Microwave-induced combustion method for the determination of trace and ultratrace element impurities in graphite samples by ICP-OES and ICP-MS

Graphite is extremely difficult to digest even using concentrated acids and quality control of impurities is critical for its industrial application. In this work, microwave-induced combustion is proposed for graphite digestion and further determination of Ba, Ca, Cd, Co, Cr, Cu, Fe, K, Li, Mg, Mn, Mo, Na, Ni, Sr, V and Zn by inductively coupled plasma optical emission spectrometry (ICP OES). A relatively high graphite mass (400 mg) was completely burnt using 20 bar O-2 and HNO3 (1-14.4 mol L-1) as absorbing solution. A high digestion efficiency (>99%) was obtained with recoveries better than 95% for all analytes just using a solution as diluted as 4 mol L-1 HNO3. Determination was also performed by inductively coupled plasma mass spectrometry (ICP-MS) with an agreement better than 97% with ICP OES results. Additionally, a microwave-assisted acid digestion/extraction method using concentrated HNO3 and high-pressure system was performed and an agreement better than 95% was achieved in comparison to MIC results. Analysis of certified reference materials was also performed (agreement >95% to certified values). The proposed method allowed using diluted acids, resulting in digests fully compatible with multielemental analysis allowing lower blanks and better limits of quantification. (C) 2015 Elsevier B.V. All rights reserved.