Benzoic acid as a food additive, its amount will directly affect human health. This paper reviews the basic principles of high performance liquid chromatography, capillary electrophoresis, gas chromatography, ultraviolet spectrophotometry and thin layer chromatography, and the research progress in benzoic acid detection technology in recent years. Finally, we look forward to these tests. The method has a prospect in the detection of benzoic acid. The appearance of benzoic acid is white crystal with benzoin or styrene odor. Its vapor is very irritating. It is mainly used as a food additive. It has the effect of inhibiting the proliferation or killing of microorganisms in food, preventing food from spoiling and spoiling, and maintaining the freshness of food. However, if it is added in excess, it can not only destroy vitamin B1, but also cause calcium to form insoluble substances, affecting the body's absorption of calcium, and also has a stimulating effect on the gastrointestinal tract; excessive consumption can induce cancer [1], long-term use can induce asthma, Allergic reactions such as urticaria and angioedema have adverse effects on human health. In recent years, food safety has become a common concern of the whole society. Benzoic acid as a food additive, China's GB2760? 1996 "Sanitary Standards for the Use of Food Additives" stipulates that its use limit should be <0.1g / kg, so the research on the detection of benzoic acid content has also received much attention. In this paper, the research progress of benzoic acid detection methods is reviewed, which provides a reference for the detection of benzoic acid in food additives in China. 1. High performance liquid chromatography High performance liquid chromatography (HPLC) has been developed since the late 1960s. It has small and uniform filler particles and high column efficiency. This method is currently the most widely used chromatographic method. Compared with classical liquid chromatography, it has the advantages of high resolution, high sensitivity, low sample volume, easy recovery and reusable column. [2] China National Quality Supervision Bureau issued a method for the determination of benzoic acid and sorbic acid in milk and dairy products by high performance liquid chromatography. The standard specifies the detection method of benzoic acid in dairy products and the method for determination of high performance liquid chromatography. Determination of benzoic acid and sorbic acid content in dairy products. [3] The milk powder, yoghurt and other fermented dairy products were treated with zinc acetate and potassium ferrocyanide solution as precipitants, respectively, and then the content of benzoic acid was determined by reversed phase chromatography. It proves that the method has the advantages of simple pretreatment, high convenience, high sensitivity and good reproducibility. In addition to the benzoic acid content of dairy products, liquid chromatography can also determine its content in other foods. Tfouni et al [4] used high performance liquid chromatography to determine the content of benzoic acid in Brazilian food. The foods such as beverage, juice, butter and cheese are pulverized, mixed with distilled water, and the pH is adjusted to be alkaline with sodium hydroxide solution. Finally, the supernatant is centrifuged, and the supernatant is taken for reverse phase chromatography. The precision and accuracy of the inspection can meet the analytical requirements. Liu et al [5] used liquid chromatography to determine the content of benzoic acid in flour and fried foods. The sample was sonicated by ethanol and then extracted with benzoic acid, and then eluted with a gradient on a C18 column. The linear detection range of benzoic acid was 0.50~15.06mg/L, and the minimum detection limit was 0.22mg. 2. Capillary electrophoresis Capillary electrophoresis (referred to as CE) is a new type of high-efficiency separation technology developed in the early 1980s [6]. The capillary is used as the separation channel and the high-voltage branching electric field is used as the driving force. The fused silica tube with an inner diameter of 25,000~100,000 nm is usually used. The capillary is characterized by small volume and large side-to-cut ratio. A free solution or gel can be used as a supporting medium, and a planar current field can be generated under the solution medium [7]. The method has the advantages of high efficiency, rapidity, small sample amount and low measurement cost. [8] Using p-hydroxybenzoic acid as internal standard, the content of benzoic acid in food was detected by