METHOD 5035 IS A TECHNIQUE FOR GATHERING AND INTRODUCING SOIL SAMPLES FOR VOLATILE ANALYSIS THAT GREATLY DECREASES LOSS OF ANALYTE DUE TO MICROBIAL DEGRADATION AND VOLATILIZATION. SAMPLES ARE EITHER FROZEN OR PRESERVED WITH METHANOL TO PREVENT MICROBIAL DEGRADATION. SAMPLES ARE SEALED UNTIL THE TIME OF THE ANALYSIS THUS ELIMINATING LOSS DUE TO VOLATILIZATION.
Low Level Samples:
Samples with expected concentrations less than 200 μg/kg are gathered in low level vials. Low level vials consist of three, 40 mL vials with stir bars, labeled with their tare weights. A disposable coring tool is used to add about 5 grams of soil to each of the three 40 mL vials. The same coring tool can be used for all three vials and also used for that sample’s high level vials. The exact weight of the soil plug is determined by the difference between the tare weight and the final weight in the lab. It is critical not to use Custody Seals or do anything that would alter the tare weight of the vials. For the MS/MSD five bottles should be used. Low level samples that are frozen or packed on dry ice on the same day they are gathered have a 14 day holding time. Low level samples that are stored at 4° C (or packed on normal ice) have a 48 hour holding time. If samples are being hand delivered to lab the same day they are gathered, it is recommended but not required to use dry ice in the field; normal ice is adequate. Caution: Dry ice can freeze the methanol in high level vials and cause them to break.
High Level Samples:
Samples with expected concentrations greater than 200 μg/kg are gathered in high level vials. High level vials consist of two 40 mL vials each containing 10 mL of methanol, labeled with their tare weights. The vials are prepared by the manufacturer and are never opened in the lab. They are stored at 4˚C and are re-tare weighed immediately before they are used. An approximate ten gram plug of soil is carefully added so as not to splash out any of the methanol. The exact weight of the sample is determined in the lab. If any methanol is splashed out, that bottle should be discarded. High level samples stored at 4° C (or packed on normal ice) have a 14 day holding time.
Unknown Level Samples: Samples with unknown concentrations should be gathered in both low and high level vials unless project action levels preclude the necessity of either low or high level data. Typically the low level vials are run first. If the resulting data is over the linear range of the analysis, the high level vials are used. The client is only charged for one analysis.