Mass spectrometry instrument and sample selection method

Mass spectrometry is widely used in modern development in areas such as organic chemistry, biochemistry, drug metabolism, clinical, toxicology, pesticides, environmental protection, petrochemistry, geochemistry, food chemistry, plant chemistry, cosmochemistry, and defense chemistry. In protein analysis and identification and other experiments have a non-negligible role.

Mass spectrometry

There are many kinds of mass spectrometers, and the working principle and application range are also very different. From the application point of view, the mass spectrometer can be divided into the following categories:

Organic mass spectrometer : Due to different application characteristics, it is divided into:

1 Gas chromatography-mass spectrometry (GC-MS) In this type of instrument, because of the different working principle of the mass spectrometer, there are gas chromatography-quadrupole spectrometer, gas chromatography-time of flight mass spectrometer, gas chromatography-ion trap mass spectrometry. Instrument and so on.

2 Liquid chromatography-mass spectrometry (LC-MS) Also, there are liquid chromatography - quadrupole mass spectrometer, liquid chromatography - ion trap mass spectrometer, liquid chromatography - time of flight mass spectrometry, and various Liquid chromatography-mass spectrometry-mass spectrometry.

3Other organic mass spectrometers, mainly include matrix-assisted laser desorption time-of-flight mass spectrometry (MALDI-TOFMS) and Fourier transform mass spectrometry (FT-MS).

Inorganic mass spectrometers , including:

1 spark source double focus mass spectrometer.

2 inductively coupled plasma mass spectrometry (ICP-MS).

3 Secondary Ion Mass Spectrometry (SIMS)

However, the above classification is not very strict. Because some instruments have different accessories, they have different functions. For example, a gas chromatograph-double-focus mass spectrometer, if switched to a fast atom bombardment ionization source, is no longer a gas chromatograph-mass spectrometer but a fast atom bombardment mass spectrometer (FABMS). In addition, some mass spectrometers can be connected to gas chromatography and liquid chromatography, so they are not good to a certain class. Among the above types of mass spectrometers, the largest number and the most widely used are organic mass spectrometers.

In addition to the above classifications, the mass spectrometers can also be classified as dual focusing mass spectrometers, quadrupole mass spectrometers, time-of-flight mass spectrometers, ion trap mass spectrometers, Fourier transform mass spectrometers, and the like, from the mass analyzers used in the mass spectrometer.

Mass spectrometer selection tips

There are many kinds of mass spectrometers, and the characteristics of different instruments are also different. Generally speaking, GC-MS can be used for the analysis of samples that can be vaporized around 300C. Since GC-MS uses EI sources, many mass spectrometry information can be obtained. Library search. Capillary column separation is also good. If it cannot be vaporized at around 300°C, LC-MS analysis is required. At this time, molecular weight information is mainly obtained. If it is tandem mass spectrometry, some structural information can also be obtained. If it is a biological macromolecule, it is mainly analyzed by LC-MS and MALDI-TOF, and the molecular weight information is mainly obtained. For protein samples, the amino ACID sequence can also be determined. The resolution of the mass spectrometer is an important technical indicator. High-resolution mass spectrometers can provide compound compositions, which is very important for structural determination. Dual-focus mass spectrometers, Fourier transform mass spectrometers, and time-of-flight mass spectrometers with reflectors all have high-resolution capabilities.

Sample selection in mass spectrometry

Mass spectrometry has certain requirements for the sample. The sample to be analyzed by GC-MS should be organic solution. The organic matter in the aqueous solution can generally not be measured, and it must be extracted and separated into organic solution, or the headspace sampling technique should be used. Some compounds are too polar and easily decompose in the heating process, such as organic acid compounds. At this point, esterification can be carried out. The acid is converted into an ester and then analyzed by GC-MS. From the analysis results, the structure of the acid can be inferred. If the sample cannot be vaporized and cannot be esterified, LC-MS analysis can only be performed. The sample for LC-MS analysis is preferably an aqueous solution or a methanol solution. The LC mobile phase should not contain non-volatile salts. For polar samples, the ESI source is typically used, and for non-polar samples, the APCI source is used.