Formation Of Azo Dye Research Articles

Electrochemical Determination of Food Preservative Nitrite with Gold Nanoparticles/p-Aminothiophenol-Modified Gold Electrode.

Due to the negative impact of nitrate and nitrite on human health, their presence exceeding acceptable levels is not desired in foodstuffs. Thus, nitrite determination at low concentrations is a major challenge in electroanalytical chemistry, which can be achieved by fast, cheap, and safe electrochemical sensors. In this work, the working electrode (Au) was functionalized with p-aminothiophenol (p-ATP) and modified with gold nanoparticles (Au-NPs) to manufacture the final (Au/p-ATP-Aunano) electrode in a two-step procedure. In the first step, p-ATP was electropolymerized on the electrode surface to obtain a polyaminothiophenol (PATP) coating. In the second step, Au/p-ATP-Aunano working electrode was prepared by coating the surface with the use of HAuCl4 solution and cyclic voltammetry. Determination of aqueous nitrite samples was performed with the proposed electrode (Au/p-ATP-Aunano) using square wave voltammetry (SWV) in pH 4 buffer medium. Characteristic peak potential of nitrite samples was 0.76 V, and linear calibration curves of current intensity versus concentration was linear in the range of 0.5–50 mg·L−1 nitrite with a limit of detection (LOD) of 0.12 mg·L−1. Alternatively, nitrite in sausage samples could be colorimetrically determined with high sensitivity by means of p-ATP‒modified gold nanoparticles (AuNPs) and naphthylethylene diamine as coupling agents for azo-dye formation due to enhanced charge-transfer interactions with the AuNPs surface. The slopes of the calibration lines in pure NO2− solution and in sausage sample solution, to which different concentrations of NO2− standards were added, were not significantly different from each other, confirming the robustness and interference tolerance of the method. The proposed voltammetric sensing method was validated against the colorimetric nanosensing method in sausage samples.

PH and temperature responsive redox behavior of biologically important aniline derivatives

The electrochemical oxidation of anilines resulted in azodye formation which was evidenced by the appearance of a new peak in the UV-visible spectra (A) and colour change of the solution (B).

4-Aminothiophenol Functionalized Gold Nanoparticle-Based Colorimetric Sensor for the Determination of Nitramine Energetic Materials

The heterocyclic nitramine compounds, hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), are two most important military-purpose high explosives. Differentiation of RDX and HMX with colorimetric methods of determination has not yet been made because of their similar chemical structures. In this study, a sensitive colorimetric method for the determination of RDX and HMX was proposed on the basis of differential kinetics in the hydrolysis of the two compounds (yielding nitrite as a product) followed by their colorimetric determination using 4-aminothiophenol (4-ATP) modified gold nanoparticles (AuNPs) and naphthylethylene diamine (NED) as coupling agent for azo-dye formation, abbreviated as "4-ATP-AuNP+NED" colorimetric method. After alkaline hydrolysis in a 1 M Na2CO3 + 0.04 M NaOH mixture solution at room temperature, only RDX (but not HMX) was hydrolyzed to give a sufficient colorimetric response in neutralized solution, the molar absorptivity (ε) at 565 nm and the limit of detection (LOD) for RDX being (17.6 ± 1.3) × 10(3) L mol(-1) cm(-1) and 0.55 μg mL(-1), respectively. On the other hand, hot water bath (at 60 °C) hydrolysis enabled both nitramines, RDX and HMX, to give substantial colorimetric responses; i.e., ε and LOD for RDX were (32.8 ± 0.5) × 10(3) L mol(-1)cm(-1) and 0.20 μg mL(-1) and for HMX were (37.1 ± 2.8) × 10(3) L mol(-1)cm(-1) and 0.24 μg mL(-1), respectively. Unlike other AuNP-based nitrite sensors in the literature showing absorbance quenching within a relatively narrow concentration range, the developed sensor operated with an absorbance increase over a wide range of nitrite. Synthetic mixtures of (RDX + HMX) gave additive responses, and the proposed method was statistically validated against HPLC using nitramine mixtures.

