Precautions for use of the hottest gas chromatogra

2022-07-28
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Precautions for the use of gas chromatograph

I. precautions for sample injection

do not hold the needle of the syringe or the parts with samples There should be no bubbles (the sample should be aspirated slowly and quickly, and then aspirated slowly. Repeat for several times. The volume of the metal needle of the 10ul syringe is 0.6ul, and no bubbles can be seen. Suck more UL. Move the needle tip of the syringe upward to the top of the bubbles, and then push the needle rod to eliminate the bubbles. (refers to the 10ul syringe, the syringe with a core feels flat). The sample injection speed should be fast (but not very fast). Keep the same speed for each injection, Start to inject the sample from the tip of the needle to the middle of the vaporization chamber

II. Install chromatographic column

1 The chromatographic column must be installed and disassembled under normal temperature

2. The filling column has ferrules. In addition to the service life of such missing teeth, there are other belt fracture life seals and gasket seals. There are three types of ferrules: metal ferrules, plastic ferrules and graphite ferrules, which are not easy to tighten during installation. Gasket type seal replace the chromatographic column with a new gasket each time (Shimadzu chromatography is sealed with 354 gaskets)

3. Whether the two ends of the chromatographic column are plugged with glass wool. Jinan new period assay instrument Co., Ltd. is a national enterprise producing experimental machines. Prevent the glass wool and filler from being blown into the detector by the carrier gas

4. The installation and insertion length of capillary chromatographic column shall be determined according to the instructions of the instrument. Different chromatographic vaporization chambers have different structures, so the insertion length is also different. It should be noted that if you use a capillary chromatographic column with no flow separation, and the vaporization chamber uses a packed column interface, the capillary column connected to the vaporization chamber can not probe too much, just slightly beyond the ferrule

III. Influence of the ratio of hydrogen to air on FID detector

the ratio of hydrogen to air should be 1:10. When the ratio of hydrogen to air is too large, the sensitivity of FID detector drops sharply. When other conditions remain the same when using the chromatography, check the gas flow velocity of hydrogen and air. There is a kind of gas between hydrogen and air. When it is insufficient to ignite, it will make a bang and then put out the fire. Generally, when you ignite, it will go out, and then it will be ignited and then it will go out again. This is the lack of hydrogen

IV. use TCD detector

1 When hydrogen is used as carrier gas, the tail gas must be discharged outdoors

2. Nitrogen as carrier gas bridge flow cannot be set too large, which is much smaller than that when hydrogen is used

3. Bridge flow cannot be supplied without carrier gas. Bridge flow shall be supplied after the instrument temperature is stable and before sampling

v. how to judge whether the FID detector is on fire

different instruments have different judgment methods. If there is a basic flow display, see the size of the basic flow. If there is no basic flow display, use a wrench with a polished surface to approach the detector outlet to observe whether there is water condensation on its surface

VI. how to judge whether the sealing gasket at the injection port should be replaced

it is particularly easy to inject samples. Regular small peaks appear on the recorder when the TCD detector does not inject samples, indicating that the sealing gasket should be replaced due to air leakage. Do not tighten the sealing gasket too tightly. Generally, it is replaced at normal temperature. It will be tighter when the temperature rises. Tightening the sealing gasket too tightly will cause difficulty in sample injection and often bend the syringe needle

VII. How to select the appropriate gasket

the gasket is divided into general gasket and high-temperature gasket. When the temperature of the vaporization chamber exceeds 300 ℃, the high-temperature gasket is used. One side of the high-temperature gasket has a layer of film, and the side with the film is facing down during use

VIII. How to prevent unremitting transformation is the strongest competitive advantage of the enterprise. Stop the sample injection needle from bending.

many novices in chromatographic analysis often bend the needle and syringe rod. The reason is:

1 The injection port is screwed too tight. It is screwed too tight at room temperature. When the temperature of the vaporization chamber rises, the silicone gasket will be more tight after expansion. At this time, it is difficult for the syringe to penetrate

2. The needle is stuck in the metal part of the injection port when the position is not found

3. The bending of the syringe rod is caused by too much force during sample injection. The imported chromatograph is equipped with an injector frame, and the syringe rod will not be bent by using the injector frame for sample injection

4. Because the inner wall of the syringe is polluted, the needle rod is pushed and bent during injection. When the syringe is used for a period of time, it will be found that there is a small black thing near the top of the needle tube. At this time, the sample aspirating injection feels difficult. Cleaning method: pull out the needle rod, inject a little water, insert the needle rod into the polluted position, push and pull repeatedly, and do not inject water again until the pollutants are removed. At this time, you will see that the water in the syringe becomes turbid. Pull out the needle rod, wipe it with filter paper, and then wash it with alcohol for several times. When the analyzed sample is a solid sample dissolved in solvent, wash the syringe with solvent in time after sample injection

5. Be sure to be steady during sample injection. If you are eager to be quick, the syringe will be bent. As long as you are skilled in sample injection, it will be fast

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