Someone asked me today, why is there a cumulative number of syringes after the number of sample injections in the Column Usage Record?
Applying the philosophical point of view, any matter has a longevity, as large as the universe, as small as an atom, but different material lifetimes are different.
Each column has a rough needle life, which can theoretically be specified. When the number of needles is reached, it is forced to be scrapped. However, it seems that there is no such regulation, so it can also be used as a reference. When the column performance parameters of the column (that is, the theoretical number of plates, the resolution, the tailing factor, etc.) are not up to standard, the number of syringes is referred to. Judging is that the life of the column is up, it is an irreversible factor and can only be changed. For other reasons, such as the wrong preparation of the mobile phase, or the deterioration of the mobile phase, the strength of the diluent may be too large, or the method may be wrong, or the sample itself may be a problem.
However, the cumulative damage of the column is not a one-off event. The column performance is slowly decreasing, but there is no specific standard, depending on the specific analysis method, and it is also related to the column model. The C18 column life is very long under conventional analytical methods, because the C18 column is the most advanced, most reliable, and most widely used column, and is basically not damaged under conventional analytical methods. However, if the mobile phase is special, such as high salt, high pH>8, low pH<1, high column temperature, high proportion of aqueous phase, high proportion of organic phase, etc., the column damage will be correspondingly increased.
These can be counted as chemical damage. If it is not properly operated, for example, the mobile phase and the sample solution are not filtered, or impact on the column, etc., it will also cause physical damage, which will seriously affect the life of the column, or even "a trick." .
As mentioned above, the column model has different lifespans for different types of columns. Similar to the C18 mentioned above, the CN columns, phenyl columns and other bonded silica columns have a long service life. However, all silica-based columns have a natural weakness, that is, silica gel can be dissolved by water. Although the solubility is very small, it has been used for many years, especially in reversed-phase chromatography systems, adding high salt, high pH and high. After the column temperature and high proportion of water are equal to the method parameters, the loss of silica gel is particularly obvious. I have done a project where the mobile phase contains salt and the column temperature is as high as 50 degrees. Basically, one column is scrapped in half a year. However, there is a way to solve this problem by adding a pre-column of the same type as the column in front of the column, also called a guard column. When the silica in the mobile phase is dissolved in the mobile phase, it is not The column's silica gel is then eroded to greatly extend column life. However, it is not necessary to use a particularly harsh mobile phase. It is necessary to know that the core of the precolumn is very expensive. That is a short column. Even if the column is kept, it is too much to change the core.
But there are some types of columns that are inherently short-lived ghosts, such as the NH2 column. Sometimes it's hard to balance the system. It takes a few dozen needles to OVER, like a one-off. Like a firework, it is gorgeous and appears to be annihilated in a flash. This is left to the column experts to develop new fillers that are more stable and reliable.
There is also a type of column, which is a chiral separation column, which is a great application in the pharmaceutical industry. Usually the chiral column is a normal phase column, which requires us to replace the system before using the chiral column, and then connect the column with a mobile phase to flush the injection. Usually the order of methanol, isopropanol, n-hexane + isopropanol, mobile phase, if you forget this process, it will cause a lot of trouble. Moreover, some chiral columns are coated columns. Macromolecule coating columns such as starch and cellulose are very afraid of water. If the original reverse phase mobile phase in the system is not replaced, it will cause irreversible damage to the column, or even scrap. . In recent years, scientists have also developed a bonded chiral column that is much more stable than a reversed-phase chromatography system.
It is also important to store the column after use, especially when using a buffer system. A general flushing procedure for a reversed-phase chromatography system is recommended here: replace all channels with an aqueous phase containing a lower organic phase, such as 10-30% acetonitrile or methanol, then rinse for 1 hour, then increase the organic phase by gradient. Each rinse is for a certain period of time and is finally retained in the rinse solution of the high organic ratio. The low organic phase rinse is designed to flush the buffer salt as much as possible. Usually the low-pressure gradient elution liquid chromatograph uses a quaternary pump, which is a single-pump four-channel, proportional valve mixing. The disadvantage of this type of mixing is that the mixing effect is poor because the different ratios of the channels are controlled by switching the time of each channel valve. For example, acetonitrile: buffer salt = 50:50, if the flow rate is 1.0mL / min, it is not said that acetonitrile and buffer salt are mixed at a flow rate of 0.5mL / min; but the flow rate is always 1.0mL / min, but in reciprocating During the pump's back and forth time, the two channels are opened for half of the time, which means that the system pipe is a piece of acetonitrile and a buffer salt. This will cause the precipitation of salt. Therefore, it is often a mixture of two channels. Even if buffer salts are not used, it is recommended to mix them first, and then go through a single channel. Otherwise, the salt will be precipitated or the baseline will fluctuate. When gradient elution is carried out, a certain proportion of water is often added to the organic phase channel (B), or the aqueous phase channel (A) is formulated into an initial ratio of gradient elution, and the organic phase channel (B) is subjected to gradient washing. Take off the final ratio.
