Determination of Cadmium in the Tap Water by Flameless Atomic Absorption Spectrometry

Significance of the Topic

Cadmium is a toxic heavy metal regulated at extremely low levels in drinking water. In April 2010, Japan lowered its allowable cadmium concentration in tap water from 0.01 mg/L to 0.003 mg/L. Sensitive, reliable methods are essential to ensure public health and regulatory compliance.

Objectives and Study Overview

This application note demonstrates the determination of trace cadmium in tap water using flameless atomic absorption spectrometry (AAS). The study evaluates the Shimadzu AA-7700 system with automatic dilution and re-analysis functions, applying it to certified reference material and spiked tap water samples.

Methodology and Instrumentation

Flameless AAS was performed with the AA-7700 main unit, GFA-7000 graphite furnace atomizer, and ASC-7000/ASK-7000 autosampler.

• Wavelength: 228.8 nm; slit width: 0.7 nm; lamp current: 8 mA (BGC-D2 lamp)
• Graphite tube: pyro-coated; injection volumes 2–20 μL (total 25 μL)
• Temperature program: drying 120 °C, ashing 500 °C, atomizing 1800 °C, cleaning 2400 °C
• Matrix modifier: 5 μL palladium nitrate solution (100 ppm Pd equivalent)
• Calibration: automatic mixing of standard solution (2 ppb), diluent, and inhibitor to cover 0–1.2 ppb range

Main Results and Discussion

The calibration curve exhibited excellent linearity across the 0–1.2 ppb range. Analysis of JAC 0302 river water reference material yielded 1.00 μg/L (certified 1.01 μg/L; %RSD 2.0%). Unspiked tap water showed cadmium below 0.00002 mg/L. Tap water spiked at one-tenth of the regulatory limit (0.0003 mg/L) was measured as 0.00031 mg/L (%RSD 2.3%). The autosampler’s automatic dilution feature successfully reduced injection volume from 20 μL to 3 μL when an unknown exceeded the upper limit, maintaining accuracy over repeated analyses (average 5.01 ppb for a nominal 5 ppb sample).

Benefits and Practical Applications

• Meets stringent cadmium limits in drinking water with high sensitivity
• Automated dilution and re-analysis reduce analyst workload and potential errors
• Robust precision and accuracy support routine water quality monitoring and QC

Future Trends and Potential Applications

• Integration of real-time, online heavy metal monitoring systems
• Expansion to multi-element trace analysis via advanced graphite furnace configurations
• Adoption of AI-driven data processing and method optimization

Conclusion

The Shimadzu AA-7700 flameless AAS system with automated dilution offers a reliable, precise method for trace cadmium determination in tap water, fulfilling updated regulatory requirements while streamlining laboratory workflows.

References

• Ministry of Health, Labour and Welfare Ordinance No.18, Partial Revision Concerning Water Quality Standards, Japan, 2010
• Shimadzu Corporation, Spectrophotometric Analysis No. A426