Mean centering of ratio spectra as a new method for determination of rate constants of consecutive reactions

Multi-spectroscopic assay methods for concurrent determination of recent anti-gout combination, a comparative study

Recently, Chemometric calibration methods in spectrophotometric analysis are achieving significant attention in the quality control of resolving drug mixtures and pharmaceutical formulations containing two or more drugs with overlapping spectra. The simple univariate methods have been used over the last few decades and has proven to be highly efficient and easy to apply. In this study, a comparative study was performed between some univariate and multivariate methods to determine if chemometric methods can substitute univariate methods in pharmaceutical analysis. In this study, three chemometric techniques were compared to seven univariate techniques to resolve a mixture of mefenamic acid and febuxostat in their raw materials, dosage forms and spiked human plasma. Mefenamic acid and febuxostat were used together for treatment of gout. The applied chemometric methods are partial least squares (PLS), artificial neural network (ANN) and genetic algorithm partial least squares (GA-PLS), while the used univariate methods include first derivative, second derivative, ratio spectra, derivative ratio spectra, ratio subtraction, Q-Absorbance ratio and mean centering spectrophotometric methods. The ten proposed methods were found to be green, sensitive, and rapid. They are simple and did not require any pre-separation steps. The results of both univariate and multivariate approaches were statistically compared with the reported spectrophotometric methods using student's t test and ratio variance F-test. They were also compared with each other, using one-way analysis of variance (ANOVA). These methods were assessed and validated according to ICH guidelines. The studied drugs were analyzed in their pharmaceutical dosage forms and spiked human plasma with good recoveries using the developed methods, which qualify them for routine quality control of the studied drugs.

Three Smart and Original Spectrophotometric Data Processing Ratio Techniques for Resolving the Partial Overlapped Spectra of the Binary Antiviral Mixture Daclatasvir/Sofosbuvir: Application to Combined Dosage Form Darvoni® Tablets

BACKGROUND

The combination of Daclatasvir (DCV) and sofosbuvir (SFV) is now widely used as an ideal treatment for hepatitis C virus infection. For this purpose, simple, sensitive, rapid and smart spectrophotometric methods were developed and validated for the determination of these drugs in their combined dosage form.

OBJECTIVE

Development οf smart, sensitive, cheap spectrοphοtοmetric methοds fοr determinatiοn (DCV) and (SFV) in their combined dosage.

METHODS

Ratio subtraction (RS) and amplitude modulation (AM) and mean centering spectrophotometric methods were established and validated for the estimation of sofosbuvir (SFV) in existence of daclatasvir without previous separation, utilizing unified regression equation.

RESULTS

A linearity limit of 2.5-25.0 µg/mL was confirmed for the direct measurement of daclatasvir at 316 nm (because there is no interference from sofosbuvir). Linearity was confirmed over a concentration limit of 10.0-80.0 µg/mL for sofosbuvir. The current methods were established as stated by the ICH recommendations and by testing synthetic mixtures of both drugs, the specificity was examined. They were tested on their tablet dosage form and good recovery was obtained.

CONCLUSIONS

The current methods were tested on their tablet dosage form and good recovery was obtained. A statistical study has been established among the current ratio approaches and a published methods and there was no apparent statistical variation was obtained.

HIGHLIGHTS

Both antiviral agents can be quantified in existence of each other by the current methods, which is a great time and cost-saving valor of the developed methods. This valor is even more important in the case of the combined dosage form (Darvoni® tablets) to the pharmaceutical market.

A critical examination of the DPPH method: Mistakes and inconsistencies in stoichiometry and IC50 determination by UV-Vis spectroscopy

The DPPH method has been reported with misconceptions in a large number of studies, thus precluding comparison of results. Attention is drawn to a common mistake in the unit used to express the IC₅₀ of ascorbic acid and other antioxidant substances. Concentration of the antioxidant is widely misused with a total disregard for the DPPH^• concentration, while the molar ratio of antioxidant/DPPH^• would be the correct choice. Data from 26 studies with widely varying IC₅₀ values were renormalized according to reaction stoichiometry, resulting in values which are more coherent and closer to the ideal one of 0.25 for at least 15 of them. In addition, the model which is currently being used to calculate the DPPH^• concentration can lead to an overestimation of around 7%, as it does not take into account the small contribution of the reaction product. In view of that, we present a mathematical model to correct the overestimation of the DPPH^• concentration.

