Temperature capillary zone

FIGURE 9 Capillary zone electrophoresis of eight recombinant human anti bod ies/anti body fragments. Capillary BioCAP XL coated capillary (50 pm x 47 cm) 45 mM g-amino-n-caproic acid/ acetic acid, pH 4.5, 0.1% HPMC voltage 30kV, normal polarity capillary temperature 20°C detection, UV at 214 nm. 

A determination of PQQ by capillary zone electrophoresis was also developed <2000JCH(739)101>. The optimal separation conditions were a 50mM /3-alanine HCl pH 3.0 buffer, an applied voltage of 25 kV (negative polarity), and a temperature of 25 °C. The linear detection range for concentration versus peak area is that this assay is from 5 to 500 mM with a detection limit of 0.1-0.2 mM. 

Berzas Nevado et al. [138] developed a new capillary zone electrophoresis method for the separation of omeprazole enantiomers. Methyl-/ -cyclodextrin was chosen as the chiral selector, and several parameters, such as cyclodextrin structure and concentration, buffer concentration, pH, and capillary temperature were investigated to optimize separation and run times. Analysis time, shorter than 8 min was found using a background electrolyte solution consisting of 40 mM phosphate buffer adjusted to pH 2.2, 30 mM /1-cyclodextrin and 5 mM sodium disulfide, hydrodynamic injection, and 15 kV separation voltage. Detection limits were evaluated on the basis of baseline noise and were established 0.31 mg/1 for the omeprazole enantiomers. The method was applied to pharmaceutical preparations with recoveries between 84% and 104% of the labeled contents. 

Capillary Zone Electrophoresis. The primary advantage of capillary electrophoresis can be found in the simplicity of the instrument. Basic experimental components include a high-voltage power supply, two buffer reservoirs, a fused silica capillary, and a detector. The basic setup is usually completed with enhanced features such as multiple injection devices, autosamplers, sample and capillary temperature controls, programmable power supplies, multiple detectors, fraction collection, and computer interfacing. 

Whang, C. W., and Yeung, E. S. (1992). Temperature programming in capillary zone electrophoresis. Anal. Chem. 646, 502-506. 

Since selectivity is a prerequisite for resolution, a temperature increase strongly impacts both selectivity and resolution. The variability of the van t Hoff lines explains the seemingly erratic result of the influence of tanperature on the figures of merit of the method. For example, at lower temperatures, the resolution of model peptides with +1 and +3 net charges improved and worsened, respectively [27]. In chiral IPC, T < 0°C was successfully used to improve enantioresolution [28]. Similarly, lower temperatures provided better resolution in the analysis of a new aminoglycoside antibiotic [29] and for characterization of maize products [30]. Conversely, an increased resolution at 70°C was observed when the ion-pair mechanism was exploited under IPC-capillary zone electrophoresis of cationic proteomic peptide standards [31]. 

Aussenac et al. (1998) used capillary zone electrophoresis with UV detection at 260 nm to analyze isoflavones in soybean seeds of various varieties grown in various locations. Methanol was used for extraction. Total extraction was not affected by temperature but was affected by the composition of the solvent. Electrophoresis was conducted at pH 10.5, at which the isoflavones were weak acids and were ionized. Boric acid was added to form a negatively charged borate-isoflavone complex. A fast capillary electrophoresis method was also developed by Vanttinen and Moravcova (1999) to determine daidzein and genistein after enzyme hydrolysis in soy products. Photodiode array was used to detect the isoflavones at 254 and 268 nm, respectively. Minimum detection was 0.4 mg/L. p-Nitrophenol was used as an internal standard. 

Recently, Jalali-Heravi et al. (9,11) have developed a multivariable model in order to improve the predictive ability of the Offord model and understand the effects of further structural descriptors on electrophoretic mobility in capillary zone electrophoresis (CZE), in addition to charge and size. They generated a diverse data set based on a 125-peptide study, which ranges in size from 2 to 14 amino acids and charges of 0.743-5.843. The Pe of the peptides were measured in bare fused-silica capillaries in CZE mode using 50 mM sodium phosphate buffer at pH 2.5. The detection wavelength was 214nm and the separation temperature was 37 °C. 

