Different applications of isosbestic points, normalized spectra and dual wavelength as powerful tools for resolution of multicomponent mixtures with severely overlapping spectra

Agglomeration compaction promotes corrosion of gold nanoparticles

Engineered nanoparticles are increasingly being used in various areas of human activity. However, the degradation mechanism of nanobodies in harsh environments is still a puzzle for theory and experiment. We report here the results of optical spectroscopy and nanoparticle tracking analysis, quantifying agglomeration and sizing of 50 nm citrate stabilized gold nanoparticles (GNPs) in HCl solutions containing H2O2. The mechanism of a consecutive corrosion reaction of GNPs is discussed within the framework of the near-field approach. We found that the disappearance of single nanoparticles from a suspension does not occur due to their dissolution per se, but is a consequence of the formation of aggregates. The neutralization of electrostatic shielding at high ionic strength allows gold nanoparticles to approach the subnanometer distance within the region of capping defects, at which the Casimir and van der Waals attractive forces dominate. It is suggested that electric field fluctuations in the confined space between highly conductive gold nanoparticles cause complexant-stimulated loss of metal from the core in the contact area. Going beyond the charge screening limitations by constraining the reaction space and reducing the double electrical layer thickness allows for chemical processes flow along otherwise not accessible reaction pathways.

Simultaneous determination of meloxicam and bupivacaine via a novel modified dual wavelength method and an advanced chemometric approach

This study presents two spectrophotometric methods; a novel dual wavelength-derivative spectrophotometry and multivariate curve resolution-alternating least squares (MCR-ALS) for the simultaneous determination of a fixed dose combination of bupivacaine (BUP) and meloxicam (MEL) in a ratio of 30:1. The extended UV spectrum of MEL enables its direct determination at λmax 360 nm with no interference from BUP. The determination of BUP was unfeasible directly because the UV spectra of both drugs are moderately overlapped over the wavelength range of 250-450 nm, thus new chemometric based spectrophotometric methods should be developed for its determination. Dual wavelength-derivative method was employed based on using first derivative spectra. The selected dual wavelengths for determination BUP were 274.6 nm and 374.6 nm where the dA/dλ amplitudes differences for MET are equal to zero. MCR-ALS is advanced chemometric tool that enables analysis of multicomponent samples in complex matrices with high resolution based on the decomposition of signal/spectral data into the pure spectra and corresponding concentration profile. The figures of merits for MCR model show that there is a good agreement between the actual and predicted concentrations for MEL and BUP. The methods were validated and statistically compared with a reported HPLC method.

Simultaneous Determination of Montelukast Sodium and Loratadine by Eco-Friendly Densitometry and Spectrophotometric Methods

Recently, the aim of analytical community is to reduce the usage of hazardous chemicals; so eco-friendly, rapid, selective and cost-effective methods were developed for simultaneous determination of montelukast sodium (MKT) and loratadine (LRT). The first method was based on chromatographic separation performed on precoated silica gel 60 GF254 plates with ethyl acetate-ethanol 9: 1 (v/v) as the mobile phase. The developed plates were scanned and quantified at 260 nm. The method gives linear correlation over concentration ranges of 0.3-3.6 μg/spot and 0.2-4.0 μg/spot for MKT and LRT, respectively. It was also successfully applied to analysis of both drugs in their pharmaceutical preparation and human plasma. The other methods are UV-spectrophotometric methods based on smart spectra manipulating to zero order spectrum of each drug. These methods are named response correlation (RC), a-centering and ratio derivative methods. RC and a-centering methods were dependent on the presence of an isosbestic point between the overlapped spectra of both drugs. While ratio derivative method based on manipulation of the ratio spectra of both drugs. The two drugs obey Beer-Lambert law over the concentration ranges of 3.0-30.0 μg/mL in the three spectrophotometric methods. Moreover, the greenness of the developed methods is assessed using suitable analytical Eco-Scale and Green Analytical Procedure Index.

