Ultra-Low Level Analysis of Aldosterone in Plasma Using the Xevo TQ-XS for Clinical Research

Significance of the Topic

Aldosterone is a key mineralocorticoid hormone involved in blood pressure regulation. Accurate measurement at very low concentrations is essential for clinical research, but traditional radioimmunoassays suffer from cross-reactivity and manual extraction burdens. Modern LC-MS/MS techniques offer improved specificity, sensitivity, and automation, reducing operator error and hazardous isotope use.

Objectives and Study Overview

This study aimed to develop and validate a high-throughput LC-MS/MS method for the quantification of aldosterone in human plasma down to ultra-low physiological levels. Key goals included achieving robust selectivity against structurally related steroids, automating sample preparation, and demonstrating agreement with external quality assessment (EQA) schemes.

Instrumentation Used

• Oasis MAX µElution Plate for solid-phase extraction
• ACQUITY UPLC I-Class System with CORTECS C18 column and VanGuard cartridge
• Xevo TQ-XS Tandem Quadrupole Mass Spectrometer
• MassLynx Software with TargetLynx and LIMS interface
• Tecan Freedom Evo 100/4 Liquid Handler with File Converter v2.0

Methodology

Plasma samples (200 µL) were spiked with deuterated internal standard and protein-precipitated with zinc sulfate/methanol. Automated SPE on Oasis MAX µElution plates included conditioning, loading, washing, and low-volume elution. UPLC separation used a water/ammonium fluoride and methanol gradient on a 2.1 × 100 mm C18 column at 45 °C. Xevo TQ-XS operated in MRM mode (359.3>189.2 as quantifier) with electrospray ionization and rapid cycle times to preserve peak integrity.

Main Results and Discussion

No significant interferences were observed from closely related steroids or common endogenous compounds. The limit of quantification was 2.8 pmol/L with signal-to-noise >10 at 8.3 pmol/L. Total precision across three QC levels ranged from 2.7 to 6.3% CV, and repeatability matched these figures. Linearity was confirmed from 6.7 to 4994 pmol/L (r2 > 0.995). Matrix effect studies in six donor plasmas showed minimal ion suppression, with internal standard compensation yielding <6% variation. Comparison to EQA MS means by Deming regression and Bland–Altman plots indicated a mean bias of −3.3%, demonstrating excellent accuracy. Over 672 injections, backpressure increased by only 380 psi and peak areas varied by 3.6% RSD, underlining method robustness.

Benefits and Practical Applications

This automated LC-MS/MS workflow reduces sample handling time and exposure to radioisotopes, while delivering high sensitivity and analytical selectivity. It is well suited for clinical research studies requiring reliable low-level aldosterone quantification, such as hypertension and cardiovascular investigations.

Future Trends and Opportunities

Integration of microflow LC and advanced ionization sources may further lower limits of detection and sample volumes. Coupling with laboratory information management systems and cloud-based data analytics can enhance throughput, traceability, and real-time quality control. Expanded multiplexing could enable simultaneous steroid profiling.

Conclusion

The presented method delivers ultra-low quantification of aldosterone in plasma with excellent precision, accuracy, and robustness. Automation and stringent validation against EQA standards make it a powerful tool for clinical research applications.

Reference

• Dominic Foley and Lisa Calton. Ultra-Low Level Analysis of Aldosterone in Plasma Using the Xevo TQ-XS for Clinical Research. Waters Corporation, 2019.