Chromatography Forum

Hi All

I am very new to GC and I am having a problem with a method. I am using the GC with Headspace for residual solvent analysis. But when I inject the blank I get a peak at the same time as one of the residual solvents, at first I thought it was from contamination of glassware but after thoroughly cleaning the glassware I am are still getting the peak.

My blank is Purified water so I got purified water from two different sources and also injected them using different volumes in the vial 5ml & 10ml my peak responses are below.

Source 1 5ml vol = 10198.76
Source 1 10ml vol = 9515.02

Source 2 5ml vol = 5831.05
Source 2 10ml vol =1362.19

Is the extra peak due to some carry over from the needle or elsewhere on the equipment. and if so how do I correct this problem.

Thanks in advance

What peak does your mystery peak coelute with?

Rod

Since it seems to be inconsistent in area response from the water, it might be from the HS unit or it might be from your lab air.

I used to see methanol and acetonitrile fumes from the LC lab next door and benzene and toluene from the diesel trucks passing by outside the building.

And if I had a beer at lunch, OH MY, I saw ethanol in my samples all day long.

Rod

It is actually methanol, but would the GC not be sealed air tight so that the samples can not be compromised like this.

You are doing HS samples, no?

Are they prepared in an open lab, or an evacuated enclosed box?

Rod

It is actually methanol, but would the GC not be sealed air tight so that the samples can not be compromised like this.

The GC is as air tight as possible, but you always have small leaks. Nothing is perfect. Therefore, if you have solvents or other contaminants in or around the lab, you'll see them in your analysis. Acetone and methylene chloride are a big problem in environmental labs. They're compounds of interest in drinking and ground water analysis for volatiles. They are also used throughout the lab for cleaning and other sample prep. Even if you isolate the volatile lab, you can bring them in on your lab coat if you walk through the prep area.

As Rod mentions, you shouldn't prep your samples in an open lab.

There is an easy way to find out.
Just cap an head-space vial without adding water to it.
Inject this air-sample and see what kind of result you get from it.
if you see MeOH it's in the lab-air somewere, if not it should come from your water source.
BMU