A novel speciation alternative for the determination of inorganic arsenic in marine samples

Abstract

Arsenic (As) is bioaccumulated from seawater to concentrations in the mg/kg range in marine animals. More than 50 naturally-occurring arsenic containing species, both inorganic and organic forms, have been identified in marine animals. The organic forms are mainly considered to be non-toxic, whereas inorganic arsenic is highly toxic and exposure may lead to severe adverse effects including cancer. Since seafood is the major dietary source for arsenic exposure in the European population, arsenic speciation analysis of marine samples is highly relevant for food safety. However, most data collected in the official EU food control today are reported as total arsenic. High Performance Liquid Chromatography Inductively Coupled Plasma Mass Spectrometry (HPLC-ICP-MS) is a useful but expensive tool for metal speciation analysis. Our novel, simple and inexpensive method for determination of inorganic arsenic in marine based food is based on microwave extraction, species separation by strong anion solid phase extraction (SPE) and hydride generation atomic absorption spectrometry (HG-AAS) detection. Separation organic arsenic compounds (e.g. MA, DMA and AB) and inorganic arsenic in the form of As(V) is possible due to different charges (pKa values) of the arsenic species at a specific pH. SPE method development and sample extraction was evaluated using HPLC-ICP-MS. No degradation or conversion of organic arsenic species such as AB, MA or DMA were observed under the chosen extraction conditions. In brief: The sample is heated with a hydrochloric acid and hydrogen peroxide solution (20 minutes at 90 °C with 0.06 M HCl, 3 % H2O2). Hereby the sample is solubilised and As(III) is oxidised to As(V). Inorganic arsenic is selectively separated from other arsenic compounds using strong anion exchange SPE. The procedure include first pre-condition of the column, then loading of the buffered samples (pH 5.0-7.5), washing with 0.5 M acetic acid and finally elution of the sample from the column by 0.5 M HCl. The concentration of arsenic is determined by HG-AAS using external standards. The method SPE-HG-AAS was in-house validated by spiked and naturally incurred marine samples. Mean recoveries of the spiked samples were 101–104%. The limit of detection was determined to 0.08 mg/kg and was calculated as three times the standard deviation at intra-laboratory reproducibility conditions divided by the average recovery, both at the lowest spike level (0.5 mg/kg). The in-house reproducibility standard deviations were less than ≤13% for samples containing 0.2 to 1.5 mg/kg inorganic arsenic. The results obtained by SPE-HG-AAS and HPLC-ICP-MS detection were not significantly different (95% confidence). Acknowledgement: Funding from the European Community's Seventh Framework Programme (FP7/2007-2013) under grant agreement n° 211326.