Quantitation of free amino acids in human plasma by Single Quadrupole LC-MS

Importance of the Topic

The accurate quantitation of free amino acids in human plasma is fundamental for clinical diagnosis and monitoring of metabolic disorders. Rapid and reliable measurement of these biomolecules supports early detection of inborn errors of metabolism and guides therapeutic interventions.

Objectives and Overview

This study demonstrates a high-throughput method for quantifying 37 free amino acids in human plasma using a single quadrupole LC-MS system. The approach aims to deliver robust calibration, reproducible retention times, and streamlined sample preparation suitable for routine clinical laboratories.

Methodology and Instrumentation

Sample preparation employs the Trivitron Bome Trimaris Quantitative Amino Acids Kit, featuring acidic extraction, deproteinization, and derivatization steps.

• Sample volume: 100 µL plasma spiked with deuterated internal standards
• Reagent additions: Four sequential reagents with vortex mixing and brief incubation
• Centrifugation: 5 min at 8 000 rpm, supernatant transferred for analysis

Chromatographic separation is performed on a Trimaris Quantitative Amino Acids Column (0.5 µL injection, 0.25 mL/min, 35 %→95 % organic gradient over 20 min, column at 40 °C). Detection uses a Shimadzu LCMS-2050 single quadrupole mass spectrometer in SIM mode with DUIS positive ionization. Key MS parameters include a drying gas flow of 5 L/min and nebulizing gas of 2 L/min.

Main Results and Discussion

Calibration curves for all 37 amino acids exhibited excellent linearity (R² > 0.995) over physiologically relevant concentration ranges. Retention times were highly reproducible with intra- and inter-day RSD values below 5 %. The LabSolutions Insight software provided automated flagging of out-of-range results, aiding rapid quality control.

Benefits and Practical Applications

The single quadrupole LC-MS method offers several advantages:

• Short total analysis time (20 min per run) with minimal sample handling
• Cost-effectiveness and ease of operation compared to LC-MS/MS
• Compatibility with routine clinical workflows and basic MS expertise
• Comprehensive profiling of essential and non-essential amino acids in plasma

Future Trends and Possibilities

Advancements may include:

• Integration of tandem MS for increased specificity and multiplexed assays
• Automated sample preparation platforms to further reduce manual steps
• Application of machine learning for real-time data interpretation and anomaly detection
• Expansion to additional biomarkers such as biogenic amines and small peptides

Conclusion

The presented single quadrupole LC-MS workflow delivers fast, accurate, and reproducible quantitation of free amino acids in human plasma. Its simplicity and performance make it a valuable tool for clinical laboratories focusing on metabolic disease screening and monitoring.

Reference

Tuna Oncu, Oben Arslan, Ugur Seker, Huseyin Akpinar. Quantitation of free amino acids in human plasma by Single Quadrupole LC-MS, Shimadzu Middle East and Africa FZE, Istanbul, Turkey.