Determination of norepinephrine in small volume plasma samples by stable-isotope dilution gas chromatography-tandem mass spectrometry with negative ion chemical ionization

"Nano": An Emerging Avenue in Electrochemical Detection of Neurotransmitters

The growing importance of nanomaterials toward the detection of neurotransmitter molecules has been chronicled in this review. Neurotransmitters (NTs) are chemicals that serve as messengers in synaptic transmission and are key players in brain functions. Abnormal levels of NTs are associated with numerous psychotic and neurodegenerative diseases. Therefore, their sensitive and robust detection is of great significance in clinical diagnostics. For more than three decades, electrochemical sensors have made a mark toward clinical detection of NTs. The superiority of these electrochemical sensors lies in their ability to enable sensitive, simple, rapid, and selective determination of analyte molecules while remaining relatively inexpensive. Additionally, these sensors are capable of being integrated in robust, portable, and miniaturized devices to establish point-of-care diagnostic platforms. Nanomaterials have emerged as promising materials with significant implications for electrochemical sensing due to their inherent capability to achieve high surface coverage, superior sensitivity, and rapid response in addition to simple device architecture and miniaturization. Considering the enormous significance of the levels of NTs in biological systems and the advances in sensing ushered in with the integration of nanotechnology in electrochemistry, the analysis of NTs by employing nanomaterials as interface materials in various matrices has emerged as an active area of research. This review explores the advancements made in the field of electrochemical sensors for the sensitive and selective determination of NTs which have been described in the past two decades with a distinctive focus on extremely innovative attributes introduced by nanotechnology.

Chemical sensing of neurotransmitters

This review focuses on the chemosensors for neurotransmitters published for the last 12 years, covering biogenic amines (dopamine, epinephrine, norepinephrine, serotonin, histamine and acetylcholine), amino acids (glutamate, aspartate, GABA, glycine and tyrosine), and adenosine.

Spectrofluorimetric Estimation of Norepinephrine Using Ethylenediamine Condensation Method

A simple and sensitive method for the determination of norepinephrine is described. Norepinephrine (NE) was oxidized by mercury (II) nitrate and the oxidation product was condensed with ethylenediamine (EDA) to form a strong fluorescent compound. The addition of acetone enhances the light intensity. The measurement was carried out at 507 nm with excitation at 420 nm. A linear relationship was obtained between the fluorescence intensity and norepinephrine concentration in the range of 0.01 microM-0.014 mM; the correlation coefficient and the detection limit are 0.99813 and 2.5 nM, respectively. The interference from dopamine (DA) can be eliminated by first derivative synchronous fluorimetric method using peak to zero technique. The recovery efficiency was performed using known amounts of norepinephrine in urine sample and the results indicate a 95-98.62% recovery. The proposed method was also applied to the determination of norepinephrine in injections solution. The reaction mechanism was also described.

Determination of catecholamines and serotonin by micellar electrokinetic chromatography with laser-induced fluorescence detection

6-Oxy-(N-succinimidyl acetate)-9-(2'-methoxycarbonyl) fluorescein, a new synthesized fluorescent reagent, was established for the first time as a label for the sensitive analysis of catecholamines (CAs) and serotonin (5-HT) by micellar electrokinetic chromatography (MEKC) with laser-induced fluorescence detection. After careful study on the derivatization conditions such as pH value, reagent concentration, temperature and reaction time, the labeling reaction was accomplished as quickly as 7 min with stable yield. The separation parameters for the CAs and 5-HT were also optimized in detail. The derivatives were baseline separated in a running buffer containing 30 mM boric acid and 15 mM sodium dodeculsulfate at pH 9.0. The detection limits ranged from 5 x 10(-10) to 2 x 10(-9) M (signal-to-noise ratio = 3). The rapid and sensitive method was also applied to the determination of the CAs and 5-HT of urine samples.

Electrocatalytic Response and Determination of Noradrenaline in the Presence of L-Ascorbic and Uric Acids with Poly(Eriochrome Black T)-Modified Electrode

A poly(Eriochrome Black T) chemically modified glassy carbon electrode modified with Eriochrome Black T was prepared by cyclic voltammetry. The modified electrode showed an excellent electrocatalytic activity in oxidation of noradrenaline (NA) and could separate its electrochemical responses from those of L-ascorbic acid (AA) and uric acid (UA). Differences of the oxidation peak potentials for NA-AA and UA-NA were about 150 mV. The responses to NA, AA and UA of the modified electrode are relatively independent. Using differential pulse voltammetry, the peak currents of NA at modified glassy carbon electrode increased linearly with the concentration of NA from 0.5 to 100 μmol l-1. The detection limit was 0.2 μmol l-1. With the modified electrode, UA could be selectively determined in the presence of AA. The method showing a wide linear dynamic range and excellent sensitivity was successfully applied to the determination of NA in pharmaceutical injections and various samples.

