Stacking, derivatization, and separation by capillary electrophoresis of amino acids from cerebrospinal fluids

To Fluoresce or Not to Fluoresce: Investigation of Structural and Fluorescence Characteristics of CBI-Dopamine, CBI-Serotonin, and Their Structural Analogs

Dopamine (DA) and serotonin (5-HT) are neurotransmitters that are vital for proper brain function and are implicated in a wide variety of diseases and disorders. Unfortunately, quantitative analysis of DA and 5-HT is difficult, as they are present at low concentrations in complex biological matrices. The fluorogenic reaction of napththalene-2,3-dicarboxaldehyde (NDA) with a primary amine in the presence of cyanide (CN) creates an N-substituted 1-cyanobenz[f]isoindole (CBI) derivative, whose fluorescence can be sensitively monitored in biological matrices. Given their biological importance, there are surprisingly few reports showing fluorescence of CBI-DA and no prior publications concerning CBI-5-HT. In this work, nuclear magnetic resonance spectroscopy (NMR) was employed to determine the atom connectivity of over 10 CBI-products, including CBI-DA and CBI-5-HT. NMR and fluorescence spectroscopy were applied to CBI-DA, CBI-5-HT, and select structural analogs to determine structural correlations with the observed lack of fluorescence. Experiments with CBI-DA and structural analogs indicated fluorescence was rapidly quenched due to both complexation with the historically employed buffer and oxidation in solution. Fluorescence of CBI-DA was recovered by modifying the derivatization background to prevent complexation and oxidation. In contrast, fluorescence characterization of CBI-5-HT and its structural analogs indicated that 5-HT was acting as a quencher of the CBI-ring. The addition of acid to protonate 5-HT was found to disrupt this interaction and enable the first reported fluorescence detection of CBI-5-HT. In the future, this work will be applied to detect DA and 5-HT in biological systems to gain insight into neurobiological disease states and disorders.

Optimized derivatization of primary amines with the fluorogenic reagent naphthalene-2,3-dicarboxaldehyde toward reproducible quantitative analysis in biological systems

Primary amines are the target of many bioanalytical analyses, as they are ubiquitous in biological systems and responsible for numerous important processes including neurotransmission and cell signaling. Primary amines can be sensitively detected via fluorescence after their reaction with the fluorogenic reagent naphthalene-2,3-dicarboxaldehyde (NDA) in the presence of cyanide through the formation of fluorescent N-substituted 1-cyanobenz[f]isoindole (CBI) derivatives. While fluorogenic reagents such as NDA can be advantageous for sensitive detection, improvements in both long-term stability and speed of reaction are necessary to enable practical and reproducible quantitative analysis. In this work, various CBI-amines were interrogated for their fluorescence characteristics over time under previously reported conditions (75:25 aqueous buffer:acetonitrile). An amine-specific decline in fluorescence and delay to reach maximum fluorescence were observed. Based on structural characteristics, we hypothesized that these effects were due to the solvents employed enabling analyte intermolecular interactions that resulted in fluorescence quenching over time. To mitigate fluorescence-quenching intermolecular interactions, we developed two strategies to improve the fluorescence of the CBI-product over long time periods: (1) the addition of the complexation reagent β-cyclodextrin to the reaction matrix and (2) the substitution of acetonitrile with dimethyl sulfoxide. Both strategies improved fluorescence stability over time, and the incorporation of dimethyl sulfoxide also enabled more rapid attainment of maximum fluorescence and a higher absolute fluorescence when compared to initial conditions. When employed in combination, these two approaches further improve fluorescence stability over time for the most hydrophobic analytes. In the future, these strategies can be employed for the practical and reproducible quantitative analysis of primary amines in biological systems, including those related to neurological disorders and disease states.

Capillary electrophoresis of small ions and molecules in less conventional human body fluid samples: A review

In recent years, advances in sensitive analytical techniques have encouraged the analysis of various compounds in biological fluids. While blood serum, blood plasma and urine still remain the golden standards in clinical, toxicological and forensic science, analyses of other body fluids, such as breast milk, exhaled breath condensate, sweat, saliva, amniotic fluid, cerebrospinal fluid, or capillary blood in form of dried blood spots are becoming more popular. This review article focuses on capillary electrophoresis and microchip electrophoresis of small ions and molecules (e.g. inorganic cations/anions, basic/acidic drugs, small acids/bases, amino acids, peptides and other low molecular weight analytes) in various less conventional human body fluids and hopes to stimulate further interest in the field.

