Evaluation of MIP-OES as a detector in DLLME procedures. Application to the Cd determination in water samples.
High-power microwave induced plasma optical emission spectrometry (MIP-OES) constitutes a serious alternative to inductively coupled plasma optical emission spectrometry (ICP-OES) for elemental analysis. To improve the analytical capabilities of MIP-OES, dispersive liquid-liquid microextraction (DLLME) procedures seems to be, a priori, a very promising choice for trace and ultra-trace analysis in complex matrices. Nevertheless, up to date, DLLME has never been coupled to MIP-OES, probably due to the lack of fundamental studies about the matrix effects originated by the presence of organic solvents in high-power MIP-OES. The goal of the present work is to investigate the capability of MIP-OES as a detector in DLLME procedures. To this end, spectral and non-spectral interferences caused by the presence of common DLLME extractants (i.e., chloroform and supramolecular solvent based on 1-decanol and THF) on the emission signal of 23 elements have been tested in MIP-OES. Organics have been directly introduced into the plasma by means a flow injection manifold without air addition into the plasma gas. Results reveal the occurrence of both spectral and non-spectral interferences due to carbon-based molecular bands emission in MIP-OES. Thus, analytical figures of merit are deteriorated for the elements with emission wavelengths above 300 nm. For the remaining lines tested, the emission signal is not significantly affected by the presence of organics in the plasma source. Next, different DLLME methodologies have been tested and optimized for Cd determination in water samples (i.e., tap, sparkling and synthetic seawater) by MIP-OES. These methodologies afford similar analytical figures of merit than those previously reported for DLLME-ICP-OES. On this regard, limit of detection by DLLME-MIP-OES allows Cd determination in water samples according to current international policies.