A sheath flow cell-based laser induced fluorescence detection system with pre-imaging spatial filtering for reduced dimension separation techniques

The construction, performance, and practical implementation of a rugged dev ice for laser induced fluorescence (LIF) detection in capillary electrophor esis (CE) and liquid chromatography (LC) techniques is described. This devi ce is based on a sheath flow cell (SFC) arrangement with attributes that in clude ruggedness, simplicity, ease of use, low cost, intra-day reproducibil ity, and small size. With this design, a pre-imaging mode of spatial filter ing is employed to effectively reduce the contributions of both wall scatte r and wall fluorescence to the background signal levels. A comparison of th e pre-imaging spatial filtering and traditional methods of far-field spatia l filtering is performed. This SFC system has been designed specifically fo r use in the UV spectral region, which can be very advantageous since it br oadens the scope of the possible applications of LIF; however, fluorescence of the flow cell walls is particularly problematic in the UV region. The e ffect of flow cell geometry, slit widths, and detector position on fluoresc ent background levels are shown. The device has been applied to the fluores cence detection of three dansyl amino acids for both CE and capillary LC te chniques. Efficiencies on the order of >10(5) plates/meter and 10(4) plates /meter are shown for CE and capillary LC techniques respectively. A compari son is made with CE between on-column and post-column detection demonstrati ng the latter preserves the integrity of a chromatographic separation.