Linearity of chromatographic systems in drug analysis part I: theory of nonlinearity and quantification of curvature

Traditional approaches to the assessment of the linearity of chromatographic assays initially assume that the concentration-response relationship is linear and only deemed to be nonlinear if certain parameters lie outside pre-set acceptance criteria. A different approach is described in that the a priori assumption is made that the assay does have some curvature that can be described by fitting a nonlinear regression curve. Any nonlinearity can be quantified from the curvature terms of the resultant regression coefficients. The success of this alternative approach is dependent upon the appropriate choice of nonlinear regression to accurately describe concentration versus response relationship of the assay.