Penalization and Color Code-Technical Approaches for Methods' Greenness and Whiteness Appraisal in Veterinary Medication: Assay of Toltrazuril Suspension.

BACKGROUND: Intestinal coccidiosis is a debilitating disease in poultry and livestock, leading to economic impact worldwide. Coccidiosis is prevented and treated in broilers by the inclusion of anticoccidials in feed. Toltrazuril is administered in potable water to treat coccidiosis. OBJECTIVE: Three robust analytical methods for quantitation of toltrazuril in pure and pharmaceutical formulations are developed. Furthermore, ecological metrics; either penalization- or color-code-based techniques are applied for the appraisal of assays. METHODS: Firstly, Second-Derivative (Δλ; 5 nm) spectrophotometric method; Toltrazuril is measured from peak to peak at 244-260 nm within a linearity range of 5-25 µg/mL. The second one is a high-performance thin-layer chromatography (HPTLC) analysis performed on an aluminum sheet of silica gel using ethyl acetate, methanol, ammonium chloride buffer, and water (8:1:0.5:0.5) (%V/V) as the elution phase. Toltrazuril, at a retardation factor of 0.66 ± 0.01, is linearly determined in the range of 1-9 µg/spot at 243 nm. The third one is Reversed Phase-HPLC-diode array detection, using Agilent column C18 (5 µm, 4.6 x 150 mm) in isocratic elution mode with a mobile phase of acetonitrile and water in a ratio of 80:20 (v/v), respectively, at 1 mL/min flow rate. Toltrazuril elutes at a retention time of 2.58 ± 0.1 min and is linearly determined at 243 nm in the range of 0.25-25 µg/mL. RESULTS: Calculated 2D-values and peak areas are highly correlated to their corresponding drug concentrations at coefficients; r > 0.999. All methods were ICH validated and applied to dosage form with satisfactory % recoveries (97-103%). Statistical comparisons reported one using t-test and F-test disclose insignificant variation. Examining greenness and whiteness norms, proposed methods were evaluated and ranked alongside four different reported methods. CONCLUSION: The proposed methods are green, accurate, and can be applied in routine quality control for the determination of toltrazuril in pharmaceutical formulations.

Ecological assessment and development of analytical methods for concurrent quantification of valsartan and sacubitril: whiteness comparative study based on relative scoring.

Sustainable analytical chemistry is gaining great interest in global environmental pollution control. In addition, valsartan (VAS) and sacubitril (SAB) have been recently approved by the FDA as a fixed-dose combination "LCZ696". It showed efficacy and safety enough to extend its application from heart failure to hypertension control. VAS/SAB dual therapy is considered expensive; however, its prescription has increased significantly worldwide. This prescription increased the demand for developing sustainable analytical methods that simultaneously analyze VAS and SAB. Highly sensitive and selective spectrofluorimetric methods have been developed for this purpose. A synchronous spectrofluorimetric technique was applied. In one method, it was followed by spectral derivatization at the first-order level. The signals were recorded at 230 and 211 nm for VAS and SAB, respectively. Synchronous spectrofluorimetry was coupled to a dual-wavelength mathematical approach in the second method. Signals were derived by subtracting synchronous responses at 241 nm, 226 nm, and 239 nm from the response at 208 nm for VAS and SAB, respectively. Method validation was carried out following ICH guidelines. VAS showed linear calibration curves spanning the range of 60-200 and 80-600 ng mL-1 for the derivative and dual wavelength-assisted approaches, respectively. SAB achieved linear responses in the range of 17-190 and 30-350 ng mL-1 for the first and second methods, respectively. The green profile of the proposed methods was confirmed using the analytical eco-scale (AES), green analytical procedure index (GAPI), and analytical greenness metric (AGREE) tools. The proposed hybrid methods proved highly sustainable through the whiteness RGB 12 algorithm evaluation approach. Whiteness was comparatively assessed for the proposed and reported methods based on relative scoring depending on the parameters of each method. Despite this scoring approach being accurate as a relative score for comparative purposes, it gave rise to underestimated absolute scores. Therefore, to obtain a proper conclusion from the comparative whiteness study, all the methods were ranked according to their whiteness score, illustrating the excellent whiteness ranks of the proposed methods. Upon complete comparison with the reported methods, the suggested ones showed several advantages concerning analytical performance and the greenness level. The proven affordability and simplicity encourage their wide industrial application in developing countries.

