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

Abstract

Trace metal ions such as Cd 2+, Ni 2+, and Zn 2+ in a highly saline sample were subjected to on-line complexation with 4-(2-thiazolylazo) resorcinol (TAR) dissolved in a background electrolyte (BGE) under transient isotachophoresis (TITP) conditions. A long plug of the saline sample, containing the trace metal ions but devoid of TAR, was injected into a coated capillary filled with a BGE composed of 150 mM 2-(cyclohexylamino) ethanesulfonic acid (CHES) and 110 mM triethylamine (TEA) at pH 9.7. Since the electrophoretic mobility of TAR fell between the mobilities of the anionic leading electrolyte (Cl − in the sample) and the anionic terminating background electrolyte (CHES − ), a highly concentrated zone of TAR from the BGE was formed at the rear of the sample matrix and then the metal cations toward the cathode were swept by isotachophoretically assisted on-line complexation (IAOC) between the metal ions and the isotachophoretically stacked TAR. As a result, anionic metal-TAR complexes were formed efficiently, which satisfy the TITP conditions between Cl − and CHES − . The enrichment factors of metal ions including Cd 2+ were up to 780-fold compared to a conventional CZE mode using absorbance detection. The detection limits were 17 nM, 15 nM, and 27 nM for Ni 2+, Zn 2+, and Cd 2+ in a 250 mM NaCl matrix, respectively. Our method was successfully applied to the analysis of urine samples without desalting.

Recent advances in enhancing the sensitivity of electrophoresis and electrochromatography in capillaries and microchips (2010–2012)

“…Popularly used was CSEI‐sweeping . Other sequential stacking techniques employed were anion‐selective exhaustive injection (ASEI)‐sweeping , dynamic pH junction‐sweeping , LVSS‐sweeping , t‐ITP‐sweeping , sweeping‐MSS . The use of triple stacking was also reported such as chitosan sweeping‐reversed field stacking‐FASS , and FASS‐pH junction‐sweeping .…”

“…The recent additions to the expanding list of additives used with sweeping combination stacking were the combination of borate, SDS and Brij35 used in dynamic pH junction‐sweeping, taurine and chitosan for a multiple concentration technique of sweeping‐FASS‐reversed‐field stacking, a long chain ionic liquid cationic surfactant (i.e., N ‐Cetyl‐ N ‐methylpyrrolidinium bromide (C 16MPYBr)) in sweeping‐MSS, and 4‐(2‐thiazolylazo) resorcinol as complexing agent in tITP‐sweeping. SDS continues to be commonly used for most sweeping‐combination techniques .…”

“…However, the method is complicated and the analysis time was 150 min. tITP‐CZE was also employed for the determination of Cd 2+ , Ni 2+ and Zn 2+ after complex formation with 4‐(2‐thiazolylazo) resorcinol . Urine samples were diluted 20 times with 250 mM NaCl to minimise matrix variation between samples and to provide a constant ionic strength.…”

Recent progress in analytical capillary isotachophoresis

“…Examples analyzed in such a system included hypolipidemic, nonsteroidal antiinflammatory, and diuretic drugs where also LODs more than an order of magnitude better compared with typical injection were obtained (BGE: 30 mM ammonium acetate, 30% methanol, pH 6; base solution: 100 mM tetrapropylammonium hydroxide; UV detection). Kim et al used tITP to improve CE analysis of trace metal ions in a highly saline matrix. tITP assisted here not only in concentration but also in efficient complexation of Cd 2+ , Ni 2+ , and Zn 2+ with 4‐(2‐thiazolylazo)resorcinol by forming its highly concentrated zone at the rear of the sample matrix and sweeping the metal cations (BGE = TE: 150 mM CHES, 110 mM triethylamine, 5 mM chromate, 0.02% v/v fluorinated carbon polymer neutral, 0.2 mM 4‐(2‐thiazolylazo)resorcinol, pH 9.7; LE: 250 mM NaCl).…”

Inorganic analysis using CE: Advanced methodologies to face old challenges

“…For samples of high conductivity, transient ITP still ranks uppermost as an in‐line preconcentration technique. A recent advancement of the method is owing to a two‐fold role of ITP . At first, ITP performed a role of isotachophoretically assisted in‐capillary complexation, in which a complexing reagent is stacked to form a highly concentrated zone at the rear of the sample plug.…”