Determination of Butyltin Compounds in Environmental Samples by Isotope Dilution GC-MS

Significance of the Topic

The monitoring of organotin compounds, especially monobutyltin (MBT), dibutyltin (DBT) and tributyltin (TBT), is crucial due to their toxic effects and regulatory restrictions in aquatic environments. Routine, accurate, and sensitive speciation of these analytes in water, sediments and biota supports environmental assessment and compliance with legislative requirements.

Objectives and Study Overview

This study aimed to develop a rapid and precise isotope dilution GC-MS method for the simultaneous determination of MBT, DBT and TBT in environmental samples such as fresh and sea water, sediments and mussel tissue. By employing a mixed 119Sn-enriched spike and a single injection protocol, the method eliminates time-consuming calibration steps and enhances accuracy through internal standardization.

Methodology

The proposed workflow involves:

• Sample preparation: Spiking ~0.2 g sediment or mussel tissue (or 100 mL water) with the 119Sn-enriched standard mixture followed by extraction in acetic acid/methanol and ultrasound (for sediments), water bath incubation (for biota), or liquid–liquid extraction (for water).
• Derivatization: Ethylation with sodium tetraethylborate under controlled pH (5.4) to convert organotin species into volatile derivatives.
• Isotope dilution calculations: Correction of 13C contributions to molecular ions using simple equations based on measured m, m+1 and m+2 peak intensities.

Instrumentation

Chromatographic separation and detection were achieved on an Agilent 6890N GC equipped with an HP-5MS capillary column and an Agilent 5973 quadrupole MS operating in electron impact ionization (70 eV) and selected ion monitoring mode. Helium served as carrier gas at 1.2 mL/min with a temperature program from 60 °C to 300 °C.

Main Results and Discussion

The method exhibited detection limits of 0.1–0.2 ng/kg and quantification limits below 0.8 ng/kg for all butyltin species, with reproducibility below 3% RSD. Recoveries ranged from 97% to 104% across different concentration levels in seawater. Analysis of PACS-2 sediment and CRM-477 mussel tissue reference materials yielded results in excellent agreement with certified values for DBT and TBT; MBT values aligned with recent recertification data.

Benefits and Practical Applications of the Method

The proposed ID-GC-MS approach offers:

• Superior accuracy and precision by isotope dilution without extensive calibration.
• Fast turnaround: a single 1 µL injection quantifies all three species.
• High throughput: over 15 full analyses per day per operator.
• Cost efficiency: utilizes standard GC-MS instrumentation rather than more expensive element-specific detectors.

Future Trends and Applications

Potential developments include extending the isotope dilution approach to other organometallic pollutants, integrating automated sample preparation systems, and adapting the protocol for field-deployable instruments to support real-time environmental monitoring.

Conclusion

The described isotope dilution GC-MS method represents a practical, reliable and efficient solution for routine speciation of butyltin compounds in diverse environmental matrices, meeting stringent sensitivity and accuracy demands of modern regulatory programs.

References

• Centineo G., Rodríguez-González P., Blanco González E., García Alonso J. I. and Sanz Medel A., “Simultaneous Determination of Mono-, Di- and Tributyltin in Environmental Samples Using Isotope Dilution Gas Chromatography Mass Spectrometry,” J. Mass Spectrom., 2004, 39, 485–494.
• Centineo G., Rodríguez-González P., Blanco González E., García Alonso J. I., Sanz-Medel A., Font Cardona N., Aranda Mares J. L. and Ballester Nebot S., “Isotope Dilution GC-MS Routine Method for the Determination of Butyltin Compounds in Water,” Anal. Bioanal. Chem., 2006, 384, 908–914.