Analysis of Pb and Cr in Soil using Graphite Furnace Atomic Absorption Spectrometry

Importance of Topic

Heavy metal contamination of soil by lead (Pb) and chromium (Cr) poses a critical environmental and public health concern due to accumulation in crops and transfer through the food chain. Regulatory bodies mandate precise quantification of these elements in soil to enforce limits and guide remediation efforts.

Objectives and Study Overview

This study aimed to establish a reliable graphite furnace atomic absorption spectrometry (GFAAS) method for determining Cr in soil—filling a gap in existing standards—and to enhance the accuracy of Pb analysis by mitigating complex matrix interferences in routine soil monitoring.

Methodology and Instrumentation

Soil samples (GBW07409 certified reference material) underwent microwave-assisted digestion with a nitric acid–hydrogen peroxide–hydrofluoric acid mixture, followed by acid removal. Analysis employed an Agilent 280Z GFAAS equipped with:

• Zeeman background correction to separate analyte signals from complex soil matrix absorption
• PSD 120 autosampler and HD Tube-CAM for real-time monitoring of drying and ashing steps
• 20 g/L ammonium dihydrogen phosphate as matrix modifier to remove organics during ashing
• Surface Response Methodology tool in SpectrAA software for optimizing drying, ashing, and atomization temperatures

Main Results and Discussion

Signal profiles for Pb and Cr exhibited high sensitivity with clear, interference-free peaks. Quantitative results for the reference soil matched certified values within ±10% (Pb recovery 107%, Cr recovery 95%). The method required only 10 μL sample injections and achieved a complete analysis cycle per element in approximately 3 minutes, demonstrating both rapid throughput and robust performance in complex matrices.

Benefits and Practical Applications

The developed GFAAS protocol delivers:

• High sensitivity and accuracy for trace-level Pb and Cr in soil
• Efficient matrix interference removal via Zeeman background correction and matrix modifiers
• Rapid, low-volume analysis ideal for high-throughput environmental laboratories
• Compliance with stringent soil quality standards for annual monitoring

Future Trends and Applications

Key directions include:

• Formal adoption of GFAAS for Cr in soil into national standards
• Extension of the optimized approach to additional heavy metals and environmental matrices
• Enhanced automation and integration with online monitoring systems
• Development of portable GFAAS platforms for in-field analysis

Conclusion

The optimized Agilent 280Z GFAAS method provides a robust, sensitive, and rapid solution for quantifying Pb and Cr in soil, effectively overcoming matrix challenges and supporting regulatory compliance and remediation strategies.

Reference

• US EPA Method 7010: Determination of Chromium in Environmental Samples by Graphite Furnace Atomic Absorption Spectrometry