Rutin and total isoflavone determination in soybean at different growth stages by using voltammetric methods

Two highly sensitive differential pulse voltammetric (DPV) methods based on the oxidation of genistein and rutin in a glassy carbon electrode is presented. Under optimized conditions (0.2 M phosphate buffer, pH 6.0, 50 mV pulse amplitude, 50 mV s− 1 scan rate), the oxidation peak currents (Ip) of genistein and rutin are linear (Ipa(A) = 5.0 × 10− 8 + 0.056 [genistein] r = 0.9969; Ipa(A) = − 3.0 × 10− 8 + 0.112 [rutin] r = 0.9974) to genistein and rutin concentrations in the range of 1.0 × 10− 6-6.0 × 10− 6 M and 1.0 × 10− 6-1.2 × 10− 5 M, respectively. The detection limits obtained for genistein and rutin were 6.1 × 10− 7 M and 3.8 × 10− 7 M, respectively. The quantitation limit for both genistein and rutin was 1.0 × 10− 6 M. The repeatability of DPV methods was acceptable (relative standard deviation (RSD) < 10%). The presence of matrix effect on the genistein determination and the absence of matrix effect on the rutin determination were attested by t-test (95% confidence level). The DPV methods were applied to the determination of rutin and total isoflavones in a Brazilian soybean cultivar (BRS 217 Flora) in ten different growth stages, with recoveries of 73-109%. Flora exhibited concentration levels of rutin and total isoflavones in leaves, seeds and pods ranging from 0.44 to 1.7 mg g− 1 and 72 to 128 μg g− 1, respectively.