53 / 73
Ref. No. [UMCES] CBL 2015-014
ACT VS15-07
53
A cross-plot of the matched observations of EXO-pH1 and reference pH is given in
figure 28. The linear regression was statistically significant (p<0.001, r
2
=0.85) with a slope of
1.04 and an intercept of -0.35.
Figure 28.
GLERL field response plot for the Xylem EXO pH 1 instrument compared to reference pH
Total
samples. Fine dotted line represents 1:1 correspondence.
Time series results of the EXO-pH2 and corresponding reference pH results are given in
figure 29. Ambient pH measured by the EXO-pH2 ranged from 7.88 to 8.61, compared to the
range measured from reference samples of 8.013 to 8.526. The bottom panel presents the time
series of the difference between instrument and reference pH measurements for each matched
pair (n=98 observations). The average and standard deviation of the difference between EXO-
pH2 and reference pH over the total deployment was -0.02 ± 0.04 with a total range of -0.17 to
0.05.