Mass Spec Flashcards
GC part of GCMS
will give you retention times of compounds after separation
GC sample
must be a liquid
- but needs volatility = gas form when goes into column
different regions of a mass spec
ion source
analyzer region
electron multiplier
data system
what is a mass spec (in general;3)
- microanalytical technique that provides info on structure/MW of analyte
- characterizes fragmentation pattern (chemical fingerprint)
- destructive
what is a quadrupole?
- mass analyzer
- 4 parallel rods
> opposite rods electrically connected and combinedd dc and rf voltage applied bw two pairs
for a given combined voltage, only ions in a small-mass window have a stable oscillating path between rods through the detector
mass to charge ratio
ratio of mass number (m) of a given particle to the number of (z) of electrostatic charge units carried by the particle
T or F. Most ions have only one electrostatic-charge
T! so m/z value for a given particle referred to as the ‘mass’ of the particle
molecular ion
- results from ionization of analyte molecule
- intact molecule minus one electron
- precursor of all fragments
- m/z value or ~MW of compound
base ion
most intense peak in mass spectrum (largest number of ions)
what is deconvultion?
extracting one signal from a complex mixture involving:
- treatment of noise
- correction for baseline drift
- extraction of closely eluting peaks from one another
gas chromatography with mass spec is not ideal for these…
heat labile compounds such as oxazepam and methadone
- injection port very hot so will break down compounds = compromised analysis
acetaminophen, some opiates and some benzos = poor chromatography and extraction
how can some issues with GCMS be overcome?
use more labour intensive techniques such as derivatization, hydrolysis, SIM vs full scan
full scan vs selected ion monitoring (SIM)
full = all ions are monitored
SIM = only selected ions monitored
- often includes a derivatization step and depends on analyte function groups
- often used for QUANTITATIVE purposes
advantage: increased sensitivity
disadvantage: limited number of analytes detected
advantages if LCMS
- appropriate for volatile and nonvoltatile solutes
- appropriate for ionic/polar analytes
- good sensitivity
disadvantages of LCMS
- relatively low HPLC flow rates required
- must be able to form ions in solution
- IONS SUPPRESSION: results from the presence of less volatile compounds that can change the efficiency of droplet formation or droplet evaporation, which in turn affects the amount of charged ion in the gas phase that ultimately reaches the detector