Application of magnetic ion imprinted polymers for simultaneous quantification of Al3+ and Be2+ ions using the mean centering of ratio spectra method

Magnetic solid-phase extraction (MSPE) coupled with the spectrophotometric method for the simultaneous quantification of aluminum and beryllium ions based on mean centering of ratio (MCR) method is reported in the current work, for the first time. Two new magnetic ion-imprinted polymers (MIIPs) were synthesized using Chrome Azurol S as the ligand, (3-aminopropyl)triethoxysilane (APTES) as the functional monomer, tetraethyl orthosilicate (TEOS) as the cross-linker, and aluminum and beryllium ions as the templates, and used as magnetic sorbents. The characteristic properties of MIIPs were investigated using FT-IR spectroscopy, field emission scanning electron microscopy (FE-SEM), low angle X-ray powder diffraction (XRD), and energy-dispersive x-ray spectroscopy (EDS). Through this study, factors influencing the MSPE were studied and optimized. The proposed method exhibited good performance, with the linearity of 5.0-50.0 ng mL^-1 for aluminum ion and 2.0-40.0 ng mL^-1 for beryllium ion as well as the detection limits (DLs) of 3.2 and 0.9 ng mL^-1 for aluminum and beryllium ions, respectively. At the end of the study, the capability of the developed method for determination of target analytes was evaluated by its application in the tap and river water samples.

A comparative study of ICH validated novel spectrophotometric techniques for resolving completely overlapping spectra of quaternary mixtures

A pharmaceutically marketed mixture of Yohimbine, Alpha-tocopheryl acetate, Niacin, and Caffeine co-formulated as a promising therapy for erectile dysfunction. Simultaneous determination of the aforementioned pharmaceutical formulation without prior separation steps was applied using mean centering of ratio spectra and triple divisor spectrophotometric methods. Mean centering of ratio spectra method depended on using the mean centered ratio spectra in three successive steps which eliminated the derivative steps and so the signal to noise ratio was improved. The absorption spectra of the prepared solutions were measured in the wavelength range of 215-300 nm in the concentration ranges of 1-15, 3-15, 1-20, and 3-15 μg mL(-1) for Yohimbine, Alpha-tocopheryl acetate, Niacin, and Caffeine, respectively. The amplitudes of the mean centered third ratio spectra were measured at 250 nm and 268 nm for Yohimbine and Alpha-tocopheryl acetate, respectively and at peak to peak 272-273 and 262-263 nm for Niacin and Caffeine, respectively. In triple divisor method each drug in the quaternary mixture was determined by dividing the spectrum of the quaternary mixture by a standard spectrum of a mixture containing equal concentrations of the other three drugs. First derivative of these ratio spectra was obtained where determination could be achieved without any interference from the other three drugs. Amplitudes of 1-15, 3-15, 1-15, and 3-15 μg mL(-1) were used for selective determination of Yohimbine, Alpha-tocopheryl acetate, Niacin, and Caffeine, respectively. Laboratory prepared mixtures were analyzed by the developed novel methods to investigate their selectivity also, Super Act® capsules were successfully analyzed to ensure absence of interference from additives. The developed methods were validated according to the ICH guidelines. The proposed methods were statistically compared with each other and with the reported methods; using student t-test, F-test, and one way ANOVA, where no significant difference was found with respect to accuracy and precision.

