Section 9.3.2 states, “Laboratory fortified blank (LFB) - The laboratory must analyze at least one LFB (Section 7.9) with each batch of samples. Calculate accuracy as percent recovery using the following equation:

R = ((LFB-LRB)/s) x 100

where:

R = percent recovery

LFB = laboratory fortified blank

LRB = laboratory reagent blank

s = concentration equivalent of analyte added to fortify the LBR solution

If the recovery of any analyte falls outside the required control limits of 85-115%, that analyte is judged out of control, and the source of the problem should be identified and resolved before continuing analyses.”

The concentration ranges for the analytes in the LFB are discussed in section 7.9.