A procedure to assess linearity by ordinary least squares method

A detailed procedure for testing linearity of calibration curves in method validation by the ordinary least squares method (OLSM), including experimental design, estimation of the parameters, outlier treatment and evaluation of the assumptions, was proposed. The theoretical background was discussed and the assumptions considered were: (i) normality, homoscedasticity and independency of residuals and (ii) adjustment to the correct model. The procedure involved precise statistical techniques that were easily carried out by any commercial spreadsheet software. The suitability of the procedure for assessing linearity was demonstrated by the application in food analysis.