GC-MS measurements

Theoretical principles:

Mass spectrometry is a method for determining molar masses and characteristic structural elements in organic chemistry. The substance is first evaporated in a high vacuum and ionized in an ion source. The ionized molecules and additionally formed fragments are accelerated in an electric field and bundled into a beam. In a magnetic field, the ions are deflected onto circular paths, the radius of which depends on their mass/charge ratio, and thus separated. They are then registered in a detection device according to mass and frequency. The ionization of the molecules usually takes place by electron impact (EI), whereby molecular ions (radical cations) are formed.

In addition to electron impact ionization ("EI-MS"), chemical ionization ("CI-MS") is also used, for example. Here, the ions are generated by chemical reactions in the gas phase. A "reaction gas" (noble gases, methane or another alkane) is used, which is ionized by electron impact. The resulting ions can react directly with the molecules of the sample to be examined and ionize them by charge exchange; however, it is also possible that the ions formed from the reaction gas first change further and form more reactive ions, which then ionize the sample molecules by transferring a proton. Methane as a reaction gas, for example, mainly supplies the ion ^CH5+ as a reactive ion. Fragmentation (fragments formed) is lower with this method than with direct ionization.

Measurements can be made using the DEP or DIP method. With the DEP method, the sample is dissolved in an easily vaporizable solvent. A small "wire loop" on the DEP rod is immersed in the solution and the sample is then evaporated in a high vacuum.

The DIP method can also be used to measure non-soluble samples. For this purpose, a small amount of the substance is placed in a small glass tube and evaporated from this in a high vacuum.

Information on sample delivery:

In routine operation, measurements are made using the DEP method. For this purpose, please make an exact weighing (approx. 1-2 mg) into a glass with a large opening. The solvent must also be specified (preferably EA, DCM or acetone), as the dilutions are carried out by the measuring personnel.

Mass range: 50-2000 amu

Order forms for the MS measurements are available here.