New detector tube for the detection of nitrite in water

Abstract A new colorimetric detector tube for the detection of trace concentrations of nitrite in water was developed. The detector tube is based on a diazo coupling reaction of nitrite with dapsone and N-(1-naphthyl) ethylenediamine dihydrochloride during the formation of red-violet azo dye. Spherical granules (pellets) made from the composite material were used as the carrier of chemical reagents. They were prepared by pelletizing the mixture of microcrystalline cellulose, lactose, kaolin and polyvinylpyrrolidone. Colouring is done on a layer of silica gel impregnated with citric acid. The detector tube is highly sensitive, selective and stable when stored. The detection limit is 0.1 μg.ml-1, i.e. 0.03 μg.ml-1 N(NO2 -). The optimal measuring range of nitrite concentration in the analyzed sample ranges from 0.5 to 80 μg.ml-1, i.e. 0.15-24.36 μg.ml-1 N(NO2 -). The detector tube can easily be structurally modified for analysis of nitrates with a detection limit of 1 μg/ml-1, i.e. 0.23 μg.ml-1 N(NO3 -).

A new colorimetric method for the determination of nifedipine tablets by derivatization using 4-carboxyl-2,6-dinitrobenzene diazonium ion

Abstract Background A new sensitive colorimetric determination of nifedipine has been developed following azo dye formation with 4-carboxyl-2,6-dinitrobenzenediazonium ion (CDNBD). Judging from the various generic brands currently now available, this research was conceived as a means of developing an alternative cost-effective and readily adaptable method for the assay of nifedipine in tablets and for which official high performance liquid chromatographic technique may not be readily available. Results Nifedipine was reduced with Zn/HCl reduction system and then the diazo coupling reaction was carried out with the CDNBD reagent to generate a new azo adduct with optimal wavelength at 470 nm representing a bathochromic shift relative to nifedipine, reduced nifedipine and CDNBD reagent. Optimal temperature and time for coupling were selected as 50 oC and 15 minutes. A linear response was observed over 2.9 -14.5 µg/mL of nifedipine with a correlation coefficient of 0.9985 and the drug combined with CDNBD at a stoichiometric ratio of 2:1. The method has limits of detection and quantitation of 0.1344 µg mL-1 and 0.4074 µg mL-1 respectively. The Sandell’s sensitivity obtained is 4.673 ng/cm2 and the method was reproducible over a three day assessment. Intra- and inter-day accuracies (in terms of errors) were of the order -0.008 to 3.22 % while precisions were generally less than 3.1 % (RSD). Conclusions The developed spectrophotometric method is of equivalent accuracy (p > 0.05) with USP 2007 HPLC method. It has the advantages of speed, simplicity, sensitivity and more affordable instrumentation and could find application as a rapid and sensitive analytical method for nifedipine. It is the first described method by azo dye derivatization for the analysis of nifedipine in bulk samples and dosage forms.

Photocatalytic cleavage of hydroxytriazenes: a solid-state synthesis of azo-dyes under sunlight irradiation

Sunlight-induced decomposition of hydroxytriazenes, and green photochemical synthesis of azo-dyes is described. Three substituted hydroxytriazenes, viz: 3-hydroxy-3-(2-methylphenyl)-1-(3-chloro-4-fluorophenyl)triazene (o-CFHT), 3-hydroxy-3-(3-methylphenyl)-1-(3-chloro-4-fluorophenyl)triazene (m-CFHT), and 3-hydroxy-3-(4-methylphenyl)-1-(3-chloro-4-fluorophenyl)triazene (p-CFHT) were co-crystallized with β-naphthol in equimolar ratio and exposed to sunlight for 9–10 h. The reaction resulted in formation of azo-dyes which were identified by comparison with the products obtained by the conventional method (standard azo-dye), by use of HPLC. A probable mechanism has been suggested. This is first eco-friendly synthesis of azo-dyes using hydroxytriazenes.

Novel spectrophotometric determinations of some cephalosporins following azo dye formation with p-dimethylaminobenzaldehyde

A new simple, accurate and cost-effective spectrophotometric method has been developed for the analysis of some cephalosporins (ceftriaxone, ceftazidime, cefixime, cefotaxime and cefuroxime) in bulk samples and pharmaceutical dosage forms. The reaction involves a two-step process of diazotization of the cephalosporins with acidified NaNO2 at 0–5°C and coupling with acidified p-dimethylaminobenzaldehyde (DMAB). Optimal temperature and time for coupling were established at 50 and 60°C with coupling time ranging from 15 to 20min. All the cephalosporins gave azo adducts with DMAB that absorbed light optimally at 400–430nm. The reaction with DMAB occurred at a stoichiometric ratio of 1:1. Optimization of DMAB concentration revealed the superiority of using 0.3% DMAB in 0.0625M H2SO4 with the best diluting solvent being methanol. Beer’s law was obeyed at concentrations ranging from 5 to 60μg/mL with correlation coefficients >0.9980 in all cases. Overall recoveries were of the order of 95–103% with errors generally less than 6%. The method was successfully applied to the determination of the cephalosporins in dosage forms and it was found to be equivalent accuracy to the official (USP and BP) HPLC assay procedures for these drugs. There was no interference from commonly adopted excipients.The method could find application as a rapid and cost-effective alternative for the quality control of these cephalosporins, especially in preliminary studies.

