Efficient Method Development on Pharmaceutical Impurities Based on Analytical Quality by Design

Importance of the Topic

Analytical methods for pharmaceutical impurities must meet demanding requirements for selectivity, sensitivity and robustness to ensure drug safety and regulatory compliance. Applying Analytical Quality by Design (AQbD) to liquid chromatographic method development reduces reliance on user experience, accelerates optimization, and documents a quantifiable design space that supports method validation and robustness demonstrations.

Objectives and Study Overview

The study demonstrates use of LabSolutions MD software to (1) optimize an isocratic LC separation of ketoprofen and three related impurities, and (2) evaluate robustness across different column lots. Optimization was performed by systematically varying mobile phase composition, column oven temperature and flow rate, then visualizing compound resolution as a design space. Robustness was assessed by constructing design spaces for multiple column lots and by testing small deliberate changes around the optimum.

Methodology

The optimization workflow followed AQbD phases: screening (prior selection of promising column and mobile phase), systematic exploration of factor ranges, visualization of design spaces to locate optima, and robustness evaluation around the optimal point.

Key experimental variable ranges examined:

• Acetonitrile fraction in mobile phase (B Conc.): 40%, 45%, 50%, 55%, 60% (5 levels)
• Column oven temperature: 35, 40, 45 °C (3 levels)
• Flow rate: 0.6, 0.7, 0.8 mL/min (3 levels)

The main responses analyzed were pairwise chromatographic resolutions: ketoprofen vs. Imp2 and Imp2 vs. Imp3. After locating the optimum, finer robustness testing varied ACN by ±1% and temperature by ±1 °C around the selected point.

Used Instrumentation

Instrumentation and materials reported in the study:

• LC system: Nexera X3 Method Scouting System
• Column: Shim-pack Velox C18, 100 mm × 3.0 mm I.D., 2.7 μm (Shimadzu)
• Mobile phases: A = 0.1% formic acid in water; B = acetonitrile
• Chromatographic mode: isocratic
• Injection volume: 0.1 μL
• Detection: PDA at 254 nm (SPD-M40, UHPLC cell)
• Software: LabSolutions MD for design space generation and matrix-view chromatogram comparison

Main Results and Discussion

Visual inspection of representative chromatograms showed substantial dependence of impurity separation on acetonitrile content: at 60% ACN two impurities co-eluted on the shoulder of the ketoprofen peak, whereas at 40% ACN the peaks were resolved. Design space visualizations mapped resolution across the factorial ranges and identified an optimum region. LabSolutions MD recommended the following optimum isocratic point based on combined resolution metrics:

• ACN 40%
• Column temperature 35 °C
• Flow rate 0.6 mL/min

Robustness testing around this optimum (ACN 39–41%; temp 34–36 °C) showed that pairwise resolution remained well above target values across the explored region: ketoprofen vs. Imp2 resolution exceeded ~8, and Imp2 vs. Imp3 exceeded ~2, indicating a wide, robust design space.

To assess lot-to-lot variability, separate design spaces were built for three different column lots. The regions of high resolution were consistently present across lots and the representative chromatograms at the optimum point from each lot showed comparable resolution factors (reported near ~11–12 for ketoprofen/Imp2 and ~2.7–3.1 for Imp2/Imp3). This confirms the chosen operating point delivers reproducible separations despite column manufacturing variability.

Benefits and Practical Applications

The demonstrated AQbD-driven workflow provides several concrete advantages for impurity method development:

• Systematic and visual approach to find robust operating regions rather than single-point trial-and-error.
• Faster identification of conditions that satisfy resolution and robustness criteria.
• Objective evaluation of lot-to-lot column variability, supporting method transfer and lifecycle management.
• Matrix view enables rapid side-by-side comparison of many chromatograms, accelerating decision making.
• Built documentation (design space) supports regulatory submissions and method validation by quantifying allowable variability.

Future Trends and Applications

Extensions and likely developments building on this approach include:

• Broader factor inclusion: adding pH, buffer strength, gradient parameters and stationary-phase chemistry to enrich multidimensional design spaces.
• Integration with automated scouting and high-throughput hardware to accelerate exploration of larger factor spaces.
• Machine learning or chemometric models trained on design-space data to predict separation outcomes and reduce experimental runs.
• Standardized workflows for column aging, scale-up, and cross-instrument transfer tied to design-space acceptance criteria.
• Stronger alignment with regulatory AQbD guidance and use of design spaces as part of control strategies in quality systems.

Conclusion

The case study shows that LabSolutions MD enables efficient AQbD-based method development for pharmaceutical impurities. Visualization of design spaces and matrix chromatogram comparisons facilitated identification of a robust isocratic condition (40% ACN, 35 °C, 0.6 mL/min) that maintained high resolution across small deliberate parameter variations and multiple column lots. The approach reduces dependence on operator experience, accelerates method optimization, and yields documented robustness useful for validation and regulatory purposes.

References

• Fujisaki S. Efficient Method Development on Pharmaceutical Impurities Based on Analytical Quality by Design. Shimadzu application note. First Edition: Apr. 2026.