UV-induced carbonyl generation with formic acid for sensitive determination of nickel by atomic fluorescence spectrometry

UV-induced carbonyl generation with formic acid is used for gaseous sample introduction into an atomic fluorescence spectrometer for the determination of ultra-trace nickel. Compared with conventional carbonyl generation, no toxic gas CO is involved in this work, and volatile Ni(CO)₄ is generated with a single reagent formic acid under the irradiation of UV light (253.7 nm, 15 W). The reaction conditions, including reaction medium, UV irradiation time and reaction temperature, are optimized for the best signal. Under the optimized conditions, a limit of detection of 10 ng L⁻¹ for nickel is obtained without any analyte-pre-concentration, which is comparable to that using in situ trapping technique. Interferences from common transition metal ions, noble metal ions and mineral acids are also investigated. The proposed method is applied to the analysis of three certified reference materials and two organic acid samples for trace nickel, with analytical results in good agreement with certified values or those obtained by electrothermal atomic absorption spectrometry. This is a simple, fairly green and highly sensitive method for ultra-trace nickel determination.     

Lower limits of detection in speciation analysis by coupling high-performance liquid chromatography and chemical-vapor generation

Speciation studies are much more important than total element determination because toxicity of many elements depends on their chemical forms. Nobody can claim that a foodstuff is very dangerous to eat by determining total arsenic due to the possibility that the arsenic could be present in non-toxic forms. Hence, speciation studies are crucial in any matrix relevant to human beings.Trace-element speciation requires sufficiently sensitive procedures to monitor each species at trace levels. One way to increase the sensitivity for elements forming volatile species is coupling high-performance liquid chromatography (HPLC) with chemical-vapor generation (CVG). This review aims to highlight not only development of HPLC-CVG techniques for ultratrace-elemental speciation in a variety of matrices but also their application. In addition, we discuss the advantages and the disadvantages of these techniques.     

Spray nebulization for sample introduction in ion mobility spectrometry

A new sample introduction system based on spray nebulization has been successfully developed to perform direct analysis of liquid samples by IMS. The system comprises a concentric nebulizer that generates a spray plume which is introduced in the ionization region of the IMS instrument through a temperature controlled transfer line. This system avoids previous problems of direct injection of liquid samples and maintains the countercurrent flow of inert gas necessary for the operation of the IMS instrument. Evaluation of the qualitative and quantitative capabilities of the methodology has been performed after a carefully study of the main variables affecting the spray nebulization and the transport of the analyte molecules through the transfer line. To demonstrate the usefulness of the new sample introduction system, direct analysis of drugs and drug metabolites in saliva or urine samples have been performed, obtaining accurate, reliable and sensitive results. Moreover, analytes with physico-chemical properties that limited the capability of thermal desorption as sample introduction method such as amino acids can be analyzed by using the spray nebulization methodology.     

Efficient generation of volatile species for cadmium analysis in seafood and rice samples by a modified chemical vapor generation system coupled with atomic fluorescence spectrometry

A vapor generation procedure to determine Cd by atomic fluorescence spectrometry (AFS) has been established. Volatile species of Cd are generated by following reaction of acidified sample containing Fe(II) and l-cysteine (Cys) with sodium tetrahydroborate (NaBH₄). The presence of 5 mg L⁻¹ Fe(II) and 0.05% m/v Cys improves the efficiency of Cd vapor generation substantially about four-fold compared with conventional thiourea and Co(II) system. Three experiments with different mixing sequences and reaction times are designed to study the reaction mechanism. The results document that the stability of Cd(II)–Cys complexes is better than Cys–THB complexes (THB means NaBH₄) while the Cys–THB complexes have more contribution to improve the Cd vapor generation efficiency than Cd(II)–Cys complexes. Meanwhile, the adding of Fe(II) can catalyze the Cd vapor generation. Under the optimized conditions, the detection limit of Cd is 0.012 μg L⁻¹; relative standard deviations vary between 0.8% and 5.5% for replicate measurements of the standard solution. In the presence of 0.01% DDTC, Cu(II), Pb(II) and Zn(II) have no significant influence up to 5 mg L⁻¹, 10 mg L⁻¹and 10 mg L⁻¹, respectively. The accuracy of the method is verified through analysis of the certificated reference materials and the proposed method has been applied in the determination of Cd in seafood and rice samples.     

