Application of ion chromatography to the analysis of high-purity CdTe

Ion chromatography is widely used in different fields of analytical chemistry and there is an extensive literature dealing with it, but not many papers describe the application of ion chromatography to the analysis of high-purity materials. A matter of topical interest in this field is the determination of impurity or dopant elements in the high-purity semiconductor compounds of A(II)B(VI) type (CdTe) with detection limits from 10(-4)% to 10(-6)%. In order to eliminate the matrix effects and to reduce the detection limits, methods of concentration are commonly used; ion chromatography has been proved successful to separate impurities in the presence of large amounts of micro- and macro-components without any preconcentration and/or pre-separation steps. The proposed procedure deals with the ion chromatographic determination of chlorine, sulphur, selenium and phosphorus using a NaOH eluent, iron and copper using a PDCA eluent, lead, cobalt, zinc and nickel using an oxalate eluent. Detection limits range between 1 and 3 10(-5)% and calibration 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 determination of chloride, sulphate, selenate and phosphate ions, and a post-column membrane reactor and variable-wavelength UV-Vis detector, for 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%).