N-hydroxysuccinimidyl fluorescein-O-acetate as a fluorescent derivatizing reagent for catecholamines in liquid chromatography

Tantala-based sol-gel coating for capillary microextraction on-line coupled to high-performance liquid chromatography

A sol-gel organic-inorganic hybrid sorbent, consisting of chemically integrated tantalum (V) ethoxide (TaEO) and polypropylene glycol methacrylate (PPGM), was developed for capillary microextraction (CME). The sol-gel sorbent was synthesized within a fused silica capillary through hydrolytic polycondensation of TaEO and chemical incorporation of PPGM into the evolving sol-gel tantala network. A part of the organic-inorganic hybrid sol-gel network evolving in the vicinity of the capillary walls had favorable conditions to get chemically bonded to the silanol groups on the capillary surface forming a surface-bonded coating. The newly developed sol-gel sorbent was employed to isolate and enrich a variety of analytes from aqueous samples for on-line analysis by high-performance liquid chromatography (HPLC) equipped with a UV detector. CME was performed on aqueous samples containing trace concentrations of analytes representing polycyclic aromatic hydrocarbons, ketones, alcohols, amines, nucleosides, and nucleotides. This sol-gel hybrid coating provided efficient extraction with CME-HPLC detection limits ranging from 4.41pM to 28.19 pM. Due to direct chemical bonding between the sol-gel sorbent coating and the fused silica capillary inner surface, this sol-gel sorbent exhibited enhanced solvent stability. The sol-gel tantala-based sorbent also exhibited excellent pH stability over a wide pH range (pH 0-pH 14). Furthermore, it displayed great performance reproducibility in CME-HPLC providing run-to-run HPLC peak area relative standard deviation (RSD) values between 0.23% and 3.83%. The capillary-to-capillary RSD (n=3), characterizing capillary preparation method reproducibility, ranged from 0.24% to 4.11%. The results show great performance consistency and application potential for the sol-gel tantala-PPGM sorbent in various fields including biomedical, pharmaceutical, and environmental areas.

6-Oxy-(acetyl piperazine) fluorescein as a new fluorescent labeling reagent for free fatty acids in serum using high-performance liquid chromatography

A new fluorescein-based fluorescent derivatizating reagent, 6-oxy-(acetyl piperazine) fluorescein (APF), has been designed, synthesized and developed for carboxylic acid labeling. It was used as a pre-column derivatizing reagent for the determination of seven free fatty acids (lauric acid, myristic acid, arachidonic acid, linoleic acid, palmitic acid, oleic acid, and stearic acid) with high-performance liquid chromatography (HPLC). The derivatization reaction of APF with seven fatty acids was completed at 60 degrees C for 1 h using 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) as the condensing reagent. On a C18 column, the derivatives of APF with seven free fatty acids could be separated completely in 22 min using a mobile phase of methanol-water (88:12, v/v) containing 7 mmol L(-1) pH 6.5 Na2HPO4-H3Cit3 buffer with fluorescence detection at lambdaex/lambdaem=467/512 nm. The detection limits could reach 0.1-6.4 nmol L(-1) (signal-to-noise=3). This reagent was applied to the determination of the free fatty acids in human serum samples with satisfying recovery efficiencies varying from 93 to 105%.

Liquid chromatographic analysis of phosphoamino acids at femtomole level using chemical derivatization with N-hydroxysuccinimidyl fluorescein-O-acetate

Phosphorylation of amino acid residues in proteins plays a major role in biological systems. In this paper, a reversed-phase high performance liquid chromatographic (HPLC) method based on chemical derivatization has been described for the separation and quantification of phosphoamino acids at femtomole level, using fluorimetric detection (FLD). The protocol involved pre-column derivatization of phosphoamino acids with N-hydroxysuccinimidyl fluorescein-O-acetate (SIFA) and subsequent separation on ZORBAX Eclipse XDB-C8 column. Several experimental factors that influenced derivatization and separation were carefully investigated. The derivatization was performed at 40 degrees C for 40 min in borate buffer (pH 8.5). Under the optimum conditions, phosphoserine (P-Ser), phosphothreonine (P-Thr) and phosphotyrosine (P-Tyr) were satisfactorily separated in 8 min. The detection limits (signal-to-noise ratio=3) for the phosphoamino acids could reach 10-20 fmol, which was the lowest value reported for HPLC methods and comparable to those obtained by capillary electrophoresis with laser-induced fluorescence (CE-LIF) detection methods. The proposed method has been validated and used to characterize the phosphoamino acids in the hydrolyzed phosphorylated protein samples. The results clearly demonstrated the potential of this technique to study phosphoamino acids as well as provided a new analytical methodology that should be applicable to the study of phosphorylation of protein in biological system.

Liquid chromatography method for detecting native fluorescent bioamines in urine using post-column derivatization and intramolecular FRET detection

Liquid chromatography (LC) with fluorescence detection is described for simultaneous determination of native fluorescent bioamines (indoleamines and catecholamines). This is based on intramolecular fluorescence resonance energy transfer (FRET) in an LC system following post-column derivatization of native fluorescent bioamines' amino groups with o-phthalaldehyde (OPA). OPA fluorescence was achieved through an intramolecular FRET process when the molecules were excited at maximum excitation wavelength of the native fluorescent bioamines. Bioamines separated by reversed-phase LC on ODS column were derivatized with OPA and 2-mercaptoethanol. This method provides sufficient selectivity and sensitivity for the determination of normetanephrine, dopamine, tyrosine, 5-hydroxytryptamine, tryptamine, and tryptophan in healthy human urine without prior sample purification.

