MIP OES quantification of Cd, Co, Cr, Pb and Zn preconcentrated on multiwalled carbon nanotubes using a multifunctional ultrasonic sampler

Abstract

A new arrangement of an ultrasonic sampler system (USS) for the simultaneous multielement determination of Cd, Co, Cr, Pb, and Zn, enriched on a carbon nanomaterial and combined with on-line calibration and internal standardization (IS), using microwave-induced plasma optical emission spectrometry (MIP OES), is proposed. The dispersive micro-solid-phase extraction (DMSPE) procedure was applied for pre-concentration of analytes on oxidized multi-walled carbon nanotubes (MWCNTs) in liquid samples. The USS ensures that the suspension and liquids are introduced through separate capillaries and adequately mixed directly int the aerosol generation area. The new assembly is easy to use and enables different settings of continuous solution flow rates to perform on-line calibration (both standard and diluent), continuous flow rate of yttrium solution for IS and suspension injection in discontinuous mode. The DMSPE-USS-MIP OES technique allows microvolume (15 µL) injection of nanomaterial suspensions using a peristaltic pump, while two syringe pumps were used for on-line calibration and IS. The analytical parameters of the proposed method were evaluated by determining the limits of detection (LODs), absolute limits of detection and precision (RSDs) for all elements tested. The LODs obtained were 0.4, 1.0, 0.5, 0.1 and 0.7 ng mL⁻¹ for Cd, Co, Cr, Pb and Zn, respectively, and the precision ranged from 4% to 8%. The method was validated using certified reference materials and successfully used for simultaneous determination of metals in real water samples.