Separation and Detection of an Azido Impurity in Sartan Drug Substances Using the XSelect CSH Phenyl-Hexyl Column by UHPLC-UV-MS

Importance of the Topic

A recent wave of recalls involving angiotensin II receptor blockers known as “sartan” drugs has highlighted the critical need to detect trace amounts of a genotoxic azido impurity during pharmaceutical quality control. The azido intermediate shares a multi-ring tetrazole backbone with its parent APIs, making separation and quantification challenging. Rapid and reliable analytical methods are essential to ensure patient safety and regulatory compliance.

Study Goals and Overview

This work aimed to develop a generic, fast UHPLC-UV-MS method capable of baseline separation and accurate quantitation of three sartan APIs (irbesartan, losartan, valsartan) and their common azido impurity. A comparison was made between the United States Pharmacopeia (USP) monograph approach and an alternative column chemistry, with the objective of achieving a simple, under-3-minute isocratic analysis compatible with UV and mass detection.

Methodology and Instrumentation

Four analyte stock solutions were prepared at 1 mg/mL in 50:50 acetonitrile-water, followed by serial dilutions. Initial trials employed the USP valsartan monograph conditions on a hybrid C18 column, revealing co-elution of irbesartan and the azido impurity. Method development then focused on a charged surface hybrid phenyl-hexyl column to exploit pi-pi interactions and weak ion-exchange behavior.

Used Instrumentation

• UHPLC System: ACQUITY Arc coupled to a 2998 Photodiode Array Detector
• Mass Detector: ACQUITY QDa operating in positive electrospray ionization with SIR acquisition
• Columns: XSelect BEH C18 3.0×50 mm, 2.5 µm and XSelect CSH Phenyl-Hexyl 3.0×50 mm, 2.5 µm
• Mobile Phases: water, acetonitrile and 2% formic acid modifier under isocratic conditions
• Flow Rate: 0.85 mL/min; Column Temp: 30 °C; Injection Volume: 1 µL

Main Results and Discussion

The USP-scaled BEH C18 method failed to resolve the azido impurity from irbesartan. Switching to the CSH phenyl-hexyl column produced clear separation of all four compounds within a 3-minute isocratic run. Formic acid proved sufficient as a modifier. MS calibration demonstrated excellent linearity (R2 > 0.99) across the concentration range, with a lower limit of detection of 16 ng/mL for the azido impurity. Accuracy testing at 50 ng/mL yielded 97.4% recovery with 4.2% RSD.

Benefits and Practical Applications

• Enhanced selectivity and resolution of sartans and genotoxic impurity
• Rapid, under-3-minute analysis suitable for high-throughput QC
• Dual UV-MS detection enables mass confirmation and low-level quantitation
• Simple isocratic protocol reduces method complexity and solvent use

Future Trends and Opportunities

Expanding the application of charged surface hybrid and aromatic ligand chemistries may offer improved separations for other impurity classes. Integration of high-speed UHPLC-MS workflows into routine QA/QC and real-time monitoring can further enhance pharmaceutical safety. Emerging detectors and data analytics will continue to drive method sensitivity and throughput improvements.

Conclusion

A robust, fast UHPLC-UV-MS method using an XSelect CSH Phenyl-Hexyl column was established for simultaneous separation and quantitation of sartan APIs and a genotoxic azido impurity. This approach outperforms traditional C18 monographs, delivering high resolution, mass confirmation, and reliable quantitation in less than three minutes. Its simplicity and speed make it well suited for pharmaceutical quality control.

References

1. Waters Corporation. Separation and Detection of an Azido Impurity in Sartan Drug Substances Using the XSelect CSH Phenyl-Hexyl Column by UHPLC-UV-MS. Application Note, September 2021.
2. Mayo Clinic. Angiotensin II Receptor Blockers. Accessed August 30, 2021.
3. Government of Canada Recalls and Safety Alerts. Multiple Lots of Irbesartan, Losartan, and Valsartan Drugs Recalled Due to Azido Impurity. Accessed August 16, 2021.
4. United States Pharmacopeia. Monograph Conditions for Valsartan Tablets USP43-NF38. 2021.