Development and application of a calibration regression routine in conjunction with linear and non-linear chromatographic detector responses.

Linear regression is widely used in the calibration of chromatographic assays even in conjunction with some chromatographic detectors which show significant non-linearity in their response characteristics. A calibration routine, based upon the curve y = axlnx+bx+c is presented which describes the non-linear behaviour of some chromatographic systems, including electron capture, nitrogen-phosphorus and UV photometric detectors, and gives comparable results to weighted linear regression with assays showing linear concentration versus response relationships. The ratio of the coefficients a and b in the equation allows quantification of the deviation from linearity and provides a more sensitive indicator of linearity than the correlation coefficient often quoted with linear regression.