Recebido em 16/2/11; aceito em 12/9/11; publicado na web em 8/11/11 This paper reports the use of an electrode modified with poly(o-methoxyaniline) for detecting lithium ions. These ions are present in drugs used for treating bipolar disorder and that requires periodical monitoring of the concentration of lithium in blood serum. Poly(omethoxyaniline) was obtained electrochemically by cyclic voltammetry on the surface of a gold electrode. The results showed that the electrode modified with a conducting polymer responded to lithium ions in the concentration range of 1 x 10 -5 to 1 x 10 -4 mol L -1 . The results also confirmed that the performance of the modified electrode was comparable to that of the standard method (atomic emission spectrophotometry).

A direct non-aqueous method for simultaneous determination of propyl gallate (PG) and tert-butylhydroquinone (TBHQ) in biodiesel (B100) is described. Differential pulse voltammetry (DPV) using a Pt disk ultramicroelectrode (ume) in 1:1 (v/v) B100/ethanol containing 0.02 mol L–1 tetrahexylammonium perchlorate showed two oxidation peaks in the range from 1.20 × 10–3 to 8.9 × 10–3 mol L–1 for TBHQ and from 8.6 × 10–4 to 4.9 × 10–3 mol L–1 for PG. Simultaneous quantification and addition–recovery experiments were carried out in antioxidant-free B100 samples spiked with variable concentrations of TBHQ and PG. Because of significant overlapping in oxidation signals, the amount of TBHQ and PG in B100 was calculated through calibration graphs after voltammogram deconvolution using Microcal Origin software (version 8.0). The method provides a direct, low-cost, non-aqueous, and small volume procedure for simultaneous quantification of TBHQ and PG in B100, with 116 and 104% recovery values, respectively.

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