Analysis and Retention Indices of 61 Organic Solvent Components by Nitrogen Carriers

Significance of the Topic

Retention indices provide a standardized measure of how organic compounds interact with chromatographic stationary phases, allowing reliable identification and comparison across laboratories. For volatile and semi-volatile organic solvents, accurate retention index data support quality control, method development and compound confirmation in environmental, food, pharmaceutical and industrial analyses.

Objectives and Study Overview

This technical note reports the determination of isothermal and temperature-programmed retention indices for 61 common organic solvents. Using a nitrogen-carrier gas GC-FID system with an InertCap 25 column, the study establishes reference values under both constant temperature and linear temperature ramp conditions.

Methodology and Instrumentation

The experimental setup and conditions were as follows:

• System: Gas chromatograph with flame ionization detector (GC-FID)
• Column: InertCap 25 (0.25 mm I.D. × 60 m, film thickness 0.25 µm)
• Carrier gas: Nitrogen at 90 kPa, maintained to give constant linear flow in isothermal runs
• Injection: Split mode 1 : 50, injection port at 240 °C
• Detector: FID at 240 °C with automatic range
• Column temperature programs:
   • Isothermal at 40 °C
   • Linear ramp from 40 °C to 220 °C at 5 °C/min
• Sample: Mixed standard solution of 61 organic solvent components, injected at 0.2 µL

The retention index in isothermal analysis was calculated from the linear relationship between alkane carbon number and log retention time. In temperature-programmed analysis, a direct linear relationship between carbon number and retention time was used.

Main Results and Discussion

Retention indices for 61 solvents ranged from approximately 424 to 1137 in temperature-ramped runs. Key observations include:

• Low-molecular-weight polar solvents (methanol, ethanol) exhibited indices below 500.
• Moderate volatility ketones and esters (acetone, methyl ethyl ketone, ethyl acetate) fell between 540 and 670.
• Aromatic compounds and chlorinated solvents showed higher indices, exceeding 700 in most cases.
• Consistency of retention index values across isothermal and programmed conditions confirms reproducibility of the InertCap 25 phase with nitrogen carrier.

Components with peak symmetry factors above 1.5 were noted, indicating possible tailing that may require column maintenance or method adjustment.

Benefits and Practical Applications

This retention index dataset enables:

• Rapid qualitative confirmation of organic solvent peaks in complex samples.
• Development and validation of GC methods for industrial QC, environmental monitoring and forensic analysis.
• Cross-laboratory data comparison and database building for solvent identification.

Future Trends and Possibilities

Advances may include:

• Integration of machine-learning models to predict retention indices for novel compounds or modified stationary phases.
• Use of alternative carrier gases or advanced detectors (e.g., mass spectrometry) to expand the applicability to trace-level analyses.
• Development of software tools that automatically correct for column aging and variation in carrier gas conditions.

Conclusion

This technical note provides a comprehensive set of retention index values for 61 organic solvents on an InertCap 25 column with nitrogen carrier gas. The data serve as a reliable reference for qualitative GC analysis and method development, demonstrating robust performance under both isothermal and temperature-programmed conditions.

References

No specific literature references were cited in this report.