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Effect of pH and mobile phase additives on the chromatographic behaviour of an amide‐embedded stationary phase: Cyanocobalamin and its diaminemonochloro‐platinum(II) conjugate as a case study
Author(s) -
Ventura Giovanni,
Calvano Cosima Damiana,
Losito Ilario,
Bianco Giuliana,
Pascale Raffaella,
Palmisano Francesco,
Cataldi Tommaso R.I.
Publication year - 2019
Publication title -
journal of separation science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.72
H-Index - 102
eISSN - 1615-9314
pISSN - 1615-9306
DOI - 10.1002/jssc.201801060
Subject(s) - chemistry , conjugate , amide , elution , ammonium , phase (matter) , chromatography , formic acid , inorganic chemistry , organic chemistry , mathematical analysis , mathematics
Several mobile phase additives (i.e., organic acids and their ammonium salts) were used to modulate the chromatographic retention of cyanocobalamin and its cis ‐diaminemonochloroplatinum(II) conjugate, depending on the specific nature of the stationary phase. Regardless of the mobile phase additive, the positively charged cyanocobalamin‐ cis ‐diaminemonochloroplatinum(II) conjugate was systematically less retained than cyanocobalamin on a conventional octadecyl‐silica column. In contrast, the amide‐embedded C18 column exhibited a progressive increase in the conjugate retention time upon changing the mobile phase additive from organic (acetic, formic and trifluoroacetic) acids to ammonium salts, ultimately leading to an inversion of the elution order. This change of retention was interpreted by invoking the interplay between hydrophobic interactions, hydrogen bonding between the conjugate and the polar amide groups and the ion‐pairing ability of the lyophilic counterions, whereby the acetate anion was found to be the most suitable to control the solute retention.