5: Chromatography, Mass Spectrometry

Question 1

measure of analytes ability to dissolve in aqueous or organic phase in a biphasic system

Answer 1

Partition coefficient

Question 2

In planar chromatography: the ratio of solute’s distance travelled to the solvent’s distance travelled

Answer 2

Rf value

Question 3

Type of chromatography in which particles for SP have pores so small that only small molecules can infiltrate them; larger molecules will be excluded

Answer 3

Size Exclusion chromatography

Question 4

Phenomenon observed in chromatography when molecules arrive at around the same time – some early, some on time, some late. Consider the multiple paths a molecule may take thru the column

Answer 4

Peak Broadening

Question 5

diffusion of solute along the length of the column in the flowing mobile phase; molecules are travelling down column bc of MP flow, but they are also wanting to move in different directions – may cause peak broadening

Answer 5

Longitudinal diffusion

Question 6

flow thru column not uniform in one direction due to packings – may cause peak broadening

Answer 6

Eddy Diffusion

Question 7

pores in packing material in which analytes infiltrate; take analytes longer to pass thru column – may cause peak broadening

Answer 7

Mass transport broadening

Question 8

Separate equilibrations of sample between stationary phase and mobile phase happen here:

Answer 8

theoretical plates

more plates = more efficient separation

Question 9

H = A + B/µ + C*µ

Answer 9

Van Deemter Equation
H = HETP = height equivalent to theoretical plate; measure of
resolving power of a column (m)
A = eddy diffusion (particle size, bed uniformity)
B = longitudinal diffusion (flow rate, MP)
C = mass transfer (particle size, SP thickness)
µ = linear velocity (m/s)

Question 10

migration rate of analyte on column

Answer 10

retention factor/capacity factor (k’)

k’ = RT-MT/MT

where RT = retention time
MT = time for mobile phase to travel thru column (represents compound that doesn’t interact wit stationary phase)

Question 11

How to calculate Relative Retention Time (RRT)

Answer 11

(RT of analyte)/(RT of ISTD)

Question 12

How to calculate Response Ratio

Answer 12

(response of analyte)/(response of ISTD)

Question 13

Injection mode used for larger quantities; majority of sample split off to waste and only a fraction enters column

Answer 13

Split

Question 14

Injection mode all sample introduced to column (good for trace)

Answer 14

Splitless

Question 15

Chromatographic detector where everything eluted off column is consumed by flame; hydrogen flame; organic compounds degraded by flame to ions which are then collected by electrode and translated into an electrical current (peak)

Answer 15

Flame Ionization Detector (FID)

-He (carrier gas); H2 (fuel), Air, N2 (make-up)
-Sensitive; Large dynamic range

Question 16

Chromatographic detector where H2 and O2 burn to form plasma; collector electrode measures charged particles that hit it; Thermionic bead (NP bead) coated with alkali metal promotes ionization of compounds

Answer 16

Nitrogen Phosphorous Detector

Question 17

Chromatographic detector where radioactive nickel acts as source of beta particles (slow electrons) which pass along path of carrier gas; compounds pass thru in carrier gas an capture electrons; these compounds are typically halogens (i.e. Cl-)

Answer 17

Electron-Capture Detector (ECD)

-Selective for electronegative species

Question 18

Type of ionization method where sample exposed to 70eV electrons; energy of e- interacting w/ molecule is much greater than the bonds so ionization occurs

Answer 18

Electron ionization (EI)

-Sometimes called electron impact (wrong)

Question 19

In electron ionization, a bond breaks in such a way that each fragment gets one of the shared electrons. The result is uncharged free radicals that won’t be detected in a mass spec.

Answer 19

Homolytic Cleavage

Question 20

In electron ionization, a bond breaks in such a way that one atom gets both shared electrons; more common in polar bonds

Answer 20

Heterolytic cleavage/ ionic fission

Question 21

Types of Pumps used in a Mass Spec

Answer 21

-Turbomolecular pump: turns fast enough to direct air in a certain direction; directs remaining molecules

-Rough pump: draws out any gasses that are ejected by turbo

Question 21

Type of ionization method where a reagent gas (i.e. methane) is ionized in a simple electron impact ion source. The now charged gas collides w/ sample molecules to produce ions or adducts.

-Different mass spectra depending on the reagent gas used.

Answer 21

Chemical Ionization

Question 21

Describe how a mass spec works.

Answer 21

-Effluent dumped into ion source; filament in ion source; source of electrons causes fragmentation and production of charged particles; repeller has electrical potential applied to it so it directs charged particles then into a series of lenses

-Charged particles pass through lens stack to create a beam before entering quadrupole

-Quadrupole: opposite rods have the same charge
(+ or -); continually alternate polarity of poles to help filter specific masses of ions

-Reach detector (electron multiplier): each collision along the side results in ejection of multiple electrons which repeats down the length of the horn; this helps to take a small amount of charged particles and amplify them into a measurable signal

Question 22

Collison cell

Answer 22

Second quadrupole in a triple quad; contains argon

-ions travel thru Q1 and filter –> reach Q2 and collide with Argon to create product ions which are then filtered in Q3

Question 23

Type of mass spec analyzer where you apply voltages to ring electrodes to repel masses and trap them into space to accumulate; you then change voltage to selectively eject them; higher sensitivity than quadrupole

Answer 23

Ion Trap

Question 24

Time of Flight

Answer 24

masses form and send into TOF tube; impart kinetic energy on ions, smaller ions will travel faster with the same amount of kinetic as larger ions; detector converts time spent in tube to specific mass

Question 25

What is baseline resolution?

