Evaluation of Three Methods of Matrix Modifier Injection in Graphite Furnace AAS

Significance of the Topic

Graphite furnace atomic absorption spectroscopy (GFAAS) relies on matrix modifiers to stabilize analytes and reduce interferences. The proper introduction of modifiers greatly influences sensitivity, accuracy and precision in trace metal analysis. This is vital for environmental monitoring, quality control in water and wastewater testing, and industrial laboratories handling complex matrices.

Objectives and Study Overview

This study evaluated three methods for introducing a nickel matrix modifier in the graphite furnace. The aims were:

• To automate a preinjection wet deposition method using a graphite tube atomizer and autosampler.
• To compare the performance of preinjection wet deposition with preinjection dry deposition and traditional simultaneous injection.

Methodology and Instrumentation

Arsenic solutions at 10, 25 and 50 µg/L in 1 percent nitric acid served as test samples. Modifier solutions consisted of 50 mg/L nickel nitrate. Two GFAAS configurations were used: an Agilent SpectrAA 20ABQ and a SpectrAA 400P, both equipped with a GTA-96 graphite furnace, PSD-96 autosampler, deuterium background correction, pyrolytically coated tubes and argon gas. Instrument parameters such as furnace temperature programs, injection volumes and timing were kept consistent across methods, with variations only in modifier deposition steps to achieve wet or dry preinjection or mixed injection with the sample.

Main Results and Discussion

Sensitivity, expressed as characteristic mass, was below the published value of 10 pg for all three methods: 8.4 pg for wet preinjection, 9.1 pg for dry preinjection and 8.8 pg for simultaneous injection. Accuracy, measured by percent recovery of arsenic standards, ranged from 94.5 to 106.3 percent. Wet preinjection yielded the best recoveries and lowest standard deviations. Precision, evaluated by relative standard deviations, was highest at 3.7 percent for wet preinjection and poorest at 5.7 percent for simultaneous injection. These differences are attributed to more effective mixing and reaction time when the modifier remains wet on the furnace surface.

Benefits and Practical Applications

The wet preinjection method improves analyte stabilization and matrix interference removal, leading to enhanced sensitivity and reproducibility. Laboratories performing trace metal analysis in environmental, water quality and industrial contexts can adopt this approach to reduce calibration errors, improve detection limits and streamline automated workflows.

Future Trends and Prospects

Advances may include the use of alternative modifiers tailored to specific analytes, integration with faster autosampler systems, and software algorithms for real-time method optimization. Emerging materials for furnace coatings and microvolume injection technologies could further enhance performance and throughput.

Conclusion

Among the three tested methods, wet preinjection of the nickel modifier provided superior sensitivity, accuracy and precision for arsenic determination by GFAAS. This technique offers a robust, automated workflow suitable for a wide range of analytical laboratories.

References

• 1. Analytical Methods for Graphite Tube Atomizers, Varian Techtron Publication No. 85-100848-48 (1988)
• 2. Voth LM, Dealing with Matrix Interferences in the Determination of Priority Pollutant Metals by Furnace AA, Varian Instruments at Work No. AA-35 (1983)
• 3. US EPA Methods for Chemical Analysis of Water and Wastes, EPA-600/4-79-020 (1979)
• 4. US EPA Test Methods for Evaluating Solid Waste SW-846, 3rd Edition (1988)