Analysis of mouthwash



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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

pipet or buret

gas chromatograph

10 µL syringe

mouthwash samples .







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

95% alcohol (mL/100mL)

5%

5.26mL

10%

10.53mL

20%

21.05mL

30%

31.58mL




2.

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.

4.

5. 6.

7.

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.

Insert the needle into the GC. Press the plunger, and start the run and the same time.

After a peak is recorded, press the end button on the computer.

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 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.

Select View and then Results to obtain area data. Record results in the data table below.

Complete steps 3 through 5 for the following standards: 5%, 10%, 20%, and 30% alcohol.



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.

Percent Alcohol v/v

Area Due to Alcohol

5%




10%




20%




30%

I




7.

7.
6.


8.

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:

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.



Questions:

1. Why did you prepare a graph using standards with known alcohol contents? What Law did this demonstrate?

Brand

Area due to Alcohol

due

to

Alcohol

















































Brand

% Alcohol

Accepted Value

















































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)

Area Due to Alcohol

30

0.306

20

0.198

10

0.125

5

0.0607

Brand

Area Due to

Alcohol


% Alcohol

Accepted Value

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.

Science in Motion

Materials List

Lab: Air GC Separation of Alcohols Number of Lab Groups Prepared: Hardware

Equipment per lab group

Packed

Returned

Air GC,







Laptop with Peak Simple







Cords: serial cable,

computer power cord and



adaptor







Copy of software







Printer (optional)







Safety Goggles










Consumables

Materials

Packed

Returned

10 microliter syringe







kimwipes







Unknown samples:







At least three







Known Samples:







Methanol







Acetone







1-proponal







2-proponal







Others TBA







Lab Handouts











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