Quality Control of Mixed Acids

Importance of the Topic

Determining acid concentrations in mixed acid solutions is essential for ensuring consistent etching performance and high product quality in industrial processes. Traditional titration methods are time‐consuming when multiple acids are present, creating a need for faster, reliable alternatives.

Objectives and Study Overview

This application note evaluates near‐infrared (NIR) spectroscopy as a rapid method to quantify acetic acid (AcOH), hydrofluoric acid (HF), and nitric acid (HNO₃) in mixed solutions. The goal is to compare NIR results against conventional thermometric titration and assess time‐to‐result improvements.

Instrumentation Used

• DS2500 Liquid Analyzer (400–2500 nm spectral range)
• DS2500 4 mm vial holder and disposable 4 mm glass vials
• Vision Air Complete software for data acquisition and chemometric model development

Methodology

Mixed acid samples were analyzed in transmission mode using 4 mm pathlength disposable vials. A total of 20 Vis-NIR spectra were acquired across the full spectral range. Chemometric calibration models correlating spectral data with reference titration values were developed in Vision Air software. Model performance was validated by cross‐validation.

Main Results and Discussion

• Acetic Acid (AcOH): R² = 0.852; calibration error = 0.124 %; cross‐validation error = 0.147 %.
• Hydrofluoric Acid (HF): R² = 0.947; calibration error = 0.080 %; cross‐validation error = 0.133 %.
• Nitric Acid (HNO₃): R² = 0.849; calibration error = 0.128 %; cross‐validation error = 0.139 %.

High correlation between NIR predictions and primary method values demonstrates reliable quantification of each acid in complex mixtures within one minute per sample.

Benefits and Practical Applications

The NIR approach reduces analysis time to under one minute, compared to approximately 30 minutes for thermometric titration of three acids. Minimal sample preparation and non‐destructive measurement support high‐throughput quality control in both laboratory and production settings.

Future Trends and Possibilities

Integrating automated sampling robots and flow‐through cells can further increase throughput. Extending chemometric libraries to additional analytes and adapting portable NIR instruments may enable on‐site monitoring. Enhanced data management via networked software will facilitate regulatory compliance and long‐term process tracking.

Conclusion

Vis-NIR spectroscopy with the DS2500 Liquid Analyzer offers a fast, accurate, and robust alternative to traditional titration for mixed acid solutions. Its rapid runtime and reliable performance make it well suited for routine quality control in harsh industrial environments.