Chromatography Forum

hi,
according to suggestions you gave to me, i changed the vent filter and split vent line for both back and front . Here is my rinse(DCM:HEXANE=1:1). The problem is still there. by the way ,i scan the chroma, but i don't know how to post or attach it
There is another question: i am usign 5975 GC-MS. I use HS to inject sample(split ratio=50), sample to to one column which analyse c6 to c10, another column is connection MS. The initial tem is 60, aggetate tem is 90. I ran cals std very day. now the problem is i spike 50ul of 200ppm cals to a vial which has 10ml solvent used 20g sodium bisufate dissolve in 4L ioniazed water. I detect c6,c10 and toluene using FID. c10 is always low, sometimes is half response to c6 and toluene. I also spike 15ul of 200ppm to a vial which has 10ml same solvent. The all respond is close. I change gold seal, clean syringe,change liner and column, the problem is still there. Other instruments have the same problem,but it's not stable, sometime is good, sometimes is bad.
could you please give me some suggestions?
thank you so much
rebecca

There are instructions for attaching a chromatogram under the topic: "Embedding Chromatograms and Reports"

Your posting appears to be a continuation of a previous thread - if you would link to it, it would be easier to find it so we could associate the curent information with the previous information.

I am guessing this is the problem with an injection onto a DB-1 column at 40 degrees?
Can you give us an idea of the nature of the samples going onto the column?
In some cases trimming the front end of the column will work - in others the best solution is to change out the column.

If I understand correctly, chromatograms of this type of sample were doing well and then began to show peak tailing? Same cromatographic conditions? Same types of samples?

agree.. there must have been a history here.

jaap

Hi, thanks for replying my topic
In my lab, we extract hydrocarbon from soil and water. We use DCM&hexane. sample inject to column directly with splitless, 2ul. Like i said before, everything was ok then began to show tailing. Bothe column are new and i trim both detector and injector side. My instrument is 7890, there are other 2 similar instrument. They don't have this problem. We use the same tempearature programme.
recently, cause of the shortage of Helium, my company decided to change mobile phase from He to Nitrogen. The tailing is gone. I tried to figure out what's the difference between two gas changing like temperature prog, inlet pressure, ect
thank you so much.
rebecca

The most significant difference you should see in chromatography using nitrogen rather than helium is that the optimum linear velocity of the column is slower.


When you trim the column, how much of the column do you remove? Typically there is not a need to trim from the detector end unless you are using a mass spectromter and have a transfer line hot enough that the column may be slowly damaged.