Green and Smart Quantitative Quality Control for Veterinary Mixture of Ivermectin and Clorsulon: Ecological Evaluation of Spectral Analyses via Analytical Eco-Scale, Green Analytical Procedure Index, and Analytical GREEnness Metric Approaches.

BACKGROUND: The global financial market is still highly threatened by bovine fasciolosis, a parasitic infection that targets cattle, mainly in tropical regions. Binary combination of ivermectin (IVER) and clorsulon (CLO), in challenging concentration ratios, is typically indicated for treatment and control of fasciolosis. OBJECTIVE: The present study aims at smart simultaneous spectrophotometric assay of both compounds at their high ratio in marketed formulation and synthetic mixtures, without any prior separation. Furthermore, their greenness profile was evaluated and compared with previous reported assay methods, including the official one. METHODS: Mathematical-based proposed methods are the dual-wavelength, induced dual-wavelength, and first derivative ratio methods. Each is developed, optimized, and applied to determine simultaneously IVER and CLO at linear ranges of 1-30 and 5-40 µg/mL, respectively. They have been validated according to ICH guidelines. Statistical Student t-tests and F-tests compared the proposed methods with a USP chromatographic technique. Ecological appraisal is accomplished using three independent metrics: Analytical Eco-Scale (AES), Green Analytical Procedure Index (GAPI), and Analytical GREEnness Metric Approach (AGREE). RESULTS: Satisfactory recoveries, ICH compliance, and adherence of proposed methods to the ecological safety margin are achieved. CONCLUSIONS: Developed methods are eco-friendly and cost-effective and can accomplish a routine quantitative quality control for concurrent determination of both drugs. HIGHLIGHTS: Veterinary antimicrobials need analytical quality control using safer and green methodologies. Data manipulated spectral analyses of IVER and CLO, in a ratio of 1:10% (v/v), are developed and optimized. AES, GAPI, and AGREE approaches illustrate the high green compliance in respect to assays reported in the literature. Furthermore, the United States Pharmacopeia (USP) assay for IVER and CLO in injectable dosage form depends on analysis of each drug separately in the presence of the other drug, but it cannot determine both drugs simultaneously.

Development of validated methods for the simultaneous quantification of Finasteride and Tadalafil in newly launched FDA-approved therapeutic combination: greenness assessment using AGP, analytical eco-scale, and GAPI tools.

The primary objectives of green chemistry are the reduction of generation and use of hazardous substances. In healthcare, the most active areas of research in green chemistry are medication manufacturing and analysis. Analysts take serious steps for converting traditional analytical methods to eco-friendly ones that minimize the negative effects of solvents and chemicals on the environment and improve the healthcare. In the proposed work, two analytical methods are presented for the quantification of Finasteride (FIN) and Tadalafil (TAD) simultaneously in newly launched FDA-approved dosage form without prior separation. The first method is derivative spectrophotometry, which is based on measuring the amplitudes of first derivative spectrophotometric peaks of FIN and TAD in ethanolic solution at 221 nm and 293 nm, respectively. On the other hand, measuring the peak-to-peak amplitudes of second derivative spectrum of TAD solution at 291-299 nm was also performed. Regression equations show good linearity for FIN and TAD in the ranges of 10-60 µg mL-1 and 5-50 µg mL-1, respectively. The second method is the RP-HPLC method, where the chromatographic separation was achieved using the XBridgeTM C18 (150 × 4.6 mm, 5 µm) column. The eluent was the mixture of acetonitrile:phosphate buffer with triethylamine, 1% (v/v) adjusted to pH = 7 in the ratio of 50 : 50 (by volume). The flow rate was 1.0 mL min-1 with DAD-detection at 225 nm. This analytical procedure was linear over the ranges of 10-60 µg mL-1 and 2.5-40 µg mL-1 for FIN and TAD, respectively. The presented methods were validated (regarding ICH guidelines) and statistically compared by applying the t-test and F-test with the reported method. The greenness appraisal was performed using three different tools. The proposed validated methods were found to be green, sensitive, selective, and can be successfully used for quality control test.

