[Precision of internal standard method in HPLC analysis].

The internal standard methods are known to compensate for the errors from sample preparation and injection into an analytical instrument. However, recent HPLC apparatuses have injectors of excellent repeatability and it is dubious whether the cancellation of injection error can lead to substantial improvement in the precision of analysis. This paper answers the above question experimentally and theoretically.

[Estimation of precision in system suitability tests].

In system suitability tests, the daily conditions of an analytical instrument are checked with the standard deviation (SD) of measurements as a criterion. This paper examines how exactly the SD values obtained from the measurements can indicate instrumental conditions. The HPLC measurement for acetaminophen is repeated six times daily to obtain an SD estimate, and these procedures are repeated for seven days.