Abstract
A coaxial geometry liquid microjunction surface sampling probe (LMJ-SSP) enables direct extraction
of analytes from surfaces for subsequent analysis by techniques like mass spectrometry. Solution
dynamics at the probe-to-sample surface interface in the LMJ-SSP has been suspected to influence
sampling efficiency and dispersion but has not been rigorously investigated. The effect on flow
dynamics and analyte transport to the mass spectrometer caused by coaxial retraction of the inner and outer capillaries from each other and the surface during sampling with a LMJ-SSP was investigated using computational fluid dynamics and experimentation. A transparent LMJ-SSP was constructed to provide the means for visual observation of the dynamics of the surface sampling process. Visual observation, computational fluid dynamics (CFD) analysis, and experimental results revealed that inner capillary axial retraction from the flush position relative to the outer capillary transitioned the probe from a continuous sampling and injection mode through an intermediate regime to sample plug formationmode caused by eddy currents at the sampling end of the probe. The potential for analytical implementation of these newly discovered probe operational modes is discussed.
