How to do a simple gas chromatography configuration

    If a user purchases a gas chromatograph and requires it to be used normally, in addition to the equipment that a conventional laboratory must have, such as a laboratory bench, glassware, gas source, standard substances, etc., the following parts are also required:

　　One source of energy

　　Second host

　　Three pillars

　　Four standard substances

　　5. Others (computers, printers, workstations, etc.)

　　So, how do you choose these parts for your users? In this and the next newsletter, we will introduce how to make a simple gas chromatography configuration for your customers.

　　This time, I will introduce the first two items (the selection of gas source and host)

　　One source of energy

　　The gas source of gas chromatography can be divided into four categories according to its use: carrier gas, combustion gas, auxiliary gas and driving gas.

　　Carrier gas: It passes through the entire analysis system and requires high purity and good quality. Generally speaking, we require customers to use gases from large manufacturers and good brands, and generally require cylinder gas, and it is best not to use a gas generator. Good carrier gas is the basis for ensuring that the analysis can proceed normally. Generally speaking, commonly used carrier gases are: nitrogen, hydrogen, argon, helium, etc.

　　Gas: Hydrogen is generally used, as long as it can be ignited normally and does not interfere with the analysis. Users can use high-purity cylinder gas or a hydrogen generator. If the budget is sufficient, it is best to use a hydrogen generator because it is safer.

　　Combustion-supporting gas: Generally, air is used, as long as it can support combustion and does not interfere with analysis. Users can use high-purity cylinder gas or an air generator.

　　Driving gas: usually air.

　　So when should we mix which gas?

　　When we provide gas sources to users, we generally consider the detectors :

　　FID: It needs to be equipped with carrier gas, fuel gas, and combustion-supporting gas. Generally speaking, it is equipped with nitrogen (high-purity cylinder gas, 40L, including pressure reducing valve), hydrogen (cylinder gas or hydrogen generator), and air (cylinder gas or air source).

　　TCD: carrier gas is required. Generally speaking, in order to improve sensitivity, we recommend that customers use hydrogen (high-purity cylinder gas) or helium (high-purity cylinder gas). However, if customers want to analyze hydrogen, we need to use argon, nitrogen or helium.

　　ECD: A carrier gas is required. Generally, nitrogen (high-purity cylinder gas).

　　FPD: Same as FID.

　　TSD: Same as FID.

　　When customers purchase an automatic valve, they need to match it with driving air. Generally speaking, either an air cylinder or an air source can be used.

　　Second host

　　The host is mainly equipped with two parts for the user: the injection system and the detection system.

　　Injection system: As the name implies, it is the place where the sample enters and is also the place used to vaporize the sample. The injection system that we often hear about includes the following parts: (1) capillary injection; (2) filling injection; (3) headspace injection; (4) thermal desorption injection; (5) valve injection. [page]

　　Capillary injector: Generally speaking, a common gas chromatograph will have at least one capillary injector or a packing injector. Therefore, when we configure for customers, we must provide at least one injector (capillary or packing). When the customer's analysis requires a capillary column, we provide the customer with a capillary injector; when the customer's analysis requires a packed column, we provide the customer with a packing injector. Our factory's instruments can be equipped with up to two capillary injectors or three packing injectors or packing/capillary injectors at the same time.

    Filling the syringe: See Capillary syringe above.

　　Headspace sampling: Headspace sampling, thermal analysis, and valve sampling are usually gas sampling technologies. They do not conflict with the injector, and are additionally provided by us based on the injector according to customer requirements. Headspace sampling is generally used for the determination of volatile components. In more than 90% of cases, the boiling point of the substance to be tested is below 120 degrees Celsius. The sample can be solid or liquid. Commonly used in: determination of ethanol in blood, determination of a volatile component in interior/interior decoration materials, determination of various solvent residues, etc.

　　Thermal analysis sampling: generally used to detect certain components in indoor/car air. Common analysis: TVOC.

　　Valve injection: Six-way valve injection is often used for gas injection. If the customer's sample is gaseous and has high precision requirements, valve injection is often used.

　　Detection system: It is a system that converts the collected substances into electrical signals that can be seen on the computer. There are five commonly used detectors for gas chromatography. We need to choose the appropriate detector based on the substances that the customer needs to detect.

　　TCD: It is a universal detector. It responds to all substances with different thermal conductivity coefficients from the carrier gas, but its sensitivity is not high. It can generally only detect substances with percentage content, and cannot detect trace substances at the ppm or ppb level. It is often used in the detection of permanent gases.

　　FID: Some people say it is a general purpose detector, while others say it is a special purpose detector. It responds to organic compounds, namely C/H compounds. It has a weaker response to compounds containing heteroatoms. It can generally detect at the ppm level. It is a detector with a very wide range of uses.

　　ECD: Electron Capture Detector. It is a special detector. It is extremely sensitive to highly electronegative substances. It is generally used to detect compounds containing elements such as fluorine, chlorine, bromine, iodine and oxygen. It can achieve ppb level detection. It is often used in the detection of organochlorine pesticide residues and chloroform and carbon tetrachloride.

　　FPD: It is a special detector. It has a significant response to sulfur and phosphorus compounds. The detection level is between ppm and ppb, and the sensitivity is average. It is often used in the detection of organophosphorus pesticide residues and hydrogen sulfide and sulfur dioxide.

　　TSD: Also called NPD, nitrogen phosphorus detector. It is a special detector. It can detect compounds containing nitrogen and phosphorus. It is relatively sensitive, with a detection level between ppm and ppb. It is not commonly used. It is more difficult to maintain.