Biomedical Engineering Reference
In-Depth Information
data or will a less frequent sampling rate suffice?” If the aim is to gain process
understanding for metabolites, but conventional off-line analyses or a more frequent
sampling rate, enabled by an autosampling system will meet the requirements, then a
probe may not be the best tool of choice. It is reasonable to assume that unless the overall
objective of the tool is to use the output to control the process such as optimizing nutrient
feed times, evacuation or neutralization of deleterious by-products, or continuous
monitoring of certain critical process parameters on which process control will be
implemented, then an in-line solution may not be required. With in-line probes, there are
amultitude of risks that should be assessed prior to implementation that include cleaning,
validation, maintenance, training, process appropriate model construction, and, in the
case of cell culture, risk of bioreactor contamination.
12.2.3 Online Analytics
Sterile Sampling Systems.
Online sterile sampling systems are the linchpin in
successfully interfacing conventional off-line analytics with microbial fermenters and
cell culture bioreactors. Sampling can be passive and rely on gas or fluid dynamics to
deliver it to the analytical device or it can be active and use any number of pumping
mechanisms such as peristaltic or syringe pumps to actively pull the sample from the
tank and then push it into the analytical device. In fact, a group was formed to
specifically address these problems in the late 1990s at the University of Washington
Center for Process Analytical Chemistry called NeSSI
(New Sensor and Sampling
Initiative). It is a consortium of academia, instrument manufacturers, and industry
users to help design, build, and test new sampling and test devices. It focuses on
standardization and miniaturization of online sampling and analytics and has slowly
infiltrated areas beyond its initial chemical and petrochemical industry roots to find
applications in the automotive, food, and pharmaceutical and biopharmaceutical
industries.
When online sampling devices are coupled to bioprocesses, a reasonable level of
assurance for the prevention of microbial contamination must be provided to prevent
potential contamination from either backflow, once the sample stream passes the reactor
barrier or leaks at the port of entry. These devices are increasingly making their way into
biopharmaceutical development lab fermenters and bioreactors where they are being
coupled with existing analytical instrumentation to gain new insights into the process
during the development phase of amolecule. Apassive sampling device coupled to an ion
chromatography HPLC with a pulsed amperometric detector was used by Larson et al.
[26] to monitor amino acids and glucose during the course of a bioreactor run. A syringe
pump-driven sampling device was coupled to a conventional HPLC to yield information
such as amino acid consumption during the course of a reactor run [8] and even some
product quality attributes with the addition of two-dimensional HPLC (Fig. 12.4).
Monoclonal antibody development, in particular, is conducive to the two dimen-
sional HPLC approach from bioreactor streams, as the first dimension separation is
usually an affinity separation such as protein A or proteinG chromatography. This is then
followed by a second dimension separation that monitors a particular quality attribute
such as ion exchange, reverse phase, or size exclusion. With these tools, it is then easier
