Olajire A. Adegoke

A new approach to the spectrophotometric determination of metronidazole and tinidazole using p-dimethylaminobenzaldehyde.

A new approach to the spectrophotometric determination of metronidazole and tinidazole using p-dimethylaminobenzaldehyde A new approach to the spectrophotometric determination of metronidazole (MZ) and tinidazole (TZ) has been developed. The procedure involves coupling of diazotized nitroimidazoles with p-dimethylaminobenzaldehyde (DMAB) to form a greenish-yellow solution. Optimal temperature and time were 0 °C (iced) and 3 minutes for diazotization and 30 °C and 2 minutes for coupling for both MZ and TZ. Coloured adducts of MZ and TZ showed shoulders at 406 nm and 404 nm, respectively, which were selected as analytical wavelengths. The reaction with p-DMAB occurred in a 1:1 mole ratio. Beers law was obeyed within the 4.8-76.8 μg mL-1 concentration range with low limits of detection. The azo adducts were stable for over a week. Molar absorptivities were 1.10 × 103 (MZ) and 1.30 × 103 L mol-1 cm-1 (TZ). Overall recoveries of MZ and TZ from quality control samples were 103.2 ± 1.3 and 101.9 ± 1.3% over three days. There was no interference from commonly utilized tablet excipients. No significant difference was obtained between the results of the new method and the BP titrimetric procedures. The azo approach using the p-dimethylaminobenzaldehyde procedure described in this paper is simple, fast, accurate and precise. It is the first application of DMAB as a coupling component in the diazo coupling reaction. Novi pristup spektrofotometrijskom određivanju metronidazola i tinidazola koristeći p-dimetilaminobenzaldehid U radu je opisan novi način spektrofotometrijskog određivanja metronidazola (MZ) i tinidazola (TZ). Postupak uključuje reakciju diazotiranog nitroimidazola s p-dimetilaminobenzaldehidom (DMAB), pri čemu nastaje zelenkasto-žuta otopina. Optimalna temperatura i vrijeme za diazotaciju su 0 °C (ledena kupelj) i 3 minute, a za reakciju kondenzacije 30 °C i 2 minute. Obojeni adukti imaju maksimum apsorpcije pri 406, odnosno 404 nm pa su te valne duljine izabrane za analitički postupak. Reakcija s p-DMAB zbiva se u množinskom omjeru 1:1. Reakcija slijedi Beerov zakon u koncentracijskom rasponu 4,8-76,8 μg mL-1 s niskim granicama detekcije. Azo adukti su stabilni preko tjedan dana. Molarna apsorptivnost bila je 1,10 × 103 (MZ), odnosno 1,30 × 103 L mol1 cm1 (TZ). Ukupni povrat MZ i TZ iz kontrolnih uzoraka bio je 103,2 ± 1,3, odnosno 101,9 ± 1,3 % tijekom tri dana. Nije zamijećena nikakva interferencija uobičajenih pomoćnih tvari koje se koriste za tabletiranje. Ne postoji značajna razlika između rezultata dobivenih novom metodom i rezultata dobivenih BP titrimetrijskim postupkom. Metoda određivanja opisana u ovom radu je jednostavna, brza, pogodna, točna i precizna i po prvi puta uključuje DMAB u reakciji diazo kopulacije.

Relative predominance of azo and hydrazone tautomers of 4-carboxyl-2,6-dinitrophenylazohydroxynaphthalenes in binary solvent mixtures

Azo-hydrazone tautomerism is a phenomenon that occurs in azo dyes possessing substituents conjugated to the azo linkage which has labile proton that can be exchanged intramolecularly. Thus the predominance of one tautomer over another is a function of many factors among which are solvent polarity, solvent type, solute-solvent interactions and the structure of the dye molecule itself. The 4-carboxyl-2,6-dinitrophenylazohydroxynaphthalenes, previously shown to exhibit azo-hydrazone tautomerism, were studied for the relative predominance of one form over another based on interaction at the microenvironment of binary solvent mixtures containing DMF and non-hydrogen bonding (CCl(4)), hydrogen bond donor (toluene, chloroform), hydrogen bond acceptor (acetonitrile, acetone) and the alcohols; ethanol and methanol as solvent pairs. The three dyes gave two main bands in the 50:50 mixture of DMF with these solvents consisting of a high energy band at 250-382 nm while the low energy bands for the dyes occurred at 415-485 nm. Spectral shifts in the binary solvent mixtures were related to the solvent dipolarity, basicity of the less polar component relative to DMF, substituent type, molar transition energy, formation constant for the hydrogen-bonding solvated complexes and the standard free energy change for hydrogen bonding with DMF. The relative predominance of the hydrazone tautomer bears a direct relationship to the basicity of the solvent, presence of hydrogen bond donor substituent and was associated with high molar transition energies and low formation constant. The microenvironment surrounding the dye molecules played a major role in the stability of one tautomer relative to the other.

