Screening Analysis of Trace Heavy Elements in Powdered Milk by EDXRF

Significance of the Topic

Ensuring that powdered milk, especially for infants, is free from harmful heavy metals is critical for public health and regulatory compliance. Traditional methods such as colorimetric assays and atomic absorption spectrophotometry require complex sample preparation and can suffer from matrix interferences and operator variability. Energy dispersive X-ray fluorescence (EDXRF) offers a rapid, nondestructive alternative that can streamline quality control workflows.

Objectives and Study Overview

This study evaluates the use of EDXRF to screen trace levels of arsenic (As), cadmium (Cd), tin (Sn), lead (Pb), and mercury (Hg) in powdered milk. The primary goals are to establish calibration curves, determine detection limits and repeatability, and assess the method’s suitability for routine production-line and quality control screening.

Methodology

Standard powders were fortified with known concentrations of each element (0–10 µg/g) and additional As / Pb mixtures to correct spectral overlaps. Samples in the powdered state were placed 13 mm deep into polypropylene film holders and measured automatically in a turret. Calibration employed seven concentration levels for each element, with integration times of 3600 s for As, Hg, Pb and 7200 s for Cd, Sn. Ten blank replicates were measured to evaluate repeatability and calculate detection limits.

Used Instrumentation

• EDX-7000/8000 energy dispersive XRF system
• Silicon drift detector (SDD)
• Rhodium target X-ray tube at 50 kV (auto current)
• 10 mm collimator and primary filters #1, #4
• Air atmosphere, dead time limited to 30%

Main Results and Discussion

Calibration curves for all elements showed linear response with calibration accuracy (σc) below 0.2 ppm (As 0.13, Hg 0.04, Pb 0.12, Cd 0.11, Sn 0.08). Detection limits (3× blank standard deviation) were found to be 0.047 ppm for As, 0.069 ppm for Hg, 0.074 ppm for Pb, 0.23 ppm for Cd, and 0.57 ppm for Sn. Blank repeatability standard deviations ranged from 0.016 ppm (As) to 0.191 ppm (Sn). Screening of a 1 ppm standard yielded quantitative results within the combined error margin, enabling clear judgments against reference thresholds.

Benefits and Practical Applications

EDXRF allows direct measurement of powdered milk without acid digestion, reducing analysis time and eliminating subjective colorimetric steps. The automated sample handling and high repeatability minimize operator effects. This technique is well-suited for rapid screening of heavy metals during manufacturing and final product quality control to ensure compliance with regulatory limits.

Future Trends and Potential Applications

Advances in detector technology and spectral deconvolution algorithms are expected to lower detection limits further and improve throughput. Integration of EDXRF systems with industrial automation and real-time data analytics will enable continuous monitoring in production lines. The methodology may be extended to other food matrices and additional trace contaminants.

Conclusion

Energy dispersive XRF has been demonstrated as an effective screening tool for trace heavy metals in powdered milk, combining adequate sensitivity, accuracy, and reproducibility with simplified sample preparation. Its adoption in routine QC can enhance safety assurance and operational efficiency.

References

1. Codex Alimentarius Commission. Guidelines on Measurement Uncertainty CAC/GL 54-2004; CAC-GL 59-2006.
2. Fujimori T. Statistical Analysis Methods for Analytical Engineers. Maruzen, 2008, p 45.