Program Development
Two programs that are used as tools for the generation of new mass spectrometric methods are described below. These programs, along with auxiliary programs, provide much flexibility in the developmental process.
Two general approaches are taken, and either approach can accept LoRes or HiRes data. The choice is made during the process of setting up the analytical method. One approach utilizes peak analysis, in which the intensities of molecular ions are divided by sensitivities to give quantitative results for the components present in a mixture. The results are normalized to 100 percent. This approach can be applied to spectra obtained from experiments with low voltage ionization, field ionization, field desorption, chemical ionization and fast atom bombardment ionization.
Program HRPKAN, along with auxiliary programs, is used to set up a peak analysis method. First a table of sensitivities is generated for the molecular ions selected. For FI data, all sensitivities can be assumed to be unity (1.000) as long as the isotopic composition is taken into account. For low voltage data, a table of "theoretical" LV sensitivities can be calculated, although directly measured experimental values are to be preferred.
The second, more classical approach, utilizes type analysis, in which the sums of the intensities of group characteristic ions are used as input to a set of linear equations that are solved by matrix inversion. Data are generated by electron ionization.
Program HCGT is used to set up a new type analysis method. It uses the traditional matrix inversion process and can handle any matrix from 2x2 up to 40x40. Auxiliary programs are used to prepare the matrices and to assemble the reference files needed for a HiRes or LoRes type analysis. HCGT has been used to emulate HC22 (22x22 matrix), D2786 (8x8 matrix), and D2789 (6x6 matrix). The emulated programs yield results that are almost identical to those obtained from the original methods. HCGT has also been used to set up the Bouquet and Brument method based on a 33x33 matrix. See reference below. As might be expected, generating a table of off-diagonal matrix elements is the difficult part, but the auxiliary programs help with this process.
Method development for a type analysis can be a long process, but the programs provided by PCMASPEC greatly simplify the operation, as well as supply guidance for those who might not have the experience of creating a type analysis method. Because HCGT is a flexible and still growing program, interaction and feedback are expected from users interested in generating new chemical analyses by mass spectrometry.
Reference
Bouquet, M.; Brument, J. Characterization of Heavy Hydrocarbon Cuts by Mass Spectrometry. Routine and Quantitative Measurements. Petroleum Science and Technology. 1990, 8, 961-986.