Three new, UV spectrum filtration protocols for the synchronous quantification of ciprofloxacin HCl and ornidazole in the existence of ciprofloxacin-induced degradation compound

Three new spectrum filtration protocols have been developed and adapted to overcome some difficulties in dealing with highly overlapping triple drug mixtures by proposing new smart mathematical techniques that facilitate the resolution of the ternary mixture and the recovery of a filtrated zero-order spectrum (D0 spectrum) of each component without any overlapping from the accompanying components. The three established spectrophotometric protocols were conducted on the combination of ciprofloxacin hydrochloride and ornidazole as a green alternative to the usual chromatographic technique: the first protocol is ratio difference-isosbestic points coupled with ratio difference-areas under the curve (RD-ISO/RD-AUC); the second protocol is ratio difference-isosbestic points coupled with dual-wavelength equation (RD-ISO/DWE); and the third protocol is signal retrieval by zero-crossing point (SRZ). All three developed protocols have the power to recover a filtrated zero-order spectrum of each ornidazole and ciprofloxacin hydrochloride without any involvement from the ciprofloxacin-induced degradation substance through processing their spectral data either in the zero-order spectrum, ratio spectrum, or derivative spectrum. The correctness of the spectral filtration process for each protocol was checked by involving the spectral print recognition index to ensure the drug's purity and freeness from impurities or degradation products. The validation process was performed as per the directions of ICH, which confirmed the effectiveness of the elaborated protocols and their usability as daily analysis methods with a linearity range of (3.5-15 μg/ml) for ciprofloxacin in (RD-ISO/RD-AUC) and (RD-AUC/DWE) protocols and (1.5-15 μg/ml) in (SRZ) protocol; and a linearity range of (3-20 μg/ml) for ornidazole in (RD-ISO/RD-AUC) and (SRZ) protocols and (3-15 μg/ml) in (RD-ISO/DWE) protocol. A statistical comparison and greenness evaluation utilizing NEMI, AGREE, GAPI, and CALIFICAMET-HEXAGON tools were made with the reference approach, confirming no statistical variations and a better greenness profile for the newly established protocols.

UV spectrophotometric methods for simultaneous determination of ketorolac tromethamine and olopatadine hydrochloride: Application of multiple standard addition for assay of ophthalmic solution

Ophthalmic preparations that contain ketorolac tromethamine (KET) and olopatadine HCl (OLO) are used to relieve seasonal allergies and allergic conjunctivitis. Simultaneous quantification of KET and OLO was held by validated and simple spectrophotometric methods. KET was determined directly from the fundamental UV absorption spectra (at 323 nm), while OLO was determined after performing either dual wavelength or ratio derivative methods. The first method was based on measuring the absorbance difference (ΔA) between 243 and 291 nm, while the second depended on generating first derivative ratio spectra using 3.0 µg/mL KET as a divisor and measuring OLO responses at 234 nm (minima). Multiple standard addition method was applied to enable the determination of OLO which is considered as the weakly absorbing species as well as the minor component in a challenging dosage form ratio (4:1). The linearity ranges of the developed methods were 3-12 μg/mL and 4-40 μg/mL for KET and OLO, respectively. Simultaneous determination of both drugs was successfully implemented to lab prepared eye drops that contain KET, OLO and benzalkonium chloride as an inactive ingredient. Greenness assessment indicates minimal impact on environment. The developed methods determined the cited drugs with % recovery ± SD of 99.63 ± 0.01 for KET, 100.90 ± 0.02 and 100.31 ± 0.01 for OLO using dual wavelength and first derivative ratio methods, respectively. Using F-test and t-test at confidence level %95 to compare between the results of the presented methods and a reported method show no significant difference which allows precise, accurate, rapid, and simple quantification of quality control samples that contain KET and OLO.

