Development of an electrothermal vaporization ICP-MS method and assessmentof its applicability to studies of the homogeneity of reference materials

A method has been developed for measurement of the homogeneity of analyte d istribution in powdered materials by use of electrothermal vaporization wit h inductively coupled plasma mass spectrometric (ETV-ICP-MS) detection. The method enabled the simultaneous determination of As, Cd, Cu, Fe, Mn, Pb, a nd Zn in milligram amounts of samples of biological origin. The optimized c onditions comprised a high plasma power of 1500 W, reduced aerosol transpor t flow, and heating ramps below 300 degreesC s(-1). A temperature ramp to 5 50 degreesC ensured effective pyrolysis of approximately 70% of the organic compounds without losses of analyte. An additional hold stage at 700 degre esC led to separation of most of the analyte signals from the evaporation o f carbonaceous matrix compounds. The effect of time resolution of signal acquisition on the precision of the ETV measurements was investigated. An increase in the number of masses mon itored up to 20 is possible with not more than 1 % additional relative stan dard deviation of results caused by limited temporal resolution of the tran sient signals. Recording of signals from the nebulization of aqueous standa rds in each sample run enabled correction for drift of the sensitivity of t he ETV-ICP-MS instrument. The applicability of the developed method to homo geneity studies was assessed by use of four certified reference materials. According to the best repeatability observed in these sample runs, the maxi mum contribution of the method to the standard deviation is approximately 5 % to 6% for all the elements investigated.