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 Which Type C Silica based phase should you choose and in which mode should it be used?
Cogent Bidentate C18™, non end-capped, click here for ordering information. In acidified buffered aqueous/methanol these columns exhibit typical Reverse Phase (ARP) properties, but changing to buffered aqueous/acetonitrile and typical TYPE-C Normal Phase (ANP and ONP) selectivities are added to your selectivity options. Additional advantages include: no obvious “fold-back” when researching 100% aqueous buffers, which can give excellent selectivity for highly polar organic acids and bases without the need for Normal Phase mode (ANP); also with the Cogent Bidentate C18™ columns the option to use TFA at pH of 1.5 and above or 20mM ammonium formate buffered with ammonium hydroxide to pH 10.0. Extremely robust columns can be used at very low pH and you may be able to avoid using Paired Ion Reagents to gain retention. Retain basic compounds at low pH not high pH. Excellent Reverse Phase Columns with unique selectivites. Retain more compounds with 100% aqueous mobile phases than other commercial C18 columns. Cogent UDC-Cholesterol™, click here for ordering information. Cogent UDC-Cholesterol columns can provide unique selectivities as compared to a linear straight chain phase, such as C18 or C8 columns. In buffered aqueous/methanol these columns exhibit typical Reverse Phase (ARP) properties, but changing to buffered aqueous/acetonitrile and typical TYPE-C Normal Phase (ANP and ONP) selectivities are added to your selectivity options. Additional advantages include: the UDC-Cholesterol offers the option to use TFA at pH of 2.0 and above or 20mM ammonium formate buffered with ammonium hydroxide to pH 8.0. The planar bottom of the cholesterol moiety along with the non-planar opposite side provides many possibilities for increased selectivities. Also the cholesterol ligand can act as a liquid crystal and will change geometry at various solvent compositions as well at different temperatures. This provides shape selectivites. Excellent for steroids and some positional isomers when shape recognition is needed. Cogent Bidentate C8™, non end-capped, click here for ordering information. In acidified buffered aqueous/methanol these columns exhibit typical Reverse Phase (ARP) properties, but changing to buffered aqueous/acetonitrile and typical TYPE-C Normal Phase (ANP and ONP) selectivities are added to your selectivity options. Additional advantages include: less hydrophobic than the Bidentate C18™; also with the Cogent Bidentate C8™ columns the option to use TFA at pH of 1.5 and above or 20mM ammonium formate buffered with ammonium hydroxide to pH 10.0, all on a non end-capped silica hydride based phase. Fast equilibration between gradient runs puts these columns back in service faster than other columns. Retain polar compounds at low pH for bases and neutral pH for acids. These columns are excellent choice for complex mixtures of hydrophilic and hydrophobic compounds. Cogent Diamond Hydride™, click here for ordering information. Buffered aqueous/acetonitrile and typical TYPE-C Normal Phase (ANP and ONP) selectivities are added to your selectivity options. There is a small amount of carbon impregnated on the surface of these columns which amounts to less than 2% carbon loading. The carbon effects the adsorption and desorption of solvent creating excellent peak shapes. Additional advantages include: retain and separate without derivatizing amino acids for LCMS methods. Fast equilibration between gradient runs puts these columns back in service sooner than other columns. Useful for amino acids, nucleotides, organic acids, sugars and other hydrophilic metabolites. Cogent Silica-C™, click here for ordering information - Silica C™ (silica hydride) columns absorb and desorb solvents differently are an excellent choice for anyone doing normal phase chromatography. The advantages of the Silica-C™ over conventional silica columns is that you will not need to worry about controlling the moisture of your mobile phase to protect the columns or to get reproducible retention times. This is a favorite of “prep chromatography” for this reason. Also, these columns will outlast conventional silica columns and can be used in ANP and will be very successful at retaining polar compounds. Fast equilibration between gradient runs puts these columns back in service sooner than other HPLC columns. 
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