Effective spectrophotometric methods for resolving the superimposed spectra of Diclofenac Potassium and Methocarbamol

The UV spectra of Diclofenac Potassium DIC and Methocarbamol MET are superimposed making their analysis using direct or derivative spectrophotometric methods quite complicated. This study presents four effective spectrophotometric methods that enable simultaneous determination of both drugs without interference. The first method is based on application of simultaneous equation method on their zero order spectra where DIC has shown absorbance maxima at 276 nm and MET displays two absorbances maxima at 273 nm and 222 nm in distilled water. The second method relies on dual wavelength method, the two wavelengths (232 and 285 nm) were chosen for determination of DIC where the absorbance differences at these wavelengths are proportional to DIC concentration while the absorbance differences of MET are equal to zero. For the determination of MET, the two wavelengths (212 and 228 nm) were selected. The third method of first-derivative ratio has been applied where the derivative ratio absorbances of DIC and MET were measured at 286.1 and 282.4 nm, respectively. The fourth method utilizing ratio difference spectrophotometric (RD) method was eventually performed on the binary mixture. The amplitude difference between the two wavelengths (291and 305 nm) was calculated for DIC estimation while the amplitude difference between the two wavelengths (227and 273 nm) for MET determination. All methods show linearity range from 2.0-25 μg. mL^-1 and 6.0-40 μg. mL^-1 for DIC and MET respectively. The developed methods have been statistically compared with a reported method based on first derivative method and the results of statistical comparison confirm the accuracy and precision of the proposed methods therefore they can be effectively applied for determination of MET and DIC in pharmaceutical dosage form.

Quality Data from Messy Spectra: How Isometric Points Increase Information Content in Highly Overlapping Spectra

Spectroscopic techniques are immensely useful for obtaining information about chemical transformations while they are happening. However, such data are often messy, and it is challenging to extract reliable information from them without careful calibrations or internal standards. This short introductory review discusses how isometric points (points in a spectrum where the signal intensity remains constant throughout the progress of a chemical transformation) can be used to derive high-quality data from messy spectra. Such analyses are helpful in a variety of (bio-)chemical settings, as selected case studies demonstrate.

Theoretical and Experimental Investigation of Autoxidation Propensity of Selected Drugs in Solution State

The C-H bond dissociation energy (BDE) of drug molecules is often used to estimate their relative propensities to undergo autoxidation. BDE calculations based on electronic structures provide a convenient means to estimate the risk for a given compound to degrade via autoxidation. This study aimed to verify the utility of calculated C-H BDEs of a range of drug molecules in predicting their autoxidation propensities, in the solution state. For the autoxidation study, 2,2'-azobis (2-methylpropionitrile) was employed as the solution state stressor, and the experimental reaction rate constants were determined employing ultraperformance liquid chromatographic (UPLC) methods. Reaction rates in the solution state were compared to the calculated C-H BDE values of the respective compounds. The results indicated a poor correlation for compounds in the solution state, and their relative stabilities could not be explained with C-H BDE. On the other hand, a favorable relationship was observed between the relative extent of ionization and the autoxidation rates of the selected compounds. In the solution state, factors such as the type and extent of drug ionization, degree and type of solvation have been shown to contribute to differences in reactivity. By applying the computational method involving the effect of H-atom abstraction and potential ionization sites in the molecule, the calculated C-H BDE should relate better to the experimental autoxidation rates.

Screening Autoxidation Propensities of Drugs in the Solid-State Using PVP and in the Solution State Using N-Methyl Pyrrolidone

