Determination of kynurenic acid by capillary electrophoresis with laser-induced fluorescence detection

Electrochemical detection of kynurenic acid in the presence of tryptophan with the carbon paste electrode modified with the flower-like nanostructures of zinc oxide doped with terbium

With the help of a hydrothermal approach in this study, we could provide flower-like nanostructures (NSs) of zinc oxide (ZnO) doped with Tb (FL-NS Tb3+/ZnO). Then, FL-NS Tb3+/ZnO morphology was investigated by energy-dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), X-ray powder diffraction (XRD), and map analysis. The results revealed higher activity centers and porosity of this nanocomposite, which were followed by acceptable electrochemical function. Hence, it can be utilized for fabricating an electrochemical sensor with an appropriate response for the simultaneous determination of kynurenic acid (KYN) and tryptophan (TRP). However, as compared with the modified carbon paste electrode (FL-NS Tb3+/ZnO/CPE), the bare carbon paste electrode (BCPE) exhibited a weak response toward KYN and TRP but the modified electrode was followed by a high current response for KYN and TRP at a potential 0.35 and 0.809 V. Therefore, cyclic voltammetry (CV) was applied in optimal experimental conditions to study the electrochemical behaviors of KYN and TRP over the surface of the proposed modified electrode. Moreover, we used differential pulse voltammetry (DPV) for quantitative measurements. It was found that this new modified electrode linearly ranged from 0.001 to 700.0 μM, with detection limits of 0.34 nM and 0.22 nM for KYN and TRP, respectively. In addition, KYN and TRP in real samples can be analyzed by this sensor, with a recovery of 97.75%-103.6% for the spiked KYN and TRP in real samples.

Naphthalene-functionalized resorcinarene as selective, fluorescent self-quenching sensor for kynurenic acid

Naphthalene-functionalized resorcinarene selectively binds kynurenic acid in the presence of excess tryptophan in aqueous media, highlighting the potential of functionalized resorcinarenes as sensory recognition elements for biomolecular analytes.

Determination of kynurenic acid in rat cerebrospinal fluid by HPLC with fluorescence detection

A sensitive HPLC method using fluorescence detection was developed to determine kynurenic acid (KYNA) level in rat cerebrospinal fluid (CSF). The method development was accomplished by screening different columns, optimizing zinc acetate concentration and determining the optimal HPLC flow rate. This method allowed direct injection of the CSF samples onto an Xselect C18 column and KYNA levels were measured fluorometrically by forming a fluorescent complex with zinc acetate that was delivered post-column. The limit of quantitation was 0.2 n m with 30 μL injection, corresponding to 6 fmol (signal-to-noise ratio = 10). The improved sensitivity enabled the measurement of KYNA in naive and drug-treated rat CSF.

Simultaneous determination of tryptophan, kynurenine, kynurenic and xanthurenic acids in honey by liquid chromatography with diode array, fluorescence and tandem mass spectrometry detection

A liquid chromatography method using diode array-fluorescence detection and atmospheric pressure chemical ionization mass spectrometry (LC-DAD-FLD and LC-APCI-MS/MS) was developed to quantify the levels of tryptophan (TRP), kynurenine (KYN), kynurenic (KYNA) and xanthurenic (XA) acids in honey. This procedure involved isolating the compounds of interest via solid-phase extraction (SPE) with mixed-mode polymeric cartridges. Chromatographic separation of the analytes was performed in isocratic mode on a Synergi 4μ Hydro-RP 80 Å (150×4.60 mm i.d.) analytical column at 30 °C. The mobile phase of 20mM ammonium formate (pH 4) and methanol was passed at a flow rate of 0.5 mL/min. In replicate sets of spiked honey samples, the average analyte recoveries ranged from 60 to 98% for TRP, 55 to 120% for KYN, 65 to 106.5 for KYNA and 56 to 114% for XA. Detection limits ranged from 4 to 36 μg/kg for LC-DAD-FLD to 0.2 and 1.0 μg/kg for LC-APCI-MS/MS. A strong matrix effect was found when MS/MS was employed, necessitating calibration using the standard addition method on matrix-matched standards for each honey type. The method was used to quantify each of the compounds of interest in 17 honey samples of distinct botanical origins.

