LCGC Asia Pacific
Xiaodong Liu and Christopher Pohl, Dionex Corporation
Mixed mode chromatography combines aspects of ion exchange chromatography and conventional reversed-phase (RP) chromatography. The combination of both hydrophobic and ion-exchange properties allows for independent control of retention for ionizable and neutral molecules. Therefore, many application challenges involving hydrophilic ionizable compounds that would be difficult for C18 columns, can be easily tackled on a mixed-mode column. We have developed a new silica-based mixed-mode stationary phase, Acclaim Mixed-Mode WAX, which provides both weak anion-exchange and RP characteristics facilitated by covalently attaching a hydrophobic alkyl chain with an ionizable terminus to the silica surface. The new column features complete control of selectivity, orthogonal selectivity to RP columns, high capacity and unique selectivity for anionic molecules and multi-mode retention mechanisms (i.e., RP, anion-exchange and HILIC).
Acclaim Mixed-Mode WAX (4.6 × 150 mm, dp = 5 µm, Dionex, Sunnyvale, California, USA) columns were used for the separation. Separations were performed on a modular Summit HPLC system (Dionex) equipped with a P680 gradient pump, ASI-100 Autosampler, TCC-100 column oven and UVD 340 detector. Chromeleon 6.70 Chromatography Management Software (Dionex) was used for system control and data processing. All standards were purchased from Sigma-Aldrich (St Louis, Missouri, USA). The chromatographic conditions are given in Figure 1.
Figure 1
Figure 1 shows separation of a mixture of basic, neutral and acidic pharmaceutical-related compounds using a gradient method. We used a commonly employed mobile phase system containing acetonitrile, D.I. water and a phosphate buffer. All components in the mixture elute not only with symmetrical peaks, but also with good resolution. Unlike conventional RP columns, the unique column chemistry of the Acclaim Mixed-Mode WAX allows for fast elution of basic molecules with symmetrical peaks, high capacity and good selectivity for anionic molecules, such as acidic drugs and highly hydrophilic organic acids. Meanwhile, neutral molecules, such as steroids retained by hydrophobic interaction, usually elute after bases but before acidic molecules at pH 6. Thus, the separation is easily optimized by adjusting mobile phase ionic strength, pH and organic modifier, either independently or concurrently.
The Acclaim Mixed-Mode WAX column provides unique and adjustable selectivity, excellent peak shape for all types of molecules (i.e., acids, bases and neutrals) and multi-mode retention mechanism (i.e., RP, anion-exchange and HILIC). Therefore, it can be used as either a primary column for a broad range of applications including pharmaceuticals, food and beverage, chemical or a complementary column (to conventional RP columns) that provides orthogonal selectivity.
Xiaodong Liu and Christopher Pohl, Dionex Corporation, Sunnyvale, California, USA.
Dionex Corporation
1228 Titan Way, P.O. Box 3603, Sunnyvale,
California 94088-3603, USA
tel. +1 408 737 0700 fax +1 408 730 9403
Website: www.dionex.com
Analysis of Greenhouse Gases by Gas Chromatography
May 15th 2024This application note demonstrates the use of SCION's 8500GC system for the analysis of key greenhouse gases—carbon dioxide, methane, and nitrous oxide—in a single atmospheric air matrix. Highlighting the system's excellent sensitivity and repeatability, this method is crucial for understanding emission sources and combating climate change.
Analysis of DEHP in Drinking Water by HPLC-DAD
May 15th 2024This application note outlines a method for detecting low levels of 1,4-Dioxane, a likely carcinogenic compound, in drinking water using SCION GC-MS technology. It details the procedure for analyzing water samples spiked with 1,4-Dioxane, achieving excellent sensitivity and low detection limits, demonstrating the method's effectiveness for environmental monitoring.
Plant Protection Product Impurity Screening by GC-FID with GC-MS Confirmation
May 15th 2024This application note from SCION Instruments delves into the meticulous screening of impurities in plant protection products using GC-FID, with GC-MS for confirmation. It emphasizes the necessity of identifying and quantifying impurities to comply with regulatory standards in industries such as pharmaceuticals, food, and agriculture. The study specifically examines eugenol, showcasing how to determine significant impurities for regulatory submission. The approach integrates GC-MS and analytical standards, ensuring precise impurity identification and quantification critical for product approval.