A novel pure component contribution algorithm (PCCA) for extracting components' contribution from severely overlapped signals; an application to UV-spectrophotometric data

A novel, simple and accurate algorithm capable of extracting the contribution of each component from a mixture signal where the components are completely overlapped was developed. It is based on the development of a coded function which eliminates the signal of interfering components using mean centering as a processing tool; finally the pure contribution of each component is extracted. The algorithm allows the determination of each component as a single one. It was validated by the use of simulated data set of three overlapped signals and tested against simulated random noise. Two fit values were developed and calculated for optimization, one to test that that the absorptivity values of the extracted spectra are within the confidence limits of the slope and the other is the correlation between the pure and extracted spectra. It has been successfully applied to real UV data of binary mixture of Ibuprofen and Paracetamol and ternary mixture of Amiloride hydrochloride, Atenolol and Hydrochlorothiazide in tablets and capsules, respectively. The results were compared to previously reported separation method and no significant difference was found regarding both accuracy and precision.

Novel spectrophotometric determination of flumethasone pivalate and clioquinol in their binary mixture and pharmaceutical formulation

This work is concerned with development and validation of three simple, specific, accurate and precise spectrophotometric methods for determination of flumethasone pivalate (FP) and clioquinol (CL) in their binary mixture and ear drops. Method A is a ratio subtraction spectrophotometric one (RSM). Method B is a ratio difference spectrophotometric one (RDSM), while method C is a mean center spectrophotometric one (MCR). The calibration curves are linear over the concentration range of 3-45 μg/mL for FP, and 2-25 μg/mL for CL. The specificity of the developed methods was assessed by analyzing different laboratory prepared mixtures of the FP and CL. The three methods were validated as per ICH guidelines; accuracy, precision and repeatability are found to be within the acceptable limits.

A study of selective spectrophotometric methods for simultaneous determination of Itopride hydrochloride and Rabeprazole sodium binary mixture: Resolving sever overlapping spectra

Itopride hydrochloride (IT) and Rabeprazole sodium (RB) are co-formulated together for the treatment of gastro-esophageal reflux disease. Three simple, specific and accurate spectrophotometric methods were applied and validated for simultaneous determination of Itopride hydrochloride (IT) and Rabeprazole sodium (RB) namely; constant center (CC), ratio difference (RD) and mean centering of ratio spectra (MCR) spectrophotometric methods. Linear correlations were obtained in range of 10-110μg/μL for Itopride hydrochloride and 4-44μg/mL for Rabeprazole sodium. No preliminary separation steps were required prior the analysis of the two drugs using the proposed methods. Specificity was investigated by analyzing the synthetic mixtures containing the two cited drugs and their capsules dosage form. The obtained results were statistically compared with those obtained by the reported method, no significant difference was obtained with respect to accuracy and precision. The three methods were validated in accordance with ICH guidelines and can be used for quality control laboratories for IT and RB.

Novel spectrophotometric methods for simultaneous determination of timolol and dorzolamide in their binary mixture

Two smart and novel spectrophotometric methods namely; absorbance subtraction (AS) and amplitude modulation (AM) were developed and validated for the determination of a binary mixture of timolol maleate (TIM) and dorzolamide hydrochloride (DOR) in presence of benzalkonium chloride without prior separation, using unified regression equation. Additionally, simple, specific, accurate and precise spectrophotometric methods manipulating ratio spectra were developed and validated for simultaneous determination of the binary mixture namely; simultaneous ratio subtraction (SRS), ratio difference (RD), ratio subtraction (RS) coupled with extended ratio subtraction (EXRS), constant multiplication method (CM) and mean centering of ratio spectra (MCR). The proposed spectrophotometric procedures do not require any separation steps. Accuracy, precision and linearity ranges of the proposed methods were determined and the specificity was assessed by analyzing synthetic mixtures of both drugs. They were applied to their pharmaceutical formulation and the results obtained were statistically compared to that of a reported spectrophotometric method. The statistical comparison showed that there is no significant difference between the proposed methods and the reported one regarding both accuracy and precision.

Toward bioinspired nanostructures for selective vapor sensing: diverse vapor-induced spectral responses within iridescent scales of Morpho butterflies

The iridescent colors of Morpho butterflies have captured scientific intrigue for over a century. However, only recently photonic structures of the wing scales of Morpho butterflies have inspired new ideas in the diverse areas of technology including sensing. In this study, we performed theoretical and experimental evaluation of vapor-induced reflectance changes of the Morpho scales. These experiments provided additional details of the origin and the magnitude of vapor response selectivity in these natural photonic nanostructures and facilitated our design and fabrication of highly selective biomimetic photonic nanostructures.

