We should not think that the instrument should be maintained when the instrument has a fault. It should not only be done regularly and purposefully, but also establish a concept. An important function of maintenance and maintenance is to ensure a good inspection state and ensure accurate. The test data, the factors affecting the sustainable operation of analytical instruments are:
1. The wearing parts of the wearing parts are not cleaned up in time;
2. The hardware is not scientifically used;
3. The instrument itself is purchased and improperly configured;
※ Various analytical instruments vary greatly in structure, function, and application, but there are certain commonalities in the problems that often arise and the direction of maintenance. This commonality is: "There are few problems with the fixed components of the instrument itself, and it is easy to fail only where the user often touches."
Let's talk about the common faults and common maintenance of gas chromatograph, GC/MS, and liquid chromatograph:
Part 1: Gas Chromatograph
　　 When using a gas chromatograph (the following is mainly a gas chromatograph equipped with a split inlet and a hydrogen flame detector), the behavior that the user often does to change the structure of the instrument is to change the column, although the column is changed. Like the needle, it is the basic skill of a gas chromatographer, but at least half of the problems are related to it.
Question 1: Air leak
The injection pad leaks, and the fixing screws of the post are leaking, especially when using a packed column and a silicon graphite pad. If the rubber ring is better, but it is not needed, it needs to be replaced regularly. The capillary column is relatively better due to the use of graphite gaskets.
Question 2: Fixed position is not allowed:
This is a key point that limits sensitivity. The packed column is rigid and has a fixed size and shape, which is generally easy to grasp when changing. The problem is often the capillary column. Due to its flexibility, the length in the inlet and the detector is completely controlled by the user. If it is not accurate, it will become an important factor restricting the experimental results. The packing sizes of different company instruments are different, and there are also big differences when using different liners. Some instruments offer dedicated measurement tools, while others do not.
Question 3: Cleaning and replacement is not timely:
This is the main reason why the hardware is fault-free and the detection status is not good. The specific performance is pollution. For example, the inlet liner and glass wool pollution, column contamination, detector contamination, if not replaced or cleaned in time, will cause the baseline. Unstable, reduced sensitivity and other phenomena.
Countermeasures:
Regular cleaning, regular replacement, leak detection with leak detection, is a common but not a good treatment. I think that Zui's good method is state monitoring, always observe the state of the system, and immediately find the problem and then deal with the problem. The same machine, the same column, at the same flow rate, with the same column head pressure, should have a basically consistent signal baseline and almost the same stabilization time, different problems of the instrument state will have different reflections.
Example 1: After the column is installed, a certain flow rate is applied, and the head pressure is different and the head time is different. If the stigma pressure is significantly higher than usual, it may be that the stigma is clogged. If it is low, it may be a leak or a broken column. The air leak should be able to hear the sound after closing the oven fan. The column break can be easily seen.
Example 2: The flow rate is normal, the head pressure is normal, but the baseline signal is significantly low and stable. This phenomenon often occurs when using a capillary column, mostly because the nozzle is clogged. The way to determine whether this is the reason is to enter the blank solvent, if the signal is much lower than usual, and the peak time is later, this is basically the reason, then only shut down and clean.
Example 3: The flow rate is normal, the head pressure is normal, and after the three temperatures (OVEN, INJ, DET) reach the set value, the baseline signal is obviously high and unstable. This situation is mostly pollution. The pollution is divided into: inlet pollution, column pollution, and detector pollution. Determining which type of failure is not easy (sometimes cross-reactive), but the treatment is consistent: shutdown-cleaning-heating. I recommend that you clean the detector and the inlet every time you clean it. After all, the most time-consuming is to cool down.
