Quantification of Urea in Ethanol by Raman Spectroscopy

Significance of the topic

Quantitative analysis of urea in ethanol is crucial for agricultural fertilizer production and for characterizing stearic acid–urea inclusion compounds. Raman spectroscopy offers a fast, non-destructive approach with minimal sample preparation, enabling on-site and laboratory monitoring of nitrogen content.

Objectives and overview of the study

The aim of this work was to establish a Raman spectroscopy method to accurately quantify urea concentration in ethanol solutions and in solid inclusion compounds with stearic acid, and to validate the approach using portable instrumentation.

Methodology and instrumentation

Standard solutions were prepared by mixing urea and stearic acid stock solutions in ethanol to achieve urea concentrations from 0 to 0.042 g/g while maintaining constant total solute mass. Raman spectra were acquired with an i-Raman® Plus 785S portable spectrometer (785 nm laser, ~90 mW, 5000 ms integration, 20 accumulations) using a BCR100A cuvette holder and background corrected with BWSpec® software. Spectra in the 950–1200 cm⁻¹ region were deconvoluted by fitting four Lorentzian peaks. The ratio of the urea band at ~996 cm⁻¹ to the ethanol band at 1049 cm⁻¹ was used as the analytical parameter.

Main results and discussion

• The intensity of the urea Raman band near 996 cm⁻¹ increased linearly with concentration when normalized to the ethanol band at 1049 cm⁻¹.
• Calibration curve exhibited excellent linearity across the studied range (R² close to 1).
• Analysis of a stearic acid–urea inclusion compound dissolved in ethanol yielded a urea content of 76% w/w, consistent with literature values (~75%).

Benefits and practical applications of the method

• Rapid and non-destructive quantification of urea in liquid and solid mixtures.
• Minimal sample preparation and no significant heating or evaporation effects.
• Portable instrumentation allows on-site quality control in agricultural and industrial settings.

Future trends and potential applications

• Integration of multivariate calibration and advanced spectral processing to improve sensitivity.
• Expansion to on-line process monitoring of fertilizer production.
• Application of the method to other nitrogen-containing compounds and solvents.
• Development of automated, handheld Raman systems for field use.

Conclusion

A straightforward Raman spectroscopy method using portable instrumentation provides accurate, linear quantification of urea in ethanol up to 0.042 g/g, unaffected by stearic acid presence. This approach is suitable for analyzing fertilizer components and inclusion compounds with stearic acid.

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