The 12 hours I mentioned in my prior posting to the list have been derived
from an instrument management point of view rather than a scientific one.

It enabled me to run samples on a 2 days on, 1 day off or 5 days on, 1 day
off cycle; depending, as Deborah points out on actual sample throughput (ca.
200 individual injections per re-oxidisation cycle sounds about right for a
Finnigan combustion tube).


Cheers,

Wolfram



> -----Original Message-----
> From: Stable Isotope Geochemistry
> [mailto:[log in to unmask]] On Behalf Of Deborah Rupprecht
> Sent: 03 May 2005 10:21
> To: [log in to unmask]
> Subject: aging of Cu-tube: re-oxidising
>
>
> Dear all,
>
> using a GC-MS, we are re-oxidising the tube when copper is
> nearly completely black (we check this regularly) by heating
> the tube from 650 to 750 °C and connecting to O2/N2 gas
> ("Protec") for 10-15 minutes, then cooling down to 650°C (about 30').
>
> This is enough for next about 200 samples (two days,
> depending on re-aging). If we have to re-oxidise it every
> day, we change it completely. One tube is working in average
> for about 1000 analysis. We did not try to re-oxidise it for
> 12 hours; maybe we would not need to re-oxidise it all two
> days. Good idea.
>
> Greetings,
>  Deborah
> ********************
> Deborah Rupprecht
> Institute of Plant Nutrition
> Karlrobert-Kreiten-Str. 13
> 53115 Bonn, Germany
> Phone (+049) 0228-73-3640, -1631
> ********************
>