Precise analysis for inorganic fertilizers at the Finnish Food Authority

Significance of the topic

Control of fertilizer composition is essential for food safety, agricultural productivity and regulatory compliance. Reliable quantification of major inorganic nutrients such as potassium (K) and phosphate (PO4) is critical for labeling, import controls and environmental risk assessment. Analytical methods that increase throughput while preserving accuracy and traceability enable competent authorities and commercial laboratories to manage large sample loads and meet statutory requirements efficiently.

Objectives and overview of the study

This case study describes how the Finnish Food Authority (Evira) applied an automated discrete analyzer to routine analysis of inorganic fertilizers. Primary goals were to (1) accelerate sample throughput for ~1000 fertilizer samples per year, (2) maintain or improve analytical precision and uncertainty, and (3) meet national and accreditation requirements for fertilizer control. The laboratory validated the automated methods against established manual techniques and adapted procedures to cover the concentration ranges relevant for fertilizers.

Methodology

Sample preparation and measurement workflows used by Evira were optimized to remove interfering species and fit the capabilities of the discrete analyzer. Key steps included:

• Alkaline digestion: samples were heated for 1 hour in 10% sodium hydroxide to remove ammonium and denature organic interferences, followed by at least 4 hours rest.
• Cation chelation: a 20 mL subsample was mixed with 15 mL of 4% EDTA to complex calcium and magnesium, reducing matrix effects on colorimetric measurements.
• pH adjustment: 0.5 mL of 10% NaOH was added and pH adjusted to >12 prior to filtration and analysis.
• Calibration and dilution: potassium assays used point-by-point calibration with automatic programmable dilutions (e.g., 1:5) for high-K samples; phosphate determinations used an automated colorimetric protocol on the discrete analyzer.

Instrumentation used

Evira implemented the Thermo Scientific Gallery automated discrete analyzer (acquired 2011). The system performs reagent addition, incubation and absorbance measurement for discrete samples, and supports programmable dilution and automated calculation of results against calibration curves. The laboratory is accredited by the Finnish Accreditation Service (FINAS) and follows applicable international guidelines for seed and fertilizer analytics (e.g., ISTA for seed testing activities).

Main results and discussion

Adoption of the discrete analyzer produced substantial gains in productivity and maintained acceptable analytical performance:

• Throughput: the fertilizer K and PO4 tests that previously required two days with manual titration/gravimetric methods are now completed in approximately two hours for the same sample batch.
• PO4 performance: method validation versus a titration reference showed good agreement at high phosphate concentrations with combined uncertainty below 8%.
• K performance: the potassium method was expanded to cover 40–1000 mg/L and reported as percent K for samples in the 1–52% range. To accommodate non-linearity in calibration, point-by-point calibration curves were used with a correction factor applied where required; programmable auto-dilution manages samples above 25% K.
• Operational advantages: elimination of routine glassware cleaning and reduced manual handling lowered labor burden and potential for human error. Occasional analyses of other species (e.g., chromium VI) were performed on the same analyzer though not part of routine workflows.

Graphical data in the case material illustrated improved response-time and calibration behavior for both analytes; potassium assays required specific attention to non-linearity at higher concentrations, addressed by correction factors and defined acceptance limits.

Benefits and practical applications

Implementing the automated discrete analyzer delivered multiple practical benefits for a regulatory laboratory:

• High throughput enabling timely processing of import and market surveillance samples.
• Robust, reproducible measurements meeting accreditation and regulatory uncertainty targets.
• Reduced hands-on time, lower reagent/glassware handling, and minimized operator-dependent variability.
• Flexible assay programming (dilutions, calibration strategies) allowing a single platform to cover wide concentration ranges common in fertilizers.

Future trends and potential applications

Several developments can further improve fertilizer analytics and laboratory operations:

• Integration with laboratory information management systems (LIMS) to streamline sample tracking, results reporting and automated compliance checks.
• Expansion of discrete analyzer methods to additional analytes (trace metals, contaminants such as CrVI) with appropriate sample pre-treatment workflows.
• Advanced chemometric approaches and machine learning to improve calibration models, handle non-linear responses and detect outliers or matrix effects.
• Method miniaturization and greener reagent options to reduce waste and operational costs.
• Automated on-line or semi-automated sample preparation (filtration, digestion, chelation) to reduce manual steps and improve reproducibility.

Conclusion

Evira’s case demonstrates that automated discrete analysis can transform routine fertilizer testing by drastically reducing turnaround time while preserving analytical quality required for regulatory control. Careful sample preparation, calibration strategies and validation against reference methods are essential to ensure accuracy across wide concentration ranges. The approach supports scalable, compliant workflows suitable for national control laboratories and commercial testing services.

Reference

Thermo Fisher Scientific Inc. Case study: Precise analysis for inorganic fertilizers at the Finnish Food Authority Evira. CS71841-EN, 2018.