Chromatography Forum

Hello everybody.
I have many types of SUPELCO capillary columns ( VOCOL, PTE, EQUITY, I have a DB624 from J&W too), but I dont know which one to use for the analysis of Gasoline ( GRO) I guess VOCOL but I didnt get good results.

thank you very much.

You need to be more specific about you want to know.

There are several different types of columns available for gasoline analysis, depending on the data required. A good general purpose column is a 50m x 0.20mm ID x 0.5um poly(dimethylsiloxane) non-polar column for reasonably detailed composition.

There are specialist 100 or 150 metre column for more detailed analysis, such as separating the oxygenates and grouping the individual HCs ( eg PNA, PONA, PIANO ).

In general, gasoline is analysed according to standard ASTM methods, so you need the column that is specified in the method. Full range gasoline can have somewhere between 300 - 600 HCs, so high resolution boiling point ( nonpolar ) or lower resolution group-type ( polar ) columns are routinely used.

Bruce Hamilton

Pueblito,

Because you are using the phrase "GRO" and because you are talking about VOCOL, I will assume environmental analysis and probably purge and trap. In that case, the VOCOL probably should have done the trick so the question is why you were not happy. Other columns that would do the job include the DB-VRX, DB-624, SPB-624, or RTX-VMS. These are all pretty much set up for that type of analysis.

Tell us why you did not like the VOCOL.

Best regards.

Sorry for the lack of detail.
Im trying to perform a GC-FID, purge & trap analysis of gasoline range organics GRO, because of that, I want to do an environmental analysis rather than characterize all components of.
So, I perform VOCs analysis very well with VOCOL phase but when I tried GRO I got low responses for alcanes and good for BTEX. By contrast a DB-624 phase had better general performance and peak shape.
But there are things to consider.
I use an Agilent 6890 to analyze TPH and used it with a DB-624 to attempt GRO, and I use a Shimadzu for VOCs but I used it with a VOCOL to attempt GRO too.
It is possible that I make a mistake in the chromatographic or purge parameters that accounts for the differences betweet the two phases......or not?
Any comments appreciated.

Pueblito,

Both of those chromatographic phases should be fine for GRO so the next set of questions would concern you purge-and-trap conditions as well as what dimensions of columns you are using. Can you provide that to us?

Best regards.

my purge and trap condition and column dimension are:

For Shimadzu QP2010:
Tekmar concetrator.
Transfer line 150 ºC
sample mount 60
Dry purge Tº 40
Desorb preheat Tº 245
Desorb Tº 250


purge time 11min
preheat time 1min
dry purge time 1min
Desorb time 4min

purge flow 40ml/min
Dry p. flow 200ml/min
Desorb flow 300ml/min

column:
VOCOL 60m x 0.53mm x 3um

Inyector: 200ºC, direct, Constant flow, Total flow 9 ml/min. Helium
FID: 230ºC sampling rate 80msec, H2 40ml/min, Air 400,
mkup He, 30ml/min

Oven:
33ºC 10min
at 4º/min to 115ºC
at 25º/min to 228º hold 6 min.

For Agilen 6890:

Tekmar concetrator.
Transfer line 180 ºC
sample mount 60
Dry purge Tº 40
Desorb preheat Tº 245
Desorb Tº 180


purge time 12min
preheat time 1min
dry purge time 1min
Desorb time 1.5min

purge flow 20ml/min
Dry p. flow 200ml/min
Desorb flow 300ml/min

column:
DB 624 75m x 0.45mm x 2.55um

Inyector: 250ºC, splitless, total flow 36ml/min (splitless time 0.5 min) constant flow 8ml/min, Helium.
FID: 250ºC H2 40ml/min, Air 400,
mkup N2, 20ml/min

Oven:
45ºC 2min
at 5º/min to 100ºC hold 2 min
at 8º/min to 240º hold 7.5 min.

Hey, there are some differences betweet the two purge programs!!!!!.

many thanks.