(V), MMA and DMA were 0.81, 0.89, 0.62 and 1.00μg As L−1. The proposed method was applied for As speciation analysis in white and red wine samples originated from different grape varieties.

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.

Improvement in Determination of Methylmercury in Sediments by Headspace Trap Gas Chromatography and Atomic Fluorescence Spectrometry after Organic Extraction and Aqueous Phase Ethylation

An automated method for determination of methylmercury in sediments was developed using headspace coupled to gas chromatography with atomic fluorescence spectrometry detection and aqueous phase ethylation. The method avoids the problems associated with purge and trap techniques. The volume of ethylating agent was optimized and headspace only or headspace trap modes were evaluated. The results showed that the latter mode provided better performance for methylmercury determination than the former. An organic extraction of methylmercury from sediment samples was used involving the use of copper(II) sulfate, potassium bromide, and sulfuric acid. The method was verified by analysis of sediment reference materials (IAEA-405; IAEA-433) and the results were in good agreement with certified values. Due to the low detection limit, the method is appropriate for analysis of contaminated and uncontaminated sediment samples at ultratrace levels.

UV-induced atomization of gaseous mercury hydrides for atomic fluorescence spectrometric detection of inorganic and organic mercury after high performance liquid chromatographic separation

A novel, simple, low power, low temperature (<45 °C) and high efficiency atomization technique using ultraviolet (UV) radiation was proposed for the atomization of gaseous mercury hydrides for their determination by atomic fluorescence spectrometry (AFS). This technique was used for the detection of inorganic mercury (Hg2+) and organic mercury (MeHg+ and EtHg+) after high performance liquid chromatographic separation. In the proposed method, with 0.5% (m/v) KBH4 used as a reductant, inorganic mercury was reduced to elemental mercury, whereas the organic mercury species formed their respective volatile organic mercury hydrides (MeHgH and EtHgH) which were flushed to the UV atomizer for atomization and AFS detection. Under the optimized experimental conditions, the limits of detection were found to be 0.38, 0.41 and 0.56 μg L−1, and the relative standard deviations (n = 3) were 1.1%, 2.6% and 1.4% for Hg2+, MeHg+ and EtHg+, respectively. The accuracy of the proposed method was validated by analyzing a certified reference sample (fish muscle tissue) with a satisfactory analytical result, and two water samples with recoveries in the range of 93.8–97.4%.

A simplified method for inorganic selenium and selenoaminoacids speciation based on HPLC–TR–HG–AFS

A simplified speciation method for the determination of selenite, selenate and three selenoaminoacids (selenocystine, selenomethylselenocysteine and selenomethionine) has being developed, based on the coupling of high performance liquid chromatography (HPLC), thermoreduction (TR), hydride generation (HG) and atomic fluorescence spectrometry (AFS). Most of the existing methods based on AFS detection employ a two step procedure to reduce selenate to selenite before HG: (i) Ultraviolet radiation followed by (ii) heating, to produce volatile hydrides of the selenium compounds. The proposed simplified method HPLC–TR–HG–AFS does not require ultraviolet radiation. Instead, KBr dissolved in a HCl solution is added during the heating step (thermoreduction), resulting in an effective hydride generation of the selenium species. Different variables (temperature, HCl and NaBH4 concentrations) have been optimized, using both univariant and multivariant experimental designs. The proposed method is therefore less complex and allows limits of detection, reproducibility and repeatability values similar or better than the existing AFS detection methods described in the literature. A Certified Reference Material (SELM-1 with certified selenomethionine content) and a Se-enriched algae sample have been successfully analyzed with the proposed method. The results were also compared to an alternative technique (GC–MS) that provided similar results.

Speciation of Inorganic- and Methyl-Mercury in Biological Matrixes by Electrochemical Vapor Generation from an l-Cysteine Modified Graphite Electrode with Atomic Fluorescence Spectrometry Detection

A novel nonchromatographic speciation technique for ultratrace inorganic mercury (Hg(2+)) and methylmercury (CH(3)Hg(+)) in biological materials is developed and validated by electrolytic vapor generation (EVG) coupled with atomic fluorescence spectrometry (AFS). The studies show that CH(3)Hg(+) and Hg(2+) can be converted to Hg vapor efficiently on an l-cysteine modified graphite cathode, which has never been reported before. We observe that only Hg(2+) can be converted efficiently to Hg vapor at low current mode (0.2 A). While at high current mode (2.2 A), both CH(3)Hg(+) and Hg(2+) can be reduced efficiently. As a result, we successfully establish an exact and sensitive method based on the current control to detect mercury speciation for the first time. The factors of electrolytic conditions have been optimized, and the potential mechanism is discussed. Under the optimal conditions, the detection limits (3s) of Hg(2+) and CH(3)Hg(+) in aqueous solutions are 0.098 and 0.073 μg L(-1), respectively. The relative standard deviations for 6 replicate determinations of 2 μg L(-1) Hg are determined as 3.2% and 4.7% for Hg(2+) and CH(3)Hg(+). The accuracy of the method is verified through the analysis of certified reference materials (CRM, NRC-DORM-2), and the proposed method has been applied satisfactorily to the determination of mercury speciation in several seafood samples by calibration curve mode.

