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Interferences
Interfering Substance
Aluminum
Arsenate
Chromium
Copper
Hydrogen sulfide
Iron
Nickel
Silica
Silicate
Turbidity
Zinc
Highly buffered samples or
extreme sample pH
Treating Analysis Labware
Cleaning the Pour-Thru Cell
Reagent Preparation
PhosphorusReac_PT_Low_ASC_Eng_Ody.fm
200 mg/L
Interferes
100 mg/L
10 mg/L
Interferes
100 mg/L
300 mg/L
50 mg/L
10 mg/L
Samples with large amounts of turbidity may give inconsistent results because the acid present
in the reagents may dissolve some of the suspended particles and variable desorption of
orthophosphate from the particles may occur.
80 mg/L
May exceed the buffering capacity of the reagents and require sample pretreatment; see Section
3.3 Interferences on page 41.
All labware used in this test must be thoroughly cleaned to remove all traces of
phosphate. Clean containers with a non-phosphate detergent followed by a rinse
with deionized water. Fill and soak for 10 minutes with a 1:25 dilution of
Molybdate Reagent in deionized water. Rinse well with deionized water. Keep
containers tightly closed when not in use. Treat the Pour-Thru Cell with this
same mixture of molybdate and water followed by thorough rinsing with
deionized water.
Dedicate these containers for low-level phosphate analysis. If these containers
are rinsed and capped after use, only occasional pre-treatment is necessary.
The Pour-Thru Cell may accumulate a buildup of colored products, especially if
the reacted solutions are allowed to stand in the cell for long periods after
measurement. Remove the color by rinsing with a 1:5 dilution of Ammonium
Hydroxide (Cat. No. 106-49), followed by several deionized water rinses. Invert
a beaker over the glass funnel of the cell when not in use.
The Ascorbic Acid reagent must be prepared before use. Using a powder funnel,
add the contents of one 48 g bottle of Ascorbic Acid Reagent Powder
(Cat. No. 26512-55) to one 450 mL bottle of Ascorbic Acid Reagent Dilution
Solution (Cat. No. 25999-49). Invert several times and swirl until the powder is
completely dissolved.
This solution may develop a yellow color with time but will still give accurate
results for up to one month after mixing if stored at 20–25 °C. Record the date of
preparation on the bottle and discard any remaining solution after one month.
Do not add fresh reagent to previously mixed reagent. Use of this reagent after
one month may result in high reagent blanks and low values at high
concentrations.
Phosphorus, Reactive
Interference Levels and Treatments
Phosphorus, Reactive
Page 3 of 6
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