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    双突跃库仑滴定法测定味精中谷氨酸钠的含量

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

    • 摘要: 取0.50 g样品,用水溶解并稀释至100 mL。分取1.0 mL于含有0.5 mL中性甲醛溶液(掩蔽剂,用于掩蔽谷氨酸钠中的氨基)的1.0 mol·L-1氯化钾溶液(支持电解质) 50 mL中,搅拌10 s后,以铂丝对电极与铂片电极为工作电极对,pH复合玻璃电极为指示电极,恒电流设置为10.0 mA,通过电解水生成OH-连续滴定味精样品中游离酸(第一突跃点)与谷氨酸钠中的羧基(第二突跃点),第二突跃点出现后结束滴定,基于两个突跃点的电解时间差及法拉第电解定律计算味精样品中谷氨酸钠的含量。结果显示:电解时间为5 min左右,方法的加标回收率为99.0%~101%,测定值的相对标准偏差(n=5)小于1.0%。与国家标准GB 5009.43-2016推荐的酸度计法进行比对,3种不同品牌味精样品中谷氨酸钠测定值间无显著性差异。

       

      Abstract: 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.

       

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