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Tuesday, November 25, 2014

Advantages of Mixed Mode HPLC for Polar Compounds

It was a relief when I used the brand new Cogent UDA™ columns for analysis of closely related polar compounds. I used them in the Aqueous Normal Phase (ANP) retention mode with additional selectivity of the Ion exchange chromatography capacity.
                With the Cogent UDA 2.o™ column, you can have the best of both worlds by using each retention mode together to obtain excellent separations. In the latest study from our laboratories, we demonstrated the ion exchange characteristics of the Cogent UDA 2.o™ column by separations of three test solutes. With a carboxylic acid group at one of the bonded ligand, ion exchange propertied can be either activated or inactivated by selection of the mobile phase pH.  Under acidic conditions, the carboxylic acid is protonated and neutral and no ion exchange occurs. At mild pH, the group becomes de-protonated and anionic. When the group was ionized, increased retention and separation of the three basic test analytes were observed.
                You can read about the full investigation here.
Separation of the three analytes under ion exchange conditions

Friday, November 7, 2014

An Interesting Compound found in Green Tea

Green tea is more than just a tasty beverage. It also has a number of compounds with potential health benefits. For example, catechins found in tea are known antioxidants. Another such interesting compound is L-theanine. It is a psychoactive compound and is believed to exhibit various beneficial effects on the brain. These may include increased alertness, decreased anxiety, and general sense of well-being.

                It is a polar compound though and may be difficult to analyze by reversed phase chromatography. With the Cogent Diamond Hydride 2.o™ column, it can be well-retained using an Aqueous Normal Phase approach. There are not many other polar compounds in green tea (catechins are fairly hydrophobic), so you can obtain a nice L-theanine peak which is well-separated from the others.

                We estimated L-theanine content in a typical home-brewed green tea sample using this column and found concentrations consistent with those reported in the literature (around 10 mg/L). See the full study for more information!