Improvement of Sensitivity and Repeatability in Analysis of Formic Acid

Importance of the Topic

Accurate detection of trace levels of formic acid is critical in fields such as artificial photosynthesis research and impurity profiling of chemical feedstocks. Traditional detectors like TCD offer limited sensitivity, while methanizer-FID setups require additional gas removal steps and catalyst maintenance. A barrier discharge ionization detector (BID) coupled to gas chromatography provides a robust alternative for ppm-level analysis without the drawbacks of catalyst deactivation or complex valve systems.

Objective and Study Overview

This study demonstrates a high-sensitivity GC-BID method for quantifying formic acid at low ppm concentrations in various organic solvents. The goals were to improve repeatability through sample pretreatment, validate linearity across multiple matrices, and compare performance against conventional approaches.

Instrumental Setup

Gas chromatograph: Shimadzu Tracera (GC-2010 Plus) with BID 2010 Plus
Injection: Split mode 1:2, injector temperature 240 °C, 1 µL volume
Column: RESTEK Rtx-WAX, 60 m × 0.53 mm I.D., 1.0 µm film thickness
Carrier gas: Helium, 50 cm/s constant linear velocity
Temperature program: 80 °C hold, ramp 5 °C/min to 130 °C, then 15 °C/min to 230 °C (3 min)
Detector conditions: 240 °C, He discharge gas flow 50 mL/min

Methodology

Glass insert pretreatment:

1. Adjust wool packing to 25 mm from top of liner.
2. Immerse in 0.3 % phosphoric acid in acetone for 1 min.
3. Dry under air or nitrogen.

Column conditioning with phosphoric acid:

1. Inject four replicates of 100 ppm phosphoric acid in methanol at 150 °C.
2. Stabilize column with ten methanol injections at 150 °C.
3. Proceed with sample injections.

Calibration standards: 1, 10, 50 ppm formic acid (v/v) in solvents: acetone, N,N-dimethylacetamide, acetonitrile, methanol.

Key Results and Discussion

• Glass insert treatment eliminated peak loss observed with untreated liners, enabling clear detection of 10 ppm formic acid.
• Column phosphoric acid treatment sharpened peak shapes and stabilized retention times.
• Repeatability: CV 1.6 % over 100 injections of 10 ppm formic acid in acetone.
• Calibration linearity across all solvents: R² ≥ 0.9997, demonstrating consistent response from 1 to 50 ppm.
• The Rtx-WAX column showed excellent performance; other WAX variants require verification.

Benefits and Practical Applications

• Reliable quantification of formic acid at low ppm without a methanizer.
• Reduced downtime by avoiding catalyst deactivation and complex valve arrangements.
• High throughput with stable performance over extended runs, ideal for QA/QC and research workflows.

Future Trends and Potential Applications

• Evaluation of phosphoric acid treatment on alternative column chemistries.
• Extension of BID-GC methods to other volatile organic acids.
• Automation of liner and column pretreatment procedures.
• Integration with mass spectrometry for enhanced identification.
• Real-time process monitoring in synthetic and manufacturing environments.

Conclusion

The GC-BID approach, combined with targeted phosphoric acid pretreatments, offers a sensitive, repeatable, and maintenance-friendly solution for formic acid analysis at ppm levels. This workflow addresses key limitations of traditional detectors and supports diverse analytical demands in both research and industrial settings.

Reference

No external literature references were provided in the original document.