MEASURING PEI Polyethylenimine in biological samples

Significance of the Topic

Polyethylenimine (PEI) is widely used in industrial, biomedical and research settings, from gene delivery carriers to adhesion promoters. However, its polydisperse nature, multiple charge states, lack of strong UV chromophores and strong affinity for silica render conventional HPLC analysis challenging. A reliable quantitation method is essential for quality control, formulation development and biological sample analysis.

Objectives and Study Overview

The study aimed to develop a simple, robust HPLC method and a dedicated stationary phase for accurate quantification of PEI in liquid samples. Key goals included sensitive detection, separation of PEI species across a broad molecular weight range and compatibility with various detectors.

Methodology and Instrumentation

The approach relies on complexation of PEI with Cu(II) to form a UV/visible-active adduct, [PEI–Cu]2n+, with absorbance maxima around 285 nm and in the visible region. Sample preparation requires mixing defined volumes of PEI stock solution (10 mg/mL) and CuSO4 stock solution (10 mg/mL) with water, adjusted for PEI molecular weight. Analysis employs:

• HPLC system with a PEI-specific column (4.6 × 250 mm, 5 μm) combining ion-exclusion and size-exclusion mechanisms
• Mobile phase: 40 % acetonitrile/60 % ammonium formate buffer (20 mM, pH 3.0)
• Flow rate: 0.5 mL/min; injection volume: 10 μL
• Detection: UV-Vis at 285 nm (primary), visible detection ~630 nm (confirmatory)
• Optional detectors: ELSD, CAD, ESI-MS for evaporative or mass-based analysis without Cu(II) complexation

Main Results and Discussion

Chromatograms demonstrate clear resolution of PEI–Cu complexes across molecular weights from ~400 to 60 000 g/mol. Calibration studies showed linear response with a limit of quantitation down to ~10 ppm PEI. The dedicated PEI column effectively separates the complex from free Cu(II) and other matrix components. ELSD detection of uncomplexed PEI provides an alternative, and carryover issues are mitigated by a 2 % HClO4 needle wash between injections, reducing residual adsorption.

Benefits and Practical Applications

This methodology offers:

• High sensitivity and selectivity for PEI quantitation in diverse matrices
• Simple sample preparation via Cu(II) complexation
• Compatibility with multiple detection modes (UV, ELSD, CAD, MS)
• Effective control of carryover for reproducible results

Applications include polymer characterization, formulation monitoring, bioconjugate analysis and QC workflows.

Future Trends and Potential Applications

Advancements may involve further column optimization for faster separations, exploration of alternative metal complexing agents to tune detection wavelengths, integration with high-resolution MS for structural profiling, and automation of sample preparation. Expansion into capillary formats and microfluidic platforms could enable lower sample consumption and higher throughput.

Conclusion

The described HPLC method, leveraging PEI–Cu(II) complexation and a tailored stationary phase, provides a robust, versatile solution for accurate quantification of PEI across a broad molecular weight range. Its adaptability to various detectors and effective carryover control make it suitable for routine analytical and QC applications in research and industry.