study is based on two principles: 1. Principle of density gradient
centrifugation and; 2. Principle of solubility as affected by polarity or the
like dissolves like principle
principle of density gradient centrifugation, as stated by Rickwood and Graham
(2001), asserts that particles of different densities or specific gravities in
a solution form different layers or bands when subjected to centrifugation.
When the centrifugation is carried out for a time enough for the particles to
reach the part of gradient whose density is equivalent to that of the
particles, then it is said to be isopycnic, and the particles are separated
according to their buoyant or banding density. Thus, the gradient for the bands
formed is from a low density to a higher density.
relation to FGCT, gasoline is of lower density as compared to formalin and
fecal constituents. Thus, it is expected that the topmost layer is the gasoline
layer, underneath is the fecal plug layer which is made up of fats and other
fat-soluble substances found in the feces. Denser than these two layers is the
formalin layer and at the bottom layer settles the layer of sediments comprising
of the parasite, Ascaris lumbricoides
eggs, which are much denser that the other layers.
the other hand, as indicated by the principle of solubility by Clayden et. Al
(2000), substances have properties to dissolve in a liquid solvent to form a homogenous
or heterogenous mixture. Furthermore, the solubility of a substance is affected
by the polarity of the substance itself and the polarity of the solvent used to
dissolve it. As a rule of a thumb, maximum solubility is achieved when like
dissolves like. Thus, a solute will dissolve best in a solvent that has a
similar polarity to itself.
regards to FGCT, gasoline is the solvent used to dissolve the fat-soluble
substances and fecal debris because these substances are of the same polarity
with the gasoline, which is non-polar. Gasoline is a mixture of hydrocarbons,
including hexane, making it non-polar and lipophilic. With this, gasoline can
dissolve the fat-soluble fecal debris for a better clarity in microscopic
examination. This principle can also be correlated with the probability that
the lipid layer present in one of the four layers of Ascaris lumbricoides eggs
can be affected in a way, thus, affecting the morphology of the egg itself.