Analysis of Inorganic Elements in Urine Using EDXRF

Analysis of Inorganic Elements in Urine Using EDXRF — Summary

Significance of the topic:

The rapid identification and quantification of inorganic elements in biological fluids is critical for forensic toxicology and clinical screening of metal poisoning. Conventional ICP techniques provide very low detection limits but require chemical pretreatment (dilution, deproteinization) and specialized lab workflows. Energy-dispersive X-ray fluorescence (EDXRF) provides a non-destructive, low-preparation alternative capable of ppm-level quantitation in liquid urine matrices, enabling fast screening when time and sample handling are limiting factors.

Objectives and study overview:

- Evaluate quantitative performance of an EDXRF spectrometer (Shimadzu EDX-7200) for 15 inorganic elements relevant to poisoning cases.
- Compare conventional calibration-curve quantitation with the instrument’s Fundamental Parameter (FP) based qual-quantitative method that requires no external standards.
- Demonstrate a fast, simple sample preparation and measurement workflow suitable for forensic screening.

Methodology and sample preparation:

- Target elements: 15 metals and metalloids commonly implicated in poisoning (examples include V, Cr, Mn, Co, Ni, Cu, Zn, As, Se, Mo, Cd, Sn, Hg, Tl, Pb).
- Calibration standards: ICP standard solutions (1000 µg/mL) diluted to 0, 1, 5, 10, 25, 50 µg/mL in ultrapure water. 2.5 mL of each standard placed into sample cells sealed with a 5 µm polypropylene film.
- Urine samples: commercially sourced human urine spiked to 10 µg/mL per element by adding 0.25 mL of a 100 µg/mL standard to 2.25 mL urine; 2.5 mL aliquots transferred to sample cells (5 µm film). No protein removal or other chemical pretreatment was applied.
- Overlap and matrix corrections: internal standard correction using scattered X-rays for matrix effects; overlap-correction applied for coexisting lines where spectral interference occurs (element pairs with significant line overlap were corrected).

Instrumentation (Used Instrumentation):

- Spectrometer: Shimadzu EDX-7200 energy-dispersive X-ray fluorescence spectrometer.
- Detector: Silicon drift detector (SDD).
- X-ray tube: Rhodium target.
- Collimator: 10 mm diameter.
- Atmosphere: measurement in air.
- Primary filters: different filter settings used depending on element group; several numbered filters (#1–#5) were selected to optimize sensitivity and reduce background for different element ranges.
- Tube voltages and measurement modes: variable settings—examples include 30 kV for light-to-mid elements and 50 kV for heavier elements; calibration and FP modes used distinct voltage/filter combinations optimized per element.
- Integration times: typical analysis used 60 s × 4 or 60 s × 5 channel measurements; calibration standards were measured with 120 s per channel for improved precision. Dead time was maintained below 30%.

Main results and discussion:

- Linearity: Calibration curves showed excellent linearity for the calibrated elements with correlation coefficients (R) typically in the range ~0.993 to >0.99999 across the studied elements, indicating reliable response in the 0–50 µg/mL range.
- Quantitative accuracy: Using the calibration-curve method, measured accuracies for urine spiked at 10 µg/mL were in the range of approximately 90–111% relative to target values. The FP (qual-quantitative) method, which treats non-measured organic/matrix components as an H2O balance, produced accuracies in the broader range of about 86–124%. Typical absolute uncertainties (3σ) were element dependent and generally under 1 µg/mL for many elements; some heavier elements showed larger σ values.
- Sensitivity limitations: For elements such as Ni and Sn, the 1 µg/mL calibration point was excluded because sensitivity and measurement time were insufficient to obtain reliable data at that low level under the chosen conditions.
- Spectral observations: Native urine contained light elements and common biological matrix signals (P, S, Cl, K, Ca) and trace halogens (Br, Rb). Overlaid spectra confirmed clear peaks for spiked V, Mn, Zn, Se at 10 µg/mL above the blank urine background.
- Throughput: Complete qualitative and quantitative screening could be achieved in approximately 10 minutes per sample, including the measurement scheme used in the study.

Benefits and practical applications:

- Minimal sample pretreatment: Direct analysis of urine without deproteinization or chemical digestion simplifies workflow and reduces contamination risk.
- Rapid screening: Short measurement times (approx. 10 minutes/sample) enable higher throughput in forensic and clinical screening contexts.
- Standards-free option: The FP method allows semi-quantitative to quantitative estimates without external calibration standards, useful for field screening or when standards are not available—accuracy around ±20% in this study.
- Non-destructive analysis: Samples remain intact and do not require conversion to other sample forms, facilitating archiving or further confirmatory tests with orthogonal techniques (e.g., ICP-MS).

Limitations and considerations:

- Detection limits: EDXRF provides ppm-level sensitivity adequate for many poisoning scenarios but is less sensitive than ICP-MS for trace-level work; very low-concentration determinations may be unreliable.
- Spectral overlaps and matrix effects: Accurate quantitation requires overlap corrections and appropriate internal standard/matrix corrections; complex matrices can still challenge FP-only quantitation for some element pairs.
- Element-specific performance: Some elements (e.g., Ni, Sn) had insufficient sensitivity at the lowest calibration points used, requiring method optimization if lower limits are needed.

Future trends and potential applications:

- Integration into rapid-response workflows: EDXRF protocols like this can be incorporated into emergency and forensic triage procedures for immediate screening and prioritization of samples for confirmatory analysis.
- Method optimization for lower detection limits: Improvements in detector technology, increased measurement time, and optimized filters/collimators could extend sensitivity toward sub-ppm levels for more elements.
- Hybrid workflows: Use EDXRF for rapid screening followed by targeted ICP-MS or AAS confirmation balances throughput and sensitivity in routine forensic laboratories.
- Automation and sample handling: Automated sample changers and standardized thin-film cells could increase throughput and reproducibility for high-volume screening operations.

Conclusion:

EDXRF using the Shimadzu EDX-7200 can quantitatively determine multiple inorganic elements in urine at ppm levels with minimal sample preparation and rapid turn-around. Calibration-based quantitation delivered accuracies near unity (90–111%), while the FP qual-quantitative approach provided acceptable screening accuracy (approximately 86–124%), supporting its suitability for forensic poisoning screening where speed and low preparation burden are priorities. Method limitations include higher detection limits compared with ICP-MS and the need to manage spectral overlaps and matrix effects.

References:

• Shimadzu Corporation. Energy Dispersive X-ray Fluorescence Spectrometer EDX-7200: Application note — Analysis of Inorganic Elements in Urine Using EDXRF. First Edition May 2026.