|New Approach to
Soil Handling for Volatiles
Freezing Samples to Increase 5035 Holding Times
The new method of volatiles sampling, preservation and analysis under EPA method 5035 reduces volatilization during sampling and analysis by minimizing the handling of the sample. In addition, biodegradation is reduced by preservation with Sodium Biosulfate or with methanol. Preservation can occur either in the field or the laboratory. Field preservation has proven difficult and impractical so more often sample preservation occurs at the laboratory. Intact 5 gram samples arrive at the laboratory generally in EnCore® sampling devices and must be preserved within 48 hours for holding times to be met. The laboratory then has 14 days for analysis. It is this short holding time that has increased the difficulty for both sampling personnel and laboratory staff.
Experiments have recently been performed to assess the most effective preservation technique for soil Volatiles analysis. The effect of temperature and biodegradation on spiked samples in different soil types have been studied by government scientists. Clean soils were spiked with BTEX and some chlorinated volatile compounds, stored under different temperature regimes and then analyzed multiple times over a 14 day period. Loss of volatiles in soil samples were evaluated over time for different soil types under the current refrigerated storage conditions as well as with the soils frozen.
The outcome of the studies clearly demonstrated that freezing samples without preservation significantly diminished the effects of volatilization and biodegradation. Soils retained over 90% of the analyte concentrations over a fourteen day period. Secondly, freezing samples streamlines the preparation and analysis time by the laboratory. Instead of preserving three (two low level and one high level) aliquots within 48 hours of sample receipt, just one may be preserved and analyzed. As long as the analysis of the first aliquot is within the calibration range of the instrument the analysis is complete. Finally, freezing soils in sealed sampling devices whether the EnCore® samplers or by a modified syringe and 40ml vial arrangement, eliminates the need for acidification of the soil sample which has proven to be incompatible with certain soil types. An example is carbonate soils which effervesce causing pressure buildup in the VOA vial. We are hopeful that frozen storage will be included in future revisions of SW-846 as the best approach for soil preservation.
Even before a change in SW846 5035 allows for soils to be frozen upon receipt at the laboratory, you may still want to consider this approach for assessment projects that are not required by regulatory agencies. This approach has the advantage of allowing for the cost effective collection of additional samples to be put on hold pending analysis without incurring a sample preparation charge.
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