Hach DR/850 Procedures Manual page 352

PHOSPHORUS, REACTIVE,
Method Performance
Precision
Estimated Detection Limit (EDL)
Interference
Summary of Method
In a single laboratory using a standard solution of 1.00 mg/L
PO and two lots of reagents with the instrument, a single
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operator obtained a standard deviation of ±0.05 mg/L PO
In a single laboratory using a standard solution of 1.00 mg/L
PO and two representative lots of AccuVac ampuls with the
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instrument, a single operator obtained a standard deviation of
±0.03 mg/L PO
The EDL for program 79 is 0.05 mg/L PO
on the estimated detection limit, see Section 1.
Interfering Substance
Aluminum
Arsenate
Chromium
Copper
Hydrogen sulfide
Iron
Nickel
Silica
Silicate
Turbidity or color
Zinc
Highly buffered
samples or extreme
sample pH
Orthophosphate reacts with molybdate in an acid medium to
produce a Phosphomolybdate complex. Ascorbic acid then
reduces the complex, giving an intense molybdenum blue color.
continued
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Interference Levels and Treatments
Greater than 200 mg/L
All levels
Greater than 100 mg/L
Greater than 10 mg/L
All levels
Greater than 100 mg/L
Greater than 300 mg/L
Greater than 50 mg/L
Greater than 10 mg/L
Large amounts may cause inconsistent results in the test
because the acid present in the powder pillows may dissolve
some of the suspended particles and because of variable
desorption of orthophosphate from the particles. For highly
turbid or colored samples, add the contents of one Phosphate
Pretreatment Pillow to 25 mL of sample. Mix well. Use this
solution to zero the instrument.
Greater than 80 mg/L
May exceed the buffering capacity of the reagents and require
sample pretreatment.
pH 2 to 10 is recommended.
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