Cadmium(II) determination in production waters from petroleum exploration after its separation from the highly saline matrix mediated by a semipermeable membrane device

Abstract

This paper reports the development of a novel approach for the separation of Cd(II) from production waters generated during petroleum prospection. The analyte was separated from the highly saline waters as a dithiocarbamate (DDTC) complex using a low-density polyethylene semipermeable membrane device (SPMD) filled with chloroform. The quantification of cadmium(II) in the extracts was performed by graphite furnace atomic absorption spectrometry (GF AAS). Several parameters that could affect the performance of the SPMD (pH of the sample, concentration of DDTC, type and volume of solvent used to fill the device, and extraction time) were evaluated in order to achieve maximum transference of Cd(II) and sensitivity. Under the best conditions, the SPMD was filled with 3.0 mL of CHCl3 and used to extract Cd(II) (as Cd(DDTC)2 complex) from a solution containing 3.75 × 10−4 mol L−1 of sodium dithiocarbamate at pH = 9.0. The SPMD was maintained in contact, under shaking, with the sample solution for 90 min. After that, the inner solvent containing the extracted Cd was collected and diluted to 5.0 mL with ethanol prior to analyte quantification by GF AAS. External calibration was possible using Cd(II) standard solutions prepared in a 10% (m/v) NaCl medium. The limits of detection and quantification of the method were 0.08 and 0.24 µg L−1, respectively. The method was employed for the quantification of Cd(II) in four samples of real production waters with high salinity and in a certified reference material of seawater (MX014, from National Measurement Institute of Australia). Recovery tests were also performed by spiking the samples Cd(II), resulting in the recovery percentages in the range of 90 – 132%.