Utilização de radiação de microondas na determinação espectrofotométrica de cromo com 4- (2- TIAZOLILAZO) - RESORCINOL (TAR).

Abstract

In the present work it was developed an spectrophotometric method for fast determination of total chromium in the forra of Cr(III) through the formation of a colored compound with the 4-(2 -tiazolilazo resorcinol)-TAR reagent. The complexation reactions of chromium (III) with other organic reagents, in aqueous médium, is quite slow due to the formation of the hexaaquocomplex [CríIfeO^]3* that is inert. However, in this method the complexation ofCr(HI) was accelerated by the action ofthe microwave radiation that acts mainly in water molecules vibrating them and breaking the layer of solvency of the aquo-complex of chromium, allowing therefore its interaction with the complexant reagent Besides the irradiation, it was also used the surfactant cetyltrimetylamonium bromide(CTAB), for bettersolubilization ofthe compound in médium aqueous, because both the organic reagent and the compound which was formed are not much soluble in water. It was also verified that the presence of CTAB in the system promotes an increase sensitivity for the chromium spectrophotometric determination. The reaction between TAR and Cr(HI) occurs between pH 5,2 and 6,0, and the complex presents an absorption maximum at 545nm. The absortion signal maximum after 5min of 700W irradiation. The complex is stable for at least 2 hours. The developed method allowed the determination of chrome in the concentration range 1,63 x 10^ and 5,76 x 10'5 mol.LT1 and presented molar absortivity of 2,72 x 104 L.mol^cm1. The analytic curves were traced against a blank of the reagent and presented correlation coefficient of 0,9998 and the variation for the measurements estimated as was 1,1%. The addition ofsodium citrate and EDTA after the irradiation increases the selectivity ofthe reagent for determination of chromium. Synthetic samples, simulating steel-alloys composition, containing different proportions of Cr and the possible interferents (Cu, Mn, Ni, Mo, Co, W, V, Si, Al e Ti) were tested. in A tolerance limit was of± 3% established and it was verified that there are no interference of any ofthe species mentioned in the presence ofthe complexing agents. Iron interferes and it should be previously separated. The method was applied in the determination of chroraium in steel-alloys, steei-tools, river waters and residues of tanning industries and the obtained results were compared with the certified values. A application ofthe paired t-test (95% confidence levei) revealed that there are not significant differences among the obtained results and the certified values and those obtained by ICP-OES.