Hyphenation of flow injection/sequential injection with chemical hydride/vapor generation atomic fluorescence spectrometry

The dominant role played by flow injection/sequential injection (FI/SI, including lab-on-valve, LOV) in automatic on-line sample pretreatments coupling to various detection techniques is amply demonstrated by the large number of publications it has given rise to. Among these, its hyphenation with hydride/vapor generation atomic fluorescence spectrometry (HG/VG-AFS) has become one of the most attractive sub-branches during the last years, attributed not only to the high sensitivity of this technique, but also to the superb separation capability of hydride/vapor forming elements from complex sample matrices. In addition, it also provides potentials for the speciation of the elements of interest.It is worth mentioning that quite a few novel developments of sample pretreatment have emerged recently, which attracted extensive attentions from the related fields of research. The aim of this mini-review is thus to illustrate the state-of-the-art progress of implementing flow injection/sequential injection and miniaturized lab-on-valve systems for on-line hydride/vapor generation separation and preconcentration of vapor forming elements followed with detection by atomic fluorescence spectrometry, within the period from 2004 up to now. Future perspectives in this field are also discussed.     

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.     

Preconcentration and speciation of chromium in a sequential injection system incorporating dual mini-columns coupled with electrothermal atomic absorption spectrometry

A procedure for chromium preconcentration and speciation with a dual mini-column sequential injection system coupled with electrothermal atomic absorption spectrometry (ETAAS) was developed. At pH 6, the sample solution was firstly aspirated to flow through a Chlorella vulgaris cell mini-column on which the Cr(III) was retained. The effluent was afterwards directed to flow through a 717 anion exchange resin mini-column accompanied by the retention of Cr(VI). Thereafter, Cr(III) and Cr(VI) were eluted by 0.04 mol L^− 1 and 1.0 mol L^− 1 nitric acid, respectively, and the eluates were quantified with ETAAS. Chemical and flow variables governing the performance of the system were investigated. By using a sampling volume of 600 µL, sorption efficiencies of 99.7% for Cr(III) and 99% for Cr(VI) were achieved along with enrichment factors of 10.5 for Cr(III) and 11.6 for Cr(VI), within linear ranges of 0.1–2.5 µg L^− 1 for Cr(III) and 0.12–2.0 µg L^− 1 for Cr(VI). Detection limits of 0.02 µg L^− 1 for Cr(III) and 0.03 µg L^− 1 for Cr(VI) along with RSD values of 1.9% for Cr(III) and 2.5% for Cr(VI) (1.0 µg L^− 1, n = 11) were obtained. The procedure was validated by analyzing a certified reference material of GBW08608 and further demonstrated by chromium speciation in river and tap water samples.     

Determination of total arsenic in seawater by hydride generation atomic fluorescence spectrometry

In this work, the determination of total As in seawater by hydride generation atomic fluorescence spectrometry was studied. The influence of the chemical, flow and instrumental parameters were investigated and optimized. The pre-reduction of As(V) to As(III) was performed using KI plus ascorbic acid in 3.5 mol L^− 1 HCl medium. No multiplicative interference was present and external aqueous calibration could be used. The limit of detection was 36 ng L^− 1, while the repeatability was 2% (n = 10), at a 500 ng L^− 1 concentration level. The sample throughput was 15 h^− 1 if triplicate measurements were made. The accuracy was assessed by the analysis of a seawater certified reference material and excellent agreement between the obtained and certified values was verified. The procedure was used for the analysis of seawater offshore samples collected at the Brazilian coast and results ranging from 860 to 1200 ng L^− 1 were found.     

顺序注射氢化物发生-原子荧光光谱法同时测定硒和砷的研究

建立了一种顺序注射氢化物发生-原子荧光光谱法测定试样中Se和As的方法,同时讨论了共存离子的干扰情况.在最佳实验条件下,Se和As的检出限分别为0.16和0.095 μg/L,加标回收率为92.4%～104.7%.     

