Troubleshooting an FID

[karwaldo]

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?

[dblux_]

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

[rb6banjo]

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.

[Peter Apps]

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

[dblux_]

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.

[Peter Apps]

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

[karwaldo]

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.