In the use of gas chromatograph, aging chromatographic column is very important and common operation, gas chromatograph, new replacement for new purchase of chromatographic column, for a long time for a long time without gas chromatograph, long-term in the running state of gas chromatograph and gas chromatograph analysis of complex samples such as using chromatographic column of a scenario must be aging on a regular basis.
The aging of gas chromatograph column refers to the operation of chromatograph for a long time under the condition of lower carrier gas flow rate, higher than normal sample column temperature and lower than the maximum service temperature of chromatograph column, also known as "baking chromatograph column".
Aging chromatographic column is to completely remove the residues and some volatile substances in the column filling, so that the separation performance of the column can reach the best state and obtain a stable chromatographic baseline.
1. When is the aging column needed?
The aging plan of the chromatographic column was made according to the use of the chromatographic column, and it was recommended to carry out the aging of the column periodically according to the week, month or quarter. In addition, aging columns need to be carried out in a timely manner when the following four conditions occur:
(1) Baseline noise is too large;
(2) difference of peak separation;
(3) miscellaneous peaks;
(4) Peak tailing is serious.
Figure 1 Example of column aging
2. "Chromatographic short-circuit" operation between gas chromatograph and LabSOLAR-6A all-glass automatic online trace gas analysis system
In the aging process of chromatographic columns, the preset column temperature is often higher than the normal column temperature to ensure sufficient desorption of the residue. Higher column temperature will make the gas chromatograph column pressure higher than the normal column pressure, and the Labsolar 6A all-glass automatic online Trace gas analysis system requires that the column pressure should not be higher than 0.2mpa. In order to avoid damage to the gas chromatograph and labSOLAR-6A all-glass automatic on-line trace gas analysis system, it is recommended to disconnect and short-circuit the gas chromatograph and labsolar-6A all-glass automatic on-line trace gas analysis system during aging chromatography, that is, to perform "chromatographic short-circuit" operation.
A manual four-way valve or 3-to-3 two-way connector should be purchased in advance before "chromatographic short-circuit" operation, as shown in Figure 2. The "chromatographic short-circuit" operation can be divided into the following two methods. Choose one of them according to the actual situation.
1) Use four-way valve
A four-way valve is installed in the loading pipe between the gas chromatograph and the Labsolar-6A all-glass automatic online trace gas analysis system. The on-off operation of the gas chromatograph and the system can be completed by turning the valve handle, as follows: The four-way valve can switch between two states, as shown in Figure 2. The four joints are connected in pairs. The first state is: position 1-4 connected and position 2-3 connected; The second state: bits 1-3 are connected and bits 2-4 are connected.
①when installing the four-way valve, ensure that the gas chromatograph is in a shutdown state, and the chromatographic carrier gas is in a closed state;
② Disconnect the gas pipe between the gas chromatograph and labSOLAR-6A all-glass automatic online trace gas analysis system;
③ The gas chromatograph end of the two load pipe and four valve joints are respectively connected with no. 2 and no. 4, labSOLAR-6A all-glass automatic online trace gas analysis system end of the two gas pipe is connected with no. 1 and no. 3 joints;
④ After the connection, the four-way valve for the necessary leak detection operation. The Labsolar-6A all-glass automatic online trace gas analysis system is disconnected from the gas chromatograph by turning the handle of the four-way valve during the aging of the chromatograph column, and then turning the handle of the four-way valve after the aging of the chromatograph column to connect the two.
Figure 2 Four-way valve connection operation for labSOLAR-6A All-glass automatic on-line trace gas analysis system
2) Use 3-to-3 coupling
① Ensure that the gas chromatograph is in the shutdown state, chromatographic carrier gas is in the shutdown state;
② Unscrew the two nuts of carrier gas inlet and outlet of LabSOLAR-6A all-glass Automatic online Trace Gas Analysis system;
③ Take out the 3-to-3 two-way connector, and take two waist drum washers from the spare part box of Labsolar-6A all-glass automatic online Trace gas analysis system;
④ Unscrew the nuts on both sides of the 3-to-3 two-way joint, remove the tough ring and nut, and then cover the two carrier air inlet and outlet nuts, the two gaskets and waist drum washers of the two-way joint respectively on the two carrier pipes;
⑤ Screw the two nuts to both sides of the two-way joint and tighten and fix them, as shown in Figure 3.
⑥ Open the pressure reducing valve of the carrier gas cylinder, perform the necessary leak test on the interface, and confirm whether the front pressure of the gas chromatograph column is normal.
Figure 3. Accessories required for "chromatographic short-circuit" operation of labSOLAR-6A All-glass Automatic on-line Trace gas analysis system
3. Aging column operation
① Open the pressure reducing valve of the carrier gas cylinder to confirm that the column pressure reaches the preset value;
② The "aging" method file in the operation software of gas chromatograph was used to start aging, and the aging was more than 4 h, as shown in Figure 4;
③ The aging operation was completed after the chromatographic baseline was stabilized.
Figure 4. Example of gas chromatography aging method invocation interface
If gas chromatograph operating software not being "ageing" method in the file, you can check the chromatographic column name plate as shown in figure 5 position, check the use of chromatographic column temperature range, and refer to the "sample" method in the file into the column temperature, aging temperature higher than the sample set column temperature 20 ℃, but shall not exceed the chromatographic column nameplates.it temperature, ageing, aged more than 4 h, The aging operation was completed after the chromatographic baseline was stabilized.
Figure 5 column nameplate
4. Precautions for aging chromatographic column
① The aging operation of chromatographic column must be carried out "chromatographic short connection" operation;
② The gas source shall not be disconnected during the aging process of the column;
③ The aging temperature of the column shall not exceed the service temperature of the column.
④ The aging temperature of chromatographic column is not the higher the better, but the lower the column temperature is the better under the premise of ensuring effective removal of pollutants.