Page 184 - Illustrated Pocket Dictionary of Chromatography

186 SPECIFIC PERMEABILITY, B o

specific permeability, B o Represents the resistance to mobile
phase flow through the column and for a packed column is a function
of the particle size, d p, and porosity, e:
2
3
2
(
B o = FhL pr D p = e d p 180 1 - ) e 2
where F is the flow rate, h is the viscosity, L is the column length, and
Dp is the pressure drop. This relationship is derived from the Kozeny–
Carman equation. For an open tube:
B o = d 232
c
where d c is the column diameter.

spherical, spherical packing The term spherical refers to
the shape of packing materials used in HPLC columns (compare to
irregular). In the case of spherical packing materials the diameter
ranges from 1 to 15mm.

split/splitless injector Used in GC to flush a fixed percentage
(expressed as a split ratio) of the sample to waste. This is done to prevent
overloading the column with sample and yet utilize routine syringes.
split ratio The ratio of carrier gas volume that is vented to waste
as compared with that which is sent to the column. For example, a
typical split ratio ranges from 20:1 to 100:1 (vented:on column).
Therefore, the chromatographic result must be multiplied by the split
ratio to compensate for the fraction that was vented to waste in order
to obtain the correct final result.

spotting The process of applying a sample to any thin layer sup-
port. Effective-spotting requires a concentrated sample and a small
resulting spot.

stagnant mobile phase Any part of the mobile pahse that is
within the support particle and is not freely swept when the mobile
phase is flowing through the column. It is a contributing factor to the
C term in the van Deemter equation (i.e., peak broadening).
stainless steel An iron-based alloy that, depending on the type and
amount of other materials, has varying tensile strength, resistance to cor-
rosion, etc. Most chromatographic components that are fabricated from
stainless steel (e.g., tubing, unions, end fittings, frits) are made from 316
stainless steel, which contains 2–3% molybdenum (corrosion inhibition).