Client context
Total nitrogen content is a key parameter declared on the fertilizer packaging and regulated by law (EU Regulation 2019/1009 on fertilizing products). It determines the product class and compliance with specification, and any deviation means a batch that does not match the declaration.
The measurement is hindered by the very form of the sample: granulates have an irregular surface and a coating layer, while mineral admixtures and the organic coating produce a strong fluorescence background that masks the Raman signal at shorter laser wavelengths.
Challenge.
- Total nitrogen was determined in the laboratory (Kjeldahl or Dumas), with a turnaround time of 60–90 minutes, so quality control and process correction occurred after the fact.
- The lack of on-line measurement extended the feedback loop and burdened the laboratory.
- Fluorescence from the coating and mineral admixtures hindered Raman measurement at standard wavelengths.
- The irregular surface of the granulate required a representative measurement rather than a point measurement.
Solution
The measurement was performed with a Spectrally™ X1 analyzer in an at-line configuration, with a deliberately selected 1064 nm laser, as the longer wavelength radically reduces the fluorescence background. The granulate was measured in its native form, without preparation, at a station with a rotating sample turntable and three-axis probe position control, ensuring signal averaging over a representative surface area.
For quantitative determination, we used the nitrate group band (NO₃⁻ at approximately 1050 cm⁻¹), whose main carrier in these granulates is ammonium nitrate. The best correlation with nitrogen concentration was provided by the band area, which is less sensitive to minor differences in granulate texture.
Results
| Metric | Result |
|---|---|
| Spectrum vs. total nitrogen correlation | R = 0.91 (based on 16 samples, data from the test register) |
| Sample preparation | none, measurement directly on the granulate in its native form |
| Fluorescence background | overcome with 1064 nm excitation |
| Multi-parameter potential | signal also from the coating and dolomite (several parameters in a single measurement) |
Result of a feasibility study prior to the full chemometrics stage. Client anonymized.
What this means for your process
If you produce fertilizer granulates and confirm nitrogen content only in the laboratory, the same measurement allows you to control total nitrogen on the line, without sample preparation and without shipping samples. This shortens the quality control feedback loop and supports compliance with EU Regulation 2019/1009, while the 1064 nm laser selection resolves the fluorescence issue typical for granulates.
The most reliable way to verify on a specific product is a short feasibility study on real granulate samples.