树脂分离-氢化物发生-原子荧光光谱法测定食品中无机砷、一甲基胂和二甲基胂

建立了用阴离子交换树脂分离-氢化物发生原子荧光光谱法测定食品中无机砷、一甲基胂和二甲基胂的方法.分别从样品上样条件及二甲基胂、一甲基胂、 As(Ⅲ)和As(Ⅴ)分离条件进行了优化.研究了树脂处理程序对分离的影响,并探讨了共存离子对测定砷的干扰和消除的方法.对方法的适用范围做了研究.本方法具有操作简便、快速、灵敏度高等优点.检出限(以砷计)分别为: 无机砷0.34 μg/L,一甲基胂0.57 μg/L,二甲基胂0.46 μg/L.     

Determination of arsenic in dinosaur skeleton fossils by hydride generation atomic fluorescence spectrometry

Hydride generation atomic fluorescence spectrometry was for the first time utilized to determine trace toxic element arsenic in the skeleton fossils of four dinosaurs unearthed in Sichuan Province of China. The instrumental limit of detection (LOD) for arsenic was 0.03 μg/L under optimal experimental conditions, which compared favorably to that by ICP-AES and ETAAS. The samples were digested with aqua regia in boiling water bath. The recoveries of standard addition were found to be from 97 to 109%, and the analytical results were found in good agreement with those by ICP-AES. It is a simple, reliable, sensitive yet relatively inexpensive analytical method, compared to ICP-AES, ICP-MS or ETAAS. Interesting analytical results were found that the arsenic concentrations were all abnormally high in the skeleton fossils. The established analytical method and the analytical results may be helpful in revealing the mystery of the mass extinction of the dinosaur fauna. The analytical results, together with other data available to date, supported the argument that the arsenic toxicosis could be a contributing factor for the mass extinction of the dinosaur fauna in Sichuan Province of China.     

Speciation analysis of inorganic arsenic by microchip capillary electrophoresis coupled with hydride generation atomic fluorescence spectrometry

A novel method for speciation analysis of inorganic arsenic was developed by on-line hyphenating microchip capillary electrophoresis (chip-CE) with hydride generation atomic fluorescence spectrometry (HG-AFS). Baseline separation of As(III) and As(V) was achieved within 54 s by the chip-CE in a 90 mm long channel at 2500 V using a mixture of 25 mmol l(-1) H3BO3 and 0.4 mmol l(-1) CTAB (pH 8.9) as electrolyte buffer. The precisions (RSD, n=5) ranged from 1.9 to 1.4% for migration time, 2.1 to 2.7% for peak area, and 1.8 to 2.3% for peak height for the two arsenic species at 3.0 mg l(-1) (as As) level. The detection limits (3sigma) for As(III) and As(V) based on peak height measurement were 76 and 112 microg l(-1) (as As), respectively. The recoveries of the spikes (1 mg l(-1) (as As) of As(III) and As(V)) in four locally collected water samples ranged from 93.7 to 106%.     

流动注射在线共沉淀HG-AFS测定痕量铅

建立了流动注射在线共沉淀HG-AFS测定痕量铅的分析方法。方法基于铅在碱性介质中与氢氧化镁共沉淀,沉淀收集在锥形沉淀腔中,用HCl溶洗沉淀和NaBH4反应,产生的氢化物被载气引入原子化器中进行测定。测定铅的RSD为3％(5ng/mL,n=10),检出限为0．01ng。检出限较直接进样降低了11倍。对国家标准物质中铅的测定结果与标准值相符。     

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.     

Development of a non-chromatographic method for the speciation analysis of inorganic antimony in mushroom samples by hydride generation atomic fluorescence spectrometry

A simple and sensitive method has been developed for the direct determination of toxic species of antimony in mushroom samples by hydride generation atomic fluorescence spectrometry (HG AFS). The determination of Sb(III) and Sb(V) was based on the efficiency of hydride generation employing NaBH₄, with and without a previous KI reduction, using proportional equations corresponding to the two different measurement conditions. The extraction efficiency of total antimony and the stability of Sb(III) and Sb(V) in different extraction media (nitric, sulfuric, hydrochloric, acetic acid, methanol and ethanol) were evaluated. Results demonstrated that, based on the extraction yield and the stability of extracts, 0.5 mol L^− 1 H₂SO₄ proved to be the best extracting solution for the speciation analysis of antimony in mushroom samples. The limits of detection of the developed methodology were 0.6 and 1.1 ng g^− 1 for Sb(III) and Sb(V), respectively. The relative standard derivation was 3.8% (14.7 ng g^− 1) for Sb(V) and 5.1% (4.6 ng g^− 1) for Sb(III). The recovery values obtained for Sb(III) and Sb(V) varied from 94 to 106% and from 98 to 105%, respectively. The method has been applied to determine Sb(III), Sb(V) and total Sb in five different mushroom samples; the Sb(III) content varied from 4.6 to 11.4 ng g^− 1 and Sb(V) from 14.7 to 21.2 ng g^− 1. The accuracy of the method was confirmed by the analysis of a certified reference material of tomato leaves.     

