New Developments in Surfactant Analysis Using HPLC Rainer Bauder, Xiaodong Liu, Mark Tracy, and Christopher Pohl Dionex Corporation, Sunnyvale, CA USA Abstract This presentation provides the state-of-the-art for surfactant analysis in various sample matrices using the most reliable and most advanced HPLC technology. Introduction Surfactants are widely used in the consumer product, industrial, agricultural, and pharmaceutical markets, in products as diverse as pesticides, detergents, petroleum products, cosmetics, and pharmaceuticals. Their separation and identification can be difficult due to both the diversity of surfactants and the complexity of sample matrices. Although HPLC is the preferred and commonly used approach for analyzing surfactants, and a variety of methods have been developed, it is challenging to choose proper methods for specific applications. None of the existing analytical solutions provide optimal separation for anionic, nonionic, cationic, and amphoteric surfactants in a single analysis. This presentation gives an overview on the total solution for surfactant analysis by HPLC including separation columns, instrumentation, method development, and applications. Separation Column Selection The Acclaim Surfactant column is the most versatile column and the first choice for surfactant analysis. Its advanced column technology provides ideal selectivity for anionic, nonionic, cationic, and amphoteric surfactants as well as hydrotropes (Figure ). In addition, it is the column of choice for separating cationic surfactants (Figure ). Mobile Phase: (A) CH CN, (B). M NH OAc, ph. Gradient: % to 8% A in min, then hold 8% A for min Inj. Volume: µl 6 7 Figure. Simultaneous separation of hydrotrope, cationic, nonionic, amphoteric, and anionic surfactants using the Acclaim Surfactant column. 6 7 8 9 8 9 Peaks:. Chloride. Bromide. Nitrate. Xylene sulfonate. Laurylpyridinium chloride 6. Lauryldimethylbenzylammonium chloride 7. Triton X- 8. Cetyl betaine 9. Decyl sulfate. Dodecyl sulfate. C -LAS. C -LAS. C -LAS. C -LAS (B) % acetic acid 8 8 8 (gain 8, evaporating temperature ºC) Peaks: ( µg/ml each). Lauryl pyridinium. Lauryldimethylbenzyl ammonium. Octylphenoxyethoxyethyldimethylbenzyl ammonium. Cetyltrimethylammonium. Cetylpyridinium 6. Diethyl heptadecyl imizolinium 7. Diethyl heptadecyl imizolinium 8. MHT quart 9. MHT quart. MHT quart 8 Figure. Separation of cationic surfactants using the Acclaim Surfactant column. ACS 8 Presentation ACS 8 Presentation
The Acclaim Mixed-Mode HILIC- column complements the Acclaim Surfactant column, and is suitable for analyzing ethoxylated surfactants. In HILIC mode, the degree of ethoxylation (EO) can be determined. In RPLC mode, the separation of ethoxylated oligomers is suppressed, and the alkyl chain distribution can be characterized (Figures and ). The Acclaim PolarAdvantage II (PA) column provides excellent hydrolytic stability at both acidic and alkaline conditions, and is ideal for highly selective and sensitive analysis for anionic surfactants using RPLC and suppressed conductivity detection (Figure ). AU A/B = /6 A/B = /8 A/B = / A/B = 6/8 A/B = 7/ A/B = 87./. A/B = 9/ A/B = 97./. A/B = 99/ 6 8 Column: Acclaim Mixed-Mode HILIC-, µm Mobile Phase: (A) CH CN (B). M NH OAc, ph. Flow Rate:. ml/min Detection: UV, nm Sample: IGEPAL CA-6 (.%) Figure. Dependency of separation mode on mobile phase organic content using the Acclaim Mixed-Mode HILIC- column. NP Mode RP Mode C 8 H 7 IGEPAL CA-6 (OCH CH ) n OH 6 Column: Acclaim PA, µm (B) Borate buffer (6. g boric acid in D.I. water, adjust to ph 8. with % NaOH aqueous solution) (C) D.I. water C 7 7 Inj. Volume: µl Instrument: ICS- chromatographic system mm suppressor, chemical mode at. ml/min with mn sulfuric acid) Peaks: ( to µg/ml each). Decyl sulfate. Dodecyl sulfate. Tetradecyl sulfate 6 9. Hexadecyl sulfate. Octadecyl sulfate Figure. Separation of alkyl sulfates using the Acclaim PA column and conductivity detection. Instrumentation Configuration For UV and ELSD: Summit HPLC System (Dionex) equipped with a P68 gradient pump, ASI- autosampler, TCC- column oven, and UVD detector. A Sedex 8 ELS detector (Sedere, Alfortville, France) or equivalent was used for evaporative light scattering detection. AU Acclaim Mixed-Mode HILIC-, µm