OK people, some more info for you all.
As a background, I'm the Technical Director of Chemical Generation. We make a Marquis based tester called 'E: a quick and simple test'. Try it, you may like it! I'm the one with the full chemistry degree and many years of pharmaceutical experience.
PMA - my references (published international scientific journal/papers) show that it doesn't change colour with Marquis reagent. I am sceptical about this, but until I find/see otherwise, that is the best answer I have. They haven’t been wrong thus far, so I’m tempted to believe them.
Marquis reagent reacts with many chemicals to produce a range of colours. It is not selective, and it is not foolproof. As Candyflip (and others) said, many things can colour change purple to black. Codiene is one of them, there are many others. In addition, Marquis reagent doesn’t just detect the MDxx ring! (see below)
The key to accurate testing is to WATCH the colour CHANGES. You should see a blue/purple which then changes to black over a few minutes. Keep you eyes peeled for OTHER colours that may arise in 'bits' of non-homogenous pills. The mechanism is not something I wish to disclose to shonky manufacturers, but basically it's sensitive to elements like oxygen (and others which I chose not to discolse), particularly aromatic/cyclic oxygen. The sulphuric acid degrades the substance down to its basic building blocks, which then react with one of the other components. Various colours representing the whole visible spectrum are given by a large number of compounds. Structures that tend to maintain the response to the reagent at the violet end of the spectrum contain more oxygen. As the ratio of carbon, hydrogen and nitrogen to other groups in the molecule rises, the response moves to longer wavelengths (ie to green, orange and then red).
If you have a mixture of compounds in the pill, the reagent will just react with them all, at once, and the colour change will be based on the total ratio of oxygen to carbon/hydrogen/nitrogen present. There is some scope for some things digesting/reacting faster, and for proximity, but you have to watch very carefully to see that happening. Nothing too selective, nothing fancy, just a total ratio thing. Yes indeed, you will find shonky manufacturers trying to fool Marquis based testers. I can do it with ease, so I'm assuming they can as well.
It is pleasing to see that people are questioning the selectivity of Marquis based testers. It is also very impressive to see that someone has tried just sulphuric acid on MDMA, and got a purple reaction. Yes, indeed, MDxx will turn purple if you have just sulphuric acid present (It's a dehydration mechanism). In fact, sulphuric acid will also give reactions and colours with other chemicals, but not many, and it's not as selective as Marquis reagent so beware! The colour changes are generally quite different to that of Marquis reagent. It's just that for MDxx, the other chemicals in the Marquis Reagent don't contribute to the overall colour change MUCH. You still need them in there to get the benefit of knowing what you have present (ie can refer to published colour charts), and to stabilise it somewhat. For most chemicals, the other main ingredient in the Marquis reagent acts to form conjugated compounds (those with double bonds) that absorb light at specific wavelenghts. Hence the colourful responses.
We have developed a Second Generation tester (Called E2 - Second Defence) that will pick up things that the Marquis Tester doesn't. It will react POSITIVELY to PMA (ie you get a colour change). You could also use a TLC (Thin Layer Chromatography) test, which we are also developing. TLC is a bit time consuming and requires some expertise/practice.
Incidentally - Does anyone really care to know whether they’re getting MDA, MDMA, or MDEA? I’d have thought people would be generally happy to get any one of them, and not care to distinguish. Correct me if I’m wrong!
Anyone with access to something they think might be PMA, get in contact with Chemical Generation (or my good friend Candyflip at The-Peak.com.au)) and try our new tester! We’re happy to help those mad little scientists out there to develop further products!
Any further questions, roll them out. At Chemical Generation, we KNOW about the Marquis reagent, are qualified to understand chemistry, and CAN answer many questions related to the use of this product. We are also keen to solve your specific problems wrt purity/identity.
B.
Chemical Generation - Life is about making informed decisions!
