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Sample diluent and mobile phase should be close in composition to provide good peak shape in RP systems. Is it still true for mixed mode separation?

April 26, 2017composition diluent good mobile peak phase sample shape

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Sample diluent and mobile phase should be close in composition to provide good peak shape in RP systems. Is it still true for mixed mode separation?

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No. When two interactions are involved in retention of a compound, the mobile phase composition can be very different from mobile phase as long as at least one mode of separation is not disturbed. For example, when a positively charged molecule is retained on the Primesep 100 column, the sample diluent can have any amount of MeCN. The retention will be still non-disturbed due to the insignificant effect of organic concentration on electrostatic interaction. See example here.