Sampling And Storage; Accuracy Check - Hach POCKET COLORIMETER II Instruction Manual

Sampling and Storage

Collect samples in clean glass or plastic bottles. If chlorine is present, add one drop
of 0.1 N Sodium Thiosulfate for each 0.3 mg/L Cl2 in a 1-liter sample. Preserve the
sample by reducing the pH to 2 or less with sulfuric acid (at least 2 mL). Store at
4 °C (39 °F) or less. Preserved samples may be stored up to 28 days. Warm samples
to room temperature. Neutralize with 5.0 N Sodium Hydroxide before analysis.
Correct the test result for volume additions by multiplying by final volume
(original volume plus additions) and dividing by original volume.

Accuracy Check

Standard Additions Method
1. Measure 25 mL of sample into each of three 25-mL mixing cylinders.
2. Use a TenSette
Standard, 10 mg/L as NH
3. Analyze a 10-mL portion of each solution as described in the procedure. The
ammonia nitrogen concentration should increase 0.08 mg/L for each 0.2 mL of
standard added (using the procedure without any sample dilution).
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pipet to add 0.2, 0.4, and 0.6 mL of Ammonia Nitrogen
–N to the three samples, respectively. Mix well.
3
Ammonia, Nitrogen,
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