Spectrophotometric determination of hydralazine using p-dimethylaminobenzaldehyde

A new spectrophotometric method for the assay of hydralazine hydrochloride in bulk and dosage forms has been developed. The procedure is based on a condensation reaction between alcoholic solution of hydralazine and acidic solution of p-dimethylaminobenzaldehyde to generate an instant greenish-yellow coloured product. The hydrazone formed absorbed visible light strongly and optimal detector response was obtained at a wavelength of 470 nm with a molar absorptivity of 3.652 × 103 l mol−1 cm−1. Optimization of temperature and time revealed 30 °C and 10 min as the best conditions for optimal color formation, while methanol was found to be the most suitable alcohol as diluting solvent. The reaction product is stable for at least 24 h. Beer’s law was obeyed in the concentration range of 2–10 μg ml−1. Recovery studies over three days gave a mean recovery of 101.87% with a relative standard deviation of 1.29%. There was no interference from commonly used tablet excipients. There was no significant difference between the results obtained with the new method and the BP iodimetric method (p > 0.05). The proposed method is simple, sensitive, rapid and economical, and could find application as an in-process quality control method for hydralazine.

Novel colorimetric sensors for cyanide based on azo-hydrazone tautomeric skeletons

The monoazo dyes, 4-carboxyl-2, 6-dinitrophenylazohydroxynaphthalenes dyes (AZ-01, AZ-03 and AZ-04), were evaluated as a highly selective colorimetric chemosensor for cyanide ion. The recognition of cyanide ion gave an obvious colour change from light yellow to brownish red and upon dilution with acetone produced a purple to lilac colour. Optimum conditions for the reaction between the azo dyes and cyanide ion were established at 30°C for 5 min, and different variables affecting the reaction were carefully studied and optimised. Under the optimum conditions, linear relationships between the CN(-) concentrations and light absorption were established. Using these azo-hydrazone molecular switch entities, excellent selectivity towards the detection of CN(-) in aqueous solution over miscellaneous competitive anions was observed. Such selectivity mainly results from the possibility of nucleophilic attack on the azo-hydrazone chemosensors by cyanide anions in aqueous system, which is not afforded by other competing anions. The cyanide chemosensor method described here should have potential application as a new family probes for detecting cyanide in aqueous solution.

A dual-purpose silver nanoparticles biosynthesized using aqueous leaf extract of Detarium microcarpum: An under-utilized species

The need for green synthesis of emerging industrial materials has led to the biosynthesis of nanoparticles from plants to circumvent the adverse by-products of chemical synthesis. In this study, the leaf extract of Detarium mirocarpum Guill & Perr, a small tree belonging to the family Fabaceae (Legume), was used to synthesize silver nanoparticles (DAgNPs). DAgNPs were characterized using spectroscopic techniques (Ultraviolet-Visible spectroscopy and Fourier Transform Infrared spectroscopy) which showed hydroxyl and carbonyl functional groups to be responsible for their synthesis. DAgNPs were observed to be crystalline and spherical. The average size, determined by transmission electron microscopy (TEM) was 17.05nm. The antioxidant activity of DAgNPs ranked from moderate to good. The ability of DAgNPs to sense Hg(2+) and Fe(3+) ions in aqueous medium was also investigated. The quenching of the SPR peak at 430nm was used to monitor the toxic and heavy metal ions with linear ranges of 20-70µgmL(-1) and 10-40µgmL(-1) for Hg(2+) and Fe(3+), respectively. The limit of detection (LOD) and limit of quantification (LOQ) obtained for Hg(2+) was 2.05µgmL(-1) and 6.21µgmL(-1), respectively and for Fe(3+) was 5.01µgmL(-1) and 15.21µgmL(-1), respectively. The intra- and inter-day assessments of accuracy and repeatability gave relative errors less than 1% in all instances. DAgNPs can therefore provide a convenient method of sensing the toxic metals easily.