Optimization of Zn2+-containing mobile phase for simultaneous determination of kynurenine, kynurenic acid and tryptophan in human plasma by high performance liquid chromatography

In the present work we have developed a standard-addition HPLC method using a mobile phase containing low concentration of ZnAc(2) to determine physiological level of kynurenine (KYN), kynurenic acid (KYNA) and tryptophan (TRP) in human plasma simultaneously. The method greatly improved the sensitivity of KYNA, the resolution of KYNA and TRP, and avoided clotting risk caused by high concentration of ZnAc(2) in mobile phase. Samples were deproteinized by addition of equal volume of 0.6 mol/L HClO(4). Analytes in supernatants were separated by an Agilent HC-C18 (2) analytical column; an aqueous mobile phase containing 20 mmol/L NaAc, 3 mmol/L ZnAc(2) and 7% acetonitrile at flow rate of 1.0 mL/min. Detections were performed by a variable wavelength detector at wavelength 365 nm for KYN and a fluorescence detector at wavelengths excitation 344 nm and emission 398 nm for KYNA and TRP. Good linear responses were found with r(2)>0.999 for all analytes within the concentration range of physiological levels. The limit of detection of the developed method was 0.03 micromol/L, 0.9 nmol/L and 0.4 micromol/L for KYN, KYNA and TRP respectively. Recoveries from spiked human plasma were 95.4-99.7% for KYN, 98.9-104% for KYNA and 96.5-100.2% for TRP. All CVs for the repeatability and intermediate precision were less than 5%. We conclude that the developed method is helpful for the research investigations in KYN pathway of TRP metabolism.

High throughput analysis of tryptophan metabolites in a complex matrix using capillary electrophoresis coupled to time-of-flight mass spectrometry

A capillary electrophoresis method for separation and detection with time-of-flight mass spectrometry is described for tryptophan metabolites in the kynurenic pathway. Tryptophan metabolites are usually difficult to detect with electrospray mass spectrometry since they have low surface activity and occur in low nanomolar to micromolar range in body fluids. Modification of the silica-wall with 1-(4-iodobutyl)4-aza-1-azoniabicyclo[2,2,2]octane iodide, also named M7C4I, has successfully been used to deactivate the fused silica wall and generate a stable reversed electroosmotic flow. Utilizing this advantage together with electrospray ionization time-of-flight mass spectrometry, which generates high resolution and fast acquisition monitoring of species, proved to be successful even for such a complex matrix like human cerebrospinal fluid.

Biomedical applications of capillary electrophoresis with laser-induced fluorescence detection

Capillary electrophoresis (CE) is a high-efficiency analytical technique that has had a great impact as a tool in biomedical research, clinical and forensic practice in the last ten years. Only in one of the applications, the DNA analysis, it has had an explosive exponential growth in the last few years. This impact is expressed in an enormous amount of CE articles and many reviews. The CE advantages with respect to other analytical techniques: the required very small sample volume, rapid analysis, great resolution power and low costs, have made this technique ideal for the analysis of a numerous endogenous and exogenous substances present in biological fluids. The different modes of CE have been coupled to different detection techniques such as UV-absorbance, electrochemical, mass spectrometry and laser-induced fluorescence detection (LIFD) to detect different nature and molecular size separated analytes. This review focuses mostly on the applications of CE-LIFD, to measure drugs and endogenous neuroactive substances such as amino acids and monoamines, especially in microdialysis samples from experimental animals and humans. CE-LIFD trends are discussed: automated faster analysis with capillary array systems, resolution power improvement, higher detection sensitivity, and CE systems miniaturization for extremely small sample volume, in order to make CE easier and affordable to the lab bench or the clinical bed.

Analytical considerations for microdialysis sampling

Adaptations in microdialysis probe designs have made it possible to obtain samples from the extracellular fluid of a variety of tissues with high temporal resolution. The resulting small volume samples, often with low concentration of the analyte(s) of interest, present a particular challenge to the analytical system. Rapid separations can be coupled on-line with microdialysis to provide near real-time data. By combining microdialysis sampling with a liquid chromatographic or capillary electrophoretic separation and a highly sensitive detection method, a separation-based sensor can be developed. Such sensors have been applied to the investigation of drug entities as well as to study endogenous analytes.