Carbon dots as fluorescent nanoprobes for assay of some non-fluorophoric nitrogenous compounds of high pharmaceutical interest.

Background: Carbon dots, CDs, have excellent photoluminescence properties, good biocompatibility, low toxicity and good light stability. The optical, magnetic and electronic properties of CDs make them a hugely relevant tool to be used in pharmaceutical analysis, bioimaging, drug delivery, and other fields. The fluorescence of carbon nanodots makes it suitable for assay of some nitrogenous compounds of high pharmaceutical interest. In this work, we develop simple, fast and green spectrophotometric methods for quantification of Azithromycin and Rasagiline mesilate using synthesized fluorescent CDs from garlic peels. Results: The spectrometric methods depend on stoichiometric reactions of both drugs with fluorescent CDs. Carbon dots exhibit a declared absorption peak λmax at 238 nm and potent fluorimetric emission at λem 528 nm, upon excitation at λex 376 nm. Drugs' concentrations in ppm are efficiently calculated using Stern-Volmer Equation. Decrease in fluorescence (ΔF = F o - F) and the F-ratio values are linearly correlated to molar concentration of each quencher (drug). A significant linear diminish in the dots' measured absorbance and fluorimetric emission values was observed. Validation of all the developed methods was according to the ICH guidelines. Conclusions: In a new way, this work successfully indicates, spectrometric methods for rapid detection of two non-fluorophoric nitrogenous compounds using potent carbon nanodots. Consequently, these green developed methods offer several benefits as simplicity, ease of quantification, accuracy and precision that encourage the application of the developed methods in routine analysis of Azithromycin and Rasagiline mesilate in quality control laboratories as analytical tool. Supplementary Information: The online version contains supplementary material available at 10.1186/s43088-023-00346-z.

Simple simultaneous determination of moxifloxacin and metronidazole in complex biological matrices.

A simple, sensitive and rapid RP-HPLC method is presented, for the first time, for the simultaneous determination of moxifloxacin hydrochloride and metronidazole in different biological fluids including saliva and plasma without any matrix interference. The separation was performed using ACN and phosphate buffer (30 : 70% v/v) as the mobile phase on a Zorbax Eclipse Plus-C18 column attached to a guard column. The method was validated according to the FDA guidelines for bioanalytical method validation and was successfully applied for simultaneous determination of the studied drugs in saliva and plasma samples. The good precision and selectivity of the developed method allow it to be used for routine therapeutic drug monitoring of such drugs and it presents a simple and sensitive analytical tool for performing versatile pharmacokinetics and bioavailability studies. A DAD detector is valuable to determine each drug at its maximum wavelength to ensure high sensitivity. Determination of such a combination in saliva introduces a quick and non-invasive alternative to blood analysis.

Development of hybrid spectrofluorimetric method for simultaneous determination of Valsartan and Sacubitril in LCZ696 tablets.

