Online photocatalytic device for highly selective pre-column fluorescence derivatization of 5-hydroxyindoles with benzylamine

A fluorimetric liquid chromatographic method for the determination of 5-hydroxyindoles based on the benzylamine derivatization process mediated through an online photocatalytic oxidation has been developed. In this study, we used a photocatalytic column comprising tefzel tubing packed with TiO₂-coated glass beads, as a pre-column derivatization reactor. The fluorescence derivatization of 5-hydroxyindoles using benzylamine proceeded during their passage through the reaction column under near-UV irradiation. The 5-hydroxyindole derivatives were separated continuously on a reversed-phase liquid chromatography within 50 min, using 100 mM acetate buffer (pH 4.6)-acetonitrile (72:28, v/v; isocratic elution) containing 3 mM sodium octanesulfonate; the samples were detected fluorimetrically at 465 nm upon excitation at 350 nm. The detection limits (signal-to-noise ratio = 3) of the 5-hydroxyindoles were in the range from 160 to 360 fmol per 5 μL injection. We have applied this method, which requires minimal sample pre-treatment, to the determination of 5-hydroxyindole-3-acetic acid in human urine.     

Simultaneous liquid chromatographic measurement of melatonin and related indoles through post-column electrochemical demethylation and fluorescence derivatization.

In this paper we describe a highly sensitive and selective liquid chromatographic method for the determination of 5-methoxyindoles (5-methoxyindole-3-acetic acid, 5-methoxytryptamine, 5-methoxytryptophol, and melatonin) using a post-column technique involving electrolytic demethylation followed by fluorescence derivatization with benzylamine. We separated these compounds within 30 min by reversed-phase liquid chromatography using acetate buffer (pH 6.5)-acetonitrile-methanol [8:1:1 (v/v); isocratic elution] and then demethylated them, using a commercial coulometric system, to give the corresponding 5-hydroxyindoles. Next, we converted the 5-hydroxyindole products into fluorescent derivatives by their reactions with benzylamine in the presence of potassium hexacyanoferrate(III). We detected the derivatives spectrofluorometrically at 480 nm upon excitation at 345 nm. The detection limits (signal-to-noise ratio = 3) of the 5-methoxyindoles were in the range from 12 to 93 fmol per 20-microL injection.     

Derivatization chemistries for determination of serotonin, norepinephrine and dopamine in brain microdialysis samples by liquid chromatography with fluorescence detection

The present paper provides an overview on currently developed derivatization chemistries and techniques for determination of monoamine neurotransmitters serotonin (5-HT), norepinephrine (NE) and dopamine (DA) in microdialysis samples by microbore liquid chromatography with fluorescence detection. In mild alkaline conditions, 5-hydroxyindoles and catecholamines react with benzylamine (BA), forming highly fluorescent 2-phenyl-4,5-pyrrolobenzoxazoles and 2-phenyl(4,5-dihydropyrrolo) [2,3-f]benzoxazoles, respectively. However, for derivatization of DA a higher fluorescence intensity was achieved for reaction with 1,2-diphenylethylenediamine (DPE) rather than with BA, therefore for simultaneous determination of 5-HT, NE and DA in brain microdialysates, a two-step derivatization with BA followed by DPE was developed. The detection limits for 5-HT, NE and DA were 0.2, 0.08 and 0.13 fmol, respectively, in an injection volume of 20 microL, which corresponds to concentrations of 30, 12 and 19.5 pm, respectively in standard solution prior to derivatization. The experimental data presented demonstrate the ability of the technique to simultaneously monitor neuronally releasable pools of monoamine neurotransmitters in the rat and mouse brains at basal conditions and following pharmacological treatments or physiological stimuli. These techniques play an important role in drug discovery and clinical investigation of psychiatric and neurological diseases such as depression, schizophrenia and Parkinson's disease.     

