Two coffee cups have been submitted to your lab for analysis. A
white powdery substance on the bottom of one of the cups may be poison.
Drug analysis of the white substance has been requested in order to determine
a) quantity, b) its identity, and c) if it is a poison. It will be necessary
to first separate the white drug from the coffee sludge that is at the
bottom of the coffee cup.
Procedure:
1) Record all observation about the evidence as it was received. Include
the evidence identification number in your observations.
2) Determine the exact mass of the white powdery substance.
3) Weigh out exactly 1 gram into a 50 mL Erlenmeyer flask.
4) Add up to 20 mL of hot deionized water to the flask.
5) Swirl flask to dissolve the drug. Decant dissolved drug into a second 50 mL Erlenmeyer flask.
6) Rinse undissolved material with 5 mL of warm water; decant into the unknown’s flask.
7) Set drug flask into a 400 mL beaker (or larger) with enough ice to form an ice bath. This will enable rapid recrystallization of the unknown drug.
8) Filter the solid that has formed from the remaining liquid. Set up buchner funnel with a piece of pre-weighed filter paper. Give collected crystals a small rinse with cold water. Remove filter paper carefully and slide onto watch glass cover. Put the filter paper and watch glass into the drying oven to dry your cyrstals for 15 minutes. Remove from oven and let cool to room temperature.
9) Give a description of the crystals. Determine the amount of crystals recovered. What is the mass of crystals on the filter paper –the mass of the filter paper? What percent of the 1 gram sample you analyzed is pure drug? Now determine how many grams of drug were received by your lab in the original sample. Show all calculations.
10) Determine the melting point of unknown using the melting point apparatus. Repeat this analysis on a second apparatus. Take the average of your two values. Report final melting point. Match the average melting point to the following known drugs:
Brand Name:
Generic Name:
melting point temperature,C
Advil
ibuprofen
50-53
Motrin
“
Aleve
“
Aspirin
acetylsalicylic acid
136-140
Bufferin
“
Alka-Seltzer
“
Coricidin
“
Dristan
“
Indocin
indomethacin
155-162
Tylenol
acetaminophen
167-172
NyQuil
“
11) Dissolve a small sample (a bit on the tip of the spatula) into approximately 10 mL of ethanol. Test the pH of your solution using the pH meter. Test the pH of the 3 known drugs available in the lab. Summarize the results in a table. Learn more about pH in Chapter 7 of your textbook.
12) Using the remaining solution from step #11, analyze your sample on the diode array spectrophotometer. This test is being done to match the unknown to a spectrum library of 3 known drugs. Record results in your lab notebook. Compared to the Crime Lab Library of Known Poisons does your spectrum match any of the sample spectrums?
Conclusions and Discussion:
What was the identity of the white substance brought to you for identification?
Explain, using your results, how you reached your conclusion.
Your supervisor is currently writing your evaluation. To greatly impress the supervisor you decide to put all the results from this investigation into one table. Create a table in your notebook to do this.
Explain if there was any conflicting results or if all tests indicated the same result. Give at least two sources of experimental error and explain how they each may have altered the final results.
Questions: Explain all answers.
1. To be charged with possession of a narcotic requires a minimum of 1 gram to be found on the suspect. If the unknown white powder (prior to being put into the coffee cup) was found on a person and it tested positive for cocaine, would your results indicate that enough of this toxic drug was present to allow the police to press charges for possession?
2. What causes a melting point of a substance to be lower than it actually should be?
3. The police are suspicious that the white powder is a poison. The suspect claims it is medicine. While in court you hear the suspect testify that the white powder confiscated was only ground up medicine made easier to swallow. Will the jury swallow that statement after hearing your drug analysis summary?
4. Put the following substances in order of increasing pH concentration:
Mountain Dew soda, sea water, blood, lemon juice, milk, acid rain,
coffee
Material for drug analysis was adapted from Colby’s CH112 & CH118 lab write-ups, 2000.
LMM, JAN2001