The next phase of NaR method development involved
refinement of the analytical cartridge design. For the airsegmented
continuous-flow analyzer used in this work (1-mminternal diameter conduits), optimum air segmentation
frequency (n) and flow rate (F) are about 90 bubbles min-1
and 0.5-0.7 mL min-1, respectively (21). Benefits of using
less than optimum values for n and F (45 bubbles min-1 and
0.263 mL min-1) in preliminary experimentssreduced NaR
requirement, extended residence time in reaction coils,
reduced waste stream volumeswere offset by increased
sample interaction and poor hydraulic stability that degraded
precision of analytical results. Dilution of samples prior to
addition of NaR, therefore, was explored as ameansto achieve
a more favorable balanceamongreagent conservation, waste
reduction, and analytical performance.