Analysis of Trace Elements in Water using Ultra Thin Film (2)

Significance of the Topic

Access to reliable methods for detecting trace elements in water is essential for environmental monitoring, public health assessment and industrial quality control. The described approach highlights advanced techniques for both qualitative and quantitative determination of elements at sub-ppm levels, addressing challenges related to matrix effects and method versatility.

Aims and Study Overview

This study compares two analytical strategies based on energy dispersive X-ray fluorescence: the fundamental parameter (FP) method and the calibration curve method. The objective is to evaluate accuracy, precision and applicability of each technique in quantifying trace metals in a certified river water reference material.

Sample Preparation and Methodology

• Certified reference sample: NRC SLRS-4 river water standard for trace metals.
• Pretreatment: 50 µL aliquots of sample placed on an ultra thin film substrate and dried at 70 °C for 40 minutes.
• Calibration standards: aqueous solutions of Na (0.5–5 ppm), K (0.5–20 ppm) and Fe (100–500 ppb) prepared via serial dilution.
• Instrumentation Used:

• EDX-700 system with Rh X-ray tube
• Vacuum atmosphere, no Ti filter
• Operating conditions: 50 kV and 15 kV (auto current), 3 mm measurement diameter, 1000 s measurement time, dead time 0–12%

Main Results and Discussion

Qualitative analysis of SLRS-4 identified expected trace elements including Na, Mg, K, Ca, Mn, Fe, Sr and minor halogens. Quantitative comparison against certified values shows the FP method yielded results within a few percent of reference concentrations, whereas the calibration curve approach exhibited larger deviations for samples with differing matrix compositions. Repeatability tests (n=10) using the calibration curve method for Na, K and Fe yielded coefficients of variation of 24%, 4.8% and 8.6% respectively, indicating variable precision depending on element.

Benefits and Practical Applications

• The FP method offers high accuracy across diverse sample matrices without the need for matrix-matched standards.
• The calibration curve method provides a simpler workflow and acceptable precision for routine analysis of homogeneous sample types.
• Both approaches enable rapid, non-destructive analysis of ultra-thin sample films, reducing sample preparation time and reagent usage.

Future Trends and Potential Applications

Advances in detector sensitivity and software algorithms are expected to enhance quantification limits and reduce matrix interferences. Integration of machine learning for spectral deconvolution could further improve accuracy. Application of these methods may expand to complex environmental matrices, industrial process streams and in-field portable XRF instruments.

Conclusion

The comparative study demonstrates that the FP method outperforms the calibration curve approach in accuracy for variable matrices, whereas the calibration curve method remains suitable for consistent sample types. Deploying both techniques in a complementary manner can optimize analytical workflows for trace element monitoring in water.

References

EDX-700/800 Application Data Nos. 11, 12 and 16