Determination of tin in indium phosphide by electrothermal atomic absorption spectrometry and inductively coupled plasma mass spectrometry

Abstract

Two independent methods for the determination of tin in tin-doped indium phosphide were developed and compared. The electrothermal atomic absorption spectrometry (ETAAS) method utilized both platform atomization and a chemical modifier composed of orthophosphoric acid and magnesium nitrate. The detection limit (6 sb) is 5.0 µg g–1 for a 250 mg sample. The inductively coupled plasma mass spectrometry (ICP-MS) method monitored the 120Sn isotope and a typical detection limit (6sb) of 0.5 µg g–1 for a 20 mg sample was obtained. The observed range is 0.2–0.75 µg g–1 depending on the instrumental stability and response. The matrix effect was investigated in both methods, and the results indicated that matrix-matched calibration standards should be used. Indium phosphide wafers, obtained from a single crystal grown from a tin-doped melt, were analysed by using both methods to determine the tin content and the change in concentration along the crystal. Results having means that did not differ significantly (P=0.05) were achieved. Both the ETAAS and ICP-MS techniques were useful in determining tin in the tin-doped InP, however ICP-MS without internal standardization was less precise. When real samples containing 35–149 µg g–1 of Sn were analysed, the relative standard deviation was in the range 12.9–4.3% for ICP-MS and 3.4–2.0% for ETAAS.