DETERMINATION OF TIN IN INDIUM-PHOSPHIDE BY ELECTROTHERMAL ATOMIC-ABSORPTION SPECTROMETRY AND INDUCTIVELY-COUPLED PLASMA-MASS SPECTROMETRY

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 (6s(b)) is 5.0 mug g-1 for a 250 mg sample. The inductively coupled plasma mass spectrometry (ICP-MS) method monitored the Sn-120 isotope and a typical detection limit (6s(b)) of 0.5 mug g-1 for a 20 mg sample was obtained. The observed range is 0.2-0.75 mug 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 mug 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.