Indirect UV detection of non-ionic substances in liquid chromatography by addition of a UV-absorbing uncharged compound to the mobile phase

Abstract

Chromatographic systems have been developed, which allow the detection and quantitation of non-ionic substances with low or no UV-absorptive properties. The detector response is obtained by using mobile phases containing an uncharged component with high UV-absorbance. Polar or non-polar bonded stationary phases have been selected, depending on the hydrophobic character of the analytes. The response pattern is compared to that observed in ion-pair reversed-phase systems with a UV-absorbing ion in the eluent. The influence on retention and detection sensitivity of the nature and concentration of the UV-absorbing compound and of the organic modifier added to the mobile phase has been studied. Principles for the optimisation of the response by changing the mobile phase composition are given. The wide application scope of the indirect UV-detection technique in non-ionic systems is demonstrated by examples of separations of various kinds of compounds, such as organic solvents, carbohydrates and polyols.