Isotachophoresis cations

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. 

In practice isotachophoresis is usually performed in narrow tubes with electrodes at either end and is one form of capillary electrophoresis. For the separation of a particular type of ion, e.g. an anion, two buffered electrolyte solutions are selected that have different anions but a common cation with a buffering capacity. One of the anions (termed the leading electrolyte) should show a greater mobility than the other anion and occupies the anodic end of... 

Fanali et al. have described a capillary isotachophoresis method for the determination of procaine in pharmaceuticals [ 150]. The drug was determined in a 6 pL sample of solution (Spofa product, obtained from Czechoslovakia, and diluted 180-fold) by cationic isotachophoresis in the single column mode. The system used a PTFE capillary column (20 cm x 0.3 mm) and a conductivity detector. The separation was carried out at room temperature, at 50 pA (but switched to 25 pA during detection). 

Procaine and other local anesthetics were separated by Chmela et al. with a VLD isotachophoresis apparatus, equipped with coupled PTFE separatory (23 cm x 0.8 mm) and analytical columns (23 cm x 0.8 mm) [151]. In one system, the leading cation was (0.01 M) containing 0.05 poly(vinylalcohol), with acetate as the counter-ion. The pH of the leading electrolyte was 4.75. The terminating electrolyte was 0.03 M beta-alanine. Two other systems were also reported. 

J.E. Prest, S.J. Baldock, P.R. Fielden and B.J.T. Brown, Determination of metal cations on miniaturised planar polymeric separation devices using isotachophoresis with integrated conductivity detection, Analyst, 126 (2001) 433-437. 

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. 

Isotachophoresis. This name derives from the fact that in this technique all sample bands ultimately migrate at the same velocityO). Sample is inserted between two electrolyte solutions, a leading and a terminating electrolyte. In a particular separation either cations or anions may be determined, but not both at once. 

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... 

CE is a separation technique that may be an alternative to LC to determine alkyl chain distribution of anionic and cationic surfactants. Most of the studies refer to alkylbenzyldimethylammonium with UV absorbance detection (Figure 2). Other uses of CE include the separation of homologs of anionic surfactants (as AS) and cationic (as alkyltrimethylammonium) by isotachophoresis with conductometric detection and homologs of non-UV absorbing surfactants (AS, alkylsulfonate, alkylsarcosinates and dialkyldimethylammonium) by capillary zone electrophoresis using indirect detection. 

PA Walker III, JM Shaver, MD Morris. Identification of cationic herbicides in deionized water, municipal tap water, and river water by capillary isotachophoresis/on-line Raman spectroscopy. Appl Spectrosc 51 1394-1399, 1997. 

Tribet, C., R. Gaboriaud, P. Gareil, Cg-C2o saturated anionic and cationic surfactant mixtures by capillary isotachophoresis with conductivity detection,/. Chromatogr., 1992,609,381—390. 

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