Multisyringe flow-injection system for total inorganic arsenic determination by hydride generation-atomic fluorescence spectrometry

A software-controlled time-based multisyringe flow-injection system for total inorganic arsenic determination by hydride generation atomic fluorescence spectrometry (HGAFS) has been developed. By using a multisyringe burette coupled with one multiport selection valve, the time-based injection provides precise known volumes of sample, a reducing sodium tetrahydroborate solution and a pre-reducing solution which are dispensed into a gas-liquid separation cell. An argon flow delivers the arsine into the flame of an atomic fluorescence spectrometer. A hydrogen flow has been used to support the flame.Linear calibration graphs for arsenic concentrations between 0.25 and 12 μg l⁻¹ were obtained. The detection limit of the proposed technique (3σ_b/S) was 0.07 μg l⁻¹. A sample throughput of 36 samples/h (108 injections) has been achieved. The proposed technique has been validated by means of reference solid and water materials with good agreement with the certified values. This method was compared with those reported in previous sequential injection analysis (SIA) and flow-injection analysis (FIA) systems. The proposed method offers a number of advantages in front the usual AFS applications, which are mainly a higher sampling frequency and a significant reduction in reagent consumption.     

Preconcentration and determination of inorganic arsenic using a multisyringe flow injection system and hydride generation-atomic fluorescence spectrometry

A new multisyringe flow injection system for inorganic arsenic determination at trace levels by hydride generation-atomic fluorescence spectrometry (HGAFS) is presented. Preconcentration on a solid-phase was carried out using a column packed with an anion-exchange resin (Amberlite IRA-410). The reagents are dispensed to the system using a multisyringe burette coupled with two multi-port selection valves.

Different parameters were changing in order to make the system as effective as possible. An analytical curve was obtained for arsenic determination between 50 and 2000 ng l⁻¹. This new approach improved five times the sensitivity over a MSFIA–HGAFS technique developed previously by the authors. Detection limit of the proposed technique was (3σ_b/S) of 30 ng l⁻¹. The relative standard deviation (R.S.D.) of As at 1 μg l⁻¹ was 4.8% (n=7). A sample throughput of 10 h⁻¹ has been achieved. The proposed method has been applied to different reference solid and water materials with satisfactory results.     

Speciation analysis of inorganic arsenic by a multisyringe flow injection system with hydride generation-atomic fluorescence spectrometric detection

In this study, a new technique by hydride generation-atomic fluorescence spectrometry (HG-AFS) for determination and speciation of inorganic arsenic using multisyringe flow injection analysis (MSFIA) is reported. The hydride (arsine) was generated by injecting precise known volumes of sample, a reducing sodium tetrahydroborate solution (0.2%), hydrochloric acid (6 M) and a pre-reducing solution (potassium iodide 10% and ascorbic acid 0.2%) to the system using a multisyringe burette coupled with one multi-port selection valve. This solution is used to pre-reduce As(V) to As(III), when the task is to speciate As(III) and As(V). As(V) is determined by the difference between total inorganic arsenic and As(III). The reagents are dispensed into a gas-liquid separation cell. An argon flow delivers the arsine into the flame of an atomic fluorescence spectrometer. A hydrogen flow has been used to support the flame. Nitrogen has been employed as a drier gas (Fig. 1).Several variables such as sample and reagents volumes, flow rates and reagent concentrations were investigated in detail. A linear calibration graph was obtained for arsenic determination between 0.1 and 3 μg l⁻¹. The detection limit of the proposed technique (3σ_b/S) was 0.05 μg l⁻¹. The relative standard deviation (R.S.D.) of As at 1 μg l⁻¹ was 4.4 % (n = 15). A sample throughput of 10 samples per hour was achieved. This technique was validated by means of reference solid and water materials with good agreement with the certified values. Satisfactory results for speciation of As(III) and As(V) by means of the developed technique were obtained.     

Determination of arsenic(III) and total inorganic arsenic in water samples using an on-line sequential insertion system and hydride generation atomic absorption spectrometry

A simple and robust on-line sequential insertion system coupled with hydride generation atomic absorption spectrometry (HG-AAS) was developed, for selective As(III) and total inorganic arsenic determination without pre-reduction step. The proposed manifold, which is employing an integrated reaction chamber/gas-liquid separator (RC-GLS), is characterized by the ability of the successful managing of variable sample volumes (up to 25 ml), in order to achieve high sensitivity. Arsine is able to be selectively generated either from inorganic As(III) or from total arsenic, using different concentrations of HCl and NaBH₄ solutions. For 8 ml sample volume consumption, the sampling frequency is 40 h⁻¹. The detection limit is c_L = 0.1 and 0.06 μg l⁻¹ for As(III) and total arsenic, respectively. The precision (relative standard deviation) at 2.0 μg l⁻¹ (n = 10) level is s_r = 2.9 and 3.1% for As(III) and total arsenic, respectively. The performance of the proposed method was evaluated by analyzing the certified reference material NIST CRM 1643d and spiked water samples with various concentration ratios of As(III) to As(V). The method was applied for arsenic speciation in natural waters samples.     

