The diode array detector can be used in a number of unique ways and an example of the use of a diode array detector to verify the purity of a given solute is shown in figure 31. The chromatogram monitored at 274 nm is shown in the lower part of figure 31. As a diode array detector was employed, it was possible to ratio the output from the detector at different wavelengths and plot the ratio simultaneously with the chromatogram monitored at 274 nm.

The chlorthalidone was isolated from a sample of tablets and separated by a reverse phase (C18) on a column  4.6 mm  I.D., 3.3 cm long, using a solvent mixture consisting of 35% methanol, 65% aqueous acetic acid solution (water containing 1% of acetic acid). The flow rate was 2 ml/min.

Courtesy of the Perkin Elmer Corporation

Figure 31.  Dual Channel Plot from a Diode Array Detector Confirming Peak Purity