Use of a fritless dual tapered column and a low flow interface for capillary electrochromatography–mass spectrometry

To avoid problems associated with the use of sintered frits to retain packing material, tapered columns were investigated for use with capillary electrochromatography–mass spectrometry (CEC-MS) analysis. Taking the advantage that negatively charged stationary phase particles have a net velocity directed towards the buffer reservoir (inlet) over a wide range in pH, a fritless CEC column with a single taper tip was prepared for CEC-MS analysis. During CEC-MS analysis, the tapered end was immersed in the buffer reservoir and the unmodified end was pointed toward the ionization source. For better sensitivity, this single tapered CEC column was coupled to ESI/MS using a low flow sheath liquid interface. With this setup, occasional blockage of the ESI sprayer by stationary phase particles was observed. In addition, significant dead volume was observed because the unmodified tip could not be inserted into the very end of the sprayer of the low flow sheath liquid interface. To circumvent these problems, a dual tapered CEC column was prepared. This fritless dual tapered column CEC-MS approach alleviated the problems of frit, sprayer blockage and extensive dead volume.