Hydrophilic interaction liquid chromatography in analysis of granisetron HCl and its related substances. Retention mechanisms and method development.

In this paper separation of granisetron and its two related substances in HILIC mode is presented. Separation was done on silica column derivatized with sulfoalkylbetaine groups (ZIC-HILIC). Firstly, retention mechanisms were assessed whereby retention factors of substances were followed in wide range of acetonitrile content (80-97%), at constant concentration of aqueous buffer (10mM) as well as at constant pH value of 3.0. Further, in order to developed optimal HILIC method, Design of Experiments (DoE) methodology was applied. For optimization full factorial design 3(2) was employed. Influence of acetonitrile content and ammonium acetate concentration were investigated while pH of the water phase was kept at 3.3. Adequacy of obtained mathematical models was confirmed by ANOVA. Optimization goals (α>1.15 and minimal run time) were accomplished with 94.7% of acetonitrile in mobile phase and 70 mM of ammonium acetate in water phase. Optimal point was in the middle of defined Design Space. In the next phase, robustness was experimetally tested by Rechtschaffen design. The investigated factors and their levels were: acetonitrile content (±1%), ammonium acetate molarity in water phase (±2 mM), pH value of water phase (±0.2) and column temperature (±4 °C). The validation scope included selectivity, linearity, accuracy and precision as well as determination of limit of detection (LOD) and limit of quantification (LOQ) for the related substances. Additionally, the validation acceptance criteria were met in all cases. Finally, the proposed method could be successfully utilized for estimation of granisetron HCl and its related substances in tablets and parenteral dosage forms, as well as for monitoring degradation under various stress conditions.

Theoretical Models and QSRR in Retention Modeling of Eight Aminopyridines.

In this article, retention modeling of eight aminopyridines (synthesized and characterized at the Faculty of Pharmacy) in reversed-phase high performance liquid chromatography (RP-HPLC) was performed. No data related to their retention in the RP-HPLC system were found. Knowing that, it was recognized as very important to describe their retention behavior. The influences of pH of the mobile phase and the organic modifier content on the retention factors were investigated. Two theoretical models for the dependence of retention factor of organic modifier content were tested. Then, the most reliable and accurate prediction of log k was created, testing multiple linear regression model-quantitative structure-retention relationships (MLR-QSRR) and support vector regression machine-quantitative structure-retention relationships (SVM-QSRR). Initially, 400 descriptors were calculated, but four of them (POM, log D, M-SZX/RZX and m-RPCG) were included in the models. SVM-QSRR performed significantly better than the MLR model. Apart from aminopyridines, four structurally similar substances (indapamide, gliclazide, sulfamethoxazole and furosemide) were followed in the same chromatographic system. They were used as external validation set for the QSRR model (it performed well within its applicability domain, which was defined using a bounding box approach). After having described retention of eight aminopyridines with both theoretical and QSRR models, further investigations in this field can be conducted.

Quality by Design approach in the development of hydrophilic interaction liquid chromatographic method for the analysis of iohexol and its impurities.

This study presents the development of hydrophilic interaction liquid chromatographic method for the analysis of iohexol, its endo-isomer and three impurities following Quality by Design (QbD) approach. The main objective of the method was to identify the conditions where adequate separation quality in minimal analysis duration could be achieved within a robust region that guarantees the stability of method performance. The relationship between critical process parameters (acetonitrile content in the mobile phase, pH of the water phase and ammonium acetate concentration in the water phase) and critical quality attributes is created applying design of experiments methodology. The defined mathematical models and Monte Carlo simulation are used to evaluate the risk of uncertainty in models prediction and incertitude in adjusting the process parameters and to identify the design space. The borders of the design space are experimentally verified and confirmed that the quality of the method is preserved in this region. Moreover, Plackett-Burman design is applied for experimental robustness testing and method is fully validated to verify the adequacy of selected optimal conditions: the analytical column ZIC HILIC (100 mm × 4.6 mm, 5 µm particle size); mobile phase consisted of acetonitrile-water phase (72 mM ammonium acetate, pH adjusted to 6.5 with glacial acetic acid) (86.7:13.3) v/v; column temperature 25 °C, mobile phase flow rate 1 mL min(-1), wavelength of detection 254 nm.

Chaotropic salts in liquid chromatographic method development for the determination of pramipexole and its impurities following quality-by-design principles.

