Highlights:

• Innovative QbD-based approach for robustness testing of a compendial HPLC method.
• A Design Space was constructed to study the robustness in silico.
• Required peak resolution of 2.0 could not be reached in all experiments.
• After adjusting the gradient time the requirements were fulfilled.
• A separate “Eluent Design Space” study was performed.

This study describes the development of liquid chromatographic methods for the simultaneous separation of some of the most popular local anesthetics in pharmaceutical preparations and medical praxis (benzocaine, bupivacaine, chloroprocaine lidocaine, oxybuprocaine, prilocaine, procaine, propipocaine and tetracaine) based on a systematic approach using experimental design methodology in which one or more factors are changed at the same time. The strategy employs a chromatography modeling software for the simultaneous optimization of critical chromatographic parameters, which are gradient time tG, temperature T and the ternary composition of the organic eluent B.

DryLab is one of the most established software for chromatography modeling, which allows for modeling of chromatographic separations based on input data from two or more experimental runs. The use of DryLab for HPLC modeling to facilitate methods development was well documented in the last 27 years. In this time a continuous development occurred to the software which enabled it to cope more with the ongoing technological progress. On the other hand, a number of published studies exist that deal with the use of DryLab in different chromatographic modes and wide application ranges. DryLab is applied to solve different analytical problems in pharmaceutical analysis, which deal mostly with the separation of active pharmaceutical ingredients (APIs) in the presence of their impurities and/or their degradation products. In the field of phytochemical analysis many applications on complex plant extracts are also available. Moreover, DryLab has been successfully applied to optimize the separation of different groups of environmental pollutants, peptides and proteins and metabolites.

Highlights:

• Implementation of organic solvent gradients in micellar liquid chromatography, MLC.
• Screening of β-blockers in urine samples with direct injection in gradient MLC.
• 1-Propanol gradients allows the elution of β-blockers of diverse polarity.
• Gradient elution starting with pure micellar solution benefits direct injection.
• Optimisation of organic solvent gradients in MLC can be performed with DryLab®.

Quality by design (QbD) is an approach to product development where a comprehensive understanding of the effect of various inputs (e.g. process parameters, materials) on the final product (active pharmaceutical ingredient or drug product), leads to a process or product design that ensures reliable manufacture of a high-quality product. Analogous to QbD for product, QbD may also be applied to analytical methods, by defining the required analytical performance and systematically relating how the technique and method parameters relate to analytical performance. Achieving the appropriate level of method understanding typically involves a multifactorial approach. The factors to be studied are identified via a systematic risk analysis, which allows truly impactful parameters to be further investigated in studies applying statistical design of experiments (DOE) or mechanistic models to develop a multidimensional region of experimental space in which the effects of key factors are understood and documented. An operating region can then be defined where there is high confidence that the method will operate reliably. Data generated during use of the method can be monitored over time to ensure continued adequate performance of the analysis. 

The International Conference on Harmonisation (ICH) guideline for the Validation of Analytical Procedures (ICHQ2(R1)) currently covers validation procedures for the four most common analytical tests: identification tests, quantitative tests for impurities, limit tests for the control of impurities and quantitative tests for the active moiety(ies) in APIs (active pharmaceutical ingredients) or drug products. The key underlying concepts and strategies are equally applicable to other analytical methodologies; e.g. particle size analysis, dissolution, etc. Typical validation parameters covered in the guideline include accuracy, precision, specificity, detection limits (DL / LOD) and quantitation limits (QL / LOQ), linearity, range and robustness.