Advanced separation and mass spec

Rs = (resolution)

2( tR2 - tR1)/ W2 + W1 = Difference between tr/Wav

What minimum value should Rs be for fully resolved peaks?

1.5

what is k’ ?

Capacity factor- the longer the retention time, the greater the capacity factor

tr (retention time) is 

the time at which the analyte is detected to have eluted

tM is

the time for an analyte which doesn’t interact with the stationary phase to elute

ts is

time the analyte is associated with the stationary phase, ts= tR- tM

k’=

ts/tM = ns/nM = CsVs/CmVm = K VS/VM

What is α?

selectivity factor, the ratio of analytes capacity factors

α =

k’2 / k’1 = ts2/ts1

How do we explain band broadening?

random walk in 1 dimension leading to symmetrical spread of velocities around a mean value

Variance=

σ² = 𝜏² = 2Dt

What are the two main types of skewing?

fronting- caused from overloading with too much solute and tailing- corrected by masking strong absorption sites on SP

H (plate height)= 

σ² / L

What is plate height (H) ?

the constant of proportionality between variance of the band and the distance it has travelled, it is approximately the length of column required for one equilibrium of solute between MP and SP

N (efficiency) =

t2R/ 𝜏² = L² / σ² = L/H

𝜏^{2 =} 

W/4

Rs ∝

sqrt. N

What is the van Deemter equation?

H= A + B/u + Cu

What is the A term in the van Deemter equation, how to reduce it?

relates to the multiple flow paths, reduced with smaller SP molecules

What is the B term in the van Deemter equation, how to reduce it?

related to longitudinal diffusion and reduced by faster linear flow as less time is spent in the column

What is the C term in the van Deemter equation, how to reduce it?

mass transfer/ equilibration time, reduced by decreasing thickness of stationary phase or column radius or increasing temperature

What is the order of elution in gas chromatography within a compound class?

analytes elute in order of boiling points

What is the order of elution in gas chromatography when comparing compound classes?

molecules with greatest similarity to SP are most strongly retained. eg. polar phase retains polar solutes

ln k’ ≈

(10 Tbp/T ) + c

What is the relation between k and Tbp for homologous series of analytes?

ln k’ scales with Tbp and k’ increases as Tbp increases

What is the relation between k and T for all analytes?

ln k’ scales with 1/T and k’ decreases as T increases

What is the order of elution in liquid chromatography?

analytes elute in order of hydrophobicity with the most hydrophobic eluting last

ε⁰ is…

eluent strength,as it increases solutes elute faster and in reverse phase a less polar solvent has higher ε⁰

log k’ =

log k’ (in water) - SΦ

Φ is

volume fraction of organic modifier

How to decrease phase ratio ?

use non-porous material rather than porous

How does particle diameter affect van Deemter equation?

A increases as particle diameter increases as there is a less uniform flow and C increases as it takes longer to diffuse through inner pores

what is the relation between plate height and particle size in liquid chromatography?

plate height decreases as particle size decreases

What is the limitation to using the lowest particle diameter?

resistance to solvent flow

open tubular (capillary) columns vs packed column

lower flow resistance, longer, lower phase ratio, higher efficiency, can be overloaded

Which aspect of van deemter equation is absent in open tubular (capilliary) column?

A

What kind of column does A and C not contribute to H ?

Capilliary electrophoresis

Full mass spectrum scan mode

Q1-scanned, q2-no gas,

Full product ion spectrum

Q1-Fixed DC for specific M/Z, q2-gas, Q3- scanned

Precursor ion spectrum

Q1- scanned, q2- gas, Q3- fixed DC for specific m/z

Neutral loss spectrum

Q1- scanned, q2- gas, Q3- scanned

Selected reaction monitoring

Q1- fixed DC, q2- gas, Q3- fixed DC

mass error in ppm =

(measured mass - theoretical mass)/ theoretical mass x 1000000

resolving power

m1/ change in m

Which is the cheapest mass analyser

quadrupole

Which is the least sensitive mass analyser

ICR

Which has the lowest mass resolution?

ICR