3rd meeting of young researchers at UP 1 - IJUP - Universidade do ...

Effect of dimethyldioctadecylammonium bromide on the
potenciometric determination of sulfamethoxazole
S. A.A. Almeida 1,2,3 , M.C.B.S.M.Montenegro 2 and M.G.F. Sales 3
1 REQUIMTE/Universidade do Porto, ISEP, Instituto Superior de Engenharia do Porto, Portugal.
2 INSA-Porto, Instituto Nacional de Saúde Dr. Ricardo Jorge-Porto, Portugal.
3 REQUIMTE/Serviço de Química-Física, Faculdade de Farmácia da Universidade do Porto, Portugal
Sulfamethoxazole, 4-Amino-N-(5-methyl-3-isoxazolyl)benzenesulfonamide (SMX), is an
effective antimicrobial agent in treating infections caused by Streptococcus, Staphylococcus,
Salmonella, and Coccidia [1]. It acts as a competitive antagonist of p-aminobenzoic acid
(PABA) and thus as an inhibitor of folic acid synthesis, since PABA is an integral component
of the structure of folic acid [2]. It is used for human and veterinary purposes and may be
found in the aquatic environment as a contaminant.
The determination of SMX may be carried out by means of several analytical techniques, such
as potentiometry with PVC-based ion selective electrodes (ISEs). Some important features of
the PVC-based membranes, such as the ionophore and the amount/kind of additive used,
influence significantly the analytical performance of ISEs. Hence, in this work SMX selective
electrodes were prepared with alpha-cyclodextrins (α−CD) and with or without additive
dimethyldioctadecylammonium bromide (DDABr).
A Crison ® µpH 2002 decimilivoltammeter (±0.1 mV sensitivity) was used for measuring the
potential differences between an Orion 90-02-00 double junction AgCl/Ag reference electrode
and the indicating electrode. The selective electrodes had no internal reference solution and
used an epoxy-graphite matrix as conductive solid contact [3]. Calibration curves followed the
Litre beaker method [4]. All electrodes were placed in a convenient support over a magnetic
stirrer and immersed in 50.00 ml of HEPES 0.01 M. Suitable increments of SMX standard
solution were added.
ISEs without additive did not display a potentiometric response, but electrodes with 25% of
DDABr presented sensitivities of 57 mV/decade, close to those of the Nernst equation. A slight
increase in slope was also observed for an increasing amount of additive. Both limit of
detection (LOD) and lower limit of linear range (LLLR) remained unaffected by the additive
amount.
References:
[1] JJ. Flórez, J.A. Armijo and A. Mediavilla (1999), Farmacología Humana, Masson (Ed.), 3rd ed.,
Spain, pp. 1151–1153.
[2] R.F. Bevill (1988), Veterinary Pharmacology and Therapeutics, in: N.H. Booth and L. McDonald,
Editors Iowa University Press, Ames, IA, 48.
[3] Lapa RAS, Lima JLFC and Silva AMR (1990), Construction of calcium ion-selective electrodes
without inner reference solution - an application to calcium and magnesium determinations in
parenteral and hemodialysis solution. Il Fármaco, 45, pp.901–913.
[4] Buck RP, Cosofret VV (1993), Recommended procedures for calibration of ion-selective electrodes.
Pure Appl. Chem., 65,pp. 1849–1858.
3 rd meeting of young researchers at UP 243