Photon Systems Instruments FMT150 - Page 39

© PSI (Photon Systems Instruments), spol. s r. o.
39
Chemical solution
• Electrolyte solution as supplied with the CO
2
membrane kit.
• Deionized water for preparing standard solutions.
• 32% HCl for pH adjustment.
• Standard 20 µM solution of NaHCO
3
and Na
2
CO
3
(78.24 mg of NaHCO
3
and 98.59 mg of Na
2
CO
3
in final volume of
200 ml of deionized water). The calibration solution can be used immediately or can be stored in closed air tight
vials for longer time and future calibrations.
• N
2
gas source for CO
2
removal from solutions used for calibration.
• CO
2
electrode storage solution. Prepare as follows: Dissolve 5.8 g sodium chloride (NaCl) in about 200 ml deionized
water and make up to 1,000 ml.
Calibration procedure
• Calibration and sample solutions should always be kept at the same temperature (if other vessel than PBR vessel
is used for calibration it should be thermally insulated from possible heating by the magnetic stirrer). If the PBR
vessel is used the solution within the vessel should be maintained at the temperature of the experiments.
• All measurements should be carried out under the same stirring conditions, i.e. identical stirring bars, identical
distance between electrodes and stirring bars, etc.
• When not in use, the CO
2
electrode should always be kept immersed in the storage solution.
• In all calibration and sample solutions the ionic strength should be the same, and should not exceed a maximum
value of 1.0 mol.l
-1
. During the calibration the pH value should be less than 4.0. This is achieved by adding HCl to
the solution in the vessel during calibration resulting in release of all of the CO
2
available from the calibration
solution.
• The electrode should not be immersed to a depth greater than the length of the membrane module, i.e. not more
than 6 cm.
• During the calibration procedure the photobioreactor vessels should be completely filled with liquid and be closed
to avoid any CO
2
gas loss from the system.
• If the calibration of the CO
2
probe is done in a different vessel than the photobioreactor vessel, please ensure that
it is done at the temperature of the experiment, with good stirring and in a container that can be closed to the
atmosphere to prevent loss of CO
2
gas.
Determining carbon dioxide content
• Prepare deionized or distilled water. Adjust pH of distilled water to pH=3 with HCl and place it overnight in 90 °C
water bath to remove any CO
2
gas remaining in the water (please note: Keep the lid of the container loose to
allow the CO
2
to escape from the bottle while in water bath).
• After removal of deionized water from the water bath use the N
2
gas and bubble the deionized water for at least
three hours while it is coming to experimental temperature.
• Assemble the electrode according to manufacturer´s guidelines and place it in the vessel.
• Weigh out the required amounts of NaHCO
3
and Na
2
CO
3
as mentioned above for 20 µM concentration and dry it
for 2 hours in 200 °C in the drier before preparing the standard solution with deionized water. Keep the standard
solutions closed.
• Determine the maximum volume of the vessel that will be used for the calibration. To do this, take the vessel
which will be used for the calibration and fill it completely with water. Assemble the vessel with the lid and all the