Resolution of five-component mixture using mean centering ratio and inverse least squares chemometrics

BACKGROUND

A comparative study of the use of mean centering of ratio spectra and inverse least squares for the resolution of paracetamol, methylparaben, propylparaben, chlorpheniramine maleate and pseudoephedrine hydrochloride has been achieved showing that the two chemometric methods provide a good example of the high resolving power of these techniques. Method (I) is the mean centering of ratio spectra which depends on using the mean centered ratio spectra in four successive steps that eliminates the derivative steps and therefore the signal to noise ratio is improved. The absorption spectra of prepared solutions were measured in the range of 220-280 nm. Method (II) is based on the inverse least squares that depend on updating developed multivariate calibration model. The absorption spectra of the prepared mixtures in the range 230-270 nm were recorded.

RESULTS

The linear concentration ranges were 0-25.6, 0-15.0, 0-15.0, 0-45.0 and 0-100.0 μg mL-1 for paracetamol, methylparaben, propylparaben, chlorpheniramine maleate and pseudoephedrine hydrochloride, respectively. The mean recoveries for simultaneous determination were between 99.9-101.3% for the two methods. The two developed methods have been successfully used for prediction of five-component mixture in Decamol Flu syrup with good selectivity, high sensitivity and extremely low detection limit.

CONCLUSION

No published method has been reported for simultaneous determination of the five components of this mixture so that the results of the mean centering of ratio spectra method were compared with those of the proposed inverse least squares method. Statistical comparison was performed using t-test and F-ratio at P = 0.05. There was no significant difference between the results.

Comparative study of novel spectrophotometric methods manipulating ratio spectra: an application on pharmaceutical ternary mixture of omeprazole, tinidazole and clarithromycin

Three simple, specific, accurate and precise spectrophotometric methods manipulating ratio spectra are developed for simultaneous determination of omeprazole (OM), tinidazole (TN) and clarithromycin (CL) in tablets. Method A, is an extended ratio subtraction one (EXRSM). Method B is a ratio difference spectrophotometric one (RDSM), while method C is mean centering of ratio spectra (MCR). The calibration curves are linear over the concentration range of 1-20 μg/mL, 10-60 μg/mL and 0.25-1.0 mg/mL for OM, TN and CL, respectively. The specificity of the developed methods is investigated by analyzing laboratory prepared mixtures of the three drugs and their combined dosage form. Standard deviation values are less than 1.5 in the assay of raw materials and tablets. The three methods are validated as per ICH guidelines and accuracy, precision, repeatability and robustness are found to be within the acceptable limits.

Stability-indicating methods for the determination of mosapride citrate in the presence of its degradation products according to ICH guidelines

In the present work, different spectrophotometric methods and one spectrofluorimetric method have been developed and validated for the determination of mosapride citrate in the presence of its acid-induced degradation products. The drug was subjected to stress stability study including acid, alkali, oxidative, photolytic, and thermal stress degradation. The developed spectrophotometric methods included the use of first order derivative ((1)D), derivative of ratio spectra ((1)DD), mean centring of ratio spectra (MC) and H-point standard additions (HPSAM) spectrophotometric methods. For (1)D method, the peaks amplitudes at 282.8 and 319.6 nm were measured, while for (1)DD method those at 308 nm and 323 nm were measured. Mean centring of ratio spectra method used the values at 317 nm for calibration, while for HPSAM the absorbance at 273 and 288.6 nm were used. These methods were successfully applied for determination of mosapride in the concentration range of 5-70 µg.ml(-1). The spectrofluorimetric method was based on measuring the native fluorescence of mosapride in 0.1 M NaOH using λ(excitation) 276 nm and λ(emission) 344 nm and 684 nm with linearity ranges of 50-3000 ng.ml(-1) and 50-9000 ng.ml(-1), respectively. All the developed methods were validated according to the International Conference on Harmonization (ICH) guidelines and were applied for bulk powder and dosage form. The results obtained were statistically compared to each other using one-way ANOVA testing.