Analysis of purified water

Analysis of purified water

Purified water is a fundamental and versatile substance used in various industries, including pharmaceuticals, food and beverage, and laboratory applications. Ensuring its quality and purity is of paramount importance. In this article, we will explore the methods and techniques used in the analysis of purified water to guarantee its suitability for specific purposes.

II. Sources of Impurities

Before diving into the analysis methods, it’s crucial to understand where impurities in purified water can originate. Common sources of impurities include:

• Feedwater: The quality of the source water used in the purification process can introduce impurities.
• Treatment Processes: The water purification methods employed, such as distillation, deionization, or reverse osmosis, may introduce impurities if not properly maintained.
• Storage and Distribution: Contamination can occur during storage and distribution if materials used are not inert or clean.

III. Methods of Analysis

Several methods are used to analyze purified water, each focusing on different aspects of its purity. These methods include:

A. Chemical Analysis

1. Conductivity Measurement: This method assesses the water’s ability to conduct electrical current, which is directly related to the concentration of ions. Purified water should have very low conductivity.
2. Total Organic Carbon (TOC) Analysis: TOC measures the concentration of organic carbon in the water. Elevated TOC levels can indicate the presence of organic impurities.
3. Anion and Cation Analysis: This helps identify specific ions in the water, such as chloride, sulfate, and calcium ions, which can be contaminants.

B. Microbiological Analysis

1. Total Viable Count (TVC): TVC measures the total number of viable microorganisms in the water. Purified water should ideally have zero colony-forming units (CFUs).
2. Endotoxin Testing: Endotoxins, which are part of the cell walls of some bacteria, can be harmful when present in purified water. The Limulus amebocyte lysate (LAL) test is commonly used for endotoxin detection.

C. Particulate Analysis

1. Particle Count: This method measures the concentration and size of particles in the water. Purified water should have very low particle counts.

D. pH Measurement

The pH level of purified water is an essential parameter to monitor. It should be neutral (pH 7) to avoid corrosion or other issues when it comes into contact with sensitive equipment or processes.

Determination of pH

Reference:  BP, 1988 p A-103

Equipment: pH meter

Reagents: standard buffer solutions (pH 4.0, 7.0, 9.2)

Procedure: Standardize the pH meter with pH buffer solutions of pH closer to the expected pH value of the sample at 25 ° ± 2°C. Immerse the electrode in water. Shake it for about one minute and note the constant reading of pH on the pH meter.   

Determination of total solids

Reference:  IS: 3025-1964 P18

Procedure: Note the tare weight of the Evaporating dish. Evaporate 100ml of the sample in the
evaporating dish on steam bath. Dry the residue at 105°C for one hour. Col in a desicator and weigh. Not the weight of the residue.

Total solids   =   Weight of residue (mg.) ´ 1000

(ppm)                  Volume of sample taken (ml.)

Determination of total dissolved solids

Reference: IS: 3025-1964 p 19

Procedure: Filter the sample through what man filter paper 42. Not the tare weight for the evaporating dish. Evaporate 100ml of the filtered sample in the evaporating dish on steam bath. Dry the residue at 105°C for one hour. Cool in a desicator and weigh. Note the weight of the residue.

Total dissolved Solids   =   Wt. Of residue (mg.)  ´  1000

(ppm)                                 Volume of sample taken (ml.)

Determination of total hardness

Reference: Chemical & Biological methods for water pollutions studies p-73

Reagents

BDH Total hardness indicator tablets

0.01 M EDTA Solutions

Dissolve 3.723 g of disodium salt of EDTA in water to prepare 1 Liter of solution In a volumetric flask.

Buffer Solutions

a)  Dissolve 16.9 g of NH₄CL in 143 ml. Of conc. Ammonia (25%)

b) Dissolve 1.179 g of disodium EDTA and 0.78 g of MgSO₄. 7H₂O in 60ml. Of water.

Mix both (a) and (b) solutions and dilute to 250ml. With water.

Procedure

Take 100 ml of sample in conical flask. (If sample is having higher calcium, take a smaller volume and dilute to 50ml.).

Add 1ml. Buffer and one tablet of BDH total hardness indicator.  The solution turns wine red. Titrate against EDTA solution. At the end point, Colour changes from wine red to blue.

Calculations

Total hardness (as CaCO₃) = Vol. Of 0.01 M EDTA used ´ 1000

(ppm)                                        Vol. Of sample taken

Determination of content of chloride.

Reference: IS: 3025-1964 p 34

Reagents:

0.02 N Silver Nitrate

Dissolve 3.400 g of dried AgNO₃ (AR) in water to make 1 litre of solutions in a volumetric flask. Keep this solution in an amber-coloured bottle.

Potassium Chromate solution (5%)

Dissolve 5g of potassium Chromate in water and makeup to 100ml. Add silver nitrate solution to produce slight red precipitate and filter. Keep the filtrate as indicator in a bottle.

Procedure

Take 100ml. of sample in a conical flask and add 2ml. of potassium Chromate indicator solution. Titrate with 0.02N Silver Nitrate until a persistent red tinge appears. Note the volume of silver nitrate used.

Calculations

Chloride = V ´ N ´ 1000 ´  35.5

(ppm)                   100

Where:

V= Volume of AgNO₃ Used (ml.)

N = Normality of AgNO₃

Determination of Sulphate

Reference: IS : 3025-1964 P-27

Regents

1 N Nitric Acid

BDH Total hardness tablet

Standard Barium Chloride Solution

Dissolve 2.443 g of barium Chloride in water and dilute to 1 litre in a volumetric flask.

Buffer Solution

Dissolve 67.5 g of ammonium Hydroxide (Sp. gr. 0.92) and dilute with water to 1 litre.

Standard EDTA Solution (0.01M)

Dissolve 3.723 g of disodium salt of EDTA in water to make up to 1000 ml in a volumetric flask.

Procedure

Neutralize 125 ml of the sample with dilute nitric acid (1N) adding a slight excess and boil to expel carbon dioxide. Add 10 ml or more if required, of standard barium Chloride solution to the boiling solutions and allow to cool. Dilute to 250 ml, makes and allow the precipitates to settle. Withdraw 50 ml of the clear solution; add 0.5 to 1.0 ml of buffer and one tablet of BDH total hardness indicator. Titrate with standard EDTA solution to a blue colour which does not change on addition of further drops of EDTA solutions.

Calculation 

Sulphate (as SO₄)  =  9.6 (0.1 A+B-4C)

(ppm)

Where:

A = Total hardness of the sample*

B = Volume of standard barium chloride taken (ml)

C = Volume of standard EDTA used (ml)

 *Total hardness (A)

Procedure

Take 100 ml of sample in a conical flask (if sample has higher Concentration of  Calcium, then take 25 ml of sample and dilute to100 ml) add 1 ml of buffer solution and one tablet of BDH total hardness indicator or erichrome Black T. Titrate with standard 0.01 M EDTA solution till the colour changes from wine red to blue .

Calculations 

Total hardness (as CaCO₃) = Volume of EDTA used ´ 1000

(mg / litre)                                Volume of sample taken

Determination of Calcium

Reference:  Manual on water and waste water analysis P,88

Reagents

0.01  M EDTA solutions

Dissolve 3.723 g of disodium salt EDTA in water to prepare 1 litre of solution in a volumetric flask.

2 N Sodium hydroxide

Dissolve 80.0 g of NaOH in 1000 ml in a Volumetric flask.

Muroxide indicator  or Ammonium Perpurate

Mix 0.1 gm Murexide with 10.0 gm of NaCL and grind it in pastle mortar.

Take 50 ml of sample in conical flask and add 1 ml of sodium hydroxide to raise pH to 12.0. Add a pinch of murexide or ammonium perpurate indicator.  Titrate with 0.01 M EDTA till pink colour changes to purple. Note the volume of EDTA required and keep it aside to compare end points of sample titrated.

Calculation

Calcium = Vol. Of 0.01 M EDTA used  ´ 400.8

(ppm)         Vol. Of sample taken

Determination of content of CO₂

Reference:  IP 1985 p 544

Regents

0.15% W/V Calcium Hydroxide solution in water.

