Electromembrane extraction and capillary electrophoresis with capacitively coupled contactless conductivity detection: Multi-extraction capabilities to analyses trace metals from saline samples

Abstract

Simultaneous electromembrane extraction (EME) of six trace metal cations (Cu²⁺ , Zn²⁺ , Co²⁺ , Ni²⁺ , Pb²⁺ , Cd²⁺ ) from saline samples was investigated. CE with capacitively coupled contactless conductivity detection (C⁴ D) was used to determine the metals in acceptor solutions due to its excellent compatibility with the minute volumes of acceptor solutions. Bis(2-ethylhexyl)phosphate (DEHPA) was selected as a suitable nonselective modifier for EME transport of target metal cations. Both, the individual effect of each major inorganic cation (Na⁺ , K⁺ , Ca²⁺ , Mg²⁺ ) and their synergistic effect on EME of the trace metal cations were evaluated. In both cases, a decrease in extraction efficiency was observed when major inorganic cations were present in the sample. This effect was more significant for Ca²⁺ and Mg²⁺ . The system was optimized for simultaneous extractions of the six target metals from saline samples (50 mM Na⁺ , 5 mM Mg²⁺ , 1 mM K⁺ , and 1 mM Ca²⁺ ) and following EME conditions were applied. Organic phase consisted of 1-nonanol containing 1% (v/v) DEHPA, acceptor solution was 1 M acetic acid (HAc) and sample pH was adjusted to 5. Sample was stirred at 750 rpm and EMEs were carried out at extraction potential of 10 V for 20 min. The method presented a repeatability between 8 and 21.8% (n = 5), good linearity in 0.5-10 μM concentration range (R² = 0.987-0.999) and LOD better than 2.6 nM. Applicability of the EME-CE-C⁴ D method to the analyses of metal cations in drinking water, seawater, and urine samples was also demonstrated.

Keywords: CE; DEHPA; Electromembrane extraction; Major inorganic cations; Metal cations; Saline samples.