Oxidative degradation of drugs is one of the major routes of drug substance and drug product instability. Among the diverse routes of oxidation, autoxidation is considered to be challenging to predict and control, potentially due to the multi-step mechanism involving free radicals. C–H bond dissociation energy (C–H BDE) is evidenced to be a calculated descriptor shown to predict drug autoxidation. While computational predictions for the autoxidation propensity of drugs are both swift and possible, no literature to date has highlighted the relationship between the computed C–H BDE and the experimentally-derived autoxidation propensities of solid drugs. The objective of this study is to investigate this missing relationship. The present work is an extension to the previously reported novel autoxidation approach that involves subjecting a physical mixture of pre-milled polyvinyl pyrrolidone (PVP) K-60 and a crystalline drug under high temperature and pressurized oxygen setup. The drug degradation was measured using chromatographic methods. An improved trend between the extent of solid autoxidation and C–H BDE could be observed after normalizing the effective surface area of drugs in the crystalline state, pointing to a positive relationship. Additional studies were conducted by dissolving the drug in N-methyl pyrrolidone (NMP) and exposing the solution under a pressurized oxygen setup at diverse elevated temperatures. Chromatographic results of these samples indicated a similarity in the formed degradation products to the solid-state experiments pointing to the utility of NMP, a PVP monomer surrogate, as a stressing agent for faster and relevant autoxidation screening of drugs in formulations.

Induced mathematical filtration as an innovative strategy for discrimination and estimation of glycemic control drugs in fixed dose combination

An innovative strategy was developed for the estimation of a fixed dose combination containing Alogliptin (ALO) and pioglitazone (PIO) using induced concept for resolving the overlapped spectra, lacking isoabsorptive point. This strategy is based on coupling factors as numerical values or ratios as spectrum form with the recorded signals leading to induced mathematical filtration of the drug of interest and complete elimination of the interfering one in the combination without prior physical separation. The calculated factors were factor of equality in induced dual wavelength (IDW) or absorptivity factor in induced concentration subtraction method (ICS) while absorptivity ratio spectrum for induced amplitude modulation method (IAM). The calibration curves displayed linearity within 1.0–16.0 μg/mL for ALO and 2.0–22.0 μg/mL for PIO with good correlation coefficients. The induced methods specificity was also assured through the assaying different synthetic mixtures prepared to contain the two drugs in ratios approaching the ratio actually found in the marketed dosage form. The methods were applicable and suitable for estimating ALO and PIO in both bulk form and their fixed dose combination. Induced methods have been extensively validated in accordance with ICH guidelines and results demonstrated the accuracy and reproducibility in comparison to the reported method.

A comparative study of two novel validated spectrophotometric techniques for resolution of four-component mixtures with severely overlapping spectra

Two new smart spectrophotometric methods are developed and validated for the determination of the quatertnary mixture of paracetamol (acetaminophen), diphenhydramine, p-aminophenol, and N-oxide degradate of diphenhydramine. Method A is the novel triple divisor ratio difference method, where the triple divisor ratio spectrum of the component of interest shows a significant amplitude difference at two selected wavelengths where the three interfering substances are used as triple divisor and give constant amplitude all over the spectrum. The triple divisors are normalized spectra of tertiary mixtures containing 40 μg/mL of each of the 3 interfering components. The selected wavelengths are 256-290 nm, 220-230 nm, 230-245 nm and 275-260 nm for the 4 components, respectively. Method B is double divisor - ratio difference-dual wavelength, where the double divisor ratio spectrum of the component of interest shows a significant amplitude difference at two selected wavelengths where two interfering substances are used as double divisor and give constant amplitude all over the spectrum, while the third one shows zero amplitude difference at these two selected wavelengths. The double divisors used are normalized spectra of diphenhydramine /N-oxide degradate of diphenhydramine binary mixture for both paracetamol and p-aminophenol and paracetamol/p-aminophenol binary mixture for both diphenhydramine hydrochloride and its N-oxide degradate. The double divisors binary mixtures contain 40 μg/mL of each component. The selected wavelengths are 243-233 nm, 223.8-270.2 nm, 237-250 nm and 265-234.6 nm for the 4 compounds, respectively. Both methods were successfully applied for the quantification of the four components in laboratory prepared quaternary mixtures and for the quantification of paracetamol and diphenhydramine hydrochloride in panadol night® tablets. The results obtained by the developed methods were compared with those obtained by the United State Pharmacopeial method for the analysis of paracetamol and diphenhydramine, where no significant differences were found.

