(1) Foreign determination methods
According to the research results of Dr. A.schcnck of the Bremen Fiber Research Institute, the Bremen moss melanin determination method provides a method for detecting cotton fibers that have a tendency to be sticky and contain concentrated sugar. A reliable method. It can separate all sugars and form colored complexes with orosin, making the reaction specific.
1. Determination principle
Adding the concentrated sulfuric acid solution of fusinol (3,5-dihydroxytoluene) to the water extract of cotton fiber can decompose low sugar and polysaccharide into furfural derivatives, which can interact with the fusogenic acid. Melanin produces an obvious red complex. With the different total sugar content in the sugar solution, the color of the solution after the complex is formed shows different color series from lemon yellow to deep red. By comparing with a standard color card, the sugar concentration in the extract can be detected.
2. Measurement steps
(1) Preparation of reagents: Dissolve 0.2g of 3,5-dihydroxytoluene in 100g of 95% to 97% concentrated sulfuric acid, and let it stand for about a week under refrigerated conditions at 10°C.
(2) Determination method: Place the prepared 1g cotton fiber test sample into 50mL of twice-distilled water and shake for 15min.
In order to speed up the measurement, you can use a pipette to transfer 1mL of the solution into the test tube. Take 2mL from a bottle of prepared genus melanin solution and add it to the test tube. After gently shaking, a color reaction will appear (note that the solution will Fever), after 10 minutes a set of standard color cards can be used to determine the sugar concentration of the solution (visual inspection). If you use a photometer to detect the color transparency of a solution, you must add distilled water twice to the colored measurement solution to 25 mL, set the photometer to a wavelength of 420 nm, and use water as a control to measure its transparency.
The figure shows that different sugar compositions create different color opacity. This method is very suitable for qualitative determination, but the orosin method can also be used to detect all sugar components. Comparing several curves in the picture on the left shows that different sugars will form different color depths with the same amount of melanin solution. This method can estimate the honeydew content in cotton fiber through color depth or photometric value. If you want to use this method to quantitatively measure various sugars, you must make sure that the different sugars can successfully pass the orosin test.
When using the Bremen moss melanin method to detect honeydew on cotton fibers, if the honeydew value on the cotton fibers exceeds or is equal to 5 on the color scale, it is sticky. Bremen melanin assay is a whole sugar assay. Since the conditions required for sugar to be decomposed into furfural derivatives are relatively harsh, the popularity of this method is not good.
(2) Domestic determination method
Domestically, the Bremen melanin determination method is called a quantitative method, which is a method of determination based on the melanin test method of Bremen, Germany. According to the GB/T16258-1996 standard, this method is a test method for quantitatively determining the sugar content of cotton using a 3,5-dihydroxytoluene-sulfuric acid solution as a color developer and a spectrophotometer.
1. Determination principle
Under the action of non-ionic surfactant, the sugar on the cotton fiber is dissolved in water. The sugar is converted into aldehydes in a strong acidic medium and reacts with 3,5-dihydroxytoluene. The color reaction produces an orange-yellow compound, which can be quantified using a spectrophotometer at 425nm by comparing it with the standard working curve.
2. Reagents and materials
(1) Distilled water (all water below refers to distilled water).
(2) Sulfuric acid (concentration 1.84g/mL).
(3)3,5-Dihydroxytoluene.
3,5-dihydroxytoluene-sulfuric acid solution: Weigh 0.2g of 3,5-dihydroxytoluene, place it in a 100mL beaker, add 100g (about 54mL) of sulfuric acid, and stir to dissolve it all. Ready for use.
(4) Fatty acid alkanolamide (Ninar, industrial grade).
① Fatty acid alkanolamide (0.04%) solution for measurement: Weigh 0.4g fatty acid alkanolamide and dissolve in 1000mL of water, stir evenly.
② Fatty acid alkanolamide (0.005%) solution for extraction: Measure 100 mL of fatty acid alkanolamide solution for determination, dissolve in 700 mL of water, and stir evenly.
(5)D-Fructose.
① Sugar standard stock solution: Weigh 0.200g of D-fructose, dissolve it in water, transfer it to a 100mL volumetric flask, and dilute it to the mark with water. The concentration is 2.0mg/mL.
② Sugar standard working solution: Use a pipette to absorb 0.5mL, 1.0mL, 1.5mL, 2.0mL, 2.5mL, 3.0mL, 4.0mL, 5.0mL sugar standard stock solution, and pour it into a 50mL volumetric flask respectively, with water Diluted to the mark, the sugar standard series concentrations are 01020mg/mL, 0.040mg/mL, 0.060mg/mL, 0.080mg/mL, 0.10mg/mL, 0.12mg/mL, 0.16mg/mL, and 0120mg/mL.
3. Main instruments and appliances
(1) Spectrophotometer: wavelength 200~800nm.
(2) Balance: graduation value 0.01g, 0.001g.
(3) Oscillator:>200 times/min.
(4) Constant temperature water bath.
(5) 250mL grinding
4. Preparation of test sample liquid
(1) Laboratory sample: Take laboratory samples according to the regulations of GB6097-1985.
(2) Test sample: Randomly select a test sample of no less than 15g from the laboratory samples.
(3) Test sample: Remove the coarse impurities in the test sample, mix it thoroughly (or use a mixed sample), and weigh 3 portions from it as the test sample. Each sample weighs 2.0g±0.1g. Keep the rest for later use.
5. Measurement steps
(1) Preparation of sample solution: Take 3 samples and place them in 250mL Erlenmeyer flasks. Add 200 mL of 0.005% fatty acid alkanolamide solution and shake on a oscillator for 10 minutes. Turn the cotton over with a glass rod and continue to shake for 10 minutes. Filter with quantitative filter paper to obtain 3 portions of the sample solution.
(2) Blank test: Take 1.0 mL of 0.04% fatty acid alkanolamide solution and pour it into a 25 mL colorimetric tube. Place the colorimetric tube in a 70°C constant temperature water bath, quickly add 2.0 mL of 3,5-dihydroxytoluene-sulfuric acid solution, shake well, continue to place in the water bath for 40 minutes, take it out, and add 20 mL of 0.04% fatty acid alkanolamide solution , shake well, cool to room temperature, use 0.04% fatty acid alkanolamideBring the solution to volume. Adjust the instrument, measure the absorbance value of the solution at a wavelength of 425nm, record the reading, and keep to two decimal places.
(3) Working curve drawing: Take 1.0mL of each sugar standard working solution and pour it into a 25mL colorimetric tube. Repeat step (2).
Draw a working curve with the absorbance value as the ordinate and the sugar standard working solution concentration (mg/mL) as the abscissa.
6. Calculation of results
Subtract the absorbance value of the blank solution from the absorbance value of the sample solution, find the concentration of the sample solution on the working curve, and calculate the sugar content according to the following formula.
In the formula: Amount of fatty acid alkanolamide solution added when feeding, mL; 2×1000——weight of sample, mg.
The results are rounded to two decimal places. The arithmetic mean of the three test results was used as the average sugar content of the sample. This method is suitable for the quantitative determination of the total sugar content of cotton fiber and is a relatively accurate method for determining the sugar content of cotton fiber.
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