1
Matthew T. Hall and John T. Roy, Ph.D. Impact Analytical - 1910 West St. Andrews Road, Midland, MI 48640-2696 INTRODUCTION • Many surfactants are polar molecules with poor retention by reversed-phase HPLC • Specialty columns are now available for the analysis of surfactants and polar compounds • The objective of this study was to find the best conditions for analyses of these compounds by LC-MS and by HPLC • A single chromatographic column for LC-MS/HPLC analyses will reduce the inventory of columns needed for the deformulation of cleaning products • The optimum chromatographic column will improve efficiency for the analysis of these products Comparison of Columns for the Analysis of Surfactants and Other Polar Compounds by HPLC and Liquid Chromatography-Mass Spectrometry SPECIALTY COLUMN TESTING COLUMNS & CONDITIONS Compounds were not observed by UV at 210 nm when the Acclaim column was used 1) Benzenesulfonic acid 2) Xylenesulfonic acid UV missed citric acid, but citric acid is detected by mass spectrometry Organic Acids by UV at 210 nm Mass spectrometry is useful for detecting compounds without a UV chromophore 1) Citric acid 2) Benzenesulfonic acid 3) Xylenesulfonic acid These acids were not observed when using the Acclaim column UV missed citric acid, but citric acid is detected by mass spectrometry Organic Acids - Negative ESI-MS Alkyldimethylbenzylammonium Salts - Postive ESI-MS Total Ion Chromatogram Positive ESI Mode Alkyldimethylbenzyl- ammonium salts: C12, C14, C16 All compounds are separated and detected on the three columns Contains ethoxylated alcohols, amine oxides, and ternary ammonium compounds One amine oxide was not observed on the ODS-AQ column Cleaner B - Positive ESI-MS ODS-AQ retains EO alcohols well, yielding poor detection by MS Cleaner D - Positive ESI-MS HILIC TESTING CONCLUSIONS: • Both columns retained some polar compounds well • The columns are complimentary to each other, because compounds poorly separated on one column appear well separated on the other • Additional experience is needed with the HILIC column • Initial separation aempts are favored on specialty columns (Unison CK-18 or ODS-AQ) instead of the HILIC column • Testing was done on Atlantis Hydrophilic Interaction Chromatography (HILIC) and ODS-AQ columns to determine additional options for the analysis of polar compounds • HILIC has become a popular technique in recent years, and an evaluation was needed to determine the potential of the column for the analysis of polar compounds • Impact Analytical has had lile success in the past with the HILIC column, and optimization of chromatographic conditions was desired Comparison of Columns: HILIC vs. Specialty Reversed-Phase Columns • Atlantis HILIC 4.6 x 50 mm, 3µ (90:10 v:v) acetonitrile / 0.1 M ammonium formate, pH 3.0 Conditions recommended by manufacturer • ODS-AQ 4.6 x 250 mm, 5µ Gradient with 0.1% formic acid in water / acetonitrile EXPERIMENTAL • Surfactants, polar compounds, and cleaning products were analyzed on three columns that are targeted for these analyses • The Acclaim Surfactant, Unison UK-C18, and ODS-AQ columns were tested • Columns of different dimensions and particle sizes were evaluated in this study, which complicates comparison • Actual stationary phases are proprietary, which limits understanding of separation mechanisms COLUMNS & CONDITIONS Acclaim Surfactant 4.6 x 150 mm, 5µ Unison UK-C18 4.6 x 150 mm, 3µ ODS-AQ 4.6 x 250 mm, 5µ • Gradient with 0.1% formic acid in water/acetonitrile • Detection with UV at 210 nm and electrospray-mass spectrometry (ESI-MS) • Modified conditions previously reported for this evaluation: N.E. Skelly, J. Chromatogr. Sci. 41: 22-25 (2003). Additional testing of columns for the analysis of cleaning products was initiated to improve the chromatographic separation on the Acclaim Surfactant column. This column was compared to the Unison UK-C18 column that was found to perform well. Acclaim Surfactant 4.6 x 150 mm, 5µ Unison UK-C18 4.6 x 150 mm, 3µ Gradient with 0.1 M ammonium acetate at pH 5.4 and acetonitrile Various Acids by Negative ESI-MS 1) Citric acid 2) Benzene sulfonic acid 3) Xylenesulfonic acid Citric acid and sulfonic acids are well separated on both columns with ammomium acetate in the eluent Ethoxylated Alcohols - Positive ESI-MS Background interferences are noted for the analysis of ethoxylated nonylphenol on the Acclaim column with ammomium acetate in the eluent Alkyldimethylbenzylammonium Compounds by Positive ESI-MS Alkyldimethylbenzyl- ammonium compounds are retained well with ammomium acetate in the eluent Hexadecyldimethyl- ammonium chloride is retained well and is not observed on the Unison CK-18 column eluent Only thymine and acenaphthene are separated well on this column ODS-AQ at UV 254 nm Atlantis at UV 254 nm Only cytosine and adenine are separated well on this column Atlantis compared to ODS-AQ for Thymine and Acenapthene Thymine and acenaphthene are separated well on the ODS-AQ column Atlantis compared to ODS-AQ for Cytosine and Adenine Cytosine and adenine are well separated on the Atlantis HILIC column ADDITIONAL TESTING: ACCLAIM COLUMN • The chromatographic conditons employed are important for obtaining good data for polar molecules • The Unison UK-C18 column performed very well for surfactant analyses under the conditions that were evaluated; the ODS-AQ column also performed well • A shorter ODS-AQ is available but has not been evaluated • The ODS-AQ was the longest column tested; the column retains compounds well, which yields poor detection for ethoxylated alcohols • The Acclaim column shows ethoxylated alcohols well, but citric and many other acids may be missed using this column; additional optimization is still required for this column CONCLUSIONS: SPECIALTY COLUMN TESTING THREE-COLUMN COMPARISON 1) o-phthalic acid 2) isophthalic acid These acids were not separated when using the Acclaim column Phthalic Acids - Negative ESI-MS
