Sample injection should pay attention to the problem
Hands do not take the syringe needle and sample parts, do not have air bubbles (suction samples should be slow, quickly discharged and then slow suction, repeated a few times, the 10ul syringe metal needle part of the volume of 0.6ul, there are air bubbles can not be seen, and more than suction 1-2ul syringe needle tip towards the top of the bubbles on the top go and then push) Needle bar to exclude air bubbles, (refers to the 10μl syringe, with a core syringe flat feel) the feed speed should be fast (but not easy to extra fast), each time the feed to maintain the same speed, the tip of the needle to the middle of the vaporization chamber to start injecting the sample.
Installation of the column
1. Installation and removal of the column must be at room temperature.
2. The packed column has ferrule seal and gasket seal, there are three kinds of ferrule, metal ferrule, plastic ferrule, graphite ferrule, it is not easy to tighten it too much when installing. Gasket seal every time you press the column to install a new gasket (Shimadzu chromatography is a gasket seal).
3. Whether the ends of the column are stuffed with glass wool. Prevent glass wool and packing from being blown into the detector by the carrier gas.
4. capillary column Installation insertion length according to the instrument's instructions, different chromatography vapor chamber structure is different, so the insertion length is also different. It should be noted that if you use a capillary column with no shunt, the vaporization chamber using a filled column interface with the vaporization chamber connected to the capillary column can not probe too much, slightly beyond the ferrule can be.
The ratio of hydrogen and air on the FID detector
The ratio of hydrogen and air should be 1:10, when the proportion of hydrogen is too large when the sensitivity of the FID detector drops dramatically, in the use of chromatography, other conditions remain unchanged, the sensitivity drops to check the hydrogen and air flow rate. Hydrogen and air there is a lack of gas ignition when the "bang" sound, followed by fire, generally when you light the fire on the electricity to extinguish, and then light also followed by extinguished is the amount of hydrogen is insufficient.
Using a TCD detector
1. Hydrogen carrier gas exhaust must be discharged to the outdoors.
2. Nitrogen as carrier gas bridge flow can not be set large, much smaller than when using hydrogen.
3. No carrier gas can not give the bridge flow, the bridge flow should be given after the temperature of the instrument is stabilized before starting to do the sample.
How to judge whether the FID detector is on fire
Different instruments have different ways of judging, see the size of the base flow if there is a base flow display, no base flow display with a wrench with a polished surface close to the detector outlet, observe the surface of the water vapor condensation.
How to determine whether the inlet gasket should be replaced
Feeling particularly easy to feed the TCD detector does not feed the sample when the recorder has a rule of small peaks, indicating that the gasket leakage should be replaced. Replacement of the gasket should not be screwed too tightly, the general replacement is at room temperature, the temperature will be tighter after the increase in temperature, the gasket screwed too tightly will cause difficulty in feeding the sample, often the syringe needle will be bent.
How to choose the right gasket
The gaskets are divided into general gaskets and high-temperature resistant gaskets, and when the temperature of the vaporization chamber exceeds 300℃, the high-temperature resistant gaskets are used, and the high-temperature resistant gaskets have a film on one side, and the side with the film is facing down when they are used.
How to prevent the injection needle is not bent
Many do chromatographic analysis of the work of the novice will often be the syringe needle and syringe rod bent, the reasons are:
1. Inlet screwed too tightly, room temperature screwed too tightly when the temperature of the vapor chamber will be tighter when the expansion of the silicone sealing pad will be more tightly, then it is very difficult for the syringe to be stuck in.
2. The location of the needle in the metal part of the inlet is not good.
3. The syringe rod is bent when the sample is too hard, the imported chromatography with a sampler rack, the sampler rack into the sample will not bend the syringe rod.
4. Because the inner wall of the syringe is contaminated, the injection will be pushed to bend the needle bar. Syringe with a period of time will find a small section of the needle near the top of the black stuff, this time the suction sample injection feel strenuous. Cleaning method will be pulled out of the needle bar, inject a little water, the needle bar inserted into the position of the contamination of the repeated push and pull, one can not be injected into the water until the pollutants get rid of, then you will see the water inside the syringe becomes cloudy, the needle bar pulled out with a filter paper to wipe it, and then washed with alcohol a few times. Analyze the sample for the solvent dissolved solid samples, into the sample in time to wash the syringe with solvent.
5. Into the sample must be steady, eager to fast will bend the syringe, as long as you into the sample skilled natural fast.
Several ways to improve the separation
1. Increase the column length can increase the separation.
2. Reduce the injection volume (increase the amount of solvent for solid samples).
3. Improve the injection technique to prevent double injection.
4. Reduce the carrier gas flow rate.
5. Reduce the column temperature.
6. Increase the temperature of the vaporization chamber.
7. Reduce the dead volume of the system, mainly the column connection should be inserted in place, do not divert the injection to select the non-shunt structure of the vaporization chamber.
8. Capillary columns should be shunted, choose the appropriate shunt ratio.
In summary, according to the specific circumstances in the experiment to find out, such as reducing the carrier gas flow rate, reduce the temperature of the column will make the chromatographic peaks broaden, so we need to look at the chromatographic peaks to change the conditions. The ultimate goal is to achieve good separation and fast peak time.
Installation of gas chromatography columns
The correct installation of a column ensures optimal performance and prolongs its service life. For proper installation, please refer to the following steps:
Step 1. Check the gas filter, carrier gas, injection pads, and tubing Check the gas filter and injection pads to ensure that the auxiliary gas and detector gas are flowing smoothly and efficiently. If dirty samples or highly active compounds have been made before, the liner tube of the inlet port needs to be cleaned or replaced.
