Hach DR/850 Procedures Manual page 374

PHOSPHORUS, ACID HYDROLYZABLE,
Interferences
d) Analyze each sample as described in the procedure. Use
5.0 mL of the prepared standard additions for each test;
the concentration should increase as follows: 0.2 mg/L,
0.4 mg/L, and 0.6 mg/L PO
e) If these increases do not occur, see Standard Additions in
Section 1 for more information.
Standard Solution Method
Obtain a 1.0 mg/L Phosphate Standard Solution listed under
Optional Reagents. Or, this can be prepared by pipetting 2 mL of
a Voluette Ampule Standard for Phosphate, 50 mg/L as PO
an acid washed Class A 100-mL volumetric flask. Dilute to the
mark with deionized water. Substitute this standard for the
sample and perform the procedure as described.
The following may interfere when present in concentrations
exceeding those listed below:
Substance
Aluminum
Arsenate
Chromium
Copper
Iron
Nickel
Silica
Silicate
Sulfide
continued
3- , respectively.
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Interference Level and Treatment
200 mg/L
Interferes at any level.
100 mg/L
10 mg/L
100 mg/L
300 mg/L
50 mg/L
10 mg/L
9 mg/L. Sulfide interference may be removed by
oxidation with Bromine Water as follows:
1. Measure 25 mL of sample into a 50-mL beaker.
2. Swirling constantly, add Bromine Water drop-wise
until a permanent yellow color develops.
3. Swirling constantly, add Phenol Solution dropwise
until the yellow color just disappears. Proceed with
step 1.
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3- , into
4