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.

Stability-indicating HPLC assays for the determination of prilocaine and procaine drug combinations

Stability-indicating, reversed phase high-performance liquid chromatographic (HPLC) methods have been developed for the determination of several procaine hydrochloride and prilocaine hydrochloride combinations. The separation and quantitation of epinephrine-prilocaine and epinephrine-procaine drug combinations were achieved on a phenyl column using a mobile phase of 80:20% v/v 25 mM phosphate buffer (pH 3.0) containing 50 mM heptanesulfonic acid sodium salt-acetonitrile at a flow rate of 1 ml x min(-1) and UV detection at 254 nm. The method showed linearity for the epinephrine and prilocaine hydrochloride mixture in the 0.25-2.5 and 8-200 micro g ml(-1) ranges, respectively. The intra- and inter-day relative standard deviations (RSDs) ranged from 0.26 to 2.05% and 0.04 to 0.61% for epinephrine and prilocaine hydrochloride, respectively. The epinephrine and procaine hydrochloride mixture yielded linear ranges of 0.25-2.0 and 5-100 micro g ml(-1) and intra- and inter-day RSDs ranged from 0.23 to 1.88% and 0.07 to 0.26% for epinephrine and procaine hydrochloride, respectively. The assays were shown to be suitable for measuring epinephrine-prilocaine and epinephrine-procaine combinations in their respective injection dosage forms. Stability-indicating HPLC assays were also developed for several other procaine drug combinations since their monographs are present in the USP 24; however, quantitation was not investigated since these combinations are not commercially available. A mobile phase consisting of 80:20% v/v 25 mM phosphate buffer (pH 3.0) containing 50 mM heptanesulfonic acid-acetonitrile was utilized for the levonordefrin-tetracaine-procaine drug combination, while a mobile phase consisting of 70:30% v/v 25 mM phosphate buffer (pH 3.0) containing 50 mM heptanesulfonic acid sodium salt-acetonitrile was utilized for the separation of levonordefrin-procaine-propoxycaine and norepinephrine-procaine-propoxycaine. All separations were achieved on a phenyl column at a flow rate of 1 ml x min(-1) and UV detection at 254 nm.

Catecholamines and methods for their identification and quantitation in biological tissues and fluids

Catecholamines act via dopaminergic-, and adrenergic receptors, and are involved in a variety of regulatory systems. They take part in regulation of the response to stress, psychomotor activity, emotional processes, learning, sleep and memory. Due to many catecholaminergic pathways, and a wide range of functions they are involved in, both in the central nervous system and in periphery, a development of the reliable techniques for their extraction and quantitation is essential. This paper presents an overview of the currently applied methodologies for catecholamines detection and identification in various biological samples.

Affinity chromatography as a method for sample preparation in gas chromatography/mass spectrometry

Analytical chemistry aims at developing analytical methods and techniques for unequivocal identification and accurate quantitation of natural and synthetic compounds in a given matrix. Analytical methods based on the mass spectrometry (MS) technology, e.g., GC/MS and LC/MS and their variants, GC/tandem MS and LC/tandem MS, are best suited both for qualitative and quantitative analyses. GC/MS methods not only serve as reference methods, e.g., in clinical chemistry, but they are now widely and routinely used for quantitative determination of numerous analytes. However, despite inherent accuracy, analytical methods based on GC/MS commonly consist of several analytical steps, including extraction and derivatization of the analyte. In general, unequivocal identification and accurate quantification of an analyte in very low concentrations in complex matrices require further chromatographic techniques, such as high-performance liquid chromatography (HPLC) and thin-layer chromatography (TLC) for sample purification. In recent years, affinity chromatography (e.g., boronate and immunoaffinity chromatography) has been developed to a superior technique for sample preparation of numerous classes of compounds in GC/MS. In this article, the application and importance of affinity chromatography as a method for sample preparation in modern quantitative GC/MS method is described and discussed, using as examples various natural and synthetic compounds, such as arachidonic acid derivates, nitrosylated and nitrated proteins, steroids, drugs, and toxins.