Chromatography of amino acids and short peptides. New advances

The newest results in the application of various chromatographic methods (gas-liquid chromatography, liquid chromatographic techniques, electrically driven systems) for the separation and quantitative determination of amino acids and short peptides in pure state and in complicated matrices are compiled. The results are concisely described and critically evaluated. The future trends of the chromatographic analysis of amino acids and short peptides are briefly discussed.

Determination of Catecholamines and Indoleamines in Human Urine Based on Intramolecular Excimer-forming Derivatization and Fluorescence Detection

A liquid chromatographic (LC) determination of catecholamines and indoleamines is described. This is based on intramolecular excimer-forming fluorescence derivatization with 4-(1-pyrene)butanoyl chloride, followed by reversed-phase LC. The analytes, containing an amino moiety and phenolic hydroxyl moieties in a molecule, were converted to the corresponding polypyrene-labeled derivatives by one-step derivatization. They afforded intramolecular excimer fluorescence, which can clearly be discriminated from the normal fluorescence emitted from reagent blanks. The detection limits (S/N = 3) for catecholamines and indoleamines were femto-mole levels per 20-microL injection. Furthermore, this method was applied to a urine assay.

Recent advances in methods for the analysis of catecholamines and their metabolites

Catecholamines, for example epinephrine, norepinephrine, and dopamine, are widely distributed and are important neurotransmitters and hormones in mammalian species. Several methods have been developed for analysis of catecholamines and related compounds. Determination of catecholamines in biological fluids has enabled us to clarify the physiological role played by these amines. Catecholamine levels in plasma and/or urine are also useful for diagnosis of several diseases, for example hypertension, pheochromocytoma, and neuroblastoma. This review covers reports from 2000 to the present of methods for the analysis of catecholamines and their metabolites.

New fluorescent labels: 4- and 7-chlorofluorescein

A new mixture of 4- and 7-chlorofluorescein were synthesized by condensation of resorcinol with 3-chlorophthalic anhydride in the presence of methanesulfonic acid or zinc chloride. These regioisomers were successfully separated by chromatography. The photophysical properties were examined and their absorption and emission maxima at long wavelength, high fluorescence quantum yield, and narrow emission bandwidth were found, highly favorable for detecting multiple target substances in the same sample. Furthermore, 4(7)-chlorofluorescein was found to be strongly pH-dependent between 4.0 and 8.0, and could be used as pH-sensitive fluorescent probe to measure intracellular pH.

Development of electrochemical biosensor based on tyrosinase immobilized in composite biopolymeric film

An electrochemical enzyme electrode for dopa and dopamine was developed via an easy and effective immobilization method. The enzyme tyrosinase was extracted from a plant source Amorphophallus companulatus and immobilized in a novel composite of two biopolymers: agarose and guar gum. This composite matrix-containing enzyme forms a self-adhering layer on the active surface of glassy carbon electrode, making it a selective and sensitive phenol sensor. Dopa and dopamine were determined by the direct reduction of biocatalytically liberated quinone species at -0.18V versus Ag/AgCl (3M KCl). The analytical characteristics of this sensor, including linear range, lower detection limit, pH, and storage stability, are described. It has reusability up to 15 cycles and a shelf life of more than 2 months.

6-Oxy-(N-succinimidyl acetate)-9-(2'-methoxycarbonyl)fluorescein as a new fluorescent labeling reagent for aliphatic amines in environmental and food samples using high-performance liquid chromatography

6-Oxy-(N-succinimidyl acetate)-9-(2'-methoxycarbonyl)fluorescein (SAMF), a new fluorescein-based amine-reactive fluorescent probe was well designed, synthesized and used as a pre-column derivatizing reagent for the determination of aliphatic amines in HPLC. It exhibited relatively pH-independent fluorescence (pH 4-9) and excellent photostability. The derivatization was performed at room temperature in 6min. On a C18 column, the derivatives of SAMF with eight aliphatic amines were baseline separated in 28 min with a mobile phase of methanol-water (57:43, v/v) containing 10 mmol l(-1) pH 5.0, H3Cit3-NaOH buffer. With fluorescent detection at lambda(ex)/lambda(em) = 484/516 nm, the detection limit could reach 2-320 fmol (signal-to-noise = 3), which was equivalent to or better than the detection limits obtained from other analytical methods of aliphatic amines. The proposed method has been applied to the determination of the aliphatic amines in environmental and food samples such as lake water, red wine, white wine, and cheese with satisfying recoveries varying from 95 to 106%.

Oxidation of adrenaline and noradrenaline by solved molecular oxygen in a FIA assembly

A simple and effective procedure is proposed for the study and simultaneous determination of adrenaline and noradrenaline. The fluorimetric determination of both substances is performed in a flow injection assembly and by oxidation of both drugs with the solved molecular oxygen. The influence of different parameters is empirically studied and the interpretation of the reaction mechanism is also added. The determination of adrenaline is monitored at 450 nm and the outputs at 520 nm correspond to the adrenaline and noradrenaline global amount; for both lectures lambda(exc) 329 nm. The influence of temperature is relevant and analytical determination occurred at 55 degrees C by immersing the sample loop in a water bath. The linear range for adrenaline is over 0.5-20 microg ml(-1), limit of detection for both compounds is 0.2 microg ml(-1): the influence of foreign compounds as potential interferents is also tested; and, finally the procedure is applied to determination of both chatecolamines in synthetic samples.