Desirability-based optimization and its sensitivity analysis for the perindopril and its impurities analysis in a microemulsion LC system

In the current paper the application of multiobjective optimization (MOOP) technique, via Derringer's desirability function, to a microemulsion liquid chromatographic (MELC) method is described. Chromatographic separation of perindopril tert-butylamine and its four impurities was selected as the case study. Central composite design (CCD) with fractional factorial design, ± 0.5 α star design and four replications in central point was applied for a response surface study, in order to examine in depth the effects of the most important factors. As factors that influence the system mostly (i) content of ethyl acetate and (ii) butyl acetate in composite internal phase, (iii) content of sodium dodecyl sulfate (surfactant) and (iv) n-butanol (co-surfactant), as well as (v) pH of the mobile phase were selected. Retention factor of (a) perindoprilat and (b) impurity Y 31 and (c) resolution factor for impurities Y 32 and 33 were chosen for simultaneous optimization. By adjustment of the importance coefficients and weights, according to defined objectives, the optimal mobile phase composition was predicted to be: 0.24% w/v butyl acetate, 0.3% w/v ethyl acetate, 2% w/v SDS, 7.75% w/v n-butanol and pH of the mobile phase 3.7. The sensitivity analysis of desirability function for these optimal conditions was conducted for the first time in LC separations, by applying a sensitivity procedure. The performed sensitivity analysis confirmed that the higher overall desirability does not necessarily mean a better solution. The accuracy of prediction might be affected if the optimal levels of input variables, achieved from several design points, end up with equal settings and different corresponding overall desirability. In our study this was not the issue, which confirmed the adequacy of predicted optimum.     

Advancement in optimization tactic achieved by newly developed chromatographic response function: application to LC separation of raloxifene and its impurities

In this paper a new chromatographic response function (CRF) is designed and proposed for utilization in the optimization strategies. The function capability to represent the overall quality of a experimentally obtained chromatograms was compared to the other two objective functions and proved to give more accurate and reliable results. The new CRF has improved concept of separation and time term estimation. It reflects all important defects of the chromatogram such as the appearance of asymmetrical or overlapping peaks and prolonged elution time and allows the appropriate weighting of each of them. The LC separation of raloxifene and its four impurities was evaluated through the central composite design experimental plan choosing the new CRF to be the only output of the system. The function demonstrated the ability to judge the impact of the complex interactions of the selected chromatographic parameters (acetonitrile content in the mobile phase, sodium dodecyl sulfate concentration in the water phase, pH of the mobile phase and column temperature) on the mixture behavior and led to the determination of the optimal separation conditions. The newly developed CRF proved to have the advanced performances and it presents the important step forward in the optimization of the chromatographic separation.     

Validation of an oil-in-water microemulsion liquid chromatography method for analysis of perindopril tert-butylamine and its impurities

This paper describes the development and validation of a microemulsion liquid chromatography (MELC) method for simultaneous determination of perindopril tert-butylamine and its impurities in bulk active substances and the pharmaceutical dosage form of tablets. An appropriate resolution with reasonable retention times was obtained for a microemulsion containing 0.24% (w/v) butyl acetate, 0.30% (w/v) ethyl acetate, 2% (w/v) sodium dodecyl sulfate, 7.75% (w/v) n-butanol, and 20.0 mM potassium dihydrogen phosphate, the pH of which was adjusted to 3.70 with 85% orthophosphoric acid. Separations were performed on a Nucleosil 120-5 butyl modified (C4), 250 x 4 mm, 5 microm particle size silica column at 40 degrees C, with a mobile phase flow rate of 1.25 mL/min. UV detection was performed at 254 nm. The established method was subjected to method validation, and required validation parameters were defined. Robustness testing, an important part of method validation, was performed as well. Since robustness validation can be conducted using different experimental designs, the Plackett-Burman design was applied due to its possibility of testing many factors at the same time. The validated MELC method was found to be suitable for the simultaneous determination of perindopril tert-butylamine and its impurities in pharmaceuticals.     

Influence of structural and interfacial properties of microemulsion eluent on chromatographic separation of simvastatin and its impurities

In order to calculate the structural and compositional characteristics of microemulsions, used as eluents in the investigation of HPLC separation of simvastatin and its six impurities, predictive molecular thermodynamic approach is developed. For calculating fundamental interfacial properties of microemulsions, from pure component properties, the lattice fluid self-consistent field theory (SCF), in conjunction with new classical thermodynamic expressions, was applied. Calculation of predicted radii (PR), area per surfactant (ApS) and film thickness (FT), as well as is interfacial tension and bending moment enabled better understanding of separation of such a complex mixture. The microemulsion, which contained 1% (w/w) of diisopropyl ether, 2% (w/w) of sodium dodecyl sulphate (SDS), 6.6% (w/w) of co-surfactant such as n-butanol and 90.4% (w/w) of aqueous 25 mM disodium phosphate pH 7.0 enabled appropriate chromatographic separation between investigated compounds. It has been proved that this microemulsion had the smallest droplet radii and film thickness, which enabled optimal separation. Also the interfacial tension is the smallest, so the free energy change associated with dispersing the drops favoured a large number of small droplets. Hydrophobic interactions between solutes and stationary phase, as well as the microstructural characteristics of microemulsion eluents had a significant influence on chromatographic behavior of simvastatin and its six impurities.     

Development of liquid chromatographic method for fosinoprilat determination in human plasma using microemulsion as eluent

Fosinopril sodium presents a prodrug for the active angiotensin converting enzyme (ACE) inhibitor, fosinoprilat. The dual elimination of fosinoprilat by the liver and the kidney distinguishes fosinopril from other angiotensin converting enzyme inhibitors. Such ways of elimination are important for antihypertensive therapy of patients on haemodialysis. The paper presents development and evaluation of a new and sensitive liquid chromatographic (LC) method for the analysis of fosinoprilat in plasma obtained from patients on haemodialysis. A microemulsion system mixture as mobile phase has been used for the separation and analysis of fosinoprilat in plasma samples. The plasma samples were injected directly onto the HPLC system (Waters Breeze) after appropriate sample dilution with mobile phase. Separations were performed on the Bakerbond ENV 4.6 mm x 150 mm, 5 microm particle size column with UV detection at 220 nm. The flow rate was 1.00 mL min(-1). The mobile phase consisted of 1.0% (w/v) of diisopropyl ether, 2.0% (w/v) of sodium dodecyl sulphate (SDS), 6.0% (w/v) of n-propanol and 91% (w/v) of aqueous 25 mM di-sodium hydrogen phosphate, pH adjusted to 2.8 with 85% orthophosphoric acid. The developed method was then subjected to method validation according to the criteria stated in the FDA bioanalytical method validation guidance. The results for specificity, linearity, low limit of quantification (LLOQ), precision, accuracy and stability were within the accepted criteria. The unique approach applied in this paper makes possible the determination of fosinoprilat even in the presence of metabolites of other drugs, so the method can be used for obtaining the reliable results in a fast and simple way.     

Factorial Design in Optimization of Chromatographic Separation of Ramipril and Its Impurities

In this paper optimization of chromatographic retention of ramipril and its five impurities employing factorial design is presented. On the basis of preliminary experiments three factors were chosen as inputs (acetonitrile content, pH of the mobile phase and buffer concentration) and retention factor as output. As optimal full factorial design 2³ was chosen, factors were examined at two different levels “low” and “high”. Three replications at zero level were added in order to check linearity and complete statistical tests. Relationship between inputs and output is presented in form of second order interaction model. Adequacy of model was explained using analysis of variance. After analysis of results optimal chromatographic conditions were set. Separations were conducted on a C₁₈ column with a mixture of acetonitrile and water phase (TEA in potassium dihydrogen phosphate) in ratio 23:77 v/v. Finally, the LC method was validated and applied for quality control analysis of commercially available tablets. The proposed method is simpler and faster as compared to existing official methods and therefore more adequate for routine control of ramipril during shelf life. Also a general approach which includes factorial design in method optimization offers a possibility for predicting and following the chromatographic behavior of such complex mixtures.     

