This hydrophilic (polar) endcapped C18 phase from MACHEREY-NAGEL is especially designed for the use in mobile phase systems of up to 100% water. Conventional reversed phase columns often show stability problems with highly aqueous eluents as evidenced by a sudden decrease of retention time and poor reproducibility. In the attached figure the retention behaviour of three organic acids under purely aqueous conditions on NUCLEODUR C18 Pyramid is studied in comparison with a conventionally derivatized C18 phase. The retention times for NUCLEODUR C18 Pyramid remain nearly unchanged between initial injection and restart after the flow has been stopped for 12 hours, however the conventional C18 column collapsed after the same period of time. The increase in surface polarity is not detrimental to retention characteristics and tailing factors of ionizable compounds. Even strong basic analytes are eluted with symmetric peak shapes. NUCLEODUR C18 Pyramid is LC/MS compatible. Recommended applications: Generally polar compounds e.g. drug components and drug metabolites, organic acids.