EFFECT OF SURFACE-TENSION OF THE MATRIX ON FAST-ATOM-BOMBARDMENT MASS-SPECTRAL DETERMINATION OF ETHYLENEDIAMINETETRAACETIC ACID

The importance of the influence of surface activity on the mass spectr a obtained from particle bombardment of liquid surfaces has long been known. In this work the fast-atom bombardment (FAB) mass spectral dete rmination of ethylenediaminetetraacetic acid (EDTA) in several liquid matrices is investigated. Differences in the relative molar response o bserved for glycerol, thioglycerol and triethanolamine are discussed i n terms of the surface tension of these liquids. The surface tensions of the pure liquid matrices and the EDTA solutions have been determine d at 25 and 70 degrees C using the axisymmetric drop-shape analysis pr ofile (ADSAP) technique. EDTA solutions have a higher surface tension than the corresponding pure liquid matrices, indicating that EDTA mole cules are concentrated mainly in the bulk. Furthermore, the order obse rved for the intensity of the ion signal obtained with the three matri ces, glycerol > thioglycerol > triethanolamine, follows the order of t he surface tension which is maximum for glycerol and minimum for triet hanolamine. We conclude that the surface concentration of EDTA is at a maximum in the liquid matrix with the highest surface tension, yieldi ng an optimized mass spectrum.