The analysis of nitrogen, other nutrient and toxic elements in fertilizers using the Thermo Scientific iCAP 7400 ICP-OES

Importance of the Topic

Fertilizers supply essential macro- and micronutrients to crops. Ensuring accurate nutrient content prevents under- or over-application, which can harm yields or cause environmental issues like eutrophication. Reliable multi-element analysis is therefore a key quality control step in fertilizer production and regulatory compliance.

Objectives and Study Overview

This study aimed to evaluate the Thermo Scientific iCAP 7400 ICP-OES Duo for simultaneous determination of nitrogen, primary (P, K), secondary (Ca, Mg, S) and micronutrients (B, Fe, Mn, Cu, Zn, Mo, Se), as well as trace toxic elements (As, Cd, Cr, Pb) in fertilizer matrices. Inter-laboratory reference materials were analyzed to assess accuracy and precision.

Methodology and Instrumentation

Sample Preparation:

• 1 g of each certified reference fertilizer was digested with 18.5 % HCl, boiled and diluted to 100 mL.
• Nitrogen standards prepared from ammonium dihydrogen phosphate; deionized water pre-treated to remove background N.

Instrumentation:

• Thermo Scientific iCAP 7400 ICP-OES Duo featuring axial and radial plasma views with a high-resolution Echelle spectrometer and CID detector.
• Axial view for trace-level elements; radial view for major elements to prevent saturation.
• Key operating parameters: 1350 W RF power, 0.65 L/min nebulizer gas, 16 L/min coolant gas, 50 rpm pump speed.
• Qtegra ISDS Software for plasma optimization and method control.

Analytical Conditions:

• Selected element-specific wavelengths (e.g., N at 174.272 nm, P at 177.495 nm).
• Instrument detection limits (IDL) determined via blank replicates (3σ) and converted to MDL (100× dilution).

Key Results and Discussion

Calibration for nitrogen showed excellent linearity (R² = 0.9998). MDLs ranged from 0.01 mg/kg (Cd) to 250 mg/kg (N), adequate for expected fertilizer concentrations. Recoveries for nitrogen and most nutrients fell between 89 % and 105 % relative to certified values. Some trace elements near MDL (e.g., As) could not be quantified in low-level samples. Overall precision was high, with relative standard deviations around 0.2 % for N.

Benefits and Practical Applications

• Simultaneous multi-element analysis reduces sample throughput time and cost.
• Axial and radial views permit detection of trace and major elements without torch modifications or ionization buffers.
• Low detection limits support stringent quality control and regulatory compliance in fertilizer manufacturing.

Future Trends and Potential Uses

Advances may include automated sample handling, integration with chemometric algorithms for real-time quality assessment, and field-portable or miniaturized ICP-OES systems. Emerging data analytics could further streamline fertilizer nutrient profiling.

Conclusion

The Thermo Scientific iCAP 7400 ICP-OES Duo delivers accurate, precise, and efficient multi-element quantification in fertilizer matrices, aligning with certified reference values within two standard deviations. Its combined axial/radial detection and robust software make it a versatile tool for routine fertilizer analysis.

References

• Cassap M., Application Note 40833, Thermo Fisher Scientific, 2017.