Determination of trace impurities in graphite and silicon carbide by total reflection X-ray fluorescence spectrometry after homogeneous liquid-liquid extraction

Using homogeneous liquid-liquid extraction as a pre-concentration method, a determination procedure of trace impurities (Fe, Ni and Cu) by total reflection X-ray fluorescence (TXRF) analysis was developed and optimized for graphite and silicon carbide samples. The samples were decomposed by alkali fusion. The residue was dissolved in a mixture of pentadeca-fluorooctanoic acid (PFOA), acetone and water, and the analytes were homogeneously dispersed by the aid of phenanthroline (phen). After phase separation with pH-adjustment, a portion of the sedimented water-immiscible liquid was pipetted on the polyester film that covered a silicon wafer sample-carrier. Then, the droplet was dried in a vacuum and analyzed by TXRF Analytical values in the sub-ppm or ppm level were well agreed with the certified values of the standard samples or the values observed by ICP-OES for a few samples.