Transient isotachophoresis of highly saline trace metals under strong electroosmotic flow conditions

Abstract

Transient isotachophoresis (TITP) is usually performed under low-electroosmotic flow (EOF) conditions using a coated capillary or a low pH background electrolyte. We used a bare fused-silica capillary for TITP stacking of anionic complexes of some heavy metals under high-EOF conditions (pH 9.0). The sample component chloride as a leading electrolyte induced stacking by an isotachophoretic mechanism and the complexing agent 4-(2-pyridylazo) resorcinol (PAR) acted as a terminating electrolyte. The optimized background electrolyte was composed of 150 mM N-tris(hydroxymethyl)methyl-3-aminopropanesulfonic acid, 127 mM triethylamine, and 0.1 mM PAR at pH 9.0. The strong EOF at pH 9.0 pulled the analytes against their mobilities toward the outlet side, allowing a separation in the normal polarity mode. The stacking efficiency, reproducibility, analysis time, and sample loading capacity in coated and bare capillaries were compared. The stacking efficiency and reproducibility were higher and the analysis time was shorter in the coated capillary. However, a larger volume of a sample could be injected in the bare capillary to achieve detection limits comparable to those for the coated one without compromising the resolution between the analyte peaks. The limits of detection (S/N = 3) were in the sub-ppb range for the selected metals (Fe2+, 0.3 ppb; Ni2+, 0.16 ppb; and Zn2+, 0.8 ppb) in a standard saline sample with 250 mM NaCl matrix. The proposed method was successfully applied to the analysis of reference urine samples and human urine samples.

Hybrid integrated platform of PDMS microfluidics and Silica Capillary for effective CE and ESI-MS coupling

“…To demonstrate the reliability of the iPSC CE module we separated a mixture of two analytes FL and DCF using the conditions described previously [11] (Fig. 3).…”

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

“…This condition, however, is not valid in most real biological samples, and another trendy approach is to involve t-ITP. This was shown for the determination of Zn(II), Fe(II), and Ni(II) in urine samples [17,18]. In the present case, the targeted cations are contained in 1000 ppm bore and 2 ppm lithium matrix, which has a quite low conductivity.…”

“…As their complexation chemistry is diverse, their separation can be enhanced by use of complexing agents. In literature, a variety of agents was used, e.g., a-hydroxyisobutyric acid [23][24][25][26][27][28], glycolic acid [13,26,28], lactic acid [29], tartaric acid [29], phthalic acid [29], 8-hydroxyquinoline-5-sulfonic acid [27,30], EDTA [27], cyclohexane-1,2-diaminetetraacetic acid [14], 2-(5-8-bromo-2-pyridylazo)-5-(N-propyl-N-sulfopropylamino)phenol [31], orthophenanthroline (o-Phe) [11][12][13]20], 4-(2-thiazolylazo)-resorcinol [15], 4-(2-pyridylazo)resorcinol [17,18], or mixtures of complexing agents such as lactic acid and 18-crown-6 [32,33] or a-hydroxyisobutyric acid, 18-crown-6, and sulfate [34]. They were added either to the sample solution before introduction into the capillary or to the BGE.…”

Isotachophoretically Assisted On-Line Complexation of Trace Metal Ions in a Highly Saline Matrix for Capillary Electrophoresis

“…3,4 Metal-PAR complexes were prepared off-line and subjected to TITP stacking, utilizing the sample matrix chloride as the leading electrolyte (LE) to achieve limits of detection (LOD) in the low/sub ppb range. However, the method was not applicable to some heavy metal ions such as Cd 2+ due to its weak complexation with PAR.…”