Quantification of Urea in Ethanol by Raman Spectroscopy

Significance of the topic

Urea is a widely used nitrogen-release fertilizer critical to agricultural productivity and finds applications in purification processes through complex formation. Accurate determination of urea content in solutions and solid inclusion compounds supports quality control, formulation optimization, and process monitoring.

Objectives and overview of the study

This application study develops a Raman spectroscopy method to quantify urea concentration in ethanol and demonstrates its extension to measure urea percentage in a solid inclusion compound with stearic acid. The approach offers a rapid, reagent-free alternative for binary mixtures.

Methodology and instrumentation

Standard solutions with urea concentrations between 0 and 0.042 g urea/g ethanol were prepared by mixing ethanol stock solutions of urea and stearic acid to maintain constant total mass. Raman spectra were acquired using a 785 nm laser at approximately 90 mW power (30% setting), 5 s integration time, and 20 accumulations. Spectral analysis focused on the 950–1200 cm-1 region to isolate urea and ethanol bands.
Instrumentation used:

• i-Raman Plus 785S portable Raman spectrometer featuring a TE-cooled CCD detector and 65–3350 cm-1 spectral range
• BCR100A Raman cuvette holder for 9.5 mm probes, enhancing signal intensity and reducing background fluorescence

Main results and discussion

Spectra normalized to the ethanol band at 1049–1050 cm-1 revealed a characteristic urea peak at 996–997 cm-1, corresponding to symmetric C–N stretching. Deconvolution with four Lorentzian functions in the 950–1200 cm-1 range enabled extraction of peak intensities. The ratio of the urea peak intensity to the ethanol peak intensity showed strong linearity with urea concentration, yielding a robust calibration curve. Analysis of a real sample containing urea and stearic acid resulted in a determined urea content of 76 % w/w, matching literature values for similar inclusion compounds.

Benefits and practical application of the method

This Raman-based quantification method offers:

• Rapid, non-destructive analysis without chemical reagents
• High sensitivity and selectivity for urea in complex mixtures
• Compatibility with portable equipment for on-site or in-process testing

Future trends and possible applications

Emerging developments may include:

• Integration of portable Raman spectroscopy into in-line process control for fertilizer manufacturing
• Application to other small molecules and nonpolar solvents
• Adoption of chemometric and multivariate analysis for complex mixture quantification

Conclusion

A straightforward Raman spectroscopy protocol was validated for quantifying urea in ethanol and extended to solid urea–stearic acid mixtures. The method demonstrates linear response, reproducibility, and suitability for quality control in agricultural and industrial settings.

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