A hybrid Spectrofluorimetric method was developed for the simultaneous determination of binary mixtures, without prior separation steps. It coupled synchronous spectrofluorimetry with derivative ratio mathematical treatment. The method was applied successfully to quantify a new model binary mixture consisting of Valsartan (VAL) and Sacubitril (SAC). This mixture was recently approved by FDA as LCZ696. It added a great value in reducing morbidity and mortality in resistant heart failure (HF) patients. First derivative ratio synchronous fluorescence was measured at 258-295 (peak-to-peak) and 204 nm for VAL and SAC, respectively. ICH guidelines were fulfilled for the method validation. VAL and SAC showed linear responses in the range of 60-200 and 20-200 ng mL-1, respectively. The proposed method was compared, in details, with the reported ones. Its high accuracy, selectivity, simplicity and affordable cost recommend method application in large-scale routine analysis of LCZ696 tablets. Moreover, reliable application of this new integrated spectrofluorimetric method suggests expansion of its application for various therapeutic combinations and different matrices.

Green analytical methods for simultaneous determination of compounds having relatively disparate absorbance; application to antibiotic formulation of azithromycin and levofloxacin.

Green validated spectrophotometric methods are developed for simultaneous determination of Azithromycin (AZI) and Levofloxacin (LEVO) antibiotic mixture. Determination of AZI presents a real analytical challenge as its structure lacks any chromophore, and hence it cannot be determined by direct spectrophotometry. However, the reaction of AZI with perchloric acid produces a green product that can be accurately determined spectrophotometrically. Thus, the work presented demonstrates simple green and sensitive methods for the simultaneous determination of AZI and LEVO mixture. Method I depends on direct measurement of absorbance of azithromycin and levofloxacin in perchloric acid methanolic solution at 482 nm and 224 nm, respectively. While, Method II depends on measuring the first derivative spectrophotometric peak-to-peak amplitudes of AZI and LEVO in perchloric acid methanolic solution at 475-490 nm and 280-253 nm, respectively. Regression analysis shows good linearity for AZI and LEVO over the concentration ranges of 5-50 and 2.5-20 µg/mL for method I and 5-50 and 5-40 µg/mL for method II for AZI and LEVO, respectively. The proposed methods were validated in compliance with ICH guidelines. The suggested procedures are successfully applied for the assay of AZI and LEVO mixture in bulk powder and laboratory-prepared tablets. Greenness profile of the proposed methods were compared with other published methods through applying the Eco-scale protocol. Assessment results demonstrated that the proposed methods are greener than other reported methods. Moreover, upon comparison with other methods, the proposed methods showed better or comparable sensitivity in addition to being selective and rapid with no requirement for laborious extraction techniques. These advantages encourage the application of the proposed methods in routine analysis of AZI and LEVO in quality control laboratories as green and simple analytical tool.

Gradient HPLC-DAD method for quantification of novel oral anticoagulant "Edoxaban" in plasma: Its selective determination in presence of sixteen co-administered drugs.

As an anticoagulant, Edoxaban (EDX) is a high risk drug that may cause a life-threatening bleeding. Also, it is prescribed as a chronic therapy for atrial fibrillation and venous thromboembolism patients. They are special population that needs appropriate care and optimum dosing of EDX. Hence, its monitoring in the patient plasma is fundamental, especially in emergency and special circumstances. However, such patient mostly receives many drugs of different pharmacological classes, side by side with EDX. This study represents the first attempt to quantify EDX in plasma without interference of the plasma matrix or concomitant medications. An accurate RP-HPLC-DAD method was developed for this purpose. It succeeded to monitor EDX level, selectively, without interference of plasma matrix or 16 of its frequently co-administered drugs. All drugs were extracted from plasma samples by protein precipitation followed by evaporation and concentration. EDX was well resolved from the co-administered drugs on C8 column using linear gradient elution of methanol and phosphate buffer (pH 4), at a flow rate of 1 mL/min. EDX appeared at retention time 9.6 min and was quantified at its λmax (290 nm). It exhibited a linear response over the concentration range of 0.15-2.2 µg/mL plasma which covers the reported therapeutic concentration. The suggested method fulfilled the US FDA guidelines for bioanalytical method validation. The developed method is fully discussed in comparison with the reported techniques. An in vivo study was performed to ensure applicability of the method on real plasma samples without interference from plasma matrix, co-administered drugs or the expected metabolites. It presented a unique selectivity of the method that guarantees accurate laboratory monitoring of EDX in plasma in almost all combined treatments including such novel oral anticoagulant drug.

