In concluding work, a subset of 124 natural-water samples
received at the USGS NWQL from August 3-9, 2000, were
determined for nitrate+nitrite by the CdR andNaRmethods
on August 9, 10, and 11, 2000. Linear regression of CdR
method data (x) in relation to NaR method data (y) resulted
in a slope of 1.005 ( 0.002 and a y-intercept of 0.001 ( 0.003.
The correlation coefficient r2 was 1.00 ( 0.03 and highly
significant (p < 0.0001). The difference between means of
nitrate + nitrite concentrations determined by the CdR and
NaR methods was -0.004 mg-N/L, which on the basis of a
paired t-test (degrees of freedom ) 123; t-value ) -1.457;
p-value ) 0.1477) was not significantly different from zero
at the p)0.05 level.Asubset of these data (101 paired results)
with nitrate + nitrite concentrations in the range of 0.01-
5.00 mg-N/L plotted on a log-log scale scattered about the
line of equal correlation is shown in Figure 6