Chromatographic injection needle is small but indispensable, the injection needle is connected to the sample and analytical instrument channels, with the injection needle, the sample can enter the chromatographic column, through the detector, for continuous spectral analysis, so the maintenance and cleaning of the injection needle is the analysts need to pay attention to the focus of the daily, otherwise it will not only affect the efficiency of the work, but also on the instrument will be harmed, this article introduces about the injection needle of the small knowledge.

 

Sampling needle classification

According to the appearance of the feed needle needle, can be divided into round spine-shaped needle feed needle, beveled needle feed needle, flat head feed needle.

Cylindrical needle, used for spacer sampling, can reduce the damage to the spacer, withstand multiple injections, mainly used for autosampler; beveled needle, available in the sampling spacer, easy to feed the sample operation, of which 26s-22 needle is the most suitable for use in gas chromatography in the sampling spacer; flat-tip needle, mainly used for high-performance liquid chromatographs, the injection valve and the sample suction pipe. The flat-tip needle is mainly used for the injection valve and sample suction tube of HPLC.

Sampling Methods

According to the feeding method can be divided into automatic injection needle and manual injection needle. According to the needle in the gas chromatograph, liquid chromatograph liquid in different analytical requirements, can be divided into gas phase injection needle and liquid phase injection needle. Gas chromatography injection needle is generally required to feed a little less, the most common injection volume of 0.2-1ul, so the corresponding selection of the injection needle is generally 10-25ul. The selection of the needle for the needle cone type, easy to feed the sample operation;

In contrast, the liquid chromatography injection volume is generally larger, common injection volume of 0.5-20ul, so the relative volume of the needle is also larger, generally 25-100UL, and the tip of the needle is flat, in order to prevent scratching the stator.

In chromatographic analysis, the most commonly used injection needle for micro-sampling needle, especially suitable for gas chromatography, liquid chromatography liquid for analysis. Its total capacity error ± 5%. The gas tightness can withstand 0.2mpa. It is divided into two kinds of injectors without liquid storage and with liquid storage. The specification range of the non-stored liquid micro-sampler is 0.5μL-5μL, and the specification range of the stored liquid micro-sampler is 10μL-100μL. The micro-sampling needle is a kind of indispensable precision instrument.

Use of the injection needle

1, check the feeder before use, check the barrel for cracks and the tip of the needle is hairy. 2, exclude the residual sample in the feeder, wash the feeder with solvent for 5-20 times, and discard the waste liquid of the first 2-3 times. 3, exclude the air bubbles in the feeder, submerge the tip of the needle in solvent, and repeatedly draw the sample. When the sample is excluded, the bubbles in the feeder can change with the vertical change of the tube.4. When using the feeder, first suck the feeder full of liquid, and then exclude the liquid to the desired volume of the sample.

Plunger maintenance

 

1, can not force the plunger. 2, when the needle is blocked, can not force the plunger, because the high pressure can make the plunger barrel rupture. 3, standard sampler plunger can not be interchanged, each plunger is suitable for the corresponding sampler on the adherent layer. 4, when the feeder is dry as far as possible not to pump the plunger. 5, clean the plunger with a burr-free tissue, do not bend. 6, the plunger can be used to clean the plunger. 7, the plunger should be used to clean the plunger, not to bend. 8, the plunger can not be used to clean the plunger. 9, the plunger can not be used to clean the plunger.

Needle Maintenance

1, medium to highly viscous samples should be diluted before use or select a large inner diameter of the injection needle. 2, cleaning needle should be used when cleaning tools, such as through the tube wire or tube core needle, tweezers, surface-active substances used to clean the needle wall. 3, thermal cleaning, thermal cleaning to remove organic residues on the needle, especially for trace analysis, high boiling point and viscous substances. After a few minutes of thermal cleaning, the needle cleaning tool can be used again.

Needle cleaning

1, you can use organic solvents to clean the inner wall of the needle, when cleaning, please pay attention to check whether the needle pusher can move smoothly; 2, if the needle pusher does not move smoothly, you can remove the pusher. Recommended to use a soft cloth dipped in organic solvent to wipe it clean. 3, repeat the use of organic solvent suction, if after a few times of suction on the needle pusher resistance increases very quickly, that is, there are still some small dirt exists, which occurs after the cleaning process needs to be repeated. 4, if the needle pusher can be fluent and smooth movement, check whether the needle is clogged. Repeat the rinsing of the needle with organic solvent to check the shape of the sample being pushed out of the needle. 5, if the needle is normal, the sample will flow in a straight line, if the needle is clogged, the sample will be sprayed out from a direction or an angle in the form of a fine mist. Even if the solvent sometimes flows in a straight line, check carefully to see that the flow is better than normal (just compare the flow with a new, unclogged needle). 6. Clogging in the needle can destroy the reproducibility of the analysis, and for this reason needle maintenance is essential. Remove any clogging in the needle with, for example, a metal wire. The needle should only be used if the sample flows normally. The use of a pipette to aspirate or a syringe cleaner can also be effective in removing contaminants from the syringe.

Precautions for the use of the injection needle

Hand do not take the syringe needle and have sample parts, do not have air bubbles, sucking the sample should be slow, fast discharge and then slow suction, repeated a few times, 10 μl syringe metal needle part of the volume of 0.6 μl, there are bubbles can not be seen, more suction 1-2 μl to the syringe tip of the syringe towards the upper bubbles on the top of the go to the top and then push the needle bar to exclude air bubbles, (refers to the 10 μl syringe, with a core syringe flat feeling) into the sample speed should be fast ( But not easy to fast), each time the sample to maintain the same speed, the tip of the needle to the middle of the vaporization chamber to start injecting the sample.

Frequently asked questions about the injection needle

1、How to prevent the injection needle from bending?

Answer: Many novice chromatographers will often bend the syringe needle and syringe rod, the reasons are:

(1) the inlet port is screwed too tight, room temperature screwed too tight when the temperature of the vaporization chamber will be tighter when the temperature rises after the expansion of the silica gel gasket, it is difficult to tie the syringe in.

(2) The location of the needle is not good to find the metal part of the sample inlet.

(3) The syringe rod is bent is too strong when feeding the sample, the imported chromatography with a feeder rack, feed the sample with a feeder rack will not bend the syringe rod.

(4) Because the inner wall of the syringe is contaminated, the needle bar is pushed to bend when injecting. Syringe with a period of time will be found in the syringe near the top of a small section of black stuff, this time the suction 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. Analysis of 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 stable, eager to fast will bend the syringe, as long as you into the sample skilled natural fast.

2. into the needle skills TIPs?

(1) feel the needle into the sample pad is tighter, then inject the sample after the needle should be pulled quickly, if the needle into the sample pad feel loose, then inject the sample after the needle can be slower.

(2) Pull out immediately. The sample volume should be small to ensure that the peak shape is good. Note that the sampler does not leave air bubbles, slow suction, fast hit, the air bubbles out;

(3) more suction a few times before the sample to exhaust the air bubbles, fast in and out of the sample, the needle into the position to go as far as possible to fix the position, as for the sample after the start time, do not need to be particularly fast, as long as to ensure that you each time to tie up the end of the time interval according to the start can be consistent;

(4) generally to be pulled out immediately, there is a saying is that needle Into the sample pad will reduce the sealing of the introduction of some air impurities, according to the analysis of different samples, slow sampling will also cause tail dragging, in addition to the same batch of samples is best to enter the same person to ensure that the sampling of the reproducibility of the sampling of different people into the sampling error will be a big difference, according to agilent engineers say, can ensure that the error rate of 5% or less even if it is a relatively good, the original sampling needles are very expensive, be careful. There is also a saying that the sample can be pulled out immediately after injection can play a role similar to the role of stirring, in the injector to make the sample vaporization more uniform, can reduce the shunt discrimination effect.

(5) The solution to be measured should be contained in a sealed injection bottle (some need to be stored away from light), so as not to volatilize the solvent resulting in a change in the concentration of the solution between two injections.

(6) Before injecting the sample, the injection needle should be washed with solvent about three times to ensure that there is no residue from the last injection. Wash the injection needle with the solution to be measured about three times to ensure that the concentration of the sample and the concentration of the solution to be measured is the same.

(7) Pay attention to drive the air bubbles in the injection needle, so as to avoid deviation between the actual injection volume and the labeled value. Sampling techniques to be consistent, fast.

(8) The rubber ring should be checked diligently to avoid aging.

(9) into the needle should be aligned with the center of the hole in the sampler, to avoid in the process of the needle into the sampler catheter.

3. do liquid phase experiments into the needle was oxidized astringent, affecting the sampling, how to deal with it?

(1) most people recommend methanol rinse, ultrasonic 20 minutes, and then use pure methanol ultrasonic try, generally recommend that you use methanol after water freshening, and then wash with pure methanol, so that the needle will not be astringent in general, I used to wash with soapy water inside the layer of oily material.

(2) can also be used 5% dilute nitric acid wash, because the sample is sometimes not pure methanol dissolved in methanol and water, so the iron part of the feed needle on the rust, with dilute nitric acid wash can wash off the rust.