For Volatiles In Soil Using EPA Method 5035
The methodology for sampling soils for volatile organic compounds (TPH GRO, BTEX, MTBE and Naphthalene by GC, and VOCs by GC/MS) changed with the promulgation of USEPA SW-846 3rd Edition in June, 1997. This update eliminated Method 5030 for soil volatile organic analyses. Although Method 5030 has been used extensively over the past 10 years, studies have shown that the results for many target analytes are biased low. To minimize this bias, the USEPA developed Method 5035, incorporating changes in the sampling and analysis procedures that drastically reduce the open-air handling of soil samples in the field and laboratory.
Degree of bias: Studies have demonstrated that the traditional low-level analysis using Method 5030 resulted in losses of 80% to 95% of selected volatile compounds. Typical analysis constituents such as benzene and toluene have been found to degrade by 80% or more. Losses of many extremely volatile compounds such as vinyl chloride, may be 100%.
Why loss occurs: Loss of volatiles probably occur throughout the entire collection and analysis process resulting from sample fragmentation during sampling, leakage during shipment due to soil particles on the sealing surfaces of the container, biodegredation due to insufficient cooling and at the laboratory during subsampling, weighing and transfer operations. In contrast, Method 5035 provides for collecting samples in a coring device without fragmenting the sample, then transferring it to a preservative. This consequently eliminates most opportunities for volatile loss.
Method 5035 gives a number of options for collecting soil samples including:
Field Methanolic Preservation for high level samples: Field personnel measure (using an analytical balance) and dispense 5 grams of soil into a 40 ml glass vial containing 5 ml of methanol preservative. The sample must be collected and dispensed utilizing a coring device such as a syringe with the end cut off. The vial must be quickly capped after introduction of the sample to avoid loss of methanol and shipped to the laboratory for analysis. The laboratory opens the vial and takes an aliquot of the methanol for introduction to the instrument. Multiple analyses can be made from one vial. The sample holding time is 14 days.
Field Sodium Bisulfate Preservation for low level samples: This technique is performed in a similar fashion to the field methanolic preservation procedure with the following exception. Two glass vials preserved with sodium bisulfate (sulfuric acid) are collected in addition to the methanol preserved vial. The low level analysis technique utilizes a closed system purge and trap procedure. In the low level procedure, the volatiles are liberated from the soil by agitation and purging with an inert gas into the "headspace" or gaseous layer in the vial. A special instrument is utilized that punctures the septum on the vial, and extracts an aliquot of the gaseous layer above the sample. Consequently, only one analysis can be performed on each vial. For this reason, a second vial must be collected if reanalysis is necessary. Additionally, a methanol preserved vial is required for this analysis, should the sample require reanalysis as a high level sample. Caution must be exercised with carbonate mineral soils as they may react with the acid preservative creating gas bubbles. The gas formation could cause the container to explode after capping. The easiest way to prevent this situation is to test each soil type collected with sulfuric acid to determine if they effervesce.
There are a number of potential difficulties with field preservation techniques. These include: sampling dense or highly mineral soils, inclement weather making field weighing problematic, spillage or evaporation of the preweighed methanol and shipping restrictions involving methanol.
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