Derivatization trends in capillary electrophoresis

This survey gives an overview of recent derivatization protocols, starting from 1996, in combination with capillary electrophoresis (CE). Derivatization is mainly used for enhancing the detection sensitivity of CE, especially in combination with laser-induced fluorescence. Derivatization procedures are classified in tables in pre-, on- and postcapillary arrangements and, more specifically, arranged into functional groups being derivatized. The amine and reducing ends of saccharides are reported most frequently, but examples are also given for derivatization of thiols, hydroxyl, carboxylic, and carbonyl groups, and inorganic ions. Other reasons for derivatization concern indirect chiral separations, enhancing electrospray characteristics, or incorporation of a suitable charge into the analytes. Special attention is paid to the increasing field of research using on-line precapillary derivatization with CE and microdialysis for in vivo monitoring of neurotransmitter concentrations. The on-capillary derivatization can be divided in several approaches, such as the at-inlet, zone-passing and throughout method. The postcapillary mode is represented by gap designs, and membrane reactors, but especially the combination of separation, derivatization and detection on a chip is a new emerging field of research. This review, which can be seen as a sequel to our earlier reported review covering the years 1991-1995, gives an impression of current derivatization applications and highlights new developments in this field.

Advances in the analysis of tryptophan and its related compounds by chromatography

Advances in the analysis of tryptophan,--(both in its free form and bound, alone or together with its metabolites),--has been compiled on the basis of the relevant papers published in the last 4-5 years, including author's experiences associated with the preparation of derivatives and with any of those conditions arising from the analytical procedure itself. The special requirements of various, tryptophan containing matrices were also taken into consideration (biological tissues or fluids, food and feed stuffs, etc). For the sake of completeness in addition to the most common HPLC/UV/F1 techniques, HPLC/MS, GC/MS, CE/UV/F1 and spectrophotometry will be also discussed.

Independent optimization of capillary electrophoresis separation and native fluorescence detection conditions for indolamine and catecholamine measurements

Separation conditions in capillary electrophoresis with native fluorescence detection often represent a compromise in terms of the separation and detection figures of merit. As both the separation and fluorescence properties greatly depend on pH, the ability to independently optimize pH in the separation capillary and the detection region can improve many complex separations. When using a sheath flow cell, the pH at the detection zone can be adjusted independently of the electrophoresis buffer pH. Using capillary electrophoresis with 257-nm excitation and native fluorescence detection, more than an order of magnitude improvement in the limits of detection for dopamine (from 1400 to 120 nM) and epinephrine (from 850 to 60 nM) is achieved by maintaining the basic separation conditions and an acidified sheath buffer. The detection of dopamine in an individual Aplysia californica cerebral ganglion neuron is demonstrated.

Recent advancements in amino acid analysis using capillary electrophoresis

Recent advances in the analysis of amino acids using capillary electrophoresis are addressed. This area of research continues to receive increased attention as is evident from the 62 references reviewed. This review discusses current detection strategies including UV absorbance, laser-induced fluorescence, electrochemical, and others. Separation methodologies for both derivatized and underivatized amino acids are reviewed. Both direct and indirect enantiomeric resolution of amino acids are addressed. Applications utilizing capillary electrophoresis for the analysis of amino acids are discussed. This review covers literature published in 1997 and 1998.

Assessment of pharmacodynamic and pharmacokinetic characteristics of drugs using microdialysis sampling and capillary electrophoresis

Microdialysis sampling combined with capillary electrophoresis is emerging as a new approach in drug studies. It allows the continuous monitoring, in vivo or in vitro, of changes in free endogenous compounds as well as in drug substances, following the administration of pharmacological agents. The low volume requirement of capillary electrophoresis for injection allows the collection of dialysates during short sampling times, leading to a precise temporal description of drug-induced biochemical changes or pharmacokinetics. Various protocols can be used for analyzing endogenous compounds and drug substances in microdialysis samples. Capillary electrophoresis with laser-induced fluorescence detection often affords the high sensitivity level which is needed in most studies. Furthermore, the direct on-line coupling of microdialysis, derivatization of samples, and electrophoretic analysis now brings a separation-based biosensor, allowing a real-time description of chemical events with a high molecular specificity. Microdialysis sampling combined with capillary electrophoresis has recently been used to assess pharmacodynamic and pharmacokinetic characteristics of various drugs in animal studies; it may also represent a new approach in clinical pharmacology in the near future.