GC: Why are some peaks sharp and narrow and some are wide?

[studentjelena]

Dear everyone,

Why do some analytes show sharp and narrow peaks and some analytes show broad peaks in gas chromatography?
Attached is a picture of a chromatogram of various organic solvents where you can see how methoxy-2-propanol and butanol show broad peaks compared to other analytes. Regardless of the concentration, these two analytes always appear on the chromatogram as a broad peak.
Does the temperature program of the oven have an effect on the appearance of peaks?

https://ibb.co/LQZJyjw

[mbdixon]

I get the same thing with my Glycols analysis and would like to know why.
https://photos.app.goo.gl/soyBceYcpsisxDdz6



The above chromatogram has a broad peak for ethylene glycol at 6.2 mins and a nice sharp peak for diethylene glycol at 7.8 mins.

The matrix is water and the method is :

Sample Volume (uL): 0.5
Mode Pulsed Splitless
Heater On 280 °C
Pressure On 3.2572 psi
Total Flow On 64.5 mL/min
Septum Purge Flow On 3 mL/min
Gas Saver On 20 After 2 min mL/min
Injection Pulse Pressure 20 psi Until 0.5 min
Purge Flow to Split Vent 60 mL/min at 1 min
Liner AG0-8173 Liner for Agilent (4 mm ID x 78.5 mm L x 6.3 mm OD), Split/Splitless, Dual Taper, 5/Pk
Oven
Equilibration Time 1 min
Max Temperature 250 °C
Maximum Temperature Override Disabled
Slow Fan Disabled
Temperature
Setpoint On
(Initial) 40 °C
Hold Time 0 min
Post Run 240 °C
Program
#1 Rate 20 °C/min
#1 Value 210 °C
#1 Hold Time 0 min
Column Information Phenomenex 7HG-G013-11: 1135458
ZB-WAXplus
Temperature Range -60 °C—250 °C (250 °C)
Dimensions 30 m x 250 μm x 0.25 μm
Column lock Unlocked
In Front SS Inlet H2
Out MSD
(Initial) 40 °C
Pressure 3.2572 psi
Flow 1.5 mL/min
Thermal Aux 2 (MSD Transfer Line)
Temperature
Setpoint On
(Initial) 250 °C
Post Run 0 °C
[SIM Parameters]
Group 1 Group ID : Glycols (227)
Resolution : 1
Group Start Time : 5
Number of Ions : 6
Ions
Dwell In Group Mass, Dwell) ( Mass, Dwell) ( Mass, Dwell)
( 31.10,50 ) ( 33.10,50 ) ( 45.10,50 )
( 62.00,50 ) ( 75.00,50 ) ( 76.00,50 )

[Peter Apps]

Usually that would be consentration overloading, but you have a polar column which should handle the components you have.

It might be a solvent effect from the water temporarily affecting the polarity of a short section of the column. It might improve if you start the temperature programme at a higher temperature and then ramp more slowly.