Chromatography Forum

Recently, we started to use ISO 9377-2 method for oil index in water (waste water) determination. System: Varian GC FID, 15mx0.25x0.25 VF1 column, on column injector. 5m of 0.53 precolumn. The problem is very high septum bleed - signal peaks in range of C10-C40 are in order of 30 mV (0.2 mg/l) and septum peaks are in the same order (going out ~150C. Temp. program: 50C for 2 min. and 60C/min to 320C hold for 2 min. Flow - 4 to 2 ml/min. I've tried changing almost everything, but nothing helps. And another big problem - C40/C20 ratio is very small = 0.35. It should be >0.8 according to standard. Maybe someone had the same problems? I will be glad to get any help.

Dear Remirama,

I work with a method based in 9377-2, but I work in splitless mode, at 340°C, column flow 7.4 ml/min, dtector at 325 °C. My initial temperature is 40°C for 1.50 min, then up to 60°C at 5°C/min and finally up to 315°C at 15°C/min. In such conditions C40/C20 ratio is nearly or higher than 0.80 and no bleeding or not significant.

I hope this will help you

Carmen

Thank you for your answer, but just to be sure two more questions. Are you turning on split after some time (~5 min)? Is injector isothermal (all the time 340 or temperature program)?
Now i'm working with such configuration: injector 40 to 340C, split is on initialy (vents out hexane, very nice peak), after 10s split is off for 2 min. and after on for remaining time. Injection volume - 2ul. Temp. program: 30C for 2 min, after to 330C, at 30C/min and holds for 2 min. C40 comes at 13-th minute (15mx0.25x0.25 column). C40/C20 = 0.87. With longer period of initial split on, discrimination appears for the low boiling point hydrocarbons.
I think, it is not possible to use on column injector for that analysis, at least for injectors that use hot oncolumn and do not have septum purge.
Best regards,
remi

what varian do you have?

Varian CP3800, EFC type 3 (flow) and type 1(pressure), FID detector, 1079 split/splitless(PTV) and 1041 on-column injector (isothermal), 8410 autosampler.

Dear Remirama,
I have the same system Varian CP3800.
I do C10 to C60 on it.
split ratio 1/50 after .5 min
temp. prog. start 50(2) ramp 30C/min to 350C(0)
Injector temp. 350C
detector 360C
Flow 10ml/min
used high temp column db1 (30mx 0.32id x0.1 column)
it works great!!!!!!!!have fun

dear Remirama,

I don't apply split ratio an my injector is isothermal.

Best regards

carmen

Thank you for your answer, but just to be sure two more questions. Are you turning on split after some time (~5 min)? Is injector isothermal (all the time 340 or temperature program)?
Now i'm working with such configuration: injector 40 to 340C, split is on initialy (vents out hexane, very nice peak), after 10s split is off for 2 min. and after on for remaining time. Injection volume - 2ul. Temp. program: 30C for 2 min, after to 330C, at 30C/min and holds for 2 min. C40 comes at 13-th minute (15mx0.25x0.25 column). C40/C20 = 0.87. With longer period of initial split on, discrimination appears for the low boiling point hydrocarbons.
I think, it is not possible to use on column injector for that analysis, at least for injectors that use hot oncolumn and do not have septum purge.
Best regards,
remi

Dear Remirama,
try to look at DANI web site (www.danispa.it). There is an application note with a chromatogram and instrument parameter required. I use a DANI system and I'm satisfied.