Flow injection on-line preconcentration coupled to hydride generation atomic fluorescence spectrometry for ultra-trace amounts of cadmium determination in seawater

A simple flow injection on line separation and preconcentration system coupled to hydride generation atomic fluorescence spectrometry (HG-AFS) was developed for ultra-trace cadmium determination in seawater. With the sample pH kept at 3.0, the preconcentration of cadmium on the inner walls of the knotted reactor was carried out based on the retention of cadmium complex with 1-phenyl-3-methyl-4-benzoylpyrazol-5-one. A 0.2 mol L⁻¹ HCl was introduced to elute the retained analyte complex and merge with KBH₄ solution for HG-AFS detection. Under the optimal experimental conditions, an enhancement factor of 12 was obtained with a sample consumption of 12.0 mL. The limit of detection was 3.2 ng L⁻¹ with a sample frequency of 24 h⁻¹. The developed method was validated by the analysis of cadmium in certified reference materials, and was applied to the determination of cadmium in four seawater samples with R.S.D. of around 10%. Correspondence: Hong Wu, Department of Chemistry, Xuzhou Normal University, Xuzhou 221116, P.R. China     

A hydride generation atomic fluorescence spectrometric procedure for selenium determination after flow injection on-line co-precipitate preconcentration

A flow injection (FI) on-line preconcentration procedure for ultra-trace inorganic selenium was developed with detection by atomic fluorescence spectrometry. Selenium (IV) is co-precipitated with lanthanum hydroxide and collected on a PTFE beads packed column, the precipitate is afterwards dissolved with hydrochloric acid followed by hydride generation with reduction by tetrahydroborate. A thorough scrutiny was made for chemical variables and FI parameters. With a sampling volume of 3.4 ml, quantitative retention of selenium (IV) was obtained, along with an enrichment factor of 11 and a sampling frequency of 38 h^− 1. The detection limit, defined as 3 times the blank standard deviation (3σ), was 5 ng l^− 1. The precision was characterized by a RSD value of 1.2% (at the 0.5 μg l^− 1 level, n = 11). The enrichment factor was further enhanced to 20 along with a detection limit of 3 ng l^− 1, with a sample loading volume of 6.8 ml. The procedure was validated with certified reference materials and biological samples. It was also applied to the speciation of inorganic selenium in surface waters.     

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。     

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.     

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.     

Determination of selenium in vegetables by hydride generation atomic fluorescence spectrometry

A digestion mixture of H₂SO₄/HNO₃/H₂O₂/HF/V₂O₅ was investigated for decomposition of plant samples and sensitive detection of selenium was achieved by hydride generation atomic fluorescence spectrometry (HG-AFS). The method was found to be accurate and reproducible, with a low detection limit (DL) (0.14 ng g⁻¹ solution). The repeatability of the determination was mostly around 10%, the reproducibility over a period of 8 months for determination of selenium in the standard reference material Trace Elements in Spinach Leaves, NIST 1570a, was 9% and the relative measurement uncertainty was 7% using a coverage factor of 2.3 at 95% probability. The average recovery of the whole procedure was 90%. The characteristics of this method are simple and inexpensive equipment, low consumption of chemicals and the ability to analyse many samples in a short time. The whole procedure was carried out in the same PTFE tube, and in addition only a simple cleaning procedure is needed. As a consequence of all these advantages, the described method is suitable for environmental and nutritional studies. The selenium content was determined in 44 vegetable samples from different regions of Slovenia and the contents found were in the range 0.3-77 ng g⁻¹ wet weight.     

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.     

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.     

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%.     

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%.     

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.     

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.     

Separation and preconcentration by flow injection coupled to tungsten coil electrothermal atomic absorption spectrometry

A flow injection system coupled to a tungsten coil electrothermal atomizer has been developed for on-line separation and preconcentration, using lead as a model element. The system utilizes three-way solenoid valves for sampling, buffering, washing and reconditioning solution management, and the resin column is inserted in the tip of the autosampler arm of a Varian GTA-96. The solenoid valves and tungsten coil power supply were controlled by a computer program written in Visual Basic, interfaced with the built-in Varian software. The system performance was tested by loading the resin column with the sample flowing at 3 ml min⁻¹ for 60 s. Elution was performed automatically by sampling 20 μl of the eluent from a sample cup of the autosampler, and this aliquot was delivered into a 150 W tungsten coil. With Chelex-100 resin, the separation of concomitants was tested with lead in the presence of as much as 1000 mg l⁻¹ of Ca, Mg, Na or K. The model system presented an enrichment factor of 64 at a sampling rate of 30 samples per hour.     

