Sample Type Guidelines

Blank Samples

Samples containing no analyte (or concentration ≪ LoB)

Measured repeatedly to characterize the blank distribution. Even at true zero concentration, instruments produce nonzero readings due to noise, interference, and measurement imprecision. The spread and central tendency of these blank readings form the statistical basis for the LoB calculation. Record raw values exactly as reported by the instrument — do not force values to zero.

Low-Level Samples

Samples containing analyte at a concentration near the expected LoB/LoD

Measured to characterize performance just above the detection threshold. Low-level samples are not used directly in the LoB calculation but provide essential context for interpreting the LoB result and for subsequent LoD evaluation. Pooled SD from low-level samples quantifies measurement variability at near-zero concentrations.