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3.3.7 Sensitivity <br /> Sensitivity refers to the minimum magnitude at which analytical methods can resolve <br /> quantitative differences among sample concentrations. If the minimum magnitude for a <br /> particular analytical method is sufficiently below an action level or risk screening <br /> criterion, then the method sensitivity is deemed sufficient to fully evaluate the dataset <br /> with respect to the desired reference values. Frequently, risk-based screening levels fall <br /> below the sensitivity of even the most sensitive analytical methods. In such cases, it is <br /> necessary to review the qualifications of several laboratories, both from the standpoint <br /> of sensitivity as well as other DQIs, to select the best laboratory for the project. <br /> The method detection limit (MDL) is a theoretical limit determined through an MDL <br /> study. In practice, to allow for matrix interferences and variability in instrument control, <br /> a reporting limit(RL) of 2.5 to 5 times the MDL is typically selected. <br /> Analytical sensitivity is readily evaluated by comparing MDLs or RLs to risk-based <br /> screening values. <br /> 4. SAMPLE HANDLING AND CUSTODY REQUIREMENTS <br /> Collection of environmental samples of high integrity is important to the quality of <br /> chemical data to be generated. To this end, strict field procedures have been developed <br /> that will be employed at various locations during phases of the field investigation. <br /> Detailed field activities for collecting and analyzing samples are described in the Work <br /> Plan. A summary of criteria to be met during the sample collection process to ensure <br /> that a representative sample is properly collected and transported to the laboratory, such <br /> as sample container types, preservation, and holding time requirements, is provided in <br /> Tables C-1 and C-2. <br /> 4.1 Chain-of-Custody Record <br /> The field COC is used to record the custody of all samples or other physical evidence <br /> collected and maintained. The COC also serves as a sample logging mechanism for the <br /> analytical laboratories' sample custodian. <br /> The following information must be supplied in the indicated spaces in detail to <br /> complete the field COC: <br /> • Project specific information, including the project number and project name; <br /> Appendix C 11 <br />