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How do you develop a method for GC?
Are you looking for GC method development training? I’ll give you three quick tips for GC method development.
Hi there, it is Lee Polite again from Axion labs and today I am going to answer one of the toughest questions in the GC world. That is, “how do you develop a method for GC?”
It’s like baking a cake.
Someone came up with the recipe – How much flour, butter and sugar do I need? What temperature should I use? What size pan do I need?
It’s the same thing in GC: Who chose the right column length, diameter, film thickness, stationary phase, flow rate, injector temperature, detector temperature?
It sounds daunting! But the reality is that it is a lot simpler than it sounds.
So let me give you three quick tricks for developing GC methods.
GC Method Development Tip # 1: Look in a column catalog
I know that sounds like a cop out, I know that sounds like I’m cheating here, but do not reinvent the wheel.
Column catalogs contain tens of thousands of applications that work on GC columns. So open up the Agilent catalog, open up the Phenomenex catalog and look for benzene toluene xylene for example, look for the application and that will give you the correct temperatures and flows and everything you need. The GC method that you need is likely similar – if not identical – to a GC method that already exists.
Tip # 2: Choose a really good standard column
Method development for GC often follows this scenario: Imagine that you need to develop a method from scratch. You have this total unknown but have no idea what conditions to use. If that is your reality the first thing to do is to use a really good standard GC column.
In the GC world we lik e the DB5. That is 5% phenyl 95% methyl. Everyone makes one of those.
Restek’s sells the Rtx-5, Phenomenex the ZB5, and Agilent’s is called DB5.
So choose a “5” column. It is our go to column in the GC world. It separates most things. That is what you need to develop a GC method. You will optimize the method later and might not need a 30 meter column. But starting with a long column if possible can save you from the headache of changing to a longer column during method development.
I like to have a 30 meter column, .25 millimeter diameter, 0.25 micron film thickness (aka 30 meter, 0.25, 0.25) it is my favorite. What I am getting at is to choose one good generic very long column. And then, we are going to inject our sample and we are going to run a temperature program. And what I tell people in my class is that we are going to try all the temperatures in the universe.
Now what does that mean?
Tip #3: Run a temperature program trying all the temperatures in the universe
What is the lowest temperature you can use on a GC? Anyone know? It is pretty much room temperature. You can’t go much below room temperature unless you have cryogenics on it. So room temperature – I call about 40 degrees [Celsius] – that is the lowest temperature we can use. What is the highest temperature we can use on a GC? It’s determined by the column. The column manufacturer indicates the maximum temperature on the box or on the documentation that comes with the GC column. So let’s say we’re going to go from 40 degrees to 325 degrees and we’re going to do that at 20 degrees a minute. That’s a fairly fast rate, but what we’re going to do is do a scan from 40 all the way to 325 and simply see where the peaks come off. If all the peaks come off between 250 and 325, well then there is no need to start at 40 degrees.
So one good temperature program from room temperature to column max. Hold the column max for an extra 10 minutes and simply see where the peaks come off.
That is method development for GC. It is a lot easier than it sounds.
Now what I would love to know from you guys is what works for you. What types of columns do you like use., Any tricks in method development? Anything that I missed out. I love to learn new things and I learn from you. So go ahead and chime in.
