Rapid analysis of harmful heavy metals in pet food using EDXRF

Rapid analysis of harmful heavy metals in pet food using EDXRF — Summary

Importance of the Topic

The safety of commercially produced pet foods is critical for animal health and regulatory compliance. Japan's 2009 regulation sets maximum levels for toxic heavy metals in dog and cat foods (Cd ≤ 1 μg/g, Pb ≤ 3 μg/g, inorganic As ≤ 2 μg/g). Rapid, robust screening methods are therefore needed to monitor cadmium, lead, arsenic, mercury and selenium in diverse sample matrices without the time-consuming acid digestion required by techniques such as AA or ICP-MS.

Objectives and Study Overview

The study evaluated energy-dispersive X-ray fluorescence (EDXRF) using the Shimadzu ALTRACE system as a rapid screening tool for five elements (Cd, Pb, As, Hg, Se) in pet food. Nine samples were analyzed (eight commercial pet foods and one certified reference material) to assess sensitivity, reproducibility, calibration strategy, sample preparation simplicity, and suitability for routine screening in quality control contexts.

Methods and Methodology

Sample preparation focused on minimal pretreatment: solid samples were homogenized by grinding; powdered samples were compressed into sample holders covered by 5 µm polypropylene film. No acid digestion was performed. Measurements used an ALTRACE EDXRF system with an Rh-target X-ray tube and silicon drift detector (SDD). Key analytical parameters: tube voltages (65 kV for Cd/Se, 50 kV for Pb/As/Hg), automatic tube current control, integration times of 300 s (plus an additional 100 s for internal standard correction), collimator 18 mm, and measurements in air. Calibration standards were prepared by diluting ICP standard solutions across low µg/g ranges appropriate for regulatory thresholds. Internal standard correction used scattered X-rays to compensate matrix and geometry effects; spectral-overlap corrections were applied (As calibration corrected for Pb overlap, Pb calibration corrected for Se overlap).

Pooled calibration concentration ranges:

• Cd: 0, 0.25, 0.5, 1, 2.5, 5 μg/g
• Pb: 0, 0.25, 0.5, 1, 2.5, 5 μg/g
• As: 0, 1.5, 3, 5, 7.5, 15 μg/g
• Hg: 0, 1.5, 3, 6, 15 μg/g
• Se: 0, 10, 20 μg/g

Main Results and Discussion

EDXRF demonstrated quantification limits suitable for the regulatory range (theoretical 10σ limits generally below 1 μg/g, i.e., sub-ppm). Measured calibration curves showed excellent linearity (correlation coefficients R ≈ 0.999–0.9999) and reported analytical accuracies on the order of 0.02–0.17 μg/g depending on the element. The certified reference material (CRM 7403‑a swordfish powder) produced measured values close to certified values, supporting accuracy. Among commercial samples, arsenic and mercury were detected primarily in cat-food samples containing large fish ingredients (e.g., bonito, tuna). Repeatability for a freeze-dried tuna sample (n = 10) showed low relative standard deviations (RSDs ~0.9–1.6%), indicating good precision for routine screening.

Instrumental and analytical corrections (internal standard by scattered X-rays and spectral overlap corrections) were important to address matrix effects and elemental interferences in complex pet food matrices. The study emphasizes that while EDXRF reliably quantifies elemental totals, it cannot distinguish chemical species (e.g., inorganic vs. organic arsenic) without an additional speciation method.

Použité instrumentace (Used Instrumentation)

ALTRACE energy-dispersive X-ray fluorescence spectrometer (Shimadzu Corporation) with:

• Rh-target X-ray tube
• Silicon Drift Detector (SDD)
• Collimator: 18 mm diameter
• Measurement atmosphere: air
• Integration time: typically 300 s (+100 s for internal standard)

Benefits and Practical Applications of the Method

EDXRF offers several practical advantages for pet‑food safety screening:

• Minimal sample preparation (grinding or compression) — no acid digestion.
• Rapid throughput — typical measurement times of minutes to tens of minutes per sample.
• Ability to analyze a wide elemental range (Na through U) across solids, powders and liquids.
• Quantification capability at sub-ppm levels suitable for regulatory limits on Cd, Pb, As, Hg and Se.
• Good precision and accuracy for screening and routine QA/QC; useful for identifying samples that need confirmatory analysis by ICP-MS or speciation techniques.

Limitations

EDXRF is an elemental total analysis technique and cannot speciate elements (e.g., cannot differentiate inorganic arsenic from organic arsenic species). Matrix effects and spectral overlaps must be corrected (internal standards, overlap corrections), and very low-level confirmatory analysis may still require ICP-MS or dedicated speciation methods when regulatory enforcement or toxicological speciation is required.

Future Trends and Applications (Budoucí trendy a možnosti využití)

Potential developments that will enhance EDXRF utility in pet‑food and food safety monitoring include:

• Improved detector technology (higher resolution SDDs) and optimized filters to lower detection limits and reduce overlaps.
• Automated sample handling and inline compression to increase throughput in routine QC labs.
• Advanced matrix-correction algorithms and chemometric approaches to reduce calibration dependency and improve accuracy across diverse matrices.
• Hybrid workflows integrating EDXRF screening with targeted confirmatory methods (ICP‑MS, HPLC‑ICP‑MS for speciation) for efficient regulatory compliance.
• Application expansion to surveillance programs and supply‑chain monitoring where rapid triage is required.

Conclusion

EDXRF using the ALTRACE system provides a rapid, accurate and precise screening approach for harmful heavy metals in pet food with minimal sample preparation. The technique achieves sub-ppm quantification, good reproducibility, and practical throughput for routine QA/QC. While EDXRF is not a speciation tool and confirmatory methods remain necessary in some cases, it is well suited as a frontline screening method to detect samples that require further investigation.