Chromatography Forum

When I asked the resident GC expert about this issue, he asked if I had replaced the column recently, which I haven't. There are two columns in this config; a 1.84' 20%TCEP pre-column and a 30m .53Dia HP-1 capillary column. Injections are through the TCEP.
He asked how many injections are on the column, when I said just over 500, his eyes about bugged out. (He runs pesticides and replaces his every 300)
In addition to certified commercial standards, I only run gasoline samples.

The fuels I test are normally clean, i.e. clear and bright, no visible particulates, less than .15% water, how long should I expect a column to last?

Could you check if H2 flow 40 or 50 mL/min and air flow 400 mL/min gives better flame stability ?

I agree with dblux. You are lean on fuel. Agilent FID's generally operate best with the Air:H2 at 10:1. Try making your H2 flow at 45 mL/min and see if you get a better flame.

I generally operate more like 300:30 or 350:35. When the detectors work at these flows, I don't understand why I should blow through more air and hydrogen. Noise is pretty much the same on all of my systems.

With 22.5 ml/min of carrier gas you need to adjust your flame gasses to compensate - the default settings are for narrow bore columns with flows of 1-2 ml/min.

If your carrier is hydrogen you need to reduce the hydrogen to to the flame, if it is an inert gas you need to reduce the makeup gas flow rate.

Peter

With 22.5 ml/min of carrier gas you need to adjust your flame gasses to compensate - the default settings are for narrow bore columns with flows of 1-2 ml/min.

If your carrier is hydrogen you need to reduce the hydrogen to to the flame, if it is an inert gas you need to reduce the makeup gas flow rate.

Peter

I wasn't even expecting 22.5 mL/min, but rather linear velocity 22.5 cm/s
It's really frustrating when people use values without units.

With 22.5 ml/min of carrier gas you need to adjust your flame gasses to compensate - the default settings are for narrow bore columns with flows of 1-2 ml/min.

If your carrier is hydrogen you need to reduce the hydrogen to to the flame, if it is an inert gas you need to reduce the makeup gas flow rate.

Peter

I wasn't even expecting 22.5 mL/min, but rather linear velocity 22.5 cm/s
It's really frustrating when people use values without units.

A very good point !

This thread has been a paradigm case of Rod's dictum; The more you don't tell us the more we can't help you.

Peter

I agree with dblux. You are lean on fuel. Agilent FID's generally operate best with the Air:H2 at 10:1. Try making your H2 flow at 45 mL/min and see if you get a better flame.

I generally operate more like 300:30 or 350:35. When the detectors work at these flows, I don't understand why I should blow through more air and hydrogen. Noise is pretty much the same on all of my systems.

I changed the Air/H2 flow to 300:30, the unit wouldn't stay lit. So I raised it to 450:45, Bingo!
The FID immediately lit with a strong pop, the output signal jumped to 4.5pA, and recovery jumped up about 25%. I'm wondering if the repeat ability problem I was having was due to incomplete combustion rather than a failing column.
I still need to double check the flows with a meter (our department partners have a flow meter but they are moving, and I can't borrow it right now).
For now I'll calibrate and go from there.
Thanks everyone for the useful tips.