Simultaneous speciation of inorganic arsenic and antimony in water samples by hydride generation-double channel atomic fluorescence spectrometry with on-line solid-phase extraction using single-walled carbon nanotubes micro-column

A new method was developed for the simultaneous speciation of inorganic arsenic and antimony in water by on-line solid-phase extraction coupled with hydride generation-double channel atomic fluorescence spectrometry (HG-DC-AFS). The speciation scheme involved the on-line formation and retention of the ammonium pyrrolidine dithiocarbamate complexes of As(III) and Sb(III) on a single-walled carbon nanotubes packed micro-column, followed by on-line elution and simultaneous detection of As(III) and Sb(III) by HG-DC-AFS; the total As and total Sb were determined by the same protocol after As(V) and Sb(V) were reduced by thiourea, with As(V) and Sb(V) concentrations obtained by subtraction. Various experimental parameters affecting the on-line solid-phase extraction and determination of the analytes species have been investigated in detail. With 180 s preconcentration time, the enrichment factors were found to be 25.4 for As(III) and 24.6 for Sb(III), with the limits of detection (LODs) of 3.8 ng L^− 1 for As(III) and 2.1 ng L^− 1 for Sb(III). The precisions (RSD) for five replicate measurements of 0.5 μg L⁻¹ of As(III) and 0.2 μg L⁻¹ of Sb(III) were 4.2 and 4.8%, respectively. The developed method was validated by the analysis of standard reference materials (NIST SRM 1640a), and was applied to the speciation of inorganic As and Sb in natural water samples.     

Multicommutation flow techniques in the hydride generation-atomic fluorescence determination of arsenic

This review outlines automated methodologies developed for measuring arsenic in environmental samples. We report the state of the art of the most significant methods exploiting multicommutation flow techniques coupled to hydride generation-atomic fluorescence determination. We review analytical methods used and present a comparative evaluation of them. We also discuss the on-line pre-concentration procedure as being of particular interest in the development of fully automated methods.     

A new hydride generation system applied in determination of arsenic species with ion chromatography-hydride generation-atomic fluorescence spectrometry (IC-HG-AFS)

A novel procedure was developed for the determination of arsenite (As(III)), arsenate (As(V)), monomethylarsonic (MMA) and dimethylarsinic acid (DMA) with ion chromatography-hydride generation-atomic fluorescence spectrometry (IC-HG-AFS) by employing a new gas-liquid separator (GLS). The effective separation of the four arsenic species was achieved in about 12 min. With a sample loading volume of 20 μl, the measurable minimum for As(III), DMA, MMA and As(V) were 0.02, 0.045, 0.043 and 0.166 ng, respectively, along with relative standard deviations of 1.1, 1.1, 1.7 and 2.2% at the 100 μg l⁻¹ level (n = 6) for As(III), DMA, MMA and As(V), respectively. The present procedure was applied for the speciation of arsenic in underground water and in urine samples, and the sum of the four arsenic species by IC-HG-AFS was in good agreement with the total value by HG-AFS.     

离子色谱-氢化物发生原子荧光光谱联用技术在砷形态分析中的应用

建立了离子色谱-氢化物发生原子荧光光谱联用分离4种常见有毒砷化合物的方法. 二者通过内径0.25 mm的PEEK管直接相连. 实验对影响分离度和测定灵敏度的参数进行了优化. 在优化条件下, 质量浓度均为50 μg/L的4种砷化合物混合标准溶液平行7次进样, 得到DMA、 As(Ⅲ)、 MMA和As(Ⅴ)的色谱峰面积的相对标准偏差(RSD)为2.8～3.0%. 250 μL进样的线性范围为5～1000 μg/L, 检出限为0.8～1.2 μg/L (三倍基线噪音峰高). 用建立的方法测定了砷处理后的水稻木质部伤流液中的砷量, 4种砷化合物的加标回收率为89%～105%. 该装置接口简单, 方法分离度好, 灵敏度高, 可用于实际样品中痕量砷化合物的形态分析.     