Part II: GC/MS
The GC/MS can be seen as a combination of a capillary column gas chromatograph plus a mass detector, and the common problem is the sum of the two. Our operation of the GC/MS itself is generally to change columns and clean the ion source. Most of the problems are also caused by these two steps. Their main performance is that the vacuum caused by air leakage is not normal. The problem lies in the interface of the capillary column into the mass spectrometer and the sealing ring when the mass spectrometer opens the door. The interface of the capillary column into the mass spectrometer is not tightly sealed:
Need to pay attention to are:
1. The length of the product into the mass spectrometer is not appropriate, too long or too short;
2. The gasket should be loose and suitable. If it is too loose, there will be hidden dangers of air leakage. If it is too tight, the gasket will be crushed;
When the ion source is cleaned, the cavity is not sealed after opening the cavity:
The seal on the door (the door of Shimadzu, the cover of Agilent) can cause air leaks as long as a little bit of hair or wool that is invisible to the naked eye. At this time, the general operation book requires the use of nylon gloves to clean, but this is very important for the treatment of the ion source, but for the treatment of the seal, the effect of not wearing gloves is better. The reason is that there will be some grease in the hand. As long as a circle is applied along the sealing ring, the effect of the wool thread can be effectively eliminated. These greases are far away from the heating source and far away from the ion source, and are basically macromolecular organic substances. No effect. In the usual operation of the mass spectrometer, there is a general numerical concept criterion for how long the vacuum can be achieved in the case of ventilation and non-ventilation. If the rate of vacuuming is too far from the usual after changing the column or cleaning the ion source, it is necessary to first consider whether it is a problem of improper installation of air leakage, and cool down and shut down earlier. Solvent delay is a concept not found in other gas phase detectors. If you forget to set a reasonable solvent delay time, it will cause serious damage to the filament. This is a common mistake made by mass spectrometry beginners.
Another behavior that may cause serious consequences is: I have to rush to disassemble the ion source without waiting for the temperature to drop to room temperature. There have been cases of disassembling the machine when it is hot, and not going back after it has been cold. In terms of experimental conditions, it is mainly a pollution problem. The treatment of inlet and column contamination is consistent with the normal gas phase. As far as mass spectrometry detectors are concerned, in general, more than 80% of the contamination is in the ion source. We need to pay attention to the voltage after tuning. If it is raised to a certain extent, we must consider whether to clean the ion source. The quadrupole part is generally not required to move. The daily maintenance of GC/MS is easily overlooked by the maintenance of mechanical pumps, mainly for oil and molecular sieves.
Special note: Don't forget to match UPS when buying temperament.
The third part of the liquid chromatograph
Liquid chromatographs are instruments that are easy to learn and difficult to use, with particular emphasis on "correct use" and experience. The most contacted liquid phase worker is the mobile phase, which is the mobile phase, which is the most important source of various problems in liquid chromatography. The most common faults in liquid chromatographs are blocking and second, leaking. The following two points are discussed separately. (Note: The mobile phase uses methanol as an example, and the column uses C18 as an example)
The phenomenon of "blocking" is that the column pressure is abnormally increased, and the direct cause is that the flow path is not smooth. The main location of the blockage is at the front end of the column. The main reason is that there are impurities in the mobile phase. The main source of impurities is bacteria. One of the reasons for "blocking" is bacterial contamination when preparing the mobile phase. First of all, we must realize that the general domestic methanol does not need additional filtration treatment, and there is no problem in direct use. Even some solid particulate impurities can be removed from the filter head at the forefront of the liquid phase flow system. What is really causing problems is the bacteria in the water. The newly prepared pure water will grow in the room for a few days, and these bacteria, although invisible to the naked eye, are enough to block the voids of the column packing particles, causing the column to be quickly scrapped. This is the cause of bacterial contamination during the preparation of the mobile phase. The solution to this problem is simple: to ensure the reliability of the water, there are two ways to recommend it:
(1) The most ideal way is of course to purchase a laboratory-specific pure water machine, which is convenient and reliable, and the quality is also assured. The disadvantage of Yi is that it is expensive.
(2) Buying commercially available branded pure water in a box, for example, a 500mL Yibao or Wahaha, the quality of this water is sufficient to meet the requirements of liquid chromatography. First randomly select one to do a bacterial plate experiment, and the number of colonies can be used. This way, it is convenient to open one at a time. Each cost is about 2 yuan.
Here is a special point:
In most books, when it comes to formulating the mobile phase, there is a final step of filtering. However, from the actual effect of our long-term use, this step can and should be removed as long as the quality of the water can be guaranteed. There are three reasons for this:
(1) Mobile phase filtration is theoretically beneficial. However, in practice, it is impossible to use special bottles, but it is easy to cause cross-contamination, which has a greater impact on the complex mobile phase.
(2) Mobile phase filtration is not cost effective in terms of economic costs. Buying a filter unit costs more than 6,000 yuan, and the filter is recognized as a relatively easy to damage equipment. The most important thing is that the cost of the filter is too high, and it costs tens of yuan. Calculated according to the normal service life of a typical liquid column, the cost of the filter will be much higher than the cost of the column.
