A CONSIDERATION OF THE CONTAMINATION FROM SURROUNDINGS IN SAMPLE PREPARATION FOR ULTRA-TRACE DETERMINATION

Contamination from the surroundings during sample preparation is one o f the factors affecting signals in ultra-trace determination. Ultra-pu re nitric acid and water samples were concentrated in conventional che mical and clean rooms, and sodium, calcium, iron, zinc and lead in the residue were determined by inductively coupled plasma mass spectromet ry (ICP-MS). The amounts of impurities obtained after preparation in c onventional chemical room were more than those from clean rooms, and t he differences might reflect the amounts of contamination from the sur roundings in the former. In particular, the amounts of iron contaminat ion was more than that of other elements, and the RSD(%) was also larg e. Further, the amount of contamination was found to be more in the sa mple beakers placed in front on the hot plate, and less in rear, when front door of the draft chamber was open. On the other hand, the amoun ts in rear samples were slightly more than in front, when the door was a little open. In the determination of trace iron and lead in a stand ard reference sample of rice, analytical values obtained from the two kinds of rooms agreed well with each other after subtraction of each b lank value. However, the ratio of analytical to blank signal (S/BL) fr om the clean room was higher than from the conventional room for both elements, and their RSDs(%) were also found to be smaller.