Column efficiency parameters

PRESENTED BY
SUBODH S SATHEESH
MPHARM
PHARMACEUTICS
ECPS
1
PHARMACEUTICAL ANALYSIS-GAS
CHROMATOGRAPHY

 It is expressed by the number of theoretical plates
 It is determined by the formula
 The number of theoretical plates is a measure of the
“goodness” of the column
 If the retention time is high and peak width is narrow then it
shows excellent chromatograms
2
CHROMATOGRAPHY

where tr is the retention time measured from the instant of injection
w is the peak width
W is determined by SD= σ ie w=4σ
3
CHROMATOGRAPHY

 Resolution is the ability to seperate two signals
 In chromatography its the ability to seperate two peaks.ie
seperation of constituents
where tr1 and tr2 and w1 and w2 are the times and widths,
respectively, of the two immediately adjacent peaks.
 If the peaks are sufficiently close w is nearly the same for both
peaks and resolution may be expressed as

4
CHROMATOGRAPHY

Greater the distance more resolution and vice versa.
5
CHROMATOGRAPHY

 The rates of migration of substances in chromatographic
procedures depend on the relative affinity of the substances for
the stationary and the mobile phases
 Its the difference in time between the point of injection and the
time of emergence of separation of component from the
column.
 It is actually the time required for 50% of the component to
get eluted.
 It is measure in minutes or seconds
6
CHROMATOGRAPHY

7
CHROMATOGRAPHY

 It is the volume of carrier gas required to elute
components from the column to the time the peak
maximum is obtained.
 Retention volume depends upon flowrate and retention
time
 VR= tR-FC
8
CHROMATOGRAPHY

 It is the ratio of partition coefficient of two components to be
separated.
 S= Kb/Ka = K’a/k’b= (tb-to)/(ta-to)
If peaks are far apart ie there is more difference in partition coefficient
between compounds hence more seperation factor and viceversa
Less seperation
factor
More seperation
factor
9
CHROMATOGRAPHY

 HETP is numerically equal to the column length divided by
the number of theoretical plates in the column
 It varies from to one column to another as well as one solute to
other
 The more efficient the column the better the resolution and the
smaller the HETP.
 HETP=Length of column / no of theoretical plates
10
CHROMATOGRAPHY

11
CHROMATOGRAPHY

 A chromatographic peak should be symmetrical about its
centre to follow gaussian distribution
 Asymetric factor is the measure of peak tailing or fronting.
 It is defined as the distance from the centre line of the peak to
the back slope divided by the distance from the centre line of
the peak to the front slope.
12
CHROMATOGRAPHY

The chromatographic peak in (a) is an example of tailing, which
occurs when some sites on the stationary phase retain the solute
more strongly than other sites.
The peak in (b) is an example of fronting, which most often is the
result of overloading the column with sample. For both (a) and (b)
the green chromatogram is the asymmetric peak and the red dashed
chromatogram shows the ideal, Gaussian peak shape.
13
CHROMATOGRAPHY

 Its function is to separate sample components to
discrete peaks
 It should have reasonable chemical and thermal
stability
 There are a lot liquid stationary phases available for gas
chromatography. But there is no solvent that meet all
the requirements of a perfect stationary phase
14
CHROMATOGRAPHY

 Liquid phase should not permeate too deeply into the fine
pores of the support structure as slow diffusion in and out of
pores affects column efficiency
 It should be chemically inert
 It should be a good solvent for sample component
 Liquid phase should have low volatility and high stability at
elevated temperatures otherwise they can contribute to
interference in analysis
15
CHROMATOGRAPHY


Stationary Phase Trade Name Max Temp Common
Applications
Dimethyl Polysiloxane OV – 1, SE – 30 350oC Hydrocarbons,
Polynuclear
aromatics, PCB’s
Poly(phenyl methyl)
siloxane
OV – 17 250oC Steroids, Pesticides,
Glycols
Poly (Trifluoro propyl
dimethyl) siloxane
OV – 210 200oC Chlorinated
Aromatics, Nitro
Aromatics, Alkyl
substituted Benzenes
Polyethylene Glycol Carbowax 20 M 250oC Free acids, Alcohols,
Essential Oils, Glycols
5% Diphenyl – 95%
Dimethyl polysiloxane
DB – 5 325oC Flavors,
environmental
samples and aromatic
hydrocarbons
Typical liquid stationary phases
16
CHROMATOGRAPHY

 Nonpolar solutes like pentane butane etc can be effectively
separated by nonpolar solvents like squalene. And polar
solutes can be easily separated by polar solvents eg; PEG.
 Boiling point is also a factor of consideration. among solutes
with similar polarity if there is sufficient difference in BP
effective separation can take place.
 Eg. Squalene min/max temp= 293/423 SE4 423/573
 A solvent that could generate different partition ratios
among solvents can only be useful in GLC
17
CHROMATOGRAPHY

 H KAUR Instrumental methods of chemical analysis
ninth edition 2013 ;1091-1092
 Skoog holler crouch Instrumental analysis 2012 841-
846
 B K sharma Instrumental methods of chemical analysis
twenty fourth edition 2005 c188-191
 En.wikipedia.org gas chromatography
18
CHROMATOGRAPHY

MANY THANKS
19
CHROMATOGRAPHY

Column efficiency parameters

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