ANALYSIS OF MOUTHWASH
Introduction:
Commercial mouthwashes are mixtures of water, alcohol, dyes, flavorings, and other
compounds. This experiment will allow the alcohol content of the mouthwash to be determined.
If fifty milliliters each of alcohol and water are mixed, the total volume of the mixture will not
equal one hundred milliliters. This reduction in volume is due to the attractive forces between
the alcohol and water. Since the volumes of alcohol and water are not additive when mixed, a
calibration curve must first be prepared. It will provide the correction needed for alcohol-water
mixtures. The calibration curve will be prepared by placing a known amount of alcohol in an
alcohol-water mixture. The observed percentage of alcohol will be plotted against the true
percentage of alcohol.
Once the calibration data is collected and plotted, samples of mouthwashes will be analyzed
using the gas chromatograph. The observed percentage of alcohol will be determined, and the
true percentage will be found using the calibration graph. These values may then be compared
with the values reported by the manufacturer.
Purpose:
The purpose of this experiment is to determine the amount of alcohol in a brand of mouthwash.
Equipment/Materials:
ethanol
100 mL volumetric flasks
gas chromatograph
mouthwash samples
distilled water
pipet or buret
10 L syringe
Safety:
 An apron and goggles should be worn in the laboratory at all times.
 The chemicals used in this experiment should pose no significant safety hazards.
 Good laboratory procedure should be followed at all times.
Procedure:
1. Turn on the GC.
2. Start the Peak Sample software.
3. Set the following conditions from the edit menu by selecting channels, then selecting
channel 1 and temperature change.
Start 140C
Hold 5 minutes
Ramp 0 degrees / min
Until the temperature is 140C
4. Be sure the time scale starts at zero. Use the arrow to adjust.
5. Prepare standard solutions of ethanol according to the following list if 95% ethanol is
used. Each lab group should prepare solutions as assigned by the instructor.
Solution
A
B
C
D
% volume alcohol
5%
10%
20%
30%
95 % alcohol (mL/100 mL)
5.26
10.53
21.05
31.58
6. Obtain a microliter syringe and a sample vial containing one of the samples to be tested.
7. Rinse the syringe 6 times with the sample to be tested. Then obtain 1 microliter of the
sample in the syringe.
8. Click on the Z or  button on the run screen to zero the current.
9. Insert the needle on the syringe into the injection port. At exactly the same time that one
member of the group injects a sample, a second group member will press the space bar on
the computer to begin the data collection.
10. After this peak is recorded, press the end button on the compouter.
11. Repeat steps 2 through 5 for all standards and as many unknowns as time permits.
12. Determine the area under the peak by carefully cutting out each peak and massing or by
using the equation A=1/2 bh.
13. Plot % area alcohol (y-axis) vs. % alcohol (x-axis). Draw a best fit line. Use this
calibration graph to determine the % alcohol in the original mouthwash sample.
Data Table:
Percent Alcohol (v/v)
30
20
10
5
Brand
Area Due to
Alcohol
Area Due to Alcohol
% Alcohol
Accepted Value
ANALYSIS OF MOUTHWASH
TEACHER NOTES
Standards Met:
3.7.12.B – Evaluate appropriate instruments and apparatus to accurately measure materials.
 Apply and evaluate the use of appropriate instruments to accurately measure scientific
and technologic phenomena within the error limits of the equipment.
3.1.12.A – Apply concepts of systems, subsystems, feedback and control to solve complex
problems.
 Apply systems analysis to predict results.
3.4.12.A – Apply concepts about the structure and properties of matter.
 Characterize and identify important classes of compounds (e.g., acids, bases, salts).
3.7.12.A – Apply advanced tools, materials and techniques to answer complex questions.
 Select and safely apply appropriate tools, materials and processes necessary to solve
complex problems that could result in more than one solution.
Lab Time:
40-50 minutes
Considerations:
In order to reduce the time of this lab, the alcohol standards could be prepared ahead of time.
The lab could also be done not using the standards at all and just determining the % of alcohol in
the mouthwash by the area under the peaks.
Sample data is included below:
Gas Chromatograph - Alcohol Calibration Curve
Percent Alcohol (v/v)
Area Due to Alcohol
30
0.306
20
0.198
10
0.125
5
0.0607
Brand
Area Due to
% Alcohol
Accepted Value
Alcohol
List. Cool Mint
.255
24.7
21.6
Weis Red
.156
14.9
Cepacol
.148
14.1
14
Rite Aid Rinse
.076
6.97
7.5
Green Mint
.217
18.9
Lavoris Red
.0734
6.72
Commercial brands of mouthwash vary widely in their alcohol contents. The may
percentage of alcohol may be less than 10% to over 30%. If possible, select brands so that this
range may be observed.
Last updated 11-02