Atomic absorption spectrometric determination of trace zinc in alloys and biological samples after preconcentration with [1-(2-pyridylazo)-2-naphthol] on microcrystalline naphthalene

An atomic absorption spectrometric method for the determination of trace amounts of zinc after adsorption of its [1-(2-pyridylazo)-2-naphthol] complex on microcrystalline naphthalene has been developed. This complex is adsorbed on microcrystalline naphthalene in the pH range 3.5-7.5 from large volumes of aqueous solutions of various alloys and biological samples with a preconcentration factor of 40. After filtration, the solid mass consisting of the zinc complex and naphthalene was dissolved with 5 ml of dimethylformamide and the metal was determined by flame atomic absorption spectrometry. Zinc can alternatively be quantitatively adsorbed on [1-(2-pyridylazo)-2-naphthol]-naphthalene adsorbent packed in a column and determined similarly. About 0.5 ng of zinc can be concentrated in a column from 200 ml of aqueous sample, where its concentration is as low as 2.5 pg ml-1. The calibration curve is linear in the range 0.1-6.5 ng ml-1 in dimethylformamide solution. Eight replicate determinations of 2 ng ml-1 of zinc gave a mean absorbance of 0.145 with a relative standard deviation of 1.5%. The sensitivity for 1% absorption was 0.061 ng ml-1. Various parameters, such as the effect of pH and the interference of a number of metal ions on the determination of zinc, have been studied in detail to optimize the conditions for the determination of zinc in various standard complex materials.     

Use of palladium(II) chloride as a colour-forming reagent for the determination of N-acetyl-L-cysteine in water and fluimukan injections

The formation of the complex between N-acetyl-L-cysteine and palladium(II) chloride in Britton-Robinson buffer solution in the pH range 2.08-8.00 was studied. The optimum conditions for this reaction were ascertained and a spectrophotometric method was developed for the determination of N-acetyl-L-cysteine in the concentration range 4.0-65.3 micrograms ml-1, using PdCl2 as the reagent. The detection limit was 1.63 micrograms ml-1 and the relative standard deviation varied from 0.63 to 1.92%. The method was applied to the determination of N-acetyl-L-cysteine in water and in injection solutions.     

Column preconcentration of trace manganese with the ion pair of 2-nitroso-1-naphthol-4-sulfonic acid tetradecyldimethylbenzyl-ammonium chloride supported on naphthalene and determination by derivative spectrophotometry

A column preconcentration method has been developed for the determination of trace amounts of manganese by preconcentration on 2-nitroso-1-naphthol-4-sulfonic acid (nitroso-S)-tetradecyldimethylbenzylammonium (TDBA) naphthalene as an adsorbent using a simple funnel tipped glass tube. Manganese reacts with nitroso-S to form a water soluble brown colored chelate anion. The chelate anion forms a water insoluble Mn-Nitroso-S-TDBA ion pair on naphthalene packed in a column in the pH range 9.6-10.5 at a flow rate of 1-2 ml/min. The solid mass consisting of manganese complex and naphthalene is dissolved in 5 ml of dimethylformamide (DMF) and the metal determined by second derivative spectrophotometry. The calibration curve is linear in the concentration range 0.25-35.0 micrograms of Mn in 5 ml of the final DMF solution. Eight replicate determinations of 25 micrograms of standard manganese solution give a mean peak height of 4.0 with a correlation coefficient of 0.9995 and relative standard deviation of +/- 1.1%. The sensitivity was calculated to be 0.502(d2 A/d lambda 2)/microgram ml-1 from the slope of the calibration curve. The detection limit was 0.020 microgram ml-1 for manganese at the minimum instrumental settings (signal to noise ratio = 2). Various parameters effecting the method such as the effect of pH, volume of aqueous phase and interference of a number of metal ions on the determination of manganese have been evaluated to optimize the conditions for its determination in standard alloys and biological samples.     

New method for the preparation of O-carbamoyl derivatives in the 4-hydroxyaminoimidazolidin-2-one series

The corresponding 4-(O-carbamoylhydroxyamino)imidazolidin-2-ones were obtained by cyclization of O,N-dicarbamoyl derivatives of N-(3-oximino-2-methyl-2-butyl)- and N-(1-oximino-2-cyclohexyl)methylamines in alkaline media. It was shown that the carbamoylation of 1-methyl-4,5-tetramethylene-3-(3,4-dichlorophenyl)-4-hydroxy-aminoimidazolidin-2-one gives, respectively, an O- or N-carbamoyl derivative, depending on whether it is carried out in alkaline or neutral solutions.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 399–401, March, 1984.     

