Performance Verification Statement for the Campbell Scientific Instruments pH Sensor

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Ref. No. [UMCES] CBL 2015-008
ACT VS15-01
25
RESULTS of MOORED FIELD TESTS
Moored field tests were conducted to examine the performance of the Campbell
Scientific Instruments prototype pH sensor (CSI) 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 CSI 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 CSI at each deployment site. The pH of the
reference solution is based on ACT’s spectrophotometric analysis completed at the time of exposure.
Seawater CRM provided by Andrew Dixon’s Lab (Scripps Institution of Oceanography). NIST buffer
was prepared from salts provided by Kenneth Pratt (NIST).
Deployment Site Reference
Solution
Measurement
Temperature
Reference
Solution pH
Instrument pH
MLML Seawater CRM 20oC 7.97 7.95
HIMB Seawater CRM 25oC 7.86 7.72
CBL Seawater CRM 20oC 8.00 7.88
GLERL NIST Buffer 20oC 9.23 9.01