微波辅助萃取-HG-AFS测定土壤中无机砷

采用微波辅助萃取分析物,联合原子荧光光谱技术,建立了微波辅助萃取-HG-AFS测定土壤中无机砷的分析方法。用正交试验设计结合单因素试验优化了样品粒度、萃取温度、萃取时间、固液比等微波萃取条件,研究了共存离子对无机砷测定的干扰情况。方法的线性范围为1.0~160.0μg/L,无机砷的检出限为0.20μg/L,相对标准偏差为0.3%,样品回收率为93.0%~98.5%。用本法分析3个不同产地有代表性土壤中无机砷量。     

Evaluation of a hydride generation-atomic fluorescence system for the determination of arsenic using a dielectric barrier discharge atomizer

A new atomizer based on atmospheric pressure dielectric barrier discharge (DBD) plasma was specially designed for atomic fluorescence spectrometry (AFS) in order to be applied to the measurement of arsenic. The characteristics of the DBD atomizer and the effects of different parameters (power, discharge gas, gas flow rate, and KBH₄ concentration) were discussed in the paper. The DBD atomizer shows the following features: (1) low operation temperature (between 44 and 70 °C, depending on the operation conditions); (2) low power consumption; (3) operation at atmospheric pressure. The detection limit of As(III) using hydride generation (HG) with the proposed DBD-AFS was 0.04 μg L⁻¹. The analytical results obtained by the present method for total arsenic in reference materials, orchard leaves (SRM 1571) and water samples GBW(E) 080390, agree well with the certified values. The present HG-DBD-AFS is more sensitive and reliable for the determination of arsenic. It is a very promising technique allowing for field arsenic analysis based on atomic spectrometry.     

Determination of total inorganic arsenic in water using on-line pre-concentration and hydride-generation atomic absorption spectrometry

A rapid and sensitive method for the on-line separation and pre-concentration of inorganic arsenic in water samples is described. The analyte in the pentavalent oxidation state is reduced to its trivalent form with l-cysteine and the total inorganic arsenic is sorbed onto activated alumina in the acid form in a mini-column coupled to a FI-HG AAS system. Afterwards, it is eluted with 3 mol l⁻¹ HCl. An enrichment factor of 7 was obtained, allowing an analytical flow rate of about 28 determinations per hour. The limits of detection (3σ) and of quantification (10σ) were calculated as LOD = 0.15 μg l⁻¹ of As and LOQ = 0.5 μg l⁻¹ of As, respectively. Relative standard deviations (n = 10) less than 8% were obtained for different arsenic concentrations and the accuracy was verified by analysing certified reference materials. Different kinds of samples, such as mineral water, drinking water, river water and natural spring water were analyzed and good agreement was obtained with the values from spiked experiments.     

Flow injection hydride generation electrothermal atomic absorption spectrometric determination of toxicologically relevant arsenic in urine

Analytical procedure for the determination of toxicologically relevant arsenic (the sum of arsenite, arsenate, monomethylarsonate and dimethylarsinate) in urine by flow injection hydride generation and collection of generated inorganic and methylated hydrides on an integrated platform of a transverse-heated graphite atomizer for electrothermal atomic absorption spectrometric determination (ETAAS) is elaborated. Platforms are pre-treated with 2.7 μmol of zirconium and then with 0.10 μmol of iridium which serve both as an efficient hydride sequestration medium and permanent chemical modifier. Arsine, monomethylarsine and dimethylarsine are generated from diluted urine samples (10–25-fold) in the presence of 50 mmol L⁻¹ hydrochloric acid and 70 mmol L⁻¹ l-cysteine. Collection, pyrolysis and atomization temperatures are 450, 500, 2100 and 2150 °C, respectively. The characteristic mass, characteristic concentration and limit of detection (3σ) are 39 pg, 0.078 μg L⁻¹ and 0.038 μg L⁻¹ As, respectively. The limits of detection in urine are ca. 0.4 and 1 μg L⁻¹ with 10- and 25-fold dilutions. The sample throughput rate is 25 h⁻¹. Applications to several urine CRMs are given.     