Spectrophotometric Determination of Benzocaine by Azo-Dye Formation Reaction

A spectrophotometric method for the assay of trace amounts of benzocaine was based on the reaction of benzocaine with nitrite ion to form the corresponding diazonium salt followed by coupling reaction with ethyl cyano acetate to form a stable and a soluble yellow azo dye with maximum absorption at 405 nm. Beer،¦s law was obeyed over the range 5-250ƒفg/25ml, i.e, (0.2-10ppm) of benzocaine and correlation coefficient 0.998 with a molar absorptivity of 3.1 „e104 L.mol-1.cm-1, a relative error of 0.0 to 0.25 % and a relative standard deviation of „b 0.03 to „b 0.38 %, depending on the concentration level. The method has been successfully applied for the assay of benzocaine in one pharmaceutical preparation (Lozenges).

Use of a new component during formation of insoluble azo dyes on the surface of blended fabric

It was found that methyl phloroglucinol exhibits surface-active properties. The MPG adsorption isotherms can be assigned to class S-2 in the Giles classification. In adsorption of MPG, a bimolecular layer is formed. A principle was formulated for selecting the conditions for dyeing with insoluble azo dyes on textile materials made from a fibre blend where the colors have high strength indexes. It was shown that MPG, not previously used as an azotol in dyeing blended fabrics (wool + Nitron) by formation of insoluble azo dyes on the fibre, and this allows expanding the color range and improving the technology for dyeing textile materials.

Spectrophotometric determination of trifluralin in commercial formulations and agricultural samples using factorial design

A simple spectrophotometric method was developed for determination of trifluralin in commercial formulation and food samples. The method was based on the hydrolysis of trifluralin with sodium hydroxide to form 2,6-dinitro-4-trifluoromethylaniline. The resultant aniline group was diazotized with nitrate in acidic media and the diazotized product was coupled with β-naphthol to form red colored product having λmax 550 nm. The reaction conditions were optimized for hydrolysis as well as for the diazotization reaction. The Beer’s law was obeyed over the range of 0.2–17 μg mL−1 with molar absorptivity of 1.5 × 104 L mol−1 cm−1. The relative standard deviation was found to be 3.6%. A two level factorial design of 23 was used for optimization of all parameters. The influence of different factors and their interactions on the final azo dye formation were also studied from these factorial designs. The method has been applied successfully for the analysis of commercial formulations and agricultural samples. The recovery for the determination of trifluralin was found to be in the range 95–97%.

Spectrophotometric Determination of Bromhexine Hydrochloride by Azo-Dye Formation Reaction

Spectrophotometric Determination of Bromhexine Hydrochloride by Azo-Dye Formation Reaction

Spectrophotometric Determination of Tetracycline by Azo Dye Formation with Diazotised p-Nitroaniline-Application to Pharmaceutical Preparations and Biological Fluids

This paper involves a spectrophotometric method for the determination of trace amounts of tetracycline in aqueous solution. The method is based on the coupling of tetracycline with diazotized p-nitroaniline reagent in basic medium to form a violet mono azo dye that is water – soluble, stable and shows maximum absorption at 569 nm. Beer’s law is obeyed over the concentration range 2 – 400 g / 25 ml final volume, i.e., (0.08 – 16) ppm with a molar absorptivity of 7.8  104 l.mol-1.cm-1 and sandell sensitivity index of 6.2  10-3 g cm-2. The method is applied to the determination of the compound in serum and urine by standard addition method in vitro and in vivo (serum and urine) and pharmaceutical preparation (tetracyclline’s ointment).

