Fluorescent whiteners, as dyes with whitening effect, are harmful to human body. In the detection of food contact plastic materials, if effective detection methods can be actively adopted to monitor the addition of fluorescent whitening agents, it is conducive to the maintenance of food safety. On this basis, this paper briefly analyzes the typing characteristics of fluorescent whitening agents in food contact plastic materials and their extraction paths, which can increase the reliability of the detection results through high performance liquid chromatography detection, white degree measurement detection, and ultraviolet light qualitative and quantitative detection methods, so as to provide a guarantee for the scientific supervision of food contact plastic materials in China.
1. Pyrazoline type
Fluorescent whitening agent is mainly used in the industrial field of dye additives, it can produce blue fluorescence in the actual use, thus giving a visual white bright sense, the use of which can be used to achieve the effect of complementary color whitening. After analyzing the electronic molecular distribution structure of photo whiteners, these compounds are able to successfully release light colors at wavelengths from 420mm to 450mm in a cyclic change from the ground state to the active state. They can actually be categorized into five different types. In this study, three common types are described. Among them, the pyrazole type belongs to the key subtype and its chemical formula, see (Figure 1). This type of fluorescent whitening agent can produce significant whitening effect during use, showing green fluorescent color. In China’s industrial acrylic products in the applicability of strong, but also for wool products can be used in appropriate amounts, since then to ensure that the fluorescent whitening agent to show the advantages of dyes, to open up the sales of industrial products.
2. Stilbene type
In China’s industrial field, the diphenylethylene-type fluorescent whitening agent has a wide range of applications, basically more than 80% of industrial products choose this type of fluorescent whitening agent. Especially in fiber products, can promote the product itself is more bright, to blue fluorescent color for the specific color, its chemical formula, see (Figure 2). From the specific use of fluorescent whitening agent type, this type of fluorescent whitening agent has the advantage of low cost, in the field of daily necessities production in China has a broad application space.
3. Coumarin type
Fluorescent whitening agent itself as a dye additive, it can play an auxiliary role in brightening the color of the product itself, so its application has a certain necessity, as long as it is used within the safety of the regulations can be. One of the early origins of a class of fluorescent whitening agent type that is coumarin type, it can produce blue fluorescent color. Combined with the structural features of the chemical formula (Figure 3), it is able to introduce heterocyclic aromatic groups and has relatively stable characteristics. Usually, this type of whitening fluorescent agent is used in nylon industrial products, as well as woolen fabrics, solar cells and other products. According to the above different typing characteristics, we can follow the safe dosage of fluorescent whitening agent in China, and reasonably apply it in the industrial industry.
Extraction path of fluorescent whitening agent in food contact plastic materials
In China’s food production process, food packaging materials are mostly plastic-based, both in terms of safety and economy, food plastic packaging has the corresponding choice of advantages. However, for direct contact with food plastic packaging materials, in its production, should strengthen the safety management of food packaging materials, and in the plastic packaging materials made, need to be contained in the fluorescent whitening agent to be accurately detected, to improve the safety performance of the material, so as to ensure that the plastic materials used for packaging of food do not contain fluorescent whitening agent hazardous to human health. Generally speaking, after consumers accidentally eat food containing fluorescent whitening agents in packaging materials, the human blood system, immune system, liver organs will be infringed to varying degrees. Therefore, in order to further safeguard the health of consumers, it is necessary to adopt a variety of methods to smoothly extract fluorescent whitening agents, thereby increasing the accuracy of the detection results.
1. Soxhlet extraction and hot water extraction
For fluorescent whitening agent in food plastic packaging materials, the inspector can adopt the soxhlet extraction method, hot water extraction method to be sampled. The former requires the inspector to research and take the packaging materials first, and then with the help of filter paper, the solvent is heated, and the resulting steam can be accompanied by the air conduit, prompting the fluorescent whitening agent in the packaging materials to be extracted in the form of solution flows into the extractor. This method is characterized by high efficiency, which can meet the requirements of inspectors for rapid extraction of products to be detected. The latter method relies on the stepped temperature to extract the light whitening agent. According to Li Yanhong in the comparison of hot water method and microwave method, the optimal temperature should be 80 ℃ to promote the extraction of fluorescent whitening agent.
2. Accelerated solvent extraction
When the sample is extracted for testing, the extraction operation can also be accomplished by accelerated solvent extraction. This method refers to high temperature (<200 ℃ C), high pressure (<20685kPa) conditions, the use of organic solvents, plastic packaging materials in such conditions, based on the gas-liquid differentiation of solvency, the material itself is in a high-boiling state, and then under the action of solvents, can be extracted into the solvent of the material in the fluorescent whitening agent, and then the next step in the test. Detectors use this method in the extraction operation, you can reduce the amount of solvent, accelerate the extraction speed, resulting in high recovery rate.
