CHEM 311 (Instrumental Analytical Chemistry): Final
questions with verified answers
absorbance (detector for HPLC) Ans✓✓✓ Solute-property detection for
small volumes (1 - 10 μL) at low pressures (600 psi), typically consisting
of mercury lamp with filters and PDA: lock-in technique or double-
beam setup
adsorption chromatography Ans✓✓✓ Separation based on differences
in relative adsorption strengths of analytes to silica/alumina stationary
phase: nonpolar to polar elution:
*olefins < aromatics < ethers < esters, aldehydes, ketones < alcohols,
amines < amides < carboxylic acids*
ADVANTAGES
Determination of differences in adsorption strengths; separation of
isomers
anodic stripping voltammetry (ASV) Ans✓✓✓ (1) Reduce M2+ to
M(Hg) for fixed period of time, controlling mass transport kinetics of
M2+ to Hg interface = pre-concentration;
(2) Sweep potential positively, oxidizing M(Hg) to M2+ to remove
accumulated M from drop, yielding peaks
ADVANTAGE
,[M2+] Determination from 10^-6 - 10^-9 M
arc ablation (sample introduction for atomic spectrometry) Ans✓✓✓
Conducting-solid sample introduction through thermal ionization using
high potential difference between two electrodes at T = 4 000 - 5 000 K
DISADVANTAGE
Arc wandering; frequent replacement of electrodes
atomic emission (detector for gas chromatography) Ans✓✓✓ (1) Pass
eluent into He plasma;
(2) Disperse emission, then detect with diode array
capillary zone electrophoresis Ans✓✓✓ Separation of charged species
in constant buffer composition using EOF based on characteristic
electrophoretic mobilities
chemical ionization (CI) (ion source for mass spectrometry) Ans✓✓✓
(Gas phase soft source) Ionization of volatile sample with maximum
MW = 10^3 Da through *proton/hydride transfer* using *gaseous CH5+
or C2H5+ ions* generated by EI with
large excess of methane:
MH + C2H5+ → MH2 + C2H4 (proton transfer)
, MH + C2H5+ → M+ + C2H6 (hydride transfer)
ADVANTAGE
Little fragmentation, mass spectra consist of (M+1)+ and (M-1)+
DISADVANTAGE
Not well-suited for polar compounds like proteins and carbohydrates,
and requirement of vapourization may result in thermal decomposition
before analysis
conductance (detector for ion-exchange HPLC) Ans✓✓✓ Detection
measuring changes in conductivity by resistance between two
electrodes in solution
differential pulse polarography (DPP) Ans✓✓✓ (1) Setup
polarographically for metal cation reduction into amalgam using
hanging mercury drop;
(2) Measure current scanning negative potential linearly and square
wave perturbation with 50 mV every 50 ms, yielding measurement
before potential step (S1) and after potential step (S2);
(3) Analytical signal: Δi = S2(t) - S1(t - 50 ms)
ADVANTAGE
questions with verified answers
absorbance (detector for HPLC) Ans✓✓✓ Solute-property detection for
small volumes (1 - 10 μL) at low pressures (600 psi), typically consisting
of mercury lamp with filters and PDA: lock-in technique or double-
beam setup
adsorption chromatography Ans✓✓✓ Separation based on differences
in relative adsorption strengths of analytes to silica/alumina stationary
phase: nonpolar to polar elution:
*olefins < aromatics < ethers < esters, aldehydes, ketones < alcohols,
amines < amides < carboxylic acids*
ADVANTAGES
Determination of differences in adsorption strengths; separation of
isomers
anodic stripping voltammetry (ASV) Ans✓✓✓ (1) Reduce M2+ to
M(Hg) for fixed period of time, controlling mass transport kinetics of
M2+ to Hg interface = pre-concentration;
(2) Sweep potential positively, oxidizing M(Hg) to M2+ to remove
accumulated M from drop, yielding peaks
ADVANTAGE
,[M2+] Determination from 10^-6 - 10^-9 M
arc ablation (sample introduction for atomic spectrometry) Ans✓✓✓
Conducting-solid sample introduction through thermal ionization using
high potential difference between two electrodes at T = 4 000 - 5 000 K
DISADVANTAGE
Arc wandering; frequent replacement of electrodes
atomic emission (detector for gas chromatography) Ans✓✓✓ (1) Pass
eluent into He plasma;
(2) Disperse emission, then detect with diode array
capillary zone electrophoresis Ans✓✓✓ Separation of charged species
in constant buffer composition using EOF based on characteristic
electrophoretic mobilities
chemical ionization (CI) (ion source for mass spectrometry) Ans✓✓✓
(Gas phase soft source) Ionization of volatile sample with maximum
MW = 10^3 Da through *proton/hydride transfer* using *gaseous CH5+
or C2H5+ ions* generated by EI with
large excess of methane:
MH + C2H5+ → MH2 + C2H4 (proton transfer)
, MH + C2H5+ → M+ + C2H6 (hydride transfer)
ADVANTAGE
Little fragmentation, mass spectra consist of (M+1)+ and (M-1)+
DISADVANTAGE
Not well-suited for polar compounds like proteins and carbohydrates,
and requirement of vapourization may result in thermal decomposition
before analysis
conductance (detector for ion-exchange HPLC) Ans✓✓✓ Detection
measuring changes in conductivity by resistance between two
electrodes in solution
differential pulse polarography (DPP) Ans✓✓✓ (1) Setup
polarographically for metal cation reduction into amalgam using
hanging mercury drop;
(2) Measure current scanning negative potential linearly and square
wave perturbation with 50 mV every 50 ms, yielding measurement
before potential step (S1) and after potential step (S2);
(3) Analytical signal: Δi = S2(t) - S1(t - 50 ms)
ADVANTAGE
