Capillary zone electrophoresis detection sensitivity

Very recently, HPLC with fluorescence detection was recommended for improving detection sensitivities of betalains. " While this technique may be worthwhile for betaxanthin analyses, its use for betacyanins cannot be recommended. Although this technique represents a worthwhile approach requiring low amounts of solvent and sample and generally characterized by a high separation efhciency, only one study dealt with the use of capillary zone electrophoresis for betalain analyses. ... 

Gotti et al. [42] reported an analytical study of penicillamine in pharmaceuticals by capillary zone electrophoresis. Dispersions of the drug (0.4 mg/mL for the determination of (/q-penicillaminc in water containing 0.03% of the internal standard, S -met hy I - r-cystei ne, were injected at 5 kPa for 10 seconds into the capillary (48.5 cm x 50 pm i.d., 40 cm to detector). Electrophoresis was carried out at 15 °C and 30 kV, with a pH 2.5 buffer of 50 mM potassium phosphate and detection at 200 rnn. Calibration graphs were linear for 0.2-0.6 pg/mL (detection limit = 90 pM). For a more sensitive determination of penicillamine, or for the separation of its enantiomers, a derivative was prepared. Solutions (0.5 mL, final concentration 20 pg/mL) in 10 mM phosphate buffer (pH 8) were mixed with 1 mL of methanolic 0.015% 1,1 -[ethylidenebis-(sulfonyl)]bis-benzene and, after 2 min, with 0.5 mL of pH 2.5 phosphate buffer. An internal standard (0.03% tryptophan, 0.15 mL) was added and aliquots were injected. With the same pH 2.5 buffer and detection at 220 nm, calibration graphs were linear for 9.3-37.2 pg/mL, with a detection limit of 2.5 pM. For the determination of small amounts of (L)-penicillamine impurity, the final analyte concentration was 75 pg/mL, the pH 2.5 buffer contained 5 mM beta-cyclodextrin and 30 mM (+)-camphor-10-sulfonic acid, with a voltage of 20 kV, and detection at 220 nm. Calibration graphs were linear for 0.5-2% of the toxic (L)-enantiomer, with a detection limit of 0.3%. 

Schrader, W. Linscheid, M. Styrene Oxide DNA Addncts in Vitro Reaction and Sensitive Detection of Modified Oligonn-cleotides Using Capillary Zone Electrophoresis Interfaced to ESI-MS. Archives of Toxicology 1997, 71, 588-595. 

Dedicated applications of capillary zone electrophoresis (CZE) coupled to MS are discussed, particularly in the field of drug analysis. Development of other capillary-based electrodriven separation techniques such as non-aqueous capillary electrophoresis (NACE), micellar electrokinetic chromatography (MEKC), and capillary electrochromatography (CEC) hyphenated with MS are also treated. The successful coupling of these electromigration schemes with MS detection provides an efficient and sensitive analytical tool for the separation, quantitation, and identification of numerous pharmaceutical, biological, therapeutic, and environmental compounds. 

A simple and sensitive capillary zone electrophoresis method with UV absorbance detection has been described for the quantification of ALP and its metabolite oxypurinol in aqueous solution. This method could be applied for analyzing these compounds in serum and ALP concentration in pharmaceutical preparations <2003JCH231, 2001ANA121, 2003JC(B)303>. 

Capillary electrophoresis (CE) coupled to MS has the advantage of high resolution and soft ionization for biomolecules, which may be used to differentiate post-translational modifications and variants of intact proteins and oligonucleotides. Different modes of CE (capillary zone electrophoresis, capillary isoelectric focusing, capillary electrochromatography, micellar electrokinetic chromatography, nonaqueous capillary electrophoresis) to MS as well as online preconcentration techniques (transient capillary isotachophoresis, solid-phase extraction, membrane preconcentration) are used to compensate for the restricted detection sensitivity of the CE methodology [77, 78]. 

Steuer et al. compared supercritical fluid chromatography with capillary zone electrophoresis (CZE) and high-performance liquid chromatography (HPLC) for its application in pharmaceutical analysis [24]. Efficiency, performance, sensitivity, optimization, sample preparation, ease of method development, technical capabilities, and orthogonality of the information were the parameters studied. They concluded that SFC is ideal for moderately polar compounds, such as excipients, for which mass detection is required. 

In conclusion, capillary electrophoresis in carbohydrate analysis has advantages in both separation and detection over other techniques of electrophoresis, as well as chromatography. It allows high efficiency (up to a few million plate numbers) and very good sensitivities (up to femtomolar). In addition, CE permits analysis by a variety of separation modes simply by changing the electrolyte (capillary zone electrophoresis, MEKC, CGE). 

Gas chromatography-mass spectrometry (GC-MS) provides a standard method for accurate quantification of plant hormones, but requires pre-derivatizing those to volatile compounds that may affect the yield of the analyzed compounds as hydrolysis of the derivatives, multiple-products formation, and limited volatility occur. Capillary zone electrophoresis was used to determine dissociation constants of cytokinins [284,285], to explore their separation and possible quantification [274,286], Main disadvantage of the method in trace analysis is a relatively high limit of detection coming from the restricted injection volumes that are typically in the nanoliter range. This limitation may be overcome by the use of sensitive detection systems (e.g. mass spectrometry) and/or the development of on-line stacking methods [287]. 

The most sensitive enantioselective separation technique is capillary zone electrophoresis. Here, the detectors utilized are not sensitive enough to be able to detect the enantiomers. In the case of sensors, amperometric biosensors have been found to be most sensitive.264 A better enantioselectivity was found for potentiometric, enantioselective membrane electrodes because a direct interaction between the chiral selector and enantiomer occurred.282 285... 

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. 

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