Time series: a complementary technique to control charts for monitoring analytical systems

In this study, the time series method was used as a complement to the most common control charts (X and R charts) to monitor a sequential injection analysis (SIA) system with UV/visible detection for determining sulphates in water. eries confirm the most important results of control charts and provide better understanding of how the system behaves over time. They provide information about the possible relationship between one datum and the previous data in the series. This opens up more realistic possibilities if an out-of-control point has to be substituted (once what has caused it is known) or if some missing data have to be evaluated. They also provide information for reducing the frequency of the analysis, if this proves necessary, and for avoiding autocorrelation in the data.