Validation of liquid chromatography mass spectrometry (LC-MS) methods
4.1. Repeatability, intermediate precision and reproducibility
can have different meanings, depending on what level of variability is included.
Measurement (srepeatability, sr) expresses the closeness of the results obtained with the same sample (or subsamples of the same sample) using the same measurement procedure, same operators, same measuring system, same operating conditions and same location over a short period of time. These conditions are called repeatability conditions. The short period of time is typically one day or one . Repeatability is expected to give the smallest possible variation in results.
(sintermediate precision, sRW) (occasionally called within-lab ) is, differently from the repeatability, the precision obtained within a single laboratory over a longer period of time (generally at least several months) and takes into account more changes than repeatability. In particular: different analysts, calibrants, batches of reagents, columns, spray needles etc. These factors are constant within a day (i.e. behave systematically within day timescale) but are not constant over a longer time period and thus behave as random in the context of intermediate precision. Because more effects are accounted for by the intermediate precision, its value, expressed as standard deviation (see the next section), is larger than the repeatability standard deviation.
Reproducibility (occasionally called between-lab reproducibility) expresses the precision between the measurement results obtained at different laboratories. Sometimes a mistake is made and a term reproducibility is used for a within-laboratory studies at the level of intermediate precision. Reproducibility is not always needed for single-lab validation. However, it is beneficial when an analytical method is standardized or is going to be used in more than one laboratory (e.g. method developed in R&D departments).
