Determinação da impureza de iodeto gerada na síntese de líquidos iônicos formados por sais de amônio quaternários e aminoácidos por CZE-UV

Abstract

Ionic liquids are organic salts, composed by an organic cation and an organic or inorganic anion, with melting point below 100 °C, and characteristic properties like low vapor pressure and excellent thermal stability. The amino acids have aroused great interest for the preparation of ionic liquids due to characteristics like a chiral carbon in its structure and biodegradability, being able to be present in these salts as a cation or an anion. In this work, the ionic liquids analyzed were the ones in which the amino acids L-leucine, L-valine and L-proline acted as anions, being the cations composed by salts of quaternary ammonium derivatives of glycerol. These ionic liquids synthesis generated the ion iodide as impurity. Thus, the aim of this work was to develop methods by capillary zone electrophoresis with direct UV detection for the determination of iodide as impurity in these organic salts. The methodology consisted of 40 mmol L⁻¹ of TRIS and 20 mmol L⁻¹ of HCl (pH 8.20) as background electrolyte (BGE), being performed in normal electroosmotic flow with inverted polarity and hydrodynamic injection. Coated fused silica capillary with polyimide of 35 cm (26.5 or 8.5 cm of effective length) and 75 μm of internal diameter was used. Different modes of sample injection were evaluated, conventional injection, injection from the side closest to the detector (outlet – SEIP) and multiple injection (MICZE) to reduce the total analysis time. The outlet and multiple injection methodologies were developed from the conventional one. For the outlet injection, the applied pressure and voltage were reversed in relation to the conventional method. To develop the multiple injection method, two factorial designs were performed, the first a 2³ and the second, 3², in order to obtain the best conditions that provides the higher number of injections, with better resolution and in the shortest possible time. These studies allowed to obtain a method that performs five consecutive injections in less than three minutes. After that, the sample injection mode was optimized in a way that the best condition was the one which injected the same sample in a single run, generating a five-fold analysis. The samples quantification and posterior comparison of the results using the one-way ANOVA, concluded that there is evidence of no significant differences between them, in the 95% interval, being therefore equivalents. Comparing the total analysis time of optimized methods, it was concluded that the implementation of multiple injection methodologies led to its decrease as well as the increase in analytical frequency, since it allowed thirty-one injections in one hour, while the other two methods, conventional and outlet injection, enabled seven and nine injections per hour, respectively.