Mass spectrometer #

The underlying principle of MS is the production of ions from analyzed compounds that are then separated or filtered based on their mass-to-charge ratio (m/z) and detected in a spectrometer. The mass spectrum generated plots the abundance of the produced ions as a function of m/z. The most dominant applications for quantitative bioanalysis employ tandem mass spectrometers (MS/MS) that use a triple quadrupole instrument. Two mass analyzers are used: one for selection of the precursor (father) ion in the first quadrupole, and the other for selection of the product (daughter) ion in the third quadrupole after the collision of the father ion in a collision cell (the second quadrupole). That mode of ion selection and detection is called selected reaction monitoring (SRM).

Joining MS and LC #

MS operates in a high-vacuum environment. In contrast, today’s premium separation technology, liquid chromatography (LC), is performed under atmospheric pressure. Historically, its aqueous mobile-phase flow rate was incompatible with MS. However, innovative and successful research efforts on the design of an effective interface connection between LC and MS over the past 25 years have made LC compatible with MS. Electrospray ionization (ESI) and atmospheric-pressure chemical ionization (APCI), collectively called atmospheric pressure ionization (API), have matured into the reliable interface necessary for quantitative LC/MS/MS bioanalysis.

Reference: Systematic Troubleshooting for LC/MS/MS - Part 1: Sample Preparation and Chromatography