A Comparison of GC-ICP-MS and HPLC-ICP-MS for the Analysis of Organotin Compounds

Importance of the Topic

Organotin compounds have long been recognized as environmental pollutants with toxic effects on aquatic organisms and potential human health risks. Their widespread use in marine antifouling paints, PVC stabilizers, and various industrial applications has led to their detection in sediments, water, seafood, and even human blood. Reliable speciation and quantification of these organotin species at trace and ultratrace levels are essential for environmental monitoring, regulatory compliance, and risk assessment.

Objectives and Study Overview

This study compares two chromatographic techniques—gas chromatography (GC) and high-performance liquid chromatography (HPLC)—both coupled to inductively coupled plasma mass spectrometry (ICP-MS) for organotin speciation. The primary goals are to assess the relative performance of GC-ICP-MS and HPLC-ICP-MS in terms of separation capability, sensitivity, analysis time, and method precision, and to demonstrate the advantages of isotope dilution calibration for improved accuracy.

Methodology

• Sample Preparation

• Accelerated solvent extraction (ASE) of sediment or standard solutions using 0.5 M sodium acetate/1.0 M acetic acid in methanol.
• HPLC analysis: Direct injection of diluted extracts without derivatization.
• GC analysis: Derivatization of extracts with sodium tetraethylborate (NaBEt₄) and hexane extraction.

• Chromatographic Conditions

• HPLC: C18 column, acetonitrile/water/acetic acid/triethylamine mobile phase, 0.2 mL·min⁻¹ flow.
• GC: Temperature program, deactivated fused silica transfer line linked to ICP-MS.

• Isotope Dilution Mass Spectrometry

• Use of ¹⁷⁷Sn-labeled tributyl-tin chloride spike.
• Mass-bias calibration with primary standards of natural Sn isotopic composition.
• Calculation of sample mass fractions via bracketing calibration blends.

Instrumentation Used

• Agilent 7500i ICP-MS with ShieldTorch interface and Peltier-cooled spray chamber
• Agilent 6890 GC with G3158A GC-ICP-MS interface
• Agilent 1100 HPLC system with PEEK flow path
• Dionex ASE 200 accelerated solvent extractor
• PFA MicroFlow nebulizer and optional O₂ or N₂ addition to enhance sensitivity

Main Results and Discussion

• Separation Capability

• GC-ICP-MS resolved 10–12 organotin species per run; HPLC-ICP-MS separated 5–6 species.

• Sensitivity and Detection Limits

• Adding 5 % O₂ to the ICP-MS carrier gas increased GC peak areas by 9–12×; 5 % N₂ provided up to 16× enhancement.
• GC-ICP-MS detection limits for TBT improved from 0.4 ng·mL⁻¹ (no gas) to 0.006 ng·mL⁻¹ with 5 % N₂.
• HPLC-ICP-MS detection limit for TBT in sediment was ~3 pg as Sn; GC-ICP-MS achieved 0.03 pg as Sn.

• Precision and Accuracy

• Isotope ratio precision over 15 injections: ~1.6 % RSD for HPLC-ICP-MS and ~1.7 % for GC-ICP-MS.
• Analysis of PACS-2 reference sediment yielded 864 ± 35 ng·g⁻¹ TBT by HPLC-ICP-MS versus certified 980 ± 130 ng·g⁻¹.

Benefits and Practical Applications

• GC-ICP-MS offers superior sensitivity and the ability to resolve a wider range of organotin species in a single run.
• HPLC-ICP-MS eliminates derivatization, reducing analysis time and reagent costs for high-throughput monitoring.
• Isotope dilution calibration minimizes measurement uncertainty and improves quantitative accuracy across diverse matrices.

Future Trends and Opportunities

Advances in interface design and plasma stability may further enhance sensitivity and robustness for organic solvent flows. Multi-element speciation of other volatile organometallics (e.g., Hg, Pb, Se) could be integrated into single GC-ICP-MS runs. Emerging applications include direct analysis of complex food matrices, clinical samples, and in situ environmental monitoring using portable ICP-MS systems.

Conclusion

Both HPLC-ICP-MS and GC-ICP-MS, when combined with isotope dilution calibration, provide reliable, precise, and sensitive methods for organotin speciation. HPLC-ICP-MS is well suited for rapid, cost-effective analysis of routine samples, while GC-ICP-MS excels in trace-level detection and multi-species separation. The choice of technique depends on target analyte range, required detection limits, and sample throughput needs.

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