Reducing risk in HPLC / LC-MS therapeutic drug treatment and monitoring

Significance of the Topic

High-performance liquid chromatography (HPLC) and liquid chromatography–tandem mass spectrometry (LC-MS/MS) underpin critical analyses in therapeutic drug monitoring, forensic toxicology and antibiotic dosing. Impurities in water used for mobile phases and sample preparation introduce particulates, ions and organic contaminants that degrade chromatographic performance, generate ghost peaks and compromise sensitivity. Ultrapure water (Type I, 18.2 MΩ·cm, TOC <10 ppb, <1 CFU/ml) is essential for reproducible, high-confidence results across diverse clinical and medico-legal applications.

Objectives and Study Overview

This white paper reviews four application examples to illustrate how water purity directly affects analytical robustness:

• Therapeutic drug monitoring (TDM) of immunosuppressants in transplant patients using LC-MS/MS
• UHPLC-MS/MS quantification of antipsychotic drugs in plasma for personalized psychiatry
• Forensic hair analysis of drugs of abuse with optimized extraction solvents
• Simultaneous LC-MS/MS measurement of nine antibiotics in critically ill patients

The goal is to identify sources of variability, outline methodological best practices and demonstrate the value of standardized, in-house water purification systems.

Methodology and Instrumentation

Each application follows a typical workflow:

• Sample collection (plasma, whole blood, dried blood spots or hair)
• Pre-analytical preparation (protein precipitation, solvent extraction, acidified two-step protocols)
• Chromatographic separation (UHPLC or HPLC with run times ~5–10 minutes)
• Mass spectrometric detection (tandem MS with multiple reaction monitoring)

Instrument setup consistently emphasizes the use of ultrapure water for mobile phase and sample preparation. Key instrumentation:

• LC-MS/MS and UHPLC-MS/MS platforms for multiplexed quantification
• Stable isotope-labeled internal standards to correct matrix effects
• PURELAB water purification systems delivering Type I water

Key Results and Discussion

• Immunosuppressant TDM: LC-MS/MS showed lower inter-subject variance than immunoassays, enabling tighter dose control in transplant recipients
• Antipsychotics: Validated UHPLC-MS/MS achieved ng/ml limits of detection, trueness 89–115%, precision <16%, supporting routine monitoring of seven compounds
• Forensic hair analysis: Extraction solvent choice (methanol/HCl two-step) altered recoveries; harmonized protocols and authentic hair pools improved reproducibility at cut-off concentrations
• Antibiotics in ICU patients: A single 10-minute LC-MS/MS assay quantified nine drugs over 1–100 mg/L, stable for 5 hours, supporting rapid adjustment of antibiotic regimens

Purified water minimized background noise, prevented ghost peaks and ensured consistent retention times and signal stability.

Benefits and Practical Applications

• Enhanced analytical sensitivity and specificity, reducing risks of under- or over-dosing
• Standardized workflows that support inter-laboratory comparability and regulatory compliance
• Faster turnaround times in clinical and forensic settings through simplified sample prep and short run times
• Improved patient outcomes via personalized dosing and early detection of treatment failures

Future Trends and Applications

• Integration of dried matrix spots (blood, plasma) for decentralized TDM
• Expansion of hair and alternative matrices in retrospective toxicology
• Automation and on-line sample prep linked to high-resolution MS for real-time monitoring
• Data analytics and machine learning to predict individual pharmacokinetics and optimize dosing

Conclusion

Across therapeutic drug monitoring, forensic toxicology and antibiotic dosing, water purity emerges as a critical determinant of analytical performance. Implementing reliable in-house purification systems ensures reproducible, sensitive and accurate results, driving better clinical decisions and legal outcomes.

References

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