RESUMO
A simple spcctrophotometric method for determination of total rare-earth metals in food is presented. Weigh 5 gm of dry sample in a dish. After soaking the sample more than half an hour with 10 ml 3N H2SO4, evaporate to dryness on a hot plate and ash at 600℃. Dissolve the ash in 1 ml 6N HCl, and evaporate to dryness. Dissolve the residue in 2 ml water, and transfer it to a 10 mi-graduated tube. Wash the dish repeatedly with small amount of water. Transfer the washings to the same tube, and dilute to 10 ml with water. Pipette two portions of aliquots of 4 ml sample solution to two 10ml graduated tubes in which 2 ml of HCOOH-NH3 buffer (pH 3.7) is added. After mixing, add 1 ml each of 10% sulphosalicylic acid solution and 5% ascorbic acid solution. Make volume to 8 ml with water. Mix thoroughly. After 10 minutes, add 1 ml 15% alcoholic diphenylguani-dine solution, mix and add 1 ml 0.025% arsenazo Ⅲ &K solution. Mix, and measure the optical density at 680, 660 and 640 nm against a reagent blank solution. Calculate the total rare-earth metals content with a calibration curve. The sensitivity of the method is 0.01 ?g/ml and the detection limit is 0.05ppm (5 gm of sample). The average recovery of added TRExOy is 91.9% (n = 14).