The purity of the solvent is one of the important factors affecting the use of the solvent, and is an important indicator for measuring the solvent level. In this paper, the ethanol solvent for printing was used as the analysis object. The purity of ethanol was tested by Labthink GC-7800 gas chromatograph. The process, equipment principle, parameters and scope of application were tested. Introduction, providing a reference for companies to analyze the purity of solvents.
Key words: solvent purity, gas chromatograph, ethanol, solvent for printing, solvent grade
1, meaning
Depending on the chemical composition, the solvent can be divided into an organic solvent and an inorganic solvent, both of which are used to dissolve other substances than themselves. For printing inks, solvent is an indispensable component, which can reduce the viscosity of the ink, make the ink leveling and dispersibility more excellent, and can adjust the volatilization speed, making the ink more suitable for printing. . Common printing solvents are toluene, xylene, ethanol, isopropanol, ethyl acetate, butyl acetate, acetone, cyclohexanone, etc. Before using the solvent for printing, the purity is the basic performance to be tested. First, this is because the level of the indicator reflects not only the production capacity of the solvent manufacturer, but also the printing speed and the printing quality of the printed product. For non-water-soluble inks, if the content of moisture impurities in the solvent is high, it will affect the printing suitability of the ink, and it will cause undesirable phenomena such as thickening, coarsening, precipitation and decomposition, and also affect the volatilization speed of the solvent as a whole. The printed product is prone to blocking, and the composite film may affect its composite fastness. For non-benzene solvents, if the benzene impurity is high, it may cause a residue in the printed product. Benzene solvents affect the quality and safety of the finished product; in addition, if the solvent content of the impurities in the solvent is large, it may affect the ratio of the ink solvent and adversely affect the printing process. Therefore, the solvent for printing should have a high purity.
2, test samples
The solvent sample detected in this test is a printing ethanol solvent produced by a certain company.
3, testing equipment
The test equipment used in this test is the GC-7800 gas chromatograph provided by Jinan Languang Electromechanical Technology Co., Ltd.
3.1 Test principle
Gas chromatographs use different partition coefficients of different substances in the column to achieve material separation. After the sample being tested is vaporized in the gasification chamber, the gas enters the column. Due to the difference in the partition coefficient of different substances, the flow velocity in the column is different, so the time from leaving the column to enter the detector is different. , thereby separating the mixed sample gas, which is represented by different peak times in the chromatogram, and qualitative analysis of the sample is realized; each substance entering the detector is converted into a corresponding electric signal and sent to the data processing station for processing, performance For the peaks of different areas (peak heights) on the chromatogram, the peak height or peak area depends on the amount of the corresponding substance, so that the quantitative analysis of the sample can be achieved.
When testing the purity of the ethanol solvent, since the impurities contained in the solvent are unknown, the purity calculation is performed by the area normalization method, that is, the correction factor of each substance contained in the solvent is assumed to be 1 and both peaks are generated. In the case, the peak area of ​​the ethanol is divided by the sum of the peak areas of the respective substances contained in the solvent to obtain the percentage of ethanol in the solvent.
Figure 1 GC-7800 Gas Chromatograph
3.2 Equipment parameters
The two samples were prepared in a constant temperature chamber, and the temperature control range was room temperature +5 ° C ~ 200 ° C, and the temperature control accuracy was ± 0.1 ° C.
In order to prevent sample condensation, the injection valve and sample transfer line can set the temperature and heat it. The temperature control range of both is room temperature +5 °C ~ 150 °C, and the temperature control accuracy is ±0.5 °C.
The equipment has a loop of 1.0 mL. Users can choose 0.5 mL, 2.0 mL, and 3.0 mL as needed.
The sampling line and the injection valve have a backflushing function, which can effectively avoid cross-contamination of the sample.
The patented automatic sample introduction sampling system has a sampling pump with sampling pump and injection valve. Negative pressure sampling, constant sampling pressure, accurate quantitative, good reproducibility and high sensitivity.
The gasification chamber and the detection chamber are in the temperature control range from room temperature +5 °C to 200 °C, the temperature control accuracy is ±0.1 °C, and the temperature control range is greater than 200 °C, the temperature control accuracy is ±0.2 °C.
The detector adopts a unitized combination design, adopts the plug-and-play extended control mode, and is equipped with a hydrogen flame ion detector and a thermal conductivity pool detector, which can be configured and selected according to the analysis needs.
The instrument can be operated at constant temperature and temperature, and the column chamber is equipped with a flexible rear door automatic temperature control system to achieve true near-room temperature operation.
The instrument has a low-pressure, gas-breaking protection function for the carrier gas path, and has a high-temperature protection function. When any temperature control exceeds a certain range of the set temperature, the instrument will be powered off and alarmed.
3.3 Scope of application
(1) The equipment can be used for the analysis of solvent residues in various packaging materials, and can be used for the analysis of the purity and moisture content of various packaging printing solvents.
(2) Equipment can also be used for the analysis of vinyl chloride monomer content by restructuring or adding special accessories.
4. Test process
4.1 Start up and warm up. After turning on the gas chromatograph and setting the instrument parameters and sample parameters such as gasification chamber temperature, column chamber temperature, and detection chamber temperature, click Start and the device starts to heat up and run the baseline.
4.2 Inject the sample. After each part of the device reaches the set temperature and the baseline is stable, 0.2 μL of the sample solution is taken from the sample with a sampling needle and injected into the device.
4.3 Start the test. Click on the test option, the test starts, and the device automatically analyzes the sample.
4.4 Data Processing. Click on the area normalization method, the device automatically displays the percentage of the material corresponding to each peak.
5, test results
The percentage of ethanol in the ethanol solvent for printing tested this time was 99.7%.
6 Conclusion
The purity of the solvent is an important factor affecting its use and use, and is an important basis for evaluating the solvent grade. In this paper, the purity of ethanol solvent for printing was tested by gas chromatography, and the results were analyzed by area normalization method. The whole test process is simple, Labthink GC-7800 gas chromatograph is easy to operate, the accuracy of the equipment and the accuracy of the test results are high, and the test results are stable and reliable. Jinan Languang Electromechanical Technology Co., Ltd. is a high-tech enterprise specializing in R&D, production and packaging quality testing services for packaging testing equipment. It has a professional packaging testing laboratory and has passed the CNAS accreditation. The laboratory's testing capabilities and testing data are available. Recognized internationally. At present, the testing equipment and testing services provided by the company have covered the barrier properties of packaging for oxygen, water vapor, nitrogen, carbon dioxide and other gases, physical and mechanical properties such as impact resistance, puncture resistance, heat sealing performance, smoothness and sealing performance. And chemical and hygienic properties such as solvent residue, evaporation residue, specific equipment and testing service information, you can visit to view. The more you understand, the more you trust! Labthink is looking forward to enhancing technical exchanges and cooperation with enterprises and institutions in the industry!
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