Problems in the determination of Sudan in food

Sudan red is a kind of non biosynthetic colorant used in oil color, wax, floor wax, soap and other chemical products It is not allowed to be used in food The method standard of GB / t19681-2005 "detection method of Sudan dye in food / high performance liquid chromatography" is relatively standard and has strong operability However, in practical application, the author thinks that the following aspects should be paid attention to: the influence of solvent on the determination result of Sudan red 1 When ether and n-hexane are used as solvent to prepare standard solution, Sudan red is divided into Sudan I, II, III and IV when standard solution mother liquor is prepared according to national standard test method, after dissolving with ether, it is fixed volume with n-hexane, and diluted with n-hexane to prepare standard solution (Series of standard solutions) for determination For example, when the mixed standard series solution of Sudan red (Ⅰ, Ⅱ, Ⅲ, Ⅳ) is directly injected and determined without the treatment of alumina chromatography column, the peak shape of the peaks of Sudan red (Ⅰ, Ⅱ) is very good, but the peak shape of the peaks of Sudan red (Ⅲ, Ⅳ) is poor, even in the mixed standard sample of low concentration, the peaks of Sudan red (Ⅳ) are not like the peaks, standard The linearity of the curve is very poor If the same standard series solution is evaporated to dryness after solid-phase extraction on alumina column, dissolved in acetone and fixed volume, and then injected for determination, the peak shape of Sudan red (Ⅰ, Ⅱ, Ⅲ, Ⅳ) is very good, and the detection result is also ideal 2 When acetone and acetonitrile are used as solvent to prepare standard solution, respectively weigh Sudan red (Ⅰ, Ⅱ, Ⅲ, Ⅳ), dissolve it in acetone, dilute it with acetonitrile, mix it with volume and prepare mixed standard series solution for determination For example, the peak shape of Sudan red (Ⅰ, Ⅱ, Ⅲ, Ⅳ) is very good, the linearity of standard curve is good and the test result is ideal when Sudan red (Ⅰ, Ⅱ, Ⅲ, Ⅳ) mixed standard series solution is directly injected for determination without being treated by alumina chromatography If the standard series of the same product is evaporated to dryness by solid-phase extraction on alumina column, dissolved with acetone and fixed volume, and then determined by sample injection, the peak of Sudan red (I, II, III, IV) is not very good, and the linearity of the standard curve is very poor Effect of activation and deactivation of alumina on the determination of Sudan red 1 When the alumina is not activated, the neutral alumina (100-200 mesh) is directly used as the column for chromatography After the standard sample and sample are evaporated to dryness by solid-phase extraction of the column, they are dissolved in acetone and fixed volume When the sample is injected for determination, there are many miscellaneous peaks around Sudan IV in the chromatogram, so it is difficult to judge the peaks of the tested components       2 When alumina is activated without decreasing activation, take a certain amount of neutral alumina (100-200 mesh) for chromatography and put it in a weighing dish with a height of 30 × ф 70, activate (dry) it in a constant temperature drying oven at a temperature of 100-105 ℃ for 4 hours, cool it in the dryer to room temperature to make a chromatographic column, and then the standard sample and sample are evaporated through the solid-phase extraction treatment of the chromatographic column, dissolve it with acetone and fix the volume to 5ml, after 0.45 μ M There was no peak in the chromatogram of Sudan (Ⅰ, Ⅱ, Ⅲ, Ⅳ) after filtration         3 When alumina is activated and de activated, weigh a certain amount of neutral alumina (100 mesh to 200 mesh) for chromatography and put it in a weighing dish with a height of 30 × ф 70, activate (dry) it in a constant temperature drying oven at a temperature of 100-105 ℃ for 4 hours, cool it in a dryer to room temperature, add 2.2ml of high-purity water for every 100g of alumina, cover the weighing dish and shake it up, and put it in a dryer for balance The equilibrium time is 13-18 hours After shaking, the chromatographic column is made according to the standard practice After the standard sample and sample are evaporated through the column solid-phase extraction, they are dissolved in acetone and fixed volume to 5ml After filtering by 0.45 μ m organic filter membrane, the peak shape of Sudan (Ⅰ, Ⅱ, Ⅲ, Ⅳ) in the chromatogram is very good and there is no impurity peak The detection result is also ideal In the process of detection, the standard substance ether dissolution is fixed volume with n-hexane, and the standard series solution diluted with n-hexane can not be directly injected into the standard sample for determination Instead, it must be evaporated to dryness by solid-phase extraction of alumina column, dissolved in acetone and fixed volume, and then injected for determination     2 In the detection process, the standard substance is dissolved in acetone and fixed volume, and the standard series solution prepared by diluting with acetonitrile can not be treated by alumina chromatography column, because acetone is desorption solution When the standard solution containing acetone passes through the chromatography column, part of the tested substance will be desorbed without desorbing steps in the process of adsorption, washing and desorption, which will affect the results Therefore, the direct sample injection test will be carried out Sure However, the sample must be injected after being treated according to the national standard method, and the sample of SPE cannot contain acetone The activity of alumina is the best way to adjust the recovery rate 3 The activation temperature and time should be paid attention to when activated by alumina for chromatography, and the water addition and equilibrium time should be paid attention to when the activation is reduced Alumina used for sample treatment and alumina used for standard sample treatment should be activated once in a vessel, and the activated alumina should be reduced, otherwise, the test results of samples will be affected