A new spectrophotometric method for the determination of nadolol

A new spectrophotometric method has been developed for the assay of nadolol in pure form and in tablets. The assay procedure is based on a derivatization methodology employing 4-carboxyl-2,6-dinitrobenzene diazonium ion (CDNBD) as a diazo coupling reagent. The azo dye formed between nadolol and CDNBD absorbed visible light at the wavelength maximum of 416 nm (λmax) demonstrating a bathochromic shift from the absorption maximum of nadolol. Optimization studies established an optimal reaction time of 10 min at 60 °C. The assays were linear over 1.25–10 μg ml−1 of nadolol, and the reaction occurred by a 3:1 reagent/drug stoichiometric ratio. The method is found to be selective and has a lower detection limit of 0.29 μg ml−1. Recovery studies over three days gave mean recovery of 101.4% (RSD 3.0%). This new method has been successfully applied in the determination of nadolol and nadolol/bendroflumethiazide tablets with accuracy and precision similar to the official (USP) HPLC procedure (p > 0.05). The new procedure has the advantages of high sensitivity, lower limit of detection and could find application as an in-process quality control method for nadolol.

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

BackgroundA 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.ResultsNifedipine 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).ConclusionsThe 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.

Spectrophotometric determination of metronidazole and tinidazole via charge transfer complexation using chloranilic acid

A new spectrophotometric method was developed for the determination of two important nitroimidazoles; metronidazole (MZ) and tinidazole (TZ). The method was based on the charge-transfer (CT) complexation reaction of reduced forms of metronidazole and tinidazole as n-electron donors and chloranilic acid (CAA) as π-electron acceptor to form a purple-colored complex with a new absorption band at 520 nm which was adopted as the analytical wavelength. Molar absorptivities of 2.741 × 102 L M−1 cm-1 and 2.681 × 102 L M−1 cm−1 were obtained for MZ and TZ, respectively. Optimization of reducing agent and time of reduction revealed the superiority of metal hydrides over reducing metals. Reduction of MZ and TZ was completed at 30 °C within 10 min. Optimizations of temperature and time for the complexation reaction revealed that the reaction was completed at 30 °C within 5 min. A 60:40 mixture of 1,4-dioxane:acetonitrile was found to be the best diluting solvent for optimal detector response. The complexes were stable at room temperatures for weeks. Beer’s law was observed in the concentration of 5–40 ώg ml (MZ) and 4.8–79.2 ώg ml−1 (TZ) with low limits of detection of 1.88 and 0.74 ώg ml−1, respectively. Overall recoveries of MZ and TZ from quality control samples were 103.19 ± 2.05 (%RSD = 1.99, n = 12) and 101.63 ± 1.41 (%RSD = 1.39) over three days. There was no interference from commonly utilized tablet excipients. No significant difference existed between the results of the new method and the BP titrimetric procedures (p > 0.05). The new CT procedure described in this paper is simple, fast, convenient, accurate and precise and has the novelty of carrying out the reactions at room temperature compared to previously described procedures. The new method could be adopted as an alternative procedure for the quality assessment of MZ and TZ in bulk and dosage forms.

Spectrophotometric determination of olanzapine after condensation with p-dimethylaminobenzaldehyde

Abstract A new, simple, cost-effective spectrophotometric method was developed for the determination of olanzapine in pharmaceuticals. The new method is based on formation of a yellow condensation product with p-dimethylaminobenzaldehyde, followed by measurement of absorbance at 410 nm.

New spectrophotometric method for the determination of gabapentin in bulk and dosage forms using p-dimethylaminobenzaldehyde

ABSTRACT A new simple, accurate and economic spectrophotometric method based on azo dye derivatization for the determination of gabapentin (GBP) was developed. Critical factors were optimized. The method was validated and assay of dosage forms was done. Spot tests and TLC confirmed the formation of azo adduct. A 0.3 M NaNO2 solution using 2 M HCl was used for diazotization. The optimal temperature and time were 30°C and 10 min. Azo adducts were determined at 430 nm. Methanol was found to be the best solvent. Gabapentin coupled at a ratio of 1:1 with DMAB. The assays of GBP were linear over the range 1–6 µg/mL (r = 0.9973) and LOD of 0.8322 µg/mL. The methods were accurate (error < 2%) and precise (RSD < 0.5%). The methods were successfully applied to the assay of GBP in dosage forms and compared favorably with reference method (p > .05). The successful diazotization of gabapentin and the azo adduct formation with DMAB is reported for the first time.