The application of multivariate quality control in gas chromatography

Quality control is important in present laboratory activities. Nowadays, an analysis must satisfy high requirements, which can only be met under appro priate control. An example of a rather simple and often used tool for quali ty control is the Shewhart control chart. A disadvantage of the Shewhart ch art is that it requires much effort with a risk for false alarms or mistake s, certainly when many control variables are involved. Multivariate control charts are an alternative to univariate Shewhart charts. In this paper, th e results are presented for both univariate Shewhart control charts and mul tivariate control charts applied to the capillary gas chromatographic analy sis of the fatty acid composition in BCR162 (soya-maize oil). Quite often o ne may observe a shift in the data when a process is monitored for a long p eriod. Although such a shift may result in statistical out-of-control situa tions, the analytical method may still be capable to perform within the spe cifications. In this paper, we introduce an extension of the T-2-chart for multivariate process control in order to handle statistically instable proc esses, with sufficient capability. (C) 1999 Elsevier Science B.V. All right s reserved.