TOTAL YIELD MEASUREMENTS IN MATRIX-ASSISTED LASER-DESORPTION USING A QUARTZ-CRYSTAL MICROBALANCE

A quartz crystal microbalance (QCM) is employed to determine the desor ption yield of neutral particles in matrix-assisted laser desorption i onization. For ferulic acid, the matrix substance used, the QCM mass r esolution of 1 ng corresponds to a detection limit of almost-equal-to 10(12) particles. Sample exposure effects are studied at different flu ences by measuring the total desorption yield after consecutive laser pulses fired on the same spot on the sample. The dependence of the tot al yield on the fluence is studied for different angles of incidence o f the laser beam. Varying the distance between the QCM and the sample yields information about the angular spread of the desorbed neutral pa rticles. Additional information about the fluence threshold for the pr oduction of charged particles is gained by direct electronic measureme nts of sample charging.