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CHEM 453 EXAM 2025-2026 VERIFIED
QUESTIONS AND CORRECT ANSWERS GRADED
A+
Which of the following unit is not an essential component of GC
vacuum degasser
which of the following statements with regard to split injection for GC is correct
the phenomenon of sample discrimination is caused by differences in the analytes boiling points
the following GC chromatogram was obtained by
splitless injection by solvent effect: the polarity of the sample solvent did not match the polarity of the stationary phase used in the GC column
which of the following is not one of the features of programmed temperature vaporizing inlets (PTV) used by GC
chromatographic peaks are further focused by solvent effect
which of the following statements with regard to leaks in GC-MS is true
- ferrules for GC-MS are used to seal the connections between the column and the injection and detection systems
- oxygen in the air can diffuse from the atmosphere into areas where its partial pressure is lower, which is the case with GC-MS
- the connections between a GC column injector and detector are points at which leaks can develop
which of the following statement about mass spectrometry is false
it differentiates d- and l-ketamine
which of the following is not one of the three essential components of a mass spectrometer
accelerator
the electron ionization mass spectrum shown below exhibits a M+ peak at
a M+ peak does not exist
electron ionization process is typically _______ efficient
0.1%
which of the following ions is the most stable
the left one (Benzene-CH2+)
for the electron ionization mass spectrum shown below, which of the two compounds (atomic mass: C=12, H=1, N=14, O=16) is responsible
bottom one (Benzene-CO-O-CH3)
Due to relatively low viscosity which of the following gas will require special high-performance vacuum pumping equipment in order to establish the required level of vacuum for GC-MS
hydrogen
which of the following statements about headspace GC analysis is correct
- clean-up of the sample is not necessary
- non-volatile materials are not carried into the GC
- the concentration of analytes in the headspace gas is proportional to the concentration in the original sample
the following stationary phase of capillary GC (x=0) is
nonpolar
in electron ionization, the electron kinetic energy is ______ the ionization energy of molecules
much greater than
which of the following statements about GC is not true
compounds with 1000 Da molecular weight are suitable for GC analysis
The set-up shown below is typical for a split injection routine for GC. Assuming that we are injecting 1 μL of a sample liquid that vaporizes to give 1 mL of gas. What would be the sample vapor transfer time onto the column (in seconds) under the conditions shown?
total flow = 104, septum purge flow = 3, split flow = 100, column flow = 1
which of the following is not one of the features of programmed temperature vaporizing inlets (PTV) used by GC
the solvent condenses inside the liner during sample introduction
the following mass spectrum strongly indicates that the molecular ion contains one
bromine atom
the following mass spectrum strongly indicates that the molecular ion contains one
chlorine atom
the number of carbons in the molecular ion can be estimated with the intensity of the isotope (A+1) signal. In addition, the presence many _____ atoms in the molecule should be considered due to their accumulated contribution to the isotope (A+1) signal
N
in the chemical ionization mass spectrum of a compound, the peak with the most significant intensity at the high end of the mass spectrum at m/z 227 is suspected to be MH+. if this is so the number of nitrogen atoms in the compound can be
and even number and zero
analytes must be ionized prior to entering the mass analyzer in a mass spectrometer. electron ionization and chemical ionization are two ionization techniques. which of the following statements is false regarding either technique
electron ionization gives very little fragmentation
a sample containing only carbon and hydrogen was analyzed. the molecular ion was identified to be located at m/z = 142. the normalized abundance of the m/z = 143 versus m/z= 142 was 12.3%. please estimate the number of carbons present in the molecule
11
during LC operation, air trapped in the column can result in very broad and obviously _______ chromatographic peaks
fronting
which of the following statements is false about the microporous particles of silica used by LC
the wider the pores, the larger the surface area of the silica
the _______ the particle used in LC columns, the ________ the plate height, the better the column efficiency
smaller, lower
theoretically, which of the following peptide will produce the best ESI signal
a singly-charged octapeptide with three additional amino acids of the pentapeptide
in-source collision induced dissociation (CID) can be achieved by
either increasing the potential difference between the skimmer and the RF-only multipole ΔV(S-Q) or between the nozzle and skimmer ΔV(N-S)
