A stepwise strategy employing automated screening and DryLab modeling for the development of robust methods for challenging high performance liquid chromatography separations: A case study

In Silico Method Development of Achiral and Chiral Tandem Column Reversed-phase Liquid Chromatography for Multicomponent Pharmaceutical Mixtures

Tandem column liquid chromatography (LC) is a convenient, cost-effective approach to resolve multicomponent mixtures by serially coupling columns on readily available one-dimensional separation systems without specialized user training. Yet, adoption of this technique remains limited, mainly due to the difficulty in identifying optimal selectivity out of many possible tandem column combinations. At this point, method development and optimization require laborious "hit-or-miss" experimentation and "blind" screening when investigating different column selectivity without standard analytes. As a result, many chromatography practitioners end up combining two columns of similar selectivity, limiting the scope and potential of tandem column LC as a mainstay for industrial applications. To circumvent this challenge, we herein introduce a straightforward in silico multifactorial approach as a framework to expediently map the separation landscape across multiple tandem columns (achiral and chiral) and eluent combinations (isocratic and gradient elution) under reversed-phase LC conditions. Retention models were built using commercially available LC simulator software showcasing less than 2% difference between experimental and simulated retention times for analytes of interest in multicomponent pharmaceutical mixtures (e.g., metabolites and cyclic peptides).

Development of an analytical method for the determination of pimavanserin and its impurities applying analytical quality by design principles as a risk-based strategy

Pimavanserin is an atypical antipsychotic indicated for the treatment of hallucinations and delusions associated with Parkinson's disease psychosis. As it is a relatively new drug on the market, limited number of pharmacokinetic information and analytical methods are available. This paper presents an ultra-high performance chromatography for the simultaneous determination of pimavanserin and its four process impurities. The method was developed applying analytical quality by design (AQbD) principles as a risk-based approach. Critical method attributes (CMAs) were selected as a resolution between the worst separated compounds (impurity B and impurity C), a duration of analysis defined by the retention time of the last eluting peak (impurity D), a capacity factor of the first eluted impurity (impurity A), a tailing factor and a theoretical plate number. Risk assessment in the early stage of method development pointed out critical method parameters (CMPs): column temperature, gradient time and pH-value of the mobile phase (water phase, eluent A). Design of experiments (DoE), using DryLab®4 software, was applied to evaluate the influence of CMPs on CMAs and to determine method operable design region (MODR). Based on the risk assessment and the results of robustness and precision tests, a control strategy with system suitability criteria was proposed. Developed method was validated according to ICH Q2 (R1) guideline with respect to the selectivity, LOD, LOQ, linearity, precision, accuracy, robustness and stability. A forced degradation study was performed to provide an evidence of the stability-indicating property of the method. Degradation products of pimavanserin were identified using ultra high-performance liquid chromatography coupled to high resolution mass spectrometry (UHPLC-qTOF). Additionally, potential degradation products were assessed in silico with the help of Zeneth® software and good agreement with experimentally identified degradation products was achieved. Main degradation products were formed during acid and base hydrolysis (m/z 223.16 [M+H]⁺ at RRT 0.37) and under oxidative stress conditions (m/z 444.26 [M+H]⁺ at RRT 0.57). The results revealed that the pimavanserin undergoes degradation through acid and base hydrolysis of urea and N-oxidation of aliphatic tertiary amine.

A methodology employing retention modeling for achieving control space in liquid chromatography method development using quality by design approach

This study reports the application of retention modeling and quality by design practices for reverse-phase liquid chromatographic method development of a new chemical entity. Prior to the retention modeling, preliminary screening experiments were performed for the selection of stationary phase, organic modifiers, and method parameters. Based on the results of preliminary method conditions, t_G-T (gradient time - temperature) 2-D modeling with 4 input runs, and t_G-T-t_c (gradient time-temperature-ternary composition) 3-D modeling with 12 input runs were designed to build a model for achieving the optimized separation. Modeling of reverse phase separations was based on the measurement of both retention times and peak areas. A design space with appropriate input variables and control strategy was established prior to optimization and robustness evaluation following the quality by design framework. DryLab^Ⓡ was used to predict the optimized gradient profile and separation temperature. The robustness evaluation was carried out using the multiple factors at a time approach and the control space was established. The interdependence of control space and the control strategy was demonstrated by evaluating method robustness using two levels of system suitability criteria. The predictive accuracy of the retention modeling was established through experimental verification of the in-silico predictions. The quality by design based method development approach demonstrated the in-silico optimization as an integral component of reverse-phase chromatographic method development to evaluate the interplay of factors such as organic modifiers, separation temperature and gradient time, which greatly integrated and enhanced method robustness during method development.

Pharmaceutical Analytical Profile for Novel SGL-2 Inhibitor: Dapagliflozin

Dapagliflozin (DPG) is a novel drug from class of sodium glucose co-transporter 2 (SGL-2) inhibitors which has been evolved as profound treatment option for the type-2diabetes mellitus (T2DM). Considering the severity of the disease the drug is of crucial significance for the therapy and associated research. As a pharmaceutical dosage form DPG has immense importance as an individual drug and with other antidiabetic drugs as combinations. The drugs existing in combination with DPG are Metformin (MET) and Saxagliptin (SXG). The existence of the Dapagliflozin in combinations further created more interest in reviewing its pharmaceutical, analytical and bio-analytical profile. Such estimations are always in need of precise pharmacological and physicochemical information; hence authors have presented it beforehand. Authors hereby wish to present an essential update pertaining to emergence of gliflozins and DPG. The article further presents a simultaneous and comparative assessment of the analytical investigations published in literature for pharmaceutical estimation to assist future analysis. The thorough literature searches revealed fifty three research papers in total till date. A comprehensive presentation of typical; hyphenated and unique methods used for analysis are outlined effectively. The percentile utilization of analytical approaches since appearance of first publication in 2010 is investigated to report trend in determination. The present review explores the pharmaceutical estimation of DPG to scientifically potentiate analytical research and therapeutic future of DPG as a novel SGL-2 Inhibitor antidiabetic.

Separation of atropisomers by chiral liquid chromatography and thermodynamic analysis of separation mechanism

In the pharmaceutical industry, the analysis of atropisomers is of considerable interest from a scientific and regulatory perspective. The compound of interest contains two stereogenic axes due to the hindered rotation around the single bonds connecting the aryl groups, which results in four potential configurational isomers (atropisomers). The separation of the four atropisomers is achieved on a derivatized β-cyclodextrin bonded stationary phase. Further investigation shows that low temperature conditions, including sample preparation (−70 °C), sample storage (−70 °C), and chromatographic separation (6 °C), were critical to preventing interconversion. LC-UV-Laser Polarimetric analysis identified peak 1/2 as a pair of enantiomers and peak 3/4 as another. Thermodynamic analysis of the retention data indicated that the separation of the pairs of enantiomers is primarily enthalpy controlled as indicated by the positive slope of the van’t Huff plot. The difference in absolute Δ (Δ H), ranged from 2.20 kJ/mol to 2.42 kJ/mol.

Comparison of the Retention of Aliphatic Hydrocarbons with Polar Groups in RP-HPLC Systems with Different Modifiers of the Binary Eluent

The retention of aliphatic hydrocarbons with polar groups has been compared in respect to the separation selectivity changes in reversed-phase high-performance liquid chromatography with C18 stationary phase type and binary water eluent composed of methanol, acetonitrile, or tetrahydrofuran as modifiers. The changes in separation selectivity when one modifier is replaced by another in the eluent is explained, taking into consideration molecular interactions of the solutes with components of the stationary phase region, i.e., extracted modifier, and ordering of the stationary phase by the modifier.

Exploring better column selectivity choices in ultra-high performance liquid chromatography using quality by design principles

An older method for amlodipine was reworked with the goal to reduce the analysis time of 60min below 6min. To select the best column for short and robust analysis, 9 different UHPLC column chemistries were investigated using 3-dimensional resolution spaces based on 12 experiments using modelling software. The main variables used were gradient time (tG), temperature (T) and the pH of eluent A. The best critical resolution was calculated and located in a 3-dimensional space in an automated fashion and the corresponding best experiments were carried out. The work (9×12=108 runs) was finished with an UHPLC instrument in less than 24h. The comparison between predictions and real experiments showed an excellent correlation with differences typically less than 0.04min (<3s) in average, although the set points were located at quite different conditions on gradient times, pH's and temperatures for the individual columns. All columns could perform the required baseline separation at their individual best working points with satisfactory results.

Comparison of supercritical fluid chromatography and reverse phase liquid chromatography for the impurity profiling of the antiretroviral drugs lamivudine/BMS-986001/efavirenz in a combination tablet

Dual and triple combinations of antiretroviral drugs are a cornerstone of human immunodeficiency virus type 1 (HIV-1) treatment. Supercritical fluid chromatography (SFC) and reverse phase liquid chromatography (RPLC) methods have been developed for the impurity profiling of a prototype combination tablet containing three such drugs: lamivudine, BMS-986001 and efavirenz. Separation by SFC was achieved using a Princeton 2-ethyl pyridine stationary phase and a mobile phase B consisting of methanol with 10 mM ammonium acetate and 0.1% isopropyl amine. This combination of mobile phase additives was required for both the separation of minor components and to minimize peak tailing of the active pharmaceutical ingredients (APIs). Separation by RPLC was achieved using a Discovery HSF5 stationary phase and a mobile phase consisting of 10 mM ammonium acetate, pH 5.5 and methanol. Mobile phase gradient elution was employed in each case to elute components with a wide range of polarities. Both these methods were found to have advantages and disadvantages. Out of the three APIs and 13 possible impurity/degradation products selected, all were resolved by RPLC. By SFC, 15 peaks were resolved with one co-eluting pair and a high degree of orthogonality was achieved relative to RPLC. A more even distribution of peaks across the separation space, a non-sloping baseline and fewer system peaks were significant advantages associated with the SFC method. Particular attention had to be paid to optimizing the reverse phase diluent strength/initial mobile phase composition to avoid distortion of the peak shapes for early eluting components. This was not an issue with SFC, as the diluent of choice (methanol) was also the solvent of choice (in combination with ≤20% water) for the dissolution of the triple combination tablet. As with RPLC, SFC was found to exhibit the required sensitivity for successful quantitation of potential impurities/degradation products at the 0.05-0.1 area% level.

Using an innovative Quality-by-Design approach for development of a stability indicating UHPLC method for ebastine in the API and pharmaceutical formulations

A stability-indicating ultra high performance liquid chromatographic (UHPLC) method has been developed for purity testing of ebastine and its pharmaceutical formulations. Successful chromatographic separation of the API from impurities was achieved on a Waters Acquity UPLC BEH C18, 50 mm × 2.1 mm, 1.7 μm particle size column with gradient elution of 10 mM acetate buffer pH 6.2 and a mixture of acetonitrile/2-propanol (1:1) as the mobile phase. Incorporating Quality by Design (QbD) principles to the method development approach by using the chromatography modeling software DryLab4 allows the visualization of a "Design Space", a region in which changes to method parameters will not significantly affect the results as defined in the ICH guideline Q8 (R2). A verification study demonstrated that the established model for Design Space is accurate with a relative error of prediction of only 0.6%. The method was fully validated for specificity, linearity, accuracy and precision, and robustness in compliance to the ICH guideline Q2 (R1). The method was found to be linear in the concentration range from the quantification limit (LOQ) to 125% of the specification limit for ebastine and each of the impurities with correlation coefficients of not less than 0.999. The recovery rate was between 98.15 and 100.30% for each impurity. The repeatability and intermediate precision (RSD) were less than 3.2% for ebastine and each of the impurities. The robustness of the developed method was studied by varying the six parameters: gradient time, temperature, ternary composition of the eluent, flow rate and start and end concentration of the gradient at 3 levels (+1, 0, -1). The resulting 729 experiments were performed in silico from the previously constructed model for Design Space and showed that the required resolution of 2.0 can be reached in all experiments. To prove the stability-indicating performance of the method, forced degradation (acid and base hydrolysis, oxidation, photolytic and thermal stress conditions) of ebastine was carried out. Baseline separation could be achieved for all peaks of the impurities, the degradation products and the API. Total run time was only 4 min, which is an impressive 40-fold increase in productivity in comparison to the method published in the Ph. Eur. monograph and allowed purity testing of more than 360 samples per day.