A multicommuted flow-system for spectrophotometric determination of tannin exploiting the Cu(I)/BCA complex formation

A flow system exploiting the multicommutation approach is proposed for spectrophotometric determination of tannin in beverages. The procedure is based on the reduction of Cu(II) in the presence of 4,4′-dicarboxy-2,2′-biquinoline, yielding a complex with maximum absorption at 558 nm. Calibration graph was linear (r = 0.999) for tannic acid concentrations up to 5.00 μmol L− 1. The detection limit and coefficient of variation were estimated as 10 nmol L− 1 (99.7% confidence level) and 1% (1.78 μmol L− 1 tannic acid, n = 10), respectively. The sampling rate was 50 determinations per hour. The proposed procedure is more sensitive and selective than the official Folin–Denis method, also minimizing drastically waste generation. Recoveries within 91.8 and 115% were estimated for total tannin determination in tea and wine samples.