Multielemental determination of arsenic, selenium and chromium(VI) species in water by high-performance liquid chromatography-inductively coupled plasma mass spectrometry

A new method for the simultaneous chromatographic separation and determination of arsenite, arsenate, mono-methylarsonic acid, dimethylarsinic acid, selenite, selenate and hexavalent chromium in water is presented. Speciation was achieved by on-line coupling of anion-exchange LC and inductively coupled plasma mass spectrometry (ICP-MS). Optimisation of the chromatographic conditions led to baseline separation of the seven species in 14 min using gradient elution with NH4NO3 20 mM, pH 8.7-NH4NO3 60 mM, pH 8.7 as mobile phase. Detection limits are in the range 40-60 ng l(-1) for arsenic species, around 130 ng l(-1) for Cr(VI), and higher for Se(IV) and Se(VI) (1.2 and 1.4 microg l(-1) respectively). The method showed good accuracy and repeatability, and no interference of chloride on 75As, 77Se or 53Cr was observed. The developed method was applied to the analysis of several environmental surface water samples.     

液相色谱-电感耦合等离子体质谱法测定稻米中的5种砷形态

建立了稻米中砷酸根[As（Ⅴ）]、亚砷酸根[As（Ⅲ）]、砷甜菜碱（AsB）、一甲基砷（MMA）和二甲基砷（DMA）的液相色谱-电感耦合等离子体质谱（LC-ICP-MS）检测方法。以0.3 mol/L硝酸水溶液为提取试剂,样品在石墨消解仪中于95 ℃消解1.5 h,上清液供LC-ICP-MS分析。5种砷形态采用Dionex IonPac AS19阴离子交换柱（250 mm×4 mm）分离,经ICP-MS检测。比较了4种提取液对稻米中5种砷形态的提取效率,并对提取溶剂的浓度、提取温度和提取时间等条件进行了优化。通过加标回收试验结合测定标准物质考察了方法准确度及精密度,在2个加标水平上各形态的回收率为89.6%~99.5%,RSD（n=5）不大于3.6%,大米标准物质中各形态之和的测定结果与其标准值吻合,5种砷形态的线性范围AsB和DMA为0.05~200 μg/L,As（Ⅲ）和MMA为0.10~400 μg/L,As（V）为0.15~600 μg/L,方法检出限为0.15~0.45 μg/kg。结果表明,本方法简单、灵敏、耐用,可用于稻米中5种砷形态的准确定量和风险评估。     

Simultaneous determination of arsenic species by ion chromatography-inductively coupled plasma mass spectrometry

Six arsenic species, arsenite, arsenate, monomethylarsonic acid, dimethylarsinic acid, arsenobetaine and arsenocholine, were separated by coupled column ion chromatography using carbonate and nitric acid as eluents, and were detected by inductively coupled plasma mass spectrometry. Coupling of an anion column with a cation column made the simultaneous determination of both the cationjic and the anionic arsenic species possible by ion chromatography. Extremely low detection limits, below 0.2 μg/1 (as arsenic), were obtained for all the species studied.     

Measurement of arsenic species in marine sediments by high-performance liquid chromatography-inductively coupled plasma mass spectrometry

Extraction of sediments with phosphoric acid (0.5 M) and hydroxylamine hydrochloride (0.1 M) allowed the measurement of labile arsenic species while preserving the two redox states of arsenic. The forms and concentrations of arsenic species were measured using HPLC-ICP-MS. A Hamilton PRP X-100 strong anion exchange column using a 20 mM ammonium phosphate buffer (pH 6 and 9.2) was used to separate arsenic species. Recoveries of sediments spiked with As(V) were quantitative whereas for sediments spiked with As(III) recoveries of between 89 and 104% were obtained from four oxic certified reference sediments and an anoxic sediment. Application of the method to sediment samples from the marine Lake Macquarie, NSW, Australia, indicate that anoxic sediments can contain high concentrations of As(III), and two arsenosugars (sulfonate-ribose and sulfate-ribose). Extraction efficiencies for arsenic ranged between 6 and 82%. The arsenic species measured in sediments are strongly depended on the extraction procedure used. As(III) and arsenosugar concentrations in sediments that were freeze dried and oxidised were much less than in sediments that were not freeze dried and when exposure to air was keep to a minimum. Corresponding, As(V) concentrations tended to be higher in samples that were exposed to air.     

