Sampling And Storage; Interferences - Hach POCKET COLORIMETER II Instruction Manual

Digestion for Total Phosphorus,
continued

Sampling and Storage

Collect samples in plastic or glass bottles that have been acid-cleaned with
1:1 Hydrochloric Acid Solution and rinsed with deionized water. Do not use
commercial detergents containing phosphate for cleaning glassware used in
this test.
Analyze samples immediately after collection for best results. If prompt analysis is
impossible, preserve samples up to 48 hours by storing at or below 4 °C. Warm to
room temperature before testing.

Interferences

For turbid samples, use 50 mL of sample and double the reagent quantities. Use
25 mL of the digested sample to zero the instrument in the reactive phosphorus
procedure. This compensates for any color or turbidity destroyed by this procedure.
For alkaline or highly buffered samples, it may be necessary to add more acid in
step 3 to drop the pH of the solution below 1.
1—35