**Hydrophobicity Parameter():**
was calculated according to equation (1)

^{1}:

ln(k) =

x V – 3.068 (1)

where V is the molar volume of the analyte (acenaphthene or naphthalene).

*Results obtained are presented in the Table below:*
**Silanophilic Interaction Parameter(S):**
of amitriptyline was calculated according to equation (2)

^{1}
S = ln (k

amitriptyline) – 0.7124 x ln
(k

acenaphthene) + 1.9748 (2)

*Results obtained are presented in the Table below:*
Two tests using the methods for HPLC packings by Neue, et. al. [1] were run in order to understand some of
the retention and surface characteristics of the hydride stationary phases compared to typical commercially
available reverse phase packings. The first test is for Hydrophobicity which compares the retention of
naphthalene and acenaphthene under a standard set of conditions.

The hydrophobicity parameters (

) for the two TYPE-C
silicon-hydride phases were as follows:

Bidentate C18™ = 0.0397

UDC-Cholesterol™ = 0.0339

In order to verify that the measurements were done correctly the same determination was made on a Phenomenex
Luna C18 column. The experimentally determined value of

was 0.0400 for this column, in comparison to the reported value of 0.0397 [1] in the literature.

The hydrophobicity of the Bidentate C18™ column with respect to the more than 100 commercial packings
tested [1] is similar to the Luna® C18 and the Zorbax® Eclipse XDB C18. These stationary phases are at
the higher end of the hydrophobicity values of the phases tested and reported.

The UDC-Cholesterol™ has lower hydrophobicity as expected and is similar to many of the C8 phases [1].

The other phase property tested was the silanophilic interaction parameter

**(S)**. The values determined
were as follows:

Bidentate C18™ = 1.429

UDC-Cholesterol™ = 0.949

In comparison to the more than 100 columns tested [1], the Cogent Bidentate C18™ is at the low end of
classical packings, particularly with respect to its silanol activity and assymetry. The UDC-Cholesterol™
phase has an even lower S parameter and is similar to many phases with polar embedded groups as well as some
phenyl and cyano phases. The “S” test is based on the retention of the polar compound amitriptyline.

For both TYPE-C™ (hydride) phases the peak symmetry was excellent indicating that relatively few silanol
groups were interacting with this basic solute, A

_{S} values were
found:

Bidentate C18™ = 1.02

UDC-Cholesterol™ = 0.95