DETERMINATION OF MINERAL AND TRACE-ELEMENTS IN TOTAL DIET BY INDUCTIVELY-COUPLED PLASMA-ATOMIC EMISSION-SPECTROMETRY - COMPARISON OF MICROWAVE-BASED DIGESTION AND PRESSURIZED ASHING SYSTEMS USING ACID MIXTURES

The effectiveness of different acid mixtures for the de-mineralization of total diet samples of different origin and composition by means of a closed microwave-based technique and a pressurized-ashing technique were investigated. The aim was to obtain complete acid solubilization for the subsequent accurate determination of Al, Ca, Cu, Fe, K, Mg, N a, P and Zn by means of inductively coupled plasma atomic emission spe ctrometry (ICP-AES). The sampling and sample preparation steps for the trace element analysis are described. The special care taken in the s ampling design to ensure the representativeness of the sample for the: population studied is also mentioned. The regions and population group s were selected from the high mountain valleys, where a high incidence of stomach cancer exists, and a low altitude valley at the foot of th e Andes, which is a low stomach cancer incidence region, both located in the state of Tachira, Venezuela. Total diets including breakfast, l unch, supper, snacks and drinks from the whole-day intake of 140 adult s were collected. The collection of the total diet was made according to the double-portion technique. The most reliable digestion procedure for the determination of Al, Ca, Cu, Fe, K, Mg, Na, P and Zn in total diet by means of ICP-AES was a microwave-based technique using HNO3 a lone or with the mixture HNO3 +H2O2 (2+1). In comparison, a pressurize d-ashing technique is faster although lower values for It (13 and 11%) were obtained. Despite low sensitivity for the ICP-AES measurements, the microwave-based digestion using HNO3 + H2SO4 (4+1) also gave good agreement for the determination of Al, Ca, Cu, Fe, It, Mg, Na, P and Z n by means of ICP-AES. Because of the simple and rapid procedure, the pressurized-ashing technique using the mixture HNO3 +H2O2 (2+1) was se lected to perform the digestion of the total diet samples collected. T he results of the mean daily intake of the population investigated sho wed for the high mountain valleys (high stomach cancer incidence area, n=77) as compared with the low altitude valleys (low stomach cancer i ncidence area, n=33) significantly higher;daily intake with respect to Na (2082 versus 1471 mg), It (1190 ver 731 mg), P (640 versus 381 mg) and a significantly lower daily intake with respect to Ca (925 versus 1379 mg) and Cu (2.78 versus 4.66 mg). No differences were obtained w ith respect to Al, Fe, Mg and Zn.