Ultrasensitive determination of selenium by atomic fluorescence spectrometry using nano-TiO2pre-concentration and in situhydride generation

An ultrasensitive, simple and interference-free method using nano-TiO2 preconcentration and in situ slurry hydride generation (HG) coupled with atomic fluorescence spectrometry (AFS) was developed for the determination of trace selenium. Total Se reduced in Se(IV) form can be selectively adsorbed on TiO2 at pH < 8 for pre-concentration, and then separated and slurried/released by a mixture containing 3% (m/v) KBH4 and 1% (m/v) KOH. The slurry solution was mixed with 25% (v/v) HCl to generate selenium hydrides, which was subsequently separated from the liquid phase for subsequent AFS detection. Optimum conditions for adsorption, disadsorption and hydride generation of selenium as well as potential interferences from concomitant ions were investigated. Due to the repulsive force between the positively charged TiO2 and metal cationic ions, this approach permits 1000 mg L−1 for Fe3+, Ni2+ and Co2+, 500 mg L−1 for Cu2+ or 100 mg L−1 for Ag+ and Au3+ present in a 5 μg L−1Se(IV) solution without any significant interferences. A limit of detection of 0.0006 μg L−1 was obtained by sampling a 40 mL sample solution. Compared to the conventional HG method, the sensitivity and the limit of detection were improved 17- and 16-fold by the present method, respectively. The proposed method was successfully applied for the determination of trace selenium in several real samples.

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).

Atomic Fluorescence Spectrometry: a suitable detection technique in speciation studies for arsenic, selenium, antimony and mercury

Atomic Fluorescence Spectrometry (AFS) is an ideal detection technique for speciation studies concerning hydride forming elements (mainly As, Se and Sb) and Hg. The analytical features of AFS, such as detection limits below the µg L−1 and the wide linear calibration range, up to the mg L−1, allow its application to a great variety of environmental, biological and food samples. AFS represents a suitable alternative to other atomic spectrometers commonly employed in speciation studies such as Atomic Absorption Spectrometry (AAS) and Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). The instrumentation used for AFS and the design of the vapour generation and optical layouts required to sustain the full benefits of the AFS approach are also described. The present review explains and comments on the instrumental couplings of chromatographic (HPLC and GC) and non-chromatographic separations (CE) with AFS detection, with online hydride generation for the speciation of inorganic and organic compounds of As, Se and Sb, and cold vapour for Hg. Other optional intermediate steps are online photo-oxidation (UV), pyrolysis or Microwave Assisted Digestion (MAD) for non-directly reducible compounds. Many different sample types (e.g. water, soils, air, biota, food) have been analysed using these instrumental couplings with AFS detection. These are summarised and discussed.

Thiourea catalysis of MeHg ligand exchange between natural dissolved organic matter and a thiol-functionalized resin: a novel method of matrix removal and MeHg preconcentration for ultratrace Hg speciation analysis in freshwaters

Ultratrace analysis of dissolved MeHg in freshwaters requires both dissociation of MeHg from strong ligands in the sample matrix and preconcentration for detection. Existing solid phase extraction methods generally do not efficiently adsorb MeHg from samples containing high concentrations of natural dissolved organic matter. We demonstrate here that the addition of 10-60 mM thiourea (TU) quantitatively releases MeHg from the dissolved matrix of freshwater samples by forming a more labile complex (MeHgTU+) that quantitatively exchanges MeHg with thiol-functionalized resins at pH approximately 3.5 during column loading. The contents of these columns were efficiently eluted with acidified TU and MeHg was analyzed by Hg-TU complex ion chromatography with cold-vapor atomic fluorescence spectrometry detection. Routinely more than 90% of MeHg was recovered with good precision (average relative standard deviation of 6%) from natural waters-obtained from pools and saturated sediments of wetlands and from rivers-containing up to 68.7 mg C L-1 dissolved organic matter. With the preconcentration step, the method detection limit of 0.29 pg absolute or 0.007 ng L-1 in 40-mL samples is equivalent to that of the current state-of-the- art as practiced by skilled analysts. MeHg in 20-50-mL samples was completely trapped. On the basis of our knowledge of the chemistry of the process, breakthrough volume should depend on the concentrations of TU and H+. At a TU concentration of 12 mM breakthrough occurred between 50 and 100 mL, but overall adsorption efficiency was still 85% at 100 mL. Formation of artifactual MeHg is minimal; only about 0.7% of ambient MeHg is artifactual as estimated from samples spiked with 4 microg L-1 HgII.

