Page 9 - Illustrated Pocket Dictionary of Chromatography
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2     ACETONE

        viscosity (15°C): 1.31cP; polarity index (P¢): 6.2; Hildebrand solubility
        parameter (d): 12.4; pK a = 4.7. Miscible with water. Acetic acid is a
        weak acid that is frequently used as a mobile-phase modifier directly
        or as a buffer (acetic acid/acetate) in LC, TLC, and CE techniques.
        Pungent odor.
                                     O
                                     C
                                 H 3 C  OH
                                  Acetic acid
        acetone   Molecular weight: 58.1; boiling point: 56°C; refractive
        index (20°C): 1.3587; density (20°C): 0.79g/mL; viscosity (20°C): 0.36
                                              o
        cP; UV cutoff: 330nm; eluotropic strength (e )—on alumina: 0.56, on
        silica: 0.53; polarity index (P¢): 5.1; Hildebrand solubility parameter
        (d): 9.6. Miscible with water. Extremely volatile and flammable.
        Acetone is known as a “universal” solvent in that it is miscible with
        an extremely wide range of commonly used polar and nonpolar sol-
        vents. [Note that this fact does not imply anything about the solubil-
        ity of salts and buffers in acetone.] Because of this, acetone may be
        used as the intermediate solvent when changing from HPLC reversed-
        phase systems (i.e., aqueous/organic solvents) to normal-phase
        systems (i.e., nonpolar solvents) and vice versa. Acetone is also used
        as a solvent in TLC and a sample solvent in GC.

                                    O
                                    C
                                H 3 C  CH 3
                                  Acetone

        acetonitrile Molecular weight: 41.1; boiling point: 82°C; refractive
        index (20°C): 1.3441; density (20°C): 0.78g/mL; viscosity (15°C): 0.38
                                              o
        cP; UV cutoff: 190nm; eluotropic strength (e )—on alumina: 0.65, on
        silica: 0.52; polarity index (P¢): 5.8; Hildebrand solubility parameter
        (d): 11.7. Miscible with water. Volatile and flammable. Acetonitrile is
        one of the most commonly used solvents in reversed-phase HPLC
        because of its low viscosity and very low UV cutoff. It should be noted
        that phosphate buffers have a limited solubility in aqueous/acetoni-
        trile solvents. This solubility decreases as the phosphate ion increases
                                         3-
                                  -
        in charge (i.e., goes from H 2 PO 4 to PO 4 ). Acetonitrile is not miscible
        with alkanes. Acetonitrile has found limited use in TLC and GC.
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