Elimination of chloride interference on arsenic speciation in ion chromatography inductively coupled mass spectrometry using an octopole collision/reaction system

Anion-exchange chromatography with inductively coupled plasma mass spectrometry (ICP-MS) is often used for the speciation of arsenic (As). In this work, either He or H₂ was introduced to the octopole collision/reaction cell to eliminate chloride (Cl⁻) interferences during As speciation by ICP-MS. Polyatomic species, ⁴⁰Ar³⁵Cl and ³⁸Ar³⁷Cl, which are formed in high chloride matrices interfere with the ICP-MS detection of ⁷⁵As. These interferences were reduced or eliminated by introducing He or H₂ to the collision/reaction cell, with some loss in sensitivity when compared to the standard mode (no gas). For example, the sensitivity of As(V) was 30.4 and 17.7% of that observed in standard mode when introducing He and H₂, respectively. Chloride interference was completely eliminated using a flow rate of 3.0 mL min^− 1 with H₂ as a reaction gas with detection limits in the range of 0.3-0.6 μg L^− 1. The developed method was applied to determination of arsenic species in waters containing high concentrations of chloride by following a simple procedure and without modification of the ICP-MS instrument.     

Vanadium determination in chloride matrices using ICP-MS: finding the optimum collision/reaction cell parameters for suppressing polyatomic interferences

Efficiencies of He/NH₃ and He/H₂ collision gases were compared in a conventional type of hexapole cell of an inductively coupled plasma mass spectrometer (ICP-MS). The optimum conditions [hexapole and quadrupole bias voltage (V_H and V_Q) and collision/reaction gas flow rates] were tested for vanadium determination (⁵¹V) in chloride matrices. When the He/H₂ mixture was used, the optimum values of V_H and V_Q were −10.0 and −8.0 V, respectively. This set-up corresponds to the kinetic energy discrimination effect. When the He/NH₃ mixture was used, the optimum values of V_H and V_Q were +10.0 and −7.0 V, respectively. Positive V_H values correspond to the ion kinetic energy effect, which allows the reactivity of the ions entering the collision/reaction cell with the reaction gas to be controlled. The obtained results showed that the He/H₂ mixture is not optimal for V determination in samples containing chlorides due to the insufficient suppression of the polyatomic interference of ³⁵Cl¹⁶O⁺. Data obtained from vanadium determination using the He/NH₃ mixture were consistent for all selected Cl⁻ concentrations, and the results were acceptable. The detection limit was comparable with detection limits obtained from ICP-MS equipped with a dynamic reaction cell. Analyses of elements forming interfering molecules, e.g., iron (⁵⁶Fe), arsenic (⁷⁵As) and selenium (⁸⁰Se), were in good agreement with the certified values for both studied collision/reaction gas mixtures.     

Determination of chromium, iron and selenium in foodstuffs of animal origin by collision cell technology, inductively coupled plasma mass spectrometry (ICP-MS), after closed vessel microwave digestion

The determination of chromium (⁵²Cr), iron (⁵⁶Fe) and selenium (⁸⁰Se) isotopes in foodstuffs of animal origin has been performed by collision cell technology (CCT) mode using an inductively coupled plasma mass spectrometry (ICP-MS) as detector after closed vessel microwave digestion. To significantly decrease the argon-based interferences at mass to charge ratios (m/z): 52 (⁴⁰Ar¹²C), 56 (⁴⁰Ar¹⁶O) and 80 (⁴⁰Ar⁴⁰Ar), the gas-flow rates of a helium and hydrogen mixture used in the hexapole collision cell were optimised to 1.5 ml min⁻¹ H₂ and 0.5 ml min⁻¹ He and the quadrupole bias was adjusted daily between −2 and −15 mV. Limits of quantification (LOQ) of 0.025, 0.086 and 0.041 mg kg⁻¹ for Cr, Fe and Se, respectively, in 6% HNO₃ were estimated under optimized CCT conditions. These LOQ were improved by a factor of approximately 10 for each element compared to standard mode.Precision under repeatability, intermediate precision reproducibility and trueness have been tested on nine different certified reference materials in foodstuffs of animal origin and on an external proficiency testing scheme. The results obtained for chromium, iron and selenium were in all cases in good agreement with the certified values and trueness was improved, compared to those obtained in standard mode.     

