WPI ISO-HPO-2, Руководство пользователя

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4 World Precision Instruments
8. Allow the sensor to polarize for at least 2 hours to reach a stable baseline current
of about 800–900pA before it is used for measurement.
9. During initial polarization the current is typically high, but within an hour it will be-
gin to decrease rapidly. After several hours the current will fall. The range should
always be set to 10nA, regardless of how low the baseline falls.
10. In two hours or less, the sensor should achieve a stable baseline current value.
A typical baseline value is about 800–900pA. At this time, the sensor is ready for
calibration. If the baseline value does not drop within 2 hours, see “Replacing the
Membrane Sleeve” on page 7.
NOTE : This polarization procedure assumes the temperature is 25ºC. At 37ºC the
baseline current is higher.
Calibrating the Sensor
Hydrogen peroxide (H
2
O
2
) is a very important product in the biological system. The
determination of H
2
O
2
requires an accurate method of calibration. Amperometeric
(electrochemical) determination using the TBR4100/1025 is a very reliable method to
measure H
2
O
2
. The instrument measures the amount of H
2
O
2
oxidized on the surface
of the sensor using a poise voltage of +450mV. The oxidation of H
2
O
2
at the sensor
surface produces a small current (pA), which is detected by the TBR4100/1025 .
The amount of current produced is linearly proportional to amount of H
2
O
2
in the
experiment.
Items Required
• One glass vial
• 1.0mM H
2
O
2
. standard solution (To make standard solution, see “Making Standard
1mM HPO Solution” on page 4.)
• 0.1M PBS buffer solution (PBS buffer tablets) (To make standard solution, see
“Making of 0.1M PBS Buffer Solution” on page 5.)
NOTE : The multi-port measurement chamber (WPI # NOCHM-4 ) can be used as
an alternative calibration kit, specifically for use at different temperature condition.
Calibration temperatures from 4 - 40°C can be controlled using an external circulating
bath (contact WPI for information).
Making Standard 1mM HPO Solution
Hydrogen peroxide solution is commercially available and is commonly sold with
a stabilizer compound in solution. Usually these solutions are within a known
concentration range (for example, 2-4% H
2
0
2
). There are many published procedures
for standardizing H
2
O
2
solutions, such as the titration method using potassium
permanganate. The H
2
O
2
sensor can detect low nM concentrations, so, WPI
recommends the following procedure.
1. Weigh 67.5mg Acetanilide (Sigma-Aldrich 397237) and dissolve it into 250mL of
deionized water in a volumetric flask.
2. Remove 1mL of this solution and put it in a clean container.