Chemistry Reference
In-Depth Information
contrary, would bring potential powers or capacities to light. This type of reasoning,
however, ignores the active contribution of the apparatus to the constitution of the
bodies. Should the results of experimentation seen in this light be qualified
by
ceteris paribus
clauses?
Many changes have occurred during the course of the experimental procedure
implying that many factors have unavoidably moved at the same time. Chemicals
are reactive, so is, at least, a part of the apparatus. A mixture of chemical bodies
is being separated or transformed while, for example, the active area of the working
electrode - or that of a catalyst - changes and permanently alters the ensuing
process. The quantities of bodies, the composition of the liquid phase, the dynamics
of adsorption and desorption at the surface of the electrodes, sometimes the
temperature depending on the energy released during the transformation are all
factors that can change simultaneously or almost simultaneously. Sure enough, one
could easily claim that everything depends on the scale of the factors at play. Local
changes can sometimes be subsumed under a global invariant factor. But is it
basically just a problem of scale? Choosing a relevant scale is part of a problem
of modeling and depends on chemists
purposes and standards for normalization.
According to the argument presented here it is, first and foremost, a problem in the
method of choosing and preparing a specific apparatus for studying a particular
collection of bodies and, correlatively, a problem in preparing the same collection
of bodies for developing a useful interaction with the apparatus when an associated
milieu of a certain type and a particular device are being used. The central problem
is that of
the co
-
stabilization
of an apparatus with the set of bodies with which
it interacts; a problem which includes various acts of modeling as part of the
global project.
It is the whole complex composed by the apparatus, the methods carried out for
calibrating and using it, the bodies, the associated milieu, and the ancillary devices
which should be the starting point of our epistemological enquiry. To investigate
the meaning of the
ceteris paribus
clause in chemistry requires an investigation
of the conclusions that chemists can relevantly draw from comparisons with
reference to the complex {apparatus-methods-bodies-associated milieu-devices}.
Ultra High Pressure Liquid Chromatography-UPLC-is a column chromatogra-
phy used to separate, identify, and quantify chemical bodies. A set of pumps pushes
the mixture, the mobile phase, through the columns which are filled with a packing
material, the stationary phase. As the mobile phase is passing through the stationary
phase a specific detector shows the retention times of the different molecules.
Retention time varies depending on the interactions between the stationary phase,
the molecules being analyzed, and the solvent used. The particle size within UPLC
columns decreases to less than 2.5
'
m requiring a higher pressure in order to push
the mixture through the columns. Since both efficiency and optimum flow rate are
inversely proportional to particle size, the UPLC system thus increases efficiency
and speeds up the flow rate which, in turn, allows for narrower and taller peaks and,
eventually, provides a greater resolution (Alan Xu
2013
).
A coupling between the UPLC system and a mass spectrometer enables chemists
to combine the physical separation capabilities of liquid chromatography with
μ
