Adriana M. Pimenta

A sequential injection analysis system for potassium clavulanate determination using two potentiometric detectors.

Two almost independent potentiometric methods were implemented in a multi-task flow system based on the concept of sequential injection analysis for the analytical control of potassium clavulanate in pharmaceutical formulations. In addition to in-line preparation of the solutions submitted to the analysis, the system simultaneously detected the clavulanate anion and the potassium cation using two potentiometric detectors selective to each of the species referred. For the two determinations, the system developed presented an analytical range of 2 mM-0.1 M. Relative standard deviations of 0.5 and 0.6%, respectively, for clavulanate and potassium, were calculated from the signals obtained for 10 consecutive injections of a solution of 5x10(-3) M potassium clavulanate. The frequency of sampling was 53 samples h(-1). The quality of results supplied was evaluated by comparison with the reference procedure revealing relative errors less than 2% for the two determinations. The simultaneous attainment of two measurements permitted the standardisation of results in real time, the detection of faults in the procedure and monitoring the chemical stability of clavulanate.

Determination of hydrogen peroxide by near infrared spectroscopy

Near infrared (NIR) spectroscopy has been employed for the determination of hydrogen peroxide in antiseptic pharmaceutical preparations where it is found in concentrations of about 3.0% (w/v). Standard solutions containing hydrogen peroxide in the range 0–10% (w/v) were prepared and split into two groups, which were used for partial least squares (PLS1) modelling and for initial evaluation of the model performance. Absorbance spectra, in the wavelength range from 850 to 1800 nm, were obtained using a transflectance probe with optical path of 1.0 mm. The first derivative of the absorption spectra were employed for PLS1 modelling, which requires two factors, resulting in a root mean square error of cross-validation of 0.07% obtained by full cross-validation. The model was evaluated by using prepared and commercial samples of pharmaceuticals containing H2O2 in the range from 1 to 20% resulting in a root mean standard error of prediction of 0.05%.

Cathodic voltammetric detection of diltiazem at a bismuth film electrode: application to human urine and pharmaceuticals

In this work it was developed a novel application of bismuth film electrodes (BiFEs) for the determination of the antihypertensive and coronary vasodilator diltiazem by square wave cathodic voltammetry. The bismuth film was deposited ex situ on a glassy carbon electrode for 90 s at -1.4 V vs. Ag/AgCl, from an acetate buffer (pH 4.5; 0.10 mol L-1) containing 5 or 30 mg L-1 Bi. Diltiazem analytical signal was obtained in phosphate buffer (pH 7.4; 0.25 mol L-1) where reduction takes place at -1.5 V vs. Ag/AgCl. The proposed methodology was applied to the quantification of diltiazem in pharmaceutical samples (dynamic linear range comprised between 90 and 900 µg L-1) and in human urine (dynamic linear range comprised between 45 and 270 µg L-1, and detection limit of 12 µg L-1).

Lead migration from toys by anodic stripping voltammetry using a bismuth film electrode.

ABSTRACT Metals may be released from toys via saliva during mouthing, via sweat during dermal contact, or via gastric and intestinal fluids after partial or whole ingestion. In this study, we determined the lead migration from toys bought on the Portuguese market for children below 3 years of age. The lead migration was performed according to the European Committee for Standardization EN 71–3, which proposes a 2-hour migration test that simulates human gastric conditions. The voltammetric determination of migrated lead was performed by anodic stripping voltammetry (ASV) at a bismuth film electrode (BiFE). For all the analyzed toys, the values of migrated lead did not exceed the limits imposed by the European Committee for Standardization EN 71–3 (90 mg kg−1) and by the EU Directive 2009/48/EC (13.5 mg kg−1) on the safety of toys.