Liquid chromatographic--cold vapour atomic fluorescence spectrometric determination of mercury species

Solvent extraction, sonication, and microwave-assisted extractions in the presence of extraction agents (thioacetic acid, citric acid, cysteine, 2-mercaptoethanol, HCl + NaCl, etc.) were tested for the isolation of mercury species. A mixture of 6 M HCl and 0.1 M NaCl was selected as the most suitable extraction agent. The extraction efficiency was about 10% higher and the RSD below 3.3% when microwave-assisted extraction was applied instead of sonication. The liquid chromatography-cold vapour atomic fluorescence spectrometry (LC/CV-AFS) method was optimised and used for separation and determination of inorganic mercury cations and alkylated and arylated mercury species. Isocratic elution at a flow rate of 0.15 mL/min (with a mobile phase containing 0.05% 2-mercaptoethanol (pH = 5) and 7% methanol and with a stepwise increase of methanol content up to 100% MeOH in the 15th min) was used for separation of mercury species on a Hypersil BDS C18 RP column. The limits of detection of the LC/CV-AFS system were estimated as 0.2 microg/L (3%) for MeHg+, 0.07 microg/L (5.3%) for inorganic Hg, 0.06 microg/L (3.4%) for PhHg+, and 0.12 microg/L (4.4%) for EtHg with the corresponding RSDs at 5 microg/L (n = 10) given in parentheses. The concentrations (2-10 mg/kg fresh weight) of total mercury and methylmercury (90-99% of the total mercury) in selected fish obtained by HPLC/CV-AFS were in good agreement (absolute deviations 0.05 mg/kg) but more precise (RSDs <5.4% at 5 mg/L, n = 10) than those determined by GC coupled to an electron capture detector. The RSDs (3.1-8.2% and 4.1-9.0%) of the overall analytical procedure for the determination of total mercury (AMA 254) and methylmercury (HPLC/CV-AFS) were determined for intra-day and inter-day assays, respectively.     

Ultratrace determination of mercury in water following EN and EPA standards using atomic fluorescence spectrometry

Chemical vapour generation has been used in combination with atomic fluorescence spectrometry to determine mercury at ultratrace concentrations down to 0.1 ng L^–1. A time-based injection of 1 mL of solution for measurement was sufficient to generate a steady-state detector response in the direct mode of measurement. The detection limit calculated from a ten-point calibration curve according to DIN 32645 was 0.26 ng L^–1. Instrument noise is limited by reflected radiation from the light source rather than by the dark current of the photomultiplier. The detection limit is directly influenced by the reagent blank which was 2 ng L^–1 in the experiments described. Focusing by amalgamation and subsequent thermal desorption generates a detector response which is about eight times higher in peak intensity and about twice as large in integrated intensity. The detection limit under these conditions is 0.09 ng L^–1 which can be further improved by preconcentration of larger volumes of solution for measurement. The cycle time for one individual reading is about 40 s without amalgamation and 125 s with amalgamation. The linear dynamic range of the system is five orders of magnitude with a single photomultiplier gain setting. The carry-over is less than 0.3% in direct measurement mode. Reference water samples and a surface water containing approximately 5 ng L^–1 were used to prove the validity of the method for real samples. Good accuracy and recoveries of 103% were calculated using the fast direct determination technique.     

Determination of mercury and methylmercury in seafood by ion chromatography using photo-induced chemical vapor generation atomic fluorescence spectrometric detection