3. Ultrasonic oscillation and auxiliary extraction
Under the action of ultrasound, can also be extracted from the fluorescent whitening agent in plastic packaging materials, and then in accordance with standardized testing steps to complete the detection task. Which can be combined with the oscillation mode, auxiliary mode, to be extracted. The so-called ultrasonic oscillation is in the cavitation reaction and thermal effect, to promote the effective dissolution of the substance to be tested, so as to achieve efficient extraction. The ultrasonic assisted method is to purify the material to be detected in the packaging material with the assistance of the extraction solution, which can ensure that the fluorescent whitening agent sample is detached from the plastic packaging with the participation of solvents, and increase the convenience of the subsequent detection steps.
Detection of fluorescent whitening agents in food contact plastic materials
High Performance Liquid Chromatography (HPLC)
When detecting fluorescent whitening agents in plastic materials for food contact, inspectors can use advanced high-performance liquid chromatography (HPLC) to carry out comprehensive testing to ensure that the detection results are more reliable. Generally speaking, detectors need to follow the following steps to complete the detection task step by step.
The first step is to prepare the reagents, instruments and test articles needed for this detection method. Combined with the relevant requirements of high performance liquid chromatography detection method, you can use the Agilent 1200 high performance liquid chromatography for its detection. At the same time, the inspectors also need to be prepared in the testing laboratory Kedi high-speed centrifuge and Hangzhou FY-ADCY4S nitrogen blowing instrument, Shandong HD-ZF-109 fluorescence detector, HAD-TM1F vortex oscillator, Jiemeng ultrasonic cleaner, electronic balance, filters, etc., and also need to configure an appropriate amount of reagents such as chloroform and other reagents, and to be tested in the plastic packaging products (polyethylene plastic). In the testing process, inspectors need to follow standardized reagent and instrument use regulations to improve the effectiveness of this testing method.
In the second step, after preparing the above infrastructure, the inspectors need to enter the fluorescent whitening agent standard solution preparation and sample processing. The solution used in the detection process of high performance liquid chromatography is mainly based on acetonitrile solution. After extracting the samples, the inspectors can dilute and mix with the solvents, and then prepare a standard sample containing 100mg of fluorescent whitening agent concentration per 1L. In addition, it is also necessary to set the sample storage temperature, based on 4 ℃, and can also be continuously diluted into different concentrations of the solution to be tested, such as 1mg children’s l, 3mg/l and so on. As for the purification of the sample, the standard can be purchased, prepared in accordance with different concentrations, and then carry out a blank test, integrate the results from different concentrations of fluorescent whitening agent, and draw the corresponding detection curve, to be sampled into the on-line testing. At the same time, the same acetonitrile solution, trichloromethane solution with 70%, 30% dosage standard, the sample to be tested for ultrasonic centrifugation (speed: 9000r/min, temperature: 50 ℃, ultrasonic time: 0.75 hours, centrifugation time: 5 minutes), and the use of the above mentioned ammonia blowing apparatus and other instruments, after centrifugation of the sample for blowing dry. In the sample processing stage before the detection of high performance liquid chromatography, methanol and acetonitrile solution can also be used to wash the sample to ensure that after blow-drying to become a sample to be detected.
The third step is to improve the detection conditions. In the high performance liquid chromatography detection method, you can use a photometer to detect the wavelength of fluorescent whitening agent, and then determine the length of the chromatographic separation column. Afterwards, the chromatogram is drawn according to the above sample, from which the separation pattern is analyzed. Generally, it is necessary to use 80% acetonitrile solution with 20% ammonium acetate solution as the mobile phase if the elution time is within 1.5 minutes. For elution times up to 4 minutes, the ratio of A and B mobile phases was 4:1 or A mobile phase was dominant. As the elution time increased, the proportion of mobile phase A gradually increased, then decreased to 30% A at 8.5 min to 12.5 min, and then increased to 80% A again. The reliability of this test can be increased as the conditions of the liquid chromatography are improved. At the same time, the inspector also needs to strengthen the sample extraction and preparation, and organize the relevant data to deduce the specific results.
The fourth step is to make relevant inferences in the data summary. In the dilution of the standard sample dissolved wave, its concentration gradually decreases, and at this time, according to the comparison with the reference group, it can be found in the participation of high performance liquid chromatography can be derived from the specific test results, and also need to be matched with repeated tests to increase the accuracy of the detection data, to avoid the influence of error, resulting in the decline in the recovery of fluorescent whiteners, or the detection of the content of the consequences of the implausibility of the detection of the content of the product, in addition to the detection of fluorescent whitening agent in the basis of the In addition, in the detection of fluorescent whitening agent based on high performance liquid chromatography, if fluorescent whitening agent is measured in polyethylene plastic packaging, it can be inferred that the quality of this type of packaging is unqualified, and need to be recycled in a timely manner to optimize the effect of food packaging safety management.
