Gas chromatograph routine maintenance and operation precautions
Gas chromatograph routine maintenance and operation precautions
First, the host gas system:
(1) Gas source requirements:
Carrier gas: N2, He, H2: Purity: >99.995% inlet pressure: 0.42 Mp constant.
Gas: H2 purity: >99.995% inlet pressure: 0.3 Mp constant.
Gas: Air oil-free water inlet pressure: 0.42M constant.
(2) Pipelines and components:
The pipeline and filter, the injector, the steady flow valve, the pressure regulator valve, and the detector base should be kept clean. The interface with the external air circuit should be sealed with a plug or a cap when the instrument is not used for a long time. In order to prevent airway pollution, the ECD should remove the bee from the sample removal filter when it is not used for a long time. When not in use for a short period of time, do not close the air supply source and keep the internal pressure of the carrier gas path above atmospheric pressure to prevent the air from entering the deoxidation filter and making it invalid. .
(3) Flow regulating valve:
H2 valve, air valve, and blow-off valve During the flow adjustment process, the inner valve needle can only adjust the flow rate and is not allowed to close, otherwise the inner needle valve will be damaged. The switch operation should rotate the outer needle valve.
Capillary splitting system should pay attention to the shunt switch operation during the shunt operation can only be completed by the time program control solenoid valve. The diverter valve on the front of the injector can only regulate the split flow. Cannot be used for the switch, otherwise the valve stem will be damaged.
(4) When replacing the sample pad, pay attention to the direction of the sample pad. The smooth side should be oriented downwards.
(5) Activation of the carrier gas filter:
Connect a clean Ñ„3 stainless steel tube to the outlet of the injector inside the oven and connect it to the outlet of the carrier gas filter. Activation conditions:
Flow rate: large filtration gas: 60mL/min
Flow rate: small filter gas: 30mL/min
Oven temperature: 275 ° C
Time: >8 hours.
Second, the detector system:
(1) Thermal conductivity detector:
(1) Before the TCD operation, the carrier gas flow rate should be measured first from the TCD outlet, and the oven and TCD pool temperature should not be raised when no carrier gas passes. It is even more impossible to add bridge current.
(2) When using the machine, it is necessary to first set the temperature of the injector, the temperature of the detector, and the temperature of the column to the operating temperature before setting the temperature of the hot wire or the current.
(3) In the process of using TCD, pay attention to the limit of the hot wire temperature. The difference between the hot wire temperature and the cell temperature does not exceed 80 ° C unless high sensitivity or high boiling point materials must be used. For better stability when using, try to be as
Reduce fluctuations in room temperature.
(B), flame ionization detector (FID):
(1) If the use temperature of FID is higher than 300 °C, the sealing ring on the ceramic nozzle must use stone grinding material, otherwise it will affect the airtightness.
(2), the use temperature of the FID is not lower than 150 °C. Because below this temperature, the detector collection tube is prone to condensed water, resulting in the appearance of noise.
(3) Before sealing the FID, the sealed aluminum gasket must be replaced, otherwise it will cause air leakage and affect the ignition or sensitivity.
(4) The signal and the ignition arm must be kept clean. Do not touch the ceramic part and the wire by hand. Pay attention to the positive notch when installing the probe arm. Avoid damage to the wire.
(3) Electronic capture detector (ECD):
(1) When using ECD, be sure to install a deoxidizing filter behind the carrier gas filter. The deoxygenation filter should be replaced after using three bottles of high purity nitrogen. To prevent oxygen from entering the detector.
(2), before starting the power must first pass nitrogen, pay attention to the temperature rise sequence when starting, detector → injection sample → column temperature. Keep the detector temperature above the column temperature by 50 ° C to prevent residual samples in the column from contaminating the detector. The detector temperature is recommended to be greater than 250 °C.
(3) After the sample analysis is completed, increase the carrier gas flow rate to about 40-50 ml/min, the detector is heated to 350 ° C, and baked for 30-60 minutes. To prevent residual samples from remaining in the detector.
(4) Since the stability of ECD under high sensitivity is easily affected by the ambient temperature, the instrument should be placed in a place where the indoor temperature is not easily changed or there is no strong airflow to obtain a stable baseline.
