Measurement of Cesium in Tap Water and Soil by Atomic Absorption Spectrometry

Significance of the topic

Efficient removal and monitoring of radioactive cesium isotopes, especially Cs-137, from environmental matrices like water and soil is critical for public health and environmental protection. Stable Cs-133 serves as a nonradioactive surrogate for assessing removal processes, and reliable analytical techniques are needed to evaluate both treatment efficacy and residual contamination levels.

Objectives and study overview

This application note demonstrates the use of atomic absorption spectrometry (AAS) for quantifying cesium in tap water and soil extracts. Key goals include

• Establishing calibration methods for flame AAS and electrothermal AAS (ETAAS)
• Comparing sensitivity and quantitation limits for both techniques
• Assessing method performance through spike recovery and detection threshold evaluations

Methodology and Instrumentation

Sample preparation

• Tap water: analyzed directly without pretreatment
• Soil: 1 g digested with aqua regia on a hot plate, filtered, and diluted to 50 mL for analysis

Analytical techniques

• Flame AAS (Air–C2H2) with Na interference suppressant (0.1 %) for soil extracts
• Electrothermal AAS (ETAAS) using pyrolytic graphite furnace and Na/Ca/Mg mixture as matrix modifier

Applied Instrumentation

Shimadzu AA-7700 atomic absorption spectrophotometer configured for automated switching between flame and furnace atomizers. Key settings included a 852.1 nm wavelength, 0.7 nm slit width, 16 mA lamp current, and non–background correction mode. ETAAS temperature program spanned from 120 °C ramp to a 2000 °C step atomization stage; flame AAS employed a 7 mm burner height.

Main Results and Discussion

Tap water analysis

• No detectable cesium in unspiked samples (< 0.2 µg/L)
• Recovery of 97 % for 1 µg/L spike, confirming method accuracy

Soil analysis

• Flame AAS quantitation limit: 3 µg/g in solid soil
• ETAAS quantitation limit: 0.2 µg/g in solid soil
• Comparative calibration curves show linear response up to 15 µg/L (ETAAS) and 0.2 mg/L (flame AAS)

ETAAS provided superior sensitivity, while flame AAS offered fast throughput. Automated atomizer switching and compact design enhance laboratory efficiency.

Benefits and Practical Applications

• Highly sensitive detection of trace-level cesium supports environmental monitoring and remediation studies
• Spike recovery and low detection limits ensure reliable quantification for both water and soil matrices
• Automated dual-mode operation reduces setup time and potential for alignment errors

Future Trends and Potential Applications

Advances may include coupling AAS with automated sample preparation for high-throughput screening, integration of novel matrix modifiers to further lower detection limits, and adaptation to in-field portable AAS systems for real-time cesium monitoring during remediation operations.

Conclusion

The AA-7700 spectrophotometer effectively measures cesium in environmental samples using both flame and electrothermal techniques. Good spike recoveries, low quantitation limits, and streamlined operation make this approach suitable for research and routine QA/QC monitoring of radioactive cesium surrogates.

Reference