IGEPAL CA-6 IGEPAL CO-6 Acclaim Surfactant, µm IGEPAL CA-6 IGEPAL CO-6 Mobile Phase: CH CN,/D.I. H O v/v / Flow Rate:. ml/min Detection: UV, nm C 8 H 7 IGEPAL CA-6 (OCH CH ) n OH For suppressed conductivity detection: ICS- Chromatography System (Dionex) equipped with a DP Dual Pump module, an AS autosampler with μl injection loop, a DC Detector/Chromatography module with a conductivity detector. A CSRS ULTRA II mm suppressor was used in external water mode for detecting cationic surfactants and an AMMS III mm suppressor was used in chemical mode for detecting anionic surfactants. Software: Chromeleon 6.7 Chromatography Management Software (Dionex) C 9 H 9 (OCH CH ) n OH 8 IGEPAL CO-6 7 Figure. Separation of alkylphenol ethoxylates by hydrophobe using the Acclaim Mixed-Mode HILIC- column. New Developments in Surfactant Analysis Using HPLC
Method Development Consideration ELS detection is a universal detection method, compatible with gradient methods and inexpensive compared to MS. Therefore, it is widely used for surfactant analysis when pursuing exploratory work or performing routine analysis of high-concentration samples. ELS can show response changes due to instability of the forming aerosol and shows mobile phase influences that can decrease reproducibility. UV is the preferred detection method for surfactants with chromophores and is complementary to ELSD. However, many surfactants cannot be detected by UV. Suppressed conductivity detection (SCD) provides good sensitivity and excellent selectivity for ionic species, making it the detection of choice for ionic surfactants in a wide range of sample matrices. Table shows a comparison of the three aforementioned detection methods. An ammonium acetate/acetonitrile system is the preferred mobile phase because of its compatibility with ELSD, MS, and UV detections. Applications Response (B) mm ammonium acetate, ph. UV, nm 7 7 8 8 Detection: UV, nm and ELS detector ELS detector Sample: Nasal spray sinus relief (direct injection) Peaks:. Chloride. Oxymetazoline. C Dimethyl benzyl ammonium. C Dimethyl benzyl ammonium. C 6 Dimethyl benzyl ammonium Figure 6. Ingredients in nasal spray using the Acclaim Surfactant column and ELSD and UV detections. 8 An acetic or formic acid/acetonitrile mobile phase is recommended for analyzing cationic surfactants using suppressed conductivity detection on the Acclaim Surfactant column. A borate buffer/acetonitrile mobile phase is required for analyzing anionic surfactants using suppressed conductivity detection on the Acclaim PA column. Table. Comparison of ELSD, UV, and Suppressed Conductivity Detection (SCD) for Surfactant Analysis ELSD UV SCD Versatility Universal Limited Limited 6 8 Mobile Phase: (A) 7% Acetonitrile in D.I. water (B) mm formic acid (C) D.I. water C 7 6 6 Inj. Volume: µl Detection: Suppressed conductivity detection (CSRS ULTRA II mm suppressor, external water mode at. ml/min, current ma) Sample: Nasal spray sinus relief (direct injection) Peaks:. C Dimethyl benzyl ammonium. C Dimethyl benzyl ammonium. C 6 Dimethyl benzyl ammonium. C 8 Dimethyl benzyl ammonium 8 Sensitivity Poor to fair Fair to good Good Signal Response Quadratic Linear Linear Selectivity Non-selective For surfactants with chromopores For ionic surfactants Figure 7. Cationic surfactants in nasal spray using the Acclaim Surfactant column and suppressed conductivity detection. Resistence to Matrix Interference Poor to good Poor to good Good Reproducibility Poor to fair Good Good Mobile Phase Volatile Non-UV absorbance Conductivity suppressible Suitability for Surfactant Analysis Suitable for most applications Limited use Suitable for anionic and cationic surfactants Recommended applications. High concentration samples. Surfactants with chromophores. Trace level analysis (ppb). Pre-MS application development. Applications that need universal detection. Complement to ELSD. Complex sample matrices. Selective analysis ACS 8 Presentation
