Determination of Sodium Glutamate in MSG

MSG is an important condiment of daily life, the main component of acid a sodium salt

1.

(1) Master the use methods and skills of polarimeters

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

2.

The sodium L-glutamate in MSG exists in the form of L-glutamate in the hydrochloric acid solution

3.

(1) Circular circulator

(2) Constant temperature water

(3) Volumetric flask: 50mL

(4) Measuring cylinder: 100mL

(5) Beaker: 250mL

(6) Hydrochloric acid solution (1+1)

(7) Commercially available MSG

4.

Do not look directly at the source of the sodium light at close range; the concentration of the hydrochloric acid solution is high, do not pour it, so as not to corrode the instrument and burn clothes and skin

5.
Operation steps

(1) Sample processing Accurately weigh 5.
00g of a well-mixed MSG sample, add 20-30mL of water, add 16mL of hydrochloric acid solution (1+1) under stirring to dissolve all, cool to room temperature, transfer to a 50mL volumetric flask and add water To the mark, shake well
.
Place it in a constant temperature water bath for 15 minutes to make the solution temperature 20°C
.

(2) There are two calibration methods for the zero-point calibration of the polarimeter.
One is the blank solution calibration method, that is, take 16 mL of hydrochloric acid solution (1+1) into a 50 mL volumetric flask, dilute to the mark with water, and measure the optical rotation on the polarimeter.
Degree (the liquid temperature should be kept at 20℃ when using the blank solution for calibration)
.
The other is the air method, that is, without the solution and the polarizer, and the instrument is empty to observe its optical rotation
.

Add or subtract the zero-rotation correction value measured by the above-mentioned correction method in the formal measurement
.

(3) Sample solution measurement Rinse the vortex tube with a small amount of sample solution for 3 times, then fill a tube, push the cover glass horizontally from the side of the tube to cover it, tighten the screw cover appropriately, and wipe the cover sheet with a dry cloth
.
Turn on the polarimeter light source and calibrate the zero point after stabilization
.
Put the sample into the polarimeter tube, record the reading of the polarimeter, and record the temperature during the measurement
.

6.
Result calculation

(1) Data logging

(2) Result calculation When the temperature of the solution is 20℃, it is directly calculated by the following formula:

In the formula, X——the content of sodium glutamate in the sample (containing one molecule of crystal water), g/100g

d ₂₀ ——The optical rotation observed at 20℃

32—— Specific rotation of glutamic acid at 20℃

187.
13- Sodium glutamate contains 1 molecule of crystal water with relative molecular mass

147.
13-relative molecular mass of glutamic acid

2——The length of the polarizer

If the temperature is not 20°C, the measurement result should be corrected
.
When the temperature is t, the relationship between the specific rotation of L-glutamic acid and the temperature can be expressed by the following formula:

Where 0.
06—the temperature correction coefficient of the specific rotation of L-glutamate

The content of sodium glutamate in the sample (including 1 molecule of crystal water) is calculated as follows:

In the formula, d——the degree of optical rotation observed when the temperature is t

t—Temperature during measurement, ℃

7.
Tips

(1) As acid corrodes the instrument, special care should be taken during operation to avoid acid dripping on the instrument
.
When installing the polarimeter, be sure to wipe the outside clean to prevent the solution from entering the instrument and damaging the instrument
.

(2) After the experiment, the upper and lower nozzles of the polarizer must be opened and rinsed, otherwise the polarizer is easy to corrode
.