FID not giving signal

[Rargh]

Hiya

First post here so firstly hello.

I am using a Perkin Elmer Autosystem XL coupled with a HS40XL headspace unit using FID for detection
The system has been working fine for years.
I changed the column a couple of days ago and since i cant get a useful chromatogram
A link is attached showing the signal i am getting.

The transfer line is intact and i have checked there is flow coming out prior the injection port. It is inserted 55 mm into the injector. I have then attached the column and checked the flow coming out and its flowing. I purged the column as directed and then installed into the FID (insertion depth 70mm). The FID is definately lit.
I am guessing its something physical when i have put the column in.
Ideas on a postcard!

http://s4.photobucket.com/albums/y122/d ... togram.jpg

Thanks in advance

[Peter Apps]

Steps:

1. leak check

2. inject (with a syringe to the GC inlet) some methane or gas from a cigarette lighter - do you get a peak and what is the retention time ?

Peter

[8jw8]

perhaps the injector end of the column is not up far enough or the detector end is not where it needs to be? try resetting it and see if it works. the baseline rise makes sense when installing a new column.

[Rargh]

Sorry for the delay.
I did a manual injection and i get a signal. So i am guessing there is a leak somewhere between the vial and the injector.

[Peter Apps]

Either a leak or a blockage is possible but it could also be that the tip of the tansfer line (55 mm into the inlet if I understand right) is actually below the tip of the column. A standard microsyringe needle is 50 mm long.

If you are sure that you have inserted either the column or the transfer line into the inlet according to specifications, then consider the possibility that the before you did maintenance one or the other was inserted less deeply (either by accident or design).

Peter

[abhinitsure]

Hi,

Yes as per graph attached , i have not seen any injection bump at the start of run caused by pressure difference(injection).
So i guess there must be major leak somewhere...


Abhi

[Rargh]

Hiya

Well Peter's last comment about a blockage rang a bell. The only thing I didn't check was the inside of the needle. I cleaned the exterior of the needle but didn't flush it. When I tried to flush it it was blocked solid.
After lots of trying managed to get it unblocked by putting it in a 550C furnace (platinum iridium needle). Reassembled and its fine.
Trust the needle to be blocked coincidently when I change the column.

Thanks for the help all, hopefully I can be of use at some point.

Cheers

[Peter Apps]

Thanks for the feedback - now the puzzle is how the needle got blocked - was it a piece of injector septum perhaps ?

Peter

[Rargh]

I had a look at the needle under a microscope. The bottom hole that goes beneath the septum appeared clear. The top hole looked as though there was some brown 'stuff' clogging it. Presumably the stuff must have been forced up the needle over time.

The analysis that is routinely done on the machine is looking at volatile fatty acid content in anaerobic digester samples (digesting sewage sludge, food waste, wheat, along with other things). Since finding the source of the problem I have spoke to a few colleagues and it seems that the needle has not been flushed for several years perhaps doing it every once in a while will prevent it becoming blocked again

[Peter Apps]

The transfer line and the needle should have only headspace samples and gas going through them. It sounds as if some crud is getting up into the line, which could cause all sorts of other problems - absorption, tailing peaks and carryover for example. I have never seen a Perking elmer headspacer in the flesh, is there a ferrule in the connection between transfer line and needle ?, and could a fragment of that be what was causing the blockage.

Peter