Abstract: Liquid milk is a nutritious food that is commonly used by the public. It is often packaged in black and white film. During the packaging process or when unpacking, occasionally it will smell like paint, which is caused by the residual organic solvent in the bag. In this paper, Labthink GC-7800 gas chromatograph is used to test the solvent residue of the packaging bag, and the principle, equipment parameters and testing process of the equipment are described. It has certain guiding significance for the enterprises that are troubled by the packaging odor problem.
Key words: dairy products, liquid milk, black and white film, solvent residue, odor, printed film, gas chromatograph
1, meaning
Liquid dairy products are used as nutritious foods for the general public. The safety quality directly affects the health of consumers. Liquid milk often has bitter taste, flocculent precipitation, and mildew mold in the milk bag during the shelf life. The odor is packaged. The odor is similar to the smell of paint or other chemical agents. In severe cases, odor will migrate to the dairy product, making the dairy product inedible. The main reason for the appearance of odor is that the black and white film used in liquid milk generally adopts a surface printing process, that is, a special water-resistant and high-temperature resistant surface printing ink is printed on the outer surface of the black and white film packaging. At the same time, the resin materials and inks used in the manufacturing process and printing process of black and white film are prone to harmful small molecular substances or organic solvent residues. Therefore, dairy companies should strengthen the detection of solvent residues in liquid black and white film packaging.
Figure 1 Liquid milk black and white film packaging
2, the implementation of standards
This test can refer to GB/T 10004-2008 "Plastic composite film for packaging, bag dry composite, extrusion compounding" in the standard for the detection of solvent residues.
3, test samples
Black and white film bags from a dairy factory.
4, test equipment
GC-7800 gas chromatograph produced by Jinan Languang Electromechanical Technology Co., Ltd.
Figure 2 GC-7800 Gas Chromatograph
4.1 Test principle
Gas Chromatograph is a separation and analysis tool for multi-component mixtures. It uses inert gas as the mobile phase and uses column separation technology. When multiple analytes enter the column, the flow coefficients of the components in the column are different due to the different partition coefficients of the components in the column. After a certain column length, the mixed components leave the column separately. After entering the detector, after being detected, it is converted into an electrical signal and sent to the data processing workstation, thereby completing the detection and analysis of the tested substance.
4.2 Scope of application
(1) Solvent residue: It is suitable for solvent residue analysis and testing of various foods, plastic film for pharmaceutical packaging, paper-plastic composite film, cigarette packets and other materials.
(2) Purity analysis: Suitable for purity analysis of various packaging printing solvents.
(3) Moisture analysis: Suitable for solvent moisture content analysis in the packaging and printing industry.
(4) Special accessories or modifications are required to expand and apply to the analysis of vinyl chloride monomer content
4.3 Equipment parameters
The instrument is capable of constant temperature and temperature programmed operation. The column chamber is equipped with a flexible rear door automatic temperature control system, which can realize the near-room temperature operation in the true sense. The temperature control range of the column chamber is room temperature +3 °C ~ 400 °C, the temperature control accuracy is better than ±0.1 °C, the deviation between the set temperature and the display temperature is not more than 1 °C, the deviation between the set temperature and the actual temperature. Not more than 2%.
The instrument can be programmed to increase temperature, the heating order is 5 steps, the heating rate is 0.1 ~ 30 °C / min, and the repeatability of the program temperature is not more than 2%.
The temperature control accuracy of the gasification chamber and the detection chamber in the temperature range from +15 °C to 200 °C is ±0.1 °C, and the temperature control accuracy is ±0.2 °C when it is greater than 200 °C.
The basic configuration of the instrument is a hydrogen flame ionization detector (FID) with a detection limit of no more than 2 × 10-11 g/s (benzene), a noise of no more than 0.025 mV, and a drift of no more than 0.15 mV/h.
The detector adopts a unitized combination design and adopts a plug-and-play extended control mode. The hydrogen flame detector and thermal conductivity detector can be configured according to the needs of the user's analysis. The instrument can be installed with up to four detectors at the same time.
The injection system is available with a variety of injection devices such as packed column head injection, capillary column split/splitless injection with diaphragm cleaning.
The response signal can reach a wide range of 1500 mV with good consistency and can meet the needs of high-purity sample analysis.
Excellent chromatographic oven performance, at room temperature +3 °C near room temperature in both the detector and gasification chamber, and the instrument has good temperature-program repeatability, ensuring the retention of complex component samples. Time consistency.
The instrument has a high temperature protection function. When any temperature control exceeds a certain range of the set temperature (set value is 20 °C), the instrument will be powered off and alarmed. The instrument has a low pressure and gas shutoff protection function for the carrier gas path.
The unique operation and control system software and hardware design, the instrument automatically implements the whole process software monitoring during the operation process, which fundamentally eliminates the phenomenon that the instrument temperature and operating parameters are out of control. It achieves no “fault†over-temperature protection, as well as a unique active over-temperature protection function and dual hardware self-locking over-temperature control structure to ensure that the instrument operates safely when unattended.
5, the test process
(1) Set the test parameters. After clicking Start, the GC-7800 gas chromatograph starts the baseline balance.
(2) After the baseline of the instrument is stable, mix the mixed standards of different concentrations, inject them into the sealed headspace bottle, and place them in a constant temperature room at 80±2 °C for 30 min.
(3) Take a certain amount of standard sample gas from the above-mentioned headspace bottle with a sampling needle, quickly inject it into the chromatograph, or configure the autosampler to automatically inject. A standard curve of the peak area of ​​each reference material and the corresponding concentration is plotted.
(4) Quickly cut the 0.2 m2 sample into 10 mm × 30 mm pieces, place it in a clean bottle preheated at 80 ± 2 °C, quickly seal it, and place it in a constant temperature room at 80 ± 2 °C. Leave for 30 min. Note that the sample should be protected from contamination during the sample preparation process.
(5) Use a sampling needle to take a sample gas from the thermostated vial and quickly inject it into the chromatograph, or configure the autosampler to automatically inject.
(6) The concentration of the component is read from the standard curve of the corresponding component based on the peak area of ​​the sample.
6, test results
The total amount of solvent residues of the liquid milk package for black and white film packaging was 7.5792 mg/m2, and the benzene type was 0.1411 mg/m2.
7. Conclusion
From the above test results, the reference to GB/T 10004-2008 "Packaging plastic composite film, bag dry composite, extrusion compounding" in the solvent residue is the total solvent residue ≤ 5.0 mg / m2, of which benzene Solvents should not be detected (< 0.01 mg/m2), so the total amount of solvent residues in the samples tested in this paper exceeded the standard. The odor of the samples was mainly caused by the high residual solvent. Labthink GC-7800 gas chromatograph has the advantages of high test accuracy, good accuracy and safe use in testing solvent residues. It can truly reflect the hygienic chemical properties of packaging materials and help dairy companies solve the problem of packaging odor. In addition to black and white film, GC-7800 gas chromatograph can also be used to test solvents in plastic composite film, aluminum-plastic composite film, aluminum-plated composite film, paper-based composite film, printed single-layer film and other packaging materials. Residual amount. Labthink has been committed to providing professional testing services and equipment to customers around the world. Over the years, it has provided thousands of solvent residue testing services to customers around the world, providing customers with reliable technical solutions. For more information on related test instruments, you can log in to view specific information. Labthink is looking forward to enhancing technical exchanges and cooperation with users in various industries.
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