[plctech]

I am running an assay for Benzalkonium chloride (BKC) in a product.  Another lab is testing the same product but getting vastly different (lower) results.  They say the difference is they are testing for active BKC and I am testing for BKC solution.  Does this make any sense to anyone?  I cant find any references anywhere for this.  Just about every published assay for BKC that I have found is essentially the same as my assay.

[discodermolide]

Well I would suggest that you obtain a copy of their method and compare it with yours. See if you can reproduce their results in your lab with their method using your samples and their samples.
Perhaps this will get you further.