MSACL 2018 US Abstract

Topic: Practical Training

Choosing the Right Internal Standard for Good LC-MS/MS Method Development

Imir Metushi (Presenter)
Endocrine Sciences (LabCorp)

Bio: Imir finished his BS in Chemistry from York University (Toronto, Canada) specializing in analytical chemistry. He then went to pursue a Ph.D in Pharmacology at the University of Toronto where he developed an interest in biomarker development for adverse drug reactions (ADRs). He did a one year post doc at the La Jolla Institute for Allergy and Immunology where he worked on the development of immunoassays used to pre screen for drugs that could have an HLA-linked ADR. His interests are in biomarker discovery as well as performing immunoassay and mass spectrometry applications utilized in the clinical chemistry laboratory. Imir graduated from the Clinical Chemistry fellowship program at UC San Diego and is currently working as a laboratory director for LabCorp (Esoterix site in Calabasas).

Authorship: Imir G. Metushi
Endocrine Sciences, 4301 Lost Hills Rd, Calabasas, CA, 91301

Short Abstract

Developing good methods for analyte quantification by liquid chromatography (LC) triple quadrupole mass spectrometry (MS/MS) is an important first step when developing new assays. The choice of internal standard is critical for optimal performance. This session will use examples to discuss why choosing the right internal standard is important, when it should be added and what can go wrong.

Long Abstract


Liquid chromatography coupled to mass spectrometry (LC-MS/MS) has become the primary choice for several applications, some of which include: therapeutic drug monitoring, endocrinology and drugs of abuse testing. Choosing the correct internal standard (IS) is critical for developing good LC-MS/MS assays. The focus of this talk will be to highlight the importance behind choosing the right internal standard, when you should add it and what can go wrong.


This presentation will define the general use of the internal standard used for LC-MS/MS analysis. It will highlight how the choice of a good internal standard can improve accuracy by normalizing the difference in sample extraction, injection, chromatography, ionization and detection. Using examples, this this presentation will highlight when the IS should be added to the samples and illustrate how a poorly chosen IS can affect the assay calibration/results.


General basic principles will be used to describe the choice of internal standards for LC-MS/MS assays and what basic rules should be used to obtain good linearity during assay setup. Using CLSI guidelines, this presentation will highlight what an acceptable matrix is and how the addition of IS can compensate for matrix deviation. It will describe how use of external calibrators can have significant impact on accuracy with poor internal standardization vs. good internal standardization. It will explain the importance of interferences from chemical modification in preparation, source or incomplete labeling of internal standards. Also, it will explain, how non-equivalency (by not adding IS in the right step, or not adding IS in miscible solution) can significantly impact assay performance.

Conclusions & Discussion

By the end of this session users should be able to:

1. Describe why a good internal standard (IS) makes LC-MS/MS a special technique.

2. Describe when IS should be added to samples.

3. Explain how interferences and non-equivalency can cause assay problems.

References & Acknowledgements:

Financial Disclosure

Board Memberno
Stockyes LabCorp

IP Royalty: no

Planning to mention or discuss specific products or technology of the company(ies) listed above: