The MOLNÁR-INSTITUTE DryLab® modelling proves viability of unique PGC graphite stationary phase in HPLC

Berlin: – Specialists in chromatographic separation and analytical modelling have participated in a research study highlighting the use of DryLab® with a porous graphite carbon column as an alternative to traditional silica-based stationary phases.

The study ‘Linear solvent strength model on porous graphitic carbon stationary phase using high-temperature liquid chromatographic method for allopurinol related substances analysis’ has been authored by Barnabás Soós and Róbert Kormány from the Drug Substance Analytical Development Division of Budapest-based Egis Pharmaceuticals, together with Krisztián Horváth from the Department of Analytical Chemistry, at Hungary’s University of Pannonia. It is published in the Journal of Pharmaceutical and Biomedical Analysis (JPBA).

Advantages of PGC

The study demonstrates the development of a high-performance liquid chromatography (HPLC) method for analysing allopurinol and its European Pharmacopeia (EP) specified impurities, utilizing a porous graphitic carbon (PGC) stationary phase combined with systematic modelling approaches.

This new stationary phase material unlocks several potential industrial applications. Porous graphitic carbon (PGC) is a crystalline material characterized by intertwined graphitic ribbons, where carbon atoms are arranged in a hexagonal pattern and bonded covalently. This structure provides exceptional chemical stability. Due to the two-dimensional ribbon arrangement and the smooth, highly bonded surface of PGC particles, porous graphitic carbon columns exhibit a non-polar nature.

As a result, PGC stationary phases demonstrate superior temperature and pH stability compared to traditional silica-based phases, along with a completely unique chromatographic selectivity distinct from octadecyl silica stationary phases. Solute retention on PGC phases is generally greater than on conventional reversed-phase (RP) systems; however, highly polar analytes can also be retained effectively. Conversely, many compounds separable only by hydrophilic interaction liquid chromatography (HILIC) can achieve adequate retention on this stationary phase.

Multidimensional Modeling of PGC Separations

Demonstrating the versatility of chromatography-based modelling approaches, the team utilized the MOLNÁR-INSTITUTE’s DryLab®4 analytical and modelling platform to investigate and optimize the retention behaviour of solutes across a broad temperature range (30–90 °C) and varying gradient times (5–20 minutes).

Since DryLab®4 software is grounded in robust scientific principles that describe separation dynamics, the team hypothesized that it could effectively optimize the critical parameters of a PGC liquid chromatography system. Consequently, a three-dimensional model was developed to optimize gradient time, column temperature, and the pH of eluent A. Using input data from 12 runs, a 3-D design space was constructed, enabling the identification of the optimal working point based on critical resolution.

PGC Optimization with DryLab®

The team’s data analysis confirmed the distinct retention mechanisms between reversed-phase and PGC stationary phases. Nevertheless, the retention of Allopurinol and its specified impurities on PGC phases was successfully modeled using DryLab®. This modeling tool proved invaluable for contextualizing the complex chromatographic landscape and optimizing separation within a broad method operable design region. Under the optimized conditions (tG = 6 min, T = 65 °C, pH = 2.0), all solutes were separated within 6 minutes with baseline resolution.

A comparison of predicted and experimentally measured chromatograms further validated the effectiveness of the modeling platform in developing analytical methods for PGC-based HPLC systems. Consequently, the innovative methodology outlined in this study provides a robust framework for method development on PGC phases across a variety of applications.

Key insights

In conclusion, the authors highlight that PGC stationary phases in HPLC offer a viable alternative to traditional silica-based phases, particularly when solutes exhibit highly variable chemical properties.

The study states: ‘While HPLC optimization software based on linear solvent strength theory can simplify and accelerate method development, it may face challenges with non-conventional phases like PGC. However, our findings clearly demonstrate that PGC can be effectively modeled using the software, despite its significantly different retention behavior compared to RP-HPLC.’

Additionally, the study emphasizes that analytical method development using commercial chromatographic modeling software is both fast and efficient, with excellent agreement between calculated and measured chromatograms. This approach provides a general framework for exploring the behavior of other non-conventional phases and for developing methods tailored to PGC columns.

About The MOLNÁR-INSTITUTE

Founded in 1981, The MOLNÁR-INSTITUTE develops DryLab®4, a software for UHPLC modelling for a world-wide market. Its powerful modules gradient editor, peak tracking, automation, robustness and Design Space Comparison allow for the most sophisticated method development as required across modern pharma industries. Analytical scientists use DryLab®4 to understand chromatographic interactions, to reduce analysis time, to increase robustness, and to conform to Analytical Quality by Design (AQbD) principles, according to the recently published ICH Q14 regulatory framework.

The Molnár-Institute is a registered partner of the US-FDA, CDC and many other regulatory bodies. DryLab®4 pioneered AQbD long before regulatory agencies across the world encouraged such submissions. Widely implemented by thought leaders, the software contributes substantially to the paradigm shift towards a science and risk driven perspective on HPLC Quality Control and Assurance.

Further information at: http://www.molnar-institute.com

Resources

Click on Linear solvent strength model on porous graphitic carbon stationary phase using high temperature liquid chromatographic method for allopurinol related substances analysis to access full study.