Under ESI conditions, some molecules produce abundant adduct ions. in the following positive-ion ESI spectrum, [M+H]+ ions is at m/z
213
in the presence of only water in an APCI source, cascade reactions ultimately result in production of _____ in the positive ion mode
H3O+(H2O)n
which of the following compounds has the highest proton affinity
ammonia
which of the following buffer is the least appropriate for LC-ESI/MS
low concentration of trifluoroacetic acid
a study of acids, bases, amphoteric and polar neutral drugs showed that in positive- ion ESI, _______ generally gave 10-20% higher signals than _________. interestingly, these increases in sensitivity were not seen in negative-ion mode
methanol, acetonitrile
which of the following statements with regard to normal phase liquid chromatography (NPLC) is false
the order of elution is most polar first, following by decreasingly polar (more hydrophobic) analytes
in reverse phase liquid chromatography, which of the following statements about isocratic elution is true
as the organic solvent content increases, the affinity of analytes for the mobile phase increases
which of the following statements about silica based C18 reverse phase stationary phases is false
during ESI, the formation of a stable nebulization aerosol is dependent upon all the following factors except
the analyte concentration of the LC eluate
which of the following solvents will lead to bigger droplets being produced and a decrease in ESI sensitivity
water
LC solvent degassing into the flow cell can cause
spurious peaks
larger ions will have _____ spheres of hydration
smaller
theoretically, which of the following ions will produce the best ESI signal
Pen4N+
which of the following ionization methods is suitable for biomolecules such as peptides, proteins, oligonucleotides, and DNAs
ESI
how polybrominated diphenyl ethers or PBDEs can be ionized by negative-ion APCI
dissociative electron capture
in positive-ion ESI/MS analysis of a basic analyte with known pKa, the signal intensity will be maximized when
pH < pKa - 2
in positive-ion ESI/MS which of the following compounds show best sensitivity
compounds that have functional groups such as basic nitrogen atoms
during the ESI process, as the droplet shrinks due to solvent evaporation, its radius (r) decreases but its charge (q) remains constant. this will lead to a ______ in the charge separation (inter-ionic distance) at the droplet surface and an _____ in repulsion between the surface charges
decrease, increase
the mass spectrum of the protein transferrin is as follows. what is the molecular weight of this protein
79552
the following two mass spectra were acquired with linear and reflectron TOF. which of them was acquired with reflectron TOF
bottom
the following ion stability diagram of a quadrupole mass analyzer shows that a combination of RF and DC voltages of _____ and _____ will allow mass 219 pass through the quadrupole mass analyzer
400, 40
the mode of operation for a quadrupole mass analyzer in which the DC voltage is removed is often referred to as ____ mode
ion bridge
for a given quadrupole assembly, to transmit ions of subsequently higher unit mass, the voltages U and V are ______ whilst the ratio U/V is fixed
increased
according to the following ion stability diagram of a quadrupole ion trap, which of the following combination values of Vrf and Udc can allow all three ions to be trapped (the three areas from the smallest to the biggest is for m/z 10, 50, and 100, respectively)
79.8, 0
in comparison with 2D ion traps, 3D ion traps are more than 30 times ______ in ion trapping capacity and more than 10 times _____ in trapping efficiency
lower, lower
which of the following mass spectrometers usually operates at unit resolution range
paul ion trap
which of the following mass analyzers offers the best resolution
orbitrap
an orbitrap mass spectrometer produces maximum resolving power 140000 at m/z
- what is the maximum resolving power at m/z 800 can this instrument produce
70000
low-energy collisions of a peptide fragmentation primarily along the peptide backbone. at low energies, get mostly
b- and y-ions of tryptic peptides
which of the following mass spectrometers records mass spectra with the fastest speed
time-of-flight
quadrupole mass analyzers require mechanical accuracy of the rods in the _____ region
μm
which of the following two amino acids is an alpha amino acid
right
which of the following amino acids can originate N-linked glycosylation of proteins
asparagine
which of the following amino acids can not be phosphorylated
tryptophan
the following schematic diagram shows that the ion beam is
both direction and kinetic energy focused
the resolving power of the ______ mass analyzers decreases in proportion to 1/ √m/ z
orbitrap
the following mass spectra demonstrate resolving power (RP) increases in proportion to the scan time. which of the following mass analyzers can produce these mass spectra
orbitrap
a vacuum is defined as less than 1 atmosphere of pressure. a high vacuum refers to the pressure less than _____ mbar