A novel method based on photo-induced chemical vapor generation (CVG) as interface to on-line coupled Hg-cysteine ion chromatograpy (IC) with atomic fluorescence spectrometry (AFS) was developed for rapid determination of methylmercury (MHg) in seafood. Separation of inorganic mercury (Hg²⁺) and methylmercury(CH₃Hg⁺) was accomplished on a Hamilton PRP X-200 polymer-based exchange column with a mobile of 3% acetonitrile, 1% (w/w) L-cysteine and 20 mmol L^{− 1} pyridine and 160 mmol L^{− 1} formic acid, at pH 2.4 within 7 min. Once separated, both species are reduced by formic acid in mobile phase under UV radiation to convert Hg⁰ on-line, which is subsequently swept (by argon carrier gas) into an atomic fluorescence spectrometry (AFS) for measurement. Under the optimized experiment conditions, the detection limits (as Hg), based on three times the standard deviation of a standard solution, were found to be 0.1 ng mL^{− 1} for mercury and 0.08 ng mL^{− 1} for methylmercury, with an injection volume of 100 μL. The developed method was validated by determination of certified reference material DORM-2 and was further applied in determination of seafood samples.     

Atomic fluorescence spectrometry combined with reduction aeration for the determination of mercury in biological samples

A sensitive atomic fluorescence system for the determination of mercury was optimized. The system consists of a continuous-flow mercury vapour generator coupled to a fluorescence spectrometer specific for mercury. A new gas-liquid separator was developed. A detection limit of 0.9 ng Hg 1^?1 was obtained. The system was combined with a microwave oven for dissolving samples in closed Teflon PFA vessels. Accurate results were obtained for certified reference materials, and biological samples such as urine and hair were analysed.     

Direct determination of mercury in white vinegar by matrix assisted photochemical vapor generation atomic fluorescence spectrometry detection

This paper proposes the use of photochemical vapor generation with acetic acid as sample introduction for the direct determination of ultra-trace mercury in white vinegars by atomic fluorescence spectrometry. Under ultraviolet irradiation, the sample matrix (acetic acid) can reduce mercury ion to atomic mercury Hg⁰, which is swept by argon gas into an atomic fluorescence spectrometer for subsequent analytical measurements. The effects of several factors such as the concentration of acetic acid, irradiation time, the flow rate of the carrier gas and matrix effects were discussed and optimized to give detection limits of 0.08 ng mL⁻¹ for mercury. Using the experimental conditions established during the optimization (3% v/v acetic acid, 30 s irradiation time and 20 W mercury lamp), the precision levels, expressed as relative standard deviation, were 4.6% (one day) and 7.8% (inter-day) for mercury (n = 9). Addition/recovery tests for evaluation of the accuracy were in the range of 92–98% for mercury. The method was also validated by analysis of vinegar samples without detectable amount of Hg spiked with aqueous standard reference materials (GBW(E) 080392 and GBW(E) 080393). The results were also compared with those obtained by acid digestion procedure and determination of mercury by ICP-MS. There was no significant difference between the results obtained by the two methods based on a t-test (at 95% confidence level).     

Improvement of analytical performances for mercury speciation by on-line derivatization, cryofocussing and atomic fluorescence spectrometry

A modified automated on-line hyphenated system for simultaneous inorganic ionic mercury (Hg²⁺) and monomethylmercury (MeHg⁺) analysis by hydride generation (HG) or ethylation (Eth), cryofocussing, gas chromatography (GC) separation and atomic fluorescence spectrometry (AFS) detection has been improved. Both derivatization methods are investigated with respect to the chromatographic and analytical performances. They can be both affected by interferences when the AFS detection system is used. Water vapor removal using a soda lime moisture trap improves significantly the chromatographic performances, the reproducibility and the detection limits for Hg²⁺ and MeHg⁺ analyzed with both methods. For ethylation (Eth) derivatization, a scattering interference generated from low-quality ethylation reagent has also been eliminated. For HG, improved detection limits are 0.13 ng l⁻¹ and 0.01 ng l⁻¹ for Hg²⁺ and MeHg⁺, respectively (0.1 l water sample), and reproducibility are 5% for Hg²⁺ (20 ng l⁻¹) and MeHg⁺ (5 ng l⁻¹). Improved detection limits for Eth are 0.22 ng g⁻¹ for Hg²⁺ and 0.02 ng g⁻¹ for MeHg⁺ (1 g dry sediment sample) and the reproducibility are 5-6% for Hg²⁺ and MeHg⁺ (1-2 ng g⁻¹).     