Successive Stability Indicating Spectrophotometric Technique for Simultaneous Determination of Quetiapine Fumarate and its Three Major Related Compounds

Background:

Quetiapine Fumarate (QTF) is an atypical antipsychotic drug used to treat mental disorders as depression and schizophrenia. The analysis of the dug in the presence of its precursors, degradants and impurities without interference represents a challenge for the analysts. The regulatory requirements recommended by ICH stated that the impurities above or equal to 0.1% must be identified, characterized and determined. The aim of this work was to introduce three smart and selective spectrophotometric methods that could resolve the complete overlapping of QTF drug with its three related compounds; namely lactam (LAC), N-oxide (OXD) and des-ethanol (DES) without prior separation or extraction step.

Methods:

So far there is no spectrophotometric method reported in the literature for the analysis of QTF drug with its three related compounds without interference. The First derivative zero crossing (1D-ZC), Spectrum subtraction (SS), and Simultaneous derivative ratio (S1DD) are well-developed methods used for determination and resolution of multicomponent mixtures. While Ratio difference isosbestic point method is a new method that needs two isoabsorptive points for its application and was successfully adopted for simultaneous estimation of ternary mixtures.

Results:

The linearity range was found in the range of (6-50 μg/mL) for Quetiapine fumarate, (6-110 μg/mL) for lactam, (4-28 μg/mL) for N-oxide and (6-32 μg/mL) for Des-ethanol. The method validation was performed according to ICH guidelines. The results were statistically compared with a reported HPLC method and no significant difference was obtained.

Conclusion:

The presented spectrophotometric technique highlighted the significance of different tools such as normalized spectra and isoabsorptive points, especially when combined together for the determination and resolution of complex quaternary mixtures as that of QTF and its three major impurities. The proposed methods were smart, accurate and sensitive and were able to determine the four components showing sever overlap without prior separation. The proposed methods are rapid, cheap ecofriendly (green method) and didn’t require any sophisticated programs and could be easily adopted for the routine determination of complex multicomponent mixtures with minimum sample preparation.

A Smart Green Spectrophotometric Method for Simultaneous Determination of Severely Overlapped Binary Mixtures Using Normalized Spectrum and Isosbestic Point as Resolving Tools

Background:

The ability of the normalized spectra when used as a divisor and in combination with isosbestic point to resolve complex binary or ternary mixtures, Candesartan and Hydrochlorthiazide binary mixture was taken as a model.

Introduction:

A green simple smart and accurate method using ethanol as a solvent namely simultaneous derivative ratio (SIDD) was applied to prove the power of normalized spectra and isosbestic point as spectrophotometric resolving tools.

Methods:

In the proposed SIDD method, the zero order spectra of drugs were simply manipulated using the normalized spectra of CAN as divisor to obtain the ratio and first derivative spectra in two successive steps. Firstly, the total amplitude at isosbestic point 255.4 nm of the ratio spectra of the mixture was measured representing the total actual concentration of both drugs in the mixture. Then, the first derivative of the ratio spectra was obtained to determine Hydrochlorothiazide concentration at 233 nm. While the concentration of Candesartan was determined subsequently by subtracting the Hydrochlorothiazide concentration calculated after derivatization from the total concentration of both drugs obtained at the ratio spectra before the derivatization step.

Results:

The SIDD was successfully applied for simultaneous determination of both drugs in their pure form or in their binary mixture either in synthetic prepared mixtures or in combined dosage form the adopted method was validated according to the ICH guidelines and the results were found to be within the acceptable limits.

Conclusion:

The adopted method highlighted the important role of normalized spectrum when used as a divisor in addition to the importance of isosbestic point to resolve severely overlapped spectra. All the measurements were carried using ethanol which is considered one of the greenest solvents making the method an environmentally friendly one. the adopted method was validated according to the ICH guidelines and the results were found to be within the acceptable limits.

