主题：(原创)专家解答疑问(GC/MS)

One metal ball which surface has paint,it is immersed in lime slurry and the paint will gradually solve into the lime slurry. I want to identify the components of the paint in the lime slurry. So i should compare between the lime slurry without paint and the lime slurry with paint erosion.

I prepare the two samples for gc-MS test. First I adjust the pH value by adding sulfic acid to 6.0-7.0.  Then I extract them with Hexane solvent and concentrate the extraction.      The two sample be injected to gc. The amount is about 1-2(ul) micro liter.The heating program is following: ramp rate varies from 5C/min to 50C/min; target temperature 300 or 320C. I repeat many times(about 100 times). every time i got the different peak table even all parameters are the same.From the Mass spectrum picture, I found many compounds contained  m/z 73,147,221,281,327, 404, 454. I think it may be due to DB-5 phase flow. How I should do if you make sure the DB-5 phase flow?
If the peak table has many compounds, but the similarities of compounds are very low(less than 750) for most of compunds in the peak table. The name of  many compounds shows UNKNOW. What is problem with our gc/MS?

专家答疑:
It sounds like the column in the gc is "bleeding."  You should proably check the column for excessive bleed by just ramping the column without injecting a sample.  This will give you a good indication of the state of the column.  After that, you can just inject a microliter or two of the hexane extraction solvent and compare that chromatogram
with the one from above.

If there are significant differences (i.e. more peaks in the solvent injectin than in the blank gc ramp) then you mught have "junk" in your liner in the gc inlet.  These should be changed ever so often, depending on how many samples you
run, their cleanliness, etc.  Some labs replace them every day, others after so man injections, say, 50 to 100.

As for the differences in the peak tables, it might be that you are not holding your final oven temperature long enough to allow the compounds to elute from the
column.  You should hold it at the upper temperature until you do not see any more peaks.