Sensitivity Enhancement for Flame AAS Using an Atom Concentrator Tube for Elements Dissolved in Organic Solvents

Importance of the topic

Flame atomic absorption spectrometry (FAAS) is widely used for trace metal analysis due to its robustness and rapid throughput. However, sensitivity and detection limits limit its use for low‐level analytes in complex matrices. Enhancing atom residence time in the optical path and exploiting organic solvent atomization can markedly improve FAAS performance. Combining liquid‐liquid extraction with an atom concentrator tube offers a path to achieve detection limits competitive with graphite furnace AAS while retaining flame‐based advantages.

Study objectives and overview

This application note evaluates the sensitivity enhancement achieved by coupling two approaches: extraction of metal ions into methyl isobutyl ketone (MIBK) and use of a slotted quartz atom concentrator tube (ACT) on an acetylene/air flame. The study compares calibration responses for Ag, Cu, Pb, Fe and Ni in aqueous and organic media, with and without ACT, to quantify total enhancement factors and explore practical implementation.

Instrumentation used

• Agilent SpectrAA-10BQ atomic absorption spectrometer
• Mark VI burner head with acetylene/air flame
• Agilent Atom Concentrator Tube (ACT 80), 150 mm quartz tube with dual slits
• Epson RX-80 printer for signal recording
• Optional SPS-5 Flame Sampler probe for automated extraction

Methodology

Metal standard solutions (0–10 mg/L) of Ag, Cu, Pb, Fe and Ni were prepared in water and in MIBK after complexation. Each set was analyzed under four conditions: aqueous, aqueous + ACT, MIBK, MIBK + ACT. Gas flows were optimized at 1.8 L/min acetylene for aqueous and 1.2 L/min for organic solutions, with 12 L/min air. Measurement and delay times were both 4 s, using three replicates. Calibration graphs were generated automatically, and enhancement factors at 6 mg/L were calculated from absorbance ratios.

Main results and discussion

The atom concentrator tube alone improved sensitivity by factors of 2–5 for easily atomized elements. Extraction into MIBK afforded an additional 3–5× gain due to favorable exothermic atomization. Combined with ACT, total enhancement factors of 120–300× relative to untreated aqueous solutions were predicted theoretically. Experimentally, MIBK + ACT delivered enhancement factors in the range of 2–11 for individual elements, yielding overall sensitivity improvements consistent with theory. Pb, Cu and Ag showed the highest gains, while Fe and Ni—more refractory—exhibited minimal benefit from ACT, reflecting lower tube temperatures.

Benefits and practical applications

• Detection limits comparable to graphite furnace AAS but with flame‐based simplicity
• Enhanced sensitivity for routine trace metal monitoring in water, environmental and industrial samples
• Rapid, cost‐effective alternative for sea‐water and low‐level analyses
• Potential for automation using programmable flame sampler probes, eliminating manual separatory funnels

Future trends and possibilities

Automation of microextraction and online solvent introduction will streamline high‐throughput workflows. Integration with flow injection and sequential injection systems can further reduce manual handling. Advances in tube materials or heating may extend enhancement to more refractory elements. Coupling enhanced FAAS with chemometric calibration and hybrid detector architectures could broaden its applicability in emerging fields such as speciation analysis and on‐site monitoring.

Conclusion

The combination of organic solvent extraction and a quartz atom concentrator tube significantly enhances FAAS sensitivity, achieving up to two‐hundred‐plus fold improvements for readily atomized metals. This approach offers a practical, flame‐based alternative to graphite furnace techniques for many trace metal determinations. Selection of elements and optimization of tube conditions are key to maximizing benefits.

References

• 1. R. Watling, J. Anal. Chim. Acta, 1977, 94, 181.
• 2. R. Watling, J. Anal. Chim. Acta, 1978, 97, 395.
• 3. H. T. Delves, Analyst, 1970, 95, 431.
• 4. R. Bye, Fresenius’ Z. Anal. Chem., 1981, 306, 30.
• 5. A. Taylor and A. A. Brown, Analyst, 1983, 108, 1159.
• 6. A. A. Brown and A. Taylor, Analyst, 1984, 109, 1455.
• 7. A. A. Brown, B. A. Milner and A. Taylor, Analyst, 1985, 110, 501.
• 8. M. Harriot, D. Thorburn Nurns and N. Chimpales, Anal. Proc., 1991, 28, 193.
• 9. S. Xu, L. Sun and Z. Fang, Talanta, 1992, 39, 581.
• 10. J. Moffet, Spectroscopy, 1990, 5, 41.
• 11. J. Moffet, AA-91 Varian Instruments At Work, 1989.
• 12. K. Kramling and H. Peterson, Anal. Chim. Acta, 1974, 70, 35.
• 13. L. G. Danielsson, B. Magnusson and S. Wasterlund, Anal. Chim. Acta, 1978, 98, 47.
• 14. J. D. Kinrade and J. G. Van Loon, Anal. Chem., 1974.
• 15. J. G. Welz, Atomic Absorption Spectrometry, Verlag Chemie, Weinheim, 1976.
• 16. R. Bye, T. Agasuster and A. Asheim, Fresenius’ J. Anal. Chem., 1993, 345, 111.