Answer 25

1.5

Question 26

Ideally, will an ISTD elute before, after, or at the same time as the compound of interest

Answer 26

Before

Question 27

Representation of data where one or more m/z values representing one or more analytes of interest are recovered from the entire data set for a chromatographic run

Answer 27

Extracted Ion Chromatogram

Question 28

Quadrupoles use alternating:

Answer 28

radio frequencies and DC voltages

Question 29

the point at which the droplets break apart and a charge is imparted to the molecules within

Answer 29

Rayleigh Instability Limit

Question 30

What types of compounds will exhibit M+ as their base peak? Those that readily fragment Those that do not readily fragment

Answer 30

Those that do not readily fragment

Question 31

Ionization technique that uses a fine spray of LC effluent that is vaporized in a high temperature tube

Answer 31

APCI

Question 32

Ionization technique that uses photons as the energy source for the ionization process

Answer 32

APPI

Question 33

Column efficiency must be calculated from an isothermal GC or isocratic LC run True False

Answer 33

True

Question 34

a variant of normal phase chromatography that partly overlaps with other chromatographic applications such as ion chromatography and reverse phase LC

Answer 34

Hydrophilic interaction chromatography (HILIC)

Question 35

Non-Polar Stationary Phase (think opposite) -Polar matrix -Non-polar analyte of interest -Aqueous samples -Elute using non-polar solvent to disrupt analytes attraction to stationary phase

Answer 35

Reverse Phase SPE

Question 36

Polar Stationary Phase (think opposite) -Polar analytes in non-polar sample -Not as useful in toxicology

Answer 36

Normal Phase SPE

Question 37

Which ionization technique produces less fragmentation as compared to the other? Chemical Ionization Electron Ionization

Answer 37

Chemical Ionization

Question 38

Sensitive detection of organic compounds over a wide linear dynamic range: TCD NPD ECD PFPD FID

Answer 38

FID

Question 39

Selectivity and sensitivity for trace-level detection and analysis of compounds with electronegative functional groups: NPD TCD ECD FID PFPD

Answer 39

ECD

Question 40

This for an analyte is a function of temperature, pressure, stationary phase and mobile phase: The distribution/partition coefficient Column efficiency The resolution coefficient Theoretical plates

Answer 40

The distribution/partition coefficient

Question 41

In gas chromatography, the vaporization chamber in the injection port is typically heated: Above the lowest boiling point of the sample To be equivalent to the lowest boiling point of the sample Below the lowest boiling point of the sample

Answer 41

Above the lowest boiling point of the sample

Question 42

Put these solvents in the order of increasing elution strength for a polar molecule for reverse phase HPLC: acetonitrile, water, tetrahydrofuran, methanol water methanol tetrahydrofuran acetonitrile

Answer 42

__1__ water __2__ methanol __4__ tetrahydrofuran __3__ acetonitrile

Question 43

Base peak

Answer 43

the ion with the highest abundance in the mass spectrum which is assigned a relative value of 100%

Question 44

The incorporation of each deuterium adds _____ mass unit(s) to the fragment in the mass spectrometer.

Answer 44

1

Question 45

The factors that can be modified to control or modify resolution are: Temperature, Velocity and Capacity Pressure, Solubility and Capacity Selectivity, Velocity and Capacity Selectivity, Capacity and Efficiency Temperature, Pressure and Solubility

Answer 45

Selectivity, Capacity and Efficiency

Question 46

Absorption in chromatography is a process of: Partitioning Attenuation Bulk phenomenon Surface property None of the above

Answer 46

Partitioning

Question 47

The Retention Factor describes: The distribution of an analyte between the stationary and the mobile phase The migration rate of an analyte through a column The velocity of the mobile phase a and b b and c

Answer 47

The migration rate of an analyte through a column

Question 48

The term used when several different precursor-product ion pairs are monitored

Answer 48

Multiple reaction monitoring

Question 49

LC ionization methods differ from GC ionization methods in that: Polar molecules poorly ionize A greater amount of energy is required LC ionization requires the analyte to be stable at high temperature and pressure The length of time it takes to ionize an analyte is longer LC ionization can occur at atmospheric pressures

Answer 49

LC ionization can occur at atmospheric pressures

Question 50

In a triple quad instrument, the second quadrupole is where: Masses are stored The mass of the ion is determined The mass axis is calibrated Fragmentation takes place Detection occurs

Answer 50

Fragmentation takes place

Question 51

In TOF testing, the time it takes for ions generated and accelerated to reach the detector is used to determine the _________ of the ion. Mass Retention Time Absorbance m/z ratio Structure

Answer 51

Mass

Question 52

Describes the relative interaction of two analytes with the stationary phase: Selectivity Column Performance Efficiency Capacity Effectivity

Answer 52

Selectivity