Capillary isotachophoresis electrolytes

Isotachophoresis. In isotachophoresis (ITP), or displacement electrophoresis or multizonal electrophoresis, the sample is inserted between two different buffers (electrolytes) without electroosmotic flow. The electrolytes are chosen so that one (the leading electrolyte) has a higher mobility and the other (the trailing electrolyte) has a lower mobility than the sample ions. An electric field is applied and the ions start to migrate towards the anode (anions) or cathode (cations). The ions separate into zones (bands) determined by their mobilities, after which each band migrates at a steady-state velocity and steady-state stacking of bands is achieved. Note that in ITP, unlike ZE, there is no electroosmotic flow and cations and anions cannot be separated simultaneously. Reference 26 provides a recent example of capillary isotachophoresis/zone electrophoresis coupled with nanoflow ESI-MS. 

Capillary isotachophoresis (CITP) is an electromigration technique, which is performed using a discontinnous buffer system, formed by a leading electrolyte (LE) and a terminating electrolyte... 

Capillary isotachophoresis is usually performed in constant current mode, which implies the invariable ratio between concentration and electrophoretic mobility of ions. Therefore, bands that are less concentrated than the LE are sharpened, whereas those that are more concentrated than the LE are broadened to adapt their concentration to the requested constant value between concentration and electrophoretic mobility. The consequence of this unique property of CITP is that each sample component can be concentrated to an extent that depends on its initial concentration and the concentration of the leading electrolyte. Therefore, the opportune selection of composition and concentration of the leading electrolyte allows the enrichment of diluted analytes. 

Kostelecka and Haller have determined procaine in mass-produced and extemporaneous pharmaceuticals by capillary isotachophoresis [152]. The method was carried out using pH 4.85 acetate buffer solution, and 0.01 M formic acid as leading and terminating electrolytes, respectively. 

In the electrolyte system used in capillary isotachophoresis (cITP), the sample zone migrates between a leading electrolyte at the front and a different, trailing electrolyte at the end. The leading electrolyte contains a coion with mobility greater than that of any of the analyte ions. The trailing electrolyte contains a coion with mobility that is lower than that of any of the analyte ions. In isotachophoresis, it is possible to analyze for anions or cations, but not both simultaneously. Analyses are usually performed in the constant-current mode. 

Capillary isotachophoresis (CITP) — An electrophoretic separation technique (-> electrophoresis) in a discontinuous -> buffer system, in which the analytes migrate according to their -> electrophoretic mobilities, forming a chain of adjacent zones moving with equal velocity between two solutions, i.e., leading and terminating electrolyte, which bracket the mobility range of the analytes. Ref [i] Riekkola ML, Jonsson jA, Smith RM (2004) Pure Appl Chem 76 443... 

Capillary Isotachophoresis. In isotachophoresis, the capillary is first filled with a buffer of higher mobility than any of the solutes, then the sample, and, finally, a second buffer with lower mobility than any of the analytes. Separation occurs in the zone formed between the two electrolytes. 

Fig. 6.32. The principle of preparative capillary isotachophoresis. (A) Schematic representation of the analytical equipment. (B) The preparative version with the additional flow of the leading electrolyte. L, Leading electrolyte T, terminating electrolyte D, UV detector S, sample v, migration velocity m,. mj, semipermeable membranes A, flow of L to elute the sample zones.

Electrolyte solutions and operating conditions for capillary isotachophoresis are selected based on a knowledge of sample properties. Table 8.8 [12,386,397]. The... 

Capillary isotachophoresis is a rapid, accurate, and potential detection technique for TTX. A small amount of TTX in contaminated extracts can be determined by this method (Shimada et al, 1983). It is performed using a cationic system, as TTX exists as cation under acidic and neutral conditions. Conditions for capillary isotachophoresis composed of 5 mmol/liter potassium acetate (pH 6.0) as an electrolyte, containing 0.2% Triton X-100 and 0.5 volume of dioxane, and 10 mmol p-alanine adjusted to pH 4.5 with acetic acid as a terminating electrolyte. When TTX is applied to isotachophoretic analyzer (Shimadzu IR-2A) equipped with a potential gradient 0.32, it is eventually monitored by the detector. PU is expressed as (PGs-PGl), where PGs, PGl, and PGt stand for potential gradient values for sample, leading ion, and... 