Multisyringe flow injection system for total inorganic selenium determination by hydride generation-atomic fluorescence spectrometry

A new multisyringe flow injection system for total inorganic selenium determination by hydride generation-atomic fluorescence spectrometry (HGAFS) has been proposed. The flow methodology is based on the simultaneous injection of sample in the acid media (50% HCl), a reducing sodium tetrahydroborate solution (0.18%) and a solution of hydrochloric acid (50%) which are dispensed into a gas-liquid separation cell by using a multisyringe burette coupled with one multiport selection valve. The usage of the time-based injection increases the sample throughput and provides precise known volumes of sample. The hydride of selenium is delivered into the flame of an atomic fluorescence spectrometer by means of an argon flow. A hydrogen flow has been used to support the flame.The technique can be applied over a wide range of concentrations of selenium between 0.1 and 3.5 μg l⁻¹ with good repeatability (relative standard deviation (R.S.D.) values 4.6-7% for 1 μg l⁻¹ of Se). The detection limit of the developed technique (3σ_b/S) was 0.01 μg l⁻¹. A sample throughput was 28 samples per hour (84 injections). The multisyringe technique has been validated by means of reference solid (sea lettuce) and water (hard drinking water) materials with good agreement with certified values. The analytical features were compared with those obtained by using of the commercial flow injection analysis (FIA) system. The proposed method provides a higher sampling frequency and a significant reduction of reagent and sample consumption in front the flow injection application.     

Use of a surfactant in the determination of arsenic by flow injection hydride generation atomic absorption spectrometry

The possible benefits of the addition of an anionic surfactant, didodecyldimethylammonium bromide, in the determination of arsenic, by flow injection hydride generation atomic absorption spectrometry using a flame-heated quartz tube atomizer, were studied in the light of previous reports concerning the effects of surfactants on chemical vapor generation procedures. Concentrations of arsenic between 5 and 30 μg l⁻¹ were used. Calibrations in the presence and absence of the surfactant in the sample solution were not significantly different, either for the case where vesicles were formed in the presence of the analyte or where they were preformed in the surfactant solution and then added to the analyte. The surfactant had no effect on recoveries in the presence of copper, nickel or bismuth. The addition of the surfactant to the acid carrier and/or borohydride streams had no effect. It is proposed that there may be a greater role for surfactants in the improvement of the processes by which the hydride is transferred to the bulk gas phase than has been attributed in previous reports on this subject.     

Determination of As(III) and total inorganic arsenic by flow injection hydride generation atomic absorption spectrometry

A simple procedure was developed for the direct determination of As(III) and As(V) in water samples by flow injection hydride generation atomic absorption spectrometry (FI–HG–AAS), without pre-reduction of As(V). The flow injection system was operated in the merging zones configuration, where sample and NaBH₄ are simultaneously injected into two carrier streams, HCl and H₂O, respectively. Sample and reagent injected volumes were of 250 μl and flow rate of 3.6 ml min⁻¹ for hydrochloric acid and de-ionised water. The NaBH₄ concentration was maintained at 0.1% (w/v), it would be possible to perform arsine selective generation from As(III) and on-line arsine generation with 3.0% (w/v) NaBH₄ to obtain total arsenic concentration. As(V) was calculated as the difference between total As and As(III). Both procedures were tolerant to potential interference. So, interference such as Fe(III), Cu(II), Ni(II), Sb(III), Sn(II) and Se(IV) could, at an As(III) level of 0.1 mg l⁻¹, be tolerated at a weight excess of 5000, 5000, 500, 100, 10 and 5 times, respectively. With the proposed procedure, detection limits of 0.3 ng ml⁻¹ for As(III) and 0.5 ng ml⁻¹ for As(V) were achieved. The relative standard deviations were of 2.3% for 0.1 mg l⁻¹ As(III) and 2.0% for 0.1 mg l⁻¹ As(V). A sampling rate of about 120 determinations per hour was achieved, requiring 30 ml of NaBH₄ and waste generation in order of 450 ml. The method was shown to be satisfactory for determination of traces arsenic in water samples. The assay of a certified drinking water sample was 81.7±1.7 μg l⁻¹ (certified value 80.0±0.5 μg l⁻¹).     

Separation of trace antimony and arsenic prior to hydride generation atomic absorption spectrometric determination

A separation method utilizing a synthetic zeolite (mordenite) was developed in order to eliminate the gas phase interference of Sb(III) on As(III) during quartz furnace hydride generation atomic absorption spectrometric (HGAAS) determination. The efficiency of the proposed separation method in the reduction of suppression effects of transition metal ions on As(III) signal was also investigated. Among the volatile hydride-forming elements and their different oxidation states tested (Sb(III), Sb(V), Se(IV), Se(VI), Te(IV), and Te(VI)), only Sb(III) was found to have a signal depression effect even at low (μg l⁻¹) concentrations under the experimental conditions employed. It has been shown that mordenite adsorbs Sb(III) quantitatively, even at a concentration of 1000 μg l⁻¹, at pHs greater than two, and also, it reduces the initial concentrations of the transition metal ions to lower levels which can be tolerated in many studies. The adsorption of Sb(III) on mordenite follows the Freundlich isotherm and is endothermic in nature.     

