Determination of Sodium Glutamate in Monosodium Glutamate by Two-Abrupt-Change Coulometric Titration

Sample of 0.50 g was taken, dissolved and diluted to 100 mL by water. An aliquot (1.0 mL) was mixed with 50 mL of 1.0 mol·L^-1 potassium chloride solution (supporting electrolyte) containing 0.5 mL of neutral formaldehyde solution (masking agent, used to mask the amino group of sodium glutamat) by stirring for 10 s. With platinum wire pair electrode and platinum sheet electrode as working electrode pairs, and pH composite glass electrode as indicating electrode, electrolysis was made at constant current of 10.0 mA. In which, water was electrolyzed to generate OH^- to continuously titrate the free acid (the first jump point) and the carboxyl group (the second jump point) of sodium glutamate in the monosodium glutamate sample. After the second jump point occurred, the titration was completed. The sodium glutamate amount was calculated using Faraday's electrolysis law based on the difference in electrolysis time between the 2 jump points. It was shown that the electrolysis time was completed in about 5 min, and results of tests for recovery by standard addition method were found in the range of 99.0%-101%, with RSDs (n=5)of the determined values less than 1.0%. Compared with the acidity meter method recommended in the national standard of GB 5009.43-2016, there was no significant difference between the determined values of sodium glutamate in 3 monosodium glutamate samples with different brands.