Results will vary depending on sample adulteration, quantity, temperature, lighting, exposure to air, storage, as well as reagent quality and degradation. Colorimetric techniques have been developed.
If more than one bottle are open at the same time and the cap are put on the wrong reagent bottle, this may cross-contaminate the reagents and ruin them.
According to a 2003 research published in Pharmacotherapy, neither the Marquis, Mecke, nor Simon's reagents should be used by the public for harm reduction purposes. These agents do not help identify pure MDMA tablets. The research team suggests using gas chromatography-mass spectrometry as the most sensitive and specific testing method for identifying MDMA and its contaminants but this is out of reach for users in most countries and reagent tests remain popular, often distributed by harm-reduction organisations due to their low cost and high utility when multiple test reagents are used.