Study of interferences by transition metal ions in hydride generation atomic absorption spectrometry of antimony

The mechanism of the interference of metal ions in the hydride generation atomic absorption spectrometry (AAS) of antimony was studied. Experiments on the decomposition rate of sodium tetrahydroborate in acidic media were done in the presence of interfering metals, with and without the addition of masking agents. The results were compared with experiments on the sensitivity of AAS in the presence of the same interfering metals with and without the addition of the same masking agents. AAS experiments are described in which the product of the reaction between sodium tetrahydroborate and one of the interfering metals was present during hydride formation. This reaction product was certainly one of the causes of interference, but the contribution of the catalytic decomposition of sodium tetrahydroborate to interference is not clear.     

高效液相色谱-氢化物发生-原子荧光光谱在线联用系统分析中成药中砷化合物形态

建立了高效液相色谱-氢化物发生-原子荧光光谱砷形态分析在线联用系统,考察了不同实验条件对4种砷形态化合物（As^Ⅲ,DMA^Ⅴ,MMA^Ⅴ和As^Ⅴ）分离分析的影响,优化了实验条件.在优化的实验条件下,采用pH 5.8的磷酸盐缓冲溶液为流动相,梯度洗脱,10 min之内4种砷形态达到基线分离.进样20μL,测定4种形态的检出限分别为：As^Ⅲ2.76 ng/mL,DMA^Ⅴ7.37 ng/mL,MMA^Ⅴ2.86 ng/mL和As^Ⅴ5.22 ng/mL,相对标准偏差RSD在2.9%～4.2%之间.该联用系统灵敏度高,准确性好,分离分析了部分市售中成药中的不同砷形态化合物.     

Determination of cadmium in polyethylene by analytical atomic spectrometry with gas-phase sample introduction technique

Cadmium in polyethylene was determined by both inductively coupled plasma atomic emission spectrometry (ICP-AES) and atomic absorption spectrometry (AAS) with continuous-flow gas-phase sample introduction in a reaction medium of ascorbic acid. In the presence of mixture of cobalt and thiourea in the ascorbic acid solution, the sensitivities by both ICP-AES and AAS for cadmium were greatly enhanced. The gaseous cadmium species was phase-separated in a gas–liquid separator and directed via a stream of argon carrier gas to an inductively coupled plasma and an electrically heated quartz tube atomizer (QTA) for atomic spectrometry. Under the optimized experimental conditions, the best attainable detection limits at Cd I 228.802 nm line were 1.3 and 0.017 ng/ml with linear dynamic ranges of 10–500 ng/ml and 0.1–1 ng/ml in concentrations by ICP-AES and QTA-AAS, respectively. The instrumental precisions expressed as the relative standard deviation (R.S.D.) from ten replicate measurements of 50 and 1 ng/ml cadmium by ICP-AES and QTA-AAS were 5.6% and 3.2%, respectively. With the use of ICP-AES and QTA-AAS with gas-phase sample introduction method, six- and 200-fold improvements in detection limits for cadmium were obtained in comparison with their conventional solution nebulization methods, respectively. After the effects of several diverse elements on the determination of cadmium by ICP-AES and QTA-AAS with the present gas-phase sample introduction systems were examined, these methods were applied to the determination of low concentrations of cadmium in polyethylene. The results obtained by the present method were in good agreement with the certified values.     

Determination of As, Sb, Se, Te and Bi in milk by slurry sampling hydride generation atomic fluorescence spectrometry

A simple and fast analytical procedure has been developed for the determination of As, Sb, Se, Te and Bi in milk samples by hydride generation atomic fluorescence spectrometry (HG-AFS). Samples were treated with aqua regia for 10 min in an ultrasound water bath and pre-reduced with KBr for total Se and Te determination or with KI and ascorbic acid for total As and Sb, the determination of Bi being possible in all with or without pre-reduction. Slurries of samples, in the presence of antifoam A, were treated with NaBH₄ in HCl medium to obtain the corresponding hydrides, and AFS measurements were processed in front of external calibrations prepared and measured in the same way as samples. Results obtained by the developed procedure compare well with those found after microwave-assisted complete digestion of samples. The proposed method is simple and fast, and only 1 ml of milk is needed. The values obtained for detection limit are 2.5, 1.6, 3, 6 and 7 ng l⁻¹ for As, Sb, Se, Te and Bi respectively in the diluted samples, with average relative standard deviation values of 3.8, 3.1, 1.9, 6.4 and 1.2% for three independent analysis of a series of commercially available samples of different origin. Data found in Spanish market samples varied from 3.2±0.3 to 11.3±0.2 ng g⁻¹ As, from 3.1±0.2 to 11.6±0.4 ng g⁻¹ Sb, from 10.7±0.5 to 25.5±0.4 ng g⁻¹ Se, from 0.9±0.2 to 9.4±0.6 ng g⁻¹ Te and from 11.5±0.1 to 27.7±0.4 ng g⁻¹ Bi.     

