YSI 600DW-B Sonde - Manual (Page 237)

Principles of Operation Section 5
present at the site, the quality of the data obtained with a rhodamine WT sensor that has no capability of
mechanical cleaning may be compromised. Like the 6026 /6136 turbidity and 6025 chlorophyll probes
described above, the 6130 rhodamine WT probe is equipped with a mechanical wiper that makes it ideal for
unattended applications. The wiper can be activated in real-time during discrete sampling operations or
will function automatically during long term unattended sampling studies. The number of wiper
movements and the frequency of the cleaning cycle for the unattended mode can be set in the sonde
software. Generally one movement is sufficient for most environmental application, but in media with
particularly heavy fouling, additional cleaning cycles may be necessary.
CALIBRATION AND EFFECT OF TEMPERATURE
The sonde software offers the option of 1 point, 2 point, or 3 point calibrations procedures. For most
applications, a 2-point calibration at 0 and 100 ug/L is sufficient. However, for maximum accuracy over
the entire 0-200 ug/L range of the sensor, a 3-point calibration procedure can slightly enhance the accuracy
of the sensor. Note that YSI does not offer rhodamine WT standards, but does suggest a vendor for user-
production of standards and, later in this section, provides instructions for preparing a solution which is 100
ug/L in Rhodamine WT.
While the effect of temperature on the rhodamine sensor and electronics is small, the fluorescence of
rhodamine WT changes significantly with temperature. The combination of the two factors is
automatically taken into account by the sonde software providing temperature compensated readings.
RHODAMINE WT STANDARD SOLUTION – PREPARATION AND USE
CAUTION: Before using concentrated rhodamine WT solution to prepare standards, be certain to read
the safety instructions provided by the supplier with this chemical. Remember that only trained
personnel should handle chemicals.
PREPARATION
Use the following procedure to prepare a 100 ug/L solution that can be used to calibrate your rhodamine WT
sensor for field use:
1. We recommend that rhodamine WT concentrate be purchased from Keystone Aniline Corporation, 2501
W. Fulton Street, Chicago, IL 60612 (Telephone: 312-666-2015) under the name KEYACID
RHODAMINE WT LIQUID (Part # 70301027). As purchased, the solution is approximately 20 %
rhodamine WT by weight, i.e., 200 g/L.
2. Accurately weigh 0.500 g of the 20 % rhodamine concentrate, quantitatively transfer the viscous liquid to
a 1000-mL volumetric flask and fill the flask to the top graduation. This solution contains 100 mg of
rhodamine WT per 1000 mL of water.
3. Accurately transfer 1.0 mL of the solution prepared in the above step to a 1000 mL volumetric and then
fill the flask to the top graduation with purified water. Mix well to obtain a solution that is 100 ug/L
(0.10 mg/L) in water (a 1000:1 dilution of the concentrated solution).
YSI Incorporated Drinking Water Monitoring Systems Operation Manual 5-24