Quantitative Analysis of MEA-Triazine Hydrogen Sulfide Scavengers Through Innovative Transmission FTIR Spectroscopy

Importance of the Topic

Hydrogen sulfide (H₂S) contamination in oil and gas streams poses serious safety, environmental, and operational risks. Monoethanolamine-triazine (MEA-triazine) is widely used to scavenge H₂S, but accurate determination of its concentration in viscous aqueous solutions remains challenging. Conventional techniques—such as Kjeldahl digestion, ion-exchange chromatography, and gas chromatography—are often time-consuming, labor intensive, and prone to error. A rapid, robust analytical approach is essential for quality control in both laboratory and field environments.

Objectives and Study Overview

This study aimed to develop and validate a mid-infrared (mid-IR) transmission FTIR method using the Agilent Cary 630 spectrometer equipped with a DialPath accessory. Key objectives included:

• Establishing a calibration model for MEA-triazine in water over a broad concentration range.
• Evaluating method linearity, precision, and accuracy.
• Assessing the impact of common viscosity-reducing additives (methanol, isopropyl alcohol) on quantification.

Methodology

Calibration and interference samples were prepared as follows:

• Calibration standards: MEA-triazine in water at 15, 20, 25, 30, 40, 50, 60, and 75 % w/w.
• Interference sets: 25 % and 50 % MEA-triazine with added MeOH or IPA at 10, 15, and 25 % v/v.
• Spectra acquisition: 32 scans, 4 cm⁻¹ resolution, 4000–650 cm⁻¹, 50 µm path length, 7 µL sample volume.
• Quantification metric: peak area between 1284.07 and 1203.93 cm⁻¹, reflecting characteristic triazine absorbance.

Instrumentation

The analysis employed:

• Agilent Cary 630 FTIR spectrometer with ZnSe optics.
• DialPath transmission module offering three selectable path lengths.
• Agilent MicroLab Quant software for automated calibration curve generation, cross-validation, and independent-set prediction.

Main Results and Discussion

The method exhibited excellent linearity (R² = 0.9993) across the calibration range. Cross-validation yielded a standard error of 0.116 %.

Interference study findings:

• Methanol addition caused a slight negative bias in measured MEA-triazine, with maximum deviation of 0.98 % at 25 % MeOH for a 25 % MEA sample and 4.36 % at 25 % MeOH for a 50 % sample.
• Isopropyl alcohol induced a positive bias, up to 5.78 % deviation at 25 % IPA for the 25 % sample and 6.55 % for the 50 % sample.
• Spectral overlays revealed an IPA-induced new band at 1325–1275 cm⁻¹, whereas MeOH only attenuated water-related absorptions.

The DialPath design minimized common errors—eliminating leaks, bubbles, and complex cell assembly—and high repeatability was achieved even with viscous solutions.

Benefits and Practical Applications

This FTIR-based approach offers:

• Rapid analysis (<5 minutes per sample) with minimal sample volume.
• Reduced susceptibility to pipetting and solvent-handling errors.
• Flexible path length adjustment to limit water absorption interferences.
• High throughput enabled by quick window cleaning and automated software routines.

These advantages suit both routine laboratory QC and potential on-site process monitoring.

Future Trends and Opportunities

Potential developments include:

• Expanded calibration models that account for mixed-solvent matrices.
• Inline or at-line FTIR probes for real-time scavenger monitoring.
• Application of multivariate chemometric techniques to enhance selectivity in complex matrices.
• Adaptation of the method for other amine-based scavengers or contaminants in process streams.

Conclusion

The Agilent Cary 630 FTIR with DialPath module, combined with MicroLab Quant software, provides a fast, accurate, and user-friendly method for quantifying MEA-triazine in aqueous solutions. It overcomes limitations of traditional analytical techniques, delivers high precision, and streamlines workflow, making it well suited for industrial quality control and process monitoring.

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