Which reagent is used for field testing methamphetamine and heroin?

The Marquis Reagent is a chemical reagent widely used in the field of forensic science for the identification of various substances, particularly illicit drugs. When it comes to testing for methamphetamine and heroin, the Marquis Reagent is particularly effective due to its ability to produce distinct color changes when it comes into contact with these substances.

For methamphetamine, the reaction typically yields a deep purple color, which is indicative of its presence. Heroin, on the other hand, tends to produce a brownish color when subjected to the Marquis Reagent. These color reactions are crucial for quick preliminary testing at crime scenes or in field settings, allowing law enforcement to make informed decisions about the substances they encounter.

The other reagents listed do not provide the necessary specificity or effectiveness for testing these particular drugs. For instance, Benedict's Reagent is primarily used for detecting sugars, while Ninhydrin Reagent is utilized for detecting amino acids and proteins. Litmus Reagent, on the other hand, is used to test acidity and alkalinity, making it unsuitable for identifying narcotics or dangerous drugs. Therefore, the choice of Marquis Reagent is well-founded for the field testing of methamphetamine and heroin due to its reliable and characteristic reactions with these substances.