Functional group analysis on oxidized surfaces of synthetic textile polymers

A comprehensive collection of wet-chemical analyses of functional groups on oxidatively treated surfaces of hydrophobic polymers like poly(ethylene terephthalate) or polyolefine is presented. New methods are introduced. Textiles and foils have been subjected to advanced oxidation processes and the different oxygen functions have been quantified. Analysis of surface functional groups includes radical site determination with radical scavengers like diphenylpicrylhydrazyl, reduction of peroxides determined iodometrically, cationic dyestuff adsorption, carbonyl binding to Girard reagent P and surface hydroxyl group determination by surface nitrosation and subsequent azo-dye formation photometrically determinable. Use of potential surface swelling agents has been excluded except for addition of wetting agent. Wet-chemical analyses on textile surfaces bear the benefit of integrating over (relatively) large sample areas, a point which is interesting when regarding inhomogenities of textile or other surface constructions. In addition examples for visualisation for the existence of surface groups are described.

Determination of N-species in soil extracts using microplate techniques

Colourimetric methods for the determination of NO 3 −, NH 4 + and total N in water extracts of soils using 96-well microplate techniques are described. Nitrate was determined by azo dye formation after reduction to NO 2 − using a solution of hydrazine sulphate. Ammonium in the soil extracts was purified and concentrated by diffusion as NH 3 from small volumes (750 μL) of extract treated with MgO into a H 2SO 4 collector using a double-plate, MicroResp™ method and subsequently determined by the Berthelot reaction. For the determination of total N, samples were oxidised with K 2S 2O 8 at 110 °C in a 96 × 1.1 mL polytetrafluoroethylene block with a lid that closed individual wells. The oxidised solutions were transferred to standard plates for colourimetric analysis of NO 3 −. The recovery of N, measured as NO 3 −, from NH 4NO 3 and a range of organic-N compounds was >95%. The limits of quantitation of the colourimetic assays were 0.020 mg N L −1 for NO 3 − and 0.051 mg N L −1 for NH 4 +. The methods were tested on water extracts derived from a range of 10 nutrient poor soils from Scotland. There were acceptable linear correlations between the results obtained by established methods. For soil extracts analysed by the microplate method, the relationship for NO 3 − was 1.03× result from ion chromatography + 0.0055 ( R 2 = 0.9961); for NH 4 + determined by the microplate method, the relationship was 0.9696 × result from a discrete analyser − 0.0169 ( R 2 = 0.9757) and for total N determined by oxidation in the PTFE microplate the relationship was 0.9435 × result obtained by combustion + 0.0489 ( R 2 = 0.9743). Purification of the NH 4 + in water extracts from the 10 different soils by the diffusion method did not result in any systematic difference (paired t-test, p = 0.05) between measured concentration values determined before and after diffusion.

Reactions of the synthesis of azo dyes in solidified gelatin gel and their analytical application in the determination of nitrites

The interaction of aromatic sulfonates of azo and diazo components in diazotization and azocoupling reactions electrostatically immobilized on gelatin solidified gel was studied. It was found that, among the variety of the functional groups of the polymer (amino, hydroxy, and carboxy groups and guanidine, phenol, and sulfur-containing amino acid residues), some groups are capable of protonation and are responsible for the efficient electrostatic immobilization of aromatic sulfonates with amino and hydroxy groups. A sufficiently high capacity of the polymer gel causes the formation of a relatively large amount of immobilized compounds, which makes it possible to conduct different types of synthetic analytical reactions of the formation of azo dyes in these gelatin gels in the real-time mode. It was demonstrated that, in all cases, the rate-determining step is external diffusion. These effects were used for the preparation of irreversible sensing elements suitable for measurements of calibration functions using the fixed-time technique or the tangent method in the determination of nitrites in solutions.

Bioassay for the Determination of the Intra‐ and Extracellular Activity of Aminopeptidases in Immobilized Tomato Cells

Permeabilized tomato cells were cross-linked with glutaraldehyde in the absence of a carrier. The immobilized cells demonstrated significantly lower aminopeptidase (AP) activities than untreated control cells. However, when immobilized with pectate and alginate gels, the tomato cells retained their AP activities. A new method for the determination of the activity of both extra- and intracellular AP was developed, based on enzyme-catalyzed hydrolysis of a series of synthetic beta-naphthylamides (betaNA) of the L-amino acids Ala, Arg, Leu, Pro, Tyr, or of the synthetic beta-methoxynaphthylamides (betaMNA) of Ala and Arg. Extracellular AP--produced by calli, cell-suspension culture, or seedlings of tomato cells grown on agar--hydrolyzed these peptidic substrates to the free naphthalene amines and amino acids. Staining with Fast Garnet GBC salt under formation of bright reddish azo dyes readily allowed the determination of AP activities. For the tomato-cell suspension, the intracellular activity accounted for 91.3-93.9% of the total activity, and the extracellular one for 6.1-8.7%, respectively. Our method permits the rapid, simple, and specific determination of plant aminopeptidases.

