ANALYTES: Polychlorinated biphenyls (PCBs)
RANGE OF DETECTION: 500 ppb to 10 ppm
SDI PCB RaPID Assay® Kit. SDI RaPID Prep® PCB Sample Extraction Kit. SDI RaPID Prep Soil Collection Kit. Reagents: table salt (sodium chloride) or salt packets used by restaurants (e.g. Dixie CrystalsÒ Salt, Savannah Foods & Industries, Inc., Savannah, GA). Equipment: Electric hand or hammer drill with masonry drill bit (¾” bit was used to validate this procedure), 1/8 teaspoon (for measuring table salt).
Caution: Wear safety glasses and a dust mask for this procedure.
Concrete structures, walls, floor or slabs. Sample concrete by drilling holes and collecting the residual powder or dust. Three holes drilled to a depth of 1” with ¾” bit will generate at least 10 grams of powder, the amount of sample required for extraction and analysis. The analyst should determine how to sample an area for contamination area, that is, the number of samples to collect and the depth of sampling (drilling).
EXTRACTION AND ANALYSIS:
Concrete powder (dust) can be extracted and analyzed as “soil” in the package insert of the RaPID Prep PCB Sample Extraction Kit. In this procedure at Step 3.2 of the extraction procedure, add approximately 0.5 g of salt (the equivalent of a salt packet or 1/8th teaspoon) to the soil collector. The diluted extract is measured as “sample” according to the package insert of the PCB RaPID Assay (PCB RaPID Assay kit procedure step #3).
Calculate the PCB concentration in concrete fines by multiplying the assay result by the appropriate factors introduced by the procedure. For the procedure given in the PCB Sample Extraction Kit, this factor is 2000.
Immunoassay results that are above or below the limits of the RaPID Assay Kit standard curve are considered estimated concentrations. Extrapolated assay concentrations should never be multiplied by the dilution factor and reported as a concrete PCB concentration. If the calculated result is greater than the upper limit of the detection range or a higher concrete PCB concentration range is of analytical interest, an additional 1:10 dilution of the 1:2000 diluted extract is suggested. The assay result obtained on this sample is then multiplied by 20,000 to determine the original concentration of PCBs in the concrete. The useful range of detection would then be 5 to 100 ppm of PCBs in concrete.
Due to the magnitude of the correction factor used, the accuracy of the final result will depend on the care taken in making dilutions. Recoveries of PCBs will vary depending on the mechanism of retention of the PCBs, the nature of the solvent, the apparatus used in the extraction, the length of the extraction period and the levels of potentially interfering substances in the concrete sample. In a study, concrete powder was fortified and equilibrated with PCBs (Aroclor 1254) and then extracted using the procedures described above with a 1-minute shake and an overnight (18-hour) continuous mechanical-shake. Recoveries of PCBs are presented below. Typical recoveries for spikes of 10 to 100 ppm PCBs were in the range of 70 to 80% for a 1-minute shake. Longer extraction times improve extraction efficiency.