Güçlü Kubilay, Sözgen Kevser, Tütem Esma, Ozyürek Mustafa, Apak Reşat
Istanbul University, Faculty Chemistry Department, Avcilar, 34320 Istanbul, Turkey.
Talanta. 2005 Mar 15;65(5):1226-32. doi: 10.1016/j.talanta.2004.08.048.
The proposed method for ascorbic acid (Vitamin C) (AA) determination is based on the oxidation of AA to dehydroascorbic acid with a Cu(II)-2,9-dimethyl-1,10-phenanthroline (neocuproine (Nc)) reagent in ammonium acetate-containing medium at pH 7, where the absorbance of the formed bis(Nc)-copper(I) chelate is measured at 450nm. This chelate was formed immediately and the apparent molar absorptivity for AA was found to be 1.60 x 10(4)dm(3)mol(-1)cm(-1). Beer's law was obeyed between 8.0 x 10(-6) and 8.0 x 10(-5)M concentration range. The relative standard deviation for 90mug AA was 3%. The Cu(II)-Nc reagent is a milder and therefore more selective oxidant than the conventional Fe(III)-1,10-phenanthroline (phen) reagent used for the same assay. This feature makes the proposed method superior for real samples such as fruit juices containing weak reductants such as citrate, oxalate and tartarate that otherwise produce positive errors in the Fe(III)-phen method when equilibrium is achieved. The developed method was applied to a number of commercial fruit juices, pharmaceutical preparations containing Vitamin C, and red wine. The meta-bisulfite content of wine was removed with an anion exchanger at pH 3 prior to analysis, and a difference extractive-spectrophotometric method of AA assay in wine was developed so as to suppress the interferences caused by wine anthocyanins and polyphenols. The findings of the developed method for fruit juices and pharmaceuticals were also statistically compared with those of HPLC so as to establish it as a reliable novel method.
所提出的测定抗坏血酸（维生素C）（AA）的方法基于在pH 7含醋酸铵的介质中，用Cu（II）-2,9-二甲基-1,10-菲咯啉（新铜试剂（Nc））试剂将AA氧化为脱氢抗坏血酸，在此处于450nm处测量形成的双（Nc）-铜（I）螯合物的吸光度。该螯合物立即形成，发现AA的表观摩尔吸光系数为1.60×10⁴dm³mol⁻¹cm⁻¹。在8.0×10⁻⁶至8.0×10⁻⁵M浓度范围内符合比尔定律。90μg AA的相对标准偏差为3%。与用于相同测定的传统Fe（III）-1,10-菲咯啉（邻菲啰啉（phen））试剂相比，Cu（II）-Nc试剂是一种更温和因而更具选择性的氧化剂。这一特性使得所提出的方法对于诸如含有柠檬酸盐、草酸盐和酒石酸盐等弱还原剂的果汁等实际样品更为优越，否则在达到平衡时这些样品在Fe（III）-邻菲啰啉方法中会产生正误差。所开发的方法应用于多种市售果汁、含维生素C的药物制剂和红酒。在分析前，用阴离子交换剂在pH 3下去除葡萄酒中的偏亚硫酸氢盐含量，并开发了一种葡萄酒中AA测定的差示萃取分光光度法，以抑制葡萄酒中花青素和多酚引起的干扰。还将所开发的果汁和药物方法的结果与HPLC的结果进行了统计学比较，以将其确立为一种可靠的新方法。
