Collaborative study of an liquid chromatographic method for the determination of R-timolol and other related substances in S-timolol maleate

in Analytica Chimica Acta (2005), 546(2), 182-192

A collaborative study applying an enantiomeric liquid chromatographic (LC) method was carried out to determine the content of the enantiomeric impurity R-timolol and other related substances in three ... [more ▼]

A collaborative study applying an enantiomeric liquid chromatographic (LC) method was carried out to determine the content of the enantiomeric impurity R-timolol and other related substances in three different S-timolol maleate samples. Eight laboratories, all located in Europe, participated in the study. The quantitative results obtained were used to estimate the uncertainty on the content of the different impurities. For that purpose, a set-up was adapted from the ISO guidelines 5725-2, which allowed the estimation of the different variances, i.e. the between-laboratories (s(laboratories)(2)), the between-days (s(days)(2)) and the between-replicates (s(replicates)(2)), The variances of repeatability (s(r)(2)) and reproducibility (s(R)(2)) were then calculated using the equations s(r)(2) = s(replicates)(2) and s(R)(2) = s(replicates)(2) + s(days)(2) + s(laboratories)(2). For the timolol impurities, it was found that the estimated uncertainty seem to be concentration-dependent. Since the LC method which combines the compendial ones for enantiomeric purity and related substances testing was applied to evaluate uncertainty in this collaborative study, it was shown how a laboratory can evaluate the uncertainty of its results when applying the method in the future. (c) 2005 Elsevier B.V. All rights reserved. [less ▲]

Interlaboratory studies on two high-performance liquid chromatographic assays for tylosin (tartrate)

in Journal of Chromatography. A (1999), 830(1), 3-28

An interlaboratory study was performed on two high-performance liquid chromatographic methods to determine tylosin. The first method is a reversed-phase HPLC on a C-18 column, while the second is a method ... [more ▼]

An interlaboratory study was performed on two high-performance liquid chromatographic methods to determine tylosin. The first method is a reversed-phase HPLC on a C-18 column, while the second is a method using a polymeric stationary phase. The first method is described in several pharmacopoeia monographs on tylosin, to determine the composition of a tylosin mixture, while the second method is recently proposed to determine both the composition and the contents in such a mixture. The interlaboratory studies were set-up and interpreted according to ISO guidelines. This paper is written as a tutorial type of article explaining the principles and methods of these guidelines. The results of both methods were compared. Both were found to have disadvantages but in general the old method is still preferred, both for composition determination and to assay the components. (C) 1999 Elsevier Science B.V. All rights reserved. [less ▲]