Electrochemical determination of histamine derivatized with o-phthalaldehyde and 2-mercaptoethanol

High-performance liquid chromatography coupled with electrochemical detection was used to determine histamine following precolumn derivatization with o-phthalaldehyde (OPA) and 2-mercaptoethanol. The isoindole derivative which is obtained as reaction product was electrochemically active at a moderate potential (peak potential +0.4 V). Direct oxidation of histamine required a much higher potential (peak potential +1.05 V) and was of no practical use. No electrochemical signal was observed for the reaction product of histamine with OPA. Changing the pH of the mobile phase had little effect on the electrochemical response of the isoindole derivative of histamine, which was well separated from analogous derivatives of methylated histamines, mono- and polyamines and amino acids by isocratic elution from a reversed-phase column. An example of a practical application of the method to the estimation of histamine in rat brain is presented.     

Kinetic fluorimetric determination of histidine,histamine and their mixtures

Kinetic fluorimetric methods for the determination of histidine and histamine, both separately and in mixtures, are described; the methods are based on the accelerating effect of these compounds on the oxidation of 1,1,3-tricyano-2-amino-1-propene by hydrogen peroxide in the presence of copper. A differential rate method is used for resolution of mixtures of these compounds (10^?5 M level), in which synergic effects are taken into account. The relative standard deviations for histidine and histamine are 1.4% and 2.1%, respectively, for separate determinations but 4.0% and 3.4%, respectively, for determinations of mixtures. Histamine/histidine ratios between 1:1 and 16:1 are satisfactorily resolved.     

Analytical applications of ternary complexes-VIII An improved reagent system for the spectrophotometric determination of aluminium

Aluminium ions form a ternary complex with Catechol Violet (CV) and cetyltrimethylammonium bromide (CTAB) in which an Al(3)+:CV:CTAB ratio of 1:2:5 is observed. The sensitivity of the binary complex between aluminium and Catechol Violet (615nm) = 1.50 x 10(3) l. mole (-1). mm(-1) is enhanced on ternary complex formation to (670nm) = 5.30 x 10(3) l. mole(-1). mm(-1). The colour is formed instantaneously, stabilizes within 20 min, and may be used for the detection of aluminium in the range O.27-54 pm in the presence of EDTA which prevents the interference of most ions. A benzoate extraction procedure for aluminium is used to prevent interference from hundredfold amounts of Cr(VI), Fe(II), Fe(III), Hg(II), Sb(III), Ti(IV) and acetate, but Be, Cr(III), rare earths, V(V), Zr and tartrate must be absent, as must high concentrations of phosphate and fluoride ions.     

Evaluation of the proteolysis degree with the o-phthalaldehyde/N-acetyl-L-cysteine reagent

Summary The o-phthalaldehyde/N-acetyl-L-cysteine (OPA-NAC) reagent is applied to the spectrophotometric evaluation of the proteolytic activity of enzymes. The high stability of the OPA-NAC isoindoles makes a strict control of the time of reaction unnecessary. A mathematical expression is proposed to calculate proteolysis degrees, where the absorbance decrease of the OPA-NAC derivative of the protein itself during the hydrolysis process is taken into account. The method is applied to bovine serum albumine, caseine, lysozyme, lactoglobuline and protamine sulphate as substrates, and pronase, papaine, trypsin and chymotrypsin as enzymes.     

Determination of clenbuterol in pharmaceutical preparations by reaction with o-phthalaldehyde using a flow-injection fluorimetric procedure

A new procedure for the determination of clenbuterol is proposed using flow-injection and fluorimetric detection. The method is based on the derivatization reaction of the primary amine group with o-phthalaldehyde in the presence of 2-mercaptoethanol. The calibration graph based on peak area was linear in the range 0.2-5 mug ml(-1) and the detection limit was 0.06 mug ml(-1). The method was validated using a reference spectrophotometric procedure and was applied to the determination of the drug in commercial pharmaceutical preparations.     

Advances in the o-phthalaldehyde derivatizations. Comeback to the o-phthalaldehyde-ethanethiol reagent

