HPLC Analysis of Surfactants(S0, S1, and S2)

Rice Consortium MeetingApril 26, 2011

1

Amir Amini, Clarence Miller, and George Hirasaki

HPLC Columns

Column Surfactant C18

Brand and size Dionex Acclaim Surfactant, 4.6 ×250mm Dionex Acclaim C18, 4.6 ×250mm

Packing5µm silica coated with

linear alkyl chains, tertiary amino and polar amide groups

5µm silica coated withoctadecyl dimethyl siloxane

Average pore size 12 nm 12 nm

Separation mechanism

Reversed phase, ion-exchange, and dipole-dipole interactions

Reversed phase

Mobile phaseACN/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

3

Method Development*

*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.

Retention time for different surfactant

↑ Anionic Cationic Nonionic

Ionic Strength ↓ ↑ -

Mobile Phase pH ↓ ↑ -

Organic Modifier ** ↓ ↓ ↓

Temperature*** ↓ ↓ ↓

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)

7

Motivation

• Oil/brine/surfactant phase behavior using different samples of S1 as surfactant shows non-identical results

• No middle-phase microemulsion (type III) was observed (direct transition from type I to II with increase of salinity) !

8

Are these surfactants the same? Are these surfactants the same?

Constituent components of a surfactant may partition differently into the oil phase ?

Can chromatographic separation occur when S1, S0 or their mixture is injectedinto the reservoir?

Constituent components of a surfactant may partition differently into the oil phase ?

Can chromatographic separation occur when S1, S0 or their mixture is injectedinto the reservoir?

Need a way to analyze these surfactants, both qualitatively and quantitatively Need a way to analyze these surfactants, both qualitatively and quantitatively

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

9

10

Area Under the ELSD Signal Curve Concentration ?

Peak Area = a .(Concentration)bPeak Area = a .(Concentration)b

11

old sample contains more of the salts (sulfates, …) and other hydrophilic componentsQ: origin? A: hydrolysis as indicated by the slightly acidic PH of the sample.

Lab sample has more of the high PO number and less of the low PO number components

13

Components with lower number of PO groups elute earlier from the column

14

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

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)

15

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)

• Evaluating the concentration of each component in S1 /S2 blend after :

possible partitioning into oil phase, dynamic adsorption, core flood

16

Can we separate a blend of two surfactants into their pure components ? Can we separate a blend of two surfactants into their pure components ?

How can we measure the concentration of each component?How can we measure the concentration of each component?

Need a way to analyze these surfactants, both qualitatively and quantitatively Need a way to analyze these surfactants, both qualitatively and quantitatively

17

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

18

Several gradient patterns were tried BUT surfactant column was not able to separate S1 and S2

19

20

S1 and S2 are separated!Now we can measure the concentration of S1 and S2 individually in their mixture

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.

21

Acknowledgement

• Tiorco

• Kinder Morgan

• Addax

22

Back-Up Slides

23

24

25

26

27

28

29

30

ELSD

N2

Liquid waste

Gas waste to exhaust hood

Chemstation