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 (Cu , Zn , Co , Ni , Pb , Cd ) from saline samples was investigated. CE with capacitively coupled contactless conductivity detection (C 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 , Ca , Mg ) 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 Ca and Mg . The system was optimized for simultaneous extractions of the six target metals from saline samples (50 mM Na , 5 mM Mg , 1 mM K , and 1 mM Ca ) 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 (R = 0.987-0.999) and LOD better than 2.6 nM. Applicability of the EME-CE-C D method to the analyses of metal cations in drinking water, seawater, and urine samples was also demonstrated.

Analytical Performance of Electromembranes as a Tool for Nanoconcentrations of Silver in Waters

“…As can be seen in Figure 3 , the enrichment factor decreased as salinity increased achieving a value of 12.4 ± 1.3 for a typical salinity of seawater. This behaviour has been previously related to the formation of silver chloride complexes that could be not extracted by Cyanex 471x due to its polarity [ 27 , 28 , 33 , 39 ].…”

“…The first works in this field were focused on biological samples [ 15 , 16 ] and, a few years later, the first paper on the analysis of metals in water samples appeared [ 26 ]. However, EME applications to real water samples are still very scarce and almost unavailable in the case of seawater, with only a couple of applications to metal analysis in real seawater samples [ 17 , 27 ].…”

Application of Capillary Electrophoresis for Determination of Inorganic Analytes in Waters

“…In order to obtain high separation efficiency with low conductivity and appropriate ionic strength, organic acids are used as components of BGEs, including acetic acid [41][42][43][44][45], acetic acid with histidine [8,[46][47][48][49][50][51][52][53][54][55][56][57][58], 3-(N-morpholino)propane-sulfonic acid (MOPS) and bis(2-hydroxyethyl)amino tris(hydroxymethyl)methane (bis-tris) [59], 2-(N-morpholino) ethanesulfonic acid (MES) with histidine [51,60,61], pyromellitic acid (PMA) with histidine [62], and lactic acid with histidine [49,63]. For instance, the determination of selected anions has been carried out under conditions with suppressed electroosmotic flow by appropriate pH and polarity switching, with capillary coating [54,62], or by reversing the direction of the EOF by adding an EOF modifier (e.g., cetyltrimethylammonium bromide (CTAB) [61].…”

“…The limits of detection obtained in the EME-CE-C 4 D determination ranged from 25 to 200 nM, which is one to two orders of magnitude improved, compared to CE-C 4 D without sample treatment. A similar set-up was used for metal determination in diluted saline samples, however due to substantial matrix effects, the obtained sensitivity was worse (500 nM) [41]. An EME with a porous polypropylene hollow fiber impregnated with 1-heptanol was applied for perchlorate extraction from drinking water [53].…”

An electromembrane microextraction-based green method for the determination of trace copper in natural waters

“…17 Some of these reagents, such as DEHPA, provide very good results for multi-element extraction, mostly for divalent cations, but may exhibit lower selectivity for a specific element, especially in complex matrices such as seawater. 16 Moreover, high salinity in water samples may lead to adverse effects in EME systems due to a decrease in the analyte flux because of the competition between the analyte and the ions of the matrix, the formation of ion pairs with Cl − or the decrease of solution resistance. 12 Therefore, for the sake of selectivity other reagents have been investigated, such as di-2-pyridylketone benzoylhydrazone (dPKBH), a synthesized compound which has proven its good performance for the extraction of copper by HF-LPME in the presence of high NaCl concentrations (0–0.58 mol L −1 ) and also by EME in aqueous solutions.…”