When a lab proposes a method for several drugs in one urine extract, the validation tells you which analytes, matrix and concentration range the results support.
Choudhary and colleagues added known amounts of citalopram, prochlorperazine, midazolam and chlordiazepoxide to drug-free urine. They separated the compounds on a high-performance thin-layer chromatography plate, then sampled the bands for mass spectrometry. The paper reports a calibration range of 3–7 micrograms per milliliter for each drug and describes checks on precision and recovery.
Spiking lets researchers compare the measured amount with a known amount. The validated targets and range define the scope of that comparison. For a case specimen, ask whether the laboratory used the same matrix and method, whether the result fell inside its calibration range, and whether it separately validated any metabolite cited in the report. A urine concentration also leaves the time of exposure and the degree of impairment unresolved.
Choudhary et al., validation of a urine HPTLC–MS method (full text) · DOI