Water Quality Testing
ENV-202
LECTURE #6
APRIL 19, 2016
DR. DANIEL VIDT
Schedule
2
Week
#6
Lecture #6 Topics:

Phosphate Testing Rational

Types of Phosphorous

Orthophosphate

Condensed phosphates

Organic phosphates
Week
#7
Week
#8
3

http://www.dispatch.com/content/sto
ries/local/2016/05/08/grand-lake-st-marys-polluted-again-with-toxicalgaes-nerve-toxin.html
Forms of Phosphate
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 Phosphorus occurs in natural waters and in waste water almost
solely as phosphate, 𝑃𝑂43−
 These are classified as:
 Orthophosphates
 Condensed phosphates
 Organically bound phosphates
Orthophosphates

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These are applied as fertilizers in both agriculture an residential
applications
 Orthophosphoric Acid (A.K.A.: phosphoric acid or monophosphoric
acid) is the simplest form of phosphate:
𝐻3 𝑃𝑂4
Other “Simple” Phosphates
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 The negatively charged sections of a phosphate can also bond
ionically with other metals to create phosphates salts
 These salts, specifically sodium salts, are used to control “caustic
attack” in boiler waters
High pH values lead to “caustic waters”
Excess hydroxide ions in the water
 High temperatures can cause the phosphate to precipitate
causing deposits in the system
Examples of sodium phosphate
treatment
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 Under Basic or
“Caustic” condition, the salt reacts with
hydroxides to reduce the pH (make acidic):
𝑁𝑎𝐻2 𝑃𝑂4 + 𝑁𝑎𝑂𝐻 ⟶ 𝑁𝑎2 𝐻𝑃𝑂4 + 𝐻2 𝑂
𝑁𝑎2 𝐻𝑃𝑂4 + 𝑁𝑎𝑂𝐻 ⟶ 𝑁𝑎3 𝑃𝑂4 + 𝐻2 𝑂
 Under Acidic conditions, the fully deprotonated (no hydrogens)
will react to increase the pH (make basic)
𝑁𝑎3 𝑃𝑂4 + 𝐻2 𝑂 ⟶ 𝑁𝑎2 𝐻𝑃𝑂4 + 𝑁𝑎𝑂𝐻
Condensed Orthophosphates
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
The term “Condensed” means to
bond together many phosphate
groups

Hence, the names have “poly” in
them.
Organic Orthophosphates
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 These are mainly formed in “biological” processes
 Phosphorous is an essential growth element for biological
organisms
 As such it is considered a “nutrient” similar to ammonia and nitrate
 It can cause eutrophication of waters if too much is present.
Organic Orthophosphates
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
ATP is an example of the use of phosphorus in living organism

ATP is Adenosine triphosphate and is used for energy transfer in living
cells
Sample Collection/ Preservation
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 Collect Samples in Polyethylene bottles
However, glass should be used for long storage
because
phosphates may be absorbed onto the walls of plastic
bottles
 Store orthophosphate samples at 4°C and analyze within 48
hours of collection
 Preserve total phosphorus samples at time of collection by
adding concentration sulfuric acid to adjust the pH of
sample to less than 2
Testing Procedures

From the Standard Methods 22nd Edition:

The flow chart starts with either filtration
or no filtration
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Basic Testing Procedure
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 Two basic procedures
 Orthophosphates
 Total phosphates (when condensed phosphates are present)
 Orthophosphates
 Colorimetric procedure to determine orthophosphates
 Total Phosphates
 First, a digestion that converts all phosphates to orthophosphates
 Same Colorimetric procedure as for orthophosphates
Considerations for Orthophosphate
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 Suitable for clear and colorless waters only
 May need to filter with 0.45μm membrane filters
 Need to prewash filters in distilled water to remove any trace phosphate
 Cannot use commercial detergents that contain phosphate to
clean glassware for these tests
 Acid rinse all glassware after washing to minimize contaminants
 10% HCl is good for glassware not being used also for trace-metals
 Rinse with lots of Distilled Water after submerging in acid bath for at
least one hour.
Methods

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4500-P E. Ascorbic Acid Method (EPA recognized)
 Ammonium molybdate and antimony potassium tartrate react in acid
medium with orthophosphate to yield a molybdenum blue solution
 Measured with a spectrophotometer or colorimeter with a wavelength of
880nm

Other standard test for orthophosphate by HACH for the DR900 is the
Molybdovanadate method
 4500-P C. Vanadomolybdophosphoric
Acid Colorimetric Method
 Uses wavelength of 470nm
 Useful since the IR light (880nm) is a more expensive
instrument
New Tech to remove from water

https://www.sciencedaily.com/releases/2012/08/120815112243.htm
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Wisconsin State Laboratory of Hygiene
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Things to think about
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 Keep an eye on the expiration date of chemicals
 Watch the cleanliness of the cuvette
 Be deliberate and mindful when adding chemicals
 Don’t touch pipets to inner surfaces of reagent bottles, sample vials, or
cuvettes.
 Make sure you are adding the correct chemicals for the test being
performed.
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