Determination of monosodium glutamate in monosodium glutamate

1. Purpose requirements

(1) Master the usage methods and techniques of a polarimeter.

(2) Learn to calculate the content of sodium glutamate in monosodium glutamate.

2. Principles of Practical Training

L-glutamic acid sodium in monosodium glutamate exists in the form of L-glutamic acid in hydrochloric acid solution. L-glutamic acid has optical rotation, and under certain conditions, the magnitude of its optical rotation is directly proportional to its concentration. Measure its specific rotation at a certain temperature and compare it with the specific rotation of pure L-glutamic acid at that temperature to obtain the mass fraction of sodium glutamate in monosodium glutamate, which is the purity of monosodium glutamate.

3. Training supplies

(1) Disk polarimeter.

(2) Constant temperature water.

(3) Capacity bottle: 50mL.

(4) Measuring cylinder: 100mL.

(5) Beaker: 250mL.

(6) Hydrochloric acid solution (1+1).

(7) Commercially available monosodium glutamate.

4. Safety Reminder

Do not look directly at the sodium light source at close range; Hydrochloric acid solution with high concentration should not be spilled to prevent corrosion of the instrument and burns to clothing and skin.

5. Operation steps

(1) Accurately weigh 5.00g of well mixed monosodium glutamate sample, add 20-30mL of water, stir and add 16mL of hydrochloric acid solution (1+1) to dissolve completely, cool to room temperature, transfer to a 50mL volumetric flask, add water to the mark, and shake well. Place the solution in a constant temperature water bath for 15 minutes to maintain a temperature of 20 ℃.

(2) There are two calibration methods for zero point calibration of polarimeters. One is the blank solution calibration method, which involves taking 16mL of hydrochloric acid solution (1+1) and placing it into a 50mL volumetric flask, diluting it with water to the mark, and measuring its rotation on the polarimeter (the liquid temperature should be kept at 20 ℃ when using blank solution calibration). Another method is the air method, which does not require a solution or a polarimeter, and observes its optical rotation with an empty instrument.

Add or subtract the zero point correction value of the optical rotation measured by the above correction method in the formal measurement.

(3) Use a small amount of sample solution to moisten the optical tube three times for sample solution determination, then fill one tube, horizontally push the glass cover from the side of the tube, tighten the screw cover appropriately, and wipe the cover with a dry cloth. Turn on the light source of the polarimeter, stabilize it, and then correct the zero point. Place the sample in the polarimeter tube, record the reading of the polarimeter, and record the temperature during measurement.