6.4.2 Data analysis system
A quadrupole mass spectrometer provides a large amount of information within a short time which is ideal for displaying and storing on a PC. This is the reason why the electrical controls on Pfeiffer Vacuum mass spectrometers only have rudimentary control and display elements. QUADERA® software is used both for controlling purposes as well as to display, analyze and save data on a PC.
Pfeiffer Vacuum’s QUADERA® mass spectrometer software is a modular system for use with PrismaPlus and HiQuad devices. The PC can communicate with the mass spectrometers via Ethernet which means that the length of the cable between the spectrometer and computer is immaterial.
To perform certain measurement tasks, the PC transfers parameter records to the mass spectrometer in order to set the device. The data read out during or after the measurement is transferred to the computer, where it can be analyzed, displayed or stored.
Typical display formats are:
- Mass spectra with adjustable mass range, and linearly or logarithmically scaled axes for the concentration
- Trend display of the chronological sequence of partial pressures
- Bar graph to reduce the quantity of data
Typical measuring tasks, such as residual gas analysis or leak detection, are pre-programmed and can be launched with a mouse click.
If quantitative analysis is to be performed, the mass spectrometer must be calibrated beforehand. If this involves recurring processes, such as calibration with subsequent quantitative analysis, these processes can be programmed with VSTA (Visual Studio Tools for Applications). Programming skills are not required, as pre-engineered modules are available for this purpose.
To solve complicated measurement tasks, a library containing fragment ion distributions for several frequently occurring gases and compounds is available in the QUADERA® software. However these and other distributions obtained from spectra libraries can only be viewed as guideline values, as they are influenced by various parameters, such as ionization energy, temperature or the transmission characteristics of the mass analyzer.
In analyzing mixtures containing multiple gas components, the problem of overlapping ion currents of differing origin on the same mass numbers is one that frequently occurs. There are mass numbers whose intensity is produced exclusively by a single gas component (e. g. argon on mass number 40, oxygen on mass number 32, carbon dioxide on mass number 44 and water on mass number 18).
In the case of other mass numbers, the overall intensity of the detected ion current is governed by the overlapping of various concentrations of fragment ions from different gas components. Depending upon the composition and concentration ratios in the gas mixture to be analyzed, suitable algorithms and calibration procedures must also be formulated for the measurement task in question. Before carrying out quantitative gas analyses by applying suitable calibration gas mixtures that each have non-overlapping components, the calibration factors for each single gas component must be determined for all overlapping mass numbers. The concentration and/or partial pressure for these gases can then be determined by a matrix calculation. The QUADERA® mass spectrometer software performs the matrix calculation and provides the necessary gas-specific calibration routines.
