Is the 1.0 N HCl required for the Nitrate, UV Screening Method 10049?
UV screening method for Nitrate.
In method 10049 for Nitrate analysis using UV screening, the 1.0 N HCl adjusts the pH so the sample is always acidic and establishes a background baseline against which all future samples can be prepared. Leaving it out may have a positive or negative effect based on the pH sensitivity of other components present. Check this by running the sample with and without the HCl being present to see if there is a pH sensitivity of the sample water. Repeat with and without the acid on a standard to check for its effects on nitrate only. Calibration was done on nitrate standards using the HCl.