(5) Because the linear range of ECD is relatively narrow, the linear range of γ-666 is about 10-9 to 10-13 grams. Excessive concentration or throughput will saturate the detector and return to normal working conditions. It takes a long time. Therefore, dilution is required when the sample is very concentrated.
In addition, when analyzing certain natural samples, due to the large amount of pollutants, it must be purified beforehand, otherwise the pollution caused by it is difficult to remove.
(6) In order to eliminate the pollution of the chromatographic system by the electronegative compound, it is good to use an alkane, benzene or toluene instead of using a halide, acetone or the like as a solvent. Do not contact the electronegative solvent for the injection injector, column, sample bottle, etc. for operation.
(7) Cleaning of the ECD detector:
When the ECD detector is used for a period of time, there will be a phenomenon that the fundamental frequency is increased, the noise is increased, and the sensitivity is lowered. At this time, the nickel source of the detector needs to be cleaned.
The cleaning method is as follows:
1. Replace the clean empty column and adjust the flow rate of the carrier gas: about 100ml/min. Injector temperature: 250 ° C, oven: 190 ° C, detector temperature: 350 ° C, baking for two to three days.
2, the conditions are the same as (1), injection of deionized water 100uL twice a minute, injection 9-10 times.
3. Carrier gas flow rate: 30ml/min, the temperature of the heating zone is the same as (1) The hydrogen flow valve is opened, and high-purity hydrogen is introduced. Flow rate: 50 ml/min. After 15-20 minutes of cleaning, close the H2 flow valve and recover for half an hour.
Please note! Both methods have a certain impact on the life of the nickel source sheet, please use it with caution.
4. After the ECD core is cooled down, it is taken out in a pure acetone solution for a day and night, and then placed on the instrument and baked for 48 hours according to the conditions (1).
(8) Since most samples detected by ECD are toxic, in order to prevent radioactive debris and harmful samples from causing harm to the human body, wash hands after operating ECD, do not directly touch the anti-shooting source, and apply plastic at the exit of ECD source core. The pipe is connected to the outside.
(4) Flame Photometric Detector (FID):
(1) The fragile component of the FID detector is a photomultiplier tube. Therefore, the high voltage power supply on the FID must be turned off before replacing the filter chip. Otherwise, the photomultiplier tube may be overexposed to affect the service life.
(2) In order to extend the service life of the photomultiplier tube, try to use a lower multiplication when sensitivity is allowed.
(3) The operating temperature of the detector is recommended to be between 150 °C and 250 °C. Excessively high temperature may cause aging of the sealing rubber ring in the base and the detector, causing air leakage.
(4) The detector should not be placed in a dry place for a long time to prevent the filter from getting wet.
(5), the burning part should pay attention to frequent cleaning, when the transparency of the quartz window becomes worse, it should be replaced in time. Take care to prevent fingerprints on the quartz window, lens, and photomultiplier tube during cleaning. When cleaning, the Zui is easily scrubbed with cotton yarn, acetone or ethanol.
(6) Since FID is a hydrogen-rich flame operation, the hydrogen flow rate is large, so when measuring the hydrogen flow rate, attention should be paid to indoor ventilation. After the end of the hydrogen measurement, the corresponding on-off valve should be closed in time to prevent the accumulation of hydrogen.
(5), thermionic detector (TSD, NPD):
The consumable component of TSD is the bead. During the operation, increasing the bead current can improve the sensitivity, but it will also cause the bead to overheat and reduce the service life.
(1) Avoid using high é“· current when sensitivity is acceptable. Otherwise, uneven heating of the beads will affect the service life.
(2) Generally, the sensitivity of the bead is attenuated with the use time. In order to restore the sensitivity, the current can be appropriately increased, especially in the days before the new bead starts to be used, the current is adjusted almost every day.
(3) Since TSD is very sensitive to nitrogen and phosphorus compounds, column fillers containing these two elements should be avoided. If they are not used, in addition to sufficient aging, lower column temperatures should be used as much as possible.
(4) When the TSD is not used for a long time, the bead should be kept dry and clean to prevent moisture.
(5), TSD bead will attach some pollutants on the surface of the bead after long-term use, which will increase the noise of the TSD detector and reduce the sensitivity. Gently rub the dirt off with a fine gauze paper
YT-M95
YT-M95
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