Sample introduction on the GCT instrument occurs using a probe or GC interface. The TOF analyzer enables high resolution (5000-7000) mass measurements with an accuracy of ~5 ppm. EI/CI is most suitable for low molecular weight, low polarity compounds (m/z range ~1500). The probe may be heated to 650°C to vapourize low volatility compounds (although evaporation may be in competition with decomposition).
High resolution data for a Ge containing compound, MW=378. (WJL Group)
This state-of-the-art triple quadrupole (Q1Q2Q3) instrument is dedicated to LC/MS and LC/MS/MS applications using electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI). ESI offers unique possibilities for the analysis of high molecular weight (100 - 100,000 Dalton range)compounds and polar or charged species such as peptides, proteins, nucleic acids and nucleotides. On the other hand, low molecular weight polar and non-polar compounds can be analyzed by APCI. These approaches typically yield mass spectra that show ions characteristic of the molecular weight of the sample in question with little or no structurally significant fragment ions being observed as shown below for salicylic acid.
This drawback can be eliminated by performing MS/MS. In one type of MS/MS experiment (daughter ion scan), the ion of interest typically the molecular ion [M+H]+, [M+Na]+ or [M-H]- for example, is mass selected by the first quadrupole (Q1) and all other ions are rejected and eliminated into the vacuum pumps. Following mass selection, the ion is subjected to collisions with a stationary target gas (usually argon or nitrogen) in Q2 in a so-called collisional activation (CA) experiment. This causes the ion to dissociate in a manner characteristic of its structure. Scanning Q3 allows one to generate the mass spectrum of the structurally significant fragment ions derived from the originally isolated ion of interest. This is shown below for the [M-H]- ion from the ESI spectrum of salicylic acid (the peak at m/z 93 is loss of CO2 from the [M-H]- ion).
Micromass MALDI MicroMX
This Matrix-Assisted Laser Desorption/Ionization Time-of-Flight instrument has delayed extraction (DE) and a reflectron for high resolution and mass accuracy. The 96 spot plate format allows for high sample throughput.
This instrument is a quadrupole time-of-flight mass spectrometer that has dual ionization capabilities, MALDI and ESI. This instrument is mainly used for the analysis of proteins and peptides. Protein/peptide identification and sequencing can be done via ESI ionization by introducing the sample through the CapLC system (capillary liquid chromatograph). For this system, low amounts of sample can be analyzed since uL flow rates are used. The CapLC system allows for data dependant scanning which performs MSMS experiments on peaks detected in MS mode. High resolution accuracy mass measurements are also performed on this instrument using the lock spray probe which allows for the introduction of a reference standard in a separate MS channel.