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

• Microwave-induced combustion was applied for graphite digestion.
• Graphite is a very difficult matrix to digest due to its stable structure.
• Digestion efficiency was higher than 99% (RCC lower than 1%).
• Digests were suitable for inorganic impurities determination in graphite by ICP OES and ICP-MS.
• Up to seventeen elements were determined using 4 mol L− 1 HNO3 as absorbing solution.

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 O2 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.