Speciation of glyphosate, phosphate and aminomethylphosphonic acid in soil extracts by ion chromatography with inductively coupled plasma mass spectrometry with an octopole reaction system

Ion-pairing chromatography coupled with inductively coupled plasma mass spectrometry (ICP-MS) used for the speciation of phosphorus is limited as the mobile phase containing organic solvents changes in detection sensitivity and the carbon precipitates on torch and cones. To address this issue, anion-exchange chromatography with ICP-MS has been used for the speciation of glyphosate, phosphate and aminomethylphosphonic acid in soil extracts. The separation of the targets on a new column was achieved within 5 min using an eluent containing 20 mM NH₄NO₃ at pH 5.1. Furthermore, since the polyatomic ions such as ¹⁴N¹⁶O¹H⁺ and ¹⁵N¹⁶O⁺ from a nitrogen-based ion-pairing reagent interfered with ICP-MS detection of ³¹P, an octopole reaction system was investigated to determine whether the polyatomic interferences could be reduced. The results show that addition of He to the cell can benefit analyses by reducing such interferences, but at the expense of reduced sensitivity. The detection limits in the range of 1.0-1.5 μg L⁻¹ (expressed as P) was achieved when 50 μL was injected using He as the collusion gas.     

Simultaneous speciation of arsenic (As(III), MMA, DMA, and As(V)) and selenium (Se(IV), Se(VI), and SeCN−) in petroleum refinery aqueous streams

High-performance liquid chromatography (HPLC) coupled to an ICP-MS with an octapole reaction system (ORS) has been used to carry out quantitative speciation of selenium (Se) and arsenic (As) in the stream waters of a refining process. The argon dimers interfering with the ⁷⁸Se and ⁸⁰Se isotopes were suppressed by pressurizing the octapole chamber with 3.1 mL min⁻¹ H₂ and 0.5 mL min⁻¹ He. Four arsenic species arsenite—As(III), arsenate (As(V)), monomethylarsonic acid (MMA), and dimethylarsinic acid (DMA)—and three inorganic Se species—selenite Se(IV), selenate Se(VI), and selenocyanate (SeCN⁻)—were separated in a single run by ion chromatography (IC) using gradient elution with 100 mmol L⁻¹ NH₄NO₃, pH 8.5, adjusted by addition of NH₃, as eluent. Repeatabilities of peak position and of peak area evaluation were better than 1% and about 3%, respectively. Detection limits (as 3σ of the baseline noise) were 81, 56, and 75 ng L⁻¹ for Se(IV), Se(VI), and SeCN⁻, respectively, and 22, 19, 25, and 16 ng L⁻¹ for As(III), As(V), MMA, and DMA, respectively. Calibration curve R ² values ranged between 0.996 and 0.999 for the arsenic and selenium species. Column recovery for ion chromatography was calculated to be 97 ± 6% for combined arsenic species and 98 ± 3% for combined selenium species. Because certified reference materials for As and Se speciation studies are still not commercially available, in order to check accuracy and precision the method was applied to certified reference materials, BCR 714, BCR 1714, and BCR 715 and to two different refinery samples—inlet and outlet wastewater. The method was successfully used to study the quantitative speciation of selenium and arsenic in petroleum refinery wastewaters.     

Capillary electrophoretic determination of ammonia using headspace single-drop microextraction

A new method involving headspace single-drop microextraction (SDME) and capillary electrophoresis (CE) is developed for the preconcentration and determination of ammonia (as dissolved NH₃ and ammonium ion). An aqueous microdrop (5 μL) containing 1 mmol/L H₃PO₄ and 0.5 mmol/L KH₂PO₄ (as internal standard) was used as the acceptor phase. Common experimental parameters (sample and acceptor phase pH, extraction temperature, extraction time) affecting the extraction efficiency were investigated. Proposed SDME-CE method provided about 14-fold enrichment in about 20 min. The calibration curve was linear for concentrations of NH₄⁺ in the range from 5 to 100 μmol/L (R² = 0.996). The LOD (S / N = 3) was estimated to be 1.5 μmol/L of NH₄⁺. Such detection sensitivity is high enough for ammonia determination in common environmental and biological samples. Finally, headspace SDME was applied to determine ammonia in human blood, seawater and milk samples with spiked recoveries in the range of 96-107%.     

