High moisture content (>30% by weight) can significantly lower concentrations of analytes detected in the RaPID Prep soil methods. In these methods, water associated with a sample will increase the volume of the extraction solution (liquid phase) and decrease the amount of soil (solid phase) in a weighed sample. In some cases, water may also decrease the extraction efficiency of the extracting solvents, lowering recovery even further. The incremental contribution of soil water to the final volume of soil extract can be corrected by adjusting the dilution factor used with the procedure. Estimation of and correction for loss of extraction efficency, however, is a more complex task. In situations where volatile chemicals are to be analyzed, air drying of moist samples is not feasible because analyte will be lost to vaporization. For these reasons, determination and correction of moisture content is not practical in many field testing situations. The procedure described below is a quick and simple approach to reducing the moisture content of most soils and sediments to less than 30% for processing in the RaPID Prep Soil Collection and Sample Extraction kits prior to analysis by the RaPID Assays. For some analytes, it may be appropriate to also test the water phase of a moist sediment or soil sample. We recommend sampling the water phase prior to dewatering the sample for soil analysis.
MATRIX: Sediment or soil samples with greater than 30% moisture content
SDI RaPID Prep Soil Collection kit and the appropriate RaPID Prep Sample. Materials: Coffee filters (e.g. Mr. CoffeeÒ #2 cone filters), paper towels and disposable plastic teaspoons, gloves, and disposable plastic cups (optional)
Measure 4 teaspoons of moist soil or sediment sample into a coffee filter. Squeeze the sample within the coffee filter using gloved hands. A disposable plastic cup can be used to collect water from the sample as it drains. Paper towels can be wrapped around the outside of the coffee filter to assist in absorbing water. Remove as much moisture as possible from the sample. Open up the coffee filter and remove a 10 gram sample of the treated sediment or soil. Process the soil according to the directions on the package inserts of the Soil Collection kit or the Sample Extraction kit. In most cases, no correction for moisture content is required when calculating the analyte concentration (refer to procedural notes).
Sediments or soils high in organic matter content (>40%) may have greater than 30% moisture content after performing the above procedure. For organic samples, we recommend following the above procedure and adjusting the dilution factor for moisture content. Moisture content can be determined or estimated for site representative samples prior to analysis.