Analysis of non-volatile compounds by off-line LC/MS.

Abstract

Polar and non-volatile pharmaceutical substances were analyzed by off-line LC/MS. Cisplatin in rat plasma was derivatized to a Pt(II)-DDTC chelate by reaction with sodium diethyldithiocarbamate(DDTC). VK₃-2, 3-epoxide, active metabolite of VK₃, was reacted with 2-mercaptoethane sulfonic acid sodium salt(MESNA) and a VK₃-MESNA adduct was obtained. quantitatively. These samples were separated by reversed phase paired ion HPLC using phosphate buffer and acetonitrile. The objective peaks were collected into a reversed phase mini-column(C8) cartridge containing 500 to 750 μl of water by means of a pressured, tight valve with low dead volume (5μl).After discarding most of the inner solvent by connecting to a vacuum line, 200μl of acetonitrile was added to achieve the elution. The eluent was dropped onto a modified sample holder, and acetonitrile was evaporated under nitrogen flow. After addition of matrix(glycerol or m-nitrobenzylalcohol) to the holder, molecular SIMS was conducted to each measurement. The total recoveries were achieved to 60%. On the otherhand, PGE₂ was able to be determined by field desorption MS without any special pretreatment i. e. PGE₂ was separated by reversed phase micro-LC using phosphoric acid solution as a mobile phase, and the corresponding peak was trapped in a microsyringe (10 μl). The trapped sample was transferred to the silicone emitter. The present method makes it possible to remove interfering substances which cause trouble in on-line LC/MS, and are recognized to be not only simple but also efficient methods without employing any expensive apparatus.