Baseline separation of amino acid biomarkers of hepatocellular carcinoma by polyvinylpyrrolidone-filled capillary electrophoresis with light-emitting diode-induced fluorescence in the presence of mixed micelles

Separation of amino acid biomarkers could be performed by polyvinylpyrrolidone-filled capillary electrophoresis in the presence of mixed micelles.

Analysis of cerebrospinal fluid γ-aminobutyric acid by capillary electrophoresis with laser-induced fluorescence detection

The measurement of γ-aminobutyric acid (GABA) is suitable for investigating various neurological disorders. In this study, a sensitive and selective method for free GABA quantification in cerebrospinal fluid (CSF) has been standardised. This method is based on CE with LIF detection using 4-fluoro-7-nitrobenzo-2-oxa-1,3-diazole (NBD-F) as a derivatisating agent. The reaction conditions (NBD-F concentration, pH, temperature and reaction time) and the electrophoretic parameters (run buffer composition and pH and separation voltage) were optimised to obtain the maximum derivatisation efficiency and electrophoretic resolution. The best resolution was obtained using 200 mM sodium borate, 10 mM SDS, 8.5 mM β-CD, pH 10 and 20 kV voltage. The method was linear in the concentration range of 2.5-1000 nM with good inter- and intra-assay precision values. The effects of CSF handling on free GABA concentrations were also evaluated. Our results show that the time delay between CSF collection and freezing strongly increases the CSF GABA values. Age-related reference values were established in 55 paediatric controls. The influence of antiepileptic therapy on free CSF GABA was studied in 38 neuropaediatric patients. Significantly, higher GABA values were obtained in patients taking valproic acid or vigabatrin therapy, which are antiepileptic drugs that modulate GABA metabolism.

Separation of amino acids by capillary electrophoresis with light-emitting diode-induced fluorescence in the presence of electroosmotic flow

In this chapter, we describe a method to identify amino acids (AA) by capillary electrophoresis in conjunction with light-emitting diode-induced fluorescence (LEDIF). First, amino acids labeled with naphthalene-2,3-dicarboxaldehyde (NDA) in the presence of cyanide are converted to highly fluorescent cyanobenz[f]isoindole (CBI) derivatives. Next, they are separated by gel electrophoresis in the presence of EOF. In the process, the CBI products were excited by a violet LED to produce green fluorescence. In addition to the optical setup of light-emitting diode-induced fluorescence, the preparation of poly(ethylene) oxide for amino acid separation is also described in this chapter.

Capillary electrophoresis with LED-induced native fluorescence detection for determination of isoquinoline alkaloids and their cytotoxicity in extracts of Chelidonium majus L

In this study, we introduced a simple and sensitive method of capillary electrophoresis with ultraviolet light-emitting diode-induced native fluorescence (UV-LEDIF) detection for the determination of isoquinoline alkaloids in extracts of Chelidonium majus L. Samples were extracted with acidic methanol and the extracts were directly analysed by CE. Simultaneous determination of protopine, chelidonine, coptisine, sanguinarine, allocryptopine, chelerythrine and stylopine was performed in 20mM phosphate buffer (pH 3.1). The baseline separation of these alkaloids was finished within 20 min. As these alkaloids have native fluorescence, they were directly detected using the commercially available UV light emitting diode without troublesome fluorescent derivatisation. Satisfactory LOD values were obtained for the studied compounds considering their appearance in natural extracts. Lower limits of detection were 0.05 μg/mL for protopine, 0.06 μg/mL for stylopine and allocryptopine, 0.07 μg/mL for chelidonine, 0.22 μg/mL for sanguinarine, 1.7 μg/mL for chelerythrine and 5.5 μg/mL for coptisine. The developed method was successfully applied to determine the contents of seven alkaloids in the aerial parts of Chelidonium majus L, which varied from 0.025 to 0.763% (w/w). Also, to demonstrate the potential of the proposed CE method, an estimation of the cytotoxic properties of selected Celandine alkaloids in a natural extract was carried out.