Hantzsch pre-column derivatization for simultaneous determination of alendronate sodium and its pharmacopoeial related impurity: Comparative study with synchronous fluorometry using fluorescamine.

High performance liquid chromatographic (HPLC) method with a pre-column derivatization based on Hantzsch condensation reaction was applied for simultaneous determination of alendronate sodium (ALN) and its main related impurity, 4-Aminobutanoic acid (ABA) at its pharmacopeial limit. The separation of colored condensation products of ALN and ABA were achieved on Agilent Zobrax Eclipse SB-C18 analytical column (250 × 4.6 mm, 5 µm) using a mobile phase composed of acetonitrile-0.1 M acetate buffer, pH 5.0 (15:85, v/v). The flow rate was 1 mL min-1. The detection was carried out at 340 nm using photo-diode array detector. Peak areas were used for the linear regression line in the range of 10-500 and 0.2-40 µg mL-1 for ALN and ABA, respectively. Different conditions for the optimization of the derivatization reactions as well as for the HPLC measurement were studied. The proposed method was validated for linearity, precision, accuracy, specificity and robustness. This method was used to check the purity of ALN in the presence of ABA (related impurity) at the pharmacopeial limit (0.5%). For comparison purpose, another method was proposed which involves synchronous fluorescence measurement after ALN reaction with fluorescamine. In this method, the third derivative synchronous spectra were estimated as peak to peak measurement from 339 to 370 nm for ALN determination with LOD and LOQ of 24 and 73 ng mL-1, respectively, showing very high sensitivity. Both methods have been applied for determination of the alendronate sodium (ALN) in bulk and pharmaceutical preparations without interference of additives in tablets or oral solution.

Development and validation of spectrophotometric and HPTLC methods for simultaneous determination of rosiglitazone maleate and metformin hydrochloride in the presence of interfering matrix excipients.

Two simple methods have been developed and validated for the simultaneous determination of rosiglitazone maleate (ROS) and metformin hydrochloride (MET) in synthetic mixtures and coated tablets in a ratio of 1:250 (ROS:MET). The first method was a spectrophotometric one. The minor component, ROS was determined by measuring the values of absorbance at λmax 312 nm and the D1 amplitudes at 331 nm where MET shows no absorption contribution. However, absorbance interferences from tablet excipients were successfully corrected by D1 at 331 nm zero-crossing technique. Study of spectral interference from tablet excipients was included in the text. Standard curves for Amax and D1 methods were in the concentration range 20.0-80.0 µg mL(-1). The major component, MET was determined both in binary mixtures and tablets by measuring its Amax at 236 nm. Extensive dilution eliminated any absorption contribution from the coexisting ROS or tablet matrix. Standard curves showed linearity in the concentration range 4.0-12.8 µg mL(-1). The second method was based on high performance thin layer chromatography (HPTLC) separation of the two drugs followed by densitometric measurements of their spots at 230 nm. The separation was carried out on Merck HPTLC aluminium sheets of silica gel 60 F254 using methanol:water:NH4Cl 1% w/v (5:4:1 v/v/v) as the mobile phase. Linear calibration graphs of peak area values were obtained versus concentrations in the range of 0.4-2.0 µg band(-1) and 20.0-100.0 µg band(-1) for ROS and MET, respectively. According to International Conference on Harmonisation (ICH) guidelines, different validation parameters were verified for the two methods and presented.

Validated stability-indicating methods for the simultaneous determination of amiloride hydrochloride, atenolol, and chlorthalidone using HPTLC and HPLC with photodiode array detector.