2. White degree measurement detection method
In the detection of food contact plastic materials, you can also use the white degree measurement detection method to accurately analyze whether such packaging plastic bags are illegal to use fluorescent whitening agent, if the test is determined to contain hazardous whitening agent, it should be immediately disposed of properly, to avoid inflow into the market, harming the rights and interests of consumers. The so-called white degree measurement test method, is based on the specific performance of fluorescent whitening agent, to determine whether the bag to maintain the original white degree. Once the degree of white of the bag is found to exceed the standard range, i.e. over-white, the deep white color caused by the fluorescent whitening agent can be considered. However, when testers use this method, they can only obtain two types of measurement results, “used” or “not used”, to screen for non-compliant products by qualitative analysis, and cannot give a clear result on the amount of fluorescent whitening agent incorporated. Therefore, in order to meet the needs of large-scale safety testing of plastic materials for food contact, the whiteness testing method can be preferred.
3. UV qualitative and quantitative detection method
3.1. Qualitative detection by ultraviolet irradiation
In qualitative detection, the UV detection method can also be used to analyze the distribution of fluorescent whitening agents. If, according to the qualitative detection method, it is detected that the product to be tested does contain fluorescent whitening agent, it should immediately contact the manufacturer of plastic packaging products to prohibit the sale of this batch of products. And for the packaging products that have been sold, should establish a communication relationship with food manufacturers to ensure that the plastic packaging of food into the market in line with the safety of sales regulations.
For the UV irradiation qualitative detection method, it is the use of UV irradiation light absorption rate, from the visible light characteristics of the object to be tested to infer whether the bag contains fluorescent substances. The inspector can place the plastic material for food contact under the condition of UV irradiation, after irradiation, the surface of the material to be tested will be affected by the near-ultraviolet light (the wavelength range between 300nm and 400nm), and feedback with blue fluorescence and violet fluorescence. At this point, the inspector can visually detect the presence of fluorescent whitening agent on the test article. This method in the application of ultraviolet irradiation lamps and other equipment, can realize convenient detection, has the advantage of easy operation. However, because this detection method mainly relies on the detector’s visual observation. Therefore, it is a large error, and human risk is high, requiring the use of this method of testing personnel with a solid business foundation, but also need to do a good job of personal protection, so as not to be in the ultraviolet light irradiation, the personal safety of the test personnel to bring the threat. Detection in the laboratory, but also according to the release range of ultraviolet radiation lamps, will be set within the confines of the space, always safety detection as a benchmark, to promote qualitative detection of ultraviolet light to obtain more reliable results.
3.2 Quantitative UV Spectrophotometric Detection
In fact, in the detection of fluorescent whitening agents in food contact plastic materials, in addition to qualitative detection, quantitative detection methods should also be used to know the content of whitening agents and their varieties, so as to provide the basis for the relevant departments to provide directional verification. Under the ultraviolet irradiation technology, the whitening agent content can also be determined based on the immediate external spectrophotometry.
First, the inspector can prepare a sample of plastic material for food contact as a solution to be tested. Detection of the solution can increase the standardization of the detection process, to avoid direct detection of solid materials, increasing the tediousness of the detection step; Secondly, the inspector can choose the ultraviolet spectrophotometer, which has a wavelength of 200nm to 1000nm, can be divided into different wavelengths to be measured under different conditions, the material to be measured into different light zones. In the application of this detection method, the inspector needs to choose from a number of types of photometer, can choose the 721 type photometer, which is suitable for the wavelength of 360nm to 800nm environment, and can also utilize the 722 type photometer, which can release the ultraviolet light of 330nm. The smaller the wavelength accuracy of the photometer, the better it performs. Detectors choose a good photometer and other detection tools, but also should be prepared in accordance with the provisions of the standard solution, which should be prepared by gradient concentration parameters; again, the detectors should use the photometer to test the solution to be tested, it can be directly detected in the actual content of the whitening agent, but for the different types of whitening agent can not be given a clear boundary: Finally, the detectors need to record the results of the detection of different samples to obtain the average value can be used as a reference value, and the results can be used as a reference value. Finally, the tester should record the detection results of different samples and take the average value as a reference value to verify the general content of fluorescent whitening agents. In addition, the detector should also pay attention to the following matters, one of which is that the detector should fully consider the error factor in the detection of ultraviolet photometer. Since the fluorescent whitening agent is not the only one in plastic packaging materials that can absorb ultraviolet light. Therefore, this results in a wealth of other light-absorbing substances in plastic packaging materials, will increase the value of fluorescent whitening agent content; Secondly, the detector should wear good protective clothing, one to avoid the impact of ultraviolet light irradiation by the UV photometer, resulting in physical aggression; Secondly, we should keep the test reagents, to prevent direct contact with the reagents, resulting in the injury of the detector. In the face of different types of detection methods, detectors should be based on the purpose of fluorescent whitening agent detection to determine the detection method.