Response UV, nm (B) mm ammonium acetate, ph. (C) H O C 7 7 ELS detector 8 6 8 Detection: UV, nm and ELS detector Sample: Scope (direct injection) 8 6 Peaks:. C 6 Pyridinium. Benzoate. Saccharinate Figure 8. Ingredients in mouthwash liquid using the Acclaim Surfactant column and ELSD and UV detections. 8 PEG- PEG- PEG- PEG- PEG-6 8 6 Column: Acclaim Mixed-Mode HILIC-, µm Mobile Phase: (A) CH OH (B) D.I. H O Gradient: % to 9% A in min Inj. Volume: µl Samples: Various PEGs (.% each) Figure. Separation of polyethylene glycols (PEGs) using the Acclaim Mixed- Mode HILIC- column. 6 6 8 Mobile Phase: (A) 7% Acetonitrile in D.I. water (B) mm formic acid (C) DI water C 7 6 6 Inj. Volume: µl Detection: Suppressed conductivity detection (CSRS ULTRA II mm suppressor, external water mode at. ml/min, current ma) Sample: Scope (fivefold dilution) Peaks:. Cetylpyridinium Figure 9. Cationic surfactants in mouthwash liquid using the Acclaim Surfactant column and suppressed conductivity detection. 8 Xylene sulfonate Dodecyl sulfate Tetradecyl sulfate 8 6 Column: Acclaim PA, µm (B) Borate buffer (6. g boric acid in D.I.water, adjusted to ph 8. with % NaOH aqueous solution) 7 7 Instrument: ICS- chromatographic system mm suppressor, chemical mode at. ml/min with mn sulfuric acid) Sample: Dial Complete Antibacterial Foaming Hand Soap with Lotion (% in D.I. HO) Figure. Anionic surfactants in antibacterial foaming hand soap using RPLC and suppressed conductivity detection with the Acclaim PA column. 7 Hydrophobe Separation (RPLC mode, CH CN/.M NH OAc v/v 7/) EO Oligomer Separation (HILIC mode, CH CN/.M NH OAc v/v 9/) Column: Acclaim Mixed-Mode HILIC-, µm Mobile Phase: See chromatogram for details. Inj. Volume: µl Sample: Brij ( mg/ml) Figure. Analysis of ethoxylated fatty alcohols Brij [lauryl alcohol condensed with moles ethylene oxide, molecular formula: (C H O) n C H 6 O] in both RPLC and HILIC modes with the Acclaim Mixed-Mode HILIC- column. In RPLC mode, the surfactant is separated into four single peaks, corresponding to the alkyl chain distribution. Under this condition, all EO oligomers with the same hydrophobe collapse into a single peak. In HILIC mode, on the other hand, all EO oligomers are separated in addition to the hydrophobe-based separation. Thus, the degree of ethoxylation can be determined. 8 Saccharin Colgate Total Advanced Fresh Lauryl (C ) sulfate Advance White C sulfate C 6 sulfate 8 6 Column: Acclaim PA, µm (B) Borate buffer (6. g boric acid in D.I. water, adjusted to ph 8. with % NaOH aqueous solution) 7 7 Instrument: ICS- chromatographic system mm suppressor, chemical mode at. ml/min with mn sulfuric acid) Sample Prep:. g sample suspended in ml H O and ml alcohol, sonicated for 6 min, then filtered through a.-µm membrane filter. Figure. Anionic surfactants in toothpaste using RPLC and suppressed conductivity detection with the Acclaim PA column. New Developments in Surfactant Analysis Using HPLC
References. Schmitt, T.M. Analysis of Surfactants; Marcel Dekker: New York,.. Liu, X.; Pohl, C.; Weiss, J. New Polar-Embedded Stationary Phase for Surfactant Analysis. J. Chromatogr. A 6, 8, 9-.. Liu, X.; Pohl, C.; A Versatile Column for Surfactant Analysis by HPLC. American Laboratory, 7 (), 7-.. Liu, X.; Pohl, C.; New Hydrophilic Interaction/Reversed-Phase Mixed-Mode Stationary Phase and Its Application for Analysis of Nonionic Ethoxylated Surfactants. J. Chromatogr. A, In press.. Liu, X.; Bordunov, A.; Pohl, C. Preparation and Evaluation of a Hydrolytically Stable Amide-Embedded Stationary Phase. J. Chromatogr. A 6, 9, 8-. 6. Dionex Website New Acclaim Mixed-Mode HILIC- Columns. http://www.dionex.com/en-us/columns_accessories/speccons687.html (accessed Mar 7, 8). Advance White is a registered trademark of Church and Dwight Company. Colgate Total is a registered trademark of Colgate-Palmolive Company. Dial Complete is a registered trademark of The Dial Corporation. Scope is a registered trademark of Proctor & Gamble. Acclaim, AMMS, Chromeleon, CSRS, and Summit are registered trademarks of Dionex Corporation. Passion. Power. Productivity. Dionex Corporation north America Europe Asia Pacific 8 Titan Way U.S. (87) 9-7 Austria () 66 Benelux () 68 9768; () 9 Australia (6) 9 China (8) 8 8 India (9) 76 7 P.O. Box 6 Canada (9) 8-96 Denmark () 6 6 9 9 France () 9 Germany (9) 66 99 Japan (8) 6 688 Korea (8) 6 8 Singapore (6) 689 9 Sunnyvale, CA Ireland () 6 6 Italy (9) 6 67 Sweden (6) 8 7 8 Taiwan (886) 87 66 south America ACS 8 Presentation LPN - 9/8 988-6 Switzerland () 6 9966 United Kingdom () 76 697 Brazil () 7 8 Dionex Corporation (8) 77-7 www.dionex.com