Studies on the origin and transformation of selenium and its chemical species along the process of petroleum refining

Inductively coupled plasma optical emission spectrometry and mass spectrometry (ICPMS), the latter hyphenated to flow injection hydride generation, electrothermal vaporization or ion chromatography, have been applied to the chemical characterization of crude oil, aqueous process stream samples and wastewaters from a petroleum refinery, in order to get information on the behavior of selenium and its chemical species along effluent generation and treatment. Multielemental characterization of these effluents by ICPMS revealed a complex composition of most of them, with high salinity and potential spectral and non-spectral interferents present. For this reason, a critical re-assessment of the analytical techniques for the determination of total selenium and its species was performed. Methane was employed as gas in dynamic reaction cell ICPMS and cell parameters were optimized for a simulated brine matrix and for diluted aqueous solutions to match the expected process and treated wastewaters samples. The signal-to-background ratios for ⁷⁸Se and ⁸⁰Se were used as criteria in optimization, the first isotope resulting in better detection limits for the simulated brine matrix (⁷⁸Se: 0.07 μg L^− 1, ⁸⁰Se: 0.31 μg L^− 1). A large variability in the concentration of selenium (from < 10 μg kg^− 1 up to 960 μg kg^− 1) was observed in 16 of the most frequently processed crude oil samples in the refinery here investigated, which may explain the pronounced concentrations changes of this element measured in aqueous process stream and wastewater samples. Highest concentrations of total selenium were analyzed in samples from the hydrotreater (up to about 1800 μg L^− 1). The predominance of selenocyanate (SeCN⁻) was observed in most of the wastewaters so far investigated, but also other species were detected with retention times different from Se(IV), Se(VI) and SeCN⁻. Colloidal selenium (Se⁰) was the only Se-species observed in samples from the atmospheric distillation unit, but was also identified in other samples, most probably formed by the decomposition of SeCN⁻ or other unstable species.     

Signal enhancement in solution-cathode glow discharge — optical emission spectrometry via low molecular weight organic compounds

HCOOH, CH₃COOH, and CH₃CH₂OH were used as chemical modifiers in a solution-cathode glow discharge. Emission was measured directly from the discharge, without a gas–liquid separator or a secondary excitation source. Emission from Ag, Se, Pb, and Hg was strongly enhanced, and the detection limits (DL) for these elements were improved by up to an order of magnitude using a combination of HCOOH and HNO₃ compared to using HNO₃ alone. The DL was measured for Mg (1 μg/L), Fe (10 μg/L), Ni (6 μg/L), Cu (6 μg/L), Pb (1 μg/L), Ag (0.1 μg/L), Se (300 μg/L), and Hg (2 μg/L). Coefficients of determination (R²) were between 0.9986 and 0.9999. A voltage of 1 kV was used, which produced a current of approximately 70 mA.     

Voltammetric determination of Se(IV) and Se(VI) in saline samples—Studies with seawater, hydrothermal and hemodialysis fluids

Determination of Se(IV) and Se(VI) in high saline media was investigated by cathodic stripping voltammetry (CSV). The voltammetric method was applied to assay selenium in seawater, hydrothermal and hemodialysis fluids. The influence of ionic strength on selenium determination is discussed. The CSV method was based on the co-electrodeposition of Se(IV) with Cu(II) ions and Se(VI) determined by difference after sample UV-irradiation for photolytic selenium reduction. UV-irradiation was also used as sample pre-treatment for organic matter decomposition. Detection limit of 0.030 μg L⁻¹ (240 s deposition time) and relative standard deviation (RSD) of 6.19% (n = 5) for 5.0 μg L⁻¹ of Se(IV) were calculated. Linear calibration range for selenium was observed from 1.0 to 100.0 μg L⁻¹. Concerning the pre-treatment step, best results were obtained by using 60 min UV-irradiation interval in H₂O₂/HCl medium. Se(VI) was reduced to the Se(IV) electroactive species with recoveries between 91.7% and 112.9%. Interferents were also investigated.     

