MICROHOMOGENEITY ASSESSMENTS USING ULTRASONIC SLURRY SAMPLING COUPLED WITH ELECTROTHERMAL VAPORIZATION ISOTOPE DILUTION INDUCTIVELY COUPLEFD PLASMA MASS SPECTROMETRY (USS-ETV-ID-ICP-MS)

Authors: Miller-Ihli, Nancy; BAKER, SCOTT - 1235-15-00

Submitted to: Spectrochimica Acta
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/15/2001
Publication Date: 8/15/2001
Citation: Miller-Ihli, N.J., Baker, S. 2001. Microhomogeneity assessments using ultrasonic slurry sampling coupled with electrothermal vaporization isotope dilution inductively couplefd plasma mass spectrometry (uss-etv-id-icp-ms). Spectrochimica Acta. 56B:1673-1686.

Interpretive Summary: Ultrasonic slurry sampling electrothermal vaporization inductively coupled plasma mass spectrometry (USS-ETV-ICP-MS)was used to do homogeneity characterizations of 3 reference materials. The elements monitored were Cu, Fe and Ni. Solid samples were weighed into autosampler cups and diluted into slurries. Samples were injected into the ETV and treated using Pd and oxygen ashing and then the sample was vaporized into the ICP-MS. This approach provides excellent precision and accuracy. Results for SRM 2709 San Joaquin Soil showed that the material was extremely homogeneous (precisions of better than 6.3%)for a 0.3 mg sample. This approach provides mg and sub-mg homogeneity assessment capabilities. Producers of quality control materials as well as analysts can use this technology to provide added value to existing commercial materials.

Technical Abstract: Ultrasonic slurry sampling electrothermal vaporization inductively coupled plasma mass spectrometry (USS-ETV-ICP-MS) is a very powerful technique for the direct analysis of solid materials prepared as slurries. The use of isotope dilution USS- ETV-ICP-MS for micro-homogeneity characterization studies of powdered reference materials based on elemental analyses, was investigated. Slurry analysis conditions were optimized taking into consideration density, particle size, analyte extraction, slurry mixing, analyte transport, and sampling depth. Slurries were prepared using 1-20 mg of material and adding 1.0 mL of 5% nitric acid diluent containing 0.005% Triton X-100. Three reference materials were analyzed (RM 8431a Mixed Diet, SRM 1548a Typical Diet and SRM 2709 San Joaquin Soil). Cu and Ni were determined in each material and Fe was also determined in RM 8431a Mixed Diet. ETV conditions were optimized and the benefit of using Pd as a carrier combined with oxygen ashing was demonstrated. The accuracy and precision of the method was verified by comparing analytical results with certified values. The representative sample mass analyzed was calculated. The homogeneity of each of the materials was characterized and the San Juaquin soil proved to be the most homogeneous with variabilities of less than 7% for 0.3 mg sample sizes.