Dear David,

Another facto, not yet mentioned in the other reactions, is the
"smoothness" of your tubing inner walls. Micropores might take a long
time to empty, even in a good vacuum system. Treatment with acid rather
increases this micropore problem, and is not advisable to my opinion.
In any case, after having your nickel tubes exposed to air - as also
Torsten states - it takes a couple of runs to have them right again:
first reacting blank and next with a lab standard till the yield and
delta value are acceptable (normally I had one bad standard after the
blank and further good values on the line I worked at most).
A copper brush as Torsten prefers to use sounds rather rough to me and
might cause increased roughness in the tubes. I should prefer to use
Scotch Brite to avoid any scratches in the inside.

Cheerio,
Pier de Groot
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Dr. P.A. de Groot
University of the Witwatersrand
Economic Geology Research Unit
Department of Geology
Private Bag 3
2050 Johannesburg
South Africa
Tel.    +27 11 7162564
Fax.    +27 11 3391697
E-mail  <[log in to unmask]>

Visit the combined HOME-PAGE of EGRU-Geology on the Internet:
        http://www.wits.ac.za/science/geology/1stpage.htm
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