Is Froehde reagent reliable?

This article has been translated to English.

Froehde is reliable, and confirmation is the job it is built for. It is molybdic acid in sulfuric acid, a second acid-based reagent whose selectivity differs from Marquis, so when the two agree you have evidence rather than a repeat, and when they disagree you have found something worth chasing. Presumptive identification is built out of exactly that kind of agreement.

Where it does add something

Opioids, where it separates several compounds that Marquis groups together, and the 2C family, where its reaction is distinct enough to be worth having alongside Mecke. It is also useful on samples that gave an ambiguous Marquis result, because a second acid-based reagent with different selectivity either supports the reading or does not.

Froehde instructions

What a clear Froehde rules out

Froehde stays clear on cocaine, ketamine, the amphetamines and the MMC cathinones, and that matters because of what it does not stay clear on. MDMA and MDA turn it black instantly and heroin turns it purple, so a sample that leaves Froehde untouched has excluded the two families a powder is most often sold as. What it will not do is separate a primary amine from a secondary one, which is Simon's and Robadope work, or name a cathinone, which is Morris and Zimmermann work.

Simon's or Robadope

Questions?

Do I need Froehde if I have Marquis?

Not to begin with. It becomes useful once you want a second opinion on ambiguous results or you are testing opioids.

Is it the same as Mecke?

No. Both are acid-based but they use different metal salts and have different selectivity, which is what makes the pair informative.

Why is my Froehde result the same as my Marquis result?

That is common and it is the point. Agreement between reagents is evidence.