Further study on a flow injection on-line multiplexed sorption preconcentration coupled with flame atomic absorption spectrometry for trace element determination

A further study on a newly developed flow injection (FI) on-line multiplexed sorption preconcentration (MSP) using a knotted reactor coupled with flame atomic absorption spectrometry (FAAS) was carried out to demonstrate its applicability and limitation for trace element determination. For this purpose, Cr(VI), Cu(II), Ni(II) and Co(II) were selected as the analytes, and detailed comparison was made between the MSP-FAAS and conventional FI on-line sorption preconcentration FAAS in respect to retention efficiency and linear ranges of absorbance versus sample loading flow rate and total preconcentration time. Introduction of an air-flow for removal of the residual solution in the KR after each sub-injection in the MSP procedure played a decisive role in the improvement of retention efficiency. The linearity of absorbance versus sample loading flow rate or total preconcentration time was extended to a more degree for the metal ions with less stability of their PDC (pyrrolidine dithiocarbamate) complexes than those with more stable PDC complexes. It seems that the MSP procedure behaves advantages beyond the inflection points in the diagrams of absorbance versus total preconcentration time and sample loading flow rate obtained by conventional (a single continuous) preconcentration procedure. With a sample loading flow rate of 6.0 ml min⁻¹ and a total preconcentration time of 180 s, the retention efficiencies were increased from 25, 46, 41 and 63% with a single continuous sorption preconcentration to 44, 78, 65 and 75% with a six sub-injection preconcentration procedure for Cr(VI), Co(II), Ni(II), and Cu(II), respectively. The detection limits were 0.40, 0.33, 0.31 and 0.26 μg l⁻¹ for Cr(VI), Co(II), Ni(II), and Cu(II), respectively. The precision (R.S.D.) for eleven replicate determination of 2 μg l⁻¹ Cr(VI), Co(II) and Ni(II), and 1 μg l⁻¹ Cu(II), was 2.1, 4.1, 2.6 and 1.7%, respectively.     

Optimization of selenium determination in plant samples by hydride generation and axial view inductively coupled plasma atomic emission spectrometry

The use of hydride generation coupled with axial view inductively couple plasma atomic emission spectrometry was presented for the determination of selenium in plant samples. The chemical factors affecting potentially the hydride generation efficiency (hydrochloric acid, sodium borohydride and sodium hydroxide concentrations) were assessed through investigation of chemical interference, accuracy and repeatability. The accuracy of measurements was not affected by elements present in high concentration in the plant matrix (K, Ca, Mg, and P). No interference was also observed with transition metals. Using a real sample (maize) with standard additions, decreases of recoveries were sometimes observed for 0.1% (m/v) NaOH, and attained 13.8% in the most unfavourable case. The final accuracy of the method was verified by using two certified reference materials: CRM 402 (white clover) and CRM 279 (sea lettuce). No statistically significant differences were obtained between the measured concentrations and the certified values. The optimized method was found sensitive (detection limit 0.15 μg l⁻¹), reliable and repeatable (R.S.D. between 1.3% and 4.0%).     

Determination of tin in steels by non-dispersive atomic fluorescence spectrometry coupled with flow-injection hydride generation in the presence of L-cysteine

Flow-injection hydride generation has been coupled with a non-dispersive atomic fluorescence spectrometer for the determination of trace concentrations of tin. The use of L-cysteine in stannane generation enhances the atomic fluorescence signal for tin. In addition, it appears that the flow-injection method allows the use of a wider range of acid concentrations, and hence interference from transition elements is also reduced. An absolute detection limit of 1.3 ng was achieved with a 0.5 ml sample. Ten determinations of a solution containing 100 ng ml⁻¹ of tin(H) generated a relative standard deviation of 1.8%. The linear dynamic range of the calibration curve extended over three orders of magnitude and sample throughput rate was 144 samples h⁻¹. Application of the proposed technique is demonstrated by the determination of tin in low alloy steel standard reference materials.     

