Direct determination of manganese in produced waters from petroleum exploration by Electrothermal Atomic Absorption Spectrometry using Ir-W as permanent modifier

This present work reports the development and evaluation of a method for the direct determination of manganese in waters extracted during petroleum exploitation by Electrothermal Atomic Absorption Spectrometry (ET AAS) using Ir-W as permanent modifier. These waters, usually called produced waters, contain a wide range of organic and inorganic substances and are characterized by their high salinity. In order to achieve suitable experimental conditions for the method application, studies about the effect of operational variables (chemical modifier, pyrolysis and atomization temperatures) were performed, as well as the establishment of convenient calibration strategy. The best results were verified when the temperatures of pyrolysis and atomization were 1000 °C and 2300 °C, respectively, and using Ir-W as permanent modifier. The results showed that manganese can be determined by the standard addition method or employing external calibration with standard solutions prepared in the same salinity of the samples (with NaCl). Three real samples with salinities varying between 74 and 84‰ were successfully analyzed by the developed procedure. The limits of detection and quantification were 0.24 and 0.80 μg L−1, respectively, in purified water, and 0.34 and 1.1 μg L−1, respectively, in 0.4 mol L−1 NaCl medium (approximately 23‰ salinity).