Multi-component Luminescence Analysis of Some Nitrogen Heterocycles

Luminescence is now well established as a sensitive and selective technique for trace analysis of environmental samples.1 In pharmaceutical analysis, however, its frequency of use is reduced. This may be a result of the current ascendancy of high-performance liquid chromatography (HPLC) and the broad band width, featureless luminescence spectra of drug components. In addition, for formulated pharmaceutical products the sensitivity is not usually essential and HPLC with ultraviolet detection will often be sufficient for most analytical problems. The major advantage of luminescence methods over chromatographic methods is, however, the reduced analysis time. A typical example is the determination of two or more closely related compounds in a pharmaceutical formulation. These could consist of the parent drug and its major degradation product, which would normally be determined in a stability study. A suitable model two-component system is the antiviral agent acyclovir [9-(2-hydroxyethoxymethyl)guanine] and its major degradation product guanine, which may form by acid hydrolysis (Fig. 1). Considerable overlap occurs in the emission spectra of the components (Fig. 2). This problem is regularly found in the luminescence of drug compounds and precludes the use of single-wavelength measurement.