388. protocol deviation Documentation of an unintended departure from the study plan after the study initiation date.
389. proxy matrix A suitable matrix that can be used in place of an original matrix available in limited amounts. May serve as a surrogate matrix when studying, for example, matrix effects.
390. prozone An effect detected when increasing analyte concentrations result in either no change or decreased detector response when compared with the preceding lower analyte concentration.
391. qualified assay An assay for which not all guidance-recommended validation assessments are performed, or the extent of such assessments are limited, but which is deemed suitable (scientifically sound) in performance for the purpose of the studies it is used to support.