Many analysts will adjust the peak shape and retention time by changing pH during the method development. Because the change of pH will exert various influences on chromatographic behavior of different structures of compounds.
For example, the retention of neutral compounds in reversed-phase chromatographic systems has nothing to do with pH of mobile phase; acidic compounds will increase retention due to the inclination of being neural when pH is prone to be less than 7 (pH decreases, especially it is lower than the pka of compounds); while alkaline compounds will increase retention due to the inclination of being neural when pH is prone to be more than 7 (pH increases, especially it is higher than the pka of compounds).
However, do you know that declination of column efficiency and resolution, undesirable peak shape, shortened column lifetime will occur when pH of mobile phase is too low, which are the commons of conventional columns under low pH condition. Today, the column which can keep stability and long lifetime under acidic mobile phase condition will be introduced, that is LP series columns.
C18 columns have wide application range. Ultisil LP-C18 columns use unique silica surface treatment and solid phase bonding technique which makes the aggregation degree between bonded phase and silica matrices much higher than common reversed-phase stationary phase. Special side chain steric hindrance protection technology makes it possible to have excellent separation properties, stability and longer lifetime. LP is the abbreviation of low pH. LP-C18 is not only compatible with 100% aqueous phase, but also resistant to low pH mobile phase with good peak shape and resolution.
Except LP-C18, LP-AQ、LP-C8、LP-C3、LP-CN and UHPLC LP-C18 all have characteristics of being resistant to low pH. LP-AQ is a kind of C18 column which is compatible with 100% aqueous phase but has different selectivity than LP-C18. Retention properties of C8 and C3 to analytes may be weaker than C18, because carbon capacity influences separation effect and retention of main components a lot. When retention of analytes on the C18 column is too strong or too weak, CN column will be a good choice.
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