EPA Method 4015
Reporting Limit Determination - The RL is set at 3–5 times the MDL depending on the matrix and instrument. RLs for natural surface water should be no greater than 10% of the lowest acute toxicity (LC50) for an aquatic organism. RLs for sediment should be no greater than 1 μg/kg for sediment or 10% of lowest acute sediment toxicity value (LC50) if available.
Submitted methods may substitute LOQ for RL. 2.1.4 Method Validation – Method validation requires a minimum of five replicate analyses at two matrix spike concentrations (typically LOQ and 10XLOQ).
Method validation recoveries are acceptable between 70–120% with a relative standard deviation (RSD) <20%. 2.1.5 Storage Stability - A 28-day (minimum duration) storage stability study in both surface water and sediment matrices. The objective of the storage stability test is to determine how long environmental samples could be stored and still remain viable. Surface water matrices should be stored in a refrigerator between 2-7 ⁰C and sediment samples stored in a freezer below 0 ⁰C for the duration of the test.
The test should include at least four sampling intervals and two replicate samples at each interval to validate residue’s rate of decomposition in representative matrices. Clean water and sediment matrices should be spiked with analyte of interest at an environmentally relevant concentration (i.e., 10X LOQ). Analysis should be conducted with fully validated analytical methods and acceptable recovery range (70–120%) and RSD (<20%)
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