Total arsenic determination and speciation in infant food products by ion chromatography-inductively coupled plasma-mass spectrometry

Health risk associated with dietary arsenic intake may be different for infants and adults. Seafood is the main contributor to arsenic intake for adults while terrestrial-based food is the primary source for infants. Processed infant food products such as rice-based cereals, mixed rice/formula cereals, milk-based infant formula, applesauce and puree of peaches, pears, carrots, sweet potatoes, green beans, and squash were evaluated for total and speciated arsenic content. Arsenic concentrations found in rice-based cereals (63-320 ng/g dry weight) were similar to those reported for raw rice. Results for the analysis of powdered infant formula by inductively coupled plasma-mass spectrometry (ICP-MS) indicated a narrow and low arsenic concentration range (12 to 17 ng/g). Arsenic content in puree infant food products, including rice cereals, fruits, and vegetables, varies from <1 to 24 ng/g wet weight. Sample treatment with trifluoroacetic acid at 100 degrees C were an efficient and mild method for extraction of arsenic species present in different food matrixes as compared to alternative methods that included sonication and accelerated solvent extraction. Extraction recoveries from 94 to 128% were obtained when the summation of species was compared to total arsenic. The ion chromatography (IC)-ICP-MS method selected for arsenic speciation allowed for the quantitative determination of inorganic arsenic [As(III) + As(V)], dimethylarsinic acid (DMA), and methylarsonic acid (MMA). Inorganic arsenic and DMA are the main species found in rice-based and mixed rice/formula cereals, although traces of MMA were also detected. Inorganic arsenic was present in freeze-dried sweet potatoes, carrots, green beans, and peaches. MMA and DMA were not detected in these samples. Arsenic species in squash, pears, and applesauce were not detected above the method detection limit [5 ng/g dry weight for As(III), MMA, and DMA and 10 ng/g dry weight for As(V)].     

Simultaneous pressurized enzymatic hydrolysis extraction and clean up for arsenic speciation in seafood samples before high performance liquid chromatography-inductively coupled plasma-mass spectrometry determination

The feasibility of pressurized conditions to assist enzymatic hydrolysis of seafood tissues for arsenic speciation was novelty studied. A simultaneous in situ (in cell) clean-up procedure was also optimized, which speeds up the whole sample treatment. Arsenic species (As(III), MMA, DMA, As(V), AsB and AsC) were released from dried seafood tissues using pepsin as a protease, and the arsenic species were separated/quantified by anion exchange high performance liquid chromatography (HPLC) coupled to inductively coupled plasma-mass spectrometry (ICP-MS). Variables inherent to the enzymatic activity (pH, temperature and ionic strength), the amount of enzyme (pepsin), and factors affecting pressurization (pressure, static time, number of cycles and amount of dispersing agent, C-18) were fully evaluated. Pressurized assisted enzymatic hydrolysis (PAEH) with pepsin can be finished after few minutes (two cycles of 2 min each one plus 3 min to reach the hydrolysis temperature of 50 °C). A total sample solubilisation is not achieved after the procedure, however it is efficient enough for breaking down certain bonds of bio-molecules and for releasing arsenic species. The developed method has been found to be precise (RSDs lower than 6% for As(III), DMA and As(V); and 3% for AsB) and sensitive (LOQs of 18.1, 36.2, 35.7, 28.6, 20.6 and 22.5 ng/g for As(III), MMA, DMA, As(V), AsB and AsC, respectively). The optimized methodology was successfully applied to different certified reference materials (DORM-2 and BCR 627) which offer certified AsB and DMA contents, and also to different seafood products (mollusks, white fishes and cold water fishes).     

