Five soil sample splitting methods (riffle splitting, paper cone riffle splitting, fractional shoveling, coning and quartering, and grab sampling) were evaluated with synthetic samples to verify Pierre Gy sampling theory expectations. Individually prepared samples consisting of layers of sand, NaCl and magnetite were left layered until splitting to simulate stratification from transport or density effects. Riffle splitting performed the best, with approximate 99% confidence levels of less than 2%, followed by paper cone riffle splitting. Coning and quartering and fractional shoveling were associated with significantly higher variability and also took much longer to perform. Common grab sampling was the poorest performer, with approximate 99% confidence levels of 100%±150% and biases of 15%±20%. Method performance rankings were in qualitative agreement with expectations from Gy sampling theory. Precision results depended on the number of increments, the type of increment, and other factors influencing the probability of selecting a particle at random, and were all much higher than Pierre Gy's fundamental error estimate of 1%. A critical factor associated with good performance for these methods is a low conditional probability of sampling adjacent particles. Accuracy levels were dominated by the sampling process rather than by the analytical method. Sampling accuracy was at least two orders of magnitude worse than the accuracy of the analytical method. Published in

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Memory effects or sample carry over characteristics of five pneumatic nebulizers routinely used for sample introduction into plasma emission spectrometers are studied. It is observed that the primary source of the memory noted for the nebulizers studied is the dissipation rate of the fog produced by the nebulizer during introduction of the previous sample or samples. Contributions to memory from the aspiration tube, salt deposition at the nebulizer tip, and a chromatographic effect at the torch tip are minimal. In terms of operational stability, detection capability, tolerance for particulates, and low memory, a concentric nebulizer with a Pt: Ir needle, Teflon nose cone, and an extended spray director is superior to the others tested. Even under the most optimum conditions, the washout time required to reduce sample emission to 0.1% of its maximum intensity varies from 2 to 4 min, thereby greatly increasing per sample analysis time. The memory effect phenomena can be accurately modeled by a hyperbolic curve and can, therefore, be easily corrected for in routine analysis. The memory correction value, which is subtracted from a sample's net emission intensity, is calculated from the product of an empirically defined correction constant and the emission intensity of previously run samples divided by the washout time. Examples of the utilization of the correction are shown.

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