The aim of this paper is to present a development of liquid chromatographic method when chaotropic salts are used as mobile phase additives following the QbD principles. The effect of critical process parameters (column chemistry, salt nature and concentration, acetonitrile content and column temperature) on the critical quality attributes (retention of the first and last eluting peak and separation of the critical peak pairs) was studied applying the design of experiments-design space methodology (DoE-DS). D-optimal design is chosen in order to simultaneously examine both categorical and numerical factors in minimal number of experiments. Two ways for the achievement of quality assurance were performed and compared. Namely, the uncertainty originating from the models was assessed by Monte Carlo simulations propagating the error equal to the variance of the model residuals and propagating the error originating from the model coefficients' calculation. The baseline separation of pramipexole and its five impurities is achieved fulfilling all the required criteria while the method validation proved its reliability.

Chromatographic analysis of olopatadine in hydrophilic interaction liquid chromatography.

In this paper, chromatographic analysis of active substance olopatadine hydrochloride, which is used in eye drops as antihistaminic agent, and its impurity E isomer by hydrophilic interaction liquid chromatography (HILIC) and application of design of experiments (DoE) methodology are presented. In addition, benzalkonium chloride is very often used as a preservative in eye drops. Therefore, the evaluation of its chromatographic behavior in HILIC was carried out as well. In order to estimate chromatographic behavior and set optimal chromatographic conditions, DoE methodology was applied. After the selection of important chromatographic factors, Box-Behnken design was utilized, and on the basis of the obtained models factor effects were examined. Then, multi-objective robust optimization is performed aiming to obtain chromatographic conditions that comply with several quality criteria simultaneously: adequate and robust separation of critical peak pair and maximum retention of the first eluting peak. The optimal conditions are identified by using grid point search methodology. The experimental verification confirmed the adequacy of the defined optimal conditions. Finally, under optimal chromatographic conditions, the method was validated and applicability of the proposed method was confirmed.

Retention mechanism assessment and method development for the analysis of iohexol and its related compounds in hydrophilic interaction liquid chromatography.

Hydrophilic interaction liquid chromatography (HILIC) has emerged in recent years as a valuable alternative to reversed-phase liquid chromatography in the analysis of polar compounds. Research in HILIC is divided into two directions: the assessment of the retention mechanism and retention behavior, and the development of HILIC methods. In this work, four polar neutral analytes (iohexol and its related compounds A, B, and C) were analyzed on two silica and two diol columns in HILIC mode with the aim to investigate thoroughly the retention mechanisms and retention behavior of polar neutral compounds on these four columns. The adsorption and partition contribution to the overall HILIC retention mechanism was investigated by fitting the retention data to linear (adsorption and partition) and nonlinear (mixed-retention and quadratic) theoretical models. On the other hand, the establishment of empirical second-order polynomial retention models on the basis of D-optimal design made possible the estimation of the simultaneous influence of several mobile-phase-related factors. Furthermore, these models were also used as the basis for the application of indirect modeling of the selectivity factor and a grid point search approach in order to achieve the optimal separation of analytes. After the optimization goals had been set, the grids were searched and the optimal conditions were identified. Finally, the optimized method was subjected to validation.

Chemometrical tools in the study of the retention behavior of azole antifungals.

Certain chemometrical tools allow an efficient way to provide valuable data to evaluate the retention behavior of analytes in liquid chromatography. In this study of the retention behavior of azole antifungals, the experimental design was applied in combination with artificial neural networks (ANNs). Three potentially significant factors (methanol content, pH of the mobile phase and column temperature) were incorporated in the plan of experiments, defined by central composite design. As the system outputs, the retention factors of all six investigated substances (fluconazole, ketoconazole, bifonazole, clotrimazole, econazole and miconazole) were determined. The pattern for the analyzed behavior of the system was created by employing ANNs. The final, optimized topology of the highly predictive network was 3-8-6. Twelve experiments were used in a training set, whereas a back-propagation algorithm was optimal for network training. The ability of the defined network to predict the retention of the investigated azoles was confirmed by correlations higher than 0.9912 for all analytes. The presented approach allowed the adequate prediction of the retention behavior of azoles, in addition to the extraction of important information for a better understanding of the analyzed system.

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 × 10(3) ng ml(-1)).

Robust optimization of psychotropic drug mixture separation in hydrophilic interaction liquid chromatography.

