Star Series
Method Note
M-1811
Surfactants in
Cleaners Key Words
Introduction
• Surfactants
This procedure measures anionic surfactants in dish washing liquid using a manual titration technique with
a surfactant electrode and the Thermo Scientific Orion 4-Star Plus pH/ISE meter. The Thermo Scientific
Orion surfactant electrode, Cat. No. 9342BN, is a potentiometric sensor, which indicates the endpoint in
the titration of surfactants in solution.
• Household
Cleaners
• Titration
• Surfactant
Ion Selective
Electrode (ISE
Recommended Equipment
Cat. No.
1. 4-Star Plus Benchtop pH/ISE meter
1115000
2. Surfactant half-cell electrode
9342BN
3. Double junction reference half-cell electrode
900200
4. Stirrer probe (or magnetic stir plate and bar)
096019
5. Swing arm electrode stand 090043
7. 500 mL and 1000 mL volumetric flasks
8. 150 mL beakers
9. 1 mL, 3 mL and 25 mL pipettes
10. 10 mL buret with 0.01 mL subdivisions
Required Solutions
Cat. No.
1. Dilute Triton X-100 sample additive
654203
2. 0.01 M sodium lauryl sulfate (SLS) standard
654202
3. 0.05 M Hyamine 1622 titrant
654201
4. Reference electrode filling solution (for inner chamber)
900002
5. Reference electrode filling solution (for outer chamber)
810007
6. Electrode acid rinse solution (mix 50 mL of 0.1 M HCl with 1000 mL of deionized water)
7. pH adjusting solution (0.01 M HCl)
8. Deionized water
Sample Preparation
1. Weigh 10 grams of dish washing liquid into a 500 mL volumetric flask and dilute to the mark with
deionized water. Mix the solution well.
2. Pipette 25 mL of the prepared solution into a beaker and add 25 mL of deionized water, 3 mL of 0.01 M HCl and 1 mL of dilute Triton-X.
3. Repeat steps 1 and 2 for additional samples.
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Surfactants in
Cleaners Results
Five aliquots of prepared dish washing liquid were analyzed by manual titration. An Excel spreadsheet was used
to find the end point by plotting milliliters of Hyamine added versus millivolt readings. The concentration of
the anionic surfactants in percent (w/w) as sodium lauryl sulfate is calculated using the following formula:
Anionic Surfactant Concentration as % (w/w) = VH * ConcH * FW * 100/1000 * W
VH = volume of titrant, Hyamine, in milliliters
ConcH = concentration of the titrant, in moles
FW = molecular weight of Sodium Lauryl Sulfate (288.5 g/mol)
W = sample weight in the aliquot of sample solution (0.5 g)
Dish Washing Liquid
% Sodium Lauryl Sulfate
Sample #1:
8.66
Sample #2:
8.66
Sample #3:
7.93
Sample #4:
7.93
Sample #5:
8.66
Mean:
8.37
Standard Deviation:
0.40
%CV:
4.78
Electrode Storage
The surfactant electrode should be stored dry. The double junction reference electrode may be stored in
deionized water between sample measurements and up to 1 hour. For short-term storage up to one week, store
the reference electrode in its filling solution or deionized water. The solutions inside the reference electrode
should not be allowed to evaporate and crystallize. For storage longer than one week, drain the reference
electrode completely, rinse with deionized water and store it dry.
Equipment Setup
Electrode Setup – Surfactant Electrode
Before using the surfactant electrode, soak the tip in a 0.0001 M sodium lauryl sulfate solution for 10 minutes. Prepare the 0.0001 M sodium lauryl sulfate solution by diluting 1 mL of the 0.01 M SLS standard with 100 mL of deionized water.
Electrode Setup – Double Junction Reference Electrode
1. To fill from the flip-spout bottle, lift the spout to the vertical position, place the spout in the electrode fill
hole and firmly squeeze the bottle.
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2. Inner Chamber – Use Cat. No. 900002 as the inner chamber filling solution only. Unscrew the electrode
cap and move the cap and spring up the cable. Push down on the top of the inner chamber until the cone
at bottom end can be grasped using a lint-free tissue. Grasp the cone and pull the inner chamber free
of the outer body. Slide the rubber sleeve at the top of the inner chamber down to uncover the fill hole. Using the flip-spout bottle, fill the inner chamber up to the fill hole and slide the rubber sleeve back up. If you have trouble filling the inner chamber, add some solution, shake the electrode down like a clinical
thermometer, and repeat until the electrode is filled. Wipe excess filling solution off the inner chamber
surfaces and slide the inner chamber completely up into the outer body. Place the spring back on the inner
chamber and screw the cap on finger-tight.
