Extraction of Three Phosphatidylethanol (PEth) Biomarkers in Human Whole Blood Using ISOLUTE® SLE+ Prior to LC/MS-MS Analysis

Significance of the Topic

Phosphatidylethanol (PEth) species in blood serve as reliable biomarkers for monitoring alcohol intake. Their structural similarity to common phospholipids demands robust sample preparation to eliminate interferences and maintain sensitivity. An efficient extraction and quantification protocol enhances clinical diagnostics, forensic investigations, and quality control in research settings.

Objectives and Study Overview

The study aimed to develop a streamlined supported liquid extraction (SLE) workflow using ISOLUTE SLE+ plates for isolating three PEth variants (16:0, 16:0/18:1, 16:0/18:2) from whole blood. Key goals included achieving high recovery (>60%), low variability (RSD <10%), broad linearity (0.5–5000 ng/mL, r2 >0.999), and clean extracts free of phospholipid interferences prior to LC–MS/MS analysis.

Methodology and Instrumentation

Sample Preparation

• Spike 100 µL whole blood with deuterated internal standard (final 25 ng/mL).
• Dilute with water–acetonitrile (80:20), then load 200 µL onto ISOLUTE SLE+ 400 µL wells.
• Equilibrate 5 minutes under gravity or low positive pressure.
• Elute sequentially with 700 µL ethyl acetate:isopropanol (95:5) three times.
• Evaporate at 40 °C (20–40 L/min) and reconstitute in 200 µL isopropanol.

Chromatography and Detection

• UHPLC: Shimadzu Nexera X2, Agilent Poroshell C8 column (2.1×50 mm, 2.7 µm), 0.3 mL/min, 5 mM ammonium formate/IPA gradient.
• MS/MS: Shimadzu 8060 triple quadrupole with ESI, positive mode MRM transitions for each PEth.

Main Results and Discussion

The SLE approach provided clean extracts with minimal phospholipid carryover. Mean recoveries exceeded 60% for all PEth species, with RSDs below 10% (n=7). Lower limits of quantification were 0.5 ng/mL for 16:0 and 16:0/18:1, and 5 ng/mL for 16:0/18:2. Calibration curves displayed excellent linearity (r2 >0.999) across a 0.5–5000 ng/mL range. Underloading the plate improved cleanliness by preventing cell breakthrough and reducing phospholipid coelution.

Benefits and Practical Applications

This method simplifies bioanalytical workflows by eliminating emulsions inherent to liquid–liquid extraction, reducing sample handling time, and extending column and MS lifespan. Its sensitivity and reproducibility make it suitable for clinical toxicology, forensic screening, and research on alcohol-related disorders.

Future Trends and Opportunities

Advancements may include miniaturized SLE formats for microsampling, integration with automated robotic platforms for high throughput, and coupling with high-resolution MS for non-targeted lipidomics. Novel sorbent chemistries could further enhance selectivity against phospholipids, broadening applications in complex matrices.

Conclusion

The presented ISOLUTE SLE+ based protocol achieves reliable isolation and quantitation of three PEth biomarkers from whole blood with high recovery, precision, and sensitivity. It offers a robust alternative to traditional extraction methods, improving analytical efficiency and data quality in alcohol biomarker studies.

Used Instrumentation

• ISOLUTE SLE+ 400 µL 96-well plate (Biotage)
• Biotage PRESSURE+96 Positive Pressure Manifold
• Biotage SPE Dry-96 evaporator
• Shimadzu Nexera X2 UHPLC
• Agilent Poroshell 120 EC-C8 column (2.1×50 mm, 2.7 µm)
• Shimadzu 8060 Triple Quadrupole MS with ESI interface