HPLC Analysis of Surfactants
(S0, S1, and S2)
Amir Amini, Clarence Miller, and George Hirasaki
Rice Consortium Meeting
April 26, 2011
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HPLC Columns
Column
Surfactant
C18
Brand and size
Dionex Acclaim Surfactant, 4.6 ×250mm
Dionex Acclaim C18, 4.6 ×250mm
Packing
5µm silica coated with
linear alkyl chains, tertiary amino and
polar amide groups
5µm silica coated with
octadecyl dimethyl siloxane
Average pore size
12 nm
12 nm
Separation
mechanism
Reversed phase, ion-exchange, and
dipole-dipole interactions
Reversed phase
Mobile phase
ACN/NH4OAC or Methanol/DI,
0%-100% organic in mobile phase
ACN/DI or Methanol/DI, 15%-100%
organic in mobile phase
Operating
PH range
2.5 – 7.5
2.0 – 8.0
What Can HPLC Do For Us?
• Measuring surfactant concentration
– Total surfactant concentration
– Individual concentration of components in a mixture
• Separation of Mixtures
• Thermal Stability
• Quality Control
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Method Development*
Retention time for different surfactant
↑
Anionic
Cationic
Nonionic
Ionic Strength
↓
↑
-
Mobile Phase pH
↓
↑
-
Organic Modifier **
↓
↓
↓
Temperature***
↓
↓
↓
*Product manual for Acclaim Surfactant column from Dionex
**Acetonitril is preferred over methanol because it generates less back pressure
on the column.
***Temperature has little effect on the selectivity of surfactants. Higher
temperature makes all the surfactants elute earlier.
Example: Triton X100 Analysis By Surfactant Column
0.4 wt% Triton X100, Injection: 10 µL, Temperature 25oC,
Mobile Phase: 45% ACN / 55% Ammonium Acetate (50mM), Flow rate: 1 ml/min
Evaporative Light Scattering Detector (ELSD)
• Mobile phase should be a
solvent with low boiling point.
• If any acids, bases and salts are
used to modify mobile phase,
they also need to be readily
evaporated.
.
• The intensity of the scattered
light is a function of the mass of
the scattering particles and
generally follows a power-law
relationship
PART I
HPLC Analysis of S1 (old & new commercial samples
as well as the lab sample), S0, and Their Mixtures
S1 old sample (commercial): activity = 19.45 wt%
S1 new sample (commercial): activity = 19.45 wt%
S1 lab sample: activity = 84.32 wt%
S0 lab sample: activity = 85.50wt%
S1 new / S0 lab mixture: (70 wt% S1, 30 wt% S0)
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Motivation
•
Oil/brine/surfactant phase behavior using different samples of S1 as surfactant
shows non-identical results
Are these surfactants the same?
•
No middle-phase microemulsion (type III) was observed
(direct transition from type I to II with increase of salinity) !
Constituent components of a surfactant may partition differently
into the oil phase ?
Can chromatographic separation occur when S1, S0 or their mixture is injected
into the reservoir?
Need a way to analyze these surfactants, both qualitatively and quantitatively
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Experimental Conditions for HPLC Analysis of PART I
• Mobile Phase: Acetonitrile (B) / DI water (A)
• Column: C18 column at 25 oC
• Flow Rate: 1mm/min
• Sample Volume: 50 µL
• Detector: Evaporative light scattering (ELSD) at 60 oC and 3.5 bar
• Gradient: Linear 0/80/95/110 min with 40/60/80 /80 %B
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Area Under the ELSD Signal Curve
Concentration ?
Peak Area = a .(Concentration)b
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old sample contains more of the salts (sulfates, …) and other hydrophilic components
Q: origin?
A: hydrolysis as indicated by the slightly acidic PH of the sample.
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Lab sample has more of the high PO number and less of the low PO number components
Components with lower number of PO groups elute earlier from the column
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The mixture signal is NOT the linear superposition of the individual components signal!
Total areas are within 5% of each other: 16.8 vs 16.0 V.min
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PART II
HPLC Analysis of S1 (new commercial sample), S2,
and Their Mixture
S1 new sample (commercial): activity = 19.45 wt%
S2 (commercial): activity = 22.38wt%
S1 new / S2 mixture: (90 wt% S1, 10 wt% S2)
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Motivation
•
Composition of a blend of two surfactants may change as salinity changes (e.g. in
phase behavior experiments) or as it interacts with rocks and oil (e.g. in core
flooding experiments)
Can we separate a blend of two surfactants into their pure components ?
•
Evaluating the concentration of each component in S1 /S2 blend after :
possible partitioning into oil phase, dynamic adsorption, core flood
How can we measure the concentration of each component?
Need a way to analyze these surfactants, both qualitatively and quantitatively
16
Experimental Conditions for HPLC Analysis of PART II
• Mobile Phase: Acetonitrile (B) / 100mM Ammonium Acetate, PH=5.5 (A)
• Column: Surfactant column at 25 oC
• Flow Rate: 1mm/min
• Sample Volume: 50 µL
• Detector: Evaporative light scattering (ELSD) at 60 oC and 3.5 bar
• Gradient: Linear 0/60/80 min with 25/80/80 %B
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Several gradient patterns were tried BUT
surfactant column was not able to separate S1 and S2
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19
S1 and S2 are separated!
Now we can measure the concentration of S1 and S2 individually in their mixture
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Conclusion
• Composition changes in different batches of the same surfactant can be
identified
• Chromatographic separation of S1/S0 and S1/S2 may occur during
surfactant flooding
• Blends of S1 and S2 can be separated; this gives a way to measure the
concentration of each of those components:
– Analysis of oleic and aqueous phases to determine partitioning
– Analysis of effluent in surfactant flooding, dynamic adsorption, etc.
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Acknowledgement
• Tiorco
• Kinder Morgan
• Addax
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Back-Up Slides
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Gas waste to
exhaust hood
N2
Chemstation
ELSD
Liquid waste
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