Formation of pyrrole derivatives through aminolysis of 2-azetidinone derivatives

A mixture of 3-(α,β-epoxyisopropyl)-1-phenyl-2-azetidinone and benzylamine was heated in a sealed tube at 120–130° yielding 4-anilinomethyl-1-benzyl-3-hydroxy-3-methyl-2-pyrrolidinone as a mixture of diastereoisomers. By this method, 4-anilinomethyl-3-hydroxy-3-methyl-1-phenyl-2-pyrrolidinone and 4-anilinomethyl-3-hydroxy-3-methyl-1-(3,4-dimethoxyphenethyl)-2-pyrrolidinone were obtained by using aniline and 3,4-dimethoxyphenethylamine, respectively, instead of benzylamine. The reaction of 4-formyl-1-phenyl-2-azetidinone with 3,4-dimethoxyphenethylamine afforded 4-anilino-1-(3,4-dimethoxyphenethyl)-2,3-dihydro-2-oxopyrrole. In a similar fashion, the 1-n-butyl and 1-isobutyl analogues were obtained by the use of n-butylamine and isobutylamine, respectively, instead of 3,4-dimethoxyphenethylamine.     

Condensation reaction of 3,4-dibenzoyl-1-methyl-2,5-diphenylpyrrole and -1-phenylpyrazole with methylamine derivatives affording pyrrolo [3,4-c]pyridine and 2H-pyrazolo[3,4-c]- and [4,3-c]pyridines

The reaction of 3,4-dibenzoyl-1-methyl-2,5-diphenylpyrrole ( 1 ) and -1-phenylpyrazole ( 2 ) with methylamines ( 3a-c ) afforded pyrrolo[3,4-c]pyridine ( 4 ), and isomeric 2H-pyrazolo[3,4-c]pyridines ( 5a-c ) and [4,3-c]pyridines ( 6a-c ), respectively.     

The effects of some operational parameters in photodegradation of benzylamine and aniline and their kinetics in aqueous suspension of TiO2 and Pt -loaded TiO2

Photocatalytic degradation of benzylamine and aniline on TiO2, Pt-modified TiO2, ZnO and ZnS in aqueous solution has been investigated. The degradation of the compounds follows a pseudo-first-order kinetics according to Langmuir-Hinshelwood model. The degradation process of benzylamine and aniline was evaluated by ninhydrin spectrophotometric method using UV-visible spectrophotometer in lambda(max) = 538 and 525 nm, respectively. The results showed the order of Pt/TiO2 > TiO2 > ZnO > ZnS for photocatalytic activity. In addition increasing of the Pt-loading was found to enhance the degradation rate of the compounds up to the optimal amount of 5 wt. % onto the surface of TiO2 so that the rates of degradation were increased about two times. Rate constants for photodegradation of benzylamine and aniline were found to be 1.4 x 10(-3) min(-1) and 0.7 x 10(-3) min(-1) for TiO2 as photocatalyst, while 2.7 x 10(-3) min(-1) and 1.7 x 10(-3) min(-1) for (5 wt.%) Pt/TiO2 as photocatalyst. Running the reactions in various pH (5-11), indicated that the pH = 8 and 10 or Higher are the optimum pH for photocatalytic degradation of benzylamine and aniline respectively. The effects of some other parameters such as amount of photocatalyst, flux of oxygen and irradiation time were evaluated. Furthermore, the Langmuir-Hinshelwood rate constant k(r) and adsorption constant K(A) for the titled compounds are reported.     

Kinetic determination of tellurium based on its inhibitory effect on the palladium(II)-catalysed reaction between pyronine G and hypophosphite ion

A kinetic method for the determination of Te based on its inhibitory effect on the PdII-catalysed reaction between pyronine G and H2PO2- is described. The influence of experimental variables on the rate of the process and the potential interfering effect of a large number of ions has been studied. Under the selected experimental conditions: 6 x 10(-5) M pyronine G; 0.6 M H2PO2-; pH 2.6, adjusted with Britton-Robinson buffer; 0.80 microgram ml-1 of PdII; and a temperature of 22 +/- 0.2 degrees C, Te was determined in the concentration range 0.08-0.85 microgram ml-1. The method was applied to the determination of Te in waters and lead concentrates.     