Isoelectronic Aluminium Analogues of Carbonyl and Dioxirane Moieties

We report the anion [Al(NON^Ar)(Se)]^? (NON^Ar=[O(SiMe₂NAr)₂]^2?, Ar=2,6‐iPr₂C₆H₃), which is an isoelectronic Group 13 metal analogue of the carbonyl group containing an aluminium–selenium multiple bond. It was synthesized in a single step from the reaction of the aluminyl anion [Al(NON^Ar)]^? with elemental selenium. Spectroscopic, crystallographic, and computational analysis confirmed multiple bonding between aluminium and selenium. Addition of a second equivalent of selenium afforded the diselenirane, [Al(NON^Ar)(κ²‐Se₂)]^?, which is an isoelectronic analogue of the dioxirane group.     

Nano TiO2-based preconcentration for the speciation analysis of inorganic selenium by using ion chromatography with conductivity detection

A simple, sensitive, and cost-effective analytical method was developed for the speciation analysis of inorganic selenium by combining a nano-TiO₂ preconcentration with an ion chromatography-conductivity detection (IC-CD) system. The experimental conditions for the simultaneous adsorption and desorption of Se(IV) and Se(VI) were carefully investigated. Under the established optimum condition, the Se(IV) and Se(VI) ions could been simultaneously adsorbed onto the nano-TiO₂ surface at pH 4.0, and then effectively desorbed by 0.1 M sodium hydroxide eluent. The adsorption process was fast and reached adsorption equilibrium within 10 min. The nano-TiO₂ also exhibited high adsorption capacity with 11.3 mg g^? 1 for Se(IV) and 8.34 mg g^? 1 for Se(VI). The enrichment factors for Se(IV) and Se(VI) were calculated to be 39 and 30, respectively, with sample volume of 50 mL. The detection limits (3σ) were 0.8 μg L^? 1 for Se(IV) and 0.4 μg L^? 1 for Se(VI), which were sensitive enough for the routine analysis of water and drink samples. The relative standard deviation was calculated to be < 4% (n = 6) for detection of 30 μg L^? 1 Se(IV) and 30 μg L^? 1 Se(VI). The results of the present work confirmed that our developed nano-TiO₂-IC-CD method could be applied for the detection of inorganic selenium species in tap water and drink samples with good recoveries in the range of 82%–108%.     

Capabilities of mixed-mode liquid chromatography coupled to inductively coupled plasma mass spectrometry for the simultaneous speciation analysis of inorganic and organically-bound selenium

This work investigates for the first time the potential of mixed-mode (anion-exchange with reversed-phase) high performance liquid chromatography coupled to inductively coupled plasma mass spectrometry (ICP-MS) for the simultaneous retention and selective separation of a range of inorganic and organically-bound selenium (Se) species. Baseline separation and detection of selenocystine (SeCys₂), Se-methyl-selenocysteine (SeMC), selenomethionine (SeMet), methylseleninic acid (MSA), selenite, γ-glutamyl-methyl-selenocysteine (γ-glutamyl-SeMC), and selenate in a Se standard mixture by mixed-mode HPLC-ICP-MS was achieved by switching between two citrate mobile phases of different pH and ionic strength within a single chromatographic run of 20 min. Limits of detection obtained for these Se species ranged from 80 ng kg^?1 (for SeMC) to 123 ng kg^?1 (for selenate). Using this approach as developed for selenium speciation, an adequate separation of inorganic and organic As compounds was also achieved. These include arsenite, arsenate, arsenobetaine (AsB) and dimethylarsenic acid (DMA), which may coexist with Se species in biological samples. Application of the newly proposed methodology to the investigation of the elemental species distribution in watercress (used as the model sample) after enzymatic hydrolysis or leaching in water by accelerated solvent extraction (ASE) was addressed. Only SeMet, SeMC and selenate could be tentatively identified in watercress extracts by mixed-mode HPLC-ICP-MS and retention time matching with standards. Recoveries (n = 3) of these Se species from samples spiked with standards averaged 102% (for SeMC), 94.9% (for SeMet) and 98.3% (for selenate). Verification of the presence of SeMet and SeMC in an enzymatic watercress extract was achieved by on-line HPLC-ESI MS/MS in selected reaction monitoring (SRM) mode.     