Two stability-indicating chromatographic methods are described for simultaneous determination of amiloride hydrochloride (AMI), atenolol (ATE), and chlorthalidone (CHL) in combined dosage forms. The first method was based on HPTLC separation of the three drugs followed by densitometric measurements of their bands at 274 nm. The separation was carried out on Merck HPTLC silica gel 60F254 aluminum sheets using chloroform-methanol-ammonia 27%, w/w (9 + 2 + 0.3, v/v/v) mobile phase. Analysis data was used for the linear regression graph in the range of 0.1-0.5, 0.8-5.0, and 0.3-1.5 microg/band for AMI, ATE, and CHL, respectively. The second method was based on an RP-HPLC separation of the cited drugs performed on an RP stainless steel C18 analytical column (250 x 4.6 mm id) with a gradient elution system of methanol and 0.05 M aqueous phosphate buffer adjusted to pH 4 as the mobile phase, at the flow rate of 1.0 mL/min. Quantitation was achieved with photodiode array detection at 275 nm for AMI and 225 nm for ATE and CHL. The calibration graphs for each drug were rectilinear in the range of 2-50, 25-150, and 2-100 microg/mL for AMI, ATE, and CHL, respectively. The proposed chromatographic methods were successfully applied for determination of the investigated drugs in pharmaceutical preparations. Both methods were validated in compliance with International Conference on Harmonization guidelines in terms of linearity, accuracy, precision, robustness, LOD, and LOQ.

Simultaneous determination of montelukast and fexofenadine using Fourier transform convolution emission data under non- parametric linear regression method.

New hybrid chemometric method has been applied to the emission response data. It deals with convolution of emission data using 8-points sin xi polynomials (discrete Fourier functions) after the derivative treatment of these emission data. This new application was used for the simultaneous determination of Fexofenadine and Montelukast in bulk and pharmaceutical preparation. It was found beneficial in the resolution of partially overlapping emission spectra of this mixture. The application of this chemometric method was found beneficial in eliminating different types of interferences common in spectrofluorimetry such as overlapping emission spectra and self- quenching. Not only this chemometric approache was applied to the emission data but also the obtained data were subjected to non-parametric linear regression analysis (Theil's method). The presented work compares the application of Theil's method in handling the response data, with the least-squares parametric regression method, which is considered the de facto standard method used for regression. So this work combines the advantages of derivative and convolution using discrete Fourier function together with the reliability and efficacy of the non-parametric analysis of data. Theil's method was found to be superior to the method of least squares as it could effectively circumvent any outlier data points.

Bioavailability study of triamterene and xipamide using urinary pharmacokinetic data following single oral dose of each drug or their combination.

An efficient chromatographic method for the simultaneous determination of triamterene (TRI) and xipamide (XIP) in urine samples, based on high performance liquid chromatography with photodiode array detector (HPLC-DAD) has been developed. The HPLC separation was performed on a RP stainless-steel C-18 analytical column (250 mm × 4.6 mm, 5 µm) with a gradient elution system of 0.05 M phosphate buffer adjusted to pH 4.0 and methanol as the mobile phase. The method was used to determine the urinary excretion profile and to calculate different urinary pharmacokinetic parameters following oral dose of their combination compared with single oral doses of each drug and hence comparing their bioavailability. Quantitation was performed using chlorthalidone as internal standard. The calibration graphs of each drug were rectilinear in the range of 0.2-40 µg/mL urine for TRI and 0.2-15 µg/mL urine for XIP. An HPLC-DAD method was also successfully developed for the simultaneous determination of the investigated drugs in pharmaceutical preparations. The methods were validated in terms of linearity, accuracy, precision, selectivity, limits of detection and quantitation and other aspects of analytical validation.

Kinetic spectrophotometric methods for the determination of artificial sweetener (sucralose) in tablets.