The main aims of this work were (a) to present the characteristics and stability of the o-phthalaldehyde (OPA)-ethanethiol (ET) derivatives of 22 amino acids, including the believed-to-be less stable OPA derivatives providing glycine, gamma-aminobutyric acid, beta-alanine, histidine, ornithine, lysine and the C(1)-C(5) aliphatic amines; (b) to compare the stability properties of the most common amino acids and amines as OPA-ET-fluorenylmethyl chloroformate (FMOC) derivatives to the corresponding ones obtained from OPA reagents containing various (SH)-additives; (c) to show the molar responses of alanine and lysine depending on the OPA reagent's composition; as well as (d) to prove the practical utility of these basic researches, by the simultaneous HPLC separation of 22 amino acids and 15 amines as their OPA-ET-FMOC derivatives. Investigations have been carried out by varying the composition of the reagents, the molar ratios of reactants and the reaction time, applying diode array and fluorescence detections simultaneously. Average reproducibility of quantitations, characterized with the relative standard deviations (RSDs) based on the fluorescence intensities of derivatives, in the order of listing, proved to be 1.2-5.9% for amino acids and 1.1-8.7% for amines. The practical utility of the method is demonstrated by the analysis of the amino acid and amine contents of mouse tissues, with an average reproducibility of 3.5%.     

Effect of nucleophilic agents and organized media on the fluorimetric determination of histamine with o-phthalic aldehyde

The addition of nucleophilic agents, 2-mercaptoethanol, 3-mercaptopropionic acid (3-MPA), and N-acetyl cysteine, to the system histamine-o-phthalic aldehyde (OPA) resulted in the following effects: the exclusion of the acidification step, the 1.5-2-fold increase in the time of attaining the optimum fluorescence, the shift of the pH of fluorophore formation of a less alkaline region by 2 units and the widening of its range by two to three times, and the twofold increase in the fluorophore stability (in time in the case of 3-MPA). The addition of surfactant micelles reduced the time of attaining the optimum fluorescence intensity by two times, but its intensity increased (by a factor of 1.3–1.5) only in the presence of nonionic surfactant block copolymers. The widest plateau range (2 pH units), the highest stability of an analytical signal in time (3 h), and the best reaction sensitivity were obtained after the addition of 2-hydroxypropyl-β-cyclodextrin to the histamine-OPA-3-MPA system. Procedures were proposed for the determination of histamine in fish products and wine using nucleophilic agents and different organized media.     

Observations of the use of o-phthalaldehyde condensation for the measurement of histamine

The in vitro study of mast cell degranulation utilises the measurement of histamine as a quantitative marker of this process. Histamine is most commonly assayed, following organic extraction, by condensing it with o-phthalaldehyde (OPT) and thereby obtaining a highly fluorescent adduct. A number of variables that might affect the performance of this assay, including assay conditions, stability and purity, were evaluated during the course of developing this assay for use in our laboratory. We observed the stability of OPT-histamine and found it to be very stable at 0 and 25 degrees C, following acidification. Derivatisation conditions and the purity of the leukocyte histamine extract were also assessed, and indicated that derivatisation at low temperatures slows down decay, providing a greater over-all fluorescence intensity. Extraction procedures are necessary, prior to condensation with OPT, to eliminate both positive and negative interfering substances from leukocyte preparations.     

Di-2-pyridyl ketone 2-furoylhydrazone as a reagent for the fluorimetric determination of low concentrations of aluminium

The synthesis and properties of di-2-pyridyl ketone 2-furoylhydrazone as an analytical reagent are described. A rapid procedure for the fluorimetric determination of aluminium at the 10-100 ng ml level, at pH 6.1-6.5 (lambda(exc) 395 nm, lambda(em) 465 nm) has been established. Interferences have been evaluated, and the procedure has been applied satisfactorily to determination of aluminium in sea-water.     

Selective fluorimetric method for the determination of histamine in seafood samples based on the concept of zone fluidics

In the present article we report our results on the development of a selective automated method for the determination of histamine in seafood using the concept of zone fluidics. The method is based on the sequential on-line reaction of the analyte with o-phthalaldehyde in the absence of a nucleophilic reagent, followed by acidification. The careful selection of the chemical and instrumental variables enabled the determination of the analyte with adequate sensitivity at the low micromolar level and with specificity against other biogenic amines and amino acids such as histidine. The LOD was 0.05 μmol L⁻¹ (0.6 mg kg⁻¹) and linearity was obeyed in the range of 0.5–15 μmol L⁻¹ (5.5–170 mg kg⁻¹). The proposed method offers a satisfactory sampling rate of 15 h⁻¹ and adequate accuracy and precision for the analysis of seafood products after minimum sample preparation and without employing a separation technique.     

An automated fluorimetric method for the determination of nanogram quantities of selenium

An automated solvent extraction method, based on the fluorescence of 4,5-benzopiazselenol has been developed for the determination of nanogram quantities of selenium. Sample extracts, analysed at a rate of 40 per hour, gave standard deviations of 0.022, 0.054, 0.096 ng g^-1 at levels of 1, 5 and 10 ng g^-1 respectively. The detection limit was therefore approximately 0.044 ng g^-1. Of the more common ions at 1 mM concentration, only palladiuim(II) and tin(IV) caused appreciable interference in the presence of oxalate or ethylenediaminetetraacetic acid.     

