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Use of the Retention Index to Secure Correct Identities in GC/MS
Piet Christiaens1, Dennis Jenke2, Jan Baeten3
1Scientific Director, Nelson Labs Romeinsestraat 12 3001 Heverlee BELGIUM.
PDA Journal of Pharmaceutical Science and Technology
|August 29, 2025
Summary
Mass spectral matching (MSM) for identifying leachables can be improved using retention index (RI) data. A difference of less than 20 in RI values strongly corroborates identified compounds, enhancing patient safety.
Area of Science:
- Analytical Chemistry
- Pharmacology
- Toxicology
Background:
- Non-targeted analysis and Gas Chromatography-Mass Spectrometry (GC/MS) are used to detect organic leachables in drug products and medical devices.
- Mass Spectral Matching (MSM) is a common method for identifying compounds, but can lead to misidentifications.
- Inaccurate identification of leachables can impact toxicological risk assessments and patient safety.
Purpose of the Study:
- To investigate the use of retention index (RI) matching to corroborate Mass Spectral Matching (MSM) identities.
- To develop a strategy for using RI data to support, accept, or reject candidate MSM identifications.
- To improve the accuracy of leachable identification in pharmaceutical and medical device analysis.
Main Methods:
- Comparison of experimental RI values with experimental and calculated RI values from the NIST23 library for 3140 compounds.
- Utilizing a confusion matrix to evaluate the precision of RI matching in corroborating MSM identities.
- Defining thresholds for the absolute difference in RI (|ΔRI|) to assess identification reliability.
Main Results:
- Both experimental and calculated NIST23 RI values correlated well with experimental RI values for confirmed compounds.
- An absolute RI difference (|ΔRI|) ≤ 20 strongly corroborated MSM-based identities with high precision.
- An absolute RI difference (|ΔRI|) > 50 indicated very low precision, leading to rejection of identifications.
- RI differences between 20 and 50 were indiscriminate, yielding tentative identifications.
Conclusions:
- Retention index matching is an effective method for corroborating or refuting Mass Spectral Matching (MSM) identities.
- A strategy using NIST23 RI data can significantly enhance the reliability of leachable identification.
- Implementing RI matching improves the accuracy of toxicological risk assessments by reducing misidentifications, thereby ensuring patient safety.
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