Elution order Using the Retention Index Table below determine the elution order

Question

Elution order

Using the Retention Index Table below determine the elution order of the following compounds from columns containing (a) (diphenyl)0.35(dimethyl)0.65-polysiloxane, and (b) poly(ethylene glycol);

1-pentanol, 2-hexanol, heptane, octane, nonane, decane

TABLE 24-2 Retention indexes for several compounds on common stationary phases Retention index OH Butanol 2-Pentanone b.p. 102 667 689 Benzene 1-Nitropropane Phase Poly(dimethylsiloxane) (Diphenyl)oos(dimethyl)oss 80°C bp 132°C 651 651 705 667 746 721 667 733 778 779 743 867 881 938 1 230 polysiloxane (Diphenyl)o.3s (dimethyl)o6s 773 784 825 998 polysiloxane Cyanopropylphenyl)o4 (dimethyDoss polysiloxane (DiphenyDoss(dimethyl)o3s 794 polysiloxane Poly(ethylene glycol) 963 158 a. For reference, boiling points (bp.) for various alkanes are: hexane, 69C; heptane, 98°C, octane, 126 C; nonane, 1sr C; decane, 174 C; undecane, 196C; dodecane, 216 C. Retention indexes for the straight-chain alkanes are fixed values and do not vary with the stationary phase: hexane, 600; heptane, 700: octane, 800; nonane, 900: decane, 1 000: undecane, 1 100: dodecane, 1 200. Benzene accounts for dipole-induced dipole interactions; butanol for hydrogen bond donating and accepting: 2-pentanone and nitropropane for dipole-dipole interactions Data from Restek Chromatog raphy Products Catalog, 2013-2014, Bellefonte, PA.

Explanation / Answer

a) in (diphenyl)0.35(dimethyl)0.65-polysiloxane

The elution order will be:

butanol < benzene < 2-pentanone < 1-nitropropane

b) polyehtylene glycol

benzene < 2-pentanone < butanol < 1-nitropropane

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