Liquid chromatography is a powerful technique for analyzing complex mixtures. Detection of compounds in mass spectrometry relies on the ability to ionize target compounds. In complex mixtures, low abundance compounds or those that are difficult to ionize may be masked by higher abundance, easily ionized compounds. This type of interference is referred to as “suppression”. Suppression effects can be reduced or eliminated by separating the compounds to be analyzed before they are introduced into the mass spectrometer. We have a Thermo LTQ-MS and a Thermo Velos-Pro Orbitrap MS instrument to use with a variety of columns and solvent systems to screen for compounds of interest. We also frequently use this instrument for analysis of natural products mixtures, to follow the progress of synthetic reactions and to analyze constituents of other bio-materials such as fuels or fluids.

MSn for Structural Analysis

The structure of a compound can be deduced by fragmenting the parent ion and measuring the masses of the fragment ions. The MS facility has a Thermo LTQ-MS and an LTQ-Orbitrap Velos Pro-MS. The LTQ is an electrospray ionization (ESI) mass spectrometer with a linear ion trap analyzerand a mass range of up to 4000. The LTQ can be set up to collect full scan MS and MSn (n=2-10) data. Advanced scanning modes include data-dependent scans, zoom scans, and ultra zoom scans.The LTQ is designed with interchangeable probes of electrospray ionization and atmospheric pressure chemical ionization (APCI). The Orbitrap can iteratively isolate parent ions and measure the masses of fragments produced by collision induced dissociation (CID), pulsed Q collision-induced dissociation (PQD) and high energy collision induced dissociation (HCD, Orbitrap only). Thus we can sequentially break the parent compound into smaller and smaller pieces to learn about its structure. 

Accurate Mass Analysis

When characterizing novel compounds a mass measurement with sufficient resolution and mass accuracy can be used to generate a molecular formula. Publication of new compounds in ACS journals requires MS accuracy data at the level of 3 mmu. Our Orbitrap mass spectrometer is capable of mass measurements with sub-ppm mass accuracy and resolution (FWHM) in the range of 4,000 amu. This is sufficient for assigning formulae for most compounds up to ~500 amu. 

Proteomics Mass Analysis

LTQ is designed to assist with proteomics type studies. For example, proteins are digested with trypsin and the resulting peptides are analyzed by LC/MS/MS. The peptides are fragmented in the mass spectrometer to yield diagnostic patterns that can be matched to protein sequence databases via computer algorithms. The sensitivity of this technique is 1 ng or less starting material for a given protein.

file:Services R2, Rev 4/2715