Analysis of sub‐ppb levels of Fe(II), Co(II), and Ni(II) by electrokinetic supercharging preconcentration, CZE separation, and in‐capillary derivatization

Abstract

The analysis of sub-ppb levels of Fe(II), Co(II), and Ni(II) in heat exchanger fluids of nuclear power plants is needed to monitor corrosion. A method involving preconcentration with electrokinetic supercharging (electrokinetic injection with transient ITP), CZE separation, and in-capillary derivatization with ortho-phenanthroline (o-Phe) for direct UV detection was thus developed. First, a multizone BGE was loaded into the capillary by successive hydrodynamic introduction of zones of (i) o-Phe-containing BGE, (ii) BGE for the zonal separation, and (iii) ammonium-based leading electrolyte. Metal cations were electrokinetically injected and stacked at the capillary inlet behind this last leading zone. Finally, a terminating electrolyte zone was hydrodynamically introduced. When a constant voltage was applied, metal ions kept on concentrating isotachophoretically, then separated in CZE mode, were complexed by migrating through an o-Phe zone, and finally detected by direct absorbance. To detect extremely thin peaks, it was attempted for the first time to focus the derivatization reagent by inducing a second transient ITP, before labeling analytes, already separated in CZE mode. With this arrangement, LODs were about 30 ppt in pure water. In heat exchanger fluid matrices containing 1000 ppm bore and 2 ppm lithium, only Fe(II) cation was detected among the three cations of interest at the 1 ppb level using the present method, and its LOD was about ten times higher, due to the lower loading rate during electrokinetic injection.

Analysis of phenolic acids by non-aqueous capillary electrophoresis after electrokinetic supercharging

“…Electrokinetic supercharging (EKS) is the combination of t-ITP and FASI and enhancement factors more than 1000 have been reported in the literature [35][36][37][38][39][40]. EKS involves electrokinetically injecting the sample between hydrodynamically introduced leading and terminating ions.…”

“…Most of the on-line preconcentration methods in capillary electrophoresis (CE) are based on changes in analyte migration due to conductivity difference, buffer pH difference or the association between the analytes and the surfactants, and the combination of these approaches. Thus methods such as field-amplified sample stacking (FASS) [5][6][7], field-amplified sample injection (FASI) [8], large-volume stacking using the EOF pump (LVSEP) [9][10][11][12][13][14][15][16], fieldamplified sample injection with matrix removal via an EOF pump (FAEP) [17,18], dynamic pH junction (DypH) [19][20][21], transient isotachophoresis (tITP) [22,23], pseudo-transient isotachophoresis (Pseudo-tITP) [24][25][26][27][28], sweeping [29][30][31][32], micelle collapse (MC) [33,34] and various combinations including electrokinetic surpercharging (EKS) [35][36][37][38][39][40][41], selective exhaustive injection [42] and selective exhaustive injection-sweeping (SEI-sweeping) [43][44][45], dynamic pH junction-sweeping [46], and large-volume stacking using the EOF pu...…”

“…It has been shown to be particularly powerful for on-line concentration with enhancements of 3-4 orders of magnitude readily achieved for peptide analysis [37], non-steroidal anti-inflammatory drugs in water samples [38,39] as well as inorganic cations such as Fe(II), Co(II) and Ni(II) analysis [40]. Previously we investigated EKS in non-aqueous conditions and obtained modest enhancements of 300-440 [41].…”

High‐sensitivity capillary and microchip electrophoresis using electrokinetic supercharging

“…Moving to another complicated sample matrix, Gareil and co-workers [35] developed an EKS system for determination of Fe(II), Co(II), and Ni(II), in heat exchange fluid samples. The separation and preconcentration protocol was combined with in-capillary derivatization.…”

A rapid and sensitive CE method with field‐enhanced sample injection and in‐capillary derivatization for selenomethionine metabolism catalyzed by flavin‐containing monooxygenases

“…This limitation has compromised the application of the in-capillary derivatization technique. To further improve the sensitivity, some online sample preconcentration techniques, such as normal sample stacking [15], field-enhanced sample injection (FESI) [16], large-volume stacking [17], pH junction [18], transient isotachophoresis [19] and stacking based on viscosity [20], have been developed in combination with in-capillary derivatization. In general, on-line sample preconcentrations are designed to compress analyte bands within the capillary, thereby increasing the volume of the sample that can be injected without loss of CE efficiency [21].…”