Optosensor for cinchona alkaloids with C18 silica gel as a substrate

A flow-through optosensor for cinchona alkaloids with C18 silica gel as a substrate is proposed. The sensor is developed in conjunction with a flow-injection analysis system and is based on the retention of the cinchona alkaloids on a C18 column and the enhancement of their fluorescence. The analytical performance characteristics of the proposed sensor for the detection and quantification of these alkaloids were as follows: the detection limits of quinine, cinchonine, quinidine and cinchonidine were 2.3, 31.6, 2.3 and 31.6 ng ml-1, respectively, with relative standard deviations of 0.9% for quinine and quinidine (20 ng ml-1, n = 7) and 1.1% for cinchonine and cinchonidine (4.0 micrograms ml-1, n =7), respectively. Most of the common species did not interfere. The recommended method has been successfully tested for determination of quinine in pharmaceutical preparations and soft drinks.