Determination of Arsenic Species in Marine Samples by HPLC-ICP-MS

Shizuko HIRATA, Hideki TOSHIMITSU, Masato AIHARA
2006 Analytical Sciences  
Introduction As far we have developed the very high sensitive methods for determining trace and ultratrace elements by combination between flow injection analysis (FIA) with on-line column preconcentrating techniques and inductively coupled plasma mass spectrometry (ICP-MS), such as trace metals (Cr(III), Al, V, Mn, Co, Ni, Cu, Zn, Mo, Cd, Pb and U) in seawater 1-3 and rare earth elements (Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu) in seawater. 4-6 Therefore, since an ICP-MS
more » ... e, since an ICP-MS instrument is a high sensitive detector, a hyphenated method by combination between high performance liquid chromatography (HPLC) and ICP-MS, is promising to be sensitive. Speciation of arsenic has acquired significant attention over the past 20 years in both mechanistic and exposure assessment research, because of toxicity of arsenic. While inorganic arsenic species As V and As III have been classified as carcinogenic, the methylated forms, MMA, and DMA have recently been identified as cancer promoters. It is believed that arsenobetaine and arsenocholine, which are highly methyl substituted, are considered to be non toxic. Depending on the kind of organism, different kind and concentrations of arsenic compounds were observed. In fish and crustaceans, arsenobetaine is a dominant species along with trace of MMA, DMA, TeMAs and TMAO. 1-6 In marine organism, more than 17 different inorganic and organic species have been reported. 7 In marine algae, arsenosurgars compounds (derivatives of dimethylarsinoylribosides and trimethylarsonioribosides) are most abundant. [2] [3] [4] [5] [6] [7] The analytical speciation of arsenic has been achieved with the use of coupled techniques, which combine a separation process (chromatography) with suitable detection. Hydride generation atomic absorption spectrometry (HG-AAS) has been used for arsenic speciation in which online thermal or microwave oxidation was employed for converting many organoarsenicals into hydride forming one. 8 Better sensitivity has been achieved with the use of HG-atomic fluorescence spectrometry (HG-AFS). [9] [10] [11] Nevertheless, ICP-MS 12-19 is widely used for arsenic speciation analysis since it offers extremely high sensitivity, large dynamic range and easy coupling to HPLC. Especially, electrospray tandem mass spectrometry (ES-MS/MS) 4,20-23 was used for structural verification of arsenosugar compounds. Arsenicals have widely varying ionic characteristics, which are pH dependent. The anionic species As III , As V , DMA and MMA, can usually be resolved using anion exchange HPLC. Arsenobetaine (pKa 2.2) may be cationic or zwitter ionic. Cation exchange can be used to separate the cationic species arsenobetaine, arsenocholine, TeMAs and TMAO. 13 Alternatively, ion pairing reversed phase HPLC can be used to resolve inorganic and organoarsenicals in single chromatographic run with help of ion pairing agents. Tetrabutyl ammonium hydroxide is common ion pairing agent used for separating anionic species and pentanesulfonate or hexanesulfonate 16 for separating cationic species. Kohlmeyer et al. 7 have demonstrated the separation of 17 arsenic species (eight arsenic species, two arsenosugars and seven unknown species) from various seafood products using nitric acid pH 39 Arsenic speciation analysis in marine samples was performed using high performance liquid chromatography (HPLC) with ICP-MS detection. The separation of eight arsenic species viz. arsenite (As III ), monomethylarsonic acid (MMA), dimethylarsinic acid (DMA), arsenate (As V ), arsenobetaine, trimethylarsine oxide (TMAO), arsenocholine and tetramethylarsonium ion (TeMAs) was achieved on a Shiseido Capcell Pak C18 column by using an isocratic eluent (pH 3.0), in which condition As III and MMA were co-eluted. The entire separation was accomplished in 15 min. The detection limits for 8 arsenic species by HPLC/ICP-MS were in the range of 0.02 -0.10 µg L -1 based on 3σ of blank response (n = 9). The precision was calculated to be 3.1 -7.3% (RSD) for all eight species. The method then successfully applied to several marine samples e.g., oyster, scallop, fish, and shrimps. For the extraction of arsenic species from seafood products, the low power microwave digestion was employed. The extraction efficiency was in the range of 52.9 -112.3%. Total arsenic concentrations were analyzed by using the microwave acid digestion. The total arsenics in the certified reference materials (DORM-2 and TORT-2) were analyzed and agreed with the certified values. The concentrations of arsenics in marine samples were in the range 6.6 -35.1 µg g -1 .
doi:10.2116/analsci.22.39 pmid:16429770 fatcat:hb2ruqpffnbqblnayrhcci7ivm