Halogen and sulfur in chlorinated and brominated halobutyl rubber applying Combustion IC

Importance of the topic

Halobutyl rubber compounds are widely used in pharmaceutical stopper production due to their low gas permeability and strong chemical resistance. Accurate determination of halogen and sulfur contents is essential for ensuring product safety, regulatory compliance and consistent material performance.

Aims and study overview

This application note describes a validated workflow for quantifying fluorine, chlorine, bromine and sulfur in chlorinated and brominated butyl rubber samples. The study integrates pyrohydrolysis digestion with subsequent ion chromatographic separation to deliver precise and reproducible results.

Methodology

Samples undergo pyrohydrolysis to convert bound halogens and sulfur into ionic species. The gaseous products are absorbed in an aqueous solution and introduced into the ion chromatograph using a Partial Loop Injection Technique with inline matrix elimination. Key operational parameters include:

• Combustion gas flow: argon at 100 mL/min and oxygen at 300 mL/min at 1100 °C, with a 500 s post-combustion hold
• Absorption: 4.0 mL of absorber solution, water inlet at 0.2 mL/min
• Chromatographic columns: Metrosep A Supp 16 (150×4.0 mm) with guard, and Metrosep A PCC 1 HC (4.0 mm)
• Eluent composition: 7.5 mmol/L sodium carbonate and 0.75 mmol/L sodium hydroxide; suppressor regenerant: 250 mmol/L sulfuric acid
• Flow rate: 0.8 mL/min; injection volume: 20 µL; run time: 18 min; column temperature: 45 °C

Used Instrumentation

• 930 Compact IC Flex with conductivity detector and sequential suppression
• MSM Rotor A and suppressor Vario adapter sleeve
• 920 Absorber Module and Combustion Module (oven and ABD)
• Autosampler MMS 5000 with solid sampling kit

Main results and discussion

The method demonstrated high precision across both sample types, with relative standard deviations below 4% for most analytes. Key results:

• Chlorinated butyl rubber: fluorine 36 mg/kg (RSD 1.2%), chlorine 6582 mg/kg (RSD 2.6%), sulfur 62 mg/kg (RSD 2.9%)
• Brominated butyl rubber: fluorine below detection limit, chlorine 290 mg/kg (RSD 23%), bromine 8595 mg/kg (RSD 1.9%), sulfur 2509 mg/kg (RSD 3.6%)

The chromatogram for the brominated sample confirmed clear separation of bromide from other anions.

Benefits and practical applications

This combustion IC approach offers high sensitivity, minimal sample preparation bias and fast throughput. It is ideal for quality control in pharmaceutical packaging production and for meeting stringent regulatory requirements.

Future trends and applications

Advancements may include coupling with mass spectrometric detection for enhanced selectivity, reducing sample requirements through cell miniaturization, and integrating automation for inline monitoring in production environments.

Conclusion

The presented combustion ion chromatography method delivers reliable simultaneous analysis of halogens and sulfur in halobutyl rubbers, supporting robust quality assurance and compliance with pharmaceutical industry standards.