Analysis and Retention Index of 61 Components of Organic Solvents using Nitrogen Carrier Gas - Using InertCap Pure-WAX

Significance of the Topic

The retention index is a fundamental parameter in gas chromatography (GC) that correlates the elution behavior of organic compounds to a homologous series of n-alkanes. It provides a reproducible metric for compound identification, improving qualitative analysis in research, quality control, environmental monitoring and industrial applications.

Objectives and Study Overview

This technical note aimed to determine both isothermal and temperature-programmed retention indices of 61 common organic solvents on an InertCap Pure-WAX capillary column using nitrogen as the carrier gas. Key goals were:

• To generate a comprehensive retention index database for solvents ranging from low-molecular-weight alcohols and ketones to aromatics and chlorinated compounds.
• To validate linear relationships between retention index and carbon number under different thermal conditions.

Methodology and Instrumentation

Gas chromatographic analyses were performed with a GC-FID system. The following conditions were applied:

• Column: InertCap Pure-WAX, 0.25 mm I.D. × 60 m, 0.25 µm film thickness.
• Carrier gas: Nitrogen at 90 kPa.
• Injection: Split ratio 1:50, injector temperature 240 °C.
• Detection: Flame ionization detector at 240 °C.
• Sample volume: 0.2 µL of a mixed standard solution.
• Analysis modes: Isothermal runs at 40 °C, 80 °C, 120 °C and 160 °C; temperature programming from 40 °C to 220 °C at 5 °C/min.

Main Results and Discussion

Retention indices for all 61 solvents were successfully measured under both isothermal and temperature-ramp conditions. Key observations included:

• Strong linear correlation between retention index and carbon number in n-alkanes for temperature programming, confirming theoretical expectations.
• Consistency of isothermal retention indices across multiple temperatures, with slight shifts attributed to column phase interactions and vapor pressure.
• Resolution and retention times for compounds such as benzene, toluene, xylenes and chlorinated solvents were reproducible, facilitating unambiguous identification.

Benefits and Practical Applications

The retention index database enables analytical chemists to:

• Rapidly confirm solvent identities in complex mixtures.
• Improve method development for environmental and industrial sample screening.
• Standardize comparisons across laboratories using nitrogen carrier gas.

Future Trends and Potential Applications

Emerging directions include:

• Extension of the database to additional column chemistries and alternative carrier gases (e.g., helium, hydrogen).
• Integration with retention-time prediction software and machine-learning models for automated identification.
• Application of retention indices in comprehensive two-dimensional GC and high-throughput screening.

Conclusion

This study provides a robust set of isothermal and temperature-programmed retention indices for 61 organic solvents on an InertCap Pure-WAX column using nitrogen carrier gas. The data support reliable qualitative GC analysis and serve as a reference for method validation and routine quality control.

Instrumentation Used

Gas chromatograph with flame ionization detector (GC-FID); InertCap Pure-WAX capillary column (0.25 mm I.D., 60 m, 0.25 µm); nitrogen carrier gas; split injection system.