The Analysis of Organotin Compounds in Water by GC-MS using Large Volume Injection

Importance of the Topic

Environmental monitoring of organotin compounds such as tributyl tin and triphenyl tin is essential due to their listing as priority pollutants and the requirement to detect them at concentrations as low as 0.1 μg/L. Traditional derivatisation methods using Grignard reagents are laborious, time consuming and resource intensive, creating a demand for more efficient analytical workflows.

Objectives and Study Overview

This work aims to develop a simplified gas chromatography mass spectrometry method for the analysis of organotin compounds in water samples. By employing sodium tetraethyl borate for derivatisation combined with large volume injection, the study seeks to enhance sensitivity while eliminating the need for extensive pre concentration steps.

Methodology and Instrumentation

The sample preparation and analysis workflow includes the following steps:

• Extraction: 200 mL water sample is spiked with tripentyl tin internal standard, salted, and reacted with sodium tetraethyl borate.
• Phase Separation: Iso octane is added, the mixture is shaken and the organic layer is collected for analysis.

Instrumentation configuration:

• Optic 2-200 programmable injector in large volume injection mode (50 μL injection).
• HP5890 gas chromatograph equipped with a DB1-MS column.
• HP5972 mass selective detector operating in selected ion monitoring mode.

Main Results and Discussion

The derivatised organotin compounds were chromatographically resolved, and detection limits of approximately 5 ng/L were achieved. Large volume injection enhanced the analyte response, allowing direct analysis without a prior concentration stage. Chromatograms demonstrated clear separation of tributyl, tripentyl and triphenyl tin derivatives with reliable signal to noise ratios.

Benefits and Practical Applications

• Simplicity: Sodium tetraethyl borate derivatisation is less complex than Grignard techniques.
• Efficiency: Elimination of pre concentration reduces analysis time and resource use.
• Sensitivity: Achieves sub-ppb detection limits suitable for compliance monitoring.

Future Trends and Potential Applications

Prospective developments include further automation of sample handling, integration with advanced detectors for multi element or multi class contaminant screening, and adaptation of the methodology for the analysis of other organometallic pollutants in environmental and industrial matrices.

Conclusion

The presented GC-MS method using sodium tetraethyl borate derivatisation and large volume injection offers a streamlined approach for the determination of organotin compounds in water at trace levels. It provides high sensitivity, reduced sample preparation complexity and robust performance for routine environmental analysis.

Reference

Bob Green and Diane Nicholas. Application Note No. 046. GL Sciences B.V., Eindhoven, The Netherlands.