GC-MS

Content
1. What is GC-MS?
2. Application of GC-MS
3. GC-MS working principle
4. Advantages of using GC-MS
5. Composition of GC-MS
6. Types of GC-MS
7. GC-MS specifications and features
8. How to maintain GC-MS?
9. How to order GC-MS?

The full name of GC-MS is gas chromatography-mass spectrometry, which is an instrument that combines gas chromatography and mass spectrometer.
While mass spectrometry can perform effective qualitative analysis, it is powerless for the analysis of complex organic compounds, while chromatography is an effective separation and analysis method for organic compounds and is particularly suitable for performing quantitative analysis of organic compounds, but qualitative analysis is more difficult. Therefore, the effective combination of these two will certainly provide chemists and biochemists with an efficient tool for performing qualitative and quantitative analysis of complex organic compounds.

GC-MS is widely used for the separation and identification of complex components. With the high resolution of GC and the high sensitivity of mass spectrometry, they are effective tools for the characterization and quantification of drugs and metabolites in biological samples. The basic components of a mass spectrometer are: ion source, mass filter and detector, which are placed in the vacuum master tube. Interface: The sample from the GC enters the mass spectrometer through the interface, which is the key to the gas-mass spectrometry system.

Gas chromatography-mass spectrometry (GC-MS), referred to as gas-mass spectrometry, is a chromatography-mass spectrometry technique in which a gas chromatograph and a mass spectrometer are connected through an interface component, and gas chromatography is used as a means of sample separation and preparation, and mass spectrometry is used as an online detection means of gas chromatography for qualitative and quantitative analysis, complemented by a corresponding data collection and control system.

Gas chromatography technique is to use the difference of distribution coefficients of different compounds in the mobile phase (carrier gas) and stationary phase at a certain temperature to make different compounds flow out in the column successively according to time, to achieve the purpose of separation and analysis.

The mass spectrometry technique converts vaporized sample molecules into charged ions in a high vacuum ion source, which are ionized, induced, and focused into a mass analyzer, where they are separated by a mass-to-charge ratio (ratio of mass to charge, m/z) under the action of a magnetic or electric field, in time sequence or spatial location, and finally detected by an ion detector.

Using GC-MS has the following advantages,
Portable: As a fully self-contained field analyzer, it can operate for up to 2.5 hours on battery power, while the built-in gas cylinder can accommodate approximately 150 samples.
Reliable: The rugged design makes it as reliable as laboratory equipment when operating in harsh environmental conditions. Daily calibration and automatic performance checks provide reliable instrument performance and excellent reproducibility.
Fast: The instrument is ready for sample analysis within minutes from "cold start". Using a low thermal mass capillary column with a ramp rate of up to 2.5°C/s, the instrument can typically perform sample analysis in less than 5 minutes and up to 12 sample analyses per hour, providing a fast solution for field testing.
Easy to use: Using the color touch screen control panel, the entire process of sample injection and analysis can be completed by following the interactive interface prompts. Deconvolution analysis and qualitative analysis of target compounds can be performed through self-contained spectral library search. Experimental results are displayed directly on the screen, and its data analysis is simple and fast.

GC-MS is generally composed of the following parts: chromatograph, interface part, mass spectrometer analyzer and computer data processing system.

Gas chromatograph
The gas chromatograph mainly consists of 5 major systems: gas circuit system, sample injection system, separation system, temperature control system, and detection and recording system.
Carrier gas system: including gases source, gas purity, gas flow rate controls and measurements.To obtain pure and stable flow rate of carrier gas.
Injector system: including injector and gasification chamber. The injector is divided into gas injector and liquid injector, and the gasification chamber is a device for instantaneous gasification of liquid samples.
Separation system: It includes the column and the column temperature chamber and temperature control device. According to the difference of the distribution coefficient or adsorption coefficient of each component in the mobile phase and stationary phase, the components are separated in the column.
Temperature control system: control the temperature of the gasification chamber, the column box and the detector.
Detection and recording system: Includes detector, amplifier, recorder, or data processing unit, workstation (chromatogram). The concentration or mass of each component is converted into an electrical signal and recorded.