There are two points to be explained here. First, it is generally believed that the chromatographic system, including the washing or even preservation of the column, can use the mobile phase, except that no buffer, acid or alkali is added. For example, the above mentioned acetonitrile: buffer salt = 50:50, after the sample is finished, it can be washed with 50% acetonitrile / water. There are some brands of columns, such as Shiseido, suggesting that washing is not recommended if it is not salty or strong acid or alkali. However, this is only suitable for short-term preservation, that is, it will be used again after a long time. Chromatographic systems that have not been used for a long time include columns or should be rinsed and stored in a high proportion of low polarity solvent systems. It is generally recommended that the normal phase system be stored in n-hexane: isopropanol = 90:10 and the reverse phase system stored in acetonitrile: water = 90: 10 or 100% acetonitrile. Second, with the development of rapid separation columns, many low-particle columns are used, and often the column temperature is also high, usually reaching 50 degrees or more. This chromatographic system usually has a higher column pressure. A high proportion of aqueous phase flushing may cause the system to overpressure. You can first rinse with the mobile phase, or disconnect the column, rinse the system with a high proportion of aqueous phase, then connect the column to gradually increase the organic flush, or you can lower the flow rate first. Moreover, it is preferable to lower the column temperature when the flushing is about to end.
Let's talk about the GC column. Nowadays, the packed column has almost withdrawn from history. It is said that the GC column is naturally a quartz capillary column.
Compared with the liquid chromatography column, the gas phase column is much simpler, and often the specificity between the gas column types is not so strong. Usually, a sample is analyzed by a variety of columns, and the phase can be obtained by adjusting the temperature program. Similar analysis results. Combined with the title of this article, the number of syringes in the GC column is also for reference only and cannot be used as the only parameter for the lifetime of the column. The factors affecting the life of the GC column are high temperature, high temperature time, and high boilers in the sample ( This includes some methods that are not suitable, decomposition of the sample or polymer, and purity of the carrier gas.
A conventional gas chromatograph column is usually a liquid filler coated on the surface of a quartz tube, so in general, the separation of the gas chromatograph is actually achieved by different properties of the vaporized sample dissolved and re-evaporated in the liquid filler. Then since the filler is a liquid, it will naturally evaporate, and the most influential factor of the life of the GC column is here. The GC column will have a limit temperature, and the general use temperature will be about 20 degrees at this limit temperature. Usually the gas phase analysis method is programmed, and the high temperature and retention time determine the effect of each injection on the column. However, different types of columns have different extreme temperatures due to their different nature of the filler, and the natural maximum use temperature is different. Conversely, at the same temperature of use, their lifespan is also different.
Regardless of the analytical method, the solvent and all the substances in the sample should be reacted as much as possible. The first condition for gas chromatography analysis is that the sample should be vaporized, that is, the inlet temperature and the final temperature of the program are larger than the sample. Boiling point (this is not absolute), when there are high boiling substances in the sample, even inorganic salts, mechanical impurities, can not be gasified and left in the liner, or even left in the column, will be on the column There is damage. In this case, it is best to treat the sample. Extraction, distillation, and filtration are common methods. If it is unavoidable, it is necessary to change the septum, the liner glass wool, etc., and cut off the front section of the column for a certain period of time, usually about 1 meter. In addition to these, attention should be paid to the understanding of the nature of the sample. If the thermal stability of the sample is poor, decomposition or polymerization occurs during the injection analysis, and high boilers will have a great effect on the column if these substances cannot be solvent. If it is washed, the damage is irreversible and the analysis results are not accurate. In this case, the temperature should be lowered appropriately until such a reaction does not occur. Or change to other analysis methods.
Usually the carrier gas we use is high purity nitrogen, the reason is two words - cheap! However, excluding economic factors, this is not the best choice. Because the production of nitrogen is the evaporation of liquid air, but because of the close nature of nitrogen and oxygen, it is generally difficult to prevent a small amount of oxygen in high-purity nitrogen. Oxygen on the high temperature column has an adverse effect on the entire GC system, including the column. Therefore, general instrument manufacturers still recommend the use of high-purity bismuth, especially in the high-standard analysis of measurement, verification, etc., but a bottle of high-purity bismuth can be exchanged for 5 bottles of high-purity nitrogen, the general user still chooses to use high-purity nitrogen. In fact, in terms of instrument performance, high-purity hydrogen can also be used as carrier gas. Low oxygen content, low background, and low price are good choices. Of course, hydrogen leakage and storage and transportation risks are generally considered. Excluded. However, gas chromatography with a TCD detector often uses high purity hydrogen as the carrier gas.
Having said that, I finally summed it up emotionally. Really do instrumental analysis, you can find different brands of instruments, and even each instrument is different, only you really love instrument analysis, treat each instrument as a good friend, lover, lover, child, understand their temper, habits With a sincere heart to treat them, you can truly do what you want, human and machine.
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