Salt Removal from Microliter Sample Volumes by Multiple Phase Microelectromembrane Extractions Across Free Liquid Membranes.

Abstract

A new concept for rapid and efficient salt removal from minute volumes of saline samples is presented by using multiple phase microelectromembrane extraction (μ-EME). A disposable μ-EME unit is filled with five consecutive plugs of immiscible aqueous and organic solutions; the aqueous sample forms the central phase and is encompassed by two free liquid membranes (FLMs) and two extraction solutions. Salt cations and anions migrate in opposite directions from the sample solution on application of 300 V dc electric potential, cross the neighboring FLM, and are transferred to the corresponding extraction solution. At the same time, the two FLMs selectively eliminate μ-EME transfers of target analytes, which are retained in the sample, and the resulting salt-free sample is then used for subsequent analysis. At optimized conditions (FLMs consisted of 1-pentanol and extraction solutions of deionized water and 100 mM NH4OH), more than 99.3% NaCl was removed from samples containing physiological NaCl concentrations. Simultaneously, more than 95% of model biochemical species (human serum albumin, neurotensin, creatinine, glycine, and alanine) were retained in the samples for subsequent analyses. Good quality capillary electrophoresis with capacitively coupled contactless conductivity detection (CE-C4D) electropherograms and interference-free electrospray ionization mass spectrometry (ESI-MS) spectra of selected biochemical species were obtained after μ-EME salt removal from samples containing micromolar concentrations of the target analytes and 150 mM of NaCl.