Two simple and sensitive kinetic spectrophotometric methods for the determination of sucralose are described. The first method is based upon a kinetic investigation of the oxidation reaction of the drug with alkaline potassium permanganate at room temperature for a fixed time of 30 min. The absorbance of the green coloured manganate ions produced was measured at 610 nm. The second method is based on the reaction of sucralose with cerium (IV) ammonium sulfate in the presence of perchloric acid with the subsequent measurement of the excess unreacted cerium (IV) ammonium sulfate at 320 nm at a fixed time of 30 min in a thermostated water bath at 60 ± 1 °C. This principle is adopted to develop a kinetic method for sucralose determination. The absorbance concentration plots in both methods were rectilinear over the range 4-16 and 10-30 µg ml(-1) , for the first and second methods, respectively. The different experimental parameters affecting the development and stability of the colours were carefully studied and optimized. The determination of sucralose by rate constant method, fixed concentration method, and fixed-time method was also feasible with calibration equations obtained but the latter method was found to be more applicable. The two methods have been applied successfully to commercial tablets.

Enhanced spectrophotometric determination of two antihyperlipidemic mixtures containing ezetimibe in pharmaceutical preparations.

Two spectrophotometric methods are presented for the simultaneous determination of ezetimibe/simvastatin and ezetimibe/atorvastatin binary mixtures in combined pharmaceutical dosage forms without prior separation. The first is the derivative ratio method where the amplitudes of the first derivative of the ratio spectra ((1) DD) at 299.5 and 242.5 nm were found to be linear with ezetimibe and simvastatin concentrations in the ranges 0.5-20 µgml(-1) and 1-40 µgml(-1) , respectively, whereas the amplitudes of the first derivative of the ratio spectra ((1) DD) at 289.5 and 288 nm were selected to determine ezetimibe and atorvastatin in the concentration ranges 5-50 µgml(-1) and 1-40 µgml(-1) , respectively. The second is the H-point standard additions method; absorbances at the two pairs of wavelengths, 228 and 242 nm or 238 and 248 nm, were monitored while adding standard solutions of ezetimibe or simvastatin, respectively. For the analysis of ezetimibe/atorvastatin mixture, absorbance values at 226 and 248 nm or 212 and 272 nm were monitored while adding standard solutions of ezetimibe or atorvastatin, respectively. Moreover, differential spectrophotometry was applied for the determination of ezetimibe in the two mixtures without any interference from the co-existing drug. This was performed by measurement of the difference absorptivities (ΔA) of ezetimibe in 0.07 M 30% methanolic NaOH relative to that of an equimolar solution in 0.07 M 30% methanolic HCl at 246 nm. The described methods are simple, rapid, precise and accurate for the determination of these combinations in synthetic mixtures and dosage forms.

Electrochemical study of spiramycin and its determination in pharmaceutical preparation.

Spiramycin (SPY) is a medium-spectrum antibiotic with high effectiveness against Gram-positive bacteria. The voltammetric behaviour of spiramycin was studied using differential pulse polarography (DPP) and square wave polarography (SWP). The drug in Britton-Robinson buffer (pH 11.5) is reduced at - 1.45 V, giving rise to a well-defined cathodic peak using hanging mercury drop electrode (HMDE) versus Ag/AgCl electrode. This peak is attributed to the reduction of the aldehyde group. The results proved that the reduction of SPY is an irreversible diffusion-controlled process. The diffusion current-concentration relationship was shown to be rectilinear over the range of 20-80 and 0.8-80 µg ml(-1) using DPP and SWP modes, respectively, with detection limit of 8.5 µg ml(-1) (1.01 × 10(-5) M) and 0.46 µg ml(-1) (5.46 × 10(-7) M) for DPP and SWP modes, respectively. A mechanism is postulated for the reduction of SPY. The proposed techniques were successfully applied to the determination of the studied compound either in pure form or in its formulation.

Determination of mirtazapine in spiked human plasma and tablets by first derivative spectrofluorimetric method.

