We have shown that 252Cf-PDMS is capable of producing mass spectra of quasi-molecular ions for a wide variety of compounds, including amino acids, moderately large peptides, nucleotides, and natural products. Positive and negative ion mass spectra can be obtained, and in many cases quasi-molecular ions are observed in both. The method is nondestructive, as only a relatively few molecules are used and samples can be recovered after the measurement is made. Fragmentation patterns are obtained which can yield structure information. The present sensitivity of the method is at the nanogram level and there are possibilities for reducing this to picograms. The mass resolution is sufficient to give elemental identification up to mass 500. This may be extended to higher masses with improved time-of-flight techniques. There are indications that 252Cf-PDMS may extend the mass range of molecules that can be studied to as high as 3000 or more.

An electrospray system and procedure has been developed for the routine preparation of thin films of involatile molecules for analytical measurements. An anode-cathode design has been developed and conditions for reproducible performance have been established. Solvent systems for polar and nonpolar molecules have been investigated and electron microscopy measurements have been made on the microstructure of the deposits and fraction of surface coverage. The method does not appear to degrade thermally-lablle molecules.The preparation of thin solid films of involatile molecules is a problem frequently encountered in analytical measurements that are sensitive to the nature of the sample surface. The problem is particularly important in "solid state" mass spectroscopy where ions are produced at the surface of a solid film and intensities depend on the fraction of the surface covered. This includes field desorption (1), 252Cf-plasma desorption mass spectrometry (PDMS) (2), secondary ion mass spectrometry (3), and laser desorption (4).Various techniques have been employed in the past for producing thin films on a solid backing. These include high

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