03/24/200
University of Minnesota
Department of Geology & Geophysics
Geochemical Lab
Samples are analyzed on a Thermo Scientific iCAP 6500 duo optical emission spectrometer (serial no. 20083410) fitted with a simultaneous charge induction detector. The system has separate slit openings for the low wavelengths < 232 nm and for those greater. Elemental emissions can be viewed axially, down the barrel of the plasma for optimum sensitivity, or radially, across the plasma for maximum linear range and reduced matrix effects. All elements are measured on the most appropriate wavelength that is determined by the estimated composition, need for sensitivity, and the avoidance of element spectral overlaps. For each sample, standard, and blank the data is replicated 5 times to determine a mean and standard deviation for each selected elemental wavelength. Calibration is accomplished by comparing a NIST traceable single or multi-element standard solution to the unknowns. All blanks, standards, and samples are acid matrix matched to lessen matrix effects and are diluted such that element concentrations are in the linear working range of the standard and detector combination. Calibration blocks consist of a blank, standard(s), and up to 5-8 unknown samples. The internal standard element yttrium is added to diluted samples to further compensate for drift and for matrix effects when widely varying major elements concentrations are expected. On each day, before acquiring data, the spectrometer is checked for accuracy by looking at all the element detector array results for the elements to be analyzed to insure optimum peak and background selection. All blanks, standards, and samples must be in aqueous solution and are atomized and introduced to the instrument by a free aspiration or peristaltic pump rate of approximately 1 ml/min into a standard meinhardt concentric nebulizer. The probe and all sample introduction tubing are made of Teflon and are flushed for a minimum time of 45 seconds with clean matrix acid to prevent carryover between samples.