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Determination of monosodium glutamate content in monosodium glutamate by fully automated potentiometric titration
1. Introduction
Monosodium glutamate (MSG), chemically known as sodium α-aminoglutarate, is formed by the mixture of sodium ions and glutamate ions. MSG, a commonly used seasoning, is primarily composed of MSG, and its content is an important technical indicator for evaluating its quality. Common methods for measuring MSG content include optical rotation and perchloric acid non-aqueous titration. However, when sucrose is present in the sample, the optical rotation method cannot accurately measure the MSG content because sucrose, like MSG, is optically active. Potentiometric titration effectively eliminates interference from substances like sucrose, thus accurately determining the MSG content.
2. Instruments and Equipment
2.1 Instruments
JH-T6 fully automatic potentiometric titrator, non-aqueous pH composite electrode.
2.2 Reagents
Perchloric acid standard solution (0.1 mol/L), formic acid, glacial acetic acid.
3 Experimental Methods
3.1 Experimental Procedures
1. Preparation of Perchloric Acid Solution: Referring to the national standard GB/T 601-2016, accurately measure 8.7 mL of perchloric acid. Add 500 mL of glacial acetic acid while stirring, then add 20 mL of acetic anhydride dropwise. Stir until the solution is homogeneous. After cooling, dilute to 1000 mL with glacial acetic acid. Accurately weigh 0.1 g (accurate to 0.001 g) of potassium hydrogen phthalate and place it in a titration cup. Add 40 mL of glacial acetic acid (ensuring the solution level covers the electrodes). Place the cup on the potentiometric titration stage, turn on the stirrer to mix the sample evenly, insert the electrodes and titration head, and after the potential stabilizes, titrate to the endpoint with the prepared perchloric acid standard solution. Record the volume of perchloric acid consumed and calibrate its concentration. Perform a blank test simultaneously. Record the temperature t0 at that time.
2. Sample Testing: First, record the titration temperature to calibrate the concentration of the perchloric acid solution. Accurately weigh 0.1 g (accurate to 0.0001 g) of the sample into a dry titration cup. Using a pipette, accurately pipette 3 mL of formic acid into the titration cup, sonicate until completely dissolved, then add 40 mL of glacial acetic acid, ensuring the electrode is submerged. Start stirring and continue stirring until the solution is homogeneous. Titrate with a calibrated 0.1 mol/L perchloric acid solution to the midpoint or endpoint. Simultaneously perform a blank test.
3.2 Parameter Settings
4. Results and Discussion
4.1 Experimental Results
Calculation formula:
In the formula:
X -- Monosodium glutamate (MSG) content in the sample, in g/100g;
V1 -- Volume of perchloric acid standard titration solution consumed by the sample, in mL;
c -- Calibrated concentration of the perchloric acid solution, in mol/L;
V0 -- Volume of perchloric acid standard titration solution consumed by the blank, in milliliters (mL);
m -- Mass of the sample, in g;
0.09357 -- Mass of MSG containing one molecule of water of crystallization equivalent to 1.00 mL of perchloric acid standard titration solution [c(HClO4) = 1.000 mol/L], in grams (g).
4.2 Spectrum
4.3 Conclusion
According to the literature requirements, the absolute difference between two independent determinations obtained under repeatability conditions should not exceed 0.5 g/100 g.
References
[1] GB/T 601-2016 Preparation of standard titration solutions for chemical reagents - Preparation of standard perchloric acid solution [S].
[2] GB 5009.43-2016 National Food Safety Standard - Determination of monosodium glutamate in monosodium glutamate [S].
Keyword:
automated potentiometric titration
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