Kfivtokovd, L., Gebauer, R, Thormann, W., Mosher, R.A., and Bodek, P, Options in electrolyte systems for online combined capillary isotachophoresis and capillary zone electrophoresis, J. Chromatogr., 638, 119,1993. 

Capillary Isotachophoresis CIT is a moving-boundary technique. The sample is sandwiched between a leading electrolyte with mobility higher than any of the sample components, and a terminating electrolyte with mobility lower than any of the sample components. Upon application of the electrical field, the sample ions are separated into bands according to their electrophoretic mobility. Once the band is formed, all ions that are separated migrate at the same velocity. 

Figure 5 Configuration of capillary isotachophoresis. The arrangement shown is close to a real Instrument. The capillary is often made of plastic. The semipermeable membrane prevents electro-osmotic and hydrodynamic flows of the electrolyte but allows electromigration of ions. A conductivity detector is often used. It has miniature electrodes placed inside the capillary.

Figure 6 Longitudinal profiles of analytes in capillary isotachophoresis as calculated from eqn [8] by a computer. Leading electrolyte 20mmoll acetic acid/IOmmoll" potassium. Terminating electrolyte 20 mmol r acetic acid/IOmmoir am-mediol. Sample introduction 6 mm plug of mixture of 5 mmol U Na", 5 mmol I Li + ions, injected at position of 7 mm. Current density y=75Am . The picture shows resulting profiles at f = 650 s, when sodium and lithium are separated. They form isotachophoretic zones with virtually rectangular profiles stacked one by one.

Figure 10 ITP-CZE analysis of lO il of five times diluted untreated serum. (A) ITP step in the preseparation capillary, ID 0.8 mm, LE 10mmoll HCI + j3-alanine, pH 3.3, TE lOmmoll" propionic acid. Denoted components migrating behind lactic acid are driven to the second capillary. (B) CZE step in the analytical capillary, ID 0.2mm, BGE SOmmolP propionic acid + -alanine, pH 3.8. The combination of electrolytes corresponds to the T-S-T, system as shown in Figure 6. LOD 5x10 moll ascorbate. Estimated concentration of ascorbic acid in serum 1 5.74mg in serum 2 12.15mg l (Reprinted with permission from Prochazkova A, Kfivankova L, and Bocek P (1998) Quantitative trace analysis of L-ascorbic acid in human body fluids by on-line combination of capillary isotachophoresis and zone electrophoresis. Electrophoresis, vol. 10, p. 302 Wiley-VCH.)...

An on-line coupling of capillary electrophoresis or reversed anionic capillary isotachophoresis (CITP) with electrospray ionization mass spectrometry has been described for the separation of monophosphate nucleosides, pyridine, and flavin dinucleotides (87). The combination with CITP gives an enhancement of sample loadability and concentration sensitivity in capillary zone electrophoresis/ mass spectrometry (CZE/MS). MS-compatible buffer systems were developed (trailing electrolyte, 10 mM caproic acid pH 3.4 leading electrolyte, 7 mM HCl/ 13 mM P-alanine pH 3.9). This technique seems to be valuable for the trace analysis of DNA and RNA, e.g., to study radiation-induced DNA damage. 

C8-C20 alkyl sulfates and alkanesulfonates separation by increasing alkyl chain length Capillary isotachophoresis (CITE) FIFE, 0.55 mm x 22 cm Leading electrolyte 0.01 M L-histidine hydrochloride, apparent pH 4.88, 2% tetraethylene glycol Terminating electrolyte 0.01 M picolinic acid both in 80 20 MeOH/H20 Conductivity 1... 

Capillary tube isotachophoresis using a potential gradient detector is another technique that has been applied to the analysis of alcohol sulfates, such as sodium and lithium alcohol sulfates [303]. The leading electrolyte solution is a mixture of methyl cyanate and aqueous histidine buffer containing calcium chloride. The terminating electrolyte solution is an aqueous solution of sodium octanoate. 

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