Ligand exchange is the preferred method for the separation of many sugars and sugar alcohols due to the simple water eluent. In ligand exchange, the negatively charged hydroxyl groups on the carbohydrate molecule interact with the positively charged metal loaded groups on the chromatography substrates. The carbohydrates are eluted by the polar water eluent mobile phase which competes for the sites on the metal ion. Besides the ligand exchange mechanism, several secondary mechanisms’ processes are also involved in the separation of the carbohydrates including size exclusion and normal phase partitioning. HPLC columns packed with low cross-linked polymers (gels) serve as the primary packings for carbohydrate analysis columns, and are available from a number of suppliers. In order to maximize the separation of a wide variety of samples, Concise Separations has developed the most complete line of carbohydrate analysis columns available on the market by combining ligand exchange (metals), size exclusion and partitioning (cross-linkage of polymer), particle size (column efficiency) and column size (speed versus resolution).
Since polymers are chemically stable, as long as the columns are used within the operating parameters, they last a long time. The key to long column lifetime when using polymeric gels to keep the column at all times below the pressure maximum. Since temperature is a key component of pressure along with flow rate, it is extremely important to allow the column to reach temperature before starting the flow. The columns are also sensitive to water quality, so water purity is essential (minimum purity requirements 18 Mohm). Sample preparation as well as the use of guard columns and in-line filters reduce contaminants from entering the column and will extend a column’s lifetime. In general, the higher the cross-linkage of the polymer and the larger the particle size, the greater the flow rate that can be used before reaching the maximum allowable pressure.