Annexes
3.3. Orthophosphates
REAGENTS
A. Ammonium heptamolybdate solution (1 liter)
Required chemicals: Potassium antimony(III)
oxide tartrate ............ 230 mg.
K2(SbO)2C8H4O10.3H2O
Sulfuric acid # ............ 69.4 ml.
H2SO4 (95‐97%)
Ammonium
heptamolybdate .............. 6 g.
(NH4)6Mo7O24.4H2O
Distilled water
H2O
FFD6 ............................... 2 ml.
Preparation: Dissolve the potassium antimony(III)
oxide tartrate in ± 800 ml distilled water. Add
carefully, while constant swirling and
cooling the sulfuric acid. Add the ammonium
heptamolybdate and dissolve.
Fill up to 1 liter with distilled water, add the FFD6
and mix.
Note: Do not use metal spoons for ammonium
heptamolybdate. The sensitivity can be increased by
50% by using 35 ml concentrated sulfuric acid
instead of 69.4 ml. With the 35 ml the interference
of the silicate is 10% for 300 ppb Si and 10% for 10
ppm Si in a range of 100 μg P/liter. The end pH
must be < 1. Solution is stable for 5 days. Store at
4°C when the solution is not used.
B. L(+)Ascorbic acid solution (1 liter)
Required chemicals: L(+)Ascorbic acid ......... 11 g.
C6H8O6
Acetone ........................ 60 ml.
C3H6O
Distilled water
H2O
FFD6 ............................... 2 ml
C. Rinsing liquid sampler
Required chemicals: Distilled water
H2O
STANDARDS
Stock solution 100 mg P/liter (1 liter)
Required chemicals: Potassium dihydrogen
phosphate .............. 439.4 mg.
KH2PO4
Distilled water
H2O
Preparation: Dissolve the ascorbic acid in ± 800 ml
distilled water. Add the acetone. Fill up to 1 liter
with distilled water, add the FFD6 and mix.
Note: Solution is stable for 5 days. Store at
4°C when the solution is not used.
Note: For sea water samples, adjust the salinity of
the rinsing water sampler to the same level as the
salinity of the sea water samples when matrix peaks
reach the same level as the detection limit. Use ultra
pure sodium chloride or “zero” seawater for
adjustment. Refresh weekly.
Preparation: Dissolve the potassium dihydrogen
phosphate in ± 800 ml distilled water. Fill up to 1 liter with
distilled water and mix.
Note: Solution is stable for 4 weeks. Store at
4°C when the solution is not used.