70
International, Lutterworth, UK, 229-0592. Clips, tub-
ing—40 mm: VWR International, Lutterworth, UK, 229- 0593.
Keck ramp clamp tubing clamps—3/8′′: Cole-Parmer, Hanwell,
London, UK, KH-06835-07. Keck ramp clamp tubing
clamps—1/4′′: Cole-Parmer, Hanwell, London, UK,
KH-06835-03.- Store the pH probes in 3 M KCl and rinse with distilled water
before use. Oxygen probes are stored dry. Change the mem-
brane on the oxygen probe and refill with fresh electrolyte
when the membrane has lost integrity and/or when the elec-
trolyte level is low. - There are three thicknesses of tubing. To achieve a precise flow
rate the internal diameter of the tubing that runs through the
medium pump head should have a bore width of no more than
1 mm. However, thicker tubing with a wider bore width of
4 mm is used for the medium and effluent lines, and the thick-
est tubing with a bore width of 6 mm is used for all gaseous
inlets and outlets. - Dead ends (some of which will be used for drawing off medium
or cell samples), such as air outlets, sample port side arms,
waste bottles, collection bottles and medium bottles, flow rate
measurement devices, also need to be fitted with vent filters to
ensure that gas can be released continuously from the culture
during growth and pressure does not build up in the vessel.
The air outlet/off-gas line can be fed into a CO 2 analyzer for
measurement of CO 2 levels. - Do not calibrate oxygen probes before autoclaving because the
electrolyte is affected by the heat. Oxygen is only transferred
evenly throughout the culture if it is stirred or shaken effec-
tively. Standing cultures of M. tuberculosis will result in micro-
environments in which the oxygen levels will be very low
reaching microaerophilic or anaerobic levels. - There is a pH/temperature compensation mode on the
Eycoferm controller to compensate for temperature differ-
ences because pH calibration is done at room temperature.
Fittings that are exposed to the acid or alkali should be made
of inert metal such as titanium to prevent corrosion caused
particularly by the acid. - The heat pad is electronically controlled by the Eycoferm con-
troller unit to maintain temperature at 37 °C. - The dissolved oxygen tension (DOT) is maintained by an
immediate response of the Eycoferm controller to a drop in
oxygen level, which in turn alters the stirrer speed to draw
more air into the medium. The Eycoferm controller unit auto-
matically controls the extent to which the culture is stirred via
a magnetic stirring device and a flea. A DOT of 10% is equiva-
Charlotte L. Hendon-Dunn et al.