Journal of Chromatography A, 1345 (2014) 212–218 Contents lists available at ScienceDirect Journal of Chromatography A jo ur nal ho me pag e: www.elsevier.com/locate/chroma Can neutral analytes be concentrated by transient isotachophoresis in micellar electrokinetic chromatography and how much? Magdalena Matczuk a , Lidia S. Foteeva b , Maciej Jarosz a , Markus Galanski c , Bernhard K. Keppler c , Takeshi Hirokawa d , Andrei R. Timerbaev b,c,∗ a Chair of Analytical Chemistry, Faculty of Chemistry, Warsaw University of Technology, Warsaw, Poland b Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, Moscow, Russian Federation c Institute of Inorganic Chemistry, University of Vienna, Vienna, Austria d Graduate School of Engineering, Hiroshima University, Higashi-hiroshima, Japan a r t i c l e i n f o Article history: Received 21 February 2014 Received in revised form 6 April 2014 Accepted 7 April 2014 Available online 15 April 2014 Keywords: Transient isotachophoresis Micellar electrokinetic chromatography Preconcentration Anticancer metallodrugs a b s t r a c t Transient isotachophoresis (tITP) is a versatile sample preconcentration technique that uses ITP to focus electrically charged analytes at the initial stage of CE analysis. However, according to the ruling principle of tITP, uncharged analytes are beyond its capacity while being separated and detected by micellar elec- trokinetic chromatography (MEKC). On the other hand, when these are charged micelles that undergo the tITP focusing, one can anticipate the concentration effect, resulting from the formation of transient micellar stack at moving sample/background electrolyte (BGE) boundary, which increasingly accumu- lates the analytes. This work expands the enrichment potential of tITP for MEKC by demonstrating the quantitative analysis of uncharged metal-based drugs from highly saline samples and introducing to the BGE solution anionic surfactants and buffer (terminating) co-ions of different mobility and concentration to optimize performance. Metallodrugs of assorted lipophilicity were chosen so as to explore whether their varying affinity toward micelles plays the role. In addition to altering the sample and BGE com- position, optimization of the detection capability was achieved due to fine-tuning operational variables such as sample volume, separation voltage and pressure, etc. The results of optimization trials shed light on the mechanism of micellar tITP and render effective determination of selected drugs in human urine, with practical limits of detection using conventional UV detector. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Over the three decades of continuous methodological devel- opments, micellar electrokinetic chromatography (MEKC) has reached the status of a routine analytical tool for a great variety of substances [1–3]. This is due largely to systematically addressing the challenge of limited concentration sensitivity of MEKC by implementing an array of preconcentration techniques, operat- ing in-line, i.e., within the same capillary where separation takes place [4,5]. Of these techniques, sweeping and its modifications (or combinations) offer perhaps the most remarkable improve- ments in detection sensitivity [6]. The analytical potential of analyte stacking by virtue of sweeping phenomenon is exceptionally high ∗ Corresponding author at: Vernadsky Institute of Geochemistry and Analytical Chemistry, Kosygin St. 19, 119991 Moscow, Russian Federation. Tel.: +7 495 9397035; fax: +7 495 9382054. E-mail address: andrei.timerbaev@univie.ac.at (A.R. Timerbaev). for samples with low-to-moderate conductivity, comparable to that of the background electrolyte (BGE) solution. However, such analytical conditions are not the occurrence for a variety of applica- tions, in particular, routine clinical screening of biological samples, and contradictory results have been observed when sweeping was attempted under inhomogeneous electric field conditions, includ- ing a frequent case of high-salt sample matrices (see Ref. [7] and references therein). A theoretical analysis performed by Pyell and her coworkers [7] revealed the event of a strong deviation of the sweeping efficiency from the theoretically predicted value. Unex- pectedly high enrichment factors were ascribed by the authors to a transient isotachophoresis (tITP) state induced by the presence in the sample of a salt whose co-ion (the ion with the same charge polarity as micelles) could act as a leading ion. (It goes without say- ing that to establish the tITP setting the electrophoretic mobility of micelles has to be bracketed by the mobility of a comparatively slow, preferably BGE co-ion.) Assuming that an isotachophoreti- cally stacked zone of micelles migrates through the sample zone, it would concentrate the analytes, presumably to a greater extent http://dx.doi.org/10.1016/j.chroma.2014.04.022 0021-9673/© 2014 Elsevier B.V. All rights reserved.