Chemometrical Approach in Fosinopril-Sodium and its Degradation Product Fosinoprilat Analysis

In this paper the experimental design has been applied to define the optimum chromatographic conditions for the separation of fosinopril sodium and its degradation product, fosinoprilat. Fosinopril is a prodrug and after being hydrolysed, it becomes an active drug fosinoprilat. For experimental screening full factorial design 2³ was applied. Methanol content, pH of the mobile phase and column temperature were independent variables or factors to be investigated in two levels - »low« and »high«. Capacity and selectivity factors were chosen as dependent variables and matrix was applied to estimate coefficients of the linear model. After experimental screening, RSM (response surface methodology) was applied for optimization. Optimum conditions were: X Terra? 150 mm × 4.6 mm, 5 μm particle column at 45 °C; methanol-water (75 : 25 v/v) at pH 3.1 as a mobile phase, with a flow rate of 1 mL min^?1. UV detection was performed at 220 nm. Propylparaben was used as an internal standard. The proposed method is rapid, accurate, selective and because of its sensitivity and reproducibility, it may be used for the quantitative analysis of fosinopril sodium and its degradation product in Monopril^® tablets. Recovery values for fosinopril sodium were between 101.6% and 102.9% and content of degradation product fosinoprilat was lower than 5%. Applying the chemometrical approach enables a relatively limited number of experiments to define factors which affect the chromatographic behavior of investigated substances and obtain optimum conditions for their analysis.     

Monitoring of Simvastatin Impurities by HPLC with Microemulsion Eluents

The use of microemulsions as eluents in HPLC has shown excellent potential.We have developed a novel approach for the analysis of Simvastatin and its six impurities, applying microemulsions as mobile phase. The method was validated and applied to the analysis of commercially available tablets in order to confirm that the proposed approach is useful for the application of this technique to drug analysis. A microemulsion eluent containing 0.9% w/w of diisopropylether, 1.7% w/w of sodium dodecyl-sulphate (SDS), 7.0% w/w of co-surfactant such as n-butanol and 90.4% w/w of aqueous 25 mM di-sodium phosphate pH 7.0 was used for the analysis. Separations were performed on a 3.5 µm X Terra^TM 50 × 4.6 mm column at 30 °C. Detection was performed at 238 nm with an eluent flow rate of 0.3 mL min⁻¹. The optimized and validated method can be used for the identification and simultaneous determination of Simvastatin and its six impurities in bulk drug and in pharmaceutical dosage forms.

     

Stepwise optimization approach for improving LC‐MS/MS analysis of zwitterionic antiepileptic drugs with implementation of experimental design

In this article, a step‐by‐step optimization procedure for improving analyte response with implementation of experimental design is described. Zwitterionic antiepileptics, namely vigabatrin, pregabalin and gabapentin, were chosen as model compounds to undergo chloroformate‐mediated derivatization followed by liquid chromatography coupled with tandem mass spectrometry (LC‐MS/MS) analysis. Application of a planned stepwise optimization procedure allowed responses of analytes, expressed as areas and signal‐to‐noise ratios, to be improved, enabling achievement of lower limit of detection values. Results from the current study demonstrate that optimization of parameters such as scan time, geometry of ion source, sheath and auxiliary gas pressure, capillary temperature, collision pressure and mobile phase composition can have a positive impact on sensitivity of LC‐MS/MS methods. Optimization of LC and MS parameters led to a total increment of 53.9%, 83.3% and 95.7% in areas of derivatized vigabatrin, pregabalin and gabapentin, respectively, while for signal‐to‐noise values, an improvement of 140.0%, 93.6% and 124.0% was achieved, compared to autotune settings. After defining the final optimal conditions, a time‐segmented method was validated for the determination of mentioned drugs in plasma. The method proved to be accurate and precise with excellent linearity for the tested concentration range (40.0 ng ml^?1–10.0 × 10³ ng ml^?1). Copyright © 2013 John Wiley & Sons, Ltd.