Determinação de espécies de antimônio em antimoniato de meglumina

Abstract

In this study different methods for speciation of Sb(III) and Sb(V) in meglumine antimoniate (NMG) were evaluated. Liquid chromatography (LC) combined or not with hydride generation (HG) was investigated for separation of Sb(III) and Sb(V). Inductively coupled plasma mass spectrometry (ICP-MS) was used as detector. A flow injection system together with hydride generation (FI-HG) coupled with atomic absorption spectrometry (AAS) was also employed for the selective determination of Sb(III) in presence of Sb(V). Two anion-exchange columns (Dionex, IonPacAS14 and Hamilton, PRP-X100) were evaluated for Sb(III) and Sb(V) separation by LC. Parameters related to the mobile phase, such as type (EDTA, potassium phthalate, and potassium phthalate + EDTA), concentration (0.5 to 10 mmol L-1), pH (3.5 to 7.0), flow rate (0.25 to 1.75 mL min-1) and elution mode (isocratic and gradient) were studied. The volume of sample injected into the chromatograph was set at 200 μL. For the chromatographic separation, the mobile phase which led to improved separations of Sb(III) and Sb(V) was the EDTA in concentrations of 0.5 mmol L-1 and 1.0 mmol L-1 for the IonPac and PRP-X100 columns, respectively. The most appropriate parameters related to the FI-HG system were also evaluated and set, such as reductant of Sb(III) (NaBH4 0.1%, m/v), complexant of Sb(V) (10% m/v citric acid,), water as the sample carrier, analytical path (300 cm), volume of sample (100 μL), total flow rate of solutions (8.5 mL min-1) and flow rate of carrier gas (0.4 mL min-1). In order to identify and/or quantify the species of Sb present in the NMG, the samples were diluted in water only. Through the use of LC-ICP-MS it was only possible to quantify the Sb(V), whereas the presence of Sb(III) was not detected. The determination of Sb(III) was only possible through FI-HG AAS, FI-HG-ICP-MS and LC-HG-ICP-MS (by combination of conditions set for LC and FI-HG individually). Similar results for Sb(III) were obtained through the techniques FI-HG AAS and HGICP- MS. Thus, it was possible to quantify free Sb(III) and Sb(V), while probable compounds of Sb(III) and/or Sb(V) bound to NMG were observed but could not be identified and quantified, mainly because of lack of reference solutions and difficulty in separating the observed Sb species. The precision of methods for determination of Sb(III) and Sb(V) (expressed as relative standard deviation for 5 consecutive measurements) was about 9% and 3% respectively. As there were no certified reference materials to evaluate the accuracy of the developed methods, recovery tests of Sb(III) and Sb(V) were made, where they were in the range 96 to 101% for Sb(V) and 85 to 104% for Sb(III). Moreover, the results were compared with those obtained by official methods to quantify Sb(III), Sb(V) and Sb total in meglumine antimoniate.