Separation of epoxides using a B-bex column with acetonitrile as solvent and deterctor FID. The conditions are: oven temperature-max 70 ° C, injector 280 ° C, detector 220 ° C, pressure 38 psi. I used the method around 30 injections, all normal, when finishing one of them, the baseline jumps and generates a lot of noise, from there, in all the chromatograms the baseline shows the temperature ramp that I use. What happened to the column?
Blue line - normal chromatogram. Green line - first time it appears.
Purple line and aquamarine - chromatograms after the jump
It looks like you have a problem with high boiling compounds in your sample. These compounds stay on the cluomn after each injection and begin to elute at your highest temperature in your temp-program. At the end after many injections you find the vaporpressure of these compounds over your stationary phase B-bex. I don't know what a B-bex Phase is. Is this chemically bonded? If not, it is possible polar components could seperate your stationary Phase from your fused silica. Is this a fused silica column?
A good check is to conditionate your column over night at the highest temp. you use in your temp program and look if the first some chromatograms are clean.
Chromatography (/ˌkroʊməˈtɒɡrəfi/; from Greek χρῶμα chroma which means "color" and γράφειν graphein "to write"[1]) is a laboratory technique for the separation of a mixture. The mixture is dissolved in a fluid called the mobile phase, which carries it through a structure holding another material called the stationary phase. The various constituents of the mixture travel at different speeds, causing them to separate. The separation is based on differential partitioning between the mobile and stationary phases. Subtle differences in a compound's partition coefficient result in differential retention on the stationary phase and thus changing the separation.[2]
Chromatography may be preparative or analytical. The purpose of preparative chromatography is to separate the components of a mixture for later use, and is thus a form of purification. Analytical chromatography is done normally with smaller amounts of material and is for establishing the presence or measuring the relative proportions of analytes in a mixture. The two are not mutually exclusive.[3]
I agree with Sulaiman - you must clean your column after each injection to ensure that no high-boiling compounds remain on the column to slowly elute iin future analysis runs. This is a good practice in GC as well as HPLC analysis.
First off, do you mean a b-DEX column? That is a chiral phase, and has to be handled with great care.
You claim to be running an analysis in acetonitrile but you show that your maximum temperature is well below the boiling point of the acetonitrile. As is obvious to anyone with any experience in chromatography this would simply not be possible. If this is the actual case then you need to completely change your analysis. If you truly are using ACN as your solvent (a very poor choice for GC, by the way) then you are building up solvent all through your system and you are probably flooding your detector. This is consistent with the chromatographic traces that you have shown.
Secondly, 220C for a FID is WAY too low. You will get all kinds of crazy things happen. Raise your detector temperature up to no less than your injection temperature. 280 C as an injection temperature for a maximum oven temperature of 70 C is WAY, WAY too high!!! Lower your injection temperature.
You are in a university environment. You clearly are in need of some very basic GC training. Surely your university has someone who actually knows something about GC? You should consult them.
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