Procedure for the quantification of rider peaks

Rider peaks are small peaks which are not well resolved from a large and as ymmetrical neighbour but sit on its trailing side. The usual case is a larg e, tailed peak which is eluted just in front of the small peak, although th e opposite situation can also occur (a small peak in front of a large peak with fronting). The common integration techniques, i.e. separating the peak s by vertical drop or by a tangent and determining area or height, give err oneous results. We propose a method for their quantification with low error . It is necessary to set up a "two-dimensional" calibration by varying both concentrations, i.e. of the large peak and of the rider. This leads to a s eries of linear equations which describe the rider size, as found by the in tegrator, as a function of the size of the large peak. The y-axis intercept s i of these equations show a linear relationship with the concentration x of the rider analyte, whereas the slopes s follow a quadratic relationship. These equations can be used to solve the equation y = s(x) . z + i(x) for x (y and z are the integrated peak size of the rider and the large peak, re spectively). The procedure was tested with computer-generated peak pairs as well as with HPLC separations of 2,3-dimethylaniline (large tailing peak) and 2,3-dimethylphenol (symmetrical rider peak). (C) 2001 Elsevier Science B.V. All rights reserved.