There are many types of gas chromatography, and their performances vary. It mainly includes two systems. That is, gas circuit system and circuit system. Pneumatic system mainly includes pressure gauge, purifier, pressure stabilizing valve, flow stabilizing valve, rotameter, six-way sampling valve, sampler, chromatographic column, detector, etc .; the circuit system includes voltage stabilization of various electrical components Electronic devices such as power supply, temperature control device, amplifying circuit, automatic sampling and collection device, data processor, recorder, workstation data acquisition card and so on.
To analyze and judge the faults of the chromatograph, we must be familiar with the two major systems of gas chromatography, gas and circuit, especially the structure and function of these two system components. The faults of the chromatograph are various, and the causes of a certain fault are also various. It is necessary to adopt a partial inspection method, that is, the elimination method, in order to narrow the scope of the fault. For the failure of the gas circuit system, it is nothing more than the leakage of various gases (especially the carrier gas), the quality of the gas, the stable and stable gas flow, and so on.
For example: if the baseline drifts downwards all the time, that is, the "level" value gradually decreases to a negative number, which is most likely to be a carrier gas leak, then it is necessary to find whether there is a leak in each joint component. If there is no leak, the baseline still drifts , It may be a malfunction of the circuit system. Analysts can find and eliminate faults on the chromatographic gas path, but it is not easy to eliminate faults on the circuit. It is necessary for the analyst to have certain knowledge of electronic circuits, and to understand the host wiring diagram and various The electrical schematic diagram of the system (especially the wiring diagram). The relationship between the control unit and the controlled object is clearly drawn on these diagrams, and the number and destination of each connector lead are specifically marked. It is very convenient to check the circuit and find the fault according to the diagram.
The failure of the chromatographic circuit system is generally the failure of the temperature control system and the failure of the detection and amplification system. Of course, the failure of the power supply to each system is not excluded. The main circuit of the temperature control system (including column temperature, detector temperature control, and sampler temperature control) is composed of thyristors and heating wires. The change of the thyristor conduction angle changes the heating power and the temperature. (Constant or not constant). The control of the thyristor conduction angle changes is the auxiliary circuit (or temperature control circuit), including platinum resistance (thermosensitive element) and linear integrated circuits and so on.
As can be seen from the above, if there is a problem with the temperature control system, you should first check whether the thyristor is broken, whether the heating wire is broken (broken or short-circuited), whether the platinum resistance is broken (broken or short-circuited) or whether there is poor contact. Next, check the other electronic components of the auxiliary circuit. . Common faults of the amplification system are that the ion signal line is wet or disconnected, the high-impedance switch (that is, the sensitivity selection) is wet, and the performance of the integrated operational amplifier (such as: AD515JH, OP07, etc.) is deteriorated or bad, etc.
The elimination of chromatographic faults has to be done both locally and overall. If there is a "fruit", there must be a "cause", clarify the direction of the line, and gradually eliminate the "cause" that causes the "fruit" (fault) to narrow the scope of the fault.
For example: if there is continuous jitter of the baseline or the baseline is very noisy, you can first disconnect the signal input line of the amplifier and observe the baseline. If it returns to normal, it means that the fault is not in the amplifier and the processor (or recorder). In the gas line part or temperature control unit; otherwise, it means that the fault occurred on the amplifier, recorder (or processor) and other units. This partial troubleshooting method is very useful in practice. Notes on the use of gas chromatography 1. Pay attention to the problem of injection. Do not hold the needle of the syringe and the sample part, and do not have bubbles (slow and fast when sampling) Discharge and then slowly suck, repeat several times, the volume of the metal needle part of the 10ul syringe is 0.6ul, and there are no bubbles that can be seen. Inhale more 1-2ul and move the needle of the syringe upward to the top of the bubble and then push the needle bar to remove the bubble. Syringe, syringe with core feel flat) The injection speed should be fast (but not very fast), keep the same speed for each injection, the needle tip to the middle of the vaporization chamber to start injecting the sample.
Second, install the chromatography column
1. The column must be installed and removed at room temperature.
2. Packed column has ferrule seal and gasket seal. There are three kinds of ferrules, metal ferrules, plastic ferrules and graphite ferrules. It is not easy to tighten too much during installation. Gasket seals must be replaced with new gaskets each time the column is installed (Shimadzu chromatography is a gasket seal).