A sensitive first derivative spectrofluorimetric method ((1)D-spectrofluorimetry) was developed for the determination of mirtazapine. Calibration graph for mirtazapine determination was established using the first derivative amplitudes of the mirtazapine emission spectrum (λ ex = 314 nm) in 0.1 M sulphuric acid measured at 375-435 nm from peak to peak, as the analytical signals. Moreover, the ratio of (1)D-spectrophotometric peak amplitudes at these wavelengths was calculated and used for the detection of the presence of interferences. Linearity range was found to be between 1 and 40 ng ml(-1) with correlation coefficient (r) = 0.9999. The limit of quantitation (LOQ) was 1.0 ng ml(-1) and the limit of detection (LOD) was 0.2 ng ml(-1). The proposed method was validated according to ICH; and it has been applied for the drug determination in human plasma without prior extraction and in tablets. The proposed method's accuracy, reproducibility, selectivity and simplicity suggest its application in quality control analysis of the drug.

Simultaneous multiresidue determination of metronidazole and spiramycin in fish muscle using high performance liquid chromatography with UV detection.

An efficient multiresidue method for the simultaneous determination of metronidazole (MET) and spiramycin (SPY) in tilapia fish muscle, based on high performance liquid chromatography with UV detection (HPLC-UV), has been developed. The drugs were extracted with 0.2% orthophosphoric acid-methanol (6:4), and the extracts were cleaned up on a solid phase extraction cartridge, C18 Sep-Pak light column. The LC separation was performed on a RP stainless-steel C-18 analytical column (150 mm x 4.6 mm, 5 microm) with a gradient elution system of 0.05 M phosphate buffer adjusted to pH 2.4-acetonitrile as the mobile phase at the flow rate of 1.0 ml min(-1). A wavelength programming was applied for the UV detection of the analytes. The method not only enabled the determination of the parent drugs, MET and SPY, but also permitted the determination of their metabolites, hydroxymetronidazole (HMET) and neospiramycin (NSPY). The calibration graphs for each drug were rectilinear in the range of 0.005-1.000 microg g(-1) for MET and HMET and 0.025-1.000 microg g(-1) for SPY and NSPY. With this method, the cited drugs with their metabolites were determined in fortified fish muscle tissues at levels of 0.025, 0.1 and 1.0 microg g(-1) with good accuracy and precision. LOD and LOQ obtained for each drug were as follows: 0.002 and 0.005 microg g(-1) for MET and HMET and 0.005 and 0.025 microg g(-1) for SPY and NSPY. Utilization of the method to successfully analyze tilapia fish muscle samples incurred with MET and SPY was described.

Validated stability-indicating methods for the determination of nizatidine in the presence of its sulfoxide derivative.

Four new selective, precise, and accurate methods are described for the determination of nizatidine (NIZ) in the presence of its sulfoxide derivative in both the raw material and pharmaceutical preparations. Method A is based on zero-order (0D), first-derivative (1D), and second-derivative (2D) spectrophotometric measurement of NIZ in aqueous solution at the zero-crossing point of its sulfoxide derivative (at 314, 295-334, and 318-348 nm, respectively). Method B is a 1DD spectrophotometric method based on the simultaneous use of the first derivative of the ratio spectra and the measurement of peak amplitude at 297 nm. Method C uses a solvent-induced derivative-difference spectrophotometry with deltaD1 measurement from peak to peak at 315-345 nm. Method D involves quantitative densitometric evaluation of a mixture of the drug and its sulfoxide derivative after separation by high-performance thin-layer chromatography on silica gel plates with chloroform-methanol (9 + 1, v/v) as the mobile phase; Rf values for NIZ and its sulfoxide derivative were 0.4 and 0.2, respectively. The spot was scanned at 254 nm. The first-derivative spectrophotometric method was used to investigate the kinetics of the hydrogen peroxide degradation process at different temperatures. The apparent pseudo-first-order rate constant, half-life, and activation energy were calculated. The results obtained by the proposed methods were analyzed statistically and compared with those obtained by the official method. These methods are suitable as stability-indicating for the determination of NIZ in the presence of its oxidation-induced degradation product (sulfoxide derivative) either in the bulk powder or in pharmaceutical preparations.