Determination of arsenic compounds in beverages by high-performance liquid chromatography-inductively coupled plasma mass spectrometry

Arsenic compounds including arsenous acid (As(III)), arsenic acid (As(V)), dimethylarsinic acid (DMA) and monomethylarsonic acid (MMA) were separated by high-performance liquid chromatography (HPLC) and detected by inductively coupled plasma mass spectrometry (ICP-MS). A Hamilton PRX-100 anionic-exchange column and a pH 8.5 K₂HPO₄/KH₂PO₄ 5.0 × 10⁻³ mol L⁻¹ mobile phase were used to achieve arsenic speciation. The separation of arsenic species provided peaks of As(III) at 2.75 min, DMA at 3.33 min, MMA at 5.17 min and As(V) at 12.5 min. The detection limits, defined as three times the standard deviation of the lowest standard measurements, were found to be 0.2, 0.2, 0.3 and 0.5 ng mL⁻¹ for As(III), DMA, MMA and As(V), respectively. The relative standard deviation values for a solution containing 5.0 μg L⁻¹ of As(III), DMA, MMA and As(V) were 1.2, 2.1, 2.5 and 3.0%, respectively. This analytical procedure was applied to the speciation of arsenic compounds in drinking (soft drink, beer, juice) samples. The validation of the procedure was achieved through the analysis of arsenic compounds in water and sediment certified reference materials.     

高效液相色谱-电感耦合等离子体质谱联用同时测定鸡肉与鸡肝中的7种砷形态

建立了一种同时测定阿散酸、亚砷酸根、砷酸根、砷胆碱、砷甜菜碱、一甲基砷和二甲基砷等7种砷形态的高效液相色谱-电感耦合等离子体质谱分析方法。样品采用人工胃液作为提取液进行超声处理,再以碳酸铵溶液和水作为流动相,采用阴离子分析柱将样品提取液进行分离,最后进入电感耦合等离子体质谱测定。各砷形态在1～50 μg/kg范围内线性关系良好,相关系数r2均在0.999以上;在1、2、10 μg/kg 3个添加水平进行了方法学验证,平均回收率为84.3%～106.6%,相对标准偏差为1.4%～4.2%; 7种砷形态的定量限均为1 μg/kg。方法重现性好、灵敏度高、前处理简单,适用于鸡肉和鸡肝中主要有机砷和无机砷残留的分析检测。     

Lead speciation in rainwater by isotope dilution-high performance liquid chromatography-inductively coupled plasma-mass spectrometry

A new method for lead speciation in rainwater by isotope dilution analysis (IDA) using directly coupled high performance liquid chromatography-inductively coupled plasma-mass spectrometry (HPLC-ICP-MS) is described and demonstrated. Samples containing trimethyllead (TML) chloride and triethyllead (TEL) chloride in the presence of large amounts of inorganic lead have been analysed by HPLC-ICP-MS using reverse phase ion-pairing chromatography. The detection limit for the procedure is 3 ng g⁻¹ for TML as Pb and 14 ng g⁻¹ for TEL as Pb, with a linear range exceeding 1000 ng g⁻¹ and a relative standard deviation of 4% for TML in the range 50–1000 ng g⁻¹. TML chloride isotopically enriched in the stable 206 isotope was prepared and used to enhance the accuracy of the method by isotope dilution analysis. The IDA-HPLC-ICP-MS method was successfully applied to the analysis of a sample of artificial rainwater used in a collaborative study.     

Simultaneous determination of arsenic, selenium, and mercury by Ion exchange-vapor generation-inductively coupled plasma-mass spectrometry

Ion exchange (IE)-vapor generation (VG)-inductively coupled plasma (ICP)-mass spectrometry (MS) method has been employed to simultaneously determine trace amounts of As, Se, and Hg in acidic conditions. Before hydride generation, anion-exchange column was used to separate the analytes from the matrix. Effects of sample solution acidity, eluant conditions and concentrating time were investigated and optimized. The method sensitivity was improved, as well as the ability to refrain interference caused by chloride, mental ions and other hydride-forming elements compared with (CF)VG-ICP-MS method. Limits of detection (3σ, n = 10) for As, Se, and Hg were As, 0.0021 ng/ml; Se, 0.0022 ng/ml; Hg, 0.0007 ng/ml, respectively; and recovery values for interference experiments were between 95.6 and 100.3%. The developed method was applied to four standard biological and geological materials, and the determined results of As, Se, and Hg were consistent with the certified values.     