(3) Mobile phase filtration is not cost effective for work efficiency costs. The solvent filter has a pre-cleaning, equipment, use, post-cleaning, and drying process for at least one hour.
(4) In the actual work, no mobile phase is found to have no effect on the column life. At least we have not done mobile phase filtration for 6 years, but compared with domestic counterparts, our column life is relatively long under the same intensity of use.
The second reason for "blocking": bacterial contamination when using mobile phase:
Refers:
The mobile phase did not have long bacteria at the beginning, but it caused bacterial contamination when it was used. This is mainly caused by a bad habit of using a multi-component liquid chromatograph.
The simplest example:
50% methanol water mobile phase, there are two ways to use. One way is to mix and mix together before going on the machine. The other way is to put pure methanol in flow path A and pure water in flow path B. From the simple experimental effect, the latter has obvious advantages: First, it is simple, no need for the experimenter to calculate another mix, and secondly, the ratio is accurate, and the reproducibility of the retention time is excellent, but it has A fatal flaw is that pure water will grow bacteria in the mobile phase bottle for a few days (in many cases, not only pure water is used as the mobile phase, but buffered salt solution, which is itself a high-quality fertilizer, and the bacteria grows more rapidly) Once the bacteria column is broken, it is very fast. Therefore, this method requires the operator to use the newly prepared pure water for each experiment. It is also required to replace the water phase after each experiment and replace it with methanol. This is because many people are not aware of the actual work. They are aware that there are always one or two misses in multiple uses, but often these two times are enough to have a fatal impact. Because the clogging of the LC column is irreversible, it is better to sacrifice less retention time repeatability and do not use pure aqueous solutions as a group of mobile phases. From the actual experimental results, I suggest to use 10% methanol water instead of pure water solution (I used to do the experiment of the total number of bacteria in different proportions of methanol water, it can basically inhibit bacteria at 5%, and can completely sterilize at 10% and above. ), this can effectively eliminate the hidden dangers of long bacteria, both as a mobile phase or as a column. Even if it is difficult to calculate when preparing the mobile phase, but one trouble, lifelong benefit, the third reason for "blocking": improper operation.
There are several common problems:
(1) The model selected when replacing parts is incorrect, the interface is not very matched, and deformation occurs when tightening, which makes the pipeline blocked.
(2) The sample treatment liquid is not cleaned, and the blockage between the six-way valve and the column will be poor for a long time.
(3) When using the manual six-way valve, some people may not be able to rotate due to small hand strength, thus causing a dead block in the flow path, and the pressure rises rapidly beyond the warning value.
(4) When using a metal pipe to make a waste pipe, it should be noted that some water is first placed in the good waste liquid bottle, and the outlet end of the waste liquid pipe is placed under the liquid surface. If it is located in the liquid phase and the experiment uses a higher concentration of buffered saline solution, it may crystallize at the outlet end and cause blockage during shutdown. This situation is not common, but it does happen.
There are a lot of reasons for "blocking". Now I will introduce the method of blocking. After the phenomenon of "blocking" occurs, it is necessary to find out the cause, mainly what position has been "blocked". Note that in most cases, there will only be a blockage in the entire system. The method of checking the plugging is to open the segment from the tail to the reverse direction, and carefully observe the pressure value. If the pressure of a certain component (except the column) is large and different when it is installed and removed, the change judgment can be developed. As for the blockage of the column, it can be judged by changing the pressure of the column of the same specification.
Let’s talk about the “leakage†problem below. There are two types of “leakageâ€: leaking and leaking.
1. Leakage
The flow path from the mobile phase bottle to the waste bottle is a fully enclosed system with high internal pressure but an external leak. If a component leaks, it is the fault, there are two reasons for leakage:
(1) Improper contact hardware:
When replacing parts such as flow tubes or changing columns, the changed joint interfaces do not match, causing leakage. It should be noted that many of the column joints of different companies are different, and even the liquid column joints produced by the same company at different times are quite different. Of course, the PEEK joint is a better solution. It is not only versatile, but also can be leaked by hand twisting. Even if the interface itself is matched, if it is improperly operated, it will leak. The strength is not well grasped, it is too tight or too loose;
Another kind of misconduct is a fatal mistake: slippery wire, which is often a mistake made by workers who are not very strong in hands and rarely screwed. The consequences of slippery wire are not only as simple as leaking, but often cause scrapping of important parts. . To solve this problem, we can only experiment by making up the basics, that is, screwing.