Determination of mercury by intermittent flow electrochemical cold vapor generation coupled to atomic fluorescence spectrometry

A novel method for determination of mercury was developed using an intermittent flow electrochemical cold vapor generation coupled to atomic fluorescence spectrometry (IF-ECVG-AFS). The mercury vapor was generated on the surface of glassy carbon cathode in the flow cell. The operating conditions for the electrochemical generation of mercury vapor were investigated in detail, and the interferences from various ions were evaluated. Under the optimized conditions, no evident memory effects of mercury were observed. The calibration curve was linear up to 5 μg L⁻¹ Hg at 0.54 A cm⁻². A detection limit of 1.2 ng L⁻¹ Hg and a relative standard deviation of 1.8% for 1 μg L⁻¹ Hg were obtained. The accuracy of method was verified by the determination of mercury in the certified reference human hair. The ECVG avoided the use of reductants, thereby greatly reducing the contamination sources. In addition, the manifold of IF-ECVG-AFS was simple and amenable to automation.     

原子荧光光谱法测定蛇粉中汞的方法研究

用微波消解仪消解、氢化物发生-原子荧光光谱法测定蛇粉中的微量Hg,优化了仪器的工作条件。测定汞的检出限为0.7pg/mL。测定0.3及1ng/L Hg标准溶液,相对标准偏差分别为4.1%及0.9%,加标回收率为87%~110%。     

电化学冷蒸气发生-原子荧光光谱法测定人发中的痕量汞

采用自制的电化学流通池作为汞蒸气发生器,以玻碳为阴极材料,结合原子荧光光谱法,在断续流动条件下,建立了电化学冷蒸气发生法-原子荧光光谱联用技术(ECVG-AFS)对汞的分析方法.在优化的实验条件下,汞在0～5.0μg/L范围内荧光强度与浓度呈良好的线性关系,汞的检出限为1.2 ng/L.对1μg/L Hg测定的相对标准偏差为1.8%(n=11).可用于人发标准样品中汞的测定.     

分散固液微萃取在线热洗脱原子荧光法测定矿泉水中的痕量汞

研究制备了CI/SiO2/PDMS固相萃取剂,建立了分散固液微萃取在线热洗脱原子荧光联用测定矿泉水中痕量汞的方法。方法使用分散剂将CI/SiO2/PDMS均匀分散于样品溶液中,吸附并富集Hg2+与DDTC形成的Hg-DDTC螯合物。用磁子吸附收集固相萃取剂,并置于石英管中。利用电磁感应加热技术,在线加热洗脱,原子荧光法定量。方法的富集倍数达30倍,检出限为6.0ng/L;精密度RSD为3.8%(n=11,ρ=0.1μg/L)。     

Photochemical vapor generation of carbonyl for ultrasensitive atomic fluorescence spectrometric determination of cobalt

UV photochemical vapor generation (photo-CVG) as sample introduction was first adapted for determination of ultratrace cobalt by atomic fluorescence spectrometry (AFS). Cobalt volatile species can be generated when the buffer system of formic acid and formate containing Co (II) is exposed to UV radiation. The generated gaseous products were separated from liquid phase within a gas–liquid separator and then transported to AFS for determination of cobalt. Factors affecting the efficiency of photo-CVG were investigated in detail, including type and concentration of low molecular weight (LMW) organic acid, buffer system, UV irradiation time, reaction temperature, carrier gas flow rate and hydrogen flow rate. With 4% (v/v) HCOOH and 0.4 mol L^{− 1} HCOONa buffer solution, 150 s irradiation time and 15 W low pressure mercury lamp, a generation efficiency of 23–25% was achieved. A limit of detection (LOD) of 0.08 ng mL^{− 1} without any pre-concentration procedure and a precision of 2.2% (RSD, n = 11) at 20 ng mL^{− 1} were obtained under the optimized conditions. The proposed method was successfully applied in the analysis of several simple matrix real water samples.     