Non-chromatographic speciation analysis of mercury by flow injection on-line preconcentration in combination with chemical vapor generation atomic fluorescence spectrometry

A novel non-chromatographic approach for direct speciation of mercury, based on the selective retention inorganic mercury and methylmercury on the inner wall of a knotted reactor by using ammonium diethyl dithiophosphate and dithizone as complexing agents respectively, was developed for flow injection on-line sorption preconcentration coupled with chemical vapor generation non-dispersive atomic fluorescence spectrometry. With the sample pH kept at 2.0, the preconcentration of inorganic mercury on the inner walls of the knotted reactor was carried out based on the exclusive retention of Hg–DDP complex in the presence of methylmercury via on-line merging the sample solution with ammonium diethyl dithiophosphate solution, and selective preconcentration methylmercury was achieved with dithizone instead of ammonium diethyl dithiophosphate. A 15% (v/v) HCl was introduced to elute the retained mercury species and merge with KBH 4 solution for atomic fluorescence spectrometry detection. Under the optimal experimental conditions, the sample throughputs of inorganic mercury and methylmercury were 30 and 20 h − 1 with the enhancement factors of 13 and 24. The detection limits were found to be 3.6 ng l − 1 for Hg 2+ and 2.0 ng l − 1 for CH 3Hg +. The precisions (RSD) for the 11 replicate measurements of each 0.2 μg l − 1 of Hg 2+ and CH 3Hg + were 2.2% and 2.8%, respectively. The developed method was validated by the analysis of certified reference materials (simulated natural water, rice flour and pork) and by recovery measurements on spiked samples, and was applied to the determination of inorganic mercury and methylmercury in biological and environmental water samples.

Double Hydride Generation Gaseous Phase Enrichment with Flow Injection On‐line Automatic Preparation for Ultratrace Amounts of Total Selenium Determination by Atomic Fluorescence Spectrometry

A double hydride generation technique was developed and successfully used for the determination of total ultratrace amounts of selenium by atomic fluorescence spectrometry (AFS). In this technique, the acid digested sample solution was used for the generation of selenium hydride first, after which, the SeH2 formed was reacted with, and absorbed in, a small volume of alkaline solution (0.5 mol L−1 NaOH + 0.05 mol L−1 H2O2), in which automated organic selenium digestion by the flow injection technique was pursued. The alkaline solution with the selenium absorbed was mixed with the reductant and then acidified to achieve hydride generation for the second time. The concentration factor depends on the volume ratio of the sample and the alkaline solution. Selenium hydride was atomized in a quartz atomizer with a mini‐hydrogen diffusion flame and detected by AFS. Under the conditions employed, a detection limit of 2–6 pg Se mL−1 and 2.8% relative standard deviation (RSD) (with 1 ng mL−1 Se, n = 11), and 12% RSD (with 0.05 ng mL−1 Se, n = 7) were obtained by this enrichment technique and AFS detection. This paper was invited as a contribution to a special issue of the journal concerning Chemical Spectroscopy in China. It was presented at Sichuan University, Chengdu, China, August 1–7, 2004: the 4th Conference for Worldwide Young Chinese Chemists.

Comparison of atomic absorption and fluorescence spectroscopic methods for the routine determination of urinary arsenic

Interpretation of urinary arsenic measurements is sometimes difficult because of the absorption of seafood that contains trimethylated arsenic forms (arsenobetaine and arsenocholine). The objective of this study was to develop a rapid and robust technique for the measurement of the sum of inorganic arsenic metabolites. Measurement of arsenic was performed in urine after hydride generation in acid medium. Using atomic fluorescence spectrometry (AFS) as the detection system, we developed a rapid (one determination in less than 2 min) technique using 50 microl urine without pre-treatment. Standardisation was done externally with a mixed standard solution containing inorganic trivalent arsenic (As(i) (III)), inorganic pentavalent arsenic (As(i) (V)), monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA) (15/15/12.5/57.5). Samples distributed in the frame of an international comparison programme were used to assess accuracy of the AFS procedure, which gives a linear response up to 50 microg/l and proves more precise [coefficient of variation (CV)< 4% at 5 microg/l] and sensitive than the atomic absorption spectroscopy (AAS) technique using a quartz cell. An additional adaptation that allows the detection of non-directly reducible arsenic forms has also been validated for samples with high arsenic concentrations. The present study demonstrates the superiority of AFS over atomic absorption spectrometry (AAS) in arsenic determination and the interest of online mineralisation prior AFS detection for the determination of arsenic concentration in urine.