Fingerprint Spectrophotometric Methods for the Determination of Co-Formulated Otic Solution of Ciprofloxacin and Fluocinolone Acetonide in Their Challengeable Ratio

Six spectrophotometric methods were developed to determine a new single-dose otic solution known as "Otovel®," which consists of two components: the major one is ciprofloxacin (CIP) and the minor is fluocinolone acetonide (FLU). The ratio of (CIP) and (FLU) in Otovel® is 12 : 1, which is considered a challengeable ratio for UV determination. Thus, spectrum addition as a sample enrichment technique was required for the analysis of (FLU) low concentration. All these methods were capable of resolving the spectra for each component in D 0 belonging to the fingerprint resolution technique. The former absorptivity centering (a-centering) method was recently developed in 2018; it was effectively applied for its solution of both binary components in Otovel®, while another method, ratio subtraction (RS), is considered as an original resolution method that could be applied to determine only one component in mixtures. However, the other four methods that are related to their original method (RS) were extended ratio subtraction (EXRS), constant multiplication (CM), unified constant subtraction (UCS), and spectrum subtraction (SS). They were also easily applied for completing the quantification of binary mixture drugs present in Otovel®. The linearity ranges were found to be 3.0-15.0 μg/mL for (CIP) and (FLU), respectively. All results acquired from the proposed methods were successfully estimated according to ICH criteria and were statistically compared with official ones where no differences were noticed.

Three smart spectrophotometric methods for resolution of severely overlapped binary mixture of Ibuprofen and Paracetamol in pharmaceutical dosage form

Paracetamol is an analgesic-antipyretic drug and Ibuprofen is a non-steroidal anti-inflammatory drug. They are co-formulated as tablets to improve analgesia, to simplify prescribing and to improve patient compliance. Three accurate, simple and sensitive spectrophotometric methods were developed for the simultaneous determination of Paracetamol and Ibuprofen in their co-formulated dosage form. The first method was the ratio difference, which was based on the measurement of the difference in absorbance between the two wavelengths (210.6 and 216.4 nm) for Ibuprofen and (236.0 and 248.0 nm) for Paracetamol. The second method was constant center method which depends on using the constant found in the ratio spectra. The third method was the mean centering of ratio spectra which measured the manipulated values at 240 nm and 237 nm for Ibuprofen and Paracetamol, respectively. Beer’s law was obeyed in the concentration range of 2–50 μg/mL for Ibuprofen and 2–20 μg/mL for Paracetamol. The recovery % of the accuracy of both methods ranged from 99.64 to 100.56%. Factors affecting the resolution of the spectra were studied and optimized. The three methods are validated according to ICH guidelines and could be applied for the pharmaceutical preparation.

Dynamic Modelling of Phosphorolytic Cleavage Catalyzed by Pyrimidine-Nucleoside Phosphorylase

Pyrimidine-nucleoside phosphorylases (Py-NPases) have a significant potential to contribute to the economic and ecological production of modified nucleosides. These can be produced via pentose-1-phosphates, an interesting but mostly labile and expensive precursor. Thus far, no dynamic model exists for the production process of pentose-1-phosphates, which involves the equilibrium state of the Py-NPase catalyzed reversible reaction. Previously developed enzymological models are based on the understanding of the structural principles of the enzyme and focus on the description of initial rates only. The model generation is further complicated, as Py-NPases accept two substrates which they convert to two products. To create a well-balanced model from accurate experimental data, we utilized an improved high-throughput spectroscopic assay to monitor reactions over the whole time course until equilibrium was reached. We examined the conversion of deoxythymidine and phosphate to deoxyribose-1-phosphate and thymine by a thermophilic Py-NPase from Geobacillus thermoglucosidasius. The developed process model described the reactant concentrations in excellent agreement with the experimental data. Our model is built from ordinary differential equations and structured in such a way that integration with other models is possible in the future. These could be the kinetics of other enzymes for enzymatic cascade reactions or reactor descriptions to generate integrated process models.

