Preparation and evaluation of open tubular C18-silica monolithic microcartridges for preconcentration of peptides by on-line solid phase extraction capillary electrophoresis.

In this study, C18-silica monoliths were synthesized as a porous layer in open tubular capillary columns, to be cut later into microcartridges for the analysis of neuropeptides by on-line solid-phase extraction capillary electrophoresis with UV and MS detection (SPE-CE-UV and SPE-CE-MS). First, several types of C18-silica monolithic (MtC18) microcartridges were used to analyse standard solutions of five neuropeptides (i.e. dynorphin A (1-7), substance P (7-11), endomorphin 1, methionine enkephalin and [Ala]-methionine enkephalin). The MtC18 sorbents were especially selective against endomorphin 1 and substance P (7-11)). The best results in terms of sensitivity and inter-microcartridge reproducibility were achieved with the microcartridges obtained from a 10-cm open tubular capillary column with a thin monolithic coating with large through-pores (1-5μm). Run-to-run repeatability, microcartridge durability, linearity ranges and LODs were studied by MtC18-SPE-CE-MS. As expected due to their greater selectivity, the best LOD enhancement was obtained for End1 and SP (7-11) (50 times with regard to CE-MS). Finally, the suitability of the methodology for analysing biological fluids was tested with plasma samples spiked with End1 and SP (7-11). Results obtained were promising because both neuropeptides could be detected at 0.05μgmL(-1), which was almost the same concentration level as for the standard solutions (0.01μgmL(-1)).