Direct Determination of As, Cu and Pb in Seawater by Zeeman Graphite Furnace Atomic Absorption Spectrometry

Significance of the Topic

Environmental pollution in coastal regions and open oceans poses a serious threat to marine ecosystems and human health. Accurate determination of trace metals such as arsenic, copper and lead in seawater is essential for monitoring contamination pathways and supporting geochemical studies. However, the very low concentrations of these elements and the high salt matrix of seawater create analytical challenges that demand highly sensitive and interference-resistant methods.

Objectives and Study Overview

This study aimed to develop and validate a direct determination method for trace arsenic, copper and lead in seawater using Zeeman graphite furnace atomic absorption spectrometry (GFAAS). Key goals included minimizing matrix interferences from the high dissolved-salt content, optimizing chemical modifiers, and establishing reproducible furnace temperature programs for reliable quantification at nanogram-per-milliliter levels.

Methodology and Instrumentation

Sample Preparation:

• Seawater samples were filtered through 0.45 μm membranes and acidified to pH 2 with nitric acid.
• Chemical modifiers were applied to stabilize each analyte and suppress chloride interferences.

Zeeman GFAAS Conditions:

• Instrument: Agilent SpectrAA 400 Zeeman graphite furnace AAS with programmable sample dispenser and computer control.
• Calibration: Standard addition method to account for matrix effects.
• Arsenic and lead: Pyrolytic platform atomization with hot injection at 150 °C, ashing at 1200 °C (As) or 500 °C (Pb), atomization at 2600 °C (As) or 2100 °C (Pb).
• Copper: Wall atomization with drying steps, ashing at 1050 °C, atomization at 2350 °C.
• Chemical modifiers: 1000 mg/L Ni(NO3)2 for As, 2 %w/v ammonium nitrate for Cu, 2 %w/v ammonium oxalate for Pb; all reagents purified to remove trace metal contaminants.
• Measurement: Peak-height absorbance at element-specific wavelengths (As 193.7 nm, Cu 327.4 nm, Pb 283.3 nm).

Main Results and Discussion

Characteristic masses and detection capability were as follows: arsenic 10 pg, copper 4 pg, lead 5.5 pg. Typical seawater concentrations measured by standard addition were 0.15 ng/mL As, 0.21 ng/mL Cu and 3.50 ng/mL Pb. Platform atomization significantly improved sensitivity for As and Pb, while wall atomization was sufficient for Cu. The use of specific chemical modifiers effectively reduced chloride-related background and stabilized analytes. Multiple injection protocols further enhanced signal reproducibility and detection limits.

Benefits and Practical Applications of the Method

• Direct analysis of seawater without preconcentration steps.
• High sensitivity and low detection limits suitable for trace-level monitoring.
• Effective mitigation of salt matrix interferences via tailored modifiers.
• Applicability to environmental monitoring, marine pollution studies and coastal water quality assessment.

Future Trends and Applications

Advancements may include coupling Zeeman GFAAS with automated sampling platforms for real-time coastal monitoring, extending the approach to additional trace elements of environmental concern, and integrating data with geochemical modeling tools. Improvement in lamp technology and furnace designs could further reduce noise and increase throughput in routine monitoring laboratories.

Conclusion

Zeeman GFAAS with optimized furnace programs and appropriate chemical modifiers provides a robust, sensitive and accurate approach for determining trace arsenic, copper and lead in seawater. Platform atomization is recommended for arsenic and lead, while copper can be reliably measured by wall atomization. The method supports environmental and geochemical investigations of marine systems.

Instrumentation Used

• Agilent SpectrAA 400 Zeeman graphite furnace atomic absorption spectrometer.
• Programmable sample dispenser and IBM PS/2 Model 30 computer control.
• Pyrolytic atomization platform and high-intensity UltrAA lamps.

References

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• Methods for Chemical Analysis of Water and Wastes, U.S. Environmental Protection Agency (1979).
• R. D. Ediger, G. E. Peterson, J. D. Kerber, Atomic Absorption Newsletter, 13, 61 (1974).
• W. Slavin, The determination of trace metals in seawater, Atomic Spectroscopy, 1, 66–71 (1980).
• J. R. Montgomery, G. N. Peterson, Analytica Chimica Acta, 117, 397–401 (1980).
• T. N. McKenzie, P. S. Doidge, Paper No. 298, FACSS Conference, September 1982.