Determination of mercury by electrochemical cold vapor generation atomic fluorescence spectrometry using polyaniline modified graphite electrode as cathode

An electrochemical cold vapor generation system with polyaniline modified graphite electrode as cathode material was developed for Hg (II) determination by coupling with atomic fluorescence spectrometry. This electrochemical cold vapor generation system with polyaniline/graphite electrode exhibited higher sensitivity; excellent stability and lower memory effect compared with graphite electrode electrochemical cold vapor generation system. The relative standard deviation was 2.7% for eleven consecutive measurements of 2 ng mL^− 1 Hg (II) standard solution and the mercury limit of detection for the sample blank solution was 1.3 рg mL^− 1 (3σ). The accuracy of the method was evaluated through analysis of the reference materials GBW09101 (Human hair) and GBW 08517 (Laminaria Japonica Aresch) and the proposed method was successfully applied to the analysis of human hairs.     

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     

Ionic liquids dispersive liquid–liquid microextraction and HPLC‐atomic fluorescence spectrometric determination of mercury species in environmental waters

An ionic liquid (IL) based dispersive liquid–liquid microextraction combined with HPLC hydride generation atomic fluorescence spectrometry method for the preconcentration and determination of mercury species in environmental water samples is described. Four mercury species (MeHg⁺, EtHg⁺, PhHg⁺, and Hg²⁺) were complexed with dithionate and the neutral chelates were extracted into IL drops using dispersive liquid–liquid microextraction. Variables affecting the formation and extraction of mercury dithizonates were optimized. The optimum conditions found were as follows: IL‐type and amount, 0.05 g of 1‐octyl‐3‐methylimidazolium hexafluorophosphate; dispersive solvents type and amount, 500 μL of acetone; pH, 6; extraction time, 2 min; centrifugation time, 12 min; and no sodium chloride addition. Under the optimized conditions, the detection limits of the analytes were 0.031 μg/L for Hg²⁺, 0.016 μg/L for MeHg⁺, 0.024 μg/L for EtHg⁺, and 0.092 μg/L for PhHg⁺, respectively. The repeatability of the method, expressed as RSD, was between 1.4 and 5.2% (n = 10), and the average recoveries for spiked test were 96.9% for Hg²⁺, 90.9% for MeHg⁺, 90.5% for EtHg⁺, 92.3% for PhHg⁺, respectively. The developed method was successfully applied for the speciation of mercury in environmental water samples.     

Comparative study of atomic fluorescence spectroscopy and inductively coupled plasma mass spectrometry for mercury and arsenic multispeciation

Mercury and arsenic are two elements of undoubted importance owing to their toxic character. Although speciation of these elements has been developed separately, in this work for the first time the speciation of As and Hg using two atomic fluorescence detectors in a sequential ensemble is presented. A coupling based on the combination of high-performance liquid chromatography (where mercury and arsenic species are separated) and two atomic fluorescence detectors in series, with several online treatments, including photooxidation (UV) and hydride generation, has allowed the determination of mercury and arsenic compounds simultaneously. The detection limits for this device were 16, 3, 17, 12 and 8 ng mL^–1 for As^III, monomethylarsinic acid, As^V, Hg²⁺ and methylmercury, respectively. This coupling was compared with an analogous one based on inductively coupled plasma–mass spectrometry (ICP-MS) detection, with detection limits of 0.7, 0.5, 0.8, 0.9 and 1.1 ng mL^–1, respectively. Multispeciation based on ICP-MS exhibits better sensitivity than the coupling based on tandem atomic fluorescence, but this second device is a very robust system and exhibits obvious advantages related to the low cost of acquisition and maintenance, as well as easy handling, which makes it a suitable system for routine laboratories.     

