Quality Control of Mixed Acids

Importance of the topic

The concentration of individual acids in mixed solutions is crucial for precise control of etching processes in industries such as semiconductor manufacturing. Traditional methods like thermometric titration become time-consuming and less practical when analyzing three or more acids simultaneously or when rapid results are needed. Near-infrared spectroscopy offers a rapid, non-destructive alternative, enabling real-time quality control with minimal sample preparation.

Objectives and Study Overview

This study aimed to evaluate the feasibility of using a DS2500 Liquid Analyzer with Vis-NIR spectroscopy to quantify acetic acid, hydrofluoric acid, and nitric acid concentrations in mixed solutions. A prediction model was developed and validated to compare NIR results with those from standard thermometric titration, focusing on accuracy, precision, and analysis speed.

Methodology and Instrumentation

Mixed acid samples containing varying proportions of AcOH, HF, and HNO3 were measured in transmission mode across the 400–2500 nm range. Each sample was loaded into a 4 mm pathlength disposable vial and analyzed using the DS2500 Liquid Analyzer. Model calibration and validation were conducted using Vision Air Complete software, employing multivariate regression to correlate spectral data with reference titration values.

Instrumentation

• DS2500 Liquid Analyzer covering 400–2500 nm with temperature control up to 80 °C and compatibility with disposable vials and quartz cuvettes
• 4 mm pathlength disposable glass vials
• Vision Air Complete software for spectral acquisition and chemometric model development

Main Results and Discussion

Spectral data from 20 samples were used to create prediction models. The correlation coefficients (R2) for acetic acid, hydrofluoric acid, and nitric acid were 0.852, 0.947, and 0.849, respectively. Standard errors of cross-validation ranged from 0.133% for HF to 0.147% for AcOH, demonstrating good predictive performance. These results indicate that NIR spectroscopy can reliably quantify individual acids in complex mixtures.

Benefits and Practical Applications

• Rapid analysis, with each measurement completed in under one minute compared to approximately 25–31 minutes by thermometric titration
• Minimal sample preparation and reagent consumption
• Non-destructive testing suitable for inline or at-line monitoring in harsh production environments

Future Trends and Applications

Advances in NIR instrumentation and chemometric algorithms will further enhance sensitivity and reduce calibration requirements. Integration with automated sampling systems and process control platforms can enable real-time monitoring of chemical processes. Expansion to other industrial acid mixtures and adaptation to portable analyzers offer new opportunities in field applications.

Conclusion

NIR spectroscopy using the DS2500 Liquid Analyzer provides a fast, accurate alternative for the determination of acetic, hydrofluoric, and nitric acids in mixed solutions. This method supports efficient quality control and can be seamlessly integrated into production workflows for improved process reliability.