The use of derivatives for establishing integration limits of chromatographic peaks

Summary The paper deals with composite peaks in which the resolution is not sufficient to allow simple area determinations with conventional integrator procedures. It is proposed to use the second derivatives of composite peaks, since the derivatives accentuate envelope perturbations due to overlapped peaks. In particular, when there are two solutes in the composite, and when the peak separation is between 2 and 4σ, the second derivative of the composite has two minima and three maxima. The second maximum is indicative of the cross point of the two solutes. This point can be used to initiate and/or terminate the integration of the components in the composite. Similarly, the second minimum occurs at a point close to the true maximum of the second peak in the composite. This point can also be used for the quantitative determination of the second component in the composite. The second derivative traces can also be integrated, but their utility in quantitative analysis of the peaks is questionable. An inversion procedure is given in which the second derivative trace is inverted to yield a trace similar to the conventional chromatograms but with better apparent resolution. In special circumstances, the inverted derivatives can be used for integration purposes.