Determination of trace ethanol in fermented food by UV-1100 spectrophotometry - Master's thesis - Dissertation

Determination of trace ethanol in fermented food by spectrophotometry

Spectrophotometric determination of trace ethanol in fermented foods. Key words: spectrophotometry; ethanol; analysis instrument ; UV-1300 trace ethanol is low-degree fruit wine, alcoholic beverages and seasonings An important flavoring substance in food. At present, the determination of trace ethanol is mainly based on gas chromatography. The determination of trace ethanol content by dichromate oxidation spectrophotometry is a fast and accurate method. It has the characteristics of simple operation and simple analytical instruments. Especially suitable for daily analysis in the production and quality inspection departments. I. Determination principle In an acidic solution, ethanol can be oxidized by dichromate to form acetic acid, and hexavalent chromium in potassium dichromate is reduced to trivalent chromium. The reaction formula is: 3C2H5OH+2K2Cr2O7+8H2SO4=3CH3COOH+2K2SO4+ The trivalent chromium formed in the reaction of 2Cr2(SO4)+11H2O is green, and it has the maximum absorption peak at 585nm, and the color depth of the solution is proportional to the ethanol content, which can be colorimetrically measured on the spectrophotometer and passed through the standard series. Compare and quantify. Second, the instrument and reagent 1, UV-1300 UV-visible spectrophotometer (American instrument) 2, distillation device 3, PHS-3C acidity meter 4, ethanol standard solution: accurately absorb 2.00ml GR-grade anhydrous ethanol, placed in pre-loaded Mix in a 100ml volumetric flask with a small amount of distilled water, add water to volume, shake and set aside. 5. Potassium dichromate solution, weigh 10.00g of AR grade K2Cr2O7, dissolve it with a small amount of water, and dilute to 250ml. 6. Concentrated sulfuric acid: AR grade, content 95~98%. 7, 1% bromothymol blue indicator 8, NaoH solution: C (NaoH) = 1.0mol / L III, determination method 1, standard curve drawing Take 7 25ml grade A colorimetric tube, each adding 2.00ml heavy chromium Mix the potassium acid solution and 2.50ml of concentrated H2SO4, and cool, add 0.00, 0.20, 0.40, 0.60, 0.80, 1.00 and 1.25ml ethanol standard solution in turn, mix, react for 10 minutes, add water to the mark, mix again, Zeroing was performed with a No. 0 tube, and the absorbance was measured at a wavelength of 585 nm, and a standard curve was drawn. Table 1 standard curve drawing (L = 10mm) ethanol content ul / 25ml 0.004.008.0012.0016.0020.0025.00 absorbance 0.0000.0750.1460.2210.2920.3660.454 regression equation: y = 55.23x-0.1367 correlation coefficient r = 0.999972, sample Prepare accurately to remove 100.00ml sample in 250ml distillation flask, add 25mH2O, add a few drops of bromothymol blue indicator, titrate with NaoH solution to blue (dark sample with acidity indicator to neutralize to neutral), Add a few zeolites, connect the distillation unit for distillation, distillate is collected in a 100ml volumetric flask, the receiving bottle is cooled with an ice bath, slowly distilled to near the scale, removed, placed in a 20 ° C water bath for 30 minutes, with H2O Allow to the scale, shake it, and spare. 3. Determination of the sample Take 1.00 ml of the prepared sample, and measure according to the standard curve method. Calculate the ethanol content in the sample by using the regression equation. IV. Results and discussion 1. Selection of wavelength The 1.25 ml ethanol standard solution was taken according to the above determination method, and the sample liquid was scanned in the wavelength range of 400-800 nm. The scanning results showed that the system had the largest wavelength at 585 nm. The peak was absorbed and the reagent blank value was very low at this wavelength, so λ = 585 nm was selected as the measurement wavelength. 2, the effect of concentrated H2SO4 on the absorbance concentration H2SO4 dosage (ml) 0.600.801.001.502.002.503.00 absorbance 0.2260.2360.2440.2630.2800.2920.294 according to the reaction formula, to ensure that 2.00ml potassium dichromate solution all participate in the reaction, about 0.6 Ml98% concentrated H2SO4, in actual work, in order to ensure rapid and thorough reaction, the concentration of concentrated H2SO4 is often excessive. Under the premise of the amount of potassium dichromate solution and the reaction time, the absorbance of the mixed system increases with the increase of the concentration of concentrated H2SO4. When the amount of concentrated H2SO4 exceeds 2.50ml, the absorbance tends to be stable, so choose concentrated H2SO4. The dosage is 2.50 ml. 3, color development time and stabilization time (minutes) 104060120360 absorbance 10.0740.0740.0730.0730.07320.1450.1440.1440.1430.143 according to the test method to determine the same liquid absorbance at different times, the results show that the absorbance of the mixed system is obvious The color remains substantially stable after 10 minutes to at least 6 hours. 4, the method precision measurement times 123456XCv measurement results (%) 1.451.421.441.451.471.451.451.12 repeated measurements of the wheat fine beer samples, the coefficient of variation was 1.12% 5, sensitivity and linear range of the detection method The limit is 0.05%, and the ethanol content has a significant linear relationship in the range of 0~25ul/25ml. 6, sample determination and recovery rate (n = 3) sample sample measured value (%) added amount (%) measured value (%) recovery rate (%) wheat fine beer 1.450.752.1897.3 glutinous rice drink 1.420.501.92100.0 Soy sauce 0.670.501.1596.0 mountain wine 3.860.754.6098.7 This method is used to measure the alcoholic beverages, soy sauce, low-grade mountain wine and other samples taken from the supervision and inspection. The recoveries of the standard addition are between 96.0 and 100%. Satisfactory results: Keywords: spectrophotometry; ethanol; analysis instrument ; UV-1300