When chromatographic analysis of unknown sample materials using a gas chromatograph, the operation problems often cause contamination of the inlet, liner, splitter plate or detector, which may affect the chromatographic analysis results. Excluded, Lu Chuang analytical chromatographic analysis engineers are summarized as follows after years of experience:
(1) Analysis of the causes There are many reasons for contamination of the inlet, liner and shunt plate or detector contamination, mainly in the following aspects:
1 chromatographic 伩 has not been regularly maintained for a long time;
2 analysis of the sample composition is complex, the inlet temperature is too low, the heavier components in the sample are retained in the inlet is not vaporized;
3 The vaporization chamber and the liner often accumulate certain sediments and high-boiling substances. If a high-boiling substance is analyzed for a certain time, the peak will escape when the temperature of the inlet rises;
4 The non-volatile matter accumulates slowly in the groove of the splitter plate and in the detector, and ghost peaks appear irregularly.
5 The inlet silicone pad is not resistant to high temperature and is injected during the temperature programming process. The appearance of such ghost peaks is also contingent or not, or large or small. In some Chinese medicine factories and chemical plants, when gas chromatography is used for raw material analysis, ghost peaks often appear. If the cause of the sample is excluded, it should first be considered whether it is caused by contamination of the injection and analysis system. Because the composition of traditional Chinese medicine and chemical raw materials is complicated, if the sample is rough in pretreatment, the instrument will be used for a long time. The inlet, liner and shunt plate and detector will be polluted, and the instrument should be maintained frequently.
(2) Exclusion method Clean the parts of the instrument according to the actual pollution situation:
1 cleaning of the inlet. Remove the column, in the case of heating and aeration, inject absolute ethanol or acetone from the inlet, repeat several times, and finally heat the aeration to dry the inlet.
2 Replace the liner or clean the liner. The contaminated liner can clearly see the deposition of particles or the darkness of the glass wool. If necessary, the liner can be replaced in time. Liner cleaning method: remove the glass wool, ultrasonically treat the liner in the acid solution, then wash with organic solvent and then dry.
3 split plate cleaning. It is placed in an organic solvent such as methanol, sonicated, dried, or washed with toluene first, then with methanol. Note that the split plate can not be directly touched by hand during the disassembly and installation process to prevent pollution.
4 detector cleaning.
Gas Chromatograph Thermal Conductivity Detector: Select the cleaning solvent according to the degree of contamination of the detector. Generally, it is first immersed and washed with high boiling point solvent, then repeatedly washed with low boiling point solvent, dried and loaded into a vessel, ventilated and heated to 150. c, it can be used normally after 4 hours.
Gas Chromatograph Hydrogen Flame Detector: When the contamination is not serious, the column can be removed, replaced with an empty column and connected to the detector, and the carrier gas is introduced, and the temperature of the detector rises to 150. C, first inject distilled water from the inlet, and then inject acetone to wash repeatedly. When the pollution is serious, the detector can be removed for cleaning. The collector, the positive electrode and the nozzle are removed in turn. If the nozzle is made of stainless steel or the like, the electrode can be carefully cleaned with fine sandpaper and then ultrasonically cleaned. Finally, clean with methanol and dry in an oven.
Note: Strengthen sample pretreatment, reduce pollution, often check whether the inlet, liner and split plate are clean. Select the appropriate inlet temperature, avoiding the thermal degradation of the sample and the injection pad, and ensuring the sample composition is sufficient. Vaporization.
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