Peter,

The primary problem in regenerating Cu columns with H2 is that H2 is very
flammable in air.  As I recall mixtures of 8-88% H2 in air will burn, much
bigger range than with most gas/air  mixtures.  Therefore working with H2
around hot furnaces and electrical switches requires great care.

We used to regenerate Cu on a routine basis but stopped when we were able
to buy 0.3mm diameter copper wires which usually last over 1000
samples.  Since a reduction tube with Cu costs about US$70 to put together
(not including disposal cost) the cost per sample is only US$0.07.  Once
regenerated, a column seemed to last about half as long as the first time,
so the saving was only about US35, which didn't seem worth the risk.  We
were also running exclusively enriched N2 samples at the time, but I have
since been told by another researcher that natural abundance N2 is not very
reliable immediately after regeneration, so you would have to check that.

To do the regeneration, we connected up a six port valve around the copper
column so that the carrier normally went from the combustion tube to the
six port valve, through the copper column, then back through the six port
valve and then to the Mg(ClO4)2 trap.  We could put H2 through the six port
valve and then turn the valve so that the copper column was switched
immediately from He to H2, thus minimizing any chance of explosion due to
residual O2 being present in the copper column.  The H2 was vented through
a window.   Before we turned the valve back to the He position we
disconnected the Mg(ClO4)2 trap to so that residual H2 in the Cu column did
not go through it.  Since Mg(ClO4)2 is an oxidant it doesn't seem prudent
to pass a H2 through it.

I have since thought that a safer way to regenerate the Cu might be to use
a mixture of 5% H2 in He.  At least in theory this gas would not be
flammable as H2 would never reach the 8% concentration in air to
ignite.  However, this is just theoretical, I have never tried it.

Anyway, hope this helps.

Paul Brooks.


At 10:31 AM 9/27/00 +0200, you wrote:
>Dear listmembers,
>
>I was wondering if there are other ways to regenerate a used reduction
>column (copper), besides the use of hydrogen gas. Before I start
>experimenting myself it would be very handy to get some practical advice on
>this. Thanks.
>
>Best regards,
>
>Peter Vervloedt
>
>---
>Peter Vervloedt
>Laboratory of Applied Physical Chemistry
>Ghent University
>Coupure, 653
>9000 Gent
>Belgium
>
>tel.: +32 (0)9 264 6048
>fax.: +32 (0)9 264 6230
>http://ftlbwww.rug.ac.be/isofys
>
>"Not everything that can be counted counts, and not everything that counts
>can be counted. "
>- Albert Einstein (1879-1955)
>---