A means of monitoring biomolecule separations by mass spectrometry is described. The mixture to be separated is introduced into a first fluidic stream, which then passes through a chromatography column 103. Small samples are periodically taken from the first fluidic stream as it leaves the chromatography column and injected into a first branch of a second fluidic stream 212. Low molecular weight components detrimental to the efficient operation of the mass spectrometer are removed by an in-line dialysis cell 224. A second fraction of the second fluidic stream 214 acts as the dialysate. In a second and preferred system provided in accordance with the present teaching, the first fraction of the second fluidic stream is further split downstream of the sampling mechanism 215 through the use of a three-way connector 302. Approximately 0.3 to 5 microliters per minute continues through the dialysis cell and thereafter to the electrospray emitter 238 of the mass spectrometer. Desirably, the electrospray emitter 238, dialysis cell 224, and fluidic split 302 are provided as a demountable assembly 400. In a third embodiment of a system provided in accordance with the present teaching, the dialysate is provided separately as a third fluidic stream.
