abstract
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 inorganic
arsenic in food products. We report an HPLC–ICPMS method based on sample extraction with trifluoroacetic
acid/H2O2, 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 column
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 lg As L1 (for 20 lL injection) corresponding to an LOD of 1 lg Askg1 dry mass in the samples. The
inorganic arsenic and total arsenic content (dry mass basis) of 10 rice samples was 25–171 lg Askg1
and 36–218 lg Askg1, respectively, whereas the 24 tuna fish samples contained much lower levels of
inorganic arsenic (<2–18 lg Askg1), although the total arsenic content was much higher (730–
5030 lg Askg1). The single wheat sample contained 166 lg Askg1, which was present mainly as inorganic
arsenic (152 lg Askg1). 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.
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