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Arsenic (As) is a naturally occurring element, which is found at concentrations in the mg/kg range in marine animals. The element is bioaccumulated from seawater. It has a very complex chemistry and 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. An accurate estimation of inorganic arsenic exposure is therefore highly relevant for evaluation of food safety. However, so far most of the occurrence data collected in the official EU food control are still reported as total arsenic. A simple and inexpensive method for determination of inorganic arsenic in marine based food and feed by hydride generation atomic absorption spectrometry (HG-AAS) after microwave extraction and separation by solid phase extraction (SPE) has been developed and validated. The SPE separation is based on the different charges (pKa values) of the arsenic species at specific pH, which allow selective elution of organic arsenic compounds (e.g. MA, DMA and AB) and inorganic arsenic in the form of As(V). 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. SPE method development and sample extraction was evaluated using a selective HPLC-ICP-MS detection method. No degradation or conversion of organic arsenic species such as AB, MA or DMA were observed under the chosen extraction conditions. The results obtained by SPE-HG-AAS and HPLC-ICP-MS were not significantly different (95% confidence). The method was validated by spiked and naturally incurred marine samples. The limit of detection was 0.08 mg/kg and the in-house reproducibility standard deviations were less than ≤13% for samples containing 0.2 to 1.5 mg/kg inorganic arsenic. The method has furthermore been tested in a collaborative trial on marine feed and food with a satisfactory result and is now in the process for CEN approval as a future European standard method. Acknowledgement: Funding from the European Community's Seventh Framework Programme (FP7/2007-2013) under grant agreement n° 211326.

Keywords

  • Inorganic arsenic, speciation, solid phase extraction, atomic absorption spectroscopy, validation
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