Analysis of Organotin in Fish (1)

Importance of the Topic

Organotin compounds such as tributyltin (TBT) and triphenyltin (TPT) have been extensively used in marine antifouling applications, leading to persistent contamination of seawater and aquatic organisms. Reliable detection and quantification of these compounds in fish and water samples are critical for monitoring environmental exposure, assessing ecological risks, and supporting regulatory compliance.

Study Objectives and Overview

This work presents a GC-MS based method for selective, sensitive, and accurate analysis of organotin species in fish tissue and seawater. Key aims include:

• Developing efficient extraction and cleanup procedures for complex biological matrices.
• Optimizing GC-MS conditions for robust identification and quantification of TBT and TPT.
• Applying deuterium-labeled internal standards to improve recovery and measurement precision.
• Demonstrating method performance through extraction recoveries, calibration linearity, and real sample analysis.

Sample Preparation and Extraction Protocols

Fish tissue (10 g) and 1 L seawater undergo parallel workflows:

• Acidified ethanol extraction, followed by partitioning into ethyl acetate:hexane (3:2).
• Cation and anion exchange column chromatography to remove matrix interferences.
• Derivatization via propylation using n-propylmagnesium bromide (Grignard reagent).
• Florisil cleanup to further purify organotin derivatives.
• Final sample volume adjusted to 2 mL for GC-MS analysis.

Instrumentation and Analytical Conditions

• Gas chromatograph-mass spectrometer: Shimadzu GCMS-QP5000.
• Capillary column: DB-1, 0.32 mm i.d. × 30 m, 0.25 µm film thickness.
• Oven program: 50 °C (2 min) → 140 °C at 20 °C/min → 220 °C at 7 °C/min → 310 °C at 15 °C/min (6 min hold).
• Injection: splitless for 2 min at 280 °C.
• Interface temperature: 300 °C; carrier gas: helium at 40 kPa.
• SIM mode with selected ions:
  • d27-TBT (m/z 293, 295, 316)
  • TBT (m/z 275, 277, 291)
  • Tetra-BT (m/z 289, 291)
  • TPeT (m/z 303, 305)
  • d15-TPT (m/z 364, 366)
  • TPT (m/z 349, 351)

Main Results and Discussion

Calibration curves for TBT and TPT over 10–1000 ppb exhibited excellent linearity (r² > 0.9999) with area-to-concentration ratios of 0.00070351 and 0.00370016, respectively. The use of deuterated analogs as internal standards yielded consistent recovery rates and minimized matrix effects.

Analysis of real samples produced the following concentrations:

• Sea bream: TBT 0.436 µg/g, TPT 0.014 µg/g.
• Sea bass: TBT 0.782 µg/g, TPT 0.010 µg/g.
• Harbor water (K port): TBT 0.173 µg/L, TPT 0.019 µg/L.
• Harbor water (W port): TBT 0.068 µg/L, TPT 0.078 µg/L.

Mass spectra confirmed characteristic fragment ions and retention times, enabling unambiguous compound identification even at low levels.

Practical Benefits of the Method

• High sensitivity and selectivity for trace organotin detection in challenging matrices.
• Strong calibration linearity supports quantitative accuracy across a wide concentration range.
• Use of isotopically labeled standards improves data reliability and compensates for variable recoveries.
• Adaptability to both biota and environmental water samples facilitates routine monitoring.

Future Trends and Potential Applications

Advancements may include coupling with high-resolution MS for enhanced selectivity, miniaturized sample preparation to reduce solvent consumption, and integration with automated online extraction systems. The method could be extended to additional organotin derivatives and applied in long-term ecological surveillance, seafood safety assessment, and compliance with international pollution guidelines.

Conclusion

The presented GC-MS protocol offers a robust, accurate, and reproducible approach for determining organotin levels in fish and seawater. Its combination of targeted derivatization, isotopic standards, and SIM detection ensures reliable trace analysis, supporting environmental monitoring and food safety efforts.

Reference

(1) Shimadzu Application Note 3.3 “Analysis of Organotin in Fish and Seawater by GC-MS”.