Water Analysis

By: Munazza Nasir

Management Associate (chemist)
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 Introduction
• A description of procedures to analyze and determine water quality.
• Tests are performed to check the regulatory requirements of water samples from
different parts of plant.
• At FFBL lab, testing is performed to evaluate the quality of
 Raw water.

 Drinking water.

 Cooling water.

 Waste water.

 Boiler feed water.

 Steam condensates.

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 Total alkalinity
• Due to the presence of OH-, CO32- and HCO31- ions in water.
• Titration with 0.02N H2SO4 with mixed indicator (bromocresol green + methyl red).
• Sulfuric acid forms carbonic acid (H2CO3) and water and lowers pH.
• Titration to pH 4.5 determines endpoint.

 Arsenic
• Arsine (AsH3) reacts with silver diethyldithiocarbamate (Ag-DDTC) to make a red complex.
KI, SnCl2, Zn
As5+ + 3 HCl AsH3 + 3 Cl-
Morpholine in CHCl3

AsH3 + Ag-DDTC As-DDTC

(red complex)

• Arsine passes through a scrubber to the absorber containing Ag-DDTC, where the complex formation occurs.

• Complex absorbs at 535nm.

• Comes in the category of special analysis.

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 Aluminum by Eriochrome Cyanine R
• Al3+ reacts with eriochrome cyanine R (ECR) to make a pink complex absorbing at 535nm.
• Acetic acid/sodium acetate buffer is used to maintain a pH of 5.0.
• Interference of Fe and Mn is eliminated by adding ascorbic acid.
• Complexation with EDTA in blank to compensate for color and turbidity.

 Ammonia
• Nessler’s reagent (K2HgI4) reacts with ammonium ions in strongly basic conditions to form a brown
complex which absorbs at 425nm.
NH4OH + 2 K2HgI4 + 3 NaOH HgO.Hg(NH2)I + 3 NaI + 4 KI + 3 H2O
(brown complex)
• NaOH is added to provide the strongly alkaline conditions.
• Potassium sodium tartarate is used to minimize interference from other metal ions by complexing
with their hydroxides formed in these conditions.

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 Bacteria in cooling water by DIP slides
• Dip slides are used to determine the presence of slime forming bacteria in
cooling water systems.
• Slide is dipped in the sample and than incubated for 36 hours at 35-37 oC
in incubator.
• The pattern formed is than compared with standard pattern available to
find out the type of bacteria present.
• Reported as cfu/mL (colony forming unit per mL) of sample. Dip slides

 Bacteria in potable water

• Apparatus, demin water and
sampling bottles are sterilized in autoclave
beforehand to achieve a sterile environment.
• Nutrient broth is prepared to provide bacteria
with nutrients to grow on petridishes.
• 100 mL of sample is filtered through filteration
assembly and the petridish is incubated for Bacterial colonies

24 hours for bacteria and 72 hours for fungus.

• Reported as cfu/100 mL (colony forming unit
per100 mL) of sample.

Filtration assembly
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 BOD by oxitop bottles
• BOD (biochemical oxygen demand) is determination of oxygen consumed
by bacteria by decomposition of organic matter present in water.

• Change in dissolved oxygen concentration for a period of 5 days (BOD 5)

at 20oC.

• MgSO4, CaCl2 and FeCl3 solutions are added as nutrient source

and phosphate buffer to maintain pH (6.5-7.5).

• Small amount of sewage seed is added to dilution water before aeration

to create an oxygen demand.

Oxitop bottle
• NaOH pellets are placed in rubber sleeve in neck of bottles to detect CO 2

produced as a result of metabolism of bacteria.

• Bottles are left in incubator for 5 days.
• BOD is determined by the reading of the sensor on top of blank and sample

bottles..
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 BOD5 by titration
• Same as previuos procedure, but involves determining dissolved oxygen of blank and sample
bottles before and after 5 days.
• Winkler’s method is employed to determine DO.
• DO reacts with MnSO4 and NaOH to form basic manganese hydroxide flocs.
MnSO4 + 2 NaOH Mn(OH)2 + Na2SO4
2 Mn(OH)2 + O2 2 MnO(OH)2
manganese hydroxide

• Adding H2SO4 causes the floc to dissolve and liberation of iodine, which is titrated with Na 2S2O3
using starch indicator.
MnO(OH)2 + H2SO4 MnSO4 + 2 H2O + O
2 KI + H2SO4 + O K2SO4 + H2O + I2
I2 + 2 Na2S2O3 Na2S4O6 + 2 NaI
• Sodium azide is added to eliminate nitrite interference.
2 NaN3 + H2SO4 2 HN3 + Na2SO4
Hyrdazoic acid
HNO2 + HN3 N2O + N2 + H2O

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 COD (Chemical oxygen demand)
• Measures the amount of oxidizable organic matter in waste water by potassium dichromate under
acidic conditions.

• Sample (along with blank) is refluxed with conc. H 2SO4 and K2Cr2O7 with AgSO4 and HgSO4.

• AgSO4 is added as a catalyst to promote oxidation and HgSO 4 to reduce chloride interference.

• Solution is cooled and titrated with (Fe2(NH4)2(SO4)2).6H2O to titrate the remaining K2Cr2O7 with
ferroin indicator from greenish blue to orange brown color.

• Difference in the values of blank and sample gives COD in mg/L K 2Cr2O7.

 Chloride by ISE (Ion Selective Electrode)

• Used for samples having very low chloride concentrations.
• Ion selective electrode is first calibrated with buffers of known chloride concentrations.

