25 small tricks to get the gas chromatograph

Tate Instruments is a professional manufacturer of gas chromatographs, portable chromatographs and related chromatographic consumables (chromatographic injection pads, columns, chromatographic syringes, etc.). The equipment is in line with national standards and is favored and recognized by users in the market. Below, the technicians of Tate Instruments introduced 25 small tricks to get the gas chromatograph.

(1) The gas chromatograph should be operated strictly under the specified conditions, and corresponding measures must be taken when it is not met under certain conditions;

(2) When the FID is combined with the standard small-diameter capillary column, the capillary column can be inserted into the inner hole of the FID quartz nozzle, and the end face of the column is slightly lower than the nozzle opening of 1 to 2 mm, which can ensure excellent column efficiency;

(3) The gas pressure regulator in the gas chromatograph is generally adjusted before the factory, and the user does not have to change. If it needs to be re-adjusted, it must be noted that the regulator valve can only be regulated under the condition that the pressure difference between the valve before and after the valve is greater than 0.05MPa. The function, that is, if the output pressure of the regulator valve is required to be 0.15MPa, the input pressure of the regulator valve must be greater than 0.2MPa, and the inlet pressure of the regulator valve on the gas chromatograph must not exceed 0.6MPa, which exceeds the pressure regulator;

(4) The temperature of the oven must be set lower than the high temperature of the chromatographic fixative. The temperature of the detector should be set so that the sample does not condense in the detector. The temperature setting of the vaporizer injector system should be higher than that of the sample component. The average boiling point should generally be higher than the oven temperature by 30 to 50 ° C;

(5) The current setting of the TCD bridge current is related to the type of carrier gas, and also depends on the operating temperature of the thermal conductivity cell. The sensitivity of the object to be analyzed should be considered. For details, please refer to the current reference curve of the thermal conductivity cell bridge.

(6) When using the GC2030 gas chromatograph, be sure to check the status of the TCD bridge current toggle switch on the right side of the cabinet of the microcomputer control system. It should be in the correct position. For example, when using FID, the toggle switch should be placed on the bridge current. Open position; otherwise, accidentally pressing the TCD bridge flow button during the operation of the panel button will cause damage to the TCD thermal conduction component;

(7) The operation of the thermal conductivity detector must strictly abide by the operating principle of the thermal conductivity detector after passing the carrier gas through the thermal conduction constant current source. When restarting the operation after a long-term shutdown, the carrier gas should be passed through for 15 minutes or more, and then the detector is energized to ensure that the thermal conductive element is not oxidized or burned out;

(8) When using the thermal conductivity detector, the double column must be connected in parallel. If the TC-4 micro thermal conductivity cell is used in combination with the capillary column, the other circuit must also be equipped with a column or an empty column tube, thus ensuring thermal conductivity. The carrier gas is passed through the two air chambers of the pool. If only one column is installed, the other heat conducting element without the column will be burned out due to non-ventilation;

(9) When replacing the silicone rubber pad of the vaporization chamber, be sure to turn off the current of the thermal conductivity cell bridge first. After replacing the silicone rubber pad, turn on the bridge current after passing the carrier gas for a few minutes;

(10) When the plane six-way valve is used for gas injection, the flow rate and pressure of the sampled gas should be repeated and consistent every time to ensure the repeatability of the analysis. When the plane six-way valve rotates, it can only be placed at the two-end position and cannot be placed. In the middle, the intermediate position will cause the carrier gas to be cut off, which will cause damage to the thermal conductive element;

(11) Carrier gas 2 way, mainly for packed column, carrier gas 1 way mainly for capillary column (can also be used as packed column), when making capillary column, steady flow valve should be fully open, capillary flow flow regulator valve To adjust, to ensure that the flow rate of the capillary column is unchanged when the flow rate is adjusted; when the carrier gas is used as the packed column, the pressure regulating valve is fully opened, and the steady flow valve is used to adjust the column flow. The diaphragm purge gas flow rate is generally 2 ~ 10ml / min, can be measured at the outlet with a soap membrane flowmeter or float flowmeter;

(12) The carrier gas widely used in domestic thermal conductivity detectors is hydrogen. Before the carrier gas is passed into the gas chromatograph, it should pass through the gas purification tube. The gas purification tube is filled with molecular sieve to absorb the moisture in the carrier gas. It contains 105 catalysts to absorb oxygen in the carrier gas. The water and oxygen are removed to protect the column and detector and prolong the service life. Therefore, the adsorbent in the gas purification pipe must be periodically activated to maintain the purification effect;

