| dc.description.abstract | The preparation of thin uniform films of biomolecules has been a frequently encountered problem in chemical analysis techniques such as charged particle activation analysis, photoelectron spectroscopy, and with the recently developed technique of ²⁵²Cf plasma desorption mass spectrometry. Techniques such as vacuum evaporation from a heated filament and electrodeposition (1) which have been used to prepare thin films (<10 μg/cm²) of inorganic compounds are generally not applicable for use with biomolecules (e.g., peptides, nucleotides, steroids, vitamins). The major problems are related to the thermal instability of these molecules and the requirement that any technique used to prepare a thin film must not alter the chemical identity of the molecule. Gentle methods such as deposition of a solution on a solid surface by solvent evaporation produce films that are aggregated and non-uniform. A method has been reported for the preparation of thin films using a specially designed nebulizer to produce a condensable finely dispersed mist of the solute without decomposition (2). However, films prepared by this method are also non-uniform, thick (10-1000 μg/cm²) and require relatively large amounts of material.
With the development of the Cf-252 plasma desorption mass spectrometer (3), a better method was required for the rapid preparation of thin (<4 μg/cm²), uniform targets of small quantities of fragile biomolecules over an area less than 0.75 cm². The requirements of the method were that it had to retain the chemical identity of the sample, be non-fractionating when used with mixtures, non-contaminating, reproducible, and generally applicable to a wide range of molecules.
Carswell and Milstead developed a method which is called electrospraying for preparing thin radioactive sources (4), utilizing a phenomenon first observed by Zeleny (5). The method was modified (6,7,8) and has been used by Nawab and Mason to prepare highly uniform emulsions of water and oil (9). The purpose of this paper is to report our results on the adaptation of this method for preparing thin uniform films of biomolecules and to show that this method satisfactorily meets the criteria we had established as necessary for preparing samples for ²⁵²Cf plasma desorption mass spectrometry. | en |