Speciation of inorganic arsenic by electrochemical hydride generation atomic absorption spectrometry

A simple procedure was developed for the speciation of inorganic arsenic by electrochemical hydride generation atomic absorption spectrometry (EcHG–AAS), without pre-reduction of As(V). Glassy carbon was selected as cathode material in the flow cell. An optimum catholyte concentration for simultaneous generation of arsine from As(III) and As(V) was 0.06 mol l⁻¹ H₂SO₄. Under the optimized conditions, adequate sensitivity and difference in ratio of slopes of the calibration curves for As(III) and As(V) can be achieved at the electrolytic currents of 0.6 and 1 A. The speciation of inorganic arsenic can be performed by controlling the electrolytic currents, and the concentration of As(III) and As(V) in the sample can be calculated according to the equations of absorbance additivity obtained at two selected electrolytic currents. The calibration curves were linear up to 50 ng ml⁻¹ for both As(III) and As(V) at 0.6 and 1 A. The detection limits of the method were 0.2 and 0.5 ng ml⁻¹ for As(III) and As(V) at 0.6 A, respectively. The relative standard deviations were of 2.1% for 20 ng ml⁻¹ As(III) and 2.5% for 20 ng ml⁻¹ As(V). The method was validated by the analysis of human hair certified reference material and successfully applied to speciation of soluble inorganic arsenic in Chinese medicine.     

Investigation of on-line coupling electrothermal atomic absorption spectrometry with flow injection sorption preconcentration using a knotted reactor for totally automatic determination of lead in water samples

A flow injection on-line sorption preconcentration electrothermal atomic absorption spectrometric system for fully automatic determination of lead in water was investigated. The discrete non-flow-through nature of ETAAS, the limited capacity of the graphite tube and the relatively large volume of the knotted reactor (KR) are obstacles to overcome for the on-line coupling of the KR sorption preconcentration system with ETAAS. A new FI manifold has been developed with the aim of reducing the eluate volume and minimizing dispersion. The lead diethyldithiocarbamate complex was adsorbed on the inner walls of a knotted reactor made of PTFE tubing (100 cm long, 0.5 mm i.d.). After that, an air flow was introduced to remove the residual solution from the KR and the eluate delivery tube, then the adsorbed analyte chelate was quantitatively eluted into a delivery tube with 50 μl of ethanol. An air flow was used to propel the eluent from the eluent loop through the reactor and to introduce all the ethanolic eluate onto the platform of the transversely heated graphite tube atomizer, which was preheated to 80°C. With the use of the new FI manifold, the consumption of eluent was greatly reduced and dispersion was minimized. The adsorption efficiency was 58%, and the enhancement factor was 142 in the concentration range 0.01–0.05 μg l⁻¹ Pb at a sample loading rate of 6.8 ml min⁻¹ with 60 s preconcentration time. For the range 0.1–2.0 μg l⁻¹ of Pb a loading rate of 3.0 ml min⁻¹ and 30 s preconcentration time were chosen, resulting in an adsorption efficiency of 42% and an enhancement factor of 21, respectively. A detection limit (3σ) of 2.2 ng l⁻¹ of lead was obtained using a sample loading rate of 6.8 ml min⁻¹ and 60 s preconcentration. The relative standard deviation of the entire procedure was 4.9% at the 0.01 μg l⁻¹ Pb level with a loading rate of 6.8 ml min⁻¹ and 60 s preconcentration, and 2.9% at the 0.5 μg l⁻¹ Pb level with a 3.0 ml min⁻¹ loading rate and 30 s preconcentration. Efficient washing of the matrix from the reactor was critical, requiring the use of the standard addition method for seawater samples. The analytical results obtained for seawater and river water standard reference materials were in good agreement with the certified values.     

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.     

AE-HG-AFS测定长期汞暴露人群补硒后尿中硒的形态

建立了一种利用阴离子交换高效液相色谱与氢化物发生原子荧光光谱联用同时测定四、六价硒及硒代半胱氨酸(SeCys)形态的方法。优化了六价硒的还原条件及仪器检测参数,以不同浓度的柠檬酸铵作为流动相,在10 min内同时分离了四、六价硒及硒代半胱氨酸(SeCys)。采用加标法定量,加标回收率在90%～119%之间,相对标准偏差为1.6%～3.1%(100μg/L),四、六价硒及硒代半胱氨酸(SeCys)的检出限分别为0.32μg/L、0.47μg/L和0.44μg/L(进样量为100μL)。应用该法对长期汞暴露人群补硒后尿中的小分子硒的形态进行了分析,仅检测到硒代半胱氨酸(SeCys)。