Routine, high-sensitivity, cold vapor atomic absorption spectrometric determination of total mercury in foods after low-temperature digestion.

A cold vapor atomic absorption spectrometric method was developed for the subnanogram-per-gram determination of total Hg in a wide variety of foods. Foods were weighed into 50 mL polypropylene centrifuge tubes and dried without charring at 55 degrees C in a circulating oven. Samples were then digested at 58 degrees C with HNO3, HCl, and H2O2. After matrix modification with solutions of 2% Mg(NO3)2, 0.01% Triton X-100, and Cu(II) at 10 microg/mL, samples were analyzed by using a CeTAC Technologies M-6000A dedicated Hg analyzer. Based on a 2 g sample weight, the detection limit of the method over 12 batches averaged 0.30 ng/g wet weight and ranged from 0.03 to 0.6 ng/g. Recoveries of Hg added to 17 different foods, analyzed in a routine manner, averaged 97%, and individual recoveries ranged from 77 to 107%. Accuracy was confirmed by analysis of 7 biological reference materials from the National Research Council of Canada and the National Institute of Standards and Technology. Stabilization of low concentrations of Hg in solutions containing no sample was required to prevent loss of Hg from blanks. In a comparison of NaCl, potassium dichromate, and Au(II), chloride was much more effective for stabilization than the other two, and HCl was used for subsequent stabilization.