SKALAR METHODS
ANALYSIS: ORTHO‐PHOSPHATE
RANGE: 5 ‐ 200 µg P/liter
SAMPLE: SEA WATER
SAN++
Catnr. 503‐010w/r issue 032613/MH/99279552
PRINCIPLE
The automated procedure for the determination of ortho‐Phosphate is based on the following reaction;
ammonium heptamolybdate and potassium antimony(III) oxide tartrate react in an acidic medium with
diluted solutions of phosphate to form an antimony‐phospho‐molybdate complex. This complex is reduced
to an intensely blue‐coloured complex by L(+)ascorbic acid. The complex is measured at 880 nm.
LABORATORY FACILITIES
1. Maximum power consumption depending on the analyser configuration, 2000 VA. Check voltage at the
back of the instrument before installation.
2. Facilities for chemical wastes. Check environmental regulations for proper disposal of waste.
PROCEDURE SAMPLE PREPARATION
Water no. 1.1.3
Field of application
Sample preparation for the determination of total alkalinity, aluminium, amino acids, ammonia, anionic
surfactants (MBAS), bromide, calcium, C.O.D., chromium, conductivity, D.O.C., ethanol, hardness,
magnesium, manganese, methanol, nitrate + nitrite, nitrite, nonionics, ortho‐phosphate, potassium
permanganate, potassium, total‐N (UV digestion), protein, silicate, sodium, volatile acids and urea in water.
Principle
The sample is not preserved and analysed as soon as possible, at least within 24 hours after collection.
Store the sample at 4°C till analysis.
Note : The sample preparation in this method is only meant to be an example procedure. It requires
validation on its correct procedure for all types of samples to be analyzed, which is the responsibility of the
user.
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REAGENTS
A. Ammonium heptamolybdate solution (1 liter)
Required chemicals: Potassium antimony(III) Preparation: Dissolve the potassium antimony(III)
oxide tartrate ............ 230 mg. oxide tartrate in ± 800 ml distilled water.
K2(SbO)2C8H4O10.3H2O Add carefully, while constant swirling and
Sulfuric acid # ............ 69.4 ml. cooling the sulfuric acid. Add the
H2SO4 (95‐97%) ammonium heptamolybdate and dissolve.
Ammonium Fill up to 1 liter with distilled water, add
heptamolybdate .............. 6 g. the FFD6 and mix.
(NH4)6Mo7O24.4H2O
Distilled water Note: Do not use metal spoons for ammonium
H2O heptamolybdate. The sensitivity can be
FFD6 ............................... 2 ml. 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. Preparation: Dissolve the ascorbic acid in ± 800 ml
C6H8O6 distilled water. Add the acetone. Fill up to
Acetone ........................ 60 ml. 1 liter with distilled water, add the FFD6
C3H6O and mix.
Distilled water
H2O Note: Solution is stable for 5 days. Store at
FFD6 ............................... 2 ml. 4°C when the solution is not used.
C. Rinsing liquid sampler
Required chemicals: Distilled water Note: For sea water samples, adjust the salinity
H2O 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.
STANDARDS
Stock solution 100 mg P/liter (1 liter)
Required chemicals: Potassium dihydrogen Preparation: Dissolve the potassium dihydrogen
phosphate .............. 439.4 mg. phosphate in ± 800 ml distilled water. Fill
KH2PO4 up to 1 liter with distilled water and mix.
Distilled water
H2O Note: Solution is stable for 4 weeks. Store at
4°C when the solution is not used.
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Stock solution 10 mg P/liter
Dilute 10 ml stock solution 100 mg P/liter to 100 ml with distilled water.
Note: Prepare the stock solution 10 mg P/liter fresh weekly.
Working standards
200 µg P/liter: Dilute 2.0 ml stock solution 10 mg P/liter to 100 ml with rinsing liquid sampler.
160 µg P/liter: Dilute 1.6 ml stock solution 10 mg P/liter to 100 ml with rinsing liquid sampler.
120 µg P/liter: Dilute 1.2 ml stock solution 10 mg P/liter to 100 ml with rinsing liquid sampler.
80 µg P/liter: Dilute 0.8 ml stock solution 10 mg P/liter to 100 ml with rinsing liquid sampler.
40 µg P/liter: Dilute 0.4 ml stock solution 10 mg P/liter to 100 ml with rinsing liquid sampler.
Note:
1. Prepare the working standards fresh daily.
2. The water used for the reagents and standards must be degassed properly before making up the
reagents and standards. Especially water produced by reverse osmosis or ion exchange equipment
contains a lot of gasses, which must be removed by degassing (degassing procedure see operational
remarks and trouble shooting).
CATALOGUE NUMBERS REQUIRED CHEMICALS
Product Supplier and catnr. Danger classification
Potassium antimony(III) oxide tartrate trihydrate Merck 108092 harmful, dangerous for the
environment
Sulfuric acid (95‐97%) Merck 100731 corrosive
Ammonium heptamolybdate tetrahydrate Merck 101182
FFD6 Skalar SC 13908
L(+)Ascorbic acid VWR PRO
20150.231
Acetone Merck 100014 highly flammable, irritant
Potassium dihydrogen phosphate Merck 104873
Sodium hypochlorite solution (13% active chlorine) Acros 21925 corrosive
RECOMMENDED OPERATIONAL SETTINGS
1. System sample time: 60 sec., wash time: 60 sec., air time: 0 sec.
2. Module sample time: 60 sec., wash time: 60 sec., air time: 0 sec.
3. Calibration type: 1st order ISO 8466‐1.
4. Sampler settings normal: 2, extra: 4.
OPERATIONAL REMARKS AND TROUBLE SHOOTING
1. The stabilising time of the system is approximately 20 minutes.
2. The sensitivity of the highest standard 200 µg P/liter is ± 0.370 AU.
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3. Persons using this Skalar method should be familiar with normal laboratory practice. This Skalar
method does not purport to address all of the safety problems, if any, associated with its use. It is the
responsibility of the user to establish appropriate safety and health practices and to ensure compliance
with any national regulatory conditions.
