Turbidimetric and photometric determination of total tannins in tea using a micro-flow-batch analyzer

Both turbidimetric and photometric determinations of total tannins in samples of green and black tea, using a micro-flow-batch analyzer (mu FBA) were studied. The miniaturized system was formed using photocurable urethane-acrylate resin and ultraviolet lithography technique. The turbidimetric method was based on the precipitation reaction of Cu (II) with tannins in acetate medium at a pH of 4.5. The photometric method was based on the complexation reaction of tannins with ferrous tartrate. The turbidimetric mu FBA was able to test 200 samples per hour. The photometric mu FBA allowed 300 analyses per hour, generating 136 mu L of residue per analysis. The paired t test, at a 95% confidence level, showed no statistically significant differences between results obtained by both methods and the reference method. The urethane-acrylate mu FBA maintained satisfactory physical and chemical properties, and represents an improvement over conventional flow-batch analyzer. (C) 2011 Elsevier B.V. All rights reserved.