Pierre,
As Michael Volosin pointed out, organics can make a difference in response. Even though you digested, you may have 1% - 2% carbon content in a good digest, more in an incomplete digest. I am assuming that you dilute your samples at least 1:20 after digestion.Diluting your samples and standards into a solution with 1% methanol or 2-propanol may help. After dilution of your sample into this solution, the alcohol carbon should be the major carbon source, and the effect from each sample should be negligible, putting all samples and standards on the same level of signal enhancement.
Happy Christmas if you observe it in any way.
Steve Pappas 
CDC (de ferias em Brasil)

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From: PLASMACHEM-L: Analytical Chem.(ICP's, DCP's, MIP's). on behalf of Pierre Labelle
Sent: Thu 12/23/2010 1:52 PM
To: [log in to unmask]
Subject: Vitamin D


I have an Elan 6100 and run Vitamin D digest(Nitric+H2O2) with problems of repeatability reading for Arsenic? Is it the oily sample or somethingelse?


________________________________
Pierre Labelle
Laboratoires d'analyses S.M. inc.

Tél. +1-514-332-6001 x 5100
Téléc. 450-652-6451
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www.groupesm.com