3. Whether the two ends of the chromatography column are plugged with glass wool. Prevent glass wool and packing from being blown into the detector by the carrier gas.
4. The length of the capillary chromatographic column installation and insertion should be determined according to the instruction manual 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 without splitting, and the vaporization chamber uses a packed column interface, then the capillary column connected to the vaporization chamber cannot be probed too much, just slightly beyond the ferrule.
3. The effect of the ratio of hydrogen and air on the FID detector The ratio of hydrogen and air should be 1:10. When the ratio of hydrogen is too large, the sensitivity of the FID detector drops sharply. When other conditions are used when the chromatography is used, Check the flow rate of hydrogen and air for reduced sensitivity. There is a lack of gas in hydrogen and air to make a "pop" when it is ignited, and then extinguish the fire. Generally, when you ignite the electricity, it will extinguish.
Four, use TCD detector
1. When hydrogen is used as the carrier gas, the exhaust gas must be discharged outdoors.
2. The bridge flow of nitrogen as a carrier gas cannot be set large, much smaller than when using hydrogen.
3. The bridge flow cannot be supplied without carrier gas. The bridge flow should be supplied after the temperature of the instrument is stable before starting to sample.
Fifth, how to judge whether the FID detector is on fire. Different instruments have different methods of judgment. There is a base flow display to see the size of the base flow. If there is no base flow display, use a wrench with a polished surface to approach the detector outlet and observe whether there is condensation on the surface .
6. How to judge whether the inlet seal should be changed when the sample is injected. It is very easy to change the sample when the TCD detector does not inject the sample. There are regular small peaks on the recorder, indicating that the seal should be replaced if it leaks. Do not tighten the gasket too tightly. Generally, the replacement is performed at room temperature, and the temperature will be tighter after the temperature rises. Too tightly tightening the gasket will cause difficulty in sampling and often bend the syringe needle.
7. How to choose a suitable gasket? The gasket is divided into general gaskets and high temperature resistant gaskets. When the temperature of the vaporization chamber exceeds 300 ℃, use a high temperature resistant gasket. There is a layer of film on one side of the high temperature resistant gasket. under.
Eight, how to prevent the injection needle from bending. Many novices who do chromatographic analysis often bend the needle and syringe rod of the syringe. The reasons are:
1. The inlet is tightened too tightly, and it is tightened too tightly at room temperature. When the temperature of the vaporization chamber rises, the silicone seal will expand more tightly. At this time, it is difficult to pierce the syringe.
2. The location is not good and the needle is stuck in the metal part of the inlet.
3. The syringe rod is bent when the injection is too hard. The imported chromatogram is equipped with an injector rack, and injection of the injector rack will not bend the syringe rod.
4. Because the inner wall of the syringe is contaminated, push the needle bar during injection. After a period of time, the syringe will find that there is a small black thing near the top of the needle tube. At this time, the suction sample injection is difficult. Cleaning method: Pull out the needle bar, inject a little water, insert the needle bar to the contaminated position and push and pull repeatedly. If you don't do it again, fill the water until the contaminants are removed. Pull out the needle bar and wipe it with filter paper, then wash it with alcohol several times. When the analyzed sample is a solid sample dissolved in a solvent, the syringe should be washed with the solvent in time after injection.
5. Be sure to be steady when injecting the sample. The rush will bend the syringe if you are eager to find it. As long as you are proficient in sample injection, it will be natural.
- SAFE AND HEALTHY FOR YOUR FAMILY - We use these mixing spoons ourselves and want the best for our family and yours. Our FDA- grade silicone is safety-tested, heat resistant up to 480°F, and guaranteed 100% BPA-free
- FUNCTIONAL DESIGN: Practical and stylish non stick design suitable for a wide range of cooking endeavors; ideal for stirring, mixing and serving a variety of food
- ODOR, HEAT AND STAIN RESISTANT: Nylon body resistant to odor and stains and withstands temperatures up to 392 degrees Fahrenheit
- ELEGANT AESTHETIC: Beautiful beechwood handle finished with a trendy silver band; complete the collection with matching Typhoon Living utensils
Solid Spoon,Kitchen Solid Spoon,Mixing Serving Spoon,Silicone Soild Serving Spoon
Yangjiang Homelife Industry & Trading Co., Ltd. , https://www.kitchenutensil.de