磷铋钼蓝分光光度法测定水果、蔬菜及饮料中L-抗坏血酸

Determination of L-Ascorbic Acid in Fruits,Vegetables and Beverages by Phosphorus Bismuth Molybdenum Blue Spectrophotometry

Bi^(3+)与Mo(Ⅵ)和PO_4^(3-)在硫酸介质中反应生成黄色的磷铋钼杂多酸,然后被L-抗坏血酸还原为磷铋钼蓝,据此建立了分光光度法测定水果、蔬菜及饮料中L-抗坏血酸的方法。优化的试验条件如下:(1)测定波长为710nm;(2)1.95×10^(-2) mol·L^(-1)磷酸二氢钾溶液的用量为3.0mL;(3)6.51×10^(-2) mol·L^(-1)钼酸铵溶液的用量为4.0 mL;(4)2.06×10^(-4) mol·L^(-1)硝酸铋溶液的用量为1mL;(5)硫酸的浓度为0.16mol·L^(-1);(6)反应温度为室温。L-抗坏血酸的质量浓度在4~120mg·L^(-1)内与其对应的吸光度呈线性关系,表观摩尔吸光率为3.59×10~3L·mol^(-1)·cm^(-1),检出限(3s/k)为0.2 mg·L^(-1)。方法用于水果、蔬菜及饮料样品的分析,加标回收率为98.0%~102%,测定值的相对标准偏差(n=11)为1.1%~2.3%。

In sulphuric acid medium,Bi3＋,Mo（Ⅵ）and PO43- can react to produce yellow phosphorus bismuth molybdenum heteropoly acid,which is then reduced to phosphorus bismuth molybdenum blue by Lascorbic acid.Based on this reaction,a spectrophotometric method for determination of L-ascorbic acid in fruits,vegetables and beverages was established.The optimized conditions found were as follows：（1） wavelength of determination was 710 nm;（2）amount of 1.95×10-2 mol·L-1 KH2PO4 solution was 3.0 mL;（3）amount of 6.51×10-2 mol·L-1 ammonium molybdate solution was 4.0 mL;（4） amount of 2.06×10-4 mol·L-1 bismuth nitrate solution was 1 mL;（5） concentration of H2SO4 was 0.16 mol· L-1;（6） temperature of reaction was room temperature.Linear relationship between values of absorbance and mass concentration of L-ascorbic acid was obtained in the range of 4-120 mg·L-1,with apparent molar absorptivity of 3.59×103 L·mol-1·cm-1 and detection limit（3 s/k）of 0.2 mg·L-1.The proposed method was applied to the analysis of samples of fruits,vegetables and beverages,giving values of recovery and RSD′s（n=11）in the ranges of 98.0%-102% and 1.1%-2.3% respectively.