INSTRUMENTAL ANALYSIS ACS EXAM SCRIPT LATEST
QUESTIONS AND ANSWERS SURE A+
✔✔Graphite furnace - ✔✔-Atomization through electrical heating
-sample stays in optical path longer than flame
-uses less sample
-sample injection is tricky, precision is worse
-one wavelength, one element
✔✔How to calculate the resolution of two peaks - ✔✔R = (RT1 - RT2) / [0.5 * (W1 +
W2)]
✔✔Grating monochromator - ✔✔-disperse ultraviolet, visible, and infrared radiation
typically using replica gratings,
✔✔ How to calculate signal to noise - ✔✔S/N = mean/STDEV
-inverse of RSD
-STDEV: 5 (#STDEV gaussian curve)
-STDEV: peak-to-peak noise/5
✔✔S/N relationships - ✔✔-increase S/N, increase run time
-decrease noise, increase S/N
✔✔Beer's Law - ✔✔
✔✔Beer's Law Calculations - ✔✔
✔✔Hard ionization vs soft ionization - ✔✔-hard: no M+ peak (or small)
-soft: M+ peak is visible
✔✔MS: hard ionization sources - ✔✔-impart high quantities of residual energy in the
subject molecule invoking large degrees of fragmentation
✔✔MS: hard ionization sources examples - ✔✔-electron impact
✔✔Electron Impact (EI) - ✔✔-Uses electron impact to ionize a molecule
-gas phase
-energetic electrons
-possibility of over fragmentation
-hard
-most common
✔✔EI advantages - ✔✔-good stability
, -universal ionization
-reproducible spectra
✔✔EI disadvantages - ✔✔-MW can be hard to determine
-compatible only with volatiles (GCMS)
-Hard to make negative ions
✔✔MS: soft ionization sources - ✔✔-processes which impart little residual energy onto
the subject molecule and as such result in little fragmentation
✔✔MS: soft ionization sources examples - ✔✔-CI
-ESI
-MALDI
✔✔Chemical ionization (CI) - ✔✔-First ionizes a molecular gas which in turn ionizes the
molecule of interest. A "gentler" method of ionization.
-soft
-electron beam creates ions
-proton transfer between reagent gas and the analyte
-gives MW and MW+1 or MW-1
✔✔fragmentation in CI - ✔✔-occurs if enough excess energy after the ionization of the
analyte
✔✔CI advantages - ✔✔-MW info more readily available
-fewer fragments
-control specificity
✔✔CI disadvantages - ✔✔-fragments not very reproducible
-compatible only with volatiles (GCMS)
✔✔Electrospray ionization (ESI) - ✔✔-multiple charged ions
-can make positive or negative ions by taking on hydrogens or removing hydrogens
✔✔MALDI abreviation - ✔✔Matrix assisted-laser desorption ionization
✔✔MALDI Theory - ✔✔-non-volatile ionization
-don't want fragmentation
-TOF
-absorption of laser beam by matrix
-transfer energy form matrix to analyte
-desorption of both matrix and analyte
-transfer of proton to analyte from matrix
-large MW
QUESTIONS AND ANSWERS SURE A+
✔✔Graphite furnace - ✔✔-Atomization through electrical heating
-sample stays in optical path longer than flame
-uses less sample
-sample injection is tricky, precision is worse
-one wavelength, one element
✔✔How to calculate the resolution of two peaks - ✔✔R = (RT1 - RT2) / [0.5 * (W1 +
W2)]
✔✔Grating monochromator - ✔✔-disperse ultraviolet, visible, and infrared radiation
typically using replica gratings,
✔✔ How to calculate signal to noise - ✔✔S/N = mean/STDEV
-inverse of RSD
-STDEV: 5 (#STDEV gaussian curve)
-STDEV: peak-to-peak noise/5
✔✔S/N relationships - ✔✔-increase S/N, increase run time
-decrease noise, increase S/N
✔✔Beer's Law - ✔✔
✔✔Beer's Law Calculations - ✔✔
✔✔Hard ionization vs soft ionization - ✔✔-hard: no M+ peak (or small)
-soft: M+ peak is visible
✔✔MS: hard ionization sources - ✔✔-impart high quantities of residual energy in the
subject molecule invoking large degrees of fragmentation
✔✔MS: hard ionization sources examples - ✔✔-electron impact
✔✔Electron Impact (EI) - ✔✔-Uses electron impact to ionize a molecule
-gas phase
-energetic electrons
-possibility of over fragmentation
-hard
-most common
✔✔EI advantages - ✔✔-good stability
, -universal ionization
-reproducible spectra
✔✔EI disadvantages - ✔✔-MW can be hard to determine
-compatible only with volatiles (GCMS)
-Hard to make negative ions
✔✔MS: soft ionization sources - ✔✔-processes which impart little residual energy onto
the subject molecule and as such result in little fragmentation
✔✔MS: soft ionization sources examples - ✔✔-CI
-ESI
-MALDI
✔✔Chemical ionization (CI) - ✔✔-First ionizes a molecular gas which in turn ionizes the
molecule of interest. A "gentler" method of ionization.
-soft
-electron beam creates ions
-proton transfer between reagent gas and the analyte
-gives MW and MW+1 or MW-1
✔✔fragmentation in CI - ✔✔-occurs if enough excess energy after the ionization of the
analyte
✔✔CI advantages - ✔✔-MW info more readily available
-fewer fragments
-control specificity
✔✔CI disadvantages - ✔✔-fragments not very reproducible
-compatible only with volatiles (GCMS)
✔✔Electrospray ionization (ESI) - ✔✔-multiple charged ions
-can make positive or negative ions by taking on hydrogens or removing hydrogens
✔✔MALDI abreviation - ✔✔Matrix assisted-laser desorption ionization
✔✔MALDI Theory - ✔✔-non-volatile ionization
-don't want fragmentation
-TOF
-absorption of laser beam by matrix
-transfer energy form matrix to analyte
-desorption of both matrix and analyte
-transfer of proton to analyte from matrix
-large MW
