Quantitation of perfectly co-eluting analytes on dual-channel-subtraction chromatograms☆

Abstract A dual-channel aroyl luminescence detector (ALD) was constructed and used as a demonstration system for quantitating two perfectly co-eluting model analytes (fluorobenzaldehyde isomers) from subtraction chromatograms. The linear part of the calibration curve of either ortho- , or meta- , or para -fluorobenzaldehyde remained the same in the presence of 0.3- to 3-fold amounts of a co-eluting isomer. The accuracy of individual quantitation for two completely overlapping peaks was similar to that for a single peak: the error band started to increase only when the interfering isomer was present in more than a 10-fold excess. Formulas were developed, and experimentally confirmed, that allowed easy calculation of analyte peak size and detection limit in a subtraction chromatogram from corresponding single-channel data. The simple technique of resolving two peaks of identical retention into two quantifiable subtraction chromatograms is not restricted to the ALD, but can be carried out on various types of dual-channel detectors. A similar technique can be employed to check the purity of analyte peaks.