Lecture 13: Mass Spec Flashcards
Ideal GC/LC detector:
- detect low amounts of target analyte (sensitive) – trace analysis
- robust to temp and experimental condition changes (e.g. mobile phase composition)
- limited contribution to band broadening (resolution of peak)
- fast scanning/detection speed to capture data
- easy to use
sensitivity
- how analyte signal changes with concentration and can be determined from calibration graph
- described how low concentration you can analyse
- limit of detection (LOD) (ICH)
o lowest amount of analyte in a sample that can be detected but not quantified as exact value
o lowest amount reliably differentiated from background noise (often used as measure of sensitivity)
- most analyses carried out using UV and MS instrumentation as…
o sensitive
o good linear range of response vs concentration
o robust to changes in temp
o selective and suitable for gradient elution
mass spectrometer used to measure…
mass of gas phase ions
o for chemical identification and screening in all aspects of modern medicine (mass/drug imaging, biomarker identification, drug screening)
measures mass or m/z
requirements of m/z
- Analyte needs charge to be seen
- Either by loss of an electron M+
- Or through adduct formation [M+H] + or [M-H] - or [M+NH4]+
o pH control/additivies and pKa of analyte key for detection - multiple charging of an ion allows analysis of very large molecules like proteins
- molecule/precursor ion
formed by ionisation of analyte species
- fragment/product ion
formed by gas phase dissociation of precursor ion
- isotope
atoms of the same number of protons and electrons but different neutrons, so different m/z
- mass spectrum
plot of relative abundance of ion vs m/z
- base peak
greatest intensity peak
LCMS principle
combines 2 selective techniques that allow analytes of interest in highly complex mixtures to be isolated and measured.
- Orthogonal separation as separation by physiochemical properties and m/z
- Selective and sensitive separation
