The molecular weight, the purity, and the degree of substitution for several newly synthesized single-isomer, heptasulfated beta-cyclodextrin derivatives, heptakis-6-sulfato-beta-cyclodextrin, heptakis(2,3-diacetyl-6-sulfato)-beta-cyclodextrin, and heptakis(2,3-dimethyl-6-sulfato)-beta-cyclodextrin, were determined by electrospray ionization mass spectrometry and indirect UV detection capillary electrophoresis. The main fragmentation mechanism of these single-isomer, fully sulfated cyclodextrins involves dissociation of the sulfate groups. The extent of desulfation increases with the skimmer-collimator voltage bias and the number of charges on the electrospray ions. By reducing the skimmer-collimator voltage bias, the loss of sulfate groups could be reduced, though not completely eliminated, for the doubly charged molecular ions. Thus, ESI-MS can be used to confirm the degree of substitution for the most sulfated isomer, but not to determine the exact concentration distribution for the lower substituted isomers in a mixture.

The use of an electrostatic particle guide (EPG) for background reduction in a time-of-flight mass spectrometer is described. Operating with reverse polarity, the EPG deflects ions radially from the beam axis, separating the ionic and neutral components of the beam. Use of the deflection EPG in a synchronized pulsed mode with a barrier disk aligned in the center of the beam axis eliminates up to 80% of the spectral background in the molecular ion region of an insulin spectrum obtained by 252Cf-plasma desorption mass spectrometry. The background eliminated is due to the neutral products of metastable fragmentation and to uncorrelated events. Although peak intensities are reduced when the pulsed deflection EPG system is used, the reduction in background achieved is greater, resulting in an overall improvement in peak-to-background ratios of up to a factor of three. A new large-area stop detector designed for use with the pulsed deflection EPG is described. The new hybrid detector, which utilizes the combination of a large (75-mm active diameter) microchannel plate (MCP) and a scintillation detector, provides greater sensitivity for high-mass ions than a conventional MCP chevron detector.

Department of Chemistry, Texas A & M University, College Station, Texas, USA We present a new approach to substrate selection for californium-252 plasma desorption mass spectrometry ((252)Cf_PDMS) in which small volatile molecules that are water insoluble are used as matrices in place of the polymeric substrates used in previous studies. The desirable features of analyte adsorption are combined with the concept of using a volatile matrix to reduce the level of internal excitation of a desorbed analyte and to assist in ionization during the desorption process. Derivatives of anthracene were found to meet these requirements and to perform satisfactorily as substrates in (252)Cf-PDMS. Spectra were obtained for bovine insulin (m I z 5734) adsorbed onto 9-anthroic acid and 2-aminoanthracene and compared with spectra using a nitrocellulose substrate. Sharper peaks and lower backgrounds are observed when the 9-anthroic acid matrix is used, indicating reduced levels of internal excitation and initial kinetic energy for the desorbed molecular ion of insulin. A comparison of the performance of 9-anthroic acid and 2-aminoanthracene shows the influence of substrate functional groups on desorbed protein yields. Finally, the versatility of the small-molecule matrix concept is discussed with respect to selection of a range of functionality, solubility, and hydrophilicity.

A new approach to electrostatic ion deflection is described where an electrostatic particle guide (EPG) operating with reversed polarity is used to deflect ions in a cylindrical geometry about the axis of a time-of-flight mass spectrometer. The method has advantages over the standard parallel-plate deflector geometry in that it is more effective in deflecting ion beams that have a significant radial velocity component. The device is being used in 252cs Cf plasma desorption mass spectrometry (252cs Cf -PDMS) experiments in an on/off mode to record neutral particle spectra and in a synchronized pulsed mode to reduce the magnitude of the uncorrelated background in the time-of-flight spectrum. Radial distribution functions have been measured for various EPG voltages. Its use as a background suppression technique is demonstrated by using the 252cs Cf-PDMS spectrum of insulin. (28-36)