The Froehde reagent is used as a simple spot-test to presumptively identify alkaloids, especially opioids, as well as other compounds. It is composed of a mixture of molybdic acid or a molybdate salt dissolved in hot, concentrated sulfuric acid, which is then dripped onto the substance being tested.
The United States Department of Justice method for producing the reagent is the addition of 100 ml of hot, concentrated (95–98%) sulfuric acid to 0.5 g of sodium molybdate or molybdic acid.[1]
The Virginia Department of Forensic Science method uses 0.5 g ammonium molybdate per 100 ml H2SO4 (conc.)
Unheated sulfuric acid can be used to prepare the reagent in a less dangerous manner, but 2–4 hours must be allowed for the molybdate to dissolve.
| Substance | Color | |
|---|---|---|
| No reaction[2] or Red | ||
| No reaction[3] | ||
| No reaction | ||
| No reaction | ||
| No reaction | ||
| Black | ||
| Bright yellow | ||
| Bright yellow | ||
| Yellow > Green[4] | ||
| Light brown | ||
| Orange | ||
| Pale green | ||
| Pale green | ||
| Light yellow | ||
| Yellow - Green | ||
| Black | ||
| Yellow | ||
| Yellow > Green | ||
| Yellow > Green | ||
| Yellow > Green | ||
| Yellow > Green | ||
| Yellow | ||
| Red brown | ||
| Dark purple | ||
| Purple | ||
| Tan > Dark yellow | ||
| Light brown | ||
| Green > Black | ||
| Orange | ||
| Green > Black (fast) | ||
| Orange > Purple | ||
| Yellow[5] | ||
| Green | ||
| Red | ||
| Pale blue | ||
| Greyish purple or Blue > Purple | ||
| Purple red[6] | ||
| Green | ||
| Chlorpromazine HCl | Very deep red | |
| Contac HCl | Moderate olive brown | |
| Dimethoxy-meth HCl | Very yellow green | |
| Orange | ||
| Doxepin HCl | Deep reddish brown | |
| Light bluish green | ||
| Brown | ||
| Brilliant blue | ||
| Orange | ||
| Moderate yellow green, Yellow Green | ||
| Light olive yellow | ||
| MDA HCl | Greenish black | |
| Green or brown or light yellow | ||
| Grey | ||
| Deep orange/red[7] | ||
| Morphine monohydrate | Deep purplish Red > Slate | |
| Heroin HCl | Deep purplish red > Green | |
| Brownish black | ||
| Oxycodone HCl | Strong yellow - Blue or Green | |
| Codeine HCl | Very dark Green > Red - Brown | |
| Blue > Purple | ||
| Light Yellow | ||
| Blue | ||
| Yellow | ||
| Blue | ||
| Green | ||
| Orange | ||
| Purple red | ||
| Propoxyphene HCl | Dark greyish red or Brown | |
| Purple red | ||
| Brilliant yellow | ||
| Purple red | ||
| Purple red | ||
| Purple red | ||
| Green with purple streaks | ||
| Purple | ||
| Purple | ||
| Orange | ||
| Orange |