Eggshell membrane-based solid-phase extraction combined with hydride generation atomic fluorescence spectrometry for trace arsenic(V) in environmental water samples

The eggshell membrane (ESM) contains several surface functional groups such as amines, amides and carboxylic groups with potential as SPE adsorbent for the retention of target species of interest. In this paper, the potential use of ESM, a typical biomaterial, as solid-phase extraction (SPE) adsorbent is evaluated for analysis of trace arsenic(V) in environmental water samples in combination with hydride generation atomic fluorescence spectrometry (HG-AFS). In order to obtain the satisfactory recovery of arsenic(V), various parameters including the desorption and enrichment conditions such as pH, the flow rate and the volume of sample solution, the amount of ESM and the content of sodium chloride were systematically optimized and the effects of co-existed ions were also investigated in detail. Under the optimal conditions, arsenic(V) could be easily extracted by the ESM packed cartridge and the breakthrough adsorption capacity was found to be 3.9 μg g⁻¹. The favorable limit of detection (LOD) for arsenic(V) was found to be 0.001 μg L⁻¹ with an enrichment factor of 33.3, and the relative standard deviations (R.S.Ds) was 2.1% for 0.6 μg L⁻¹ arsenic (n = 11). The reproducibility among columns was satisfactory (R.S.D. among columns is less than 5%). The proposed method has been successfully applied to analysis of arsenic(V) in aqueous environmental samples, which suggests the ESM can be an excellent SPE adsorbent for arsenic(V) pretreatment and enrichment from real water samples.     

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.     

Precipitate coating on cellulose fibre as sorption medium for selenium preconcentration and speciation with hydride generation atomic fluorescence spectrometry

Lanthanum hydroxide precipitate is for the first time coated onto cellulose fibre and serves as a novel sorption medium for separation and speciation of inorganic selenium. A micro-column packed with precipitate-layer-coated cellulose fibre is incorporated into a sequential injection system for selenite retention from a neutral aqueous solution, which is afterwards stripped with a NaBH₄-NaOH solution as eluent. The hydride generation is actuated by merging the eluate and hydrochloric acid downstream, followed by the detection with atomic fluorescence spectrometry. Total inorganic selenium is derived by pre-reduction of selenate and speciation is estimated by difference. The coated precipitate layer can be used for 150 runs for selenium sorption, offering a clear advantage over the conventional precipitation protocols where a large amount of precipitate is dissolved into a small volume of eluent which might interfere with the detection. With a sample volume of 1.0 mL, an enrichment factor of 9.7 and a detection limit of 9 ng L⁻¹ are obtained in a linear range of 0.05-2.5 μg L⁻¹. A sampling frequency of 24 h⁻¹ is achieved along with a R.S.D. of 1.7% at 0.5 μg L⁻¹ Se(IV). The procedure is validated by analyzing selenium in a reference material GBW 10010 (rice) and a human hair sample. It is further demonstrated by speciation of inorganic selenium in surface water samples by pre-reduction of selenate.     

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.     

Determination of arsenic and antimony in milk by hydride generation atomic fluorescence spectrometry

A highly sensitive procedure has been developed for total arsenic and antimony determination in milk samples by hydride generation atomic fluorescence spectrometry after microwave-assisted sample digestion. The discrete introduction of 2 ml of digested sample in the automated continuous flow hydride generation system allows us to reduce drastically the sample and HCl consume and to determine several elements from a same sample digestion. The method provides detection limits of 0.006 and 0.003 ng ml⁻¹, a sensitivity of 2390 and 2840 fluorescence units per ng ml⁻¹ for As and Sb respectively, and average relative standard deviation of 2.3% for As and 4.8% for Sb. The analysis of cow milk samples, obtained from the Spanish market evidenced the presence of As at concentration levels from 3.4 to 11.6 ng g⁻¹ and Sb levels from 3.5 to 11.9 ng g⁻¹, thus in a proportion near to 1:1, which is in contrast with the 10:1 natural ratio between As and Sb and could evidence the effect of the introduction of new alloys and polymer materials in the industrial process of milk. The method was validated by the comparison of data found for commercial samples by using the proposed procedure and reference methods based on dry-ashing and AFS, and microwave-assisted digestion and inductively coupled plasma mass spectrometry determination.     

