Improved instrumentation for time-resolved mass spectrometry with application to laser-vaporization of solid materials

Abstract

With the exception of two or three commercially available pulse amplifiers, the techniques described here require no equipment other than the basic time-of-flight mass spectrometer (including a dual time base oscilloscope) and camera to gather time-resolved mass spectra in a concise form on Polaroid prints. Not even the amplifiers are needed for the simultaneous recording of up to six mass peak intensities during transient events. Results from time resolving spectra obtained from the combined laser and TOF mass spectrometer have demonstrated that thermally-produced free radicals and ions can be readily identified and, in many cases, their relative concentrations fairly accurately measured. Results have further shown that the common method of recording spectra from flash-heated samples (by photographing the spectral pattern on the monitor oscilloscope for exposures ranging up to several tenths of a second) will seriously discriminate against short-lived species or condensibles when in the presence of non-condensible gases. This occurs because several hundred milliseconds are required for the non-condensibles to be completely pumped out of the ion source, but the condensibles are often removed from the ionizing region in about one millisecond.