capillary electrophoresis system. The detection limit was determined to be 10-20 ng/mL. Hu Meizhen et al [9] performed ultrasonic, carbon dioxide removal on the sample, then extracted and purified with ***, and then the extract was detected by high performance capillary electrophoresis. By optimizing the experimental conditions, the final linearity of benzoic acid at a concentration of 5mg/L~50mg/L is good, and the sample recovery rate is over 95%: the experimental process is fast and the recovery rate is high, which has a good application prospect in the field of food analysis. Li Lijun et al [10] used ACS2000 high performance capillary electrophoresis apparatus to determine benzoic acid, and optimized the buffer system, detection wavelength, separation voltage and other conditions to determine the benzoic acid buffer system containing 15mmol / L cetyltrimethyl bromide The volume fraction of ammonium is 1% acetic acid, the detection wavelength is 285 nm, the separation voltage is 20 KV, and the linear range is 5-40 μg/mL. The method has good reproducibility and accuracy and can be used for quality control and detection of benzoic acid production process. 3. Gas chromatography Gas chromatography appeared in 1952 and has become a relatively mature, most commonly used, and most easily isolated analytical method in separation science [11]. The method uses gas as the mobile phase. In addition to the analysis of gas samples, it can also be analyzed for volatile or convertible into volatile liquids and solids; not only organic matter but also some inorganic substances can be analyzed. With the development of detection technology, gas chromatography-mass spectrometry technology has been used in conjunction with gas chromatography. Liu Minhong et al. acidified the sample, extracted benzoic acid with ***, and then separated and determined by a gas chromatograph with a hydrogen flame ion detector. By optimizing the conditions of the column oven and carrier gas flow, and passing the precision test, accuracy test and sensitivity experiment, the feasibility of the test method is finally proved, which provides another idea for the detection of benzoic acid. Farahani et al. [12] used gas chromatography-mass spectrometry (GC/MS) to analyze the content of benzoic acid in beverages and domestic water. First, the sample was pretreated, and then the sample was analyzed by GC/MS. The linear detection range of benzoic acid was 0.5~500μg/mL, the correlation was ≥0.99, and the repeatability was good (RSID<10.3%, n=8). ), the recovery rate is 90% to 113%, which proves that the law is accurate and effective. 4. Ultraviolet spectrophotometry The detection principle of this method is that benzoic acid is a conjugated organic compound, which has strong absorption in the near-ultraviolet region [13]. It has been confirmed by experiments that benzoic acid has a maximum absorption peak at 230 nm. The solubility of benzoic acid at 10° was 0.21 g/100 mL of water, and at 20° it was 0.28 g/100 mL of water [14]. Therefore, the standard and the sample can be dissolved in water and then detected by an ultraviolet spectrophotometer. [15] The 7520 UV spectrophotometer was used to determine the content of benzoic acid in acidic foods. It was proved by experiments that the method is simple and easy to master, and has certain advantages in operation and accuracy of results. Compared with gas chromatography, the results are extremely high. Being close will not affect the judgment of the result. Du Xiangdong [16] used 751G UV spectrophotometer to detect the addition of benzoic acid to flour. The detection principle is that after mixing benzoic acid with ***, it has typical absorption characteristics between 260 and 280 nm, and finally the lowest detection of benzoic acid is detected. The amount is 1mg/kg, and the recovery range is 84.4%~95.3%, which proves the stability, anti-interference and accuracy of UV spectrophotometry. 5. Thin layer chromatography The principle of the method is to acidify the sample, extract benzoic acid with ***, concentrate the sample extract, and spread it on the thin layer of polyamide. After color development, according to the ratio of benzoic acid on the thin layer, The standards are more qualitative and can be quantitatively quantified, [GB/T2009.29–2003]. Zhang Xiuyan [17] used polyamide film chromatography to detect benzoic acid in food. The lower limit of detection of benzoic acid was 1 μg. 6. Prospects With the establishment of benzoic acid in foods, the ideal analytical method should be simple, fast, accurate, effective, sensitive, specific, and economical.