15.5 min dwell times for the CdR and NaR methods are also
discernible in Figure 5. Interestingly,%I was less for the NaR
method than for the CdR method despite the 13-min longer
dwell time of the former. This fact indicates that analytical
stream dispersion in the dilution loop of the NaR analytical
cartridge is less than that resulting from unsegmented flow
through the PBCdR of the CdR analytical cartridge.
A natural-water sample with low nitrate and nitrite
concentrations was used to estimate method detection limits
(MDL) for the nitrite (0.001 mg-N/L), CdR nitrate + nitrite
(0.003 mg-N/L), and NaR nitrate + nitrite (0.006-N/L)
methods. These values were calculated according to the
USEPA method (26) as indicated in Table 3. The difference
between MDLs for the two nitrate + nitrite methods is
consistent with the approximately 2-fold higher dilution