Speciation analysis of organoarsenical compounds in biological matrices by coupling ion chromatography to atomic fluorescence spectrometry with on-line photooxidation and hydride generation

The optimisation of an on-line decomposition based on UV photooxidation for the analysis of organoarsenic species by coupling cation-exchange chromatography and atomic fluorescence spectrometry with hydride generation, is described. In this study, special consideration is given to the compatibility of mobile phases with post-column treatments. Results show that the most commonly used mobile phase, aqueous pyridine solutions, decreases species conversion efficiency, leading to a significant loss of sensitivity. New fully-compatible chromatographic conditions are proposed to separate arsenobetaine, arsenocholine, trimethylarsine oxide and tetramethylarsonium ion within 20 min. The very low absolute limits of detection, 4-12 pg(As), allow speciation at trace levels. Analysis of a certified reference fish tissue (DORM-2) and other seafood samples (French and Chilean oysters and mussel) highlights the robustness and the accuracy of the optimised system.     

A new vapor generation system for mercury species based on the UV irradiation of mercaptoethanol used in the determination of total and methyl mercury in environmental and biological samples by atomic fluorescence spectrometry

A new vapor generation system for mercury (Hg) species based on the irradiation of mercaptoethanol (ME) with UV was developed to provide an effective sample introduction unit for atomic fluorescence spectrometry (AFS). Preliminary investigations of the mechanism of this novel vapor generation system were based on GC–MS and FT–IR studies. Under optimum conditions, the limits of determination for inorganic divalence mercury and methyl mercury were 60 and 50 pg mL⁻¹, respectively. Certified reference materials (BCR 463 tuna fish and BCR 580 estuarine sediment) were used to validate this new method, and the results agreed well with certified values. This new system provides an attractive alternative method of chemical vapor generation (CVG) of mercury species compared to other developed CVG systems (for example, the traditional KBH₄/NaOH–acid system). To our knowledge, this is the first systematic report on UV/ME-based Hg species vapor generation and the determination of total and methyl Hg in environmental and biological samples using UV/ME–AFS. Figure A new vapor generation system for mercury species using mercaptoethanol under UV irradiation was developed as an effective sample introduction unit for atomic fluorescence spectrometry     

Determination of cadmium and lead in reference materials by volatile species generation with in situ trapping flame atomic absorption spectrometry

The analytical performance of coupled volatile species generation-integrated atom trap (VSG-IAT) atomizer flame atomic absorption spectrometry (FAAS) system was evaluated for determination of Cd and Pb in reference materials. Lead using formation of PbH₄ and Cd⁰ vapors are atomized in air-acetylene flame-heated IAT. A new design of VSG-IAT-FAAS hyphenated technique that would exceed the operational capabilities of existing arrangements (a water-cooled single silica tube, double-slotted quartz tube or an “integrated trap”) was investigated. A dramatic improvement in detection limit was achieved compared with that obtained using either of the above atom trapping techniques separately. The concentration detection limits, defined as 3 times the blank standard deviation (3σ), were 0.05 and 0.40 ng mL^− 1 for Cd and Pb, respectively. For a 120 s in situ pre-concentration time, sensitivity enhancement compared to flame AAS, was 500 and 575 folds for Cd and Pb, respectively, using volatile species generation-atom trapping technique. The sensitivity can be further improved by increasing the collection time. The precision, expressed as RSD, was 4.4% and 4.1% (n = 6) for Cd and Pb, respectively. The designs studied include slotted tube, single silica tube and integrated atom trap-cooled atom traps. The accuracy of method was verified using certified reference materials (PLANTS 3 and IAEA/W-4) by standard addition calibration technique. The measured Cd and Pb contents in two reference materials were in satisfactory agreement with the certified values.     

Comparative performance study of different sample introduction techniques for rapid and precise selenium isotope ratio determination using multi-collector inductively coupled plasma mass spectrometry (MC-ICP/MS)

The analytical performance of five sample introduction systems, a cross flow nebulizer spray chamber, two different solvent desolvation systems, a multi-mode sample introduction system (MSIS), and a hydride generation (LI2) system were compared for the determination of Se isotope ratio measurements using multi-collector inductively coupled plasma mass spectrometry (MC-ICP/MS). The optimal operating parameters for obtaining the highest Se signal-to-noise (S/N) ratios and isotope ratio precision for each sample introduction were determined. The hydride generation (LI2) system was identified as the most suitable sample introduction method yielding maximum sensitivity and precision for Se isotope ratio measurement. It provided five times higher S/N ratios for all Se isotopes compared to the MSIS, 20 times the S/N ratios of both desolvation units, and 100 times the S/N ratios produced by the conventional spray chamber sample introduction method. The internal precision achieved for the ⁷⁸Se/⁸²Se ratio at 100 ng mL⁻¹ Se with the spray chamber, two desolvation, MSIS, and the LI2 systems coupled to MC-ICP/MS was 150, 125, 114, 13, and 7 ppm, respectively. Instrument mass bias factors (K) were calculated using an exponential law correction function. Among the five studied sample introduction systems the LI2 showed the lowest mass bias of −0.0265 and the desolvation system showed the largest bias with −0.0321. Figure Illustration of the multi-mode sample introduction system for Se isotope ratiomeasurements     

