Mass Spectroscopy

The Drum lab currently operates a dedicated Agilent 6495 QqQ spectrometer with an Infinity II liquid chromatography front end and the Agilent 6550 Accurate-Mass Q-ToF LC/MS system.

Acquired in early 2017, the highly sophisticated Agilent 6550 Accurate-Mass Q-ToF LC/MS system is designed to provide unparalleled data quality and advanced analytical capabilities for profiling, identifying, characterizing, and quantifying of low molecular-weight compounds and biomolecules with confidence. Integrating three core Agilent technical innovations – True Hi-Def ToF technology, Agilent Jet Stream Thermal Focusing technology and Mass Hunter Workstation software; a multifunctional platform that is ideally suited for accurate-mass analysis of noncovalent complexes (DNA-ligand, protein-DNA, protein-metal, etc), intact protein mass measurements and small molecule analysis.

Principle of Operation

Ions produced from electron and chemical ionization (El and Cl) sources located in the first vacuum chamber are introduced into a mass filter in a second vacuum chamber. The mass filter is followed by a hexapole collision cell – a set of six small parallel metal rods with an opening through which the ions can pass. Radio frequency (RF) voltage applied to the rods creates electromagnetic fields that confine ions above a particular mass to the open center of the rod set. A collision gas in the cell enables collision induced dissociation (CID).

Figure 1 depicts the Agilent GC Q-TOF mass spectrometer.

Upon exiting the collision cell, ions enter a region where the ion beam is shaped to optimal parallelism by transfer ion optics, and excess gas from the collision cell is removed. The more parallel the ion beam, the higher the resolving power that can be achieved. After the ions have been shaped into a parallel beam, they pass through a pair of slits into the third and last vacuum stage where the time-of-flight mass analysis takes place.

In the time-of-flight mass analyzer, the nearly parallel beam of ions first passes into the ion pulser. The pulser is a stack of plates where ions pass into this stack from the side. Through a regulation of voltages applied to the back plate, this accelerates the ions through the flight tube. At the opposite end of the flight tube is a two-stage, electrostatic ion mirror that reverses the direction of the ions back towards the ion detector and producing an electrical signal.