Gas chromatograph injection needles generally use 1ul and 10ul. Although the injection needle is small, it is indispensable. The injection needle is the channel connecting the sample and the analytical instrument. With the injection needle, the sample can enter the chromatographic column and pass through the detector for continuous spectrum analysis. Therefore, the maintenance and cleaning of the injection needle is the focus of analysts’ daily attention. Otherwise, it will not only affect work efficiency, but also cause damage to the instrument. The following figure shows the components of the injection needle.
Classification of injection needles
According to the appearance of the injection needle, it can be divided into conical needle injection needles, bevel needle injection needles, and flat-head injection needles. Conical needles are used for septum injection, which can reduce damage to the septum and withstand multiple injections. They are mainly used in automatic injectors; bevel needles can be used on injection septa, which is easy to operate. Among them, 26s-22 needles are most suitable for use on injection septa in gas chromatography; flat-head injection needles are mainly used on injection valves and sample pipettes of high-performance liquid chromatographs.
According to the injection method, it can be divided into automatic injection needle and manual injection needle.
According to the different analysis requirements of the injection needle in the gas chromatograph and liquid chromatograph liquid, it can be divided into gas injection needle and liquid injection needle. The gas chromatography injection needle generally requires less injection, and the most common injection volume is 0.2-1ul, so the corresponding injection needle is generally 10-25ul. The selected needle is a cone type needle, which is convenient for injection operation; in comparison, the liquid chromatography injection volume is generally larger, and the common injection volume is 0.5-20ul, so the relative needle volume is also larger, generally 25-100UL, and the needle tip is flat to prevent scratching the stator.
In chromatographic analysis, the most commonly used injection needle is a micro injection needle, which is particularly suitable for gas chromatograph and liquid chromatograph liquid analysis. Its total capacity error is ±5%. The airtight performance withstands 0.2Mpa. It is divided into two types: liquid storage injector and liquid storage injector. The specification range of the non-liquid micro-injector is 0.5μL-5μL, and the specification range of the liquid micro-injector is 10μL-100μL. The micro-injection needle is an indispensable precision instrument.
Use of the injector
(1) Check the injector before use, check whether the syringe has cracks and whether the needle tip is burred.
(2) Remove the residual sample in the injector, wash the injector with solvent 5~20 times, and discard the waste liquid from the first 2~3 times.
(3) Remove the bubbles in the injector, immerse the needle in the solvent, and repeatedly draw the sample. When draining the sample, the bubbles in the injector can change with the vertical change of the tube.
(4) When using the injector, first fill the injector with liquid, and then drain the liquid to the required injection volume.
Maintenance of the injection needle
(1) Medium to high viscosity samples should be diluted or a large inner diameter injection needle should be selected before use.
(2) When cleaning the needle, cleaning tools should be used, such as a guide wire or a stylet, tweezers, and surfactants should be used to clean the needle wall.
(3) Thermal cleaning: Thermal cleaning is used to remove organic residues on the needle, especially for trace analysis, high boiling point and sticky substances. After a few minutes of thermal cleaning, the needle cleaning tool can be used again.
Cleaning of the injection needle
1. The inner wall of the injection needle can be cleaned with an organic solvent. When cleaning, please check whether the injection needle push rod can move smoothly;
2. If the injection needle push rod does not move smoothly, the push rod can be removed. It is recommended to wipe it clean with a soft cloth dipped in organic solvent.
3. Repeatedly use organic solvent to aspirate. If the resistance to the injection needle push rod increases rapidly after several aspirations, it means that there are still some small dirt. In this case, the cleaning process needs to be repeated.
4. If the injection needle push rod can move smoothly and steadily, check whether the needle is blocked. Repeatedly rinse the needle with organic solvent and check the shape of the sample being pushed out of the needle.
5. If the injection needle is normal, the sample will flow out in a straight line. If the needle is clogged, the sample will be sprayed out in a fine mist from one direction or an angle. Even if the solvent sometimes flows out in a straight line, be careful to check that the flow is better than normal (just compare the flow with a new, unblocked injection needle).
6. The blockage in the needle will destroy the reproducibility of the analysis. For this reason, needle maintenance is necessary. Use something like a wire to remove the blockage in the needle. The needle can only be used when the sample flows out normally. Using a pipette to aspirate liquid or a syringe cleaner can also effectively remove contaminants in the needle.
Precautions when using the injection needle
Do not hold the syringe needle and the sample part with your hands, and do not have bubbles (when aspirating, drain slowly, quickly, and then aspirate slowly, repeat several times, 10 The volume of the metal needle of the μl syringe is 0.6μl. If there are bubbles, you can’t see them. Take 1-2μl more and point the needle tip upwards until the bubbles go to the top, then push the needle rod to remove the bubbles. (Referring to the 10μl syringe, the syringe with a core feels flat) The injection speed should be fast (but not too fast), keep the same speed for each injection, and start injecting the sample when the needle tip reaches the middle of the vaporization chamber.
How to prevent the injection needle from bending? Many novices who do chromatography analysis often bend the needle and syringe rod of the syringe. The reasons are:
1. The injection port is screwed too tightly. If it is screwed too tightly at room temperature, the silicone seal will expand and tighten when the temperature of the vaporization chamber rises. At this time, it is difficult to insert the syringe.
2. The needle is stuck in the metal part of the injection port when the position is not found well.
3. The syringe rod is bent because too much force is used during injection. Awesome, imported chromatographs come with an injector rack, and injecting with the injector rack will not bend the syringe rod.
4. Because the inner wall of the syringe is contaminated, the needle rod is pushed and bent during injection. After using the syringe for a period of time, you will find a small black thing near the top of the needle tube, and it will be difficult to suck the sample and inject. Cleaning method: Pull out the needle rod, inject a little water, insert the needle rod into the contaminated position and push and pull repeatedly. If it doesn’t work once, inject water again until the contaminant is removed. At this time, you will see that the water in the syringe becomes turbid. Pull out the needle rod and wipe it with filter paper, and then wash it with alcohol several times. When the sample to be analyzed is a solid sample dissolved in a solvent, wash the syringe with solvent in time after injection.
5. Be sure to be steady when injecting. If you are eager to speed up, the syringe will be bent. As long as you are proficient in injection, it will be fast.
Post time: Jun-19-2024