Aquaprobe
®
AP-700, AP-800 & AP-2000 Instruction Manual
10401-00870 Rev R
16.5.4.
Calibration Solution Preparation
In order to 'calibrate' (actually, set the relative sensitivity) of the BGA-PC electrode, a
100µg/L calibration solution of fluorescent dye known as Rhodamine WT should be used.
This is exactly the same calibration solution that is recommended for calibration of the
RHOD electrode.
Please note: there is no direct correlation between Rhodamine concentration and the
number of BGA-PC cells/mL. Rhodamine is used as a convenient dye for setting the
sensitivity of the sensor. The subsequent display of BGA-PC in terms of cells/mL is a
generalisation based on research and experience. The only way to obtain a true value in
terms of cells/mL is to correlate the values from the Probe to quantitative data that has
been obtained by laboratory analysis of grab samples, then to apply a Grab Sample Factor.
See previous 'Limitations of Use' section.
The 100µg/L calibration solution should be freshly prepared by serial dilution from 200g/L
standard using deionised water. The following Rhodamine WT standard is recommended:
Part number: 70301027
Description: Rhodamine WT Liquid
Supplier: Keystone Europe Ltd.
Contact:
http://www.dyes.com
Be sure to handle chemicals with care and to read and comply with all health and
safety advice.
16.5.5.
Serial Dilution
The recommended Rhodamine solution is supplied as a 20% or 200g/L solution, dilution of
the stock solution should be carried out as follows.
200g/L stock → 100μg/L is recommended to be done as a two step dilution procedure.
Step 1:
weigh out 0.5g of 200g/L stock solution in a weigh boat and add this to 1L of
deionized water in a volumetric flask, use some of the water from the 1L flask to rinse the
weigh boat so no stock Rhodamine remains on the boat. Put a lid on the 1L flask and
invert 10 times.
This step results in a 1 in 2000 dilution of the stock. At this point the 1L flask will contain a
100mg/L solution.
Step 2:
Transfer 1ml of the 100mg/L solution to a 1L volumetric flask and top up to 1L with
deionized water. Put a lid on the 1L flask and invert 10 times.
This step results in a 1 in 1000 dilution of the solution from step 1. The concentration of
this solution is 100μg/L. This solution can now be used as Pt-2 calibration of the BGA-PC
sensor.
The dilute solution can be stored in a dark bottle in a refrigerator for up to five days. After
that time it must be discarded.
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