Rapid determination of total polyphenolic content in tea samples based on caffeic acid voltammetric behaviour on a disposable graphite electrode

The present paper describes the voltammetric behaviour and the quantitative determination of caffeic acid (CA) on a disposable pencil graphite electrode (PGE). The anodic peak current of CA recorded by differential pulse voltammetry (DPV) varies linearly with CA concentration in the range 1 × 10−7–3 × 10−3 M. The detection and quantification limits were 8.83 × 10−8 M and 2.94 × 10−7 M caffeic acid, respectively. The mean recoveries of CA from Turkish green, white and black teas were 98.30%, 99.57% and 91.46%. For these three tea types the corresponding total polyphenolic contents (TPCs) evaluated by DPV on PGE were 35.81, 34.59 and 31.21 mg caffeic acid equivalent/g tea, respectively. These TPC values were in good accordance with those obtained by the Folin–Ciocalteu method. The developed DPV on PGE method constitutes a simple and inexpensive tool for the rapid assessment of TPC of tea samples

Constitutivism about Epistemic Normativity

According to constitutivists about epistemic normativity, epistemic normativity is explained by the nature of belief. Specifically, it is explained by the fact that, as a matter of conceptual necessity, belief stands in a normative relation to truth. We ask whether there are persuasive arguments for the claim that belief stands in such a relation to truth. We examine and critique two arguments for this claim. The first is based on the transparency of belief. The second is based on Moore-paradoxical sentences. We develop a common objection to both. Both arguments are reliant on implausible claims about the relation between accepting a norm and being motivated by it. This point has sometimes been made in connection with the transparency of belief. But its development and application to Moore-paradoxical sentences are, we believe, novel