• 10% HNO3 is added to sample as ISAB (ionic strength adjustment buffer) solution to increase the
activity of chloride ions and to mask other chemical interferences.
• Electrode is dipped in solution to determine the amount of chlorides present. 8
 Chloride by AgNO3 Titration
• Also known as Mohr Argentometric method.

• K2CrO4 is used as indicator.

• Chlorides present react with AgNO3 to make AgCl (white precipitates).

• After all the chlorides are consumed, AgnO 3 reacts with K2CrO4 to make orange silver chromate,
which indicates the end point.
AgNO3 + Cl- AgCl + NO3-
2 AgNO3 + K2CrO4 Ag2CrO4 + 2 KNO3

 Chloride by Turbidity
• Colorimetric determination of chlorides in water.

• Chlorides are reacted with AgNO3 solution in the presence of HNO3 to produce AgCl, which
appears in the form of turbidity and is measured at 420nm.
• Turbidity is proportional to chloride concentration.

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 Chloride by Mercury thiocyanate
• Chlorides in sample react with mercury thiocyanate to make mercuric chloride and free SCN -
ions.
• In the presence of Fe3+ (ferric) ions from ferric ammonium sulphate, free SCN - forms a red orange
complex of ferric thiocyanate, which absorbs at 460nm.
Hg(SCN)2 + 2 Cl- HgCl2 + SCN-
Fe3+ + SCN- Fe(SCN)2+

(red-orange complex)

 Chromium by Diphenylcarbazide (DPC)

• Hexavalent chromium (Cr6+) reacts with DPC in acidic solution to make a violet colored complex
which absorbs at 540nm.
• Vanadium interference can be minimized by allowing the solution to stand for 15 minutes after
addition of reagent.

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 Copper by Neocuproin
• Cu2+ is reduced by NH2OH.HCl to Cu+ state.
• Cu+ reacts with neocuproin to make an orange-red complex.
• Sodium citrate is used to complex any other metal ions present.
• Ammonium hydroxide is used to maintain pH at 4.0.
• Complex is extracted in CHCl3 and absorbance is measured at 457nm.

 Ethylene glycol
• Malaparade reaction is employed here.

• HIO4 is added in excess, which reacts with ethylene glycol and breaks down into iodate (IO 3-).

C2H6O2 + HIO4 2 HCHO + HIO3 + H2O

Ethylene glycol

• Remaining iodate in solution is determined by titration with sodium thiosulfate using starch
indicator and KI to liberate iodine (iodometric titration).

5 KI + IO3- + 6 H+ 3 I2 + 3 H2O + 5 K+

I2 + 2 Na2S2O3 Na2S4O6 + 2 NaI

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 Dissolved oxygen
• Done in boiler feed water.
• Sample cup should not contain any air bubbles while
dipping of ampoule.
• Sample fills the ampoule instantly when its tip breaks
and forms colored complex with dye inside.
• The ampoule is placed in a comparator, from which the
estimate for the amount of dissolved oxygen in sample
can be made.
• Normally performed on the spot, so the sample cannot
be contaminated with oxygen from air. DO kit, including ampoules,
sample cup and comparator

1. 2. 3.
Steps to determine dissolved oxygen 12
 Formaldehyde by Chromotropic acid
• Chromotropic acid forms purple complex with formaldehyde in the presence of conc. H 2SO4 which
absorbs at 580nm.
• The most sensitive and specific method for formaldehyde determination.
• Little interference from other ions and organic species.

 Free Mineral Acidity

• A measure of total concentration of chlorides, sulfates and nitrates in the acid form, i.e. HCl,
H2SO4, HNO3.

• Determined by titrating sample with NaOH with bromophenol blue as indicator.

• Used in checking the functioning of strong acid cationic resin. Decrease in free mineral acidity
means exhaustion of cationic resin.

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 Free Carbondioxide
• CO2 in water exists as H2CO3 leaving water slightly acidic.

• Solution is titrated with NaOH with phenophthahlein as indicator till appearance of pink color.
• Free mineral acidity is usually determined previously.

 Free Chlorine by Methyl Orange

• Acidified sample containing free chlorine decolorizes methyl orange.
• Remaining methyl orange color can be read at 510nm.
• Extent of decolorization of methyl orange determines the amount of free chlorine present.

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 Free Chlorine by DPD (N, N-diethyl paraphenylenediamine)
• DPD is oxidized by chlorine causing a magenta-red color, which absorbs at 515 nm.
• The complex is read within one minute as its color fades immediately.
• pH is maintained by adding buffer solution.
• Chlorine standard solution is prepared by dissolution of NaOCl in water, which is standardized first
by titration with Na2S2O3 and KI using starch indicator (iodometric titration).

 Floride by ISE (Ion Selective Electrode)

• Electrode is first calibrated with buffer solutions with known floride concentrations (2.0 ppm and 20
ppm).
• pH of sample should be 6-8 or above to convert the hydrogen floride into floride ions.
• TISAB (total ionic strength adjustment buffer) is added to increase the activity of florides as well as
to minimize interferences of other ions.
• Electrode is dipped in solution to determine the amount of florides.

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 Total Hardness
• Sum of Ca hardness and Mg hardness.
• Ca2+ and Mg2+ form complexes with EDTA during titration with solochrome black-T as indicator.
• Total hardness buffer is used with pH ~ 10.
• End point is from red-violet to blue color.

 Calcium Hardness
• Calcium hardness buffer is used with pH ~ 12.
• Titration with EDTA using calcon indicator leads to Ca-EDTA complex formation.
• End point is from red to blue color.
• Volume of EDTA consumed is used to calculate total as well as calcium hardness.

Mg2+ Hardness = Total Hardness - Ca2+ Hardness

(ppm as CaCO3)

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Thank You

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