Asif Riaz Doo Soo Chung School of Chemistry, Seoul National University, Seoul, Korea Transient isotachophoresis of highly saline trace metals under strong electroosmotic flow conditions 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(hydrox- ymethyl)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 effi- ciency, 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 (Fe 21 , 0.3 ppb; Ni 21 , 0.16 ppb; and Zn 21 , 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. Keywords: Bare capillary / Trace metals / Transient isotachophoresis / Urine / 4-(2-Pyridylazo) resorcinol DOI 10.1002/elps.200406151 1 Introduction Over the contemporary chromatographic techniques, capillary electrophoresis (CE) has unique advantages, such as simplicity, small volume sample/reagent require- ments, short analysis time, and low waste production [1]. Since its introduction, CE has also gained special attention for metal ion analysis with its advantages of multielement analysis and elemental speciation [2, 3]. However, CE suf- fers from a low concentration sensitivity for absorbance detection because of the narrow (20–100 mm) inner capil- lary diameter being the optical path length [4]. Moreover, CE of a highly saline sample shows peak-broadening due to a lower electric field across the sample zone, and real saline samples are often subjected to tedious and time- consuming steps, such as preconcentration and matrix removal. One facile way of overcoming the poor sensitivity and salt problem in CE is transient isotachophoresis (TITP) which provides on-line preconcentration and desalting [5– 10]. The high concentration of highly mobile chloride ions in a saline sample can induce isotachophoretic stacking of suitable anionic analytes yielding a several hundredfold sensitivity enhancement [9, 11, 12]. Generally, TITP stacking is performed in a suppressed electroosmotic flow (EOF) to minimize zone-broadening due to an EOF mismatch arising from variations in the conductivities of sample zones. In order to suppress the EOF, various strategies have been used. Krˇivánková and Bocˇ ek [13] used a linear polyacrylamide-coated capillary for TITP stacking and Boden and Bachmann [12] used cationic surfactants. For tandem isotachophoresis-CE as well as for single-capillary TITP stacking, polytetra- fluoroethylene capillaries with a suppressed EOF are fre- quently used [11]. Although the low EOF in a coated cap- illary provides a shorter analysis time, high stacking effi- ciency, and good reproducibility, the process of coating itself is a time-consuming and often expensive procedure. Furthermore, a coated capillary requires proper main- tenance and its lifetime is rather short compared to a bare fused-silica capillary. Correspondence: Prof. Doo Soo Chung, School of Chemistry, Seoul National University, Seoul 151-747, Korea E-mail: dschung@snu.ac.kr Fax: 182-2-877-3025 Abbreviations: DCF, 2,7-dichlorofluorescein; PAR, 4-(2-pyridy- lazo) resorcinol; TAPS, N-tris(hydroxymethyl)methyl-3-amino- propanesulfonic acid; TEA, triethylamine; TITP, transient isota- chophoresis 668 Electrophoresis 2005, 26, 668–673  2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim