Determination of Heavy Metals in Soil, Sediment, and Rock by Inductively Coupled Plasma Optical Emission Spectrometry: Microwave-Assisted Acid Digestion Versus Open Acid Digestion Technique

A microwave acid digestion and open acid digestion technique were investigated to obtain a simple, rapid, and safe method for the determination of metals in soil, sediment, and rock samples. The digests were subsequently analyzed for heavy metal content by inductively coupled plasma optical emission spectrometry (ICP-OES). The trace elements determined were Ba, Co, Cr, Cu, Ni, Pb, Sr, and Zn; the major elements determined were Al, Ca, Fe, K, Mg, and Mn. The experimental study was conducted using three certified reference materials (CRMs): TILL-3, soil; LKSD-1, lake sediment; JB-2, basalt. Two different programs were examined to determine which was optimal for the digestion of real environmental samples. Both microwave acid digestion with an acid mixture of HF-HNO3-HCl (6:3: 1) and open digestion with a mixture of HF-HNO3-HClO4 (7:3: 1) produced the fastest, safest, and most most accurate analytical results, with an average recovery of 91 - 110% and a precision better than 5% in most cases. The experimental results obtained were in good agreement with the certified values and were precise and accurate. The developed method was applied for the analysis of six industrial soil samples, and the heavy metal were determined by ICP-OES using microwave digestion for monitoring of contaminated sites in India.