Since the end of 2015, we are be able to offer a better service. The MAT 711, built in the seventies of the previous century by the company Varian MAT retired after more than forty years of service. With access to a modern instrument, an Autospec Premier (waters Co.), we can offer not only EI, but CI and FI/FD. FI/FD are realized by the possibility to change the ion source to a LIFDI source (Linden CMS). Also, analyte mixtures can be separated by gas chromatography prior to analysis by mass spectrometry.
When EI (Electron Impact) is used for ionization, the mass spectra often show the M•+ radical cation. This is usually accompanied by characteristic fragment ions with even or odd numbers of electrons which can be used to derive conclusions regarding the structure of the analyzed molecule. Some analytes might form stable radical anions, which suggests acquisition of negatively charged species as well. The analytes should be volatile enough for vaporization before ionization (boiling point/point of sublimation below 350°C in vacuum).
Using CI (chemical ionization), often the protonated, closed shell ions ([M+H]+) are formed, especially when a bath gas like methane is used. The ionization is softer than with EI, but usually fragment ions are detected as well. In addition to that, an increased chemical noise coming from bath gas and bath gas adducts can be found. Like in EI, the analytes have to be volatile enough, i.e. the boiling point/point of sublimation is below 350°C in vacuum. The measurement of negatively charged ions is possible as well.
FI and LIFDI
After some time to become familiar with this new possibility, we will be able to offer FI (field ionization) and a special form of FD (field desorption), LIFDI. The required alternative ion source is produced by Linden CMS. The special sample introduction is very interesting for (metal-)organic compounds which are labile to oxygen and/or humidity. Typically, the M•+ radical cations are formed like in EI. Although is much softer when compared to EI and CI, fragment ions may also be detected. Nevertheless, analysis of labile compounds is possible. Another interesting fact is that the volatility of the analytes is not as important as for EI and CI.
Common remarks to the instrument
Standard measurements are performed with low resolution (R approx. 1000). To achieve good results and to prevent damage to the instrument it is generally necessary to submit solid or liquid or solid pure compounds with sufficient volatility (see above). For measurements of this kind, only the first digit is significant.
High resolution (up to R = 80.000) measurements are possible, but more complex and time-consuming. Due to loss of sensitivity, a sufficient intensity of the ion of interest is necessary. Also, the mass range fo high resolution measurements is limited to approx. one decade. The mass accuracy typically is better than 5 ppm.
Coupling to GC
If analyte mixtures with sufficient volatility are provided, coupling to GC is possible as well (precondition: the sample has to vaporize completely at 300°C or lower temperature, low boiling solvents like e.g. hexane or ethyl acetate have to be used, solutions with water or high boiling solvents cannot be analyzed to prevent the instrument from being destroyed).
Who can use the instrument?
Due to complexity of the instrument, most measurements are carried out by the service personnel. When doing a longer research project with mass spectrometry on this instrument as a major topic, independent measurements are possible as well - but only after successfully completing a special training.