Use of a time averaging computer for high resolution field desorption mass spectrometry

Field desorption mass spectra often contain few peaks, the largest of which are [M]+. and [M+H]+ ions. Because of this lack of fragmentation accurate mass measurement is of primary concern in field desorption mass spectrometry. Although total ion yield per quantity of sample may rival electron impact or chemical ionization methods, ion yield per unit time is low. For this reason and because of varying [M]+./[M+H]+ ratios, elemental compositions as determined from stable isotope peaks are difficult to obtain. Low ion yield per unit time demands an integrating method for best high resolution results. The use of photoplates to obtain high resolution field desorption data is the only method reported thus far which takes advantage of integrating capability. This paper describes the use of a time averaging computer as an integrator for peak matching high resolution field desorption mass spectrometry using electrical detection. Accuracies better than 20 ppm are consistently obtained. Due to the sensitivity of the technique a wider range of reference compounds can be employed. This method incorporates the advantages of integrating capability with electrical detection, overcoming detection sensitivity problems associated with photoplates.