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建立了一种新的快速测定柠檬酸的双波长分光光度法。在酸性Tris-盐酸缓冲介质中,甲基绿与柠檬酸反应生成具有2个明显正吸收峰(在450~750 nm范围)的绿色离子缔合物,最大和次大正吸收波长分别位于668 nm和558 nm,采用双波长叠加法测定,表观摩尔吸光系数(κ)为6.21×104L/(mol·cm),柠檬酸的质量浓度在0.02~2.7 mg/L范围内服从朗伯-比尔定律。方法用于市售新鲜柠檬中柠檬酸的测定,回收率为99.0%~102.4%,相对标准偏差为2.2%~2.6%。
A new rapid determination of citric acid dual-wavelength spectrophotometry was established. In acid Tris-HCl buffer medium, methyl green reacts with citric acid to form green ion association complex with two obvious positive absorption peaks (in the range of 450-750 nm). The maximum and the minor positive absorption wavelengths are at 668 nm and The apparent molar absorptivity (κ) was 6.21 × 104 L / (mol · cm) at 558 nm and was determined by dual wavelength superposition method. The concentration of citric acid was in the range of 0.02-2.7 mg / L, which obeys Lambert-Beer’s law. The method was applied to the determination of citric acid in commercially available fresh lemons with recovery of 99.0% -102.4% and relative standard deviation of 2.2% -2.6%.