Extraction fluorimetric determination of uranium by conventional spectrophotometry

The determination of uranium by a fluorimetric method using a conventional spectrophotometer has been elaborated. The quenching effect of the matrix was reduced by separation with liquid-liquid extraction and emulsion liquid membrane extraction methods using D2EHPA as a selective extraction reagent. The method was employed for uranium determination in radioactive waste solutions and proved to be very fast and easy to perform. It was found that it is possible to determinate as low as 0.2 ppm of uranium in a 10 ml sample.     

An improved reagent for determination of aliphatic amines with fluorescence and online atmospheric chemical ionization-mass spectrometry identification

An improved reagent named 2-[2-(dibenzocarbazole)-ethoxy] ethyl chloroformate (DBCEC-Cl) for the determination of aliphatic amines by high-performance liquid chromatography (HPLC) with fluorescence detection and post-column online atmospheric chemical ionization-mass spectrometry (APCI-MS) identification has been developed. DBCEC-Cl could easily and quickly label aliphatic amines. Derivatives were stable enough to be efficiently analyzed by HPLC and showed an intense protonated molecular ion corresponding m/z [M+H]⁺ under APCI-MS in positive-ion mode. The ratios for fluorescence responses were I_DBCEC-amine/I_BCEC-amine = 1.02-1.60; I_DBCEC-amine/I_BCEOC-amine = 1.30-2.57; and I_DBCEC-amine/I_FMOC-amine = 2.20-4.12 (here, I was relative fluorescence intensity). The ratios for MS responses were IC_DBCEC-amine/IC_BCEC-amine = 4.16-29.31 and IC_DBCEC-amine/IC_BCEOC-amine = 1.23-2.47 (Here, IC: APCI-MS ion current intensity). Detection limits calculated from 0.0244 pmol injection, at a signal-to-noise ratio of 3, were 0.3-3.0 fmol. The relative standard deviations for within-day determination (n = 6) were 0.045-0.081% for retention time and 0.86-1.03% for peak area for the tested aliphatic amines. The mean intra- and inter-assay precision for all amine levels were <3.64% and 4.67%, respectively. The mean recoveries ranged from 96.9% to 104.7% with their standard deviations in the range of 1.80-2.70 (RSDs%). Excellent linear responses were observed with coefficients of >0.9991.     

催化荧光光度法测定血红蛋白

基于血红蛋白(Hb)对过氧化氢氧化靛蓝胭脂红体系的催化作用,建立了模拟酶催化荧光光度法测定血红蛋白的新方法并对催化氧化反应的机理进行了初步探讨。实验发现体系的荧光强度与血红蛋白浓度在6.20×10-11~7.75×10-8mol/L范围内线性关系良好,方法的检出限为1.67×10-11mol/L。方法用于人血中血红蛋白含量的测定,回收率为98.8%~103.2%。     

The fluorimetric determination of formaldehyde

A sensitive fluorimetric procedure for formaldehyde has been developed. The method, which can measure 0.01 μg formaldehyde, is based on the Hantzsch reaction between acetylacetone, ammonia, and formaldehyde. The product, 3,5-diacetyl-I,4-dihydrolutidine, is colored yellow and fluoresces yellow green. Infra-red spectra indicate that this compound is ionic in dilute solution and aggregated in concentrated solution. The Hantzsch reaction may be extended for the assay of other aldehydes, amines, and β-diketones.     

Benzyl 2-pyridyl ketone 2-pyridylhydrazone as reagent for the fluorimetric determination of zinc at ng/ml levels

A sensitive fluorimetric method for the determination of zinc, based on the formation of a fluorescent chelate with benzyl 2-pyridyl ketone 2-pyridylhydrazone is described. In darkness, the fluorescence develops rapidly and remains stable for 1 hr. The detection limit is 15 ng/ml. The effect of reaction variables, and methods of removing interferences, are discussed.     

Kinetic fluorimetric determination of carbamazepine in serum by the stopped-flow technique

Summary A simple, fast method for the determination of carbamazepine in serum is reported for the first time. It is based on the fluorescent reaction of this drug with cerium(IV) in an acid medium. A stopped-flow mixing module coupled to a conventional spectrofluorimeter is used for this purpose. The linear range of the proposed method is 0.04–140 g ml^–1 of carbamazepine and the detection limit is 0.01 g ml^–1. The within- and between-assay precision data and selectivity results show the method to be adequate for the determination of carbamazepine in serum by including a preliminary extraction step with dichloromethane. Analytical recoveries from different serum samples are reported.