Mass spectrometry: Sensitivity of MALDI

Sensitivity of MALDI depends on sample preparation and the preparation of sample/matrix layer. They must be optimized by trial and error according to sample size, type, and previous history. Preparing a very thin matrix layer and applying of sample so that the sample is on the outer layer of matrix, give a sensitivity level of low attomole (10^-18). This method makes it possible for “…removal of salts present in the analyte solution by a sample washing procedure away from the sample very simply” (4). Small matrix spots using nanoliter volumes of matrix and analyte solution, combined purification, concentration, and application procedures have also given similar sensitivities (5). In this method, matrix is adsorbed to nanoliter bed volume reversed-phase column prepared in an Eppendorf GeLoder tip. Then the column is washed and the sample is eluted with a few nanoliter volume of matrix onto the target plate.

Sensitivity is reduced with increasing molecular weight. The sensitivity is two to three magnitudes lower for proteins than it is for peptides. So the sensitivity of proteins is in the femtomole range.