Sample stacking in CZE using dynamic thermal junctions II: analytes with high dpKa/dT crossing a single thermal junction in a BGE with low dpH/dT

In a previous work [M. Mandaji, et al., this issue] a sample stacking method was theoretically modeled and experimentally demonstrated for analytes with low dpK(a)/dT (analytes carrying carboxylic groups) and BGEs with high dpH/dT (high pH-temperature-coefficients). In that work, buffer pH was modulated with temperature, inducing electrophoretic mobility changes in the analytes. In the present work, the opposite conditions are studied and tested, i.e. analytes with high dpK(a)/dT and BGEs that exhibit low dpH/dT. It is well known that organic bases such as amines, imidazoles, and benzimidazoles exhibit high dpK(a)/dT. Temperature variations induce instantaneous changes on the basicity of these and other basic groups. Therefore, the electrophoretic velocity of some analytes changes abruptly when temperature variations are applied along the capillary. This is true only if BGE pH remains constant or if it changes in the opposite direction of pK(a) of the analyte. The presence of hot and cold sections along the capillary also affects local viscosity, conductivity, and electric field strength. The effect of these variables on electrophoretic velocity and band stacking efficacy was also taken into account in the theoretical model presented. Finally, this stacking method is demonstrated for lysine partially derivatized with naphthalene-2,3-dicarboxaldehyde. In this case, the amino group of the lateral chain was left underivatized and only the alpha amino group was derivatized. Therefore, the basicity of the lateral amino group, and consequently the electrophoretic mobility, was modulated with temperature while the pH of the buffer used remained unchanged.

Contemporary sample stacking in CE

Sample stacking techniques remain an important tool for enhancement of the selectivity and sensitivity of analyses in contemporary CZE. This contribution reviews new knowledge on this topic published since 2006. It is organized according to the operational principles used, which include concentration adjustment, application of a pH step, MEKC and sweeping, and transient ITP. Techniques combining several of these principles and comparative studies are also included.

Bioanalytical profile of the L-arginine/nitric oxide pathway and its evaluation by capillary electrophoresis

This review briefly summarizes recent progress in fundamental understanding and analytical profiling of the L-arginine/nitric oxide (NO) pathway. It focuses on key analytical references of NO actions and the experimental acquisition of these references in vivo, with capillary electrophoresis (CE) and high-performance capillary electrophoresis (HPCE) comprising one of the most flexible and technologically promising analytical platform for comprehensive high-resolution profiling of NO-related metabolites. Another aim of this review is to express demands and bridge efforts of experimental biologists, medical professionals and chemical analysis-oriented scientists who strive to understand evolution and physiological roles of NO and to develop analytical methods for use in biology and medicine.

Stacking and separation of fluorescent derivatives of amino acids by micellar electrokinetic chromatography in the presence of poly(ethylene oxide)

A new approach for the analysis of large-volume naphthalene-2,3-dicarboxaldehyde (NDA) derivatives of amino acids by micellar electrokinetic chromatography (MEKC) in conjunction with a purple light-emitting diode-induced fluorescence detection is described. In order to optimize resolution, speed, and stacking efficiency, a discontinuous condition is essential for the analysis of NDA-amino acid derivatives. The optimum conditions use 2.0M TB (pH 10.0) buffer containing 40mM sodium dodecyl sulfate (SDS) to fill the capillary, deionized water to dilute samples, and 200mM TB (pH 9.0) containing 10mM SDS to prepare 0.6% poly(ethylene oxide) (PEO). Once high voltage is applied, PEO solution enters the capillary via electroosmotic flow and SDS micelles interact and thus sweep the NDA-amino acid derivatives having smaller electrophoretic mobilities than that of SDS micelles in the sample zone. When the aggregates between SDS micelles and NDA amino acid derivatives enter PEO zone, they are stacked due to decrease in electric field and increases in viscosity. Under the optimum conditions, the concentration and separation of 0.53-microL 13 NDA-amino acid derivatives that are negatively charged has been demonstrated by using a 60-cm capillary, with the efficiencies 0.3-9.0x10(5) theoretical plates and the LODs at signal-to-noise ratio 3 ranging from 0.30 to 2.76nM. When compared to standard injection (30-cm height for 10s), the approach allows the sensitivity enhancements over the range of 50-800 folds for the derivatives. The new approach has been applied to the analysis of a red wine sample, with great linearity of fluorescent intensity against concentrations (R(2)>0.98) and the RSD (three repetitive runs in one day) values of the migration times for the ten identified amino acids less than 2.8%.