APPLICATION OF ION CHROMATOGRAPHY TO THE ANALYSIS OF HIGH-PURITY CDTE

Ion chromatography is widely used in different fields of analytical ch emistry and there is an extensive literature dealing with it, but not many papers describe the application of ion chromatography to the anal ysis of high-purity materials. A matter of topical interest in this fi eld is the determination of impurity or dopant elements in the high-pu rity semiconductor compounds of A(II)B(VI) type (CdTe) with detection limits from 10(-4)% to 10(-6)%. In order to eliminate the matrix effec ts and to reduce the detection limits, methods of concentration are co mmonly used; ion chromatography has been proved successful to separate impurities in the presence of large amounts of micro- and macro-compo nents without any preconcentration and/or pre-separation steps. The pr oposed procedure deals with the ion chromatographic determination of c hlorine, sulphur, selenium and phosphorus using a NaOH eluent, iron an d copper using a PDCA eluent, lead, cobalt, zinc and nickel using an o xalate eluent. Detection limits range between 1 and 3 10(-5)% and cali bration curves were found to be linear up to three orders of magnitude higher,The clear sample solutions were injected directly on to an ion chromatograph equipped both with a conductivity detector, for the det ermination of chloride, sulphate, selenate and phosphate ions, and a p ost-column membrane reactor and variable-wavelength UV-Vis detector, f or the determination of iron, copper, lead, cobalt, zinc, nickel (and cadmium, if required). Ion chromatographic responses were compared to graphite furnace atomic absorption spectrometry and results were found to be in good agreement (+/-5%).