Tufan Ayşe Nur, Baki Sefa, Güçlü Kubilay, Özyürek Mustafa, Apak Reşat
Department of Chemistry, Faculty of Engineering, Istanbul University , Avcilar, 34320 Istanbul, Turkey.
J Agric Food Chem. 2014 Jul 23;62(29):7111-7. doi: 10.1021/jf5017797. Epub 2014 Jul 14.
A novel differential pulse voltammetric (DPV) method is presented, using a chromogenic oxidizing reagent, cupric neocuproine complex (Cu(Nc)2(2+)), for the assessment of antioxidant capacity of polyphenolic compounds (i.e., flavonoids, simple phenolic acids, and hydroxycinnamic acids), ascorbic acid, and real samples for the first time. The electrochemical behavior of the Cu(Nc)2(2+) complex was studied by cyclic voltammetry at a glassy carbon (GC) electrode. The electroanalytical method was based on the reduction of Cu(Nc)2(2+) to Cu(Nc)2(+) by antioxidants and electrochemical detection of the remaining Cu(II)-Nc (unreacted complex), the difference being correlated to antioxidant capacity of the analytes. The calibration curves of individual compounds comprising polyphenolics and vitamin C were constructed, and their response sensitivities and linear concentration ranges were determined. The reagent on the GC electrode retained its reactivity toward antioxidants, and the measured trolox equivalent antioxidant capacity (TEAC) values of various antioxidants suggested that the reactivity of the Cu(II)-Nc reagent is comparable to that of the solution-based spectrophotometric cupric ion reducing antioxidant capacity (CUPRAC) assay. This electroanalytical method better tolerated sample turbidity and provided higher sensitivity (i.e., lower detection limits) in antioxidant determination than the spectrophotometric assay. The proposed method was successfully applied to the measurement of total antioxidant capacity (TAC) in some herbal tea samples such as green tea, sage, marjoram, and alchemilla. Results demonstrated that the proposed voltammetric method has precision and accuracy comparable to those of the spectrophotometric CUPRAC assay.
首次提出了一种新型差分脉冲伏安法（DPV），该方法使用一种显色氧化试剂——新铜试剂铜络合物（Cu(Nc)₂²⁺）来评估多酚类化合物（即黄酮类、简单酚酸和羟基肉桂酸）、抗坏血酸以及实际样品的抗氧化能力。通过在玻碳（GC）电极上进行循环伏安法研究了Cu(Nc)₂²⁺络合物的电化学行为。该电分析方法基于抗氧化剂将Cu(Nc)₂²⁺还原为Cu(Nc)₂⁺，并对剩余的Cu(II)-Nc（未反应的络合物）进行电化学检测，两者的差值与分析物的抗氧化能力相关。构建了包含多酚类和维生素C的各个化合物的校准曲线，并确定了它们的响应灵敏度和线性浓度范围。GC电极上的试剂对抗氧化剂保持其反应活性，各种抗氧化剂的测得的特洛克斯等效抗氧化能力（TEAC）值表明，Cu(II)-Nc试剂的反应活性与基于溶液的分光光度法铜离子还原抗氧化能力（CUPRAC）测定相当。与分光光度法相比，这种电分析方法对样品浊度的耐受性更好，并且在抗氧化剂测定中提供了更高的灵敏度（即更低的检测限）。所提出的方法成功应用于一些凉茶样品（如绿茶、鼠尾草、马郁兰和羽衣草）中总抗氧化能力（TAC）的测定。结果表明，所提出的伏安法具有与分光光度法CUPRAC测定相当的精密度和准确度。