(13) When the gas chromatograph GC2030 is shut down after use, it must be remembered to screw the bulkhead nut at the outlet of the thermal conductivity cell to prevent oxygen from returning to the column and detector system after the carrier gas is cut off. Columns and detectors, after high temperature use, pay special attention to the fact that the oven and detector temperatures must be below 70 °C to shut off the gas source;

(14) The sealing ring for column connection can be made of different materials according to different use temperatures. Generally, silicone rubber ring can be used below 200 °C, PTFE ring can be used below 200 °C ~ 250 °C, and copper ring can be used above 250 °C. Or a flexible graphite ring;

(15) When using a small-diameter capillary column to divert the sample, the user can connect a piece of activated carbon (f3×0.5mm tube, length 50-60mm) to the flow channel in front of the diverting valve in the split gas path (40～60). The adsorption tube is used to adsorb the organic matter protection diversion regulating valve;

(16) In order to ensure the stability of the baseline when the FID is used under high sensitivity, the gas should remove trace CH (hydrocarbon) impurities in the gas; the column stationary phase must be fully aged at a temperature slightly lower than the high use temperature, thereby reducing the fixative The effect of solvent residue in the loss and fixed solution on the baseline; when the vaporization chamber is used at high temperature, the silicone rubber pad of the injector must be pre-treated at high temperature and the diaphragm cleaning gas path is opened;

(17) TCD carrier gas outlet and split outlet flow rate can be accurately measured by using a soap membrane flowmeter, and a 6-60ml/min glass rotor flowmeter can be continuously monitored on the left side of the host;

(18) After analyzing a large number of samples, the FID system may contaminate the nozzle or detector seat and need to be removed and reinstalled. When recovering, it must be noted that the polar circle should be in the same plane as the nozzle. The nozzle cannot collide with the polarization pole. If the nozzle mouth is lower than the polarization pole, the noise will increase; if the nozzle mouth is higher than the polarization pole, the detection sensitivity will be lowered;

(19) Maintenance of the gas chromatograph not only enables the instrument to work properly but also prolongs the life of the instrument;

(20) After a certain number of injections using a gas chromatograph, the accumulation of some water or other substances in the column (whether it is a packed column or a capillary column) will affect the efficiency and baseline stability. Therefore, the column must be activated. The column that has been deactivated for a long time must be activated before reuse. A simple method for activation treatment on a gas chromatograph is to pass high-purity nitrogen and heat the column at a constant temperature. The nitrogen flow rate is about 50-60 ml/min, and the column activation temperature is about 10 °C lower than the fixed liquid high-use temperature. Commonly used adsorbents for chromatography: molecular sieves have an activation temperature of 300 ° C; silica gel, activated carbon, and GDX have an activation temperature of 200 ° C. The activation time is usually 3 to 4 hours and then naturally cooled (nitrogen is still in circulation). When the column is activated, the outlet end of the column must be removed from the joint of the detector to prevent contamination from being introduced into the detector system during the column activation process;

(21) When using FID when starting up, it must first pass the carrier gas, air, and then open the temperature control. When the temperature of the detector exceeds 100 °C, the hydrogen can be ignited. When the FID system is shut down, the hydrogen gas must be turned off first, then the temperature control is turned off, and the carrier gas and air are turned off when the column temperature is lowered. If the FID temperature is lower than 100 °C when starting up, it will be ignited by hydrogen, or it will be cooled without shutting down first when it is turned off. It is easy to cause the FID to collect water and reduce the insulation of the input stage of the amplifier, which will cause the baseline to be unstable.

(22) After the FID is ignited, the voltage after ignition will be higher than the original value due to the effect of the base current, and the height can be roughly judged whether the degree of gas purification and the aging of the column are good or not;

(23) The desiccant (silica gel, molecular sieve type) is placed in the shielded iron box of the FID amplifier to maintain the high insulation performance of the amplifier input stage. Due to the influence of moisture in the ambient air, after using for a period of time, the desiccant should be replaced or the desiccant originally placed inside should be taken out and baked (activated) at 150 ° C for two hours before reuse, which can reduce noise and ensure Baseline stability;

(24) The column temperature is strictly prohibited to exceed the allowable temperature of the fixed liquid in the stationary phase, and the general column temperature is lower than the allowable temperature;

(25) When the gas chromatograph is turned off, first lower the column temperature and then turn off the carrier gas source.