Chromatography Forum

Hello,

I'm currently used GC Shimadzu 2014 with agilent packed capilary column. Column diameter is 0.32 mm, Film Thickness is 0.15 um, length is 15 m and column type is 50% polysiloxane.

Can I used direct injection mode for this type of column? or should I used split or splitless mode?
Because Someone said, we can't use direct injection mode to a column with small diameters. It may cause a damage to the Advance Flow Controler (AFC). because the sample was 'Forced' entry the column.
Is that true?

If I must use split mode, what is the ideal split ratio for this small column? Is it Ok if I used 5:1?

Thank you

Vienna

What's the other 50% of your stationary phase? I'm betting you can do direct injections on this particular column. You will pretty much always get the best peak shapes with these smaller bore columns if you can do a split injection. Generally, you only want to run splitless if detection of your analyte is difficult because of low concentration. How you adjust your split ratio is a trade off between detection limits and desired chromatography.

The only phases where direct injection of liquids might not be advisable are the porous polymer (PLOT) columns which are fundamentally designed for analysis of gases (methane, ethane, ethylene, etc.). Injection of liquids on these phases will likely cause you more problems than you want.

What's the other 50% of your stationary phase? I'm betting you can do direct injections on this particular column. You will pretty much always get the best peak shapes with these smaller bore columns if you can do a split injection. Generally, you only want to run splitless if detection of your analyte is difficult because of low concentration. How you adjust your split ratio is a trade off between detection limits and desired chromatography.

The only phases where direct injection of liquids might not be advisable are the porous polymer (PLOT) columns which are fundamentally designed for analysis of gases (methane, ethane, ethylene, etc.). Injection of liquids on these phases will likely cause you more problems than you want.

My column is : 50% phenyl-50% Methylploysiloxane.
So, is Ok if I use Direct injections mode? Bcause my sample contain very small concentrate. (under 25 ppm). If I use split mode, analyte is not detected.

Thanks

What's the other 50% of your stationary phase? I'm betting you can do direct injections on this particular column. You will pretty much always get the best peak shapes with these smaller bore columns if you can do a split injection. Generally, you only want to run splitless if detection of your analyte is difficult because of low concentration. How you adjust your split ratio is a trade off between detection limits and desired chromatography.

The only phases where direct injection of liquids might not be advisable are the porous polymer (PLOT) columns which are fundamentally designed for analysis of gases (methane, ethane, ethylene, etc.). Injection of liquids on these phases will likely cause you more problems than you want.

My column is : 50% phenyl-50% Methylploysiloxane.
So, is Ok if I use Direct injections mode? Bcause my sample contain very small concentrate. (under 25 ppm). If I use split mode, analyte is not detected.

Thanks

Before you go to "direct injection" (whatever that is) try splitless. With a 1 ul injection you will have 25 ng of analyte on column, which is plenty for all except a TCD.

Peter

What's the other 50% of your stationary phase? I'm betting you can do direct injections on this particular column. You will pretty much always get the best peak shapes with these smaller bore columns if you can do a split injection. Generally, you only want to run splitless if detection of your analyte is difficult because of low concentration. How you adjust your split ratio is a trade off between detection limits and desired chromatography.

The only phases where direct injection of liquids might not be advisable are the porous polymer (PLOT) columns which are fundamentally designed for analysis of gases (methane, ethane, ethylene, etc.). Injection of liquids on these phases will likely cause you more problems than you want.

My column is : 50% phenyl-50% Methylploysiloxane.
So, is Ok if I use Direct injections mode? Bcause my sample contain very small concentrate. (under 25 ppm). If I use split mode, analyte is not detected.

Thanks

Before you go to "direct injection" (whatever that is) try splitless. With a 1 ul injection you will have 25 ng of analyte on column, which is plenty for all except a TCD.

Peter

I've Try splitless. But but the analyte is not detected.
Only direct/On To column with 1 uL injection detected

Thanks

A 1 ul splitless injection and a 1 ul direct injection put the same quantity of analyte on the column, so if you see peaks with the direct injection and not with the splitless it is not injection mode that is causing the lack of signal with splitless.

Exactly how are you doing a "direct injection" to a 0.32 mm i.d. column, and what are your splitless conditions ?

What are you trying to analyse ?

Peter

A 1 ul splitless injection and a 1 ul direct injection put the same quantity of analyte on the column, so if you see peaks with the direct injection and not with the splitless it is not injection mode that is causing the lack of signal with splitless.

Exactly how are you doing a "direct injection" to a 0.32 mm i.d. column, and what are your splitless conditions ?

What are you trying to analyse ?

Peter

Direct/ on collumn injection : The analyte injected all into the collumn by closing the septum purge and split vent.

Splitless condition =
Collumn Temp : 120 C, rate : 7 C/min
Pressure : 85 Kpa, Total Flow : 7.7 mL/min, Collumn Flow : 1.57 mL/min, Sampling time : 2 min

FYI : I'm using GC 2014 Shimadzu. There's 3 type injection mode : Split, splitless and direct

I'm trying to analyse Phyrethroids

Thanks

vienna,

Direct usually means that you put the needle directly into the column. This requires a large enough bore column that the needle will fit in it. This means either a 0.53 column or a 0.53 retention gap or a fused silica needle (which I suspect you don't have) for a smaller bore column.

Splitless/split is a very good alternative and should get you pretty sensitive detection depending on a number of other factors.

Which leaves at least two big questions in my mind. 1) How high are you taking the column since Pyrethroids are very heavy. 2) How much are you injecting (not volume, concentration.)

I would start with a high level standard (200 ug/mL for example) and run it out very hot for a very long time (say 10C under your column isothermal limit for, say, 30 minutes.)

Best regards,

AICMM