Direct liquid extraction based surface sampling, a technique previously demonstrated with continuous flow and autonomous pipette liquid microjunction surface sampling probes, has recently been implemented as a liquid extraction surface analysis (LESA) mode on a commercially available chip-based infusion nanoelectrospray ionization (nanoESI) system. In the present paper, the LESA mode was applied to the analysis of 96-well format custom-made solid-phase extraction (SPE) cards, with each well consisting of either a 1 or a 2 mm diameter monolithic hydrophobic stationary phase. These substrate wells were conditioned, loaded with either single or multi-component aqueous mixtures, and read out using the commercial nanoESI system coupled to a hybrid triple quadrupole/linear ion trap mass spectrometer or a linear ion trap mass spectrometer. The extraction conditions, including extraction/nanoESI solvent composition, volume, and dwell times, were optimized in the analysis of targeted compounds. Limit of detection and quantitation as well as analysis reproducibility figures of merit were measured. Calibration data was obtained for propranolol using a deuterated internal standard which demonstrated linearity and reproducibility. A 10× increase in signal and cleanup of micromolar angiotensin II from a concentrated salt solution was demonstrated. In addition, a multicomponent herbicide mixture at ppb concentration levels was analyzed using MS(3) spectra for compound identification in the presence of isobaric interferences.
Published in 2011 by John Wiley & Sons, Ltd.