factor of the NaR method. MDLs for both methods exceed
requirements for the 0.05-5.00 mg-N/L reporting range of
USGS method I-2545-90. Tables 4 and 5 provide spike
recovery results for seven natural-water samples with ambient
nitrate concentrations in the range of 0.02-4.4 mg NO3
- -
N/L. These samples were spiked at a level of 0.25mgofNO3
- -
N/L by adding 50 íL of a 1+9 dilution of the stock nitrate