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GC workers on what should be done instrument system maintena

Source:未知 Posted:2015-08-12 23:31 Browse:

Gas Chromatograph complicated process of using a variety of problems often occur, these problems are mostly due to improper operation, caused by improper maintenance. To regulate the use by the instrument, and do high-quality instrument maintenance, instrument operator should be how to maintain the gas chromatograph in order to make better use of it?
 
cause of issue
       Quantitative gas chromatography for organic analysis instrument after running for some time, due to electrostatic reasons, easy to absorb dust inside the instrument; the circuit board and jack addition to dust, but also regular and certain organic vapor adsorption together.
       Because of the high boiling point organic part, low freezing point, in the inlet position often find remnants of solidified organic; diversion pipeline in use for some time, an inner diameter thinning, even organic blocked.
       During use TCD detector is likely to be organic pollution, FID detector time for analysis, organic matter or collector nozzle or nozzles deposition position, soot collector section frequently.
       Therefore, to ensure the gas chromatography detection precision, stability, and accuracy should periodically perform maintenance on the gas chromatograph.
 
solution
       GC gas system is a continuous system only requires the carrier gas pipeline and the specified direction of flow, demanding the seal during operation. The entire GC maintenance, mainly includes the following aspects:
① inlet maintenance standard test
       Injection system, commonly known as the gasification chamber or sample port, before the sample into the chromatograph gasification system, and analysis to ensure that the system does not leak and set up a special unit. Inlet is an important part of the instrument, but also the introduction of pollution caused by the interference of the first gate. Inlet contamination or not, direct performance chromatographic characteristics, prepare a standard test that can be verified using a standard sample inlet uncertain whether contamination.
② regular replacement of the injection septum
       Inlet septum is leaking gas chromatography common faults. After the excessive number of injections, the injection needle opening pad wear expand aging, it is easy to leak. On the one hand the loss of a carrier gas leak, resulting in a waste of resources; on the other hand, the septum to analyze aging degradation will cause interference, such as ghosting. Hence the need for regular and timely replacement. General septum can reach more than 100 times using life, the life of different materials from different manufacturers vary, such as low-bleed septa BTO up to 400 times, and red silicone septa is about 100 times.
③ timely cleaning syringe
       Clean syringes to avoid interference sample memory effect. When replacing the sample to be cleaned, when multiple injections using the same sample and the sample should be cleaned with a solvent into the syringe, usually methanol, dichloromethane, acetonitrile, acetone and n-hexane solvent cleaning, cleaning needles can not be blocked, withdrawn putter, with another syringe to inject the cleaning solvent, the solvent and then insert the plunger and gently pushed out of the needle.
       To thoroughly clean syringe, generally available following solution was washed successively with 5% aqueous sodium hydroxide solution, distilled water, acetone, chloroform, and finally drained, not washing with a strong alkaline solution. If found within the syringe when there oxide affect the normal use of stainless steel, the stainless steel core can be dipped in a small amount of soapy water squeezed the syringe, drawing back and forth several times can be removed, and then cleaned to avoid remaining cement sample needle core, causing the syringe scrapped.
       Syringes are fragile instruments should be used with caution, not when you want to wash storage, it should not return empty pumping, especially in the case of dry wet back and pull, otherwise it will seriously worn, damaged its air tightness reduce accuracy.
④ Inspect and clean the inlet and liner
       Inlet liner after long-term use, because the samples are not volatile components remaining sake, you will find the plot tar-like substance inside the liner, in addition there will be accumulation of particulate matter, such as septum, solid material in the sample , which will interfere with the analysis of normal. Therefore, periodically check and clean the inlet and the liner. After general cleaning with pure water main, methanol or ethanol and the like wash or ultrasonic cleaning, pollution cotton swab to gently wipe, do not use excessive force to avoid damage to the surface of the active sites, and then placed in an oven dry at 70 ℃ cooling sealed storage can.
⑤ timely replacement of capillary seal
       Seal leakage is one of the most common faults gas chromatograph. Do not reuse on different columns of the same seal, remove the column, even with a re-install, the best replacement of the seal. The most commonly used sealing pad, there are three: graphite, Vespel / graphite (85% / 15%), Vespel, which in turn reduces the maximum operating temperature, but in turn increases the mechanical strength and life, it should be based on the material of the gasket, the degree of consumption whether the decision needs to be replaced.
⑥ meet the standards of purity gases
       Use of high-purity carrier gas level in order to avoid interference analysis, pollution, damage columns and detectors. Because of the relatively carrier gas, the column and detector are more expensive, such as a column of more than 20 times the price of high purity nitrogen.
⑦ periodic replacement of the gas purifier filler
       Gas Purifier play a great role in the carrier gas system, it can help remove air pollution equipment and affect the results of the water, hydrocarbons, oxygen and other impurities. In addition to the water used for the color gel for the color change can be judged according to their performance, and molecular sieve adsorption of organic matter purifier is not easy to judge with the naked eye, the general experience is replaced every three months.
⑧ replacement parts to one by one
       Repair Inlet, do not replace a plurality of components, that would cause of the malfunction misjudgment. Should a replacement one, test and then replace the other parts, so that may be more accurate.
 
case analysis 
In the analysis of a vegetable oil oleic acid, linoleic acid and other fatty acids, the autosampler injection, mass spectrometry, chromatography separation and response before 9 samples were normal, but not out of the back of the sample peak.
First, the mass of the filament energy display open, there is a strong signal is detected, remove the cause of MS filament, signaling aspects. Secondly, with methanol injection and there is no peaks appear, initially concluded that nothing to do with the sample; and finally, suspect a problem occurs in the inlet or column.
This can have three aspects: First septum leakage; Second liner contamination; third column injector end stigma contamination. Then open the inlet, silicone rubber septum was found to have a clear eye of a needle, sealing effect has been completely lost, there is a leak, replace the injection septum back injector, peaks appear normal.