INSTRUMENTAL ANALYSIS ACS
EXAM CORRECT 100%
How to calculate signal to noise - ANSWERS/N = mean/STDEV
-inverse of RSD
-STDEV: 5 (#STDEV gaussian curve)
-STDEV: peak-to-peak noise/5
S/N relationships - ANSWER-increase S/N, increase run time
-decrease noise, increase S/N
Beer's Law - ANSWER
Beer's Law Calculations - ANSWER
Hard ionization vs soft ionization - ANSWER-hard: no M+ peak (or small)
-soft: M+ peak is visible
MS: hard ionization sources - ANSWER-impart high quantities of residual energy in the
subject molecule invoking large degrees of fragmentation
MS: hard ionization sources examples - ANSWER-electron impact
Electron Impact (EI) - ANSWER-Uses electron impact to ionize a molecule
-gas phase
-energetic electrons
-possibility of over fragmentation
-hard
-most common
EI advantages - ANSWER-good stability
-universal ionization
-reproducible spectra
EI disadvantages - ANSWER-MW can be hard to determine
-compatible only with volatiles (GCMS)
-Hard to make negative ions
MS: soft ionization sources - ANSWER-processes which impart little residual energy
onto the subject molecule and as such result in little fragmentation
MS: soft ionization sources examples - ANSWER-CI
-ESI
, -MALDI
Chemical ionization (CI) - ANSWER-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 - ANSWER-occurs if enough excess energy after the ionization of
the analyte
CI advantages - ANSWER-MW info more readily available
-fewer fragments
-control specificity
CI disadvantages - ANSWER-fragments not very reproducible
-compatible only with volatiles (GCMS)
Electrospray ionization (ESI) - ANSWER-multiple charged ions
-can make positive or negative ions by taking on hydrogens or removing hydrogens
MALDI abreviation - ANSWERMatrix assisted-laser desorption ionization
Sensitivity of Fluorescence methods - ANSWER-sensitivity is x1000 greater than
absorption
-leads to more accurate and precise results
-more expensive because of this
Ion Selective Electrodes (ISE) - ANSWER-transducer that converts the activity of a
specific ion dissolved in a solution into an electrical potential.
Electrochemical detector (HPLC) - ANSWER-analyte gets either oxidized or reduced at
the working electrode
-only responds to compound that can partake in redox reactions
-measures current when an electroactive solute emerges from the column and passes
over the working electrode.
Potentiometry - ANSWERthe use of electrodes to measure voltages that provide
chemical information
Coulometry - ANSWERa technique in which the quantity of analyte is determined by
measuring the number of coulombs needed for complete electrolysis
Voltammetry - ANSWERan analytical method in which the relation between current and
voltage is observed during an electrochemical reaction
EXAM CORRECT 100%
How to calculate signal to noise - ANSWERS/N = mean/STDEV
-inverse of RSD
-STDEV: 5 (#STDEV gaussian curve)
-STDEV: peak-to-peak noise/5
S/N relationships - ANSWER-increase S/N, increase run time
-decrease noise, increase S/N
Beer's Law - ANSWER
Beer's Law Calculations - ANSWER
Hard ionization vs soft ionization - ANSWER-hard: no M+ peak (or small)
-soft: M+ peak is visible
MS: hard ionization sources - ANSWER-impart high quantities of residual energy in the
subject molecule invoking large degrees of fragmentation
MS: hard ionization sources examples - ANSWER-electron impact
Electron Impact (EI) - ANSWER-Uses electron impact to ionize a molecule
-gas phase
-energetic electrons
-possibility of over fragmentation
-hard
-most common
EI advantages - ANSWER-good stability
-universal ionization
-reproducible spectra
EI disadvantages - ANSWER-MW can be hard to determine
-compatible only with volatiles (GCMS)
-Hard to make negative ions
MS: soft ionization sources - ANSWER-processes which impart little residual energy
onto the subject molecule and as such result in little fragmentation
MS: soft ionization sources examples - ANSWER-CI
-ESI
, -MALDI
Chemical ionization (CI) - ANSWER-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 - ANSWER-occurs if enough excess energy after the ionization of
the analyte
CI advantages - ANSWER-MW info more readily available
-fewer fragments
-control specificity
CI disadvantages - ANSWER-fragments not very reproducible
-compatible only with volatiles (GCMS)
Electrospray ionization (ESI) - ANSWER-multiple charged ions
-can make positive or negative ions by taking on hydrogens or removing hydrogens
MALDI abreviation - ANSWERMatrix assisted-laser desorption ionization
Sensitivity of Fluorescence methods - ANSWER-sensitivity is x1000 greater than
absorption
-leads to more accurate and precise results
-more expensive because of this
Ion Selective Electrodes (ISE) - ANSWER-transducer that converts the activity of a
specific ion dissolved in a solution into an electrical potential.
Electrochemical detector (HPLC) - ANSWER-analyte gets either oxidized or reduced at
the working electrode
-only responds to compound that can partake in redox reactions
-measures current when an electroactive solute emerges from the column and passes
over the working electrode.
Potentiometry - ANSWERthe use of electrodes to measure voltages that provide
chemical information
Coulometry - ANSWERa technique in which the quantity of analyte is determined by
measuring the number of coulombs needed for complete electrolysis
Voltammetry - ANSWERan analytical method in which the relation between current and
voltage is observed during an electrochemical reaction
