Chromatography Forum

Hi folks,

I'm an environmental engineering grad student and working on the haloacetic acid analysis using Agilent 6890 micro-ECD system. I recently encountered a weird problem with the ECD background value. When I load up the Idle method, the signal output typically reaches 844XXX (yes, that's a crazy number); however, the background signal is fine (~800, normal value) when I run my HAA method. I cleaned the inlet system and re-tighten the column connection, but it doesn't seem to help...

I'm not sure why this happens, but I guess there is an oxygen leakage somewhere . Has anyone seen a similar problem before? Any comments/suggestions would be much appreciated!

Thanks,
Teng

The signal is only changing to the high value for one specific method? Or is it an intermittent problem?

Newater,

Sounds to me like your idle method turns off some key gases and allows air to get to the ECD. Don't use your idle method. Just leave the instrument on the analytical method....

Best regards.

The signal is only changing to the high value for one specific method? Or is it an intermittent problem?

Yes, the signal only maxes out when I switch to that particular Idle method (this method is set to heat up the oven temp, cool down the detector temp, and lower down the gas flow when the instrument is not running). Once I switch to other analytical methods, the background value drops down to normal value.

Newater,

Sounds to me like your idle method turns off some key gases and allows air to get to the ECD. Don't use your idle method. Just leave the instrument on the analytical method....

Best regards.

Thanks! I will re-check the Idle method again. We use helium as the carrier gas and nitrogen as the make-up. Both gas flow rates drop quite a bit at the idle state, so that could be the problem.

The signal is only changing to the high value for one specific method? Or is it an intermittent problem?

Yes, the signal only maxes out when I switch to that particular Idle method (this method is set to heat up the oven temp, cool down the detector temp, and lower down the gas flow when the instrument is not running). Once I switch to other analytical methods, the background value drops down to normal value.

It's wise to save gases when GC is not in use.
However I would rather switch off the oven and inlet, leave ECD temp. intact and reduce column flow and makeup substantially. I would also switch off electrometer in Idle method.

In fact my Idle method is very similar.

It's wise to save gases when GC is not in use.
However I would rather switch off the oven and inlet, leave ECD temp. intact and reduce column flow and makeup substantially. I would also switch off electrometer in Idle method.

In fact my Idle method is very similar.

Thanks for your suggetions. As AICMM said, the problem comes from our Idle method coz the makeup flow is way too low and air can possibly leak into the detector.

But one of our professors also suggests that the thread on the female end of the injector may be stripped and in that case, the ECD needs to be refurbished. I will keep an eye on that and thanks a lot for all your replies~