Hydride Generation–AFS for Arsenic Speciation in Food Warren Corns and Bin Chen P S Analytical, UK www.psanalytical.com

Introduction The adverse health risk of Arsenic in the food chain has raised public awareness and concern worldwide. It is well known that the speciation of Arsenic in food is an important requirement as the toxicity of As is dependent on the species. Official mandated methods based on LC-ICPMS may work well but the cost and implementation in developing countries is not a practical long term solution. There is therefore a need to develop accurate low cost analytical procedures for Inorganic Arsenic.

Analytical Methods based on AFS Selective Hydride Generation-AFS Optimization of the extraction and hydride generation chemistry to selectively determine Inorganic Arsenic Selective Solid Phase Extraction (SPE) with Hydride Generation-AFS Selective retention and elution of As species after pre-oxidation using SAX column to determine Inorganic Arsenic Liquid Chromatography Hydride Generation – AFS Separation of Arsenic species using SAX column. Complete speciation or Inorganic Arsenic determination with summation of As (III) + As (V).

PSA 10.820 – Millennium Interface (MI)

Selective HG-AFS Hydride Generation Efficiency

Nitric/Peroxide Digestion Fast Screening of i-As in Rice using HG-AFS. Not suitable for Samples with MMA 1 Nitric/Peroxide Digestion 2 Pre-reduction by KI/HCl 3 High acidity HG 2 min per run

DMA Spike on Rice Sample

i-As in NIST1568a Rice Flour 99.97 ± 4.30 ng g-1 (n=16, RSD 4.3%) Prepared and analysed on different days

i-As in Rice (80 samples)

As in Seaweed (mg kg-1) T-As – concentrated HNO3 and H2O2, hot-block 60 min at 100˚C i-As – concentrated HCl, shaking for 2 hours, selective HG at high acidity

Online SPE – i-As in Food

SPE – Sample Preparation Centrifuge, filtration, buffering to pH 6-7 Solubilisation of sample matrix, Conversion of As(III) to As(V) Water bath, 90˚C, 1hr Sample + Extractant (0.1 M HCl or HNO3 + 3% H2O2)

i-As in Rice Samples Rice-A Rice-B Rice-C Rice-D Rice-E Extraction – 0.1M HNO3, 3% H2O2 w/v, hot water bath 60 min at 90˚C Separation – water, SAX-PE cartridge, or 20 mM phosphate buffer, pH 6, Hamilton PRP X-100 anion exchange column

HPLC-HG-AFS optional

HPLC Separation (NIST 1568a Rice Flour) Extraction – 0.28M HNO3 hot water bath 60 min at 90˚C Separation – 20 mM carbonate buffer pH 8, or 20mM phosphate buffer, pH 6, Hamilton PRP X-100 anion exchange column

i-As in Food Samples Extraction – 0.1M HNO3, 3% H2O2 w/v, hot water bath 60 min at 90˚C Separation – 20 mM phosphate buffer, pH 6, Hamilton PRP X-100 anion exchange column

As in Seaweed Extraction – water, hot water bath 60 min at 90˚C Separation – 20 mM phosphate buffer, pH 6, Hamilton PRP X-100 anion exchange column

Conclusions Selective hydride generation-AFS is accurate approach for i-Arsenic determination in food provided that the sample extract does not contain MMA. In a recent FDA study of 200+ rice samples no MMA was found. DMA was found in most samples so hydride generation conditions must be employed to prevent DMA hydride formation eg High Acidity. Possibly also suitable for other samples such as seaweed and fish. Low cost simple screening method. Solid Phase Extraction (SPE) with Hydride Generation – AFS requires a pre-oxidation to convert As (III) to As (V). The method was fully automated using sequential elution of organic arsenic and inorganic arsenic. The approach has improved selectively as MMA and DMA are separated from inorganic Arsenic. Currently evaluating the method for other foods. Liquid Chromatography Hydride Generation – AFS offers a low cost alternative to LC-ICPMS but with the added advantage of hydride generation selectivity. This negates the need for pre-oxidation of As (III) to As (V). Suitable for all samples and offers full speciation and more importantly Inorganic Arsenic speciation with relatively simple separation approaches.