Reagent kits, otherwise known as presumptive tests, do have limitations. This is particularly true in today's market, where many adulterants are used, some with the specific intention of fooling the kits. Just look at some of the posts on this board where odd reactions cannot be completely explained.
Having spent close on 4 years researching and producing reagents for commercial sale, I found the overall effectiveness to be less and less as time went by. A new range of reagents, perhaps more specific in what they detect, may help, and employing techniques like thin layer chromatography certainly do, but then again, the care and precision required with TLC tends to put people off.
So my answers are
No & No
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