Sr-90 analysis QA

[Gary Schroeder <schroede@mail.sep.bnl.gov>]

We're using a contractor laboratory to analyze for Sr-90 in potable water
samples.  As part of our QA/QC oversight, we monitor analysis parameters
like chemical yield, etc.  Under Standard Method SM-18 7500 or the EPA 900
Series methodologies, I'm trying to establish data validation and acceptance
criteria which cannot be found in the method documentation or any other
reference that I have.

What value or range of values would be considered acceptable for the following:

1.  yttrium chemical yield
2.  strontium chemical yield
3.  Y-90 ingrowth time (fraction of 1.0), i.e., for low activity
environmental samples , a full two weeks is recommended, but how much less
than that would be considered acceptable?; and 
4.  Y-90 decay time until count following chemical seperation.

General feelings/guidelines/real references all welcomed.
===============
Gary L. Schroeder
Brookhaven National Laboratory
schroede@mail.sep.bnl.gov