MSACL 2025 Abstract

Evaluation of the Detuning Ratio as a Tool to Detect Potential Interference in LC-MS/MS Analysis

Katharina Habler, Arber Rexhaj, Michael Vogeser
Institute of Laboratory Medicine, LMU University Hospital, LMU Munich, Germany.

Katharina Habler (Presenter) LMU University Hospital, LMU Munich

Relevant Financial Disclosures (within past 24 months, reported on Apr 09, 2026) No relevant financial relationship(s) to disclose. Conflict mitigation NOT REQUIRED.

INTRODUCTION:
While MS/MS is in general a highly specific technique, the presence of unexpected substances in samples can result in interference due to shared mass transitions with target analytes (isomeric/isobaric interferences). Clinical laboratories typically address this issue by monitoring ion ratios (IR) to recognize potential interferences. To supplement this approach, differential tuning effects can be assessed. We aimed to evaluate a complementary method - the detuning ratio (DR) - for its ability to detect isomeric or isobaric interferences.

METHODS:
A DR was based on differential influences of instrument settings of MS systems on the ion yield of a respective target analyte; isomeric or isobaric interferences can lead to a shift of the DR in an affected sample. By quantifying the concentration and determining the IR and DR in samples in which known isomeric interference substances have been spiked to the target analyte, the applicability of DR detection was quantitatively investigated and compared with concentration as well as IR. This experiment was performed for two compound pairs (Cortisone/Prednisolone and O-Desmethylvenlafaxine/cis-Tramadol HCl). In both pairs matching mass transitions can be observed in a collision induced dissociation scan.

RESULTS:
The DR method correctly indicated the presence of isomeric interferences in two independent test systems: Cortisone/Prednisolone and O-Desmethylvenlafaxine/cis-Tramadol HCl. In these two spiking experiments, we observed that the DR and the IR were both suited to indicate interference in a quantitative model system of interference by known compounds sharing mass transitions with the respective target analyte. DR was found highly reproducible in analytical runs (with a CV ≤5.3%, n=20).

CONCLUSION:
The DR approach provides a valuable supplementary tool for detecting isomeric or isobaric interferences in individual samples analyzed by LC-MS/MS. When used alongside conventional IR monitoring, it can improve the analytical reliability of clinical MS-based assays. A major advantage of DR over IR is its applicability to target analytes with only a single sufficiently abundant mass transition. This is particularly important for immunosuppressants such as tacrolimus and cyclosporine.

The DR principle has a broad potential and can be used in all areas of LC-MS/MS application, even beyond biomedical analyses.