Combination of cool plasma and collision-reaction interface for correction of polyatomic interferences on copper signals in inductively coupled plasma quadrupole mass spectrometry

Inductively coupled plasma mass spectrometry (ICP-MS) is an important instrumental technique for elemental analysis. However, some elements suffer from spectral interferences caused by ions derived from argon plasma gas and matrix components. The determination of copper isotopes is affected by ⁴⁰Ar²³Na⁺ and ⁴⁰Ar²⁵Mg⁺. The performance of an ICP-MS with a collision reaction interface (CRI) and cool plasma conditions for correction of spectral interferences was evaluated here. The efficiency of the CRI was studied introducing H₂ or He through sampler and skimmer cones. Gas introduction through the sampler cone was ineffective. Complete elimination of spectral interferences was reached when introducing 60 or 80 mL min⁻¹ of H₂ in the skimmer cone, but sensitivity losses were as large as 99%. Further, the effect of interferences was checked when the argon plasma was operated under cool plasma conditions. The effects of the applied radiofrequency (0.6, 0.8, 0.9, and 1.0 kW), sampling depth (5.5, 8.5 and 11.5 mm), and dwell time (25 and 50 ms) were studied considering interference reduction and sensitivities. Best conditions were reached at 0.8 kW. Subsequently, both CRI and cool plasma conditions were combined to evaluate their performance on reduction of polyatomic Na and Mg argide interferences. Spectral interferences were eliminated using a CRI with 20 mL min⁻¹ H₂ introduced through the skimmer cone, cool plasma conditions at 0.8 kW and sampling depth of 8.5 mm. This work demonstrated the feasibility of combining CRI and cool plasma for circumventing some spectral interferences on Cu determination by ICP-QMS.     

Comparison of high-resolution and dynamic reaction cell ICP-MS capabilities for forensic analysis of iron in glass

Forensic laboratories routinely conduct analysis of glass fragments to determine whether or not there is an association between a fragment(s) recovered from a crime scene or from a suspect to a particular source of origin. The physical and optical (refractive index) properties of the fragments are compared and, if a “match” between two or more fragments is found, further elemental analysis can be performed to enhance the strength of the association. A range of spectroscopic techniques has been used for elemental analysis of this kind of evidence, including inductively coupled plasma mass spectrometry (ICP-MS). Because of its excellent sensitivity, precision, and accuracy, several studies have found that ICP-MS methods (dissolution and laser-ablation) provide the best discrimination between glass fragments originating from different sources. Nevertheless, standard unit-resolution ICP-MS instruments suffer from polyatomic interferences including ⁴⁰Ar¹⁶O⁺, ⁴⁰Ar¹⁶O¹H⁺, and refractory oxide ⁴⁰Ca¹⁶O⁺ that compromise measurements of trace levels of Fe⁵⁶⁺ and Fe⁵⁷⁺, for example. This is a drawback in the analysis of glass fragments because iron has been previously identified as a good discriminating element. Currently, several techniques are available that enable reduction of such interferences. However, there are no data comparing detection limits of iron in glass using those techniques. The aim of this study was to compare, the analytical performance of high-resolution sector field inductively coupled plasma mass spectrometry (HR-SF-ICP-MS) and quadrupole ICP-MS equipped with a dynamic reaction cell (DRC-ICP-MS), for the detection of iron in glass, in terms of accuracy, precision, and method detection limits (MDLs). Analyses were conducted using conventional acid-digestion and laser-ablation methods. For laser-ablation analyses, carrier gases were compared to assess the effect on detection limits in the detection of iron isotopes. Iron polyatomic interferences were reduced or resolved by using a dynamic reaction cell and high-resolution ICP-MS. MDLs as low as 0.03 μg g⁻¹ and 0.14 μg g⁻¹ were achieved in laser-ablation and solution-based analyses, respectively. Use of helium as carrier gas improved detection limits for both iron isotopes in medium-resolution HR-SF-ICP-MS and in DRC-ICP-MS.     