Capillary electrophoresis (CE) is an emerging analytical technique for determination of catechins. The majority of CE studies involve the analysis of catechins in tea infusion, extracts as well as supplements. The three variants of CE suitable for the analysis of catechins include capillary zone electrophoresis (CZE), micellar electro-kinetic chromatography (MEKC), and microemulsion electrokinetic chromatography (MEEKC) with UV detection. In general, the resolution of MEKC was found to be superior to CZE for separation of catechins. MEEKC is a relatively new technique, and the few reports available suggest that it offers a performance similar to MEKC. CE conditions are often quite complex, and many factors, such as buffer composition, pH, presence of surfactants, and column temperature, can all affect the quality of separation and should be optimized individually. On the other hand, CE offers several advantages over HPLC. The short analysis time (<20 minutes), low running costs, and reduced use of solvents make it an attractive alternative for routine analysis of catechins. 

For capillary zone electrophoresis the electrical and thermal detection modes have insufficient sensitivity. This is because in capillary zone electrophoresis there is a relatively large background of supporting electrolyte (buffer) upon which a low concentration of sample ion is superimposed. Detecting the exceedingly small changes in electrical properties or temperature associated with sample zones is difficult. Thus UV absorption and fluorescence detection have been of greatest use in capillary zone electrophoresis. 

Recently the separation of 10 anthraquinone aglycones and two glycosides from Rheum by capillary electrophoresis was described [88] and compared with an HPLC separation. Two of the investigated aglycones also occur in madder alizarin and purpurin. Because all of the anthraquinones can be charged by means of complexation with a borate buffer, capillary zone electrophoresis (CZE) was chosen as separation mode. The separations were carried out with a 90 cm x 75 pm fused silica capillary. The detection window was located at 80 cm. Dectection occurred at 260 nm. The voltage was 23 kV and the temperature 20°C. The injection was pressure controlled (1.2 sec at 200 mbar). The total run time was 39 min (compared to 63 min for gradient RP-HPLC for the same set of test substances). 

Grushka, E., McCormick, R. M., and Kirkland, J. J., Effect of temperature gradients on the efficiency of capillary zone electrophoresis separations, Anal. Chem., 61, 241,1989. 

Xuan X, Li D (2005) Band broadening in capillary zone electrophoresis with axial temperature gradients. Electrophoresis 26 166-175... 

In capillary zone electrophoresis, tubes of small inner diameter are used to decrease the negative influence of temperature gradients on the separation efficiency and the separation system is filled with a single electrolyte of a relatively high concentration so that the electric field strength is maintained constant over the entire capillary, a uniform diameter being assumed. 

In capillary electrophoresis, where Joule heat is produced, a change in the effective mobilities of migrating ions can be observed and excessive elevation of the temperature can cause the destruction of thermolabile compounds, e.g., denaturation of proteins. For estimation of the mean temperature of zones T, equation (27) can be used ... 

Figure 15 Influence of temperature programming in capillary zone electrophoresis on the separation of fluorescent dyes in 0.01 M Tiis buffer (initial pH 8.3). (A) 20°C isothermal (B) 70°C isothermal (C) 70°C for 2 min, then step to 20°C (D) temperature gradient from °C to 20°C. (1) Riboflavin (2) coumarin (3) impurities (4) fluorescein-5-isothio-cyanate (5) fluorescein (6) 2, 7 -dichlorofluorescein. (From Ref. 92.)...

A mixture of several water-soluble vitamins including calcium pantothenate was recently evaluated by CE by Jegle (83). The sample was analyzed in a 0.02 M sodium phosphate buffer (pH 7) and separated using a three-dimensional capillary zone electrophoresis system (flised-siUca, 50 pm i.d., straight, length to detector 400 mm, total length 485 mm, injection pressure 4.6 sec at 4 kPa, postinjection pressure 4 sec at 40 kPa, polarity positive, voltage 20 kV, capillary temperature... 

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