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.
Learn more about incremental sampling methodology…
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
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August 19th, 2010 at 8:52 am
Is this method only appropriate for SVOA analysis? Interested in metals (Pb & As) and possibly PCBs.
August 19th, 2010 at 9:10 am
Thanks James, yes, MIS can be used for any analysis, except for volatiles.
August 19th, 2010 at 9:11 am
@James Young: MIS can be used for all SVOA organics (including PCBs) and metals.
August 19th, 2010 at 9:31 am
Very timely article Greg! Oregon DEQ has been advocating the use of Multi-increment sampling for it’s clean-up programs. I was wondering which labs had experience with some of the specifics of this sampling strategy (such as sieving and compositing the aliquots).
August 20th, 2010 at 6:25 am
MIS may also be used for volatile organic compounds in soils and have been successfully beta tested in Hawaii. Basically, multiple soil increments were added to methanol in field. MIS is initially developed for explosives in soils to address sample heterogeneity problems and is currently under development for metals, volatiles, PAHs, etc. ITRC is currently preparing a guidance document, which will be completed in next spring.
August 20th, 2010 at 10:13 am
Which CAS locations are routinely performing this subsampling procedure?
August 20th, 2010 at 11:56 am
Hello Lynda!
Our laboratory in Kelso, WA has had the most experience with MIS. Our other locations are at various stages in the process of bringing this on-line.
August 26th, 2010 at 3:58 pm
Hawai’i has been using MIS in the field and in the lab for over five years now for all contaminants, including VOCS (e.g., increments combined in methanol in the field or lab). Here’s the reference for the Hawai’i Dept. of Health guidance (refer to Sections 3 and 4):
HIDOH, 2009, Technical Guidance Manual (in preparation): Hawai’i Department of Health, Office of Hazard Evaluation and Emergency Response.
We routinely update our guidance; comments and suggestions can be posted to the web page and are appreciated. You’ll never go back to discrete samples once you start using MIS and “Decision Unit” approaches in the field – and you’ll wonder about all of the “hot spots” that you missed in the past…