analysis of lubricant oil

[juaant]

I have to analyze oil lubricants and paraffins with gc-ms with column Vf-5ms 50mx0,25x0,25. My conditions are: Temp inyection 310ºC, temp ramp 70ºC 1min, 150ºC to 15ºC/min, 320ºC to 5ºC/min hold time 20 min. Inyection splitless 0.8 min, flow 1,2. Ion source temp 200ºC and Interface temp 250ºC. Scan 50-350.

I have to include my sample chromatogram (real) and chromatogram for me ideal.

I want to know if is possible to obtain a chromatogram ideal as image?

This kind of chromatogram depend of kind lubricant or depend of column or ...?
Thank you

[Don_Hilton]

Lubricants are extremely complex samples. The ideal image you have shown is typical of a fairly "simple" mixture that is mostly the normal alkanes with lower levels of some branched alkanes. Even in this picture you see peaks forming a hump in the region from peaks 27 to 37. If you need to actually resolve peaks in the mixture you show, you may get some improvement with a change in condtions, but I doubt you will see the improvement you desire. If you look at GCxGC chromatograms of these materials, you will see that there are many more branced alkanes, perhaps cyclic alkanes and aromatic hydrocarbons in the mixture. And that is just of of the pretolium distillate portion of the lubricant. Depending on what is beign used, you will find other comound classes as well.

[Ron]

I agree with Don's answer, and will expand on it a little.

The ideal chromatogram looks a lot like a SIM DIS standard. This is used to determine retention times for know n-alkanes to get a boiling point - retention time correlation. It is not intended to resemble a real sample, but to calibrate software to get an accurate boiling point range for petroleum distillates.

Real world lubricant samples have a very low straight chain alkane percentage, so the samples would not be expected to look like the standard. A paraffin wax will look similar to the ideal chromatogram, but usually will have a wider boiling point range, and in many cases a bimodal distribution.

[yangz00g]

Yes, I agree that lubricant is a difficult comlex to analyze.

Have you done any sample treatment? Look like a lot of high-boiling-point compunds, like phosphates, forming the hugh peak at the end.

I would like to suggest to go deeper into the formular of the lubricant if you have one, and do some cleanup accordingly.

It it's a food grade, you have better chance to get a nice chromatogram, if not, harder.