Interface section
Interface: The sample from the GC enters the mass spectrometer through the interface, which is the key to the chromatography-mass spectrometry system. It is generally divided into a direct interface (small-bore capillary column) and an open shunt interface (large-bore capillary column), which is used to remove the carrier gas from the GC section and transfer the components. There are two roles in GC-MS coupling:
a. Pressure matching - the vacuum of the mass spectrometry ion source is at 10-3 Pa, while the GC column outlet pressure is up to 105 Pa. The role of the interface is to make the two pressure matching.
b. Concentration of components - There is a large amount of carrier gas in the gas flowing out of the GC column, and the role of the interface is to exclude the carrier gas so that the measured material is concentrated and then enters the ion source.

MS mass spectrometry section
The basic components of a mass spectrometer are: ion source, mass filter, and detector.
Ion source: The role of the ion source is to accept the sample to produce ions. Commonly used ionization methods are: electron bombardment EI; chemical ionization CI.
Mass analyzer: Its role is to separate the ions generated in the ionization chamber by mass-to-charge ratio (m/z) size for mass spectrometry detection. Common mass analyzers are: quadrupole mass analyzer; sector mass analyzer; double-focus mass analyzer; ion trap detector.
Detector: The role of the detector is to convert the ion beam into an electrical signal and to amplify the signal, commonly used detectors are electron multipliers.

Features:
1. Quadrupole GC-MS adopts new single quadrupole method compatibility to increase lab throughput.
2. Can maximize the normal working hours and planned maintenance and drastically reduce or even avoid manual cleaning of ion sources.
3. Built-in intelligence to diagnose, monitor and simplify multi-functional operations, with an integrated touch screen and browser interface to improve analysis efficiency.

The following is about the care and maintenance of GC-MS,
The tightness of the instrument
GMS is a gas-operated system, so the tightness of the instrument is very important.
Column change: The capillary column into the mass spectrometer cavity is not of appropriate length, either too long or too short.
The gasket should be tight, too loose will have the potential leakage, too tight will crush the gasket, every time the column needs to be replaced with a new sealing gasket.
Pay attention to the tightness of the cavity after opening when cleaning the ion source.

Use and preservation of chromatographic columns
When using the chromatographic column, you should pay attention to the minimum and maximum temperatures indicated in the instruction manual, and not to exceed the upper temperature limit of the column, otherwise it will cause the loss of stationary solution, and may also cause contamination of the detector. To set the maximum allowable temperature, in case of artificial or unexplained sudden temperature rise, GC will automatically stop the temperature rise to protect the column. Oxygen, inorganic acids and bases and mineral acids can cause damage to the column fixative, and these substances should be prevented from entering the column.
After the column is dismantled, the ends of the column are usually inserted into the unused injection pad, or placed in a desiccator if it is only temporarily dismantled for a few days.　

Installation of the column
The chromatographic column should be installed in accordance with the instructions, and the cutting surface should be flat with special ceramic slices. Different sizes of capillary columns use different sizes of graphite gaskets, note that the graphite gaskets used to connect the inlet end and the mass spectrometry end are different, do not mix. The length of the capillary tube into the inlet end depends on the liner tube used, the instrument company provides a special comparison tool, similarly, the length of the capillary tube into the mass spectrometry end also need to use the special tool provided by the instrument company to compare. Do not tighten the column joint nut too much, too tight to crush the graphite ring but easy to cause gas leakage, generally hand-tighten and then tighten a quarter turn with a wrench can be. Before connecting to the mass spectrometer, let the end of the column be inserted into a small beaker with organic solvent to see if there is bubble overflow and the flow rate is comparable to the set value. It is strictly forbidden to bake the column at high temperature when no carrier gas is passed through, so as not to damage the column by oxidation loss of the stationary solution.

Ion source and pre-rod cleaning
Before cleaning, prepare the relevant tools and reagents, and then open the case, carefully unplug the cable connected to the ion source, loosen the screws, and remove the ion source. Remove the main quadrupole before taking the pre-pole, put it vertically on the dust-free paper, and then remove the pre-pole to be washed. Note that the entire process must be careful, the second to avoid dust into the cavity. Separate the ion source components, among all components of the ion source, the filament, circuit board, and black ceramic ring can not be cleaned. While the ion box and its support, three lenses, stainless steel heating block, and pre-pole need to be scrubbed with alumina, 600 purpose alumina powder with glycerin or deionized water into a paste, with a cotton swab dipped in scrubbing, focusing on scrubbing the inner surface of the above components, that is, the ion channel. Alumina scrubbing is completed, rinse with water, and then deionized water, methanol, acetone soak, ultrasonic cleaning, to dry after the combination of a good ion source, first installed pre-pole, quadrupole pole, and finally carefully installed back to the ion source, cover the chassis, cleaning is complete.

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