反相离子对色谱-电感耦合等离子体质谱法测定化妆品中不同形态的铬

建立了反相离子对色谱(RP-IPC)与电感耦合等离子体质谱(ICP-MS)联用技术快速分离测定化妆品中Cr(III)和Cr(VI)的方法。样品经乙二胺四乙酸钠盐(EDTA)50 ℃水浴中提取后,采用XDB-C18色谱柱分离,以5%(v/v)甲醇-2.0 mmol/L四正丁基铵盐(TBA)水溶液(pH 6.0)作为流动相,流速为1.0 mL/min,进样量为100 μL。采用碰撞池技术消除ICP-MS测定时40Ar12C+、35Cl16O1H+对52Cr+的光谱学干扰。Cr(III)和Cr(VI)的分离过程在5 min内完成。样品中加标量为0.01～0.50 μg时,其回收率为82.7%～107.2%,相对标准偏差(RSD)小于5.62%。该方法操作简便、灵敏度高、重现性好,适合于化妆品中Cr(III)和Cr(VI)的同时分析。     

Simultaneous determination of arsenic and selenium species in fish tissues using microwave-assisted enzymatic extraction and ion chromatography-inductively coupled plasma mass spectrometry

A microwave-assisted enzymatic extraction (MAEE) method was developed for the simultaneous extraction of arsenic (As) and selenium (Se) species in fish tissues. The extraction efficiency of total As and Se and the stability of As and Se species were evaluated by analyzing DOLT-3 (dogfish liver). Enzymatic extraction using pronase E/lipase mixture assisted by microwave energy was found to give satisfactory extraction recoveries for As and Se without promoting interspecies conversion. The optimum extraction conditions were found to be 0.2 g of sample, 20 mg pronase E and 5 mg lipase in 10 mL of 50 mM phosphate buffer, pH 7.25 at 37 °C. The total extraction time was 30 min. The speciation analysis was performed by ion chromatography-inductively coupled plasma mass spectrometry (IC-ICP-MS). The accuracy of the developed extraction procedure was verified by analyzing two reference materials, DOLT-3 and BCR-627. The extraction recoveries in those reference materials ranged between 82 and 94% for As and 57 and 97% for Se. The accuracy of arsenic species measurement was tested by the analysis of BCR 627. The proposed method was applied to determine As and Se species in fish tissues purchased from a local fish market. Arsenobetaine (AsB) and selenomethionine (SeMet) were the major species detected in fish tissues. In the analyzed fish extracts, the sum of As species detected was in good agreement with the total As extracted. However, for Se, the sum of its species was lower than the total Se extracted, revealing the presence of Se-containing peptides or proteins.     

Fast determination of arsenosugars in algal extracts by narrow bore high-performance liquid chromatography-inductively coupled plasma mass spectrometry

The potential of narrow bore high-performance liquid chromatography (HPLC) with detection by inductively coupled plasma mass spectrometry (ICP-MS) for fast determination of arsenosugars in algal extracts was explored. The retention behavior of four naturally occurring dimethylarsinoylribosides on an anion-exchange microbore column was investigated, with the mobile phase flow rate ranging from 60 to 200μLmin(-1). A low sample consumption system consisting of a micronebulizer and a low inner volume cyclonic spray chamber was used as the interface between the micro-column and the ICP mass spectrometer. Both the high efficiency nebulizer, HEN, and the PFA micronebulizer were tested, with the former providing 20-50% greater sensitivity than PFA (depending on the liquid flow rate), but comparable limits of detection and slightly lower chromatographic resolution. With the setup employed and under the optimal conditions, a satisfactory separation of the arsenosugars was achieved in less than 5min. The instrumental limit of detection was 0.20μgAsL(-1) and the precision was better than 3% (RSD%, n=5). The accuracy of the determination was verified by the analysis of a reference algal extract, obtaining values in good agreement with the reference ones.     

