Determination of metals in soil by microwave plasma - atomic emission spectrometry (MP-AES) using DTPA extraction

Importance of the Topic

Soil contamination by trace metals can reduce crop yield, disrupt nutrient cycles and introduce toxic elements into the food chain. A reliable, cost-effective analytical technique for quantifying metals in agricultural soils underpins environmental monitoring, quality control and regulatory compliance.

Aims and Study Overview

This work evaluates a routine protocol combining DTPA extraction with microwave plasma–atomic emission spectrometry (MP-AES) for simultaneous determination of Cd, Cr, Cu, Fe, Mn, Pb and Zn in soils. The goals were to demonstrate method sensitivity, precision and comparability with established techniques such as flame atomic absorption (FAAS) and ICP-OES.

Methodology and Experimental Setup

Samples were shaken with a DTPA-based extracting solution at pH 7.3 to complex bioavailable metal ions. After filtration, extracts were analyzed on an Agilent 4100 MP-AES equipped with an inert OneNeb nebulizer and single-pass cyclonic spray chamber. MP Expert software automated background correction, nebulizer pressure optimization and viewing position adjustments. Multielement calibration standards were prepared in the same extraction matrix to ensure matrix matching.

Used Instrumentation

• Agilent 4100 Microwave Plasma–Atomic Emission Spectrometer
• OneNeb inert nebulizer
• Single-pass cyclonic glass spray chamber
• Peristaltic pump, shaker (220 rpm), pH meter and standard labware

Main Results and Discussion

Limits of detection (LOD) ranged from 0.4 µg/L for Cr up to 103 µg/L for Pb, with quantification limits (LOQ) accordingly. Compared to FAAS, MP-AES achieved 5–29-fold lower LODs for Cd, Cu and Fe. Precision (RSD) was generally below 5% across seven soil samples. Results were statistically equivalent (95% confidence) to those from ICP-OES, highlighting comparable accuracy and throughput.

Benefits and Practical Applications

• Elimination of flammable gases—runs on nitrogen generated from compressed air.
• Lower operational cost by avoiding acetylene, nitrous oxide and high-purity argon.
• High sensitivity and precision in complex soil matrices.
• Automated background correction and method optimization reduce analyst workload.

Future Trends and Potential Applications

Further developments may integrate MP-AES with automated soil extraction platforms for high-throughput screening. Emerging chelating protocols could extend this approach to additional contaminants. Coupling with geospatial mapping tools will enhance precision agriculture and real-time soil health monitoring.

Conclusion

The combination of DTPA extraction and Agilent MP-AES offers a robust, sensitive and cost-efficient solution for routine soil metal analysis. It achieves detection limits comparable to ICP-OES while reducing consumable costs and maintenance demands, making it well suited for environmental laboratories and agricultural quality control.

References

1. de Abreu C.A., de Abreu M.F., Soares L.H., Andrade J.C. Development of DTPA soil tests for micronutrients. Commun. Soil Sci. Plant Anal., 42:421–428, 1978.
2. Hettipathirana T. Determination of metals in soils using the 4100 MP-AES. Agilent application note PN 5990-8914EN, 2011.
3. Lindsay W.L., Norvell W.A. Development of a DTPA soil test for Zn, Fe, Mn and Cu. Soil Sci. Soc. Am. J., 42:421–428, 1978.
4. Nhan T.T. Analysis of soil extracts using the Agilent 725-ES and MP-AES. Agilent publication IO-034, 2010.