The technical solution of the present invention is illustrated below through specific specific examples. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. Moreover, unless otherwise specified, changes or adjustments to its technical content by those skilled in the art without substantial changes to the technical content shall also be regarded as the scope of the present invention.
 A solvent emptying method for a liquid chromatography-gas chromatography on-line combined interface is to connect a solvent emptying device between the retention pre-column 4 and the gas chromatography separation column 10 of the gas chromatograph; the solvent emptying device, Such as figure 2 As shown, it includes two three-way joints 5, 8 and a two-position switching valve 7 connected between the two three-way joints 5, 8.
 One of the three-way joints 5 is connected to the retention pre-column 4 of the gas chromatograph and the two-position switch valve 7 at the two ends of the straight-through joint I15, and a damping tube 6 is provided in the side end; The two ends are respectively connected to the gas chromatographic separation column 10 and the other connector II 16 adjacent to the aforementioned connector I 15 on the two-position switching valve 7, and a damping tube 9 is provided in the side end.
 The other connector III14 adjacent to the connector I15 on the two-position switching valve 7 is connected to the vapor outlet 12 of the gas chromatography; the other connector IV17 adjacent to the connector II16 on the two-position switching valve 7 is connected to the gas chromatography auxiliary carrier Gas 13 channel connection.
 The two-position switching valve 7 is a two-position six-way valve, and can also be a two-position eight-way valve or a two-position switching valve with more channels.
 The sample injection and detection system of the gas chromatograph, as shown in Fig. 1, includes an on-column injection port 1, a carrier gas 2, a deactivated pre-column 3 (deactivated quartz capillary tube, inner diameter 0.25-0.53mm, length 5 -15m), retention pre-column 4 (a GC analysis column with a length of 3-5m), solvent evacuation device (such as figure 2 Shown), gas chromatographic separation column 10 (universal GC/MS chromatographic column) and mass detector 11, connected to the vapor outlet 12 of the solvent evacuation device and auxiliary carrier gas 13.
 The solvent emptying method of the online interface of liquid chromatography-gas chromatography is applied to the LC-GC/MS online analysis of fatty acid methyl ester standard samples. The specific operation process is as follows:
 (1) Preparation of standard sample of fatty acid methyl ester: take 5 mg of methyl caproate to methyl myristate and place them in a 50 mL volumetric flask, 5 mg of methyl palmitate, 4.5 mg of methyl octadecanoate, and methyl eicosanate Ester 5mg and methyl behenate 5.3mg were also placed in a 50mL volumetric flask, and mixed with n-hexane to make a standard sample stock solution (methyl caproate to methyl myristate, methyl hexadecanoate, The concentration of methyl eicosanate is 0.1 mg/mL, the concentration of methyl octadecanoate is 0.09 mg/mL, and the concentration of methyl behenate is 0.106 mg/mL). Pipette accurately to transfer 1mL standard sample stock solution into the reagent bottle, add 9mL n-hexane, shake well, prepare standard sample for later use;
 (2) The liquid chromatographic fraction adopts automatic sampling mode, the injection volume is 20μL, the mobile phase is ether and pentane, gradient elution, the ether is linearly increased from the initial 5% (volume percentage) to 95% after 5 minutes, Hold for 45 minutes, after the UV detector detects the target fraction, the LC fraction cutting valve rotates, and the fraction enters the deactivated pre-column 3 and retention pre-column 4 of the gas chromatography;
 (3) At this time, the on-column injection port 1 and furnace temperature of the GC are 40°C and 42°C respectively, the two-position six-way valve 7 is opened, and the auxiliary carrier gas 13 passes through the two-position six-way valve 7 to the gas chromatograph. Column 10 provides auxiliary carrier gas 13. Carrier gas 2 and liquid chromatography mobile phase are all evaporated and discharged from steam outlet 12 through the two-position six-way valve. Both carrier gases are set to constant flow mode, and the flow rate is set to 2 mL/min. , The size of the gas chromatography separation column 10 is 60m×0.32mm. Through the above setting, the carrier gas flow rate of the steam outlet 12 can reach 15 mL/min. After the above process, the mobile phase of the liquid chromatography is completely discharged from the vapor outlet 12, which completely prevents the mobile phase of the liquid chromatography from entering the mass detector 11, and the components to be tested in the liquid chromatography are retained in the retention precolumn 4 due to the solvent effect. Inside;
 (4) After the mobile phase of the liquid chromatography is completely evaporated, the two-position six-way valve 7 is turned and closed, the retention pre-column 4 is connected to the gas chromatography separation column 10, the furnace temperature is programmed to increase, and the carrier gas 2 comes from the liquid chromatography fraction The components to be tested are transferred to the gas chromatography separation column 10 through the two-position six-way valve 7 for separation, and then detected by the mass spectrometer 11;
 (5) After the components to be tested are completely transferred to the gas chromatography separation column 10, the two-position six-way valve 7 is opened again, and the retention pre-column 4 and the gas chromatography separation column 10 are completely disconnected again, avoiding the retention of the pre-column 4 The internal high boiling point components enter the gas chromatographic separation column 10, and the purification process of the retention pre-column 4 is greatly accelerated (the carrier gas flow rate is greatly accelerated).
 Liquid chromatography conditions:
 Liquid chromatography column: silica gel column (5μm particle size, 2.1x150mm); liquid chromatography pump (Agilent1260). The wavelength of the UV detector is 210nm. Mobile phase: diethyl ether and pentane, the gradient elution scheme is that diethyl ether increases linearly from 5% by volume to 95% in 5 minutes, the flow rate is 0.15mL/min, the column temperature is 30℃, and the cutting time is 5.2min. Autosampler with 20μl injection volume.
 GC-MS conditions:
 On-column injection mode, the initial temperature of the on-column injection port is 40℃, keep for 11min, the two carrier gases are set to constant flow mode, the flow is 2mL/min; Chromatographic column: DB-5MS (60m×0.32mm ID, The film thickness is 0.25μm). Furnace temperature box: keep at 42°C for 11 minutes, and raise the temperature to 280°C at 5°C/min for 15 minutes. The ionization mode of the mass spectrometer: EI, electron energy 70eV, ion source temperature 180°C, scanning range 33-350amu.
 The two-position six-way valve 7 is controlled by the Valve control module on the PerkinElmer Clarus600T gas chromatograph, and only has two modes: ON/OFF. Therefore, the solvent emptying method of the present invention not only avoids the influence of a large amount of liquid chromatography mobile phase gas chromatography detector (especially the MS vacuum system), but also can flexibly isolate and connect the retention precolumn and the gas chromatography separation column.
 The LC-GC/MS detection results of fatty acid methyl ester standards are as follows image 3 As shown in Table 1:
 Table 1 LC-GC/MS detection results of fatty acid methyl ester standard sample
 keep time
 It can be seen from this that using the on-column interface method and solvent emptying method designed for the LC-GC/MS on-line coupling designed in the present invention, from methyl caproate to methyl behenate can be detected, and the peak shape is symmetrical , The resolution is relatively high, indicating that the solvent emptying method of the LC-GC online coupling interface designed and installed in the present invention does not cause the loss of low boiling point components or peak broadening. The LC-GC/MS based on the solvent emptying method of the present invention is suitable for the determination of components from low boiling point to high boiling point in a complex system, and has a wide range of application and good use effect.