High performance liquid chromatography hydride generation in situ trapping graphite furnace atomic absorption spectrometry: A new way of performing speciation analysis using GFAAS as detector

A new procedure for the speciation analysis of hydride forming elements using GFAAS as detector is proposed. The separation of the species is performed by HPLC and the eluent flow is merged with HCl and NaBH₄ solutions moved by peristaltic pumps controlled by a flow injection apparatus. As the species emerges from the column, its respective hydride is formed and carried through the autosampler capillary to an Ir treated graphite tube pre-heated at 300 °C, where it is trapped. After the hydride collection, the autosampler arm is moved from the tube and atomization takes place. The sequence is repeated for the next emerging species. The feasibility of the system was evaluated for the speciation of As (III) and As (V) in waste water samples. The retention times were previously determined using a more concentrated mixed analytical solution and a quartz tube as atomizer. The analytical curves obtained by the proposed procedure showed similar slopes for both species as well as coefficient of regression better than 0.99. Limits of detection were 0.2 ng/mL for both species, 50 times better then the same assembly using a quartz tube atomizer. In the analysis of certified reference materials the sum of the As (III) and As (V) species concentrations were in close agreement with the arsenic concentration certified for total arsenic.     

Improvements in the electrochemical generation of arsine at gold electrodes as a sample introduction strategy for arsenic determination in well-water samples by atomic absorption spectrometry

The development and evaluation of a cathode consisting of a gold electrode covered by a polyaniline film, PANI/Au modified electrode, for electrochemical generation of arsine is described. The efficiency of arsine production using the new electrode was ascertained by comparison with corresponding hydride generation atomic absorption spectroscopy determinations of arsenic (As) in aqueous standards. The PANI/Au modified electrodes provide better sensitivity, accuracy and precision than the pure Au cathodes. The PANI/Au cathodes were prepared by controlled electrodeposition cycles of polyaniline films on top of Au electrodes. Cathodes obtained after 10 electrodeposition cycles showed the best performance, while the ones obtained after five voltammetry cycles produced films too thin and those obtained after 20 voltammetry cycles produced films too thick for the purpose of this work. Under optimised conditions, the As limit of detection in aqueous solutions, according to the (3σ) criterion, was 2.48 µg L^?1. For accuracy determination, the modified electrode was applied to quantification of As(III) in acidified aqueous solutions of the certified standard reference material, NIST SRM 1643d, and in well-water samples containing possible interfering ions. Application of the Student’s t-test showed no significant difference between the expected and obtained results of the NIST SRM standard analysis at the 95% confidence level. Values for six replicate determinations of As(III) in the well-water samples showed close agreement with values obtained by analyses using hydride generation atomic absorption. Recoveries were in the range of 95–105% at test for acceptable accuracy in the analysis of real samples.     

水产品中甲基汞测定的液相色谱-原子荧光光谱联用方法的改进

对本实验室前期建立的食品中甲基汞的液相色谱-原子荧光光谱联用测定方法进行了改进。采用无毒的半胱氨酸代替有毒试剂巯基乙醇作为流动相中的配位剂,流动相组成为5%(v/v)乙腈-1 g/L半胱氨酸-50 mmol/L乙酸铵水溶液,使汞化合物分离时间缩短至8 min。在优化条件下,甲基汞标准曲线的线性范围为1～50 μg/L,检出限(S/N=3)为0.3 μg/L。采用超声波辅助5 mol/L HCl提取样品中的甲基汞,提取液经C18固相萃取小柱净化后进样。鱼、虾、贝等不同种类水产动物样品以及水产类膳食样品的甲基汞加标回收率为89%～112%。对标准参考物质NIST1566b、BCR464和GBW10029以及英国食品分析水平评估计划(Food Analysis Performance Assessment Scheme, FAPAS)的罐装鱼肉样品(样品编号07115)的测定结果与参考物定值相符,验证了该方法的可靠性与准确性。本方法可满足食品中甲基汞检测的需要。