Rita I. L. Catarino

Flow amperometric determination of pharmaceuticals with on-line electrode surface renewal

In this article, a flow system developed for the amperometric determination of a great variety of pharmaceuticals that are known to lead the rapid poisoning of the working electrode surface is described. The referred system was made up of two parallel flow channels that shared the voltammetric detector of tubular configuration, whose movement in the manifold followed the concept of multi-site location of detector. In this way, after each measurement, the conditioning of the working electrode was possible through the passage by its surface of a regeneration solution without implying the alteration of the carrier that flowed in the analytical channel of the manifold. The methodology proposed was evaluated through the determination of two drugs belonging to two distinct therapeutic groups: an antihypertensive (diltiazem) and a non-steroid anti-inflammatory (nimesulide). The results obtained after evaluation of various pharmaceutical formulations on the Portuguese market were in the case of diltiazem compared with those supplied by the reference US Pharmacopoeia XXIV method, with no statistically significant differences having been observed for a confidence interval of 95%. In the case of nimesulide, since no official reference method exists, a series of recovery experiments were proceeded with and a mean value of 101.1% with a R.S.D. of 0.7% was obtained.

Relocation of a Tubular Voltammetric Detector for Standard Addition in FIA

In this work a new strategy for the automation of the standard addition method by FIA with voltammetric detection is described, based on the concept of multi-site detection. In the system developed, a single voltammetric detector with mobility in the FIA manifold, carried out sequential measurement of the sample plug before and after addition of the standard solution. The construction and evaluation of the voltammetric detector of tubular configuration and internal diameter similar to the tubing of the FIA manifold, whose incorporation in the system allowed the measurement process to be carried out without change of the hydrodynamic characteristics of the sample plug, is also mentioned. To evaluate the usefulness of the proposed multi-site voltammetric detection system, this was used in the amperometric determination of ascorbic acid in fruit juices where the standard addition method is frequently required to overcome the matrix effect. The results obtained with the FIA system were compared with those from the reference procedure proposed by AOAC. No statistical difference between methods was found at the 95% confidence level. The relative deviations between both methods were always less than or equal to 3.8%. The sampling rate was about 55 samples per hour (110 measurements).

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.