Study of efficiency and spectral resolution for mathematical filtration technique using novel unlimited derivative ratio and classical univariate spectrophotometric methods for the multicomponent determination-stability analysis

Six simple, sensitive and selective spectrophotometric methods based on mathematical filtration technique are presented for concurrent determination of aceclofenac (ACE) and paracetamol (PAR) in presence of their degradation products, namely; diclofenac sodium (DIC) and 4-aminophenol (4-AP), respectively without preliminary physical separation procedures. This technique consists of several consecutive steps applied on built-in spectrophotometer software utilizing zero and/or derivative and/or ratio spectra of the studied components. These methods, namely, dual wavelength (DW), induced dual wavelength (IDW), derivative subtraction (DS) coupled with constant multiplication (CM), ratio difference method (RD), constant center method (CC) and the novel introduced unlimited derivative ratio method (UDD). This novel method has a very powerful competence for the analysis of the challengeable mixtures lacking zero crossing point. The linearity, accuracy and precision ranges of these methods were determined and validated as per ICH guidelines. Moreover, the specificity was checked by analyzing synthetic mixtures of both drugs. These methods were applied for the determination of the cited drugs in pharmaceutical formulation and a statistical comparison of the obtained results was made with each other and with those of reported spectrophotometric method. The comparison of the results of pure powder form showed that there is no significant difference between the proposed methods and the reported method regarding both accuracy and precision.

Novel manipulations of ratio spectra as powerful tools for resolution and quantitative determination of Pyridostigmine bromide and its' related substances; A comparative study

Resolution and quantitative determination of ternary mixture with severely overlapped spectra without any preliminary separation steps represents a big challenge for any analyst. Smart and novel spectrophotometric methods are continuously innovated for achieving the above mentioned target. Novel applications of ratio difference spectrophotometric technique utilizing ratio spectra and derivative ratio spectra are applied in presented work. The proposed methods included derivative ratio difference (DRD) and ratio subtraction ratio difference (RSRD) methods. Comparative study was achieved between the proposed methods and the recently developed induced ratio difference (IRD) method. The developed methods were assessed through the analysis of ternary mixtures with different ratios of Pyridostigmine bromide (PR) and its related substances; impurity a (IMP A) and impurity b (IMP B). Analysis of PR in a pharmaceutical dosage form without any interference from other inactive ingredients was also a successful application of the proposed methods. As per ICH guidelines, the proposed methods were validated ensuring their accuracy, precision and specificity. Statistical comparison between the developed methods and the reference method was done, where calculated F and t values were less than the theoretical ones in regards to accuracy and precision.

Testing the purity of spectral profiles: Finger-print resolution of complex matrices and extraction of absorbance signals

The application of spectrophotometric techniques has shown a tremendous development over the past few years, where it is possible to determine the concentrations of several components in complex matrix. A new feature will be introduced in this work where the application of spectrophotometric techniques will be enhanced to resolution and checking the purity of signals. The finger-print resolution "ratio subtraction method" (RSM) was coupled with the novel complementary method "unified constant subtraction" (UCS); in addition to the methods: extended ratio subtraction method (EXRSM), constant multiplication (CM) or "spectrum subtraction" (SS). These techniques were applied for the determination of the complex matrix of the binary mixture of chloramphenicol and dexamethasone. By applying official spectrophotometric methods, direct determination of the components was allowed with no need for validation procedures. The spectrophotometric techniques were successfully applied to the laboratory prepared mixtures and the combined dosage form where the purity of the extracted signals were tested by calculating the spectral contrast angle (θ) and the spectral ratio factor (SRF) where the results were compared to show the capability to recover pure spectral profiles and detect the presence of impurities. The proposed methods proved that spectrophotometric techniques can be used for identification and separation of signals, similar to chromatographic techniques.