Measurement of Chromium in Soil by Atomic Absorption Spectrophotometry

Importance of the Topic

Reliable determination of chromium species in soil is essential for environmental monitoring and regulatory compliance. Hexavalent chromium is toxic and regulated under soil contamination laws, requiring accurate analytical methods to assess contamination levels and inform remediation strategies.

Aims and Study Overview

This study applied furnace atomic absorption spectrophotometry to quantify hexavalent chromium in a certified reference soil (JSAC 0401 Brown Forest Soil). The goal was to demonstrate method performance under official Japanese protocols for both elution and total content tests.

Methodology and Instrumentation

Sample preparation followed Ministry of the Environment Bulletins 18 and 19. For the elution test, an acidic extract (pH 5.8–6.3) was obtained by shaking 50 g of soil with 1 mol/L HCl (liquid/solid ratio 10:1) for six hours, followed by centrifugation and filtration. For the content test, an alkaline extract (5 mM Na2CO3 + 10 mM NaHCO3, ratio 100:3) was prepared by shaking 6 g of soil for two hours, then filtering.

Used Instrumentation

• Atomic Absorption Spectrophotometer AA-6300
• Pyro-coated graphite furnace tubes
• BGC-D2 background correction
• Magnesium nitrate as chemical modifier

Main Results and Discussion

The calibration curve at 357.9 nm showed excellent linearity up to 10 ppb. Measured concentrations of hexavalent chromium in the soil extracts were 0.160 mg/L (elution test) and 0.0519 mg/L (content test), corresponding to 1.60 mg/kg and 1.73 mg/kg in soil. These values are lower than the certified total chromium value of 50.4 mg/kg, reflecting the fraction of hexavalent species.

Benefits and Practical Applications

Furnace AAS provides sensitive and reproducible measurements for chromium speciation in soils. Its straightforward sample preparation and established regulatory acceptance make it suitable for environmental monitoring, quality control, and remediation assessment.

Future Trends and Potential Applications

Advances may include coupling with chromatographic separation for speciation, portable AAS devices for field screening, and integration with hyphenated techniques such as ICP-MS for multi-element analysis. Automation and miniaturization are expected to enhance throughput and applicability in diverse settings.

Conclusion

Furnace atomic absorption spectrophotometry effectively quantifies hexavalent chromium in soil extracts, meeting regulatory requirements and offering reliable data for contamination assessment and environmental risk management.