Dissolved inorganic carbon effect in the determination of arsenic and chromium in mineral waters by inductively coupled plasma-mass spectrometry

The analysis of some Italian mineral waters by ICP-MS has revealed errors in the determination of As and Cr in natural effervescent or carbonated waters due to the presence of dissolved inorganic carbon (DIC). This leads to overestimate As and Cr in 1% (v/v) HNO₃ acidified samples, analysed within 1-2 h after the acidification. The overestimation of As concentration is caused by matrix interferences producing a signal enhancement due to the presence of dissolved inorganic carbon. This effect is analogous to that observed in the presence of organic carbon and occurs at millimolar DIC levels. The overestimation of Cr concentration is due to the ⁴⁰Ar¹²C⁺ species interfering with ⁵²Cr⁺ despite the use of the octopole reaction system. The optimization of the He flow in the collision cell can solve the latter problem, but the required increase in the flow rate decreases the sensitivity of the ICP-MS technique. The observed effects in CO₂ rich mineral waters and artificial NaHCO₃ solutions suggest that 5-10 mM DIC levels may affect the determination of As and Cr concentration in thermal waters, rivers, lakes and groundwaters.     

高效液相色谱-电感耦合等离子体质谱法同时测定果蔬中6种砷形态

建立了一种同时测定果蔬中亚砷酸根、砷酸根、砷胆碱、砷甜菜碱、一甲基砷酸和二甲基砷酸等6种砷形态的高效液相色谱-电感耦合等离子体质谱分析方法。样品经甲醇水提取,采用阴离子分析柱,50 mmol/L碳酸铵溶液和水作为流动相进行梯度洗脱,高效液相色谱分离,电感耦合等离子体质谱进行定性和定量分析。在0.5～50μg/kg范围内...     

Speciation and determination of thiols in biological samples using high performance liquid chromatography-inductively coupled plasma-mass spectrometry and high performance liquid chromatography-Orbitrap MS

An analytical method was developed for the determination of thiols in biological samples. Reverse phase chromatography coupled to ICP quadrupole MS or Orbitrap MS was employed for the separation and detection of thiols. For the determination of total thiols, oxidized thiols were reduced using dithiothreitol (DTT). Reduction efficiencies for species of interest were found to be close to 100%. Reduced thiols were derivatized by p-hydroxymercuribenzoate (PHMB) and then separated on a C8 column. Optimization of the extraction, separation and detection steps of the HPLC-ICP-MS and HPLC-Orbitrap MS methods was carried out. Detection limits for cysteine, homocysteine, selenocysteine, glutathione, selenomethionine and cysteinyl-glycine were found to be 18, 34, 39, 12, 128 and 103 fmol, respectively, using HPLC-Orbitrap MS and 730, 1110, 440, 1110 and 580 fmol for cysteine, homocysteine, selenocysteine, glutathione, and cysteinyl-glycine using HPLC-ICP-MS. Contrary to expectation, the LODs and RSDs are higher for the HPLC-ICP-MS instrument, therefore HPLC-Orbitrap MS was used for the determination of thiols in yeast samples. Three different brands of baker's yeast and a selenized yeast were analyzed. The GSH and cysteine levels found in these samples ranged from 4.45 to 17.87 μmol g(-1) and 0.61 to 1.32 μmol g(-1), respectively.     

Measurement of arsenic species in marine macroalgae by microwave-assisted extraction and high performance liquid chromatography-inductively coupled plasma mass spectrometry

The measurement of arsenic species (arsenoribosides, arsenate, dimethyl arsenic and monomethyl arsenic) in marine macroalgae by microwave-assisted extraction and HPLC-ICP-MS is described. The extraction of arsenic from three different macroalgae classes was optimised using a chemometric approach, with solvent composition and sample mass being the two significant factors influencing the extraction of arsenic. Extraction temperature and extraction time did not significantly influence the extraction of arsenic from macroalgae. The optimised conditions for arsenic extraction (methanol (%)) were: 56% for phaeophyta, 66% for rhodophyta and 78% for chlorophyta, (sample mass in 10 ml of solvent) 0.05 g for phaeophyta, 0.07 g for rhodophyta and 0.08 g for chlorophyta. When two extractions were used, the percentage of arsenic extracted from macroalgae was greater than 88%. Unambiguous separation and identification of three arsenoribosides (phosphate-, sulfonate- and sulfate-arsenoriboside) was achieved by chromatographing extracts on a Hamilton PRP X-100 anion exchange column with ammonium phosphate buffer as the mobile phase at a pH of 9.2. The unambiguous separation and identification of the glycerol-arsenoriboside was achieved by chromatographing extracts on a Supelcosil SCX cation exchange column with a pyridine-formic acid buffer as the mobile phase at a pH of 2.6.     

