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 = axln x + 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.