Determination of Cd, Cr, Ni and Pb in Grains using the Agilent 280Z Zeeman GFAAS

Significance of the Topic

The reliable determination of trace heavy metals such as cadmium, chromium, nickel and lead in cereal grains is critical for ensuring food safety, meeting regulatory limits and protecting public health. Analytical methods with high sensitivity, accuracy and robustness are essential for routine monitoring in agricultural and food quality control laboratories.

Objectives and Study Overview

This study aimed to adapt and validate four Chinese national methods for the quantification of Cd, Cr, Ni and Pb in wheat flour using Zeeman graphite furnace atomic absorption spectrometry (GFAAS). Key objectives included:

• Evaluating method detection limits and calibration linearity for each element.
• Verifying accuracy and precision through analysis of certified reference materials (SRMs).
• Demonstrating instrument stability over prolonged analysis sequences.

Methodology

Samples of wheat flour and certified reference materials were acid-digested according to GB 5009.12—2010 (Pb), GB 5009.15—2014 (Cd), GB 5009.123—2014 (Cr) and GB 5009.138—2003 (Ni). Appropriate chemical modifiers (ammonium dihydrogen phosphate and magnesium nitrate for Pb; ammonium dihydrogen phosphate for Cd; palladium nitrate for Cr and Ni) were added to stabilize analytes. Calibration standards were prepared automatically by the PSD 120 autosampler to ensure accurate dilution and standard additions. A 5 ppb lead standard was remeasured periodically over a 7-hour run to assess long-term stability.

Used Instrumentation

• Agilent 280Z Zeeman Graphite Furnace Atomic Absorption Spectrometer
• Agilent GTA 120 Graphite Tube Atomizer
• Agilent UltrAA hollow-cathode lamps (plug-and-play configuration)
• Agilent PSD 120 autosampler for automated standard preparation and sample introduction

Main Results and Discussion

Method detection limits achieved were 2.6 ppb for Pb, 0.37 ppb for Cd, 1.5 ppb for Cr and 6.0 ppb for Ni, all below the requirements of the respective GB methods. Measured concentrations in NIST 1567b wheat flour and DUWF-1 durum wheat flour closely matched certified values, with recoveries ranging from 92 % to 105 %. Calibration curves exhibited correlation coefficients above 0.999, indicating excellent linearity. Long-term stability testing of a 5 ppb Pb standard yielded an RSD of 1.6 % and recovery deviation under 4 % over seven hours, demonstrating robust performance.

Benefits and Practical Applications of the Method

• High sensitivity and low detection limits suitable for regulatory compliance.
• Accurate, precise results validated against certified reference materials.
• Zeeman background correction minimizes spectral interferences in complex matrices.
• Automated sample preparation reduces operator workload and variability.
• Rapid furnace cycling and low argon consumption lower running costs.

Future Trends and Applications

Advances may include integration of micro-GFAAS systems for field-deployable monitoring, coupling with hyphenated techniques (e.g., HPLC-GFAAS) for speciation analysis, and implementation of machine-learning algorithms for spectral deconvolution and method optimization. Enhanced automation and miniaturization will further improve throughput and sustainability in food safety testing.

Conclusion

The Agilent 280Z Zeeman GFAAS with GTA 120 atomizer and PSD 120 autosampler provides a sensitive, accurate and cost-effective solution for trace determination of Cd, Cr, Ni and Pb in grains according to established Chinese national methods. The method’s excellent detection limits, calibration linearity and long-term stability make it well suited for routine quality control in food testing laboratories.

References

1. GB 5009.12—2010: Determination of Lead in Food.
2. GB 5009.15—2014: Determination of Cadmium in Food.
3. GB 5009.123—2014: Determination of Chromium in Food.
4. GB 5009.138—2003: Determination of Nickel in Food.
5. Agilent Technologies, Application Note 5991-8844EN, 2019.