Recovery rates of chloride, bromide and sulfate in certified reference materials using Metrohm Combustion Ion Chromatography

Importance of the Topic

Accurate quantification of halides (chloride, bromide) and sulfur (as sulfate) is essential in environmental monitoring, materials testing and quality control in diverse industries. Traditional sample preparation methods often suffer from incomplete digestion or matrix interferences. Combustion ion chromatography (Combustion IC) overcomes these limitations by combining high-temperature pyrohydrolysis with efficient gas absorption and subsequent ion chromatographic analysis, delivering reliable results for complex solid and liquid samples.

Objectives and Study Overview

This application note presents a validation study of the Metrohm Combustion IC system using certified polyethylene pellet reference materials ERM-EC680k and ERM-EC681k. Key objectives include assessing precision (relative standard deviation), accuracy (recovery rates), and overall suitability of the method for halide and sulfate determination in solid matrices.

Methodology and Used Instrumentation

Samples undergo pyrohydrolytic combustion in the presence of oxygen and argon flows. Evolved gases are absorbed in an oxidizing aqueous hydrogen peroxide solution and directly introduced into the ion chromatograph via intelligent Partial Loop Injection Technique (MiPT) with Inline Matrix Elimination. No internal standard is required, as all dosed volumes are accounted for by the control software.

• Combustion Module with flame sensor technology
• 920 Absorber Module for gas absorption
• Autosampler MMS 5000 (MiPT injection)
• 881 Compact IC pro – Anion – MCS
• IC Conductivity Detector
• Kit for solid samples (adaptable for liquids with a specific kit)
• Columns: Metrosep A Supp 5 – 150/4.0, Metrosep A Supp 4/5 Guard/4.0, Metrosep A PCC 1 HC/4.0
• Eluent: 3.2 mmol/L sodium carbonate, 1.0 mmol/L sodium hydrogen carbonate
• Suppressor regenerant: 100 mmol/L sulfuric acid
• Absorption solution: 100 mg/L hydrogen peroxide
• Operating conditions: flow rate 0.7 mL/min, injection volume 4–100 µL, column temperature 30 °C, conductivity detection after sequential suppression
• Combustion parameters: Ar 100 mL/min, O2 300 mL/min, oven 1050 °C, post-combustion 120 s

Main Results and Discussion

Analysis of ERM-EC680k and ERM-EC681k reference materials demonstrated high precision with RSD values below 2.2 % for all analytes. Recoveries ranged from 97.9 % to 103.0 %, confirming the accuracy of the combustion IC approach. The system reliably separated chloride, bromide and sulfate peaks within a 20 min run time, with linear response over a factor of ten calibration range.

Benefits and Practical Applications

Combustion IC provides a fully automated workflow for solid and liquid samples, minimizing sample handling and potential contamination. Its high sensitivity and selectivity make it suitable for:

• Environmental analysis of plastics, sediments and soils
• Quality control in polymer and chemical manufacturing
• Food, pharmaceutical and cosmetic testing

Future Trends and Potential Applications

Emerging applications may extend to isotopic ratio analysis of halogens and sulfur by coupling to mass spectrometric detection. Integration with robotics and advanced data analytics could further increase throughput and data reliability. Development of dedicated kits for diverse sample matrices will broaden Combustion IC utility in research and industry.

Conclusion

The Metrohm Combustion IC system delivers precise, accurate and automated determination of halides and sulfate in solid and liquid samples. Validation with certified reference materials confirms its reliability, making it an attractive solution for laboratories requiring robust and interference-free analysis.