Effects of Different Acid Mixtures for Sample Digestion on the ICP-AES Determination of Heavy Metal Elements in Soil

Four different acid mixtures, i.e., ① HNO3-HClO4, ② HCl-HNO3, ③ HCl-HNO3-HF-HClO4 and ④ HCl-HNO3-HF were tested for digestion of soil sample, and their effects on the ICP-AES determination of contents of heavy metal elements (Cu, Zn, Pb, Zn and Cr) in the sample were studied. It was found that high accuracy and precision of analytical results were obtained by either of the 4 acid mixtures in analyzing standard samples of soil. But in analyzing unknown soil samples, significant effects were observed in using the 4 different acid mixtures for digestion of samples of different types (chernozem, umber, brown soil and red soil), and most obvious effect was found with the determination of chromium. It was shown that among the 4 acid mixtures, the mixtures ③ and ④ were able to digest the samples completely and were proved to give higher or in other words better results as compared with the incomplete digesting acid mixtures, i.e., the mixtures ① and ②. In fact, suitable acid mixture should be chosen according to the types of soil samples and kinds of heavy metal elements.