An improved HPLC-ICPMS method for determining inorganic arsenic in food:Application to rice, wheat and tuna fish

摘要

Because arsenic occurs in food both as toxic inorganic forms and as (presumed) non-toxic organic forms, there is a pressing need for robust analytical methods to selectively and quantitatively determine inor-ganic arsenic in food products. We report an HPLC-ICPMS method based on sample extraction with tri-fluoroacetic acid/H_2O_2, and measurement of arsenate by anion-exchange HPLC-ICPMS using aqueous malonic acid as mobile phase. The method showed good extraction efficiencies (generally >90%) and col-umn recoveries (>95%) for samples of rice, tuna fish and wheat. Moreover, the use of 5 or 10 mM malonic acid at pH 5.6 gave sharp well-resolved HPLC peaks and a conveniently short retention time of 5 min for arsenate, which together contributed to a low limit of detection based on signal to noise ratio of three of 0.05 ug As L~(-1) (for 20 uL injection) corresponding to an LOD of 1 ug As-kg~(-1) dry mass in the samples. The inorganic arsenic and total arsenic content (dry mass basis) of 10 rice samples was 25-171 μg As-kg~(-1) and 36-218 μg As-kg~(-1), respectively, whereas the 24 tuna fish samples contained much lower levels of inorganic arsenic (<2-18 ug As-kg~(-1)), although the total arsenic content was much higher (730-5030 ug As-kg~(-1)). The single wheat sample contained 166 ug As-kg~(-1), which was present mainly as inor-ganic arsenic (152 ug As-kg~(-1)). The combination of low acid concentration for extraction, high buffering capacity of malonic acid at pH 5.6, and good peak shape results in a highly reproducible and sensitive method for the determination of inorganic arsenic in food.