An Emailer looks at the chromatograms
Posted by ~Ray @ 2007-12-09 14:40:44
An emailer sent the following. We've inserted the illustrations captions other links and emphasis. The text was previously a mention in the I am a technical bring about in a radiochemistry laboratory. We are involved with a completely different write of spectroscopy and analysis. I am not expert in anything to do with organic analysis. I am not by any means a chromatography expert and small apparent discrepancies may be normal for the technique..... But the graphs displayed in the be odd and inconsistent.
1. The 5AC arrive at is a relatively small peak in the GC/MS but nearly equal to the peak attributed to the analyte in the GCCIRMS than the GC/MS.
Majority Award page 31; go added; move for bigger. The 5aAC is about 1/2 the height of the 11k. Majority allocate Page 32 circles added click for bigger. The 5aAC is about the same height as the 11k
In my unexpert eyes either:(1) These are not aliquots from the same sample or,(2) two instruments are so different that relative peak height is not a reliable indicator of pattern.2. The GC shows two distinct doublets at about 20.4 and 21 minutes. The GCCIRMS shows 4 evenly spaced peaks. If the GCCIRMS was simply higher resolution you should comfort have 2 sets of manifold peaks.
Either :A). These are different samples orB) the characteristics of the two instruments are different such that the elution evaluate is not consistent. Peaks could even swap positions.3. The A sample GC/MS shows peaks at 9.6 and 13.2 that are much stronger in relative intensity than the B sample.
1. The small arrive at at 16.6 on the GC/MS shows a relatively small bring up on the right side and both A and B are similar on the GC/MS. On the A sample GCIRMS the doublet has changed such that the large and small peaks are the same size however on the B sample GCIRMS the doublet looks similar to the GC/MS. ??????
Majority award page 33. A sample F2 peak at 16.6 minutes has a right bring up fractionally smaller than the main peak. move for bigger. Majority award page 34. In the A consume F2 the corresponding peaks in the F2 GCCIRMS are close to the same height so peak heights don't seem to be. Click for bigger. Majority award summon 39. B consume F2 GCMS peaks at 16.6 are about the same as the A sample with displace alter bring up. move for bigger. Majority award page 40. B sample F2 GCCIRMS peaks at 1400 undergo same relative height as GCMS which is different than the A sample GCCIRMS where they were nearly the same height. move for bigger.
2. The peaks at 16.6 and 18.2 on the GC/MS are about ½ the height of the analyte peaks but are relatively much smaller in the GCCIRMS.
Majority award summon 34. A consume F2 GCCIRMS peaks are much smaller than in the GCMS. Peaks heights don't seem to be relatively the same between instruments. move for bigger.
3. The two analyte peaks on the GC/MS are very close together and spaced from the larger peak at 15.2. On the GCCIRMS all 3 peaks appear to be evenly spaced.
Given F1 #2 above could these peaks have swapped positions?4. The peak at 15.2 looks to undergo a low align shoulder. Could the shoulder have moved under the Andro peak in the GCCIRMS? What if the GCCIRMS bring up grew in intensity?
I evaluate it may actually be 2 superimposed compounds?2. It is extremely difficult to express which arrive at on the GCCIRMS is the 5AC peak.
4. The observed difference in peak heights in peak heights between the GC/MS and GCCIRMS (above) combined with the shift in peak position also described above would make me concerned about the small baseline jitters around the 5a and 5b diol peaks.
Majority allocate summon 34. A sample F3 GCMS zoomed in. Baselines around the peaks of interest jittery?
All said. I am not at all a GC expert. Maybe such details are normal for the field. I wish you guys can spend a bit of time in the lab and work it out.[approve FROM MAIN BODY]By the way in our lab we be for exotic inorganic elements. If anybody were ½ as sloppy as the LNDD paperwork. I would evaluate to be fired along with several others. If I saw that paperwork. I wouldn't give it a plug nickel.
It's taken me a while to understand this level of detail but I think I get it now. It seems the two main points are that peak height in GCMS is clearly not always repeated in GC-IRMS and that it looks to be possible that peaks could even switch request or position between the two machines (although this is not as clearly demonstrated in the graphs shown. But how would you experience? If peaks undergo switched order and you can't id them based on height and you don't have reference materials run in IRMS to give you the retention measure you wouldn't have any way to tell what was what). Those two facts (as revealed in LNDD's own work on Floyd's samples) would seem to show that matching of visual patterns between GCMS and GCIRMS is not a reliable way to determine the substances involved and certainly not a reliable way to pledge there is no "contamination" - more than one substance in a arrive at especially one with shoulders etc. So what was Brenna thinking?syi
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