Step 2: Attach the nut and gasket to the column and carefully cut the ends of the column flat
Step 3: Attach the column to the inlet port The depth of insertion of the column into the inlet port will vary depending on the GC instrument being used. Correct and appropriate insertion will maximize the reproducibility of the test results. Generally speaking, the inlet of the column should be kept in the middle or lower part of the inlet port, and it is ideal if the tip of the needle is 1-2 cm away from the inlet of the column after it has been inserted completely through the spacer. (Refer to the manual of the GC you are using for the specific insertion level and method.) Avoid bending and squeezing the capillary column, and be careful not to allow sharp edged objects such as marking tags to come into contact with the capillary column, in order to prevent the column from being broken and damaged. After correctly inserting the column into the inlet port, tighten the connecting nut by hand, and after tightening it (it won't budge by hand) use a wrench to tighten it an additional 1/4-1/2 turn to ensure that the installation is sealed. This is because an installation that is not tight will not only cause leakage of the device, but may also cause permanent damage to the column.
Step 4. Turn on the carrier gas When the column is connected to the injection port, turn on the carrier gas and adjust the pre-column pressure to obtain the appropriate carrier gas flow rate (see the table below).
Pre-column pressure is set to Psi
15m 25m 30m 50m 100m
0.20mm 10-15 20-30 18-30 40-60 80-120
0.25mm 8-12 13-22 15-25 28-45 55-90
0.32mm 5-15 10 8-20 10 16-30 32
0.32mm 5-15 10-20 16-30 32
0.32mm 5-15 10-20 16-30 32 10 8-15 10-20 16-30 32-60
0.53mm 1-2 2-3 2-4 4-8 6-14
(The above are recommended starting settings only, the exact values are based on the actual carrier gas flow rate.) Insert the outlet end of the column into the sample bottle with hexane, under normal circumstances, we can see stable and continuous bubbles in the bottle. If there are no bubbles, recheck that the degassing unit and flow controller are set correctly, and check the entire gas path for leaks. When all the problems are solved, remove the column outlet from the vial and make sure there is no solvent residue at the column port before proceeding to the next step in the installation.
Step 5. Attach the column to the detector. The installation and precautions to be taken are similar to those for attaching the column to the inlet port. If the system used in the application is an ECD or NPD, etc., the column should be disconnected from the detector when aging the column so that the detector may reach stability more quickly.
Step 6. Determine the carrier gas flow rate and then check the column installation Note: Heating the column without passing the carrier gas can quickly and permanently damage the column.
Step 7. Column AgingAfter the column has been installed and the system has been checked for leaks, it is time to age the column.
The column is heated to a constant temperature, usually its upper temperature limit. Under special circumstances, it can be heated to about 10-20℃ above the maximum use temperature, but it must not exceed the upper temperature limit of the column, as it is very easy to damage the column. When the aging temperature is reached, record and observe the baseline. Initially the baseline should continue to rise, then start to fall 5-10 minutes after the aging temperature is reached, and will continue for 30-90 minutes. It will stabilize when a fixed value is reached. If the baseline fails to stabilize after 2-3 hours or does not show a significant downward trend after 15-20 minutes, there may be a leak or contamination in the system unit. In such a case, the column temperature should be immediately lowered to below 40°C, and the system should be checked and the problem solved as soon as possible. If the column continues to age, it will not only damage the column, but will also fail to provide a normal and stable baseline.
Generally speaking, the aging time for columns with polar stationary phase and thicker coating is longer, while the aging time for columns with weak polar stationary phase and thinner coating is shorter. The aging methods of PLOT columns are different.Aging steps for PLOT columns:HLZ Pora series 250℃, 8 hours or moreMolesieve(molecular sieve) 300℃ 12 hoursAlumina(alumina) 200℃ 8 hours or moreDue to the irreversible adsorption of water in the alumina and molecular sieve PLOT columns, it makes these two kinds of columns are prone to retaining behavior drift.
When the columns have separated samples containing high levels of water, the columns need to be re-aged to remove water adsorbed in the stationary phase.
Step 8. Setting and Confirming Carrier Gas Flow Rate For capillary columns, the preferred carrier gas is high purity nitrogen or hydrogen. The purity of the carrier gas should ideally be greater than 99.995%, and the less oxygen it contains, the better. If you are using a capillary column, the carrier gas should be evaluated according to the average linear velocity of the carrier gas (cm/sec) rather than the carrier gas flow rate (ml/min). The average linear velocity of the carrier gas is used to calculate the column efficiency. Recommended average linear velocity: Nitrogen: 10-12cm/sec Hydrogen: 20-25cm/sec Carrier Gas Impurity Filter Adding a gas filter to the carrier gas line not only extends the column life, but also greatly reduces background noise. It is advisable to install a high-capacity deoxygenation tube and a carrier gas purifier. When using an ECD system, it is advisable to install a deoxygenation tube in its auxiliary gas line as well.
Step 9. Column Loss DetectionAt the end of the aging process of the column, a blank test (without sample injection) is performed using a programmed temperature increase. This is typically done by ramping the column from 50°C to the maximum operating temperature at 10°C/min and holding it there for 10 min after reaching the maximum operating temperature, so that a loss diagram is obtained. These values may be useful for future comparative tests and experimental problem solving. In the chromatogram of the blank test, no peaks should appear. If there is a peak, it is usually due to contamination from the inlet. If the performance of the column begins to deteriorate under normal use, the signal value of the baseline will increase. In addition, if the baseline signal value is significantly greater than the initial value at very low temperatures, it is possible that the column and GC system are contaminated. Other: Column Storage Seal the ends of the column with a feed pad and return it to its original packaging. When installing the column, partially cut off the ends of the column to ensure that no feed pad debris remains in the column.
Note: There is a danger of explosion when the hydrogen content in the air is 4-10%. So always make sure that the lab has a good ventilation system.
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