(2) Improper use of the instrument:
If the pump is leaking, the most common cause is the buffering of the salt at the piston position. There are two reasons for the precipitation: First, when the buffer solution is suddenly added with pure methanol, the error is easily avoided. Try not to use pure methanol and pure water. As long as there is a 10% ratio to each other, this problem will not occur. Another reason is that when the buffered salt solution (regardless of the methanol content) is used as the mobile phase, the methanol water is not rinsed after the end of the experiment, so that the micro-osmotic mobile phase is dried to form crystals. However, the leakage of the transfer pump does not have to be repaired immediately. Rinse it out and use it carefully in future use. Normally it can be used normally. Leakage of the detector is a very troublesome thing, and it is generally a problem with the absorption tank, and the replacement cost is quite high. However, it does not mean that it must be replaced immediately. It can also be seen from the actual experimental results.
2. Air leak
The leakage is leaking from the inside to the outside, and the leak is the inside of the flow path where the external gas enters the liquid chromatograph. In the following, the causes of the bubbles and the corresponding solutions are analyzed on a component-by-part basis in the direction of the flow path:
(1) When the filter head is pumping, there are irregular but continuous small bubbles in the flow tube. At this time, it is considered whether the mobile phase has degassing (requires special reminder that even if there is a vacuum degasser, it must first Ultrasonic degassing can at least reduce the working pressure of the degasser and improve the working efficiency. If it has been degassed, it should be noted that the pollution of the filter head will also cause this phenomenon. The treatment method is relatively simple. Unscrew the filter head and soak it in dilute nitric acid. After ultrasonicing for half an hour, wash it and put it back.
(2) Transparent flow tube
Refers to the section of tubing between the filter head and the transfer pump. This part is often not a bit of a bubble, but often the entire tube is full of air and the operator is ignorant, so that the pump has been working for a long time and found that there is not much liquid in the mobile phase bottle. This is why we often say that the liquid chromatograph should be turned on at least once a week (we must have the concept of "micro-osmosis" in the liquid phase). If it is not used for a long time, the liquid in this section will be completely dried, and the air-filled pipeline and the liquid-filled pipeline will not be distinguished by careful observation. This situation is dangerous for the pump because the pump is designed to deliver liquid rather than gas. The internal liquid acts as an oil for the piston. If there is some buffer salt remaining on the piston rod, it is easy. Pulling, causing irreversible effects. For this situation, it is necessary to highlight "prevention first" such as: liquid chromatography users should be relatively fixed and stable, work with reasonable resources, each machine hits at least one experiment a week, such as long-term use at least weekly to flow Phase 2 hours. It is important to develop good work habits. What should I do if I accidentally have this problem? My suggestion is to use external force to fill the pipeline with liquid, as follows:
1. Find the joint of the flow pipe into the transfer pump;
2. Unscrew it;
3. Align the flat cut of the tubing with the tip of a clean ear wash;
4. Suction liquid, see the liquid level rise from the mobile phase bottle, and stop the action when it is about 5 cm away from the ear wash ball;
5. Quickly screw the joint back to the transfer pump (this process may have a little mobile phase leaking, which is normal);
6. Turn on the machine, open the drain valve, and start the transfer pump;
7. When the solution flowing out of the drain pipe has no air bubbles, close the drain valve and the instrument works normally;
(3) These parts of the pump and the column are generally not afraid of being blown, and they are washed away;
(4) Detector:
It should be said that as long as there is a bubble in the entire flow path, a strong signal is reflected on the detector, and the bubbles inside the detector can generally be washed away, but there are also cases of residual bubbles that are difficult to flush out. If there are residual bubbles in the detector, there will be obvious manifestations of the characteristic, that is, when the baseline is taken, there will be occasional intervals of signal peaks that are straight up and down. At this time, let's see if the normal flow can be washed away. If it can't be washed away, then the only way is to remove the column and connect the detector directly to the outlet of the pump. If you increase the flow by several times, you will be able to wash away the bubbles.
Power Gear Pump,Vehicle Working Hydraulic Gear Pump,Multiple Tandem Fluid Drive Gear Pump,Construction Machine Final Drive Gear Pump
HENAN MAJOR INDUSTRIES IMP. & EXP. CO., LTD. , https://www.henanminingcrane.com