Characterization of laser induced breakdown plasmas used for measurements of arsenic,antimony and selenium hydrides

Studies have been performed to characterize laser induced breakdown spectroscopy (LIBS) plasmas formed in Ar/H₂ gas mixtures that are used for hydride generation (HG) LIBS measurements of arsenic (As), antimony (Sb) and selenium (Se) hydrides. The plasma electron density and plasma excitation temperature have been determined through hydrogen, argon and arsenic emission measurements. The electron density ranges from 4.5 × 10¹⁷ to 8.3 × 10¹⁵ cm^?3 over time delays of 0.2 to 15 μs. The plasma temperatures range from 8800 to 7700 K for Ar and from 8800 to 6500 K for As in the HG LIBS plasmas. Evaluation of the plasma properties leads to the conclusion that partial local thermodynamic equilibrium conditions are present in the HG LIBS plasmas. Comparison measurements in LIBS plasmas formed in Ar gas only indicate that the temperatures are similar in both plasmas. However it is also observed that the electron density is higher in the Ar only plasmas and that the emission intensities of Ar are higher and decay more slowly in the Ar only plasmas. These differences are attributed to the presence of H₂ which has a higher thermal conductivity and provides additional dissociation, excitation and ionization processes in the HG LIBS plasma environment. Based on the observed results, it is anticipated that changes to the HG conditions that change the amount of H₂ in the plasma will have a significant effect on analyte emission in the HG LIBS plasmas that is independent of changes in the HG efficiency. The HG LIBS plasmas have been evaluated for measurements of elements hydrides using a constant set of HG LIBS plasma conditions. Linear responses are observed and limits of detection of 0.7, 0.2 and 0.6 mg/L are reported for As, Sb and Se, respectively.     

Determination of Total Selenium in Human Urine and Serum by Graphite-Furnace Atomic-Absorption Spectrophotometry with Palladium-Nickel-Ammonium Nitrates as a Matrix Modifier

After human urine or serum was diluted (1 + 9) with HNO₃ (0.2%, v/v) and standard additions of Se solution (100 μ L^?1), the diluted sample (10 μL) was introduced into the graphite cuvette. The matrix modifier [10μL, containing Pd (0.6 μg) + Ni (25 μg) + NH₄NO₃ (80 μg) in HNO₃ (0.2%, v/v) for urine, or Pd (0.3 μg) + Ni (30 μg) + NH₄NO₃ (80 μg) + Triton X-100 (0.04%) in HNO₃ (0.2%, v/v) for serum, respectively] was added and the mixture was heated according to a temperature program. The matrix modifier containing NH₄NO₃ in a suitable amount and a small amount of Pd enhanced the sensitivity for Se. The method detection limits (3σ) after dilution were about 4.9 ± 0.8 and 2.36 ± 0.18 μg L^?1 for urine and serum, respectively. The accuracy of this method was tested with SRM #2670 human urine Se and Seronorm Trace Elements #116 human serum Se, respectively, and the results of 97.6 – 101% and 100 – 104% were obtained with precision ± 0.3% and ± 2%, respectively. This method can be applied easily and accurately to the determination of concentration of total Se in human urine and serum.     

The separation of arsenic species in soils and plant tissues by anion-exchange chromatography with inductively coupled mass spectrometry using various mobile phases

Anion-exchange chromatography (Hamilton, PRP-X100) with inductively coupled plasma mass spectrometry (ICP-MS) is commonly used for the speciation of arsenic in environmental and biological samples. However, retentions for As species are frequently different because of the use of widely different mobile phases. In addition, chloride in matrices interferes with arsenic determination. In this study, we systematically investigated various mobile phases based on ammonium salts affecting arsenic retention to eliminate chloride interference chromatographically. Hence, various mobile phases based on ammonium salts, including NH₄H₂PO₄, NH₄HPO₄, NH₄Ac, NH₄HCO₃ and NH₄NO₃, were examined for reasonable resolution and to separate chloride from arsenic species. The best result was obtained with a mobile phase containing 30 mM NH₄H₂PO₄ at pH 5.6, where the separation of arsenic species, including arsenite [As(III)], arsenate [As(V)], dimethylarsinic acid (DMA) and monomethylarsonic acid (MMA)], was achieved within 9 minutes with reasonable resolution and free of chloride interference at its high level (500 mg L^− 1). The detection limits for the arsenic species were in the range of 0.1-0.3 μg L^− 1 with a direct injection of sample without removing matrix. Finally, the proposed method was used for the determination of arsenic species in contaminated soil and plant tissues.     

