Chromatography Forum

I'm using the devices as below
- Detector : PDD
- Column : Capillary Molesieve 5A
- Oven Temp : 50℃
- Carrier gas : Helium

I'm trying to find out the impurities in N50 oxygen.
and I found out three impurity peaks other than oxygen peak.
N2 impurity peak came out at RT 2.54.
and right next to N2 peak, at RT 2.68, there's a small impurity peak,
and far away, at RT 7.83, there's a small impurity peak too.
I injected CO, CH4, CO2 standards to find what it is, but it wasn't these materials.

What could it be?

Since I assume you are using a valve with loop injection you might consider the peaks you are seeing are artifacts of the injection, causes are varied, even a leak.
While krypton coelutes on a MS5a column with N2 it is unlikely to separate cleanly with your conditions, albeit it is possible.
Investigate different injection timings and see if this varies the retention times of your unknown peaks.

best wishes,

retired Rod

That is right. I'm using a valve with loop injection.
I tried injecting rare gases, and your assume was right.
It was a krypton peak. (and xenon)
I'm very thankful of you Rod.

Since I assume you are using a valve with loop injection you might consider the peaks you are seeing are artifacts of the injection, causes are varied, even a leak.
While krypton coelutes on a MS5a column with N2 it is unlikely to separate cleanly with your conditions, albeit it is possible.
Investigate different injection timings and see if this varies the retention times of your unknown peaks.

best wishes,

retired Rod