Reagent kit

A reagent kit is a drug-checking tool in which chemical reagents produce a colour change on contact with a substance sample; that colour is then matched against a reference chart to suggest which compound class is present. The purpose is to narrow down what a sample might be and to reveal when something unexpected is there instead.

Kits typically contain several individual reagents — Marquis, Mecke, Mandelin, Ehrlich, Simon's, and others — each formulated to react distinctively with different chemical families. No single reagent identifies a substance on its own; more informative protocols use several in combination.

How it is done

The test involves placing a small scraping of the sample onto a ceramic or disposable test surface and adding a single drop of reagent. The colour change usually begins within seconds and stabilises within a minute or two, at which point it is compared against the reference chart provided with the kit.

Because different reagents react to different compound classes, running several reagents on separate portions of the same sample produces a more complete picture. A sample expected to contain MDMA, for example, might be checked with Marquis, Mecke, and Simon's simultaneously — building a profile from three independent reactions rather than from one alone.

Results are read in natural light rather than artificial lighting, which can shift how colours appear, and each reagent is applied to a fresh surface to prevent one reaction from contaminating the next.

What it cannot tell you

A reagent test establishes only whether a particular chemical class is detectable in the sample. It does not measure how much of that compound is present, what its purity is, or whether a second active compound is also there.

This last point is the most significant limitation. A Marquis result consistent with MDMA means the sample contains something that reacts as MDMA does — not that it contains only MDMA.

A second compound in smaller quantities may produce no distinguishable colour shift of its own: either it reacts with the same reagent in a way that blends into the dominant colour, or it does not react with that reagent at all. A sample carrying two active compounds can return a result identical to a sample carrying one.

This is particularly relevant for potent adulterants present at low concentrations. Fentanyl may produce no visible colour shift of its own, or its reaction may be obscured by the colour the primary compound produces. Fentanyl-specific test strips were developed partly to address this gap, but no set of colorimetric tests can confirm the absence of every possible contamination.

A result that matches the expected colour is a narrowing of possibilities, not a confirmation of identity. It reduces the likelihood of certain substitutions; it does not rule out additions.