Performance Verification Statement for the Eureka Manta2 pH Sensor

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Ref. No. [UMCES] CBL 2015-009
ACT VS15-02
14
RESULTS of MOORED FIELD TESTS
Moored field tests were conducted to examine the performance of the Eureka Manta 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 Manta 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 1. 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 2. Results of the pre-deployment check for the Manta 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 provided by Andrew Dixon’s Lab (Scripps Institution of Oceanography). NIST buffer
prepared by ACT personnel from salts supplied by Kenneth Pratt (NIST).
Deployment Site Reference
Solution
Measurement
Temperature
Reference
Solution pH
Instrument pH
MLML Seawater CRM 20 oC 7.97 8.04
HIMB Seawater CRM 25 oC 7.86 7.93
CBL Seawater CRM 20 oC 8.00 8.05
GLERL NIST Buffer 20 oC 9.23 9.14