Are there instructions available for setting up a seawater calibration for Nitrate Cadmium Reduction methods?

Document ID

Document ID TE6973

Published Date

Published Date 25/01/2018
Question
Are there instructions available for setting up a seawater calibration for Nitrate Cadmium Reduction methods?
Summary
Instructions for nitrate cadmium reduction seawater calibration
Answer
These instructions are also provided in Nitrate Cadmium Reduction LR Method 8192, Nitrate Cadmium Reduction Method 8039, and Nitrate Cadmium Reduction Method 8171.

Seawater calibration

Chloride concentrations above 100 mg/L cause low results. To use this method for samples with high chloride concentrations, calibrate the instrument with nitrate standard solutions that contain the same amount of chloride as the samples. Prepare calibration standards that contain chloride and 1.0, 3.0, 5.0 and 10.0 mg/L nitrate (as NO 3 –N) as follows:
  1. Prepare 1 liter of chloride water that has the same chloride concentration as the samples.
    1. Weigh the applicable amount of ACS-grade sodium chloride: (chloride concentration of samples in g/L) x (1.6485) = g of NaCl per liter. Note: 18.8 g/L is the typical chloride concentration of seawater.
    2. Add the sodium chloride to a 1-liter volumetric flask.
    3. Dilute to the mark with deionized water. Mix thoroughly. Use this water as the dilution water to prepare the nitrate standard solutions.
  2. Use a pipet to add 1.0, 3.0, 5.0 and 10.0 mL of a 100 mg/L nitrate-nitrogen (NO3–N) standard solution into four different 100-mL Class A volumetric flasks.
  3. Dilute to the mark with the prepared chloride water. Mix thoroughly.
  4. Complete the test procedure for each of the standard solutions and for the prepared chloride water (for a 0-mg/L standard solution).
  5. Measure the absorbance of the standard solutions and enter a user calibration into the instrument.
  6. Use the user program to measure samples that contain high concentrations of chloride.