DRC™ ICP-MS coupled with automated flow injection system with anion exchange minicolumns for determination of selenium compounds in water samples

A flow injection system with anion exchange resin minicolumns was coupled with dynamic reaction cell (DRC™) ICP-MS for the determination and speciation of selenite and selenate at sub μg L⁻¹ levels. The charged selenate and uncharged selenite were separated on the first resin column in which only selenate was retained. The unretained selenite was then deprotonated with alkaline solution, and the resulting anionic selenite species was collected on the second column serially connected downstream. By setting a sample loop, total selenium can be determined together with selenite and selenate. The selenium species was eluted by nitric acid and carried to DRC™ ICP-MS for their detection. Using ammonia as reaction gas, the detection of ⁷⁸Se was improved. The enrichment factor was 20 for 10 mL of sample. The standard deviations (n = 5) of peak heights were 4.9%, 4.1%, and 7.0% for a 5.0 × 10⁻² μg L⁻¹ selenite and selenate, and total Se, respectively. The calibration graphs were linear from 2.0 × 10⁻² to 1.0 μg L⁻¹ selenite and selenate. And, the linearity for total selenium was good in the range of 10.0 × 10⁻² to 1.0 μg L⁻¹. The proposed method has been demonstrated for the application to natural and bottled drinking water samples.     

Sequential photocatalyst-assisted digestion and vapor generation device coupled with anion exchange chromatography and inductively coupled plasma mass spectrometry for speciation analysis of selenium species in biological samples

We have developed an on-line sequential photocatalyst-assisted digestion and vaporization device (SPADVD), which operates through the nano-TiO₂-catalyzed photo-oxidation and reduction of selenium (Se) species, for coupling between anion exchange chromatography (LC) and inductively coupled plasma mass spectrometry (ICP-MS) systems to provide a simple and sensitive hyphenated method for the speciation analysis of Se species without the need for conventional chemical digestion and vaporization techniques. Because our proposed on-line SPADVD allows both organic and inorganic Se species in the column effluent to be converted on-line into volatile Se products, which are then measured directly through ICP-MS, the complexity of the procedure and the probability of contamination arising from the use of additional chemicals are both low. Under the optimized conditions for SPADVD – using 1 g of nano-TiO₂ per liter, at pH 3, and illuminating for 80 s – we found that Se(IV), Se(VI), and selenomethionine (SeMet) were all converted quantitatively into volatile Se products. In addition, because the digestion and vaporization efficiencies of all the tested selenicals were improved when using our proposed on-line LC/SPADVD/ICP-MS system, the detection limits for Se(IV), Se(VI), and SeMet were all in the nanogram-per-liter range (based on 3σ). A series of validation experiments – analysis of neat and spiked extracted samples – indicated that our proposed methods could be applied satisfactorily to the speciation analysis of organic and inorganic Se species in the extracts of Se-enriched supplements.     

Application of a hexapole collision and reaction cell in ICP-MS Part I: Instrumental aspects and operational optimization

The application of an ion-guiding buffer gas-filled hexapole collision and reaction cell in ICP-MS has been studied in order to give a preliminary performance characterization of a new instrument providing this feature for increasing the ion yield and decreasing contributions from Ar induced interfering molecular ions. As buffer gas He was used while H₂ served as reaction gas. Addition of the latter can be an effective means for reduction of typical argon induced polyatomic ions (Ar⁺, ArO⁺, Ar₂ ⁺) by orders of magnitude owing to gas phase reactions. Molecular interferences generated in the cell can be suppressed by a retarding electric field established by a dc hexapole bias potential of –2 V. Received: 10 May 1999 / Revised: 4 June 1999 / Accepted: 12 June 1999