(An Aside: When last I wrote to you concerning the trials of Isodat,  
one young, astute reader of Isogeochem asked me if I maintained an  
isotope blog, as he would like to read it. Naw, we older folk know  
little of blogs, as that sounds too much like the shape of ourselves  
as we get older.)

This message concerns a contaminated molecular sieve column that is  
on-line in a TC/EA instrument. I have used the TC/EA for analyzing  
all sorts of things including rocks, plants, carbonates, etc. With  
silver phosphates, we learned to install a trap prior to the Conflo  
to keep elemental P and Si from entering the capillaries and clogging  
them.

For several years, I have been analyzing silver nitrates. Always a  
"joy" to prep and run, nonetheless silver nitrates produce nice N2  
and CO peaks that are typically straightforward to analyze, if they  
are pure. My latest challenge has been a series of silver nitrates  
prepared from nitrates leached from agricultural soils and nitrates  
found in well waters adjacent to agricultural fields.

Standards run fine, nice peaks, ample separation. Silver nitrates of  
stream waters are no problem. But after 2 or 3 soil-derived or farm  
field-derived AgNO3s are reacted, the molecular sieve GC column  
clogs. Baking at 300 C overnight, 24 hrs, 36, or 48 hours does not  
help the problem. In fact, whatever is on the column to start with  
manages to move along a bit and stop flow completely.

I have become adept at repacking molecular sieve columns, baking them  
out, and starting afresh, each time with eager anticipation of data  
to come, big ideas on revamping agricultural practices dancing in my   
head.

I am stumped. We know that there is some organic contamination on the  
silver nitrates: maybe 1% C or so. This means of course that there is  
a bit of Organic N and O as well, which we are well aware of and are  
doing tests to see what the effects are on isotopic composition or  
yield.

I don't know about S, or Fe, or K, or P. X-ray crystallography  
examinations of the offending AgNO3 crystals show only AgNO3.

If you have any information on 1) what can contaminate a Molecular  
Sieve 5A that can not be baked off at 300C? or 2) what might  
contaminate an agricultural sample other than dissolved organic  
matter? I would be happy to know this.

The postdocs in my lab have been making silent and secret bets on  
when I will give up this Fight with the Nitrates. Not yet.

Regards, Marilyn Fogel