Application of fast ultrasound water-bath assisted enzymatic hydrolysis--high performance liquid chromatography-inductively coupled plasma-mass spectrometry procedures for arsenic speciation in seafood materials

Enzymatic hydrolysis of seafood materials for isolating arsenic species (As(III), As(V), DMA and AsB) has been successfully performed by assisting the procedure with ultrasound energy (35 kHz) supplied by an ultrasound water-bath. The use of pepsin, as a proteolytic enzyme, under optimized operating conditions (pH 3.0, temperature 40 °C, enzyme to sample ratio of 0.3) led to an efficient assistance of the enzymatic process in a short period of time (from 4.0 to 30 min). The enzymatic extract was then subjected to a clean-up procedure based on ENVI-Carb™ solid phase extraction (SPE). An optimized anion exchange high performance liquid chromatography (HPLC) coupled to inductively coupled plasma-mass spectrometry (ICP-MS) permitted the fast separation (less than 15 min) of six different arsenic species (arsenite, As(III); arsenate, As(V); dimethylarsinic acid, DMA; and arsenobetaine, AsB; as well as monomethylarsonic acid, MMA; and arsenocholine, AsC) in a single run. Relative standard deviations (n = 11) of the over-all procedure were 7% for AsB and DMA, 11% for As(III) and 9% for MMA. HPLC–ICP-MS determinations were performed using aqueous calibrations covering arsenic concentrations of 0, 5, 10, 25, 100 and 200 μg L⁻¹ (expressed as arsenic) for As(III), As(V), MMA, DMA and AsC; and 0, 125, 250, 500, 750, 1000 and 2000 μg L⁻¹ (expressed as arsenic) for AsB. Germanium (5 μg L⁻¹) was used as an internal standard. Analytical recoveries from the anion exchange column varied from 96 to 105% (enzymatic digests spiked with low target concentrations), from 97 to 104% (enzymatic digests spiked with intermediate target concentrations), and from 98 to 103% (enzymatic digests spiked with high target concentrations). The developed method was successfully applied to two certified reference materials (CRMs), DORM-2 and BCR 627, which offer certified AsB and DMA contents, and also to different seafood samples (mollusks, white fish and cold water fish). Good agreement between certified and found AsB concentrations was achieved when analyzing both CRMs; and also, between certified and found DMA concentrations in BCR 627. In addition, the sum of the different arsenic species concentrations found in most of the analyzed samples was statistically similar to the assessed total arsenic concentrations after a total sample matrix decomposition treatment.     

Specific determination of selenoaminoacids in whole milk by 2D size-exclusion-ion-paring reversed phase high-performance liquid chromatography-inductively coupled plasma mass spectrometry (HPLC-ICP MS)

A procedure was developed for the quantitative recovery of selenomethionine (SeMet) and selenocysteine (SeCys) from whole milk. It was based on the protein unfolding, carbamidomethylation of the aminoacid residues using iodoacetamide and proteolysis using Protease XIV. The selenoaminoacids were specifically determined by ion-paring reversed phase HPLC-ICP MS after their isolation from the post-reaction mixture by size-exclusion LC. Se(IV) present in the sample was derivatized as well and was determined along with the selenoaminoacids. The origin and identity of species were identified by the co-elution with the Se(IV), isotopically labelled selenomethionine, and with the synthetic standard of carbamidomethylated selenocysteine. The method development for SeCys was assisted by using glutathione peroxidise as the SeCys standard. SeMet, SeCys and Se(IV) were quantified by the method of standard additions. The mass balance provided a measure of the method validation. The method was applied to monitoring selenium speciation during supplementation of cows (dose-effect study) with Se-rich yeast containing feed and during milk processing.     

高效液相色谱-电感耦合等离子体质谱法测定浒苔中总锡及有机锡形态

采用高效液相色谱-电感耦合等离子体质谱联用技术研究了青岛近海浒苔中锡元素总量及具有毒性的有机形态。方法检测限为0.035μg/g,加标回收率91%～108%,相对标准偏差为4.5%,青岛近海浒苔中锡总量在0.10～0.55μg/g范围内。对样品进行有机锡形态分析结果显示,浒苔中有机形态的锡以三苯基锡为主,其他形态的有机锡未检出。