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
distilled water
100 ml, volumetric flasks
gas chromatograph
mouthwash samples .
pipet or buret
10 µL 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:
Part I:
l.
Prepare standard solutions of ethanol according to the following list using
95% ethanol. Be careful to make accurate measurements! Pipette the
alcohol, and add to a 100mL volumetric flask. Then, carefully fill the flask to
the 100mL line with distilled water.
% Volume Alcohol
5%
10%
20%
30%
2.
95% alcohol (mL/100mL)
5.26mL
10.53mL
21.05mL
31.58mL
Set the following conditions from the edit menu by selecting
channels then selecting channel 1 and temperature change.
Start 140 C Hold 10 minutes Ramp 0 degrees/min Until the
temperature is 140 C
3. Obtain a microliter syringe. Rinse the syringe several times with the sample
to be tested. Then obtain 2 microliters of the sample in the syringe.
4. Insert the needle into the GC. Press the plunger, and start the run and
the same time.
5 After a peak is recorded, press the end button on the computer.
.
6 To obtain the area under the curve, select the edit drop down menu and
. choose the Manual integration option. Select the rubber band icon found on
6. the bottom left of the graphed results. Left click and drag across the bottom
of the curve to create a baseline. This will allow the program to calculate a
more accurate area.
7. Select View and then Results to obtain area data. Record results in the
data table below.
8. Complete steps 3 through 5 for the following standards: 5%, 10%, 20%,
and 30% alcohol.
Percent Alcohol v/v
5%
10%
20%
30%
Area Due to Alcohol
I
9. Prepare a graph with the area on the x - axis, and the percentage of alcohol on
the y - axis. Draw a "best fit" line connecting the points on your graph.
Part II:
1. Obtain mouthwash samples.
2. Follow procedure 3 through 5 from Part I with your mouthwash samples. Be
sure to rinse the syringe several times with the mouthwash sample you are
running before you insert the needle into the GC.
3. Enter your results on the table below:
Brand
Area due to Alcohol
Analysis of
Results:
1. Find the area for the mouthwash brands on your standards graph. With a
ruler, draw a straight line, parallel to the y - axis, until you intersect the
standards line graph. Draw a line straight down, parallel to the x - axis, to
find the percentage of alcohol sample in the mouthwash sample. Enter
this value onto the data table below.
2. Look at the back panel of your mouthwash samples. Find the alcohol
content, and record the accepted value on the data table below.
Brand
% Alcohol
Accepted Value
Question
s:
1. Why did you prepare a graph using standards with known alcohol contents?
What Law did this demonstrate?
due
2. What was the purpose of rinsing the syringe several times before
inserting your sample into the GC?
3. How did the accepted values match the percentage of alcohol in your
mouthwash samples? Explain your results.
Extensions:
This activity can be done with vanilla extract.
AIR GC SEPARATION OF ALCOHOLS
TEACHER NOTES
Lab Time:
45 minutes
Answers to Question:
1. Why was it important to run known samples of possible components in
the unknown mixture?
This was necessary to determine the retention times in order to identify
the components in the unknown mixture.
2. If a supposedly pure sample was properly injected into the gas chromatograph
and several peaks were observed, what can be concluded about the sample?
It contained some volatile impurities.
3. Why is it important to clean the syringe between samples?
Any trace of the previous substance will be detected by the gas
chromatograph and produce an additional peak
4. Why is it important to wipe the needle before injecting the sample into
the instrument?
If any sample is on the outside of the needle it will be vaporized and
travel through the column before the sample is injected, thus producing double
peaks.
ANALYSIS OF
MOUTHWASH TEACHER
NOTES
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 determine
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)
30
20
10
5
Area Due to
Brand
Alcohol
List. Cool Mint
.255
Weis Red
.156
Cepacol
.148
Rite Aid Rinse
.076
Green Mint
.217
Lavoris Red
.0734
Area Due to Alcohol
0.306
0.198
0.125
0.0607
% Alcohol
Accepted Value
24.7
14.9
14.1
6.97
21.6
14
7.5
18.9
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.
Science in Motion
Materials List
Lab: Air GC Separation of Alcohols
Number of Lab Groups Prepared:
Hardware
Equipment per lab group
Air GC,
Laptop with Peak Simple
Cords: serial cable,
computer power cord and
adaptor
Copy of software
Printer (optional)
Safety Goggles
Packed
Returned
Packed
Returned
Consumables
Materials
10 microliter syringe
kimwipes
Unknown samples:
At least three
Known Samples:
Methanol
Acetone
1-proponal
2-proponal
Others TBA
Lab Handouts