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PHOSPHORUS, REACTIVE,
STATISTICAL EVALUATION
A single operator repetitively tested samples of two laboratory prepared
solutions, using one DR/700, matched sample cells and representative
lots of testing reagents. Testing 20.00 mg/L PO
samples, the standard deviation was ±0.11 mg/L PO
Testing zero concentration samples, the limit of detection was 0.27 mg/L
3-
PO
. The limit of detection was calculated as three times the standard
4
deviation when testing zero concentration samples (Adapted from
Analytical (Chemistry, 1980, 52, 2242-2249).
INTERFERENCES.
Sulfide interference may be removed by oxidation with Bromine Water
as follows:
a) Measure 25 mL of sample into a sample cell.
b) Add Bromine Water drop-wise with constant swirling until
permanent yellow color develops.
c) Add Phenol Solution drop-wise until the yellow color just disappears.
Proceed with Step 5.
Positive interferences are caused by silica and arsenate only if the
sample is heated. Negative interferences are caused by arsenate,
fluoride, thorium, bismuth, sulfide, thiosulfate, thiocyanate or excess
molybdate. Blue color is caused by ferrous iron but this does not affect
results if ferrous iron concentration is less than 100 mg/L.
Ions that do not interfere in concentrations up to 1000 mg/L are
pyrophosphate, molybdate, tetraborate, selenate, benzoate, citrate,
oxalate, lactate, tartrate, formate, salicylate, Al
3+
+
+
+
Sr
, Li
, Na
, K
+
2+
2+
Hg
, Hg
, Sn
, Cu
-
4-
IO
, SiO
.
3
4
Highly buffered samples or extreme sample pH may exceed the
buffering capacity of the reagents and require sample pretreatment; see
Interferences, pH (Section 1).
+
3+
2+
, NH
, Cd
, Mn
4
2+
2+
+
4+
, Ni
, Ag
, U
continued
3-
concentration
4
4
3+
3+
, Fe
-
-
, NO
, NO
, SO
3
2
4+
-
-
, Zr
, AsO
, Br
3
42-65
3-
.
2+
2+
2+
, Mg
, Ca
, Ba
2-
2-
2+
, SO
, Pb
,
4
3
2-
-
, CO
, C10
, CN
3
4
,
-
,
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