HPLC Stationary phases for a broad range of separations
For more than 35 years, Hamilton Company has developed and manufactured pressure-stable, polymeric polystyrene-divinylbenzene (PS-DVB) HPLC columns that are used in most of the world’s top chromatography labs. With a wide range of particle sizes, pore sizes, pH stability from 1 to 14, temperature resistance over 100°C, and chemistries to match most analyte types, Hamilton polymeric columns are the chromatographer's choice for challenging separations.
Reversed-Phase HPLC Columns
Hamilton reversed-phase HPLC columns combine the best characteristics of silica-based and polymeric columns to arrive at a product that is highly inert and long-lasting. Hamilton offers four polymeric and two silica-based packing materials for reversed-phase separations.
PS-DVB resins are similar in retention characteristics to silica C18s in that retention tends to increase with lipophilicity. However, subtle differences in the chemical interaction between the analyte and stationary phase can result in differential selectivity. In many cases, analytes that co-elute on a silica C18 can be resolved on a polymeric-based support. The PRP-1 consists of a 55% cross-linked PS-DVB bead containing 100 Å pores. The properties of this base material intrinsically lend themselves to reversed-phase separations with no further surface modifications. The PRP-C18 uses the PRP-1 as the base support material with the addition of octadecyl to impart characteristics more closely related to a silica-based C18, giving slightly different selectivity than the PRP-1. To make the PRP-3, the PRP-1 is modified so that the base material contains 300 Å pores, which allows for the separation of larger molecules. The PRP-h5 utilizes the PRP-1 as its base with a pentafluorinated modification, making it more hydrophobic in nature.
Anion Exchange
In anion exchange chromatography, the stationary bed has an ionically positive (+) charged surface while the sample ions are of negative (-) charge. This technique is used almost exclusively with ionic or ionizable samples. The stronger the negative charge on the sample, the stronger it will be attracted to the positive charge on the stationary phase, and thus the longer it will take to elute. Elution in ion chromatography is effected by mobile phase pH and ionic-strength, and, to a lesser extent, operation temperature. The ability to use the full pH range and elevated temperatures are distinct advantages compared to silica-based supports.
Anion Exchange Capacity
Anion exchange capacity is a measurement of the number of negative charges (anions) that the exchange resin can bind to and is reported in singly charged ion equivalents per 1 gram of resin. Exchange capacity is dependent upon the pH of the mobile phase and in anion exchange chromatography; as mobile phase acidity decreases (pH increases), the exchange capacity decreases.
Anion exchange capacity is a measurement of the number of negative charges (anions) that the exchange resin can bind to and is reported in singly charged ion equivalents per 1 gram of resin. Exchange capacity is dependent upon the pH of the mobile phase and in anion exchange chromatography; as mobile phase acidity decreases (pH increases), the exchange capacity decreases.
Hamilton offers six polymeric packing materials for anion exchange separations.
Cation Exchange
In cation exchange chromatography, the stationary bed has an ionically negative (-) charged surface while the sample ions are of positive (+) charge. This technique is used almost exclusively with ionic or ionizable samples. The stronger the positive (+) charge on the sample, the stronger it will be attracted to the negative charge on the stationary phase, and thus the longer it will take to elute. The mobile phase is an aqueous buffer, where both pH and ionic strength are used to control elution time. Ion chromatography can employ harsh conditions requiring mobile phases that are at very high pH limits (> 11). Temperatures well above the normal operating conditions where silica materials fail can also be used.
Cation Exchange Capacity
Ion exchange capacity is a measurement of the number of positive charges (cations) that the exchange resin can bind to and is reported in singly charged ion equivalents per 1 gram of resin. Exchange capacity is dependent upon the pH of the mobile phase and in cation exchange chromatography; as mobile phase acidity decreases (pH increases), the exchange capacity increases.
Ion exchange capacity is a measurement of the number of positive charges (cations) that the exchange resin can bind to and is reported in singly charged ion equivalents per 1 gram of resin. Exchange capacity is dependent upon the pH of the mobile phase and in cation exchange chromatography; as mobile phase acidity decreases (pH increases), the exchange capacity increases.
Ion Exclusion
Ion exclusion chromatography is an alternative to ion exchange chromatography in which ionized samples are excluded from the pores of the support and elute first, while the weakly ionized and non-ionic compounds elute later. Mixtures of weak acids, like those in fruits and milk products, are frequently not very well separated by pure ion-exchange methods, nor in the reversed-phase mode.
Hamilton PRP-X300 columns offer an easy, rapid way to separate closely related alcohols and organic acids. The sulfonated poly(styrenedivinylbenzene) support separates samples via a mixed mode mechanism. Separation on the PRP-X300 is accomplished by three modes: hydrogen bonding, reversed-phase, and ion exclusion. PRP-X300 column selectivity can be altered by changing the pH of the buffer or adding an organic modifier (e.g., methanol, acetonitrile). The support’s stability to organic solvents makes it possible to analyze samples that are too highly retained on conventional ion exclusion supports.
Application Examples: Organic acids and alcohols
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