This paper presents multiobjective optimization of complex mixtures separation in hydrophilic interaction liquid chromatography (HILIC). The selected model mixture consisted of five psychotropic drugs: clozapine, thioridazine, sulpiride, pheniramine and lamotrigine. Three factors related to the mobile phase composition (acetonitrile content, pH of the water phase and concentration of ammonium acetate) were optimized in order to achieve the following goals: maximal separation quality, minimal total analysis duration and robustness of an optimum. The consideration of robustness in early phases of the method development provides reliable methods with low risk for failure in validation phase. The simultaneous optimization of all goals was achieved by multiple threshold approach combined with grid point search. The identified optimal separation conditions (acetonitrile content 83%, pH of the water phase 3.5 and ammonium acetate content in water phase 14 mM) were experimentally verified.

Chemometrically assissted optimization and validation of RP-HPLC method for the analysis of itraconazole and its impurities.

This paper presents the chemometrically assisted optimization and validation of the RP-HPLC method intended for the quantitative analysis of itraconazole and its impurities in pharmaceutical dosage forms. To reach the desired chromatographic resolution with a limited number of experiments in a minimum amount of time, Box- -Behnken design was used to simultaneously optimize some important chromatographic parameters, such as the acetonitrile content in the mobile phase, pH of the aqueous phase and the column temperature. Separation between itraconazole and impurity F was identified as critical and selected as a response during the optimization. The set optimal mobile phase composition was acetonitrile/ water pH 2.5 adjusted with o-phosphoric acid (50:50, V/V). Separations were performed on a Zorbax Eclipse XDB-C18, 4.6 × 150 mm, 5 µm particle size column with the flow rate 1 mL min-1, column temperature set at 30 °C and UV detection at 256 nm. The established method was then subjected to method validation and the required validation parameters were tested. For the robustness evaluation, fractional factorial 24-1 design was utilized and factors that might significantly affect the system performance were defined. As other validation parameters were also found to be suitable, the possibility to apply the proposed method for the determination of itraconazole, its impurities B and F in any laboratory under different circumstances has been proven.

Improved chromatographic response function in HILIC analysis: application to mixture of antidepressants.

This paper presents exploration of chromatographic behavior in HILIC system by experimental design and improved chromatographic response function denoted as N(CRF)*. As a model mixture six antidepressants were chosen: selegiline, mianserine, sertraline, moclobemide, fluoxetine and maprotiline. Due to complexity of retention mechanisms in HILIC system, detailed examination of experimental space assessing the influence of important factors (acetonitrile content in the mobile phase, buffer concentration and pH of the mobile phase) and their interactions was done by applying 3(3) experimental design. N(CRF)* is developed and designed to be the only output of the system which simultaneously measures the separation of all the examined substances, the chromatographic run duration and the quality of the obtained peaks shape. It allowed objective estimation of overall chromatogram quality and excluded the arbitrary judgment in ambiguous situations. The applied function highlighted the influence of investigated factors on entire mixture and enabled identification of experimental regions where the chromatographic behavior was satisfactory. Applied experimental design strategy combined with N(CRF)* proved to be valuable assistance in HILIC separation of complex mixtures.

Assessment of ß-lactams retention in hydrophilic interaction chromatography applying Box-Behnken design.

In this paper, the retention prediction models for mixture of ß-lactam antibiotics analyzed by hydrophilic interaction chromatography (HILIC) are presented. The aim of the study was to investigate the retention behavior of some organic acids and amphoteric compounds including cephalosporins (cefotaxime, cefalexin, cefaclor, cefuroxime, and cefuroxime axetil) and penicillins (ampicillin and amoxicillin). Retention of substances with acidic functional group in HILIC is considered to be interesting since the majority of publications in literature are related to basic compounds. In the beginning of the study, classical silica columns were chosen for the retention analysis. Then, preliminary study was done and factors with the most significant influence on the retention factors were selected. These factors with the impact on the retention factors were investigated employing Box-Behnken design as a tool. On the basis of the obtained results the mathematical models were created and tested using ANOVA test and finally verified. This approach enables the presentation of chromatographic retention in many ways (three-dimensional (3-D) graphs and simple two-dimensional graphical presentations). All of these gave the possibility to predict the chromatographic retention under different conditions. Furthermore, regarding the structure of the analyzed compounds, the potential retention mechanisms in HILIC were suggested.