4. The connection between the sampler and the sample pump tube is made of 5175 tube.
5. If a digital matrix photometer 28505901, is in use, a correction interference filter of 1010 nm ± 10 nm is
advised.
6. If reaction coils with water heating are used, the water bath has to be cooled with tap water when the
environment temperature is above 25°C.
7. The reagent bottles must be rinsed thoroughly with distilled water before refilling with fresh reagents.
This is done to remove precipitation of micro organism and other interferences.
8. If solvents or high concentrated acids (> 2M) must be controlled by a rinsing valve, use the solvent/acid
resistant type.
9. Avoid any turbidity in the reagents, filter if necessary.
10. Degassing procedures;
a) Good: degas the water with a helium gas flow of approximately 20 liter/hour with aid of a sparger.
Degas 5 liter water for 15 minutes. This procedure removes all dissolved air or, degas the water by
boiling the water for 10 minutes. Cool down to room temperature before usage.
b) Medium: degas the water with a nitrogen gas flow of approximately 20 liter/hour with aid of sparger.
Degas 5 liter water for 15 minutes. This procedure will remove most of the dissolved gasses.
c) Bad: degas the water by ultrasonic waves. This procedure will remove a small part of the dissolved
gasses.
GENERAL REMARKS
1. In most analyses, the first peak coming from the baseline is lower than it should be. The first peak
coming from the baseline is rejected and will not be included in the calculation of the CV‐value.
2. If the sample take up volume is less than 1.00 ml/min, a bypass is required to increase the sample
stream to approximately 1.00 ml/min. For SA 5210 debubbler, when the sample is 1.00 ml/min and
higher use 0.23 ml/min debubble tube.
MAINTENANCE
1. Daily; when daily analysis is finished rinse all reagent lines with distilled water for 30 minutes.
2. Weekly; to decontaminate the system, rinse with 1% diluted hypochlorite solution for 30 minutes and
with distilled water for another 30 minutes.
3. Monthly; replace all pump tubing (or shift pump tube one colour bridge on pump).
MODULE CONSUMABLES
silicone tube catnr. 3150 sleeves catnr. 5406
polyethylene tube catnr. 3142 acid flex sleeves catnr. 5415
polyethylene tube catnr. 5141 pump tube 1.00 ml/min. catnr. 3031
polyethylene tube catnr. 5142 pump tube 0.42 ml/min. catnr. 3028
sleeves catnr. 5400 pump tube 0.32 ml/min. catnr. 3027
sleeves catnr. 5401
catnr. 503‐010w/r 4 of 6
MODULE COMPONENTS
manifold holder catnr. 25200105 debubbler catnr. 5207
module catnr. 5107 reactor catnr. 25500952
end block catnr. 5109 sinkers catnr. 5380
inlet connector catnr. 5216 flow cell 50 mm catnr. 6425
inlet connector catnr. 9242 filter 880 nm catnr. 6609
REFERENCES
Chemical method (no. 503)
1. Standard Methods for Examination of Water and Waste Water. 15th edition 1980 APHA‐AWWA‐WPCF
page 410‐425.
2. Boltz, D.F., Mellon, M.G.,"Spectrophotometric determination of phosphate as molydiphosphoric acid",
Analytical chemistry, Vol. 20, No 8, August 1948, page 749‐751.
3. Walinga, I., van Vark, W., Houba, V.J.G., van der Lee, L.L., Plant analysis Procedures, Part 7, Department
of Soil Science and Plant Nutrition, Wageningen Agricultural University, Syllabus 1989, Page 138‐141.
4. ISO 15681‐2, Determination of ortho phosphate and total phosphorus contents by flow analysis, Part 2:
Method by continuous flow analysis (CFA).
5. ISO 3696:1987, Water for analytical laboratory use. Specification and test methods.
6. ASTM, D1193, Standard Specification for Reagent Water.
Sample preparation (water no. 1.1.3)
1. Environmental Protection Agency, methods for chemical analysis of water and wastes, 1983.
2. Standard Methods for the determination of water and waste water, 17th edition, 1989.
3. ASTM, 1990.
4. International Organisation for Standardisation, ISO‐5667‐3.
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FLOW DIAGRAM
waste
ml/min
25500952/5303 Flow cell 50 mm
Filter 880 nm
40°C
L(+)Ascorbic acid solution 0.32
Ammonium heptamolybdate sol. 0.32 9242 *
5207
waste
Air
Sample 1.00 5216
0.42
1.00
waste
Sampler
* polythene tube catnr. 5141
Revision: Rev 1 Rev 2 Rev 3 Method:
Date: Analysis: Phosphate
Chemists Range: 5‐200 µg P/liter
Authorization Sample: Sea water
First issued: 26‐03‐2013
catnr. 503‐010w/r 6 of 6
