Automated flow-injection system for extending the linear range

A flow system with built-in capability to adjust injection volume whenever sample concentration is higher than the upper linearity limit has been developed and its performance assessed. Solenoid valves are used to manage sample and carrier delivery. Whenever the peak height is higher than the calculated linearity limit an injection volume adjustment is made to a second determination of the same sample in such a way that the peak height will be in the linear range. Extended linear range is therefore achieved without sacrificing detection of low concentration samples. Calibration, calculation of the upper linearity limit and model fitting to calibration data (peak height vs. concentration and peak height vs. injection volume) are automatically performed with no human intervention. Performance has been tested upon assessing dissolution profiles of cephalexin tablets in a low dispersion manifold with direct UV determination. The proposed system presents a 180 determinations h(-1) throughput. Sample aspiration time was calibrated in the range 50 2000 ms, thus allowing quantification up to 1250 mg l(-1) of cephalexin, Precision is about 0.95% rsd when sample is aspirated for 2000 ms. Results obtained are comparable to those obtained by using the reference procedure. (C) 1998 Elsevier Science B.V.