Biomedical Engineering Reference
In-Depth Information
oxidase and lactate dehydrogenase were immobilized onto magnetic nanoparticles,
which were held in place with a permanent magnet.
3.3.2 Chromatography (GC and LC)
Either gas or liquid chromatographs (GC or LC) are standard equipment in ana-
lytical laboratories. However, process samples can be directly transferred to
chromatographs provided that an appropriate interface makes the link, i.e., one that
is safe for the process in not compromising its sterile barrier and safe for the
instrument by preparing the sample accordingly, e.g., filtering cells off, diluting, or
even derivatizing. Again, an FIA is a good choice here. A closer look at the
operation of a chromatograph makes this clear: it is a special case of FIA, since
there is a continuous, unsegmented flow of an inert carrier, either gas or liquid, into
which a sample is injected; downstream of the injection, the only ''reaction'' that
takes place is the separation of sample components according to the properties of
the selected chromatographic column and carrier fluid. The final detector may be a
simple
flame
ionization
detector
(FID)
or
a
mass
spectrometer
(LC-MS),
depending on the problem to be solved.
A gas chromatograph is certainly useful to separate gases or volatile com-
pounds, taken either from the exhaust gas—which is least demanding for the
interface—or from the culture supernatant—which requires an interface capable of
at least filtering and degassing. Injection valves or pistons with a metering groove
are more convenient than syringes. An interesting example is the combination of
gas chromatography with pyrolytic methylation as the sample preparation proce-
dure for determination of dihydroxyacetone [ 85 ].
Liquid chromatographs are used to analyze sugars, amino acids, and even
proteins such as vaccines [ 86 ].
A recent report described automatic analysis of extracellular glucose, ethanol,
glycerol, and acetic acid in 5-min intervals, with good consistency for three
comparable batch cultivations of S. cerevisiae [ 87 ]. Warth et al. [ 88 ] reported use
of online HPLC data to calculate volumetric and specific reaction rates (which are
themselves, then, software sensors). Cos et al. [ 89 ] reviewed the importance of
monitoring and control of methanol concentration during the induction and feed
phase in P. pastoris cultivation, which should not be too low and be kept constant
for the production of foreign proteins. Even very complex and demanding setups
have been reported for online monitoring of starting materials and intermediates in
bioprocesses, e.g., HPLC with diode array detection coupled to an electrospray
tandem mass spectrometer (ESI-MS/MS [ 90 ]).
3.3.3 Capillary Electrophoresis
Capillary electrophoresis (CE) seems to be developing rapidly along with chro-
matographic methods because it can provide higher resolution and higher speed,
works with smaller samples, and needs less carrier liquid (buffer). It is more
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