Determination of arsenic in chilli and tomato grown in North East Thailand

Abstract

Heavy metals in edible fruits constitute a health hazard. We present an analytical procedure for determining inorganic arsenic (As) species in hot chilli pepper and tomato fruits at the red-ripe stage using microwave assisted digestion (MAD) followed by flow injection-hydride generation atomic absorption spectrometry (FI-HGAAS). The optimum conditions for the acid digestion method and arsenic hydride (AsH3) determination were studied in detail. The plant sample (0.5 g) was digested with 5 ml of concentrated nitric acid by MAD programmed at 900 W for 35 min. Arsenite, As(III), in the acid digests could only be analysed by FI-HGAAS using 1% (v/v) HCl as a carrier solution and 0.5% (w/v) NaBH4 in 0.04% (w/v) NaOH as a reducing agent, while total As content was determined after pre-reduction of arsenate, As(V), to As(III) with 2% (w/v) thiourea prior to measurement. The concentration of As(V) was then calculated as the difference between total As and As(III). Detection limits for As(III) and As(V) were 0.004 and 0.006 μg/l, respectively. The relative standard deviation of the data was less than 5% (n = 10). The recovery of the samples spiked with 10 μg/l As was 98-103%. The proposed method was applied to determine traces of As in six varieties of hot chilli pepper (0.55-0.88 μg/g As(III) and 0.22-0.93 μg/g As(V)) and seven varieties of tomato (0.36-0.64 μg/g As(III) and 0.22-0.60 μg/g As(V)) samples.