Chromatography Forum

I'm trying to get a reference sample to pass and it just won't happen. I've baked, comp'd, baked, comp'd and no pass. It's always the same warning points - whats the next step? Do I need to cut the column, replace it, or recalibrate? thanks for any input.

Give us a little more detail. I am guessing that as you describe baking and comping, you are having a baseline stability problem. But then you ask about recalibrating..

If it is baseline instability, is it moving as a whole or is it a matter of changing noise? A picture or two might help.

A few other details that can help in the review. When did you last do inlet maintanance (at least liner and septum) and any recient maintanance on the detector or indication of problems there.

I do not know D3710 or the quirks it offers, but I'll just note that when I have general chromatographic problems, I check first the inlet. A cored septum or dirty liner will cause all kinds of grief - and is cheap and easy to fix. The next problem is most likely to be the next element down stream from the inlet - the column. But a quick check of the detector to be sure that it is not acting up is in order (retention time shifts or spurious peaks do not come from detectors - spikes yes, peaks no). Then comes the expen$ive part - the column. Cut or replace? This depends entirely on the types of samples you run. Some kinds of samples will kill the column from end to end and cutting it may allow you to run, but for a very few samples. (That's the kind of stuff that I've run in the past - gets expensive.)

If you have an external standard method or instabilty in an internal standard - try a different syringe. They do wear out.

I'll look to see what addtional details you can give.

Don

To be totally honest, I'm not sure what I'm talking about. I'm new to the GC stuff, just started working in a lab with 5 GCs and they hardly work right, so I'm trying to figure out more about them so I can get them in proper working order. The D3710 might just be a custom built profile for the specific compounds we are looking for, I'm not sure what it stands for, I just know we have a reference sample we run through it that only passes once every 10 or so tries, if not less often.

Maybe I should start at the very beginning - any good books to read on GC/MS ??

Also - the equipment I have is the previously mentioned machine and 3 HP 5890 Series II and a 6890 Agilent with a 5973 Mass Selective Detector on it. Point me in a direction to learn more about this equipment and I'll greatlly appreciate it!!!!

D3710 is an ASTM method. I took a quick look on the internet for details. (first it on the google list was: http://www.astm.org/Standards/D3710.htm) It is to determine boiling point distribution of gasoline and gasoline fractions. The actual method will be in the ASTM method books. (Or you can purcase a copy of the specific method on line for $43 - see the above link.) The fact that you are talking about GC/MS tells me that you are running on a modified version of the method? (Or, you mention that with reference to another instrument in the lab.)

For learning about the equipment, I would suggest the instrument training offered by the vendor. That training should give you at least a good feel for the operation of the instrument. You also need a good understanding of chromatography. I would suggest one of the two or three day classes on chromatography given at meetings like PittCon or the national ACS meetings. Or, there are classes that travel around the country. I reciently saw a flier for one given by Restek. I expect that other chromatographic suppliers give these as well. All of this works as long as you don't have to pay for it on your own...

As far as getting a book. My favorite is one that I was given a number of years ago: High Resolution Gas Chromatography by Hyver and Sandra. You can purcase it from Agilent off their web site and probably from other sources. (It was published by HP, back when Agilent was still part of HP.) There are some newer techniques than are described in the book, but it gives good coverage of the subject while remainaing an easy read (for a technical book). I've had my copy for proably 20 years now - and still refer to it.