Reducing Errors through Multi-Increment Sampling
By Gregory Salata, Ph.D.
The objective of environmental sampling is to quantify contamination at a given location. In situations where sample collection may result in discrete samples of a heterogeneous nature, results may be biased based on the particle size of each sub-aliquot collected at the site. One option to help reduce the errors associated with non-uniform sample composition is to use multi-increment sampling (MIS) to create a representative, homogeneous aliquot for analysis of analytes.
An MIS sample aliquot is prepared by first sieving the sample through a #10 (2 mm) screen to remove the coarse material, then spreading the sieved sample evenly on a steel tray to a depth of approximately ½ inch. The sieved sample is divided into 30-50 sections, and a one gram aliquot is taken from each section and placed in a single jar. Because the fines tend to settle, the spatula is scraped along the bottom of the tray to make sure all particle sizes are equally represented. The entire content of the jar (from the 30-50 1g aliquots) is then used for the sample extraction/analysis.
MIS allows for a uniform, representative sample to be generated from a discrete sample within a specified area or decision unit. MIS is particularly useful when evaluating treatment stockpiles where the distribution of contaminant concentrations and particle sizes may vary widely.
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Tags: aliquot, ammunition, contaminants, department of defense, DOD, environmental, explosives, homogeneous, Increment, incremental, MIS, multi-increment sampling, particle, Sampling, sediment, semi-volatile, sieve, soil, soil sample collection