Philip Sobolesky (Presenter)
UCSD
Bio: Philip M. Sobolesky received his Bachelor of Science degree in Biology from Bloomsburg University with a minor in chemistry in 2009 and his Doctor of Philosophy degree in Biomedical Sciences from the Medical University of South Carolina (MUSC) in 2014. He completed a two-year postdoctoral fellowship at MUSC in the Nephrology proteomics laboratory where he focused on learning tandem mass spectrometry and discovery of protein biomarkers for metabolic syndrome in bottlenose dolphins. He has four first author publications and has presented at numerous national meetings. Dr. Sobolesky is currently a Clinical Chemistry Fellow at the University of California, San Diego and is currently a member of AACC, ASMS, AACR, and MSACL. His research is on establishing the reference ranges for driving impairment following marijuana consumption.
Authorship: Philip Sobolesky (1), Robert L. Fitzgerald (1)
(1) University of California San Diego
| Short Abstract Selecting unique transition ions for quantification by tandem mass spectrometry using stable isotopically labeled standards is essential for accurate and consistent results. It is important to understand how the structure of your target compound and the contribution of naturally occurring isotopes can affect the mass to charge ratio. This session will discuss a troubleshooting case that involved the selection of a quantifier ion for deuterated lorazepam that resulted in a non-linear calibration curve due to the contribution of naturally occurring isotopes of lorazepam to the deuterated standard. |
Long Abstract
The uses of mass spectrometry in the clinical laboratory are growing beyond inborn errors of metabolism and small compound identifications, to multidrug screening panels and protein quantifications. Laboratory developed tests using mass spectrometry are important for patient care. It is crucial for Clinical Chemists to understand how to properly develop and validate a MS assay. Problems associated with method development can occur during sample preparation, liquid chromatography, data acquisition, or data analysis. The focus of this talk will be on the various considerations for troubleshooting an issue with a non-linear calibration curve that occurred during method development for lorazepam. This presentation will cover a case involving the contribution of a naturally occurring lorazepam isotope that artificially inflated the concentration of the deuterated standard due to identical quantifier ions, resulting in a non-linear calibration curve.
By the end of the session users should be able to:
1. Understand the affect naturally occurring isotopes can have on experimental outcomes
2. Be able to identify and solve issues associated with non-linear calibration curves
3. Determine how to select unique quantifier ions for each compound.
References & Acknowledgements:
We wish to thank the Toxicology laboratory at UCSD and Judy Stone, Ph.D., for originally presenting this case and helping to refine this presentation.
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