Transient isotachophoresis

A. J. Tomlinson and S. Naylor, Enhanced performance membrane preconcentration-capillary electiophoiesis-mass spectiometry (mPC-CE-MS) in conjunction with transient isotachophoresis for analysis of peptide mixtures, J. High Resolut. Chromatogr. 18 384-386(1995). 

Larsson M, Lutz ES. 2000. Transient isotachophoresis for sensitivity enhancement in capillary electroporesis-mass spectrometry for peptide analysis. Electrophoresis 21 2859. 

Timerbaev, A. R., and Hirokawa, T. (2006). Recent advances of transient isotachophoresis-capillary electrophoresis in the analysis of small ions from high-conductivity matrices. Electrophoresis 27, 323-340. 

Figure 11.18 Schematic diagram of an in-line SPE unit for CE using (a) polyester wool frits to hold the sorbent, or (b) a particle-loaded membrane. Reprinted from Journal of Capillary Electrophoresis, 2, A. J. Tomlinson and S. Naylor, Enhanced performance membrane preconcentration-capillary electrophoresis-mass spectrometry (mPC-CE-MS) in conjunction with transient isotachophoresis for analysis of peptide mixtures, pp 225 - 233, 1995, with permission from ISC Technical Publications Inc.

One explanation for the sharpening of the later-eluting impurities is a phenomenon called sample self-stacking [42,43], This is a variant of transient isotachophoresis (ITP) [44], In this case, the leading electrolyte is chloride ion, while the main component acts as the terminating electrolyte. The requirement for ITP is fulfilled since the impurity s mobility is bracketed by leader and terminator. While you may not understand all of this, accidental ITP is not rare... 

For yet larger injections, other, more specialized techniques such as pH mediated stacking [47] (for zwitterions) or transient isotachophoresis (difficult to implement) can be considered [44], Neutral molecules can also be effectively stacked using charged surfactants or CDs [48,49],... 

B Toussaint, PH Hubert, UR Tjaden, J van der Greef, J Crommen. Enantiomeric separation of clenbuterol by transient isotachophoresis-capillary zone electrophore-sis-UV detection new optimization technique for transient isotachophoresis. J Chromatogr A 871 173-180, 2000. 

C Waterval, G Hommels, 1 Teeuwsen, A Bult, H Lingeman, WJ Underberg. Quantitative analysis of pharmaceutically active peptides using on-capillary analyte preconcentration transient isotachophoresis. Electrophoresis 21 2851-2858, 2000. 

Capillary zone electrophoresis with transient isotachophoresis as the online concentration procedure was developed for the determination of iodide in seawater (Yokota et ai, 2003). The effective mobility of iodide was decreased by the addition of 10 mmol cetyltrimethylammonium... 

Mohan D, Lee C S (2002). On-line coupling of capillary isoelectric focusing with transient isotachophoresis-zone electrophoresis A two-dimensional separation system for proteomics. Electrophoresis. 23 3160-3167. 

Whether the stacking technique is called field-amplified stacking, transient isotachophoresis, or sample self-stacking, the driving force in on-column sample preconcentration for charges species is the need to satisfy the initial KRF conditions. Under separation and sample matrix conditions where the KRF is difficult to determine, simply calculations such as flcut and a offer a rapid evaluation of conditions for optimal transient ITP. 

Shim, S.-H., Riaz, A., Choi, K., and Chung, D.S., Dual stacking of unbuffered saline samples, transient isotachophoresis plus induced pH junction focusing. Electrophoresis, 24, 1603, 2003. 

T. Hirokawa, T. Ichdiara, K. Ito and A.R. Timerbaev, Trace ion analysis of seawater by eap-iUary electrophoresis Determination of iodide using transient isotachophoresis preconeentration. 

M.C. Breadmore, A.S. Palmer, M. Curran, M. Macka, N. Avdalovic and PR. Haddad, On-column ion-exchange of inorganic anions in open tubular capillary electrochromatography with elution using transient-isotachophoresis gradients. 3. Implementation and method development. Anal. Chem., 74, 2112-2118, 2002. 

K. Fukushi, Y. Nakayama and J.-l. Tsujimoto, Highly sensitive capillary zone electrophoresis with artificial seawater as the background electrolyte and transient isotachophoresis as the on-line concentration procedure for simultaneous determination of nitrite and nitrate in seawater, J. Chromatogr. A, 1005, 197-205, 2003. 

ITP, also known as displacement electrophoresis, was first performed in capillary tubes by Ever-aerts et al. [69] for the separation of strong anions using a thermocouple detector. Since then, ITP has been used for the analysis of various important chemical and biological species such as amino acids [70], peptides [71], nucleotides [72], proteins [73,74], heavy metal ions [75], and other organic/inorganic ions [76,77] on a variety of detection platforms such as UV absorbance, conductivity and fluorescence detection. Over the past 15 years, ITP has been used as a preconcentration technique in conjunction with CE [78]. This mode of ITP, referred to as transient isotachophoresis (tITP), has been implemented on microchip platform in the recent years to achieve improved sensitivity [22,79,80]. 

Jeong, Y, Choi, K., Kang, M. K., Chun, K., and Chung, D. S., Transient isotachophoresis of highly saline samples using a microchip. Sensors and Actuators B, 104, 269-275, 2005. 

Jung, B., Bharadwaj, R., and Santiago, J. G, On-chip nulUon-fold sample stacking using transient isotachophoresis. Analytical Chemistry, 78, 2319-2327, 2006. 

FAS can be implemented on microchips in a very similar manner as capillary electrophoresis. However, the requirement of low ionic strength sample buffer for FAS puts limitation on its use as general preconcentration technique. Variations of the technique, such as transient isotacho-phoresis and micellar electrokinetic sweeping, have been more successfully used. Jung et al. reported (Mi-chip transient isotachophoresis... 

On-tube detection is almost universally used in CE, and the short detection path lengths provided by fused silica capillaries result in a 100- to 400-foId reduction in detection sensitivity compared with HPLC. Although various techniques are employed in CE to regain most of this sensitivity, detectivity remains a serious concern. Therefore concentration steps are often necessary in sample preparation for CE. It should be emphasized that some concentration techniques such as evaporation and lyophilization will not change the sample ion/salt ion ratio for nonvolatile salts, so no effective concentration is achieved when electromigration injection is used. The use of transient isotachophoresis has been proposed for on-line preconcentration of proteins prior to CZE separation [41,42],... 

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