The use of experimental design in the development of an HPLC–ECD method for the analysis of captopril

Development of Response Surface Approach for Determination of Paracetamol, Chlorpheniramine Maleate, Caffeine and Ascorbic Acid by Green HPLC Method: A Desirability-Based Optimization

Design of experiment is an efficient and cost-effective tool to optimize the chromatographic separation of a multicomponent mixture. The central composite design was conducted to develop and optimize a green high performance liquid chromatography (HPLC) method for simultaneous quantitation of a quaternary mixture of paracetamol, chlorpheniramine maleate, caffeine and ascorbic acid in their pharmaceutical dosage form as well as the determination of their dissolution profile. A five-level three-factor model was performed to investigate the effect of mobile phase composition, pH and flow rate on enhanced resolution and short run time. Analysis was performed using a Kinitex EVO C18 column and a mobile phase composed of methanol: 0.02 M phosphate buffer pH 3.3 (34:66, v/v) at 1.0 mL/min using photodiode array detection. Optimum chromatographic separation was achieved in <6 min with a desirability of 0.999. Linearity was achieved over a range of 1.00-300.00, 1.00-50.00, 2.00-50.00 and 2.00-100.00 μg/mL for paracetamol, chlorpheniramine maleate, caffeine and ascorbic acid, respectively, with a limit of detection (<0.1 μg/mL). The greenness profile was evaluated using the analytical eco-scale and Analytical GREEnness Metric Approach with values of 81 and 0.77, respectively.

Electrochemical HPLC Determination of Piperazine Antihistamine Drugs Employing a Spark-Generated Nickel Oxide Nanoparticle-Modified Carbon Fiber Microelectrode

In this work, we demonstrate a sensitive high-performance liquid chromatography (HPLC) method for the determination of piperazine antihistamine drugs employing innovative electrochemical detection based on a spark-generated nickel oxide nanoparticle-modified carbon fiber microelectrode built into a miniaturized electrochemical detector. The direct carbon fiber-to-nickel plate electrode spark discharge, carried at 0.8 kV DC, with the nickel electrode connected to the negative pole of the high-voltage power supply, provides extremely fast (1 s) in situ tailoring of the carbon fiber microelectrode surface by nickel oxide nanoparticles. It has been found that nickel oxide nanoparticles exhibit an electrocatalytic effect toward the piperazine moiety electrooxidation process, as confirmed by voltammetric experiments, revealing the shift in the peak potential from 1.25 to 1.09 V versus Ag/AgCl. Cetirizine, cyclizine, chlorcyclizine, flunarizine, meclizine, and buclizine were selected as sample piperazine antihistamine drugs, while diclofenac served as an internal standard. The isocratic reversed-phase separation of the above set was achieved within 15 min using an ARION-CN 3 μm column with a binary mobile phase consisting of 50 mM phosphate buffer (pH 3) and methanol (45/55, v/v). The limits of detection (LOD) were within the range of 3.8-120 nM (for cyclizine and buclizine) at E = +1500 mV (vs Ag/AgCl), while the response was linear within the concentration range measured up to 5 μmol L-1. The method was successfully applied to the determination of piperazine antihistamine drugs in spiked plasma samples.

Drilling into "Quality by Design" Approach for Analytical Methods

The need for consistency in analytical method development reinforces the dependence of pharmaceutical product development and manufacturing on robust analytical data. The Analytical Quality by Design (AQbD), akin to the product Quality by Design (QbD) endows a high degree of confidence to the method quality developed. AQbD involves the definition of the analytical target profile as starting point, followed by the identification of critical method variables and critical analytical attributes, supported on risk assessment and design of experiment tools for the establishment of a method operable design region and control strategy of the method. This systematic approach moves away from reactive troubleshooting to proactive failure reduction. The objective of this review is to highlight the elements of the AQbD framework and provide an overview of their implementation status in various analytical methods used in the pharmaceutical field. These methodologies include but are not limited to, high-performance liquid chromatography, UV-Vis spectrophotometry, capillary electrophoresis, supercritical fluid chromatography, and high-performance thin-layer chromatography. Finally, a critical appraisal is provided to highlight how regulators have encouraged AQbD principles application to boost the prevention of method failures and a better understanding of the method operable design region (MODR) and control strategy, ultimately resulting in cost-effectiveness and regulatory flexibility.

Multiple fluorescence quenching effects mediated fluorescent sensing of captopril Based on amino Acids-Derivative carbon nanodots

Carbon nanodots (CNDs) were facilely synthesized through a pyrolysis procedure with histamine, an amino acid rich in element carbon and nitrogen, being the precursor. Taking advantage of the favorable fluorescence performance of CNDs, a multiple fluorescence quenching effects mediated fluorescent sensor was established for captopril (CAP) detection. MnO₂ NPs were firstly combined with CNDs via electrostatic attraction and subsequently quenched the fluorescence. The quenching mechanisms were concluded to be the combined effects of fluorescence resonance energy transfer (FRET) and inner filtration effect (IFE). Subsequently CAP triggered a unique redox reaction and decomposed the quencher so that renewed the fluorescence. Hence, the sensitive and selective detection of CAP was achieved through the indication of fluorescence recovery efficiency. A proportional range of 0.4 ∼ 60 μmol L^-1 with the LOD of 0.31 μmol L^-1 was obtained. The sensor was further applied to the real sample detection and the satisfactory results revealed the practical value of CNDs. The facile synthesis of CNDs and brand-new sensing mechanism made it a novel fluorescent method and could improve the analysis of CAP.

Development of an HPLC-UV Method to Assay Empagliflozin Tablets and Identification of the Major Photoproduct by Quadrupole Time-of-Flight Mass Spectrometry

Diabetes is a set of metabolic disorders that affect >400 million individuals worldwide. Empagliflozin belongs to the gliflozin class and is used orally to treat type 2 diabetes. In this study, a simple stability-indicating HPLC-UV method was developed to assay empagliflozin tablets and its main photoproduct was identified by high-resolution mass spectrometry. The mobile phase, which was optimized by Central Composite Design, was composed of methanol, acetonitrile and purified water (60:5:35 v/v), at a flow rate of 1 mL min-1. The calibration curve was linear in the range of 5-150 μg mL-1. All the validation parameters were met and the method was specific, even in the presence of degradation products. In the forced degradation study, empagliflozin standard and empagliflozin tablets were submitted to several conditions (acidic, alkaline, neutral and oxidant media, thermal, photolytic and humidity), and empagliflozin showed instability under all these conditions. A degradation product generated after drug exposure to ultraviolet C radiation was isolated and analyzed by quadrupole time-of-flight mass spectrometry, and the results suggested that empagliflozin undergoes decomposition by a dechlorination pathway. In silico toxicity was predicted for the degradation product, which showed a high risk of genotoxicity and hepatotoxicity.

Quantification and Validation of Stability-Indicating RP-HPLC Method for Efavirenz in Bulk and Tablet Dosage Form using Quality by Design (QbD): A Shifting Paradigm

The present study endeavors quality by design (QbD) assisted chromatographic method for the quantification of Efavirenz (ERZ) in bulk and tablet dosage form. Analytical QbD instigated with assignment of analytical target profile (ATP) and critical analytical attributes (CAAs). Risk assessment studies and factor screening studies facilitate to identify the critical method parameters (CMPs). Optimization was performed by employing 32 full factorial design using identified CMPs i.e., flow rate (X1) and pH of buffer (X2) at three different levels and evaluating selected CAAs i.e., retention time (Y1) and peak area (Y2). The individual and interactive influence of CMPs on CAAs were tested by statistical data and response surface plots. Analysis of variance (ANOVA) confirmed that method parameters are significant (P < 0.05). Chromatographic separation was achieved using methanol, 10 mM ammonium acetate buffer (70:30 v/v), pH adjusted at 3.1 with 0.05% ortho-phosphoric acid as a mobile phase at flow rate 1.0 mL/min, and a Nucleosil C18 (4.6 mm I.D. × 250 mm, 5 μm) column with UV detection at 247 nm. The method validation and subsequent stresses degradation studies according to ICH guidelines supported the method to be highly efficient for regular drug analysis and its degradation products. The proposed method was successfully demonstrated QbD based approach for the development of highly sensitive, reliable and suitable for routine analysis, and clinical applications.

Application of experimental design in HPLC method optimization and robustness for the simultaneous determination of canagliflozin, empagliflozin, linagliptin, and metformin in tablet

Gliflozins and gliptins represent two different pharmacological drug classes that exert different and potentially complementary glucose-lowering effect in patients with type II diabetes mellitus. A novel, selective, and sensitive HPLC method was developed for the determination of canagliflozin, empaglifozin, linagliptin, and metformin in pure form, in laboratory prepared mixtures, and in pharmaceutical dosage form. Experimental design optimization was applied by using Plackett-Burman and face-centered composite designs to achieve the best resolution with minimum experimental trials. Three significant variables affecting optimization, namely buffer pH, percentage of methanol, and percentage of acetonitrile, were studied. Chromatographic separation was achieved using an Agilent Eclipse C₈ column, and column temperature was kept at 45°C. The mobile phase was composed of dipotassium hydrogen phosphate buffer (0.05 M, adjusted to pH 6 using o-phosphoric acid):acetonitrile:methanol (50:25:25, v/v/v) at a flow rate of 1.5 mL/min. Sharp and well-resolved peaks of the cited drugs were obtained. The method was fully validated in terms of linearity, accuracy, precision, selectivity and robustness in agreement with the International Council of Harmonization (ICH) guidelines Q2 (R1). Satisfactory results were obtained by the analysis of tablets through applying the developed method. Therefore, it could be performed for the analysis of the cited drugs in quality control laboratories.

Analytical Capabilities of Coulometric Sensor Systems in the Antioxidants Analysis

The definition of antioxidants (AOs), their classification and properties as well as electrochemical sensor systems for AOs analysis are briefly discussed. The analytical capabilities of coulometric titration with electrogenerated titrants as sensor systems for AOs determination have been considered in detail. The attention focused on the individual AO quantification that was mainly used in the pharmaceutical analysis and estimation of total antioxidant parameters (total antioxidant capacity (TAC), ferric reducing power (FRP) and ceric reducing/antioxidant capacity (CRAC)) allowing the fast screening of the target samples including their quality control. The main advantages of coulometric sensor systems are pointed out. The selective quantification of individual AO in a complex matrix using a combination of chromatography with coulometric or coulometric array detection under potentiostatic mode is discussed. The future development of coulometric sensor systems for AOs analysis is focused on the application of novel coulometric titrants and the application of coulometric detection in flow injection analysis.

Crop Resilience to Drought With and Without Response Diversity

In the face of increasingly frequent droughts threatening crop performance, ecological theory suggests that higher species diversity may help buffering productivity by making systems more resistant through resource complementarity and more resilient through higher response diversity. However, empirical evidence for these diversity effects under drought stress has remained patchy. In two pot experiments, we explored whether mixing two legume species with a contrasting response to water availability, alsike clover (AC) and black medic (BM), promotes resistance to cumulative drought stress, and resilience of aboveground crop biomass to a transient drought event. The mixture was more productive than the average of the sole crops, and this mixture effect was higher in the non-stressed than in the drought-stressed plants. However, with six levels of constant drought intensities, the mixture effect was not consistently affected by drought level. Response diversity was evident as asynchrony of growth in the two species after the drought event, with BM re-growing faster than AC. Significant resilience to drought was observed in sole AC, i.e., without response diversity. Resilience was larger in AC than in BM and increased from 44 to 72 days after sowing (DAS). The mixture was more resilient than the average resilience of the sole crops at 72 DAS, but it was never more resilient than AC, indicating that resilience is promoted by, but not dependent on response diversity. We conclude that crop diversity may contribute to drought resilience through growth asynchrony, but that species identity plays a crucial role in making systems more drought-resilient.

Stability Indicating HPLC-ECD Method for the Analysis of Clarithromycin in Pharmaceutical Dosage Forms: Method Scaling versus Re-Validation

An isocratic high-performance liquid chromatographic method using electrochemical detection (HPLC-ECD) for the quantitation of clarithromycin (CLA) was developed using Response Surface Methodology (RSM) based on a Central Composite Design (CCD). The method was validated using International Conference on Harmonization (ICH) guidelines with an analytical run time of 20 min. Method re-validation following a change in analytical column was successful in reducing the analytical run time to 13 min, decreasing solvent consumption thus facilitating environmental and financial sustainability. The applicability of using the United States Pharmacopeia (USP) method scaling approach in place of method re-validation using a column with a different L–designation to the original analytical column, was investigated. The scaled method met all USP system suitability requirements for resolution, tailing factor and % relative standard deviation (RSD). The re-validated and scaled method was successfully used to resolve CLA from manufacturing excipients in commercially available dosage forms. Although USP method scaling is only permitted for columns within the same L-designation, these data suggest that it may also be applicable to columns of different designation.

Smartphone application for captopril determination in dosage forms and synthetic urine employing digital imaging

A simple, accurate, and low-cost analytical procedure for captopril determination through digital imaging is presented. The method relies on the spot test reaction between captopril and palladium (II) chloride, which produces a yellow and water-soluble complex with maximum absorption at 380 nm. A smartphone camera and a portable apparatus built for internal lighting control were put together to acquire digital images of reaction mixtures. Digital image processing through the RGB approach was used to establish a quantitative relationship between color intensity and captopril concentration. Under the most suitable operational and experimental conditions, an analytical curve was built monitoring the Blue channel within the concentration range of 3.12 × 10^-5 to 1.21 × 10^-3 mol L^-1. Limits of detection and quantification were equal to 8.06 × 10^-6 and 2.69 × 10^-5 mol L^-1, respectively. Recovery percentage in synthetic urine samples ranged from 97.1% to 102.9%. Results were compared with a reference method and no significant differences were detected at the 95% confidence level. The developed method presents budgetary and environmental advantages concerning the use of cheap and easy-handled devices and the consumption of very low volumes of reagent (800 μL per determination). It can be a useful analytical tool for laboratories with limited financial resources while abiding by green chemistry principles.

Sensitive spectrofluorimetric methods for determination of ethopabate and amprolium hydrochloride in chicken plasma and their residues in food samples

Two sensitive and selective spectrofluorimetric methods are proposed to determine ethopabate (ETH) and amprolium hydrochloride (AMP). First derivative synchronous spectrofluorimetry determines the natively fluorescent ethopabate at 288 nm in presence of amprolium hydrochloride which is a non fluorescent quaternary compound with average recovery 100.54±0.721 over a concentration range of 0.01-0.8 μg/mL. Limits of detection (LOD) and quantification (LOQ) are 0.002 and 0.007 μg/mL, respectively. The second method is direct synchronous spectrofluorimetry for determining amprolium hydrochloride at 362 nm after a reaction with 5% NaOH and 0.08% potassium ferricyanide that is optimized by a two-level factorial design. This method is linear over a concentration range of 0.01-0.65 μg/mL with average recovery 99.4±1.28. Limits of detection (LOD) and quantification (LOQ) are 0.002 and 0.006 μg/mL, respectively. The proposed methods are found to be valid and applicable for the analysis of ETH and AMP in their veterinary formulation. They are successfully applied to determine the studied drugs in chicken plasma and their residues in chicken muscle, liver, egg and chicken-based baby food product with recoveries in the ranges of 95.71-108.73% and 97.36-111.89% and for ETH and AMP, respectively.

Making methods rugged for regulated bioanalysis

Methods started in discovery are optimized as they progress through preclinical and clinical development. Making a robust assay includes testing individual steps for consistency and points of failure. Assays may be transferred, optimized and revalidated several times. A rugged assay will not only meet regulatory requirements, but will execute with a low failure rate and confirm results under repeat analysis. Challenging aspects such as differential recovery, sample stabilization, resolution of isomers or conjugate analysis must be tackled and made routine. The proper selection of the IS can overcome limitations. It is best to know the potential points of failure before a study has started, but lessons learned from each study also provide invaluable insights to improve assay ruggedness.

Determination of midodrine hydrochloride via Hantzsch condensation reaction: a factorial design based spectrophotometric approach

An experimental design was adopted for determination of MD·HCl. The novelty of the current approach arises from being multivariate compared to traditional univariate techniques.

Implementation of design of experiments for optimization of forced degradation conditions and development of a stability-indicating method for furosemide

The study involved optimization of forced degradation conditions and development of a stability-indicating method (SIM) for furosemide employing the design of experiment (DoE) concept. The optimization of forced degradation conditions, especially hydrolytic and oxidative, was done by application of 2(n) full factorial designs, which helped to obtain the targeted 20-30% drug degradation and also enriched levels of degradation products (DPs). For the selective separation of the drug and its DPs for the development of SIM, DoE was applied in three different stages, i.e., primary parameter selection, secondary parameter screening and method optimization. For these three, IV-optimal, Taguchi orthogonal array and face-centred central composite designs were employed, respectively. The organic modifier, buffer pH, gradient time and initial hold time were selected as primary parameters. Initial and final organic modifier percentage, and flow rate came out as critical parameters during secondary parameter screening, which were further evaluated during method optimization. Based on DoE results, an optimized method was obtained wherein a total of twelve DPs were separated successfully. The study also exposed the degradation behaviour of the drug in different forced degradation conditions.

A validated spectrofluorimetric method for the determination of nifuroxazide through coumarin formation using experimental design

Background

Nifuroxazide (NF) is an oral nitrofuran antibiotic, having a wide range of bactericidal activity against gram positive and gram negative enteropathogenic organisms. It is formulated either in single form, as intestinal antiseptic or in combination with drotaverine (DV) for the treatment of gastroenteritis accompanied with gastrointestinal spasm. Spectrofluorimetry is a convenient and sensitive technique for pharmaceutical quality control. The new proposed spectrofluorimetric method allows its determination either in single form or in binary mixture with DV. Furthermore, experimental conditions were optimized using the new approach: Experimental design, which has many advantages over the old one, one variable at a time (OVAT approach).

Results

A novel and sensitive spectrofluorimetric method was designed and validated for the determination of NF in pharmaceutical formulation. The method was based upon the formation of a highly fluorescent coumarin compound by the reaction between NF and ethylacetoacetate (EAA) using sulfuric acid as catalyst. The fluorescence was measured at 390 nm upon excitation at 340 nm. Experimental design was used to optimize experimental conditions. Volumes of EAA and sulfuric acid, temperature and heating time were considered the critical factors to be studied in order to establish an optimum fluorescence. Each two factors were co-tried at three levels. Regression analysis revealed good correlation between fluorescence intensity and concentration over the range 20–400 ng ml^-1. The suggested method was successfully applied for the determination of NF in pure and capsule forms. The procedure was validated in terms of linearity, accuracy, precision, limit of detection and limit of quantification. The selectivity of the method was investigated by analysis of NF in presence of the co-mixed drug DV where no interference was observed. The reaction pathway was suggested and the structure of the fluorescent product was proposed. Statistical comparison between the presented method and a reported spectrophotometric one was carried out on pure and pharmaceutical formulation and revealed no significant difference.

