Hach DR2400 - Page 673

Phosphorus, Total
Phosphorus, Total
PhosphorusTot_TNT_High_MOL_Eng_Ody.fm Page 3 of 6
Interferences
Large amounts of sample turbidity may cause inconsistent results in the test
because the acid present in the reagents may dissolve some of the suspended
particles and because of variable desorption of orthophosphate from the
particles.
The following may interfere when present in concentrations exceeding these
listed below:
13. Install the 16-mm
adapter.
Note: See Section 2.6 in the
Instrument Manual for
installation details.
Place the sample vial into
the adapter.
14. Touch Zero.
The display will show:
0.0 mg/L PO
4
3–
15. Place the prepared
sample into the cell
adapter.
16. Touch Read.
Results will appear in
mg/L PO
4
3–
.
Zero
Read
Interfering Substance Interference Levels and Treatments
Arsenate Causes positive interference if the sample is heated.*
Iron, ferrous Blue color caused by ferrous iron does not interfere if iron concentration is less than 100 mg/L.
Molybdate Causes negative interference above 1000 mg/L.
Silica Causes positive interference if the sample is heated.
Extreme pH or highly
buffered samples
May exceed buffering capacity of the reagents. See Section 3.3 Interferences on page 41. Samples
may require pretreatment. Sample pH should be about 7.
Fluoride, thorium,
bismuth, thiosulfate or
thiocyanate
Cause a negative interference.
Temperature, Cold (less
than 18 °C)
Cause a negative interference.
Temperature, Hot (greater
than 25 °C)
Causes a positive interference.
Post-digestion samples should be brought to room temperature (18–25 °C) before the addition of
the Molybdovanadate Reagent or sodium hydroxide.
The following do not interfere in concentrations up to 1000 mg/L:
Pyrophosphate, tetraborate, selenate, benzoate, citrate, oxalate, lactate, tartrate, formate, salicylate, Al
3+
, Fe
3+
, Mg
2+
, Ca
2+
,
Ba
2+
, Sr
2+
, Li
+
, Na
+
, K
+
, NH
4
+
, Cd
2+
, Mn
2+
, NO
3
–
, NO
2
–
, SO
4
2–
, SO
3
2–
, Pb
2+
, Hg
+
, Hg
2+
, Sn
2+
, Cu
2+
, Ni
2+
, Ag
+
, U
4+
, Zr
4+
,
AsO
3
–
, Br
–
, CO
3
2–
, ClO
4
–
, CN
–
, IO
3
–
, SiO
4
4–
.
* Gentle warming of the sample to reach room temperature will not cause this substance to interfere.