Effect of surface tension of the matrix on fast-atom bombardment mass spectral determination of ethylenediaminetetraacetic acid

Abstract

The importance of the influence of surface activity on the mass spectra obtained from particle bombardment of liquid surfaces has long been known. In this work the fast-atom bombardment (FAB) mass spectral determination of ethylenediaminetetraacetic acid (EDTA) in several liquid matrices is investigated. Differences in the relative molar response observed for glycerol, thioglycerol and triethanolamine are discussed in terms of the surface tension of these liquids. The surface tensions of the pure liquid matrices and the EDTA solutions have been determined at 25 and 70 °C using the axisymmetric drop-shape analysis profile (ADSAP) technique. EDTA solutions have a higher surface tension than the corresponding pure liquid matrices, indicating that EDTA molecules are concentrated mainly in the bulk. Furthermore, the order observed for the intensity of the ion signal obtained with the three matrices, glycerol > thioglycerol > triethanolamine, follows the order of the surface tension which is maximum for glycerol and minimum for triethanolamine. We conclude that the surface concentration of EDTA is at a maximum in the liquid matrix with the highest surface tension, yielding an optimized mass spectrum.