Xylem 6-Series Multiparameter - Manual (Page 277)

Principles of Operation Section 5
YSI Incorporated Environmental Monitoring Systems Manual 5-39
CALIBRATION METHODS
For calibration of the YSI BGA-PE Probe, only one type of standard will assure the best possible accuracy
for field readings: a suspension of known PE-containing BGA cells. The BGA concentration of this
suspension should be determined by either cell counting or a pigment extraction of PE. However, most users
may not have cultures of BGA available prior to field studies for use in the 2-point calibration protocol
resident in the sonde firmware and thus the best “calibration” method usually comprises the following steps:
8. Prior to use in the field, place the sensor in clean water and perform a 1-point calibration at 0 cells/mL
9. Immerse the sonde in a dye standard (see below) and record the reading. Note that you are not
“calibrating” to the dye reading, only checking its value relative to the default sensitivity of the sensor.
10. While making your field readings (sampling or unattended studies), collect a few grab samples and
record the date/time and location where they were acquired.
11. Collect and transport your field sample according to Standard Methods to ensure the BGA cells contained
in the sample are not damaged or significantly changed since the time of collection.
12. On return to the laboratory, analyze the grab samples for the amount of PE-containing BGA and record
the results for later use.
13. After the study is complete, place your YSI BGA-PE data in the column of a spreadsheet and place your
laboratory data in an adjacent column for comparison. Calculate ratios of field to laboratory results for
each grab sample point and then average the results to produce a ratio for adjustment (or
„postcalibration”) of your field results into more accurate values.
14. Use the calculating power of the spreadsheet to multiply all of your field readings by the correction ratio
to obtain the best possible accuracy for your 6132 data.
A variation of this method is to perform a 2-point calibration prior to deployment using a clear water and a
dye standard, setting the apparent PE-containing BGA equivalent of the dye standard to the value shown in
the table in the next section . However, it must be emphasized that this technique does not increase the
accuracy of the PE sensor significantly over the simple 1-point calibration recommended above – the user still
must collect grab samples and perform laboratory analysis to be assured of meaningful BGA-PE values. The
primary utility of the dye is to check for sensor drift during deployment by reanalyzing the dye solution after
sonde recovery. The use of the 2-point dye calibration procedure may make it easier to quantify the
predeployment dye value and, if so, may be preferable. Remember, however, that no real enhancement of
sensor accuracy is attained by using the dye as a calibrant.
PREPARATION OF RHODAMINE WT SOLUTIONS FOR CHECKING
SENSOR DRIFT
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.
Use the following procedure to prepare an 8 ug/L solution that can be used to “calibrate” your YSI 6132 PE
Probe 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.