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Ref. No. [UMCES] CBL 2016-013
ACT VS16-04
13
for no less than 30 minutes.
(3) The sample was then rapidly fixed as a normal sample, and on the auto titrator.
(4) A global reagent blank taken as the mean of samples fixed at each test site (0.078 ± 0.020, n=5)
and used to correct all reference values.
RESULTS of LABORATORY TESTING
Instrument accuracy for the HOBO U26 RDO sensor was tested under nine combinations
of temperature and salinity over a range of DO concentrations from 10% to 120% of saturation.
Specific test conditions are summarized in Table 1. Results are plotted as a time series of
instrument readings against the time series of comparative Winkler reference samples (Figures A-
I). The bottom panel of each figure shows the time series of the difference in instrument
measurement versus corresponding reference sample (denoted as Delta’s). Comparisons of tank
duplicates taken at opposite sides of the tank from between 9-18 of the timepoints during each trial
showed a mean difference of 0.017 mg/L, with a range over the nine trials of 0.006 – 0.038 mg/L.
Those values are within the analytical precision of the reference method and indicate conditions
throughout the tank were very homogeneous. However, small changes in measured DO
concentrations did occur during some of the sampling phases indicating the tank was slightly
moderating after sparging was stopped. Those small drifts in DO concentrations were clearly
captured by both instrument and reference sample measurements.
Table 1.
Dissolved oxygen temperature and salinity challenge trial conditions. For each trial pre and post
measurements of tank temperature (
o
C) and salinity (S) were made with an calibrated SBE26+4M CTD,
equilibrated in well mixed tank for 20 min until stable readings obtained.
Trial ID
Mean
Temperature
o
C
S.D.
Temperature
o
C
Mean
Salinity
PSU
S.D.
Salinity
PSU
Levels of
DO tested
mg/L
Figure
for
HOBO
L_T15_S00
15.44
0.03
0.00
0.000
0, 2, 5,9,10,14
A
L_T15_S10
15.47
0.01
8.82
0.003
0, 2, 8, 9, 13
B
L_T15_S35
15.39
0.03
34.20
0.009
0,2,6,8,12
C
L_T04_S00
5.40
0.08
0.00
0.000
0,4, 12, 17
D
L_T04_S10
5.30
0.03
8.98
0.009
0, 5, 12, 16
E
L_T04_S35
5.23
0.07
34.77
0.073
0, 4, 10, 14
F
L_T30_S00
30.22
0.03
0.00
0.000
0, 3, 5, 9
G
L_T30_S10
30.51
0.12
9.28
0.036
0, 3, 7, 10
H
L_T30_S35
30.61
0.07
34.43
0.050
0, 2, 6, 9
I
The mean and standard deviation of the differences between the HOBO U26 RDO and
reference measurements for each trial (n = 36 - 51) are presented in Table 2.
Explanations for the
difference between observed and possible comparative observations for the Lab trials are noted in
the respective figure legends. Mean difference among trials ranged from 0.047 to 0.314 mg/L over
all nine trials. There was a slight decrease in the magnitude of the differences across both
temperature and salinity levels (Table 2).