顺序注射氢化物发生-原子荧光光谱法同时测定中草药中铋和汞

建立了一种顺序注射氢化物发生-原子荧光光谱法测定中草药中的Bi和Hg的方法,讨论了共存离子的干扰情况。在最佳实验条件下,Bi和Hg的检出限分别为0.0057μg/L和0.0197μg/L,加标回收率为93.4%~104.7%,相对标准偏差小于4.3%,被测中草药试样中共存的离子对Bi和Hg的测定没有干扰。方法可用于中草药试样中Bi和Hg的同时测定。     

电磁感应在线消化-原子荧光光谱法测定茶水中的砷

利用电磁感应加热原理,研制了在线消化还原、氢化物发生原子荧光法分析装置,实现了茶水中As量的在线测定.对各种实验参数和干扰情况进行了研究.方法的检出限为0.063 μg/L;样品分析精密度(RSD)为2.5%(n=11).     

On-line organoselenium interference removal for inorganic selenium species by flow injection coprecipitation preconcentration coupled with hydride generation atomic fluorescence spectrometry

The existence of dimethylselenium (DMSe) and dimethyldiselenium (DMDSe) in some environmental samples can cause serious interference on Se(IV) determination by hydride generation atomic fluorescence spectrometry (HG-AFS) due to their contribution on HG-response. A flow injection separation and preconcentration system coupled to HG-AFS was therefore developed by on-line coprecipitation in a knotted reactor (KR) for eliminating interference subjected from organoselenium. The sample, spiked with lanthanum nitrate, was merged with an ammonium buffer solution (pH 8.8), which promoted coprecipitation of Se(IV) and quantitative collection by 150 cm PTFE KR. DMSe and DMDSe, however, were unretained and expelled from the KR. An air flow was introduced to remove the residual solution from the KR, then a 1.2 mol l⁻¹ HCl was pumped to dissolve the precipitates and merge with KBH₄ solution for HG-AFS detection. The interference of DMSe and DMDSe on the Se(IV) determination by conventional HG-AFS and its elimination by the developed separation and preconcentration system were evaluated. With optimal experimental conditions and with a sample consumption of 12.0 ml, an enhancement factor of 18 was obtained at a sample frequency of 24 h⁻¹. The limit of detection was 0.014 μg l⁻¹ and the precision (R.S.D.) for 11 replicate measurements of 1.0 μg l⁻¹ Se(IV) was 2.5%. The developed method was successfully applied to the determination of inorganic selenium species in a variety of natural water samples.     

On-line coupling of flow injection sequential extraction to hydride generation atomic fluorescence spectrometry for fractionation of arsenic in soils

A new flow injection on-line sequential extraction procedure coupled with hydride generation atomic fluorescence spectrometry (HG-AFS) was developed for rapid and automatic fractionation of arsenic in soils. The developed methodology involved a three-step sequential extraction procedure with deionized water, KOH solution, and HCl solution. 25 mg of the soil sample packed into a microcolumn (4 mm i.d. × 3 cm long) was dynamically extracted by continuously pumping each individual extractant through the column. The extracted arsenic solution was merged with 4% (m/v) K₂S₂O₈ solution for on-line oxidation of all arsenic species into As^V. The total extracted arsenic was on-line detected by HG-AFS, and quantitated using an on-line standard addition calibration strategy. The total time for the three-step sequential extraction and on-line detection lasted only 10 min. The developed methodology offers several advantages over conventional batch sequential extraction protocols, including minimization of readsorption/redistribution problem, improvement of accuracy, high speed, less amounts of sample/reagents required, less risk of contamination and analyte loss. The developed methodology was successfully applied to the fractionation of arsenic in certified soil reference materials.