ABSTRACT
A FIA system using a pH-sensitive detector based on a graphite/quinhydrone/silicone composite electrode was applied to determine sequentially the titratable acidity and the pH of wine, as well as the sum of calcium and magnesium ions. For all measurements the same FIA configuration was used employing different carrier solutions. The results for the determination of acidity and pH are in good agreement with those obtained by classical potentiometric titrations and by pH measurements using a conventional glass electrode. The standard deviation was less than 1.5% for both kinds of measurements and the sample volume was 150 µL. The method allows about 40 determinations of titratable acidity per hour and 30 pH measurements per hour. The titration method can be adjusted to the legal requirements in USA and Europe.
Subject(s)
Conductometry/methods , Flow Injection Analysis/methods , Potentiometry/methods , Wine/analysis , Calcium/analysis , Calibration , Conductometry/instrumentation , Electrodes , Flow Injection Analysis/instrumentation , Graphite/chemistry , Hydrogen-Ion Concentration , Hydroquinones/chemistry , Magnesium/analysis , Potentiometry/instrumentation , Reproducibility of Results , Silicones/chemistryABSTRACT
Potentiometric FIA titrations were performed to determine enzyme activities of lipase type B from Candida antarctica, CAL-B. Two substrates, triacetin and tributyrin were hydrolyzed in phosphate buffer solutions, and the concentration change of the base component of the buffer was titrated in a carrier solution containing hydrochloric acid and potassium chloride. The system was calibrated with butyric acid and acetic acid, respectively. FIA titration peaks were evaluated with respect to peak height and peak area. Butyric acid and acetic acid could be titrated in the buffer solution from 3x10(-3) mol L(-1) to 0.1 mol L(-1). The detection limit of enzyme activity was determined to be 0.07 U mL(-1) (15 min reaction time) and the minimum activity was calculated to be 0.035 units corresponding to 35 nmol min(-1). The specific activities of lipase B for the hydrolysis of tributyrin and triacetin were determined as 16+/-2 U mg(-1) and 2+/-0.2 U mg(-1) (per mg commercial lipase preparation), respectively.