Determination of thiomersal by flow injection coupled with microwave-assisted photochemical online oxidative decomposition of organic mercury and cold vapor atomic fluorescence spectroscopy

We developed a flow injection (FI) method for the determination of thiomersal (sodium ethylmercurithiosalicylate, C₉H₉HgNaO₂S) based on the UV/microwave (MW) photochemical, online oxidation of organic mercury, followed by cold vapor generation atomic fluorescence spectrometry (CVG-AFS) detection. Thiomersal was quantitatively converted in the MW/UV process to Hg(II), with a yield of 97 ± 3%. This reaction was followed by the reduction of Hg(II) to Hg(0) performed in a knotted reaction coil with NaBH₄ solution, and AFS detection in an Ar/H₂ miniaturized flame. The method was linear in the 0.01–2 μg mL⁻¹ range, with a LOD of 0.003 μg mL⁻¹. This method has been applied to the determination of thiomersal in ophthalmic solutions, with recoveries ranging between 97% and 101%. We found a mercury concentration in commercial ophthalmic solutions ranging between 7.5 and 59.0 μg mL⁻¹.     

On-line preconcentration for capillary electrophoresis-atomic fluorescence spectrometric determination of arsenic compounds

An on-line preconcentration method was developed for capillary electrophoresis (CE) with hydride generation-atomic fluorescence spectrometric (HG-AFS) detection of arsenite, arsenate, dimethylarsenic acid, and monomethylarsenic acid. These arsenic species were negatively charged in the sample solution with high pH. When the potential was applied to the electrophoretic capillary, the negatively charged analyte ions moved faster and stacked at the boundary of sample and CE buffer with low pH. So, high sample pH in combination with low buffer pH allowed the injection of large sample volumes (approximately 1100 nL). Comparison of the preconcentration of analyte solution, prepared with doubly deionized water and that prepared with lake or river water, indicated that preconcentration was independent on the original matrix. With injection of approximately 1100 nL sample, an enrichment factor of 37-50-fold was achieved for the four species. Detection limits for the four arsenic species ranged from 5.0 to 9.3 microg.L(-1). Precisions (RSDs, n = 5) were in the range of 4.9-6.7% for migration time, 4.7-11% for peak area, and 4.3-7.1% for peak height, respectively. The recoveries of the four species in locally collected water solution spiked with 0.1 microg.mL(-1) (as As) ranged from 83 to 109%.     

大体积进样-原子荧光光谱法 测定海水中痕量汞

海洋中的汞在生物体内会转化为毒性高的甲基汞,影响海洋生物体的健康,进而威胁到人类的健康。同时,由于汞元素的记忆效应,使其会残留在光谱仪器设备中,影响仪器空白值和参数设置,以及测量结果的准确性和可靠性。海水中的汞含量处于超痕量水平,其分析检测是目前的难点之一。本文研究了一种大体积进样-原子荧光光谱法测定海水中痕量汞的方法,考察了不同前处理方式、酸的种类、还原剂浓度和原子化方式对检测的影响,并针对性利用烷基汞验证了不同条件下的检测结果,对方法进行了改进和验证,并对不同海域的海水进行了检测。实验结果表明：采用大体积进样,用盐酸代替硫酸,检测低浓度样品结果更准确;用甲基汞、乙基汞加标和低浓度还原剂对比验证过硫酸钾消解前处理时室温消化24h和加热煮沸1min两种消解方式,两种方式的加标回收率均接近100%;测量不同海域海水样品平行性好,结果准确,该方法对不同海域海水具有普遍适用性。     

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。     

微波消解-氢化物发生原子荧光法同时测定土壤中的砷汞

建立了微波消解-氢化物发生原子荧光法同时测定土壤中As、Hg的分析方法。用体积分数35%的王水作为消解溶剂,在设定的微波消解条件下,可以将土壤中的As、Hg提取完全,有效解决了消解液中剩余酸过多的问题。方法用体积分数5%的HCl作为反应介质,20 g/L NaBH4作为还原剂。通过测定国家标准参考物质和加标回收实验,对方法进行了验证。已用于土壤中As、Hg的测定。