c. Urine Enrichment
Split the base pool into three smaller urine pools. Enrich one of the pools with an appropriate amount of the stock solution of each pesticide to yield an approximate concentration range of 3-10 ng/mL (QCL). Enrich the other pool to yield an approximate concentration range of 12-20 ng/mL (QCM). Use the other pool as
the matrix blank (QCB). Allow the pools to stir over night in a refrigerator to ensure a homogeneous mixture. Store at -100C or below.