Inter-element interferences in the determination of arsenic and antimony by hydride generation atomic absorption spectrometry with a quartz tube atomizer

The interferences between arsenic and antimony on each other during the hydride generation atomic absorption spectrometry (HGAAS) determination of arsenic and antimony using a quartz tube atomizer (QTA) were examined. In order to eliminate or reduce such interferences by selective heat decomposition of arsine and stibine, a Pyrex adsorption U-tube trap containing glass wool was placed between the drying tube and the quartz tube atomizer. Although at 250 °C stibine decomposes and is held almost completely by the trap, arsine is also decomposed to an extent of 24% and, therefore, thermal decomposition is not useful to eliminate antimony interference on arsenic determination. The effect of coating the glass wool in the U-tube with antimony on the arsenic suppression of the antimony signal was studied. The results showed that the antimony coating in the U-tube could not hold arsenic effectively and its interference on the antimony signal could not be eliminated by this means. In the second part of the study, oxygen was supplied to the quartz tube atomizer during atomization in order to study the effect of supplying oxygen on the antimony signal and on the interference of arsenic in the antimony determination. Sensitivity was increased in the presence of oxygen and interferences of arsenic on antimony determination was decreased by about 10% when oxygen was supplied. It was also observed that the extent of interferences depended mainly on the interferent concentration rather than the analyte concentration.     

Evaluation of the hydride generation technique for the determination of lead in commercial iron oxide pigments

Two different procedures based on lead hydride generation for determination of lead in commercial iron oxide pigments have been evaluated. As the procedure based on the prior acid-dissolution of the samples to give a 1M HCl final medium led to a high relative standard deviation (6.5%) an alternative procedure based on the use of slurries was studied. The samples were suspended in water containing 0.01% hexametaphosphate, and lead hydride was generated from a 0.7M nitric acid and 14% ammonium peroxodisulphate medium by addition of 10% tetrahydroborate solution. In this way, an improvement in reproducibility and sensitivity as well as a saving of time and effort was achieved. The procedure based on the use of a suspension of the samples is therefore recommended.     

Speciation of inorganic arsenic in a sequential injection dual mini-column system coupled with hydride generation atomic fluorescence spectrometry

The separation and speciation of inorganic arsenic(III) and arsenic(V) are facilitated by employing a novel sequential injection system incorporating two mini-columns followed by detection with hydride generation atomic fluorescence spectrometry. An octadecyl immobilized silica mini-column is used for selective retention of the complex between As(III) and APDC, while the sorption of As(V) is readily accomplished by a 717 anion exchange resin mini-column. The retained As(III)-PDC complex and As(V) are effectively eluted with a 3.0 mol L⁻¹ hydrochloric acid solution as stripping reagent, which well facilitates the ensuing hydride generation process via reaction with tetrahydroborate. With a sampling volume of 1.0 mL and an eluent volume of 100 μL for both species, linear ranges of 0.05-1.5 μg L⁻¹ for As(III) and 0.1-1.5 μg L⁻¹ for As(V) are obtained, along with enrichment factors of 7.0 and 8.2, respectively. Precisions of 2.8% for As(III) and 2.9% for As(V) are derived at the concentration level of 1.0 μg L⁻¹. The practical applicability of the procedure has been demonstrated by analyzing a certified reference material of riverine water (SLRS-4), in addition to spiking recovery in a lake water sample matrix.     

Use of hydride generation-atomic absorption spectrometry to determine the effects of hard ions, iron salts and humic substances on arsenic sorption to sorghum biomass

At present, there is a great interest in studying new sorbent materials for the removal of arsenic from aqueous solutions because of its high toxicity and adverse effects on human health. In previous research, sorghum biomass was found to be an efficient and economic sorbent for the removal of arsenic from aqueous solutions. In this investigation, the effects of CaCl₂, MgCl₂, FeSO₄, MgSO₄, Fe(NO₃)₃, and humic substances (peat moss, humin and humic acids) on arsenic binding to sorghum biomass were evaluated. Among these compounds, only iron salts were found to positively increase the sorption of arsenic to sorghum biomass. In addition, the sorption equilibrium was reached faster when the reaction mixture contained iron salts. However, an overall reduction of 21% of arsenic sorption to sorghum biomass was observed in the presence of MgSO₄. This interference may be due to the presence of sulfate ions, instead of the hard cations, that could be in competition with As for the same interaction sites or ligands. Peat moss, humins and humic acid, extracted from sphagnum peat moss, significantly decreased the arsenic sorption to sorghum biomass.