Performance Verification Statement for the In-Situ Troll 9500 pH Sensor

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Ref. No. [UMCES] CBL 2015-011
ACT VS15-04
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RESULTS of MOORED FIELD TESTS
Moored field tests were conducted to examine the performance of the In-Situ Troll 9500
pH sensor to consistently track natural changes in pH over extended deployment durations of 4-8
weeks. In addition, the field tests examined the reliability of the instrument, i.e., the ability to
maintain integrity or stability of the instrument and data collections over time. Reliability was
determined by quantifying the percent of expected data that was recovered and useable. The
performance of the Troll 9500 was examined in four separate field deployment tests at various
ACT Partner test sites to include a range of biogeochemical conditions. The range and mean for
temperature and salinity for each test site is presented in Table 2. The final reference
temperature data was computed from the mean of two RBR thermistors and the SeaBird SBE
that were mounted at the same sampling depth as the test instrument. The reference temperature
data and salinity were used to compute ambient pH results from the laboratory results using a
CO2-Sys program (Pierrot et.al. 2006). Immediately before each deployment the test instrument
was exposed to a certified or internal reference sample for 3-4 measurements to confirm good
working status and provide an initial offset against its latest calibration (Table 3).
Table 2. Range and average for temperature, and salinity at each of the test sites during the sensor field
deployment. Temperature and salinity were measured by two RBR temperature loggers and a SeaBird
SBE 26 (or SBE26plus) mounted on the instrument rack and the duration of the deployment.
SITE
(deployment period/duration)
Temperature
( 0C )
Salinity
Moss Landing Harbor Min. 14.9 30.7
26Aug – 22Sept Max. 18.6 33.7
(n = 28 days) Mean 16.6 33.0
Kaneohe Bay Min. 22.3 32.8
15Nov – 10Feb Max. 26.5 35.2
(n = 88 days) Mean 24.5 34.4
Chesapeake Bay Min. 3.4 9.3
12Mar – 10Apr Max. 10.1 14.0
(n = 30 days) Mean 5.9 12.8
Lake Michigan Min. 11.6 0.024
21Jun – 19Jul Max. 24.9 0.035
(n = 29 days) Mean 21.2 0.031
Table 3. Results of the pre-deployment check for the Troll 9500 at each deployment site. The stated pH
of the reference solution is based on ACT’s spectrophotometric analysis completed at the time of
exposure. Seawater CRM was provided by Andrew Dixon’s Lab (Scripps Institution of Oceanography).
NIST buffer was prepared by ACT from salts supplied by Kenneth Pratt, NIST.
Deployment Site Ref Solution Measurement
Temperature
Reference
Solution pH
Instrument pH
MLML Seawater CRM 20 oC 7.97 7.99
HIMB Seawater CRM 25 oC 7.86 7.94
CBL Seawater CRM 20 oC 8.00 7.95
GLERL NIST Buffer 20 oC 9.23 9.21