3. Outer Chamber – Use Cat. No. 810007 as the outer chamber filling solution. Using a flip-spout bottle or pipette, add a small amount of filling solution through the fill hole in the outer body. Tip the electrode
to moisten the O-ring on the electrode body. Hold the electrode by the outer body and push down on the cap to allow the filling solution to wet the inner cone. Release the cap and check to see that the end of
the outer body is flush with the bottom surface of the cone. Fill the outer chamber up to the filling hole
with the filling solution. If the outer body does not return to the correct position, push it gently down
into place.
Meter Setup – 4-Star Plus Benchtop pH/ISE Meter
For initial meter setup, follow the steps in the quick start guide that is included with the meter. The quick start
guide also contains a layout of the meter keypad for reference. The words in all capital letters, such as POWER,
indicate a key on the meter and words in quotations, such as “UnIt”, indicate a display on the meter screen.
1. Connect the surfactant electrode to the meter.
2. Connect the reference electrode to the meter.
3. Connect the stirrer to the meter.
4. Press the POWER key on the meter to turn the meter on.
5. Note that the arrow on the left of the screen indicates the active line. If the top line is not active, press the
LINE SELECT key to change the selected line to the top line. Press the UP or DOWN ARROW key to
change the measurement mode of the top line to mV.
6. Press the SETUP key. 7. Press the UP or DOWN ARROW key until “rEAd” is displayed on the top line. Press the LINE SELECT
key to select the middle line. Press the UP or DOWN ARROW key to select “tYPE”, which is for the
measurement mode type. Press the LINE SELECT key to select the bottom line. Press the UP or DOWN
ARROW key to select “COnt” for “tYPE”. Press the LINE SELECT key to accept the setting.
8. Press the MEASURE key to return to the measurement mode.
9. If all steps were followed correctly, the meter display will show “mV” to the right of the top line and the
AR icon will not be shown on the display. The meter and electrode are now ready for calibration.
Calibration and Analysis
1. Before the titration, rinse the surfactant electrode with the acid rinse solution and blot it dry with a lintfree tissue.
2. Place the surfactant electrode, reference electrode and stirrer into the sample beaker, so the electrode tip
is fully immersed in the solution. The stirrer should be positioned slightly below the tip of the electrode.
Press the STIR key on the meter to turn the stirrer on. 3. Fill a buret with the 0.05 M Hyamine 1622 titrant solution.
4. Wait for a stable reading, usually in 1 to 2 minutes, and record the electrode potential in millivolts (mV).
5. Start the titration by adding the 0.05 M Hyamine 1622 titrant solution in increments of 0.5 mL at the
beginning of the titration and in increments of 0.1 mL to 0.25 mL in the region of the endpoint.
6. Record the electrode potential after each addition of the 0.05 M Hyamine 1622 titrant solution.
7. The endpoint is at that volume of the titrant where the potential changes dramatically in the positive
direction. Continue the titration 1 to 2 mL past the endpoint.
8. Press the STIR key to turn the stirrer off.
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9. Use an Excel spreadsheet to find the endpoint by plotting milliliters (mL) of Hyamine added versus the electrode
potential in millivolts (mV).
10. Tabulate the data for each titration run in a spreadsheet as shown in the table below. The first column is the total volume of Hyamine 1622 added at each data point. The second column is the millivolt reading at each data point. The third column is the first derivative of the data calculated by dividing the change in
millivolt between two consecutive readings by the change in added volume between two consecutive readings.
Hyamine Added (mL)
mV
First Derivative
0.5
103.7
35.8
1.0
122.8
38.2
1.5
146.1
46.6
2.0
173.1
54.0
2.5
301.8
257.4
3.0
348.5
93.4
3.5
361.0
25.0
4.0
367.0
12.0
4.5
370.5
7.0
5.0
372.7
4.4
5.5
374.0
2.6
6.0
376.0
Note: In this example, the volume of Hyamine is shown in increments of 0.5 mL.
4.4
11. Find the endpoint by plotting a graph showing mL of Hyamine added versus first derivative as shown below.
12. Repeat steps 1 through 11 for additional samples. When all samples have been measured, rinse the electrode with
deionized water and store the electrode according to the Electrode Storage section.
©2008 Thermo Fisher Scientific Inc. All rights reserved. All trademarks are the property of Thermo Fisher Scientific Inc.
and its subsidiaries. ROSS and the COIL trade dress are trademarks of Thermo Fisher Scientific Inc.
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