A universal interface for continuous on-line liquid sample introduction directly to the time-of-flight mass spectrometer, which can further promote throughput and utility of MALDI-TOF MS, is disclosed. Preferably, the liquid sample includes a matrix, either solid or liquid, for use in matrix-assisted-laser-desorption-ionization, most particularly in a time-of-flight mass spectrometer which can further promote throughput and utility of MALDI-TOF MS. In the method of the invention, the same samples and matrices, both solid and liquid, can be used as in conventional MALDI. In practice of the method of the invention, a solution of sample containing, e.g., peptide and matrix is infused directly into the source chamber of a mass spectrometer at subatmospheric pressure, deposited on a moving sample holder, such as a rotating quartz wheel, and desorbed by, e.g., a nitrogen laser. The method of the invention is particularly amenable to multiplexing, the parallel deposition of multiple samples, e.g., from a capillary array or microchip channels, with subsequent sequential desorption with a scanning laser. This format is particularly useful for high throughput MS analysis. Also disclosed is an off-line deposition chamber and a general method of preparing a sample for analysis that results in the homogeneous deposition of small quantities of sample at improved reproducibility. This format of sample preparation is particularly useful with existing commercial mass spectrometers.