INSTRUMENTAL ANALYSIS ACS EXAM PAPER 2025/2026
QUESTIONS AND ANSWERS GUARANTEE A+
✔✔Quadrupole mass analyzer - ✔✔-oscillating electrical fields to selectively stabilize or
destabilize the paths of ions passing through the field created b/w 4 parallel rods
-mass selective filter
✔✔photomultiplier tube - ✔✔-An apparatus that converts a photon of visible light into an
electrical pulse
-most sensitive photodetector
✔✔CCD - ✔✔-is a silicon-based multichannel array detector of UV, visible and near-
infra light
-sensitive to light
✔✔Beer's Law extension to mixtures of compounds - ✔✔-can extend to sample
containing several absorbing components if there are no interactions
-individual absorbances are additive
-low concentration analytes
-assumes one monochromatic wavelength
-
✔✔Sensitivity of absorbance methods - ✔✔-low sensitivity at low sample concentrations
✔✔Sensitivity of Fluorescence methods - ✔✔-sensitivity is x1000 greater than
absorption
-leads to more accurate and precise results
-more expensive because of this
✔✔Ion Selective Electrodes (ISE) - ✔✔-transducer that converts the activity of a specific
ion dissolved in a solution into an electrical potential.
✔✔Electrochemical detector (HPLC) - ✔✔-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 - ✔✔the use of electrodes to measure voltages that provide chemical
information
✔✔Coulometry - ✔✔a technique in which the quantity of analyte is determined by
measuring the number of coulombs needed for complete electrolysis
, ✔✔Voltammetry - ✔✔an analytical method in which the relation between current and
voltage is observed during an electrochemical reaction
✔✔How does changing flow rate affect retention time? (HPLC) - ✔✔-a high flow rate
reduces retention times
✔✔How does solvent polarity affect retention time? (HPLC) - ✔✔-if polarity of stationary
phase and compound are similar, retention time increases because the compound
interacts stronger with the stationary phase.
-therefore more polar compounds have longer retention times w/ polar stationary, and
shorter with nonpolar.
✔✔GC split injection - ✔✔- high concentration
-most common
-high resolution
-best injection due to narrow width of beaks
✔✔GC splitless injection - ✔✔-trace analysis
-dilute sample
-high resolution
-requires solvent trappnig
✔✔Is split or splitless injection preferred? (GC) - ✔✔split injection
✔✔General Elution Problem - ✔✔to overcome this general elution problem and obtain
good separation of all compounds, conditions are started at a low temperature to allow
compounds with low BP to separate, then the temperature is gradually increased by
increments set by the experimenter to allow for the separation of compounds with high
BPs. This allows for a shorter run time and better overall separation.
✔✔GC Detectors - ✔✔Thermal conductivity, Flame ionization, photo ionization
✔✔Thermal Conductivity Detector - ✔✔- not as popular
-packed columns
-less sensitive than other detectors
-all analytes
-measures a change in voltage
✔✔Flame Ionization Detector - ✔✔-analyte burned in air and H2
-carrier gas: He
-flammable gas: H
-Increase current, increase ionization
-ions produced are measured by the change in voltage when the ion hits the collector
-great detector for hydrocarbons
-combust at low temperature flame
QUESTIONS AND ANSWERS GUARANTEE A+
✔✔Quadrupole mass analyzer - ✔✔-oscillating electrical fields to selectively stabilize or
destabilize the paths of ions passing through the field created b/w 4 parallel rods
-mass selective filter
✔✔photomultiplier tube - ✔✔-An apparatus that converts a photon of visible light into an
electrical pulse
-most sensitive photodetector
✔✔CCD - ✔✔-is a silicon-based multichannel array detector of UV, visible and near-
infra light
-sensitive to light
✔✔Beer's Law extension to mixtures of compounds - ✔✔-can extend to sample
containing several absorbing components if there are no interactions
-individual absorbances are additive
-low concentration analytes
-assumes one monochromatic wavelength
-
✔✔Sensitivity of absorbance methods - ✔✔-low sensitivity at low sample concentrations
✔✔Sensitivity of Fluorescence methods - ✔✔-sensitivity is x1000 greater than
absorption
-leads to more accurate and precise results
-more expensive because of this
✔✔Ion Selective Electrodes (ISE) - ✔✔-transducer that converts the activity of a specific
ion dissolved in a solution into an electrical potential.
✔✔Electrochemical detector (HPLC) - ✔✔-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 - ✔✔the use of electrodes to measure voltages that provide chemical
information
✔✔Coulometry - ✔✔a technique in which the quantity of analyte is determined by
measuring the number of coulombs needed for complete electrolysis
, ✔✔Voltammetry - ✔✔an analytical method in which the relation between current and
voltage is observed during an electrochemical reaction
✔✔How does changing flow rate affect retention time? (HPLC) - ✔✔-a high flow rate
reduces retention times
✔✔How does solvent polarity affect retention time? (HPLC) - ✔✔-if polarity of stationary
phase and compound are similar, retention time increases because the compound
interacts stronger with the stationary phase.
-therefore more polar compounds have longer retention times w/ polar stationary, and
shorter with nonpolar.
✔✔GC split injection - ✔✔- high concentration
-most common
-high resolution
-best injection due to narrow width of beaks
✔✔GC splitless injection - ✔✔-trace analysis
-dilute sample
-high resolution
-requires solvent trappnig
✔✔Is split or splitless injection preferred? (GC) - ✔✔split injection
✔✔General Elution Problem - ✔✔to overcome this general elution problem and obtain
good separation of all compounds, conditions are started at a low temperature to allow
compounds with low BP to separate, then the temperature is gradually increased by
increments set by the experimenter to allow for the separation of compounds with high
BPs. This allows for a shorter run time and better overall separation.
✔✔GC Detectors - ✔✔Thermal conductivity, Flame ionization, photo ionization
✔✔Thermal Conductivity Detector - ✔✔- not as popular
-packed columns
-less sensitive than other detectors
-all analytes
-measures a change in voltage
✔✔Flame Ionization Detector - ✔✔-analyte burned in air and H2
-carrier gas: He
-flammable gas: H
-Increase current, increase ionization
-ions produced are measured by the change in voltage when the ion hits the collector
-great detector for hydrocarbons
-combust at low temperature flame
