Simultaneous determination of Total Fatty Matter, Iodine Value, and C8–C14 in soap noodles by Vis-NIRS

Importance of the Topic

Quality control of soap noodles underpins consistent product performance, skin compatibility, and manufacturing efficiency. Traditional titration and chromatographic assays are time-consuming and resource-intensive. Implementing a rapid, non-destructive method such as visible-near infrared spectroscopy (Vis-NIRS) can accelerate routine analysis, reduce reagent use, and enable at-line or in-line monitoring.

Study Objectives

This work aimed to establish quantitative Vis-NIR models for three key soap noodle quality parameters:

• Total Fatty Matter (TFM)
• Iodine Value (IV)
• C8–C14 surfactant content

Simultaneous prediction in under one minute without sample preparation was targeted to streamline quality control workflows.

Methodology and Used Instrumentation

A set of 46 representative soap noodle samples was analyzed. Spectra were collected in reflectance mode across 400–2500 nm using a Metrohm NIRS XDS SmartProbe Analyzer. Data acquisition, management, and calibration development employed the Vision Air 2.0 Complete software. Pretreatment comprised a second derivative transformation. Partial Least Squares regression models were calibrated with 5–6 factors for each parameter.

Main Results and Discussion

Model performance metrics demonstrated strong agreement with reference methods:

• TFM (range 78.5–80 %): SEC = 0.10 %, SECV = 0.13 %
• Iodine Value (range 36–40): SEC = 0.39, SECV = 0.45
• C8–C14 content (range 1–17 %): SEC = 0.17 %, SECV = 0.21 %

Correlation plots showed high linearity between NIRS predictions and titration/chromatography results, confirming model robustness.

Benefits and Practical Applications

Vis-NIRS enables simultaneous multi-parameter analysis in less than one minute without chemical reagents or sample preparation. The user-friendly Vision Air interface allows operation by non-specialists, reducing training time and operational costs. Integrating this approach supports high-throughput QC in soap manufacturing, improving throughput and sustainability.

Future Trends and Opportunities

Further extensions include prediction of moisture, acid value, and active detergent content. Emerging directions involve inline process monitoring for real-time control, advanced chemometric techniques for enhanced accuracy, miniaturized and portable NIR probes for field applications, and integration with Industry 4.0 data platforms for automated decision support.

Conclusion

The Vis-NIR method using the Metrohm XDS SmartProbe demonstrates rapid, accurate, and simultaneous determination of TFM, iodine value, and C8–C14 in soap noodles. This approach offers a cost-effective, high-throughput alternative to conventional assays, fitting seamlessly into modern quality control strategies.

Reference

1. NIR Application Note NIR–51, Metrohm, first published November 6, 2017