Multivariate calibration transfer applied to the routine polarographic determination of copper, lead, cadmium and zinc

The application of calibration transfer methods has been successful in combination with near-infrared spectroscopy or fluorescence spectroscopy for prediction of chemical composition. One of the methods developed that provides accurate performance is the piecewise direct standardization method (PDS), which in this paper is applied to transfer from one day to another the partial least squares (PLS) models built in the polarographic determination of copper, lead, cadmium and zinc. This is an electrochemical example in which interferences have been found, making necessary the use of soft calibration models because of their ability to model this phenomenon, which implies a large number of standard samples for the calibration. Once the PLS models are built, the calibration transfer is carried out to overcome the instrumental change over time in this routine analysis, allowing one to reduce from 28 to 8 the number of calibration standards necessary for later determinations. Standard errors of prediction (SEP) are found similar to those given by the complete recalibration.