Spectrophotometric Determination of Aniline by Azo-Dye Formation with 2, 6-Dihydroxybenzoic Acid-Application to waters

A simple and sensitive Spectrophotometric method for the determination of aniline in aqueous medium is described. The method is based on the formation of a yellow coloured azo product from the diazotisation of aniline followed by a coupling reaction with 2,6-dihydroxybenzoic acid in the presence of sodium carbonate. Absorbance of the resulting yellow azo dye is measured at 432 nrn and is stable for 1 hour at least. Beer's law is obeyed in the concentration range of 5-80|ig of aniline in a final volume of 25ml, with a molar absorptivity of 4.2xl04l.morl.cm"!, a relative error of +1.13 to+ 4.40 % and a relative standard deviation of ±0.30 to ±0.76%, depending on the concentration level. The method is successfully employed for the determination of aniline in river and waste waters.

Interactions of Nitroaromatic Compounds with the Mammalian Selenoprotein Thioredoxin Reductase and the Relation to Induction of Apoptosis in Human Cancer Cells

Here we described novel interactions of the mammalian selenoprotein thioredoxin reductase (TrxR) with nitroaromatic environmental pollutants and drugs. We found that TrxR could catalyze nitroreductase reactions with either one- or two-electron reduction, using its selenocysteine-containing active site and another redox active center, presumably the FAD. Tetryl and p-dinitrobenzene were the most efficient nitroaromatic substrates with a k(cat) of 1.8 and 2.8 s(-1), respectively, at pH 7.0 and 25 degrees C using 50 muM NADPH. As a nitroreductase, TrxR cycled between four- and two-electron-reduced states. The one-electron reactions led to superoxide formation as detected by cytochrome c reduction and, interestingly, reductive N-denitration of tetryl or 2,4-dinitrophenyl-N-methylnitramine, resulting in the release of nitrite. Most nitroaromatics were uncompetitive and noncompetitive inhibitors with regard to NADPH and the disulfide substrate 5,5'-dithiobis(2-nitrobenzoic acid), respectively. Tetryl and 4,6-dinitrobenzofuroxan were, however, competitive inhibitors with respect to 5,5'-dithiobis(2-nitrobenzoic acid) and were clearly substrates for the selenolthiol motif of the enzyme. Furthermore, tetryl and 4,6-dinitrobenzofuroxan efficiently inactivated TrxR, likely by alkylation of the selenolthiol motif as in the inhibition of TrxR by 1-chloro-2,4-dinitrobenzene/dinitrochlorobenzene (DNCB) or juglone. The latter compounds were the most efficient inhibitors of TrxR activity in a cellular context. DNCB, juglone, and tetryl were highly cytotoxic and induced caspase-3/7 activation in HeLa cells. Furthermore, DNCB and juglone were potent inducers of apoptosis also in Bcl2 overexpressing HeLa cells or in A549 cells. Based on these findings, we suggested that targeting of intracellular TrxR by alkylating nitroaromatic or quinone compounds may contribute to the induction of apoptosis in exposed human cancer cells.

Spectrophotometric Determination of Benzocaine by Azo-Dye Formation Reaction with N - (1-naphthyl)ethylenediamine as Coupling Agent

Spectrophotometric Determination of Benzocaine by Azo-Dye Formation Reaction with N - (1-naphthyl)ethylenediamine as Coupling Agent

Formation of Monomeric and Novolak Azo Dyes in Nanofluid Segments by Use of a Double Injector Chip Reactor

AbstractThe azo coupling of 2‐naphthol and cresol novolaks was performed as an example for organic reactions in a microsegmented flow system with microspectrophotometric on‐line characterization. A lithographically prepared glass/glass chip microreactor was used for the generation of segments and the mixing of reaction partners. The formation of segments and their transport behavior is strongly influenced by the addition of surfactants. The reaction rates were high in alkaline media at room temperature, so that the formation of dyes could be observed by a microscope‐video system. The single reaction volumes were in the range between about 0.05 and 1 μL. The spectrum of each segment was registered with a measuring frequency of 45–50 Hz. The residence time of segments inside the optical measurement channels varied between 0.1 and 1.5 s and is in the range of 0.3 s for typical segment sizes of about 150 nL. The single reaction segments containing azo dyes as well as polymer‐based azo dyes were stored in segment sequences inside capillary Teflon tubes.