Conclusion

The proposed method was considered economic, accurate, precise and highly sensitive. It could be easily applied in laboratory quality control for the analysis of NF in pure form and in pharmaceutical dosage form.

Implementation of QbD Approach to the Analytical Method Development and Validation for the Estimation of Propafenone Hydrochloride in Tablet Dosage Form

Chromatographic and spectrophotometric methods were developed according to Quality by Design (QbD) approach as per ICH Q8(R2) guidelines for estimation of propafenone hydrochloride in tablet dosage form. QbD approach was carried out by varying various parameters and these variable parameters were designed into Ishikawa diagram. The critical parameters were determined by using principal component analysis as well as by observation. Estimated critical parameters in HPTLC method include solvent methanol, mode of detection absorbance, precoated aluminium backed TLC plate (10 cm 10 cm), wavelength: 250 nm, saturation time: 20 min, band length: 8 mm, solvent front: 70 mm, volume of mobile phase: 5 mL, type of chamber: 10 cm 10 cm, scanning time: 10 min, and mobile phase methanol : ethyl acetate : triethylamine (1.5 : 3.5 : 0.4 v/v/v). Estimated critical parameters in zero order spectrophotometric method were solvent methanol, sample preparation tablet, wavelength: 247.4 nm, slit width: 1.0, scan speed medium, and sampling interval: 0.2, and for first order derivative spectrophotometric method it was scaling factor: 5 and delta lambda 4. The above methods were validated according to ICH Q2(R1) guidelines. Proposed methods can be used for routine analysis of propafenone hydrochloride in tablet dosage form as they were found to be robust and specific.

Utility of Experimental Design in Pre-Column Derivatization for the Analysis of Tobramycin by HPLC-Fluorescence Detection: Application to Ophthalmic Solution and Human Plasma

A novel, selective, and sensitive reversed phase high-performance liquid chromatography (HPLC) method coupled with fluorescence detection has been developed for the determination of tobramycin (TOB) in pure form, in ophthalmic solution and in spiked human plasma. Since TOB lacks UV absorbing chromophores and native fluorescence, pre-column derivatization of TOB was carried out using fluorescamine reagent (0.01%, 1.5 mL) and borate buffer (pH 8.5, 2 mL). Experimental design was applied for optimization of the derivatization step. The resulting highly fluorescent stable derivative was chromatographed on C₁₈ column and eluted using methanol:water (60:40, v/v) at a flow rate of 1 mL min⁻¹. A fluorescence detector (λ_ex 390 and λ_em 480 nm) was used. The method was linear over the concentration range 20–200 ng mL⁻¹. The structure of the fluorescent product was proposed, the method was then validated and applied for the determination of TOB in human plasma. The results were statistically compared with the reference method, revealing no significant difference.

Automated determination of total captopril in urine by liquid chromatography with post-column derivatization coupled to on-line solid phase extraction in a sequential injection manifold

The present study reports a new liquid chromatographic (HPLC) method for the determination of the anti-hypertension drug captopril (CAP) in human urine. After its separation from the sample matrix in a reversed phase HPLC column, CAP reacts with the thiol-selective reagent ethyl-propiolate (EP) in a post-column configuration and the formed thioacrylate derivative is detected at 285 nm. Automated 4-fold preconcentration of the analyte prior to analysis was achieved by an on-line solid phase extraction (SPE) step using a sequential injection (SI) manifold. The Oasis HLB SPE cartridges offered quantitative recoveries and effective sample cleaning by applying a simple SPE protocol. The limits of detection and quantitation were 10 μg L(-1) and 35 μg L(-1) respectively. The percent recoveries for the analysis of human urine samples ranged between 90 and 96% and 95 and 104% using aqueous and matrix matched calibration curves respectively.