Photochemical detection in high-performance liquid chromatography and its application to cannabinoid analysis

Abstract

A novel technique of on-line photochemical derivatization is described which can enhance considerably both the sensitivity and specificity of detection in high-performance liquid chromatography (HPLC).. Material eluting from the column is irradiated with a high flux of UV light, which may induce a reaction to form fluorescent or highly UV-absorbing products. The irradiated eluent then passes into a suitable detector. The photochemical reactor as a neglible effect on resolution, and reaction is achieved in 1-5 sec. An example of the use of this technique is in the detection of cannabinol CBN), a component of cannabis, which is converted into a highly fluorescent compound on irradiation with UV light. Thus, if a sample containing CBN is chromatographed and the column eluent irradiated, CBN can be detected (as the fluorescent photoproduct) with a sensitivity of less than 1 ng. If the chromatogram is then repeated without UV irradiation, only naturally fluorescent products are detected. A compairson of the two chromatograms allows these to be eliminated and leads to a very high specificity for the method. This approach is being developed as the basis of a rapid, sensitive and specific method for the detection of cannabinoids in body fluids. It is expected, however, that photochemical derivatization will extend the use of HPLC to many substances that cannot be satisfactorily detected at present.