Peaks appear in blank Chromatogram

[najeeb]

Hi,
I’m just installing new column and baked for overnight at 300degC and run a few solvent to flush it.

Below stated the parameter used.
Initial Temperature: 35
Initial Time: 1 min
Solvent Delay: 4.5 Mins
Final Temperature: 300
Injector Temperature: 300
Temperature Ramp: 15C/min
Sample Injection: 3 ul (splitless mode)

1. Now, I ‘m facing problem on Solvent blank chromatogram. I'm using hexane JT Baker with purity 95%.The problem is, besides having solvent peaks in the range of RT4.5-RT10.0, few peaks are observed after RT 9-15min, as stated below,
RT9.637-cyclohexasiloxane, dodecanetyl-H36O6Si6C12
RT 11.11-cycloheptasiloxane,tetradecamethyl-C14H42O7Si7
RT12.54-cyclooctasiloxane, hexadecamethyl-C16H48O8Si8
RT13.71-cyclononasiloxane, octadecamethyl-C18H54O9Si9.

2.Besides that, the height of starting peak of solvent blank chromatogram is around 50,000 abundance, which is exceeded 5000 and the peak after RT10min is looks like unresolved/ Front talling.

pls help me to solve this problem.
thanks

[Peter Apps]

Either column bleed or septum bleed.

Check for leaks with a leak seeker.

If you do not have gas scrubbers on your carrier gas you need to get some, and if you have them, check that they are not exhausted.

For the septum bleed, do inlet maintenance (new liner, new septum) and check that the septum purge is flowing at the correct rate (3 - 5 ml/min on most GCs).

Peter

[dr_bahram1977]

Please let us know your column details. all this peaks seems to be from column bleeding.
your conditioning program seems to be wrong.
Please give us details about your oven program too.
maybe you've given so much heat to column.

[najeeb]

-thank for the info Mr.Peter.
Hi Dr.Bahram,
The column we using is HP-5MS (L-30m,D-0.25,F-0.25) with temperature limits from 60Cto 325C.
Oven temperature:300C
Ramp rate:15C/min.
Actually, how to do conditioning after installing new column?

[Peter Apps]

-

Actually, how to do conditioning after installing new column?

Follow the column manufacturer's instructions that come with the column and can be found on their websites.

Peter

[dr_bahram1977]

hi
1-Use pure solvents.
2-run a blank Run. ( do not inject solvent). and see if peaks are present yet or not. if peaks disappear, they are from solvent. else, they are from inlet or column.
I think your peaks are from column mainly, ( acc compounds you listed).
if possible, send me your chromatogram, so I can give you better advise.
bahram111@yahoo.com

[James_Ball]

Another problem that can occur is small particles of the septa fall into the injection port liner, and when you inject solvent it causes some of the siloxanes to come out of the particles and enter the column. Check to make sure your syringe has not cause these to fall into the liner.

If your column came with the rubber plugs on the end instead of being flame sealed, did you cut a few centimeters from each end of the column before installing it? If not, it could be some particles of those plugs are in the ends of the column and causing the same problem as septa particles in the inlet.