Aqueous solution of weak base (e.g. ammonium hydroxide) incompletely neutralized salt of an inorganic polyacid having three or more replaceable hydrogens also containing 2 to 10 weight percent dissolved alkanol or alkanenitrile buffered to a pH not exceeding 7.5 is a useful mobile phase for liquid chromatographic component separation and content determination of sample containing closely related rather polar compounds by means of a solid phase having a nitrogen-containing exchange base derived from an aminoalkyl-substituted trialkoxysilane. Such mobile phase is superior to prior suggested reverse phase made mobile phases such as 50:50 water and methanol or water and acetonitrile, or acidic aqueous solutions of strong base (e.g. sodium hydroxide) partially neutralized inorganic polyacid having at least three replaceable hydrogens.
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