Since a spectrometer is required to obtain the data from absorbance studies, you will not be asked to collect the data yourself. Instead, you will work with data that has already been collected.
Suppose you are working as a technician for a testing laboratory that has been hired by
Company Q. Your job is to independently test the quality of an over-the-counter drug made by Q. As is common, Q markets a product in which the active ingredient, M, is in
combination with inactive ingredients. Consequently, you have to devise a method whereby you can test for the presence of the active ingredient in the presence of the inactive ingredients. Typically, this is accomplished through some chemical reaction.
1. Prior to analyzing the samples provided by Q you must demonstrate for yourself and others that you, your instruments, and your company will produce reliable results. One way to do this is by making a Beer's law plot using pure M. You obtain the following
data:
Table 1- Concentration of various samples
Sample Identification Code Concentration of M (mol/L) %T
Q5000 4.00 x 10-4 17.9
Q5001 3.20 x 10-4 25.0
Q5002 2.40 x 10-4 35.7
Q5003 1.60 x 10-4 50.2
Q5004 8.000 x 10-5 70.8
Convert %T to absorbance and prepare a Beer's law plot using this data.
2. You are now ready to begin analyzing the drug. You are sent five bottles of the drug from
batch 021015. You analyze these samples and obtain the following data:
Table 2- Percent transmission of various samples
Sample Identification Code %T
Q021015-01 43.7
Q021015-02 44.1
Q021015-03 43.8
Q021015-04 44.1
Q021015-05 43.8
3. What is the concentration of M in these samples?
© Hands-On Labs, Inc. LabPaq CK-K 149
4. Company Q has reported that batch 021015 has an M concentration of 3.00 x 10-4
mol/L. Assume that your analysis is more accurate, so what is their percent error?
Remember from Chemistry 1, the formula for percent error is:
% error = theoretical value - actual value/ theoretical value x 100%
5. By law, company Q must have an M concentration of 3.00 x 10-4 mol/L +/- 5%. In other words, the M concentration must be between 2.85 x 10-4 mol/L and 3.15 x 10-4 mol/L. Does Batch 021015 meet legal requirements?