Hach PHOSPHAX sigma High Range, Руководство пользователя

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English 7
Theory of operation
Theory of operation
In an acidic solution with molybdate ions in the presence of antimony ions,
orthophosphate ions create a complex that can be reduced to phosphorus molybdenum
blue using ascorbic acid. The intensity of the color is proportional to the volume of
orthophosphate contained in the sample in the given measurement range.
Polyphosphate and some organic phosphorus compounds can be hydrolyzed to
orthophosphate by heating in a strong acidic solution. Resistant phosphorus compounds
are digested with sodium persulfate. Temperatures well in excess of 100 °C (212 °F) and
high pressures are obtained with the
PHOSPHAX sigma HR . Such short digestion times
can only be achieved under these extreme conditions.
Determination of total phosphate
• The cuvette is rinsed with the sample and reagent B.
• Reagent A, reagent B and the homogenized sample are pumped into the cuvette and
mixed.
• The solution is then briefly heated under pressure and immediately cooled again. The
phosphorus compounds are split into orthophosphate.
• Reagents C and D are pumped into the cuvette and mixed.
• The intensity of the blue coloration is measured photometrically.
Determination of orthophosphate (depending on design)
• The cuvette is rinsed with the sample and reagent B.
• Reagent A is pumped into the cuvette, heated and cooled again, which creates
sulfuric acid.
• The homogenized sample and reagents B, C and D are pumped into the cuvette and
mixed.
• The intensity of the blue coloration is measured photometrically.
Disruptions
The ions listed in the table below were checked individually up to the given concentrations.
The overall effect as well as the influence of other ions was not recorded. The following do
not cause disruption:
40 g/L SO
4
2–
200 mg/L J
–
20 g/L Cl
–
100 gm/L SiO
2
8 g/L K
+
, Na
+
80 gm/L Hg
2+
2 g/L Ca
2+
50 gm/L Sn
2+
800 mg/L Mg
2+
40 mg/L Pb
2+
400 mg/L
CO
3
2–
, NO
2
–
, Fe
3+
, Fe
2+
, Cd
2+
, NH
4
,
AL
3+
, Zn
2+
, Cu
2+
, Co
2+
, Ni
2+
, Mn
2+
20 mg/L Ag
+
, Cr
3+
2 mg/L Cr
6+