Column chromatographic pre-concentration of iron(III) in alloys and biological samples with 1-nitroso-2-naphthol-3,6-disulphonate and benzyldimethyltetradecylammonium-perchlorate adsorbent supported on naphthalene using atomic absorption spectrometry

The solid ion-pair material produced from the reaction between benzyldimethyltetradecylammonium chloride (BDTA) and sodium perchlorate on naphthalene provides the basis for a simple, rapid and selective technique for pre-concentrating iron from up to 500 ml of aqueous solution. Iron reacts with disodium 1-nitroso-2-naphthol-3,6-disulphonate (Nitroso-R salt) to form a water-soluble coloured chelate anion. The iron chelate anion forms a water-insoluble, stable iron-Nitroso-R-BDTA complex on naphthalene packed in a column. Trace amounts of iron are quantitatively retained on naphthalene in the pH range 3.5-7.5 and at a flow-rate of 1-2 ml min-1. The solid mass is dissolved out from the column with 5 ml of N,N-dimethylformamide and iron is determined by means of an atomic absorption spectrometer at 248 nm. The calibration graph is linear for concentrations of iron over the range of 0.5-20 micrograms in 5 ml of final solution. The standard deviation and relative standard deviation were calculated. The detection limit of the method was 0.0196 micrograms ml-1 of iron. The sensitivity for 1% absorption was 0.072 microgram ml-1 (0.165 microgram ml-1 by direct atomic absorption spectrometry of aqueous solution). The proposed method was applied to the determination of iron in standard alloys and biological samples.     

Determination of nucleic acids with crystal violet by a resonance light-scattering technique

For the first time, Crystal Violet (CV) was used to determine nucleic acid concentrations using the resonance light-scattering (RLS) technique. Based on the enhancement of the RLS of CV by nucleic acids, a new quantitative determination method for nucleic acids in aqueous solutions has been developed. At pH 5.03 and ionic strength 0.005 mol kg-1, the interaction of CV with nucleic acids results in three characteristic RLS peaks at 344.0, 483.0 and 666.0 nm. With 4.0 x 10(-5) mol l-1 of CV, linear relationships were found between the enhanced intensity of RLS at 666.0 nm and the concentration of nucleic acids in the range 0-2.5 micrograms ml-1 for herring sperm DNA, 0-4.0 micrograms ml-1 for calf thymus DNA and 0-4.5 micrograms ml-1 for yeast RNA. The limits of determination were 13.8 ng ml-1 for herring sperm DNA, 36.8 ng ml-1 for calf thymus DNA and 69.0 ng ml-1 for yeast RNA. The assay is convenient, rapid, inexpensive and simple.     

A flow injection sampling resonance light scattering system for total protein determination in human serum

A novel flow injection method with resonance light scattering detection was developed for the determination of total protein concentrations. This method is based on the enhancement of RLS signals from Methyl Blue (MB) by protein. The enhanced RLS intensities at 333 nm, in a pH 4.1 acidic aqueous solution, were proportional to the protein concentration over the range 2.0-37.3 and 1.0-36.0 microg ml-1 for human serum albumin (HSA) and bovine serum albumin (BSA), respectively. The corresponding limits of detection (3sigma) of 45 ng ml-1 for HSA and 80 ng ml-1 for BSA were attained. The method was successfully applied to the quantification of total proteins in human serum samples, the maximum relative error is less than 1% and the recovery is between 98% and 102%. The sample throughput was 60 h-1.     

Simultaneous determination of acetylsalicylic acid and its major metabolites in human serum by second-derivative synchronous fluorescence spectrometry.

A method is described for the simultaneous determination of acetylsalicylic, salicylic, gentisic and salicyluric acids (ASA, SA, GA and SU, respectively) in serum, based on their native fluorescence. The ASA-SA-GA-SU-containing serum samples are extracted with chloroform-1% acetic acid solution; ASA and SA are determined in the organic phase, and GA and SU in the aqueous phase, after removal of protein with trichloroacetic acid, at pH 5.0 and 11.6, respectively. The ASA-SA and GA-SU-SA mixtures are resolved using second-derivative fluorescence spectrometry and the appropriate empirical equations involving the effect of each acid on the signal of the other. Recoveries from sera spiked with ASA (1.0-10 micrograms ml-1), SA (25-50 micrograms ml-1), GA (0.05-0.2 micrograms ml-1) and SU (1.0-5.0 micrograms ml-1) ranged from 100 to 104% (mean 101%), from 93 to 99% (mean 97%), from 94 to 104% (mean 99%) and from 94 to 107% (mean 98%), respectively.     

Catalytic spectrophotometric determination of vanadium in seawaters based on the bromate oxidative coupling reaction of metol and 2,3,4-trihydroxybenzoic acid.

