2. Presumptive (Color/Crystal/Precipitation/Anion)Tests

  1. What is the practical value of color tests compared to other analytical techniques?
  2. Name three different spot tests, and what drug(s) they would be used for.
  3. List three different results from the Marquis test. What do each of those colors represent?
  4. List another color test that gives different results from different analytes.
  5. In what ways would spot tests be considered superior to instrumental analysis?
  6. In what ways are they inferior to instrumental techniques?
  7. List the reagents used to prepare the Marquis test.
  8. List the reagents used to prepare the sodium nitroprusside (SNP) test.


    1. Define the following terms: presumptive, conclusive, chromophore, reagent, primary amine, secondary amine.
    2. What two factors may inhibit the accurate description of spot/color test results?
    3. What recommendations does Clarke’s make regarding the ideal composition of a color test blank and how to make a final decision on the result of a test?
    4. In regards to color tests, Suzanne Bell states, “…a small amount of the questioned powder is placed in a well of the plate and the reagent is added.” Why would it be better to add the reagent first and then the powder to the reagent?
    5. How are color test blanks documented/recorded?
    6. Why should you use distilled water or deionized water when making aqueous reagents rather than tap water?
    7. Name three situations where color tests would be commonly used.
    8. What is the composition of the Marquis reagent?
    9. What color is produced when the Marquis reagent reacts with methamphetamine or amphetamine?
    10. Using Kovar and Laudzun’s United Nations Technical Note SCITEC/6 February 1989 as reference, draw the general mechanism for the reaction of methamphetamine/amphetamine derivatives with the Marquis reagent.
    11. At a clandestine laboratory site, a white powder is found on a piece of filter paper next to a bottle labeled “sodium cyanide.” Assuming that the powder came from the bottle and that the bottle was correctly labeled, what reaction will occur if the powder is tested with the Marquis reagent? Explain.
    12. The sodium nitroprusside-acetaldehyde/sodium carbonate test is also referred to as the ___________ test.
    13. A blue color with the sodium nitroprusside-acetaldehyde / sodium carbonate test indicates the presence of a ______________ amine.
    14. Using only the Marquis reagent and the sodium nitroprusside-acetaldehyde / sodium carbonate reagent, determine how you would distinguish between the following drugs: amphetamine, methamphetamine, MDMA, and MDA.
    15. Opium derivatives such as codeine, morphine and heroin turn what characteristic color in the Marquis reagent?
    16. Name three other terms for the para-Dimethylaminobenzaldehyde (p-DMAB) test.
    17. Find which reagent you would use to screen for the following drugs: lysergic acid diethylamide (LSD), psilocybin, dimethyltryptamine? What structural unit do these three drugs have in common?
    18. Look up the structure of the amino acid tryptophan in a reference book. Based on its structure, predict whether or not you would expect a positive purple reaction using the p-DMAB color test.
    19. Using Kovar and Laudzun’s United Nations Technical Note SCITEC/6 February 1989 as reference, draw the general mechanism for the reaction of indole derivatives with p-dimethylaminobenzaldehyde (p-DMAB) in acidic media.
    20. What is the difference between the cobalt thiocyanate test and the Scott’s test?
    21. Chemically, what imparts the pink color to the Co(SCN) 2 reagent?
    22. Chemically, what is the cause of the blue complex formed when cocaine hydrochloride is added to the Co(SCN) 2 reagent?
    23. Examine the structures of the drugs listed below. Which drugs(s), if any, would you expect to give a positive reaction to the Sanchez reagent? Why or why not? (Hint: look up the structures of procaine and benzocaine for comparison). Xylocaine, mepivacaine, procainamide, bupivacaine, prilocaine.
    24. Using only 2% cobalt(II) thiocyanate, 5% stannous chloride and Sanchez reagent (5% furfural in a 5% acetic acid solution), determine how you would distinguish between the following drugs: cocaine HCl, tetracaine HCl, procaine HCl, benzocaine.
    25. Give at least two examples of drugs that fluoresce under UV light.
    26. Using the National Institute of Justice’s Color Test Reagents/Kits for Preliminary Identification of Drugs of Abuse, NIJ Standarad-0604.01 (or any other reference(s) of your choosing) find two color tests used in the screening of barbiturates. Record the formula for each reagent, procedure for use and the expected color reaction.
    27. Find the color test useful for the identification of diazepam, a Schedule IV depressant. List the reagents, formulas, as well as the alternative names for this reaction. What functional unit on a molecule reacts with these reagents?
    28. Examine the structures of the compounds/drugs listed below. Which compounds/drugs, if any, would you expect to give a positive reaction to the diazepam test reagents? Why or why not? (Hint: look up the structures of Diazepam for comparison). Acetone, Morphine, Hydromorphone, Oxycodone, 4-Androstene-3,17-dione.
    29. Using Fiegl’s Spot Tests in Organic Analysis and Spot Tests in Inorganic Analysis, find color tests for creatine and boric acid. Photocopy and save the relevant pages for future reference.
    30. Cobalt test yields a few blue specks. How will this affect your testing scheme?
    31. A Marquis test yields a series of color that you have not yet seen. How will you document this observation?
    32. A series of color tests are negative. What additional tests should you perform, if any?
    33. Why does crack react with cobalt plus acid but not cobalt alone?
    34. What chemical moiety causes a purple color reaction with the Ehrlichs reagent


    1. Are crystals for a particulate substance unique? Explain.
    2. How do crystal tests work? (i.e. basic theory)
    3. What three metals are most commonly used in crystal reagents?
    4. How does a volatility test work?
    5. What is the difference between critical and Kohler illumination?
    6. Define: binocular microscope, virtual image, crystal form, crystal habit, crystal system.
    7. What shape crystal is obtained from cocaine HCl with the platinic chloride reagent?
    8. A suspected methamphetamine sample was submitted to the laboratory for analysis. How would you determine unequivocally the optical isomer using crystal tests? Explain your procedure carefully and logically.
    9. Why do we use acids as solvents in crystal tests?


Last Update June 2022

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