Fluorine in polyisobutene using Metrohm Combustion IC

Significance of the Topic

Fluorine content in polyisobutene is a critical quality parameter in lubricant and elastomer industries. Accurate quantification ensures product performance, regulatory compliance, and detection of contamination.

Study Objectives and Overview

This application note describes a robust workflow for determining fluoride in polyisobutene using Metrohm Combustion IC. The approach integrates flame sensor combustion, sequential suppression ion chromatography, and inline matrix elimination to achieve reliable quantification.

Applied Methodology and Instrumentation

Sample Preparation:

• Polyisobutene diluted 1:1 with n-hexane.

Combustion and Detection:

• Flame sensor combustion with intelligent Partial-Loop Injection (MiPT).
• Inline Matrix Elimination to remove organic matrix interferences.
• Conductivity detection after sequential suppression.

Chromatographic Conditions:

• Eluent: 3.2 mmol/L Na₂CO₃ and 1.0 mmol/L NaHCO₃.
• Flow rate: 0.7 mL/min; Injection volume: 50 μL; Column temperature: 30 °C; Recording time: 20 min.
• Suppressor regenerant: 100 mmol/L H₂SO₄; Absorption solution: 100 mg/L H₂O₂; Rinse with ultrapure water.
• Calibration range: 30–500 μg/L fluoride (six levels, 30, 50, 100, 150, 250, 500 μg/L); MiPT factor: 16.6.

Combustion Parameters:

• Argon: 100 mL/min; Oxygen: 300 mL/min.
• Oven temperature: 1,050 °C; Post-combustion time: 120 s; Absorption solution volume: 2.0 mL.

Used Instrumentation

• 881 Compact IC pro – Anion – MCS (Metrohm Combustion IC).
• IC Conductivity Detector.
• 920 Absorber Module; Combustion Module; Autosampler MMS 5000; Kit for liquid samples.
• Columns: Metrosep A Supp 5 – 150/4.0; Metrosep A Supp 4/5 Guard/4.0; Metrosep A PCC 1 HC/4.0.

Key Results and Discussion

The method yielded a mean fluoride concentration of 7.9 mg/kg in polyisobutene with a relative standard deviation of 2.2% (n=3). Chloride and sulfate were below quantification limits, demonstrating selective detection of fluoride. The inline matrix elimination effectively prevented matrix effects, and the combustion-IC combination provided stable baselines and reproducible peaks.

Benefits and Practical Applications

• High sensitivity and precision for low-level fluoride in hydrocarbon matrices.
• Automated sample handling and matrix removal reduce operator workload.
• Applicable for quality control in lubricant, rubber, and polymer production.

Future Trends and Potential Applications

Emerging developments may include coupling combustion-IC with mass spectrometric detectors for speciation; expanded inline cleanup approaches; and miniaturized systems for on-site petrochemical analysis.

Conclusion

The described Metrohm Combustion IC method offers a fast, precise, and robust solution for fluoride determination in polyisobutene. Inline matrix elimination and flame sensor technology ensure minimal interference and reproducible results, making it suitable for routine quality control.