ORAL PRES.: The use of microbore, capillary and nano LC-MS/MS for the quantification of small molecules in microdialysates.

Combination of miniaturised LC with electrospray ionisation (ESI) tandem mass spectrometry (MS/MS) provides a highly sensitive technique for the analysis of low concentrated compounds in microdialysates (pM-nM range). Dialysates are complex mixtures of salts and endogenous compounds, so column switching is necessary for preconcentration and desalting. Oxcarbazepine and its active metabolite were used as test compounds to investigate the suitability of miniaturised LC-MS/MS for quantification of small molecules in dialysates.
Matrix effects were investigated by comparing the responses of standards made in water, Ringer's solution (salt solution used as perfusion fluid) and blank dialysate matrix. Column switching was not able to completely eliminate salt effects, but no difference in response between Ringer's solution and blank dialysate matrix were detected, at least for capillary and nano LC-MS/MS.
Consequently, calibration standards should be prepared with Ringer's solution instead of water for quantitative analysis of microdialysates.
A microbore, capillary and nano LC-ESI-MS/MS method were compared in terms of method feasibility, linearity, sensitivity, accuracy and precision.
Downscaling microbore to capillary and nano dimensions, resulted in a gain in sensitivity of 5 and 50, respectively. Miniaturised LC-MS/MS was found to be fit for quantification of small molecules in dialysates with acceptable accuracy and method precision.