A new, simple, sensitive and selective catalytic method is developed for the determination of vanadium in natural and sea waters. The method is based on the catalytic effect of V(V) and/or V(IV) on the bromate oxidative-coupling reaction of metol with 2,3,4-trihydroxybenzoic acid (THBA). The reaction is followed spectrophotometrically by tracing the oxidation product at 380 and/or 570 nm after 5 min of mixing the reagents. The optimum reaction conditions are 6.4 x 10(-3) mol l-1 of metol, 2.0 x 10(-3) mol l-1 of THBA and 0.16 mol l-1 of bromate at 35 degrees C and in the presence of an activator-buffer solution of 1 x 10(-2) mol l-1 of tartrate (pH = 3.10). Following the recommended procedure, V(V) and/or V(IV) can be determined with linear calibration graphs up to 0.75 ng ml-1 and detection limits, based on the 3Sb criterion, of 0.008 and 0.018 ng ml-1 at 380 and 570 nm, respectively. The developed method was successfully applied, without any separation or preconcentration processes, to the determination of vanadium in natural and seawaters following the direct calibration and standard addition techniques, respectively.     

Sensitive detection of tetracyclines using europium-sensitized fluorescence with EDTA as co-ligand and cetyltrimethylammonium chloride as surfactant

The determination of tetracyclines (TC) in aqueous solutions, based on europium-sensitized fluorescence, has been improved using EDTA as co-ligand and cetyltrimethylammonium chloride as surfactant. The method involves working in slightly alkaline solutions with the formation of a new chelate where the lanthanide ion is bound to the beta-diketone group. The method is about 6 times more sensitive than that with the Eu-TC-Triton system and LODs are 2.5 x 10(-10), 5 x 10(-10), 1.5 x 10(-9) and 2 x 10(-9) mol l-1 for TC, oxytetracycline, chlortetracycline and doxycycline, respectively. The method has been applied to the determination of TC in calf serum without sample pretreatment. The mean recovery was close to 102% and the lowest concentration attainable in serum samples was better than 0.1 microgram ml-1.     

Sensitive determination of paraquat and diquat at the sub-ng ml-1 level by continuous amperometric flow methods.

Two methodologies are described for the determination of paraquat and diquat. The first is based on the pre-treatment of an electrode with a surfactant solution, which improves the electrochemical determination of the herbicides. Linear calibration graphs were obtained in the ranges 10-80 and 10-100 ng ml-1 for paraquat and diquat, respectively. The limits of detection were 6.32 for paraquat and 4.80 ng ml-1 for diquat. The method was applied to the determination of the herbicides in synthetic water samples. The second methodology is based on the preconcentration of paraquat and diquat in a minicolumn packed with a cation-exchange material. The determination ranges and detection limits depend on the sample volume used (5-50 ml). Thus, 50 ml of sample provides limits of detection of 0.016 and 0.020 ng ml-1 for paraquat and diquat, respectively. The applicability of the method was demonstrated with the determination of the herbicides in both synthetic and real water samples.     

Study of the reaction of proteins with Beryllon II-AlIII by the Rayleigh light scattering technique and its application

The determination of proteins with tetrasodium 2-(3,6-disulfo-8-hydroxynaphthylazo)-1,8-dihydroxynaphthalene-3,6-disulfonate (Beryllon II) by Rayleigh light scattering (RLS) was studied. The weak RLS of the Beryllon II-bovine serum albumin (BSA) complex can be greatly enhanced by the addition of Al3+ in the pH range 5.6-7.2; there was a maximum RLS platform at 400-420 nm. Based on the reaction between Beryllon II, Al3+ and proteins, a new method for the determination of proteins was developed. This method is very sensitive [0.20-41.42 micrograms ml-1 for BSA and 0.18-48.15 micrograms ml-1 for human serum albumen (HSA)], rapid (< 2 min), simple (one step) and tolerant towards most interfering substances. The effects of different surfactants were also examined. Four samples of protein in human serum were determined; the maximum relative error was no more than 5% and the recovery was 96-105%.     

Spectrophotometric determination of taurine in food samples with phenol and sodium hypochlorite as reagents and an ion-exchange clean-up

A simple and accurate spectrophotometric method is proposed for the determination of taurine in food samples using phenol and sodium hypochlorite as reagents, which form a blue colour with taurine at room temperature and pH 10.35. Ion exchange was used to improve the selectivity of the method. Absorbance measurements were made at 630 nm and the calibration graph was linear from 0 to 180 micrograms ml-1 of taurine with a slope of 0.00242 A (p.p.m.)-1. The precision for the determination of taurine (156 micrograms ml-1) was 0.8% (n = 10). The method was applied successfully to the determination of taurine in milk products and energy drinks.