Quantitation of Cortisone-21-Acetate Impurities using HPLC/UV with a Waters XBridge Biphenyl RP Column with MaxPeak Premier Technology

Significance of the topic

The accurate quantitation of low‑level impurities in pharmaceutical substances is essential for drug safety, regulatory compliance, and batch release. Reliable HPLC methods with flat baselines and stable stationary phases are critical when using UV detection to measure trace degradants. Biphenyl stationary phases can offer enhanced selectivity for steroidal analytes through π‑π interactions, but some commercial biphenyl columns suffer UV‑detected column bleed that compromises quantitation precision for small peaks.

Objectives and overview of the study

This application note evaluates a Waters XBridge Biphenyl RP column with MaxPeak Premier Technology (trifunctionally‑bonded BEH biphenyl) against two vendor biphenyl columns for the analysis of forced degradation products of cortisone‑21‑acetate (C21A). The primary goals were to: (1) assess UV‑detected column bleed under the chosen gradient/acidic conditions, (2) compare chromatographic selectivity and retention for key degradants, and (3) quantify the impact of column bleed on precision and accuracy of low‑level impurity integration by HPLC/UV.

Methodology

A forced degradation sample of cortisone‑21‑acetate (1 mg/mL in 50:50 water/acetonitrile) was prepared by adding 0.1 mL 1 N HCl to 0.9 mL aliquots and heating at 70 °C for 3 hours, then quenching with 0.1 mL 1 N NaOH. Analyses were performed by reversed‑phase gradient HPLC with UV detection at 254 nm. Key chromatographic conditions (same for all columns): 2.1 x 50 mm column formats, column temperature 30 °C, injection 0.1 µL, mobile phases 0.1% formic acid in water (A) and acetonitrile (B), flow 1.0 mL/min, gradient 5% to 95% B in 6.86 min, hold 95% B 1.14 min, total run 10.30 min. Triplicate injections were used to assess precision of impurity peak area integration.

Used instrumentation

• Arc HPLC system
• 2998 Photodiode Array (PDA) detector; UV detection at 254 nm
• Empower 3 Chromatography Data System (CDS) for data acquisition and processing
• Columns compared: Waters XBridge Biphenyl RP (2.1 x 50 mm, 2.5 µm, MaxPeak Premier/BEH trifunctional bonding) and two vendor biphenyl columns (2.1 x 50 mm, ~2.7 µm)

Results and discussion

Blank diluent injections revealed a pronounced baseline hump (column bleed) on both vendor biphenyl columns extending to approximately 4.3 minutes; the Waters XBridge Biphenyl column showed no detectable UV bleed under the acidic gradient used. In the forced degradation sample several degradant peaks eluted in the bleed region; one impurity of interest had relative retention times (RRT) of 1.137 on the XBridge column versus 1.114 and 1.128 on vendor R and vendor A columns, respectively. The presence of bleed on vendor columns caused baseline distortions that (a) complicated accurate integration of small impurity peaks and (b) led to slightly inflated peak areas compared to the XBridge column.

Precision metrics for the impurity peak area (triplicate injections) showed the XBridge Biphenyl column produced the best repeatability with RSD = 0.56%, compared to RSD = 1.26% (Vendor R) and 1.68% (Vendor A). Absolute peak areas on vendor columns were approximately 10% higher than those obtained on the XBridge column, corresponding to an overestimation of impurity percentage by ~0.05% of total area—an effect attributed to bleed‑related baseline elevation near the analyte.

The improved performance of the XBridge column is attributed to its trifunctionally bonded BEH chemistry, which resists acid‑catalyzed hydrolytic release of bonded‑phase fragments (column bleed) and provides stable performance across a wide pH range (reported pH stability ~1.5–10). Enhanced retention and resolution for specific corticosteroid degradants were also observed versus the competing biphenyl phases.

Benefits and practical applications

• Enables accurate and precise quantitation of low‑level impurities by UV detection in gradient separations where competing biphenyl phases produce bleed‑related baseline artifacts.
• Offers alternative selectivity to C18 phases for steroidal analytes through π‑π interactions while avoiding the bleed drawback common to some biphenyl columns.
• Improved batch‑to‑batch reproducibility and extended pH stability support routine QC workflows and stability testing in pharmaceutical laboratories.

Future trends and applications

Trends likely to continue include wider adoption of chemically robust bonded phases (e.g., BEH-type chemistries) for demanding gradient separations with UV detection, especially when quantitation of trace impurities is required. Potential extensions include: method transferability to LC‑MS workflows, screening of biphenyl selectivity for other steroid classes or π‑rich small molecules, and integration with automated impurity profiling in regulated QC environments. Continued development of stationary phases that minimize bleed while preserving unique selectivity will improve sensitivity and reduce false positives/overestimation of impurities in stability studies.

Conclusion

The Waters XBridge Biphenyl RP column with MaxPeak Premier (trifunctionally bonded BEH) provides a practical solution to the UV‑detected column bleed problem observed with some biphenyl stationary phases. In the forced degradation study of cortisone‑21‑acetate, the XBridge column delivered flatter baselines, better precision (RSD 0.56% for a low‑level impurity), more accurate area measurements, and improved chromatographic resolution for critical degradants compared with two competing biphenyl columns. These features support reliable impurity quantitation by HPLC/UV in pharmaceutical QC and development settings.

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