Take 25 ml of sample and add 25 ml of Calcium Hydroxide solutions. Find out if any turbidity is in the solutions. Absence of turbidity indicates that the carbon dioxide is not present.

Determination of Oxidisable substance 

Reference:  Analar standard of chemicals p-870

Reagents

0.01  N Potassium permanganate solution

Dilute sulphuric acid. (Appx.10%)

Procedure

Take 500 ml of sample in conical flask and add 1 ml of dilute sulphuric acid. Add 0.5 ml of 0.01 N Potassium Permanganate and heat to boiling. The pink colour does not entirely disappear.

Determination of content of Ammonia

Reference:  IP- 1985 p.544

Reagents

Dilute Ammonium Chloride solution.

Alkaline Potassium Mercury-Iodide solutions(Nessler’s Regent)

Take 3.5 g of Potassium Iodide and 1.25 g of Mercuric Chloride in a 100 ml of Volumetric Flask. Dissolve in 80 ml of water. Add a cold saturated Solution of Mercuric Chloride in flask with constant stirring until a slight red precipitate remains. Dissolve 12 g of Sodium Hydroxide in the above solution  and add a little more of cold saturated solution of Mercuric Chloride and sufficient water to produce 100 ml. Allow to stand and decant the clear liquid.

Procedure

Take 20 ml of sample in Nessler Cylinder (1) and add 1 ml of alkaline Potassium Mercuric- Iodide solution and observe the solution against While tile. Take 7.5 ml

of sample. Add 2.5 ml of Dil. Ammonium chloride and 1.0 ml of Nessler’ reagent.

NESSLER CYLINDER (1)      NESSLER CYLINDER(2)

Colour of solution (1) should be less intense as compared to (2)

Determination of Acidity or Alkalinity

Reference:  Chemical & Biological methods for water pollution studies

ACIDITY:

Reagents

0.05N NaOH

Phenolphthalein

Methyl Orange

Procedure

Take 100 ml of sample in a titration flask. Add 2-3 ml of methyl orange indicator.

1. If soln. turns yellow, Methyl orange acidity absent. In case contents turn pink, titrate with 0.05N Sodium hydroxide.

End point:  Pink to yellow

2. Now add phenolphthalein. Titrate with 0.05N Sodium hydroxide.

CALCULATIONS:

(METHYL ORANGE ACIDITY)

(mg/litre)              (A)   = VXN X 1000 X 50

vol. of sample

(PHENOLPHATHALEIN ACIDITY)

(mg/litre)               (B)  = VXN X 1000 X 50

vol. of sample

Total Acidity: (A+B) X N X 1000 X 50

vol. of sample

ALKALINITY:

Reagents

0.1N HCl

Phenolphthalein

Methyl Orange

Procedure

Take 100 ml of sample in a titration flask. Add 2-3 ml of phenolphthalein indicator.

1. Carbonate Alkalinity(CO₃)

CALCULATIONS:

(PHENOLPHTHALEIN ALKALINITY)  ———P

(mg/litre)              (P_A)   = VXN X 1000 X 50

vol. of sample

2. Bicarbonate Alkalinity(HCO₃)

CALCULATIONS:

(METHYL ORANGE ALKALINITY)  ———M

(mg/litre)              (T_A)   = VXN X 1000 X 50

vol. of sample

IF	CO3 Alkalinity	HCO3 Alkalinity
P = 0	0	T
P < ½ T	2P	T-2P
P= ½ T	2P	0
P> ½ T	2(T-P)	0
P=T	0	0

Determination of Chemical Oxygen (COD).

Reference:  IS: 2488-1966

Reagents

Conc. Sulphuric acid

Mercuric Sulphate

Silver Sulphate

0.25 N Potassium Dichromate

Dissolve 12.259 gm of Potassium Dichromate Previously dried at 110⁰ C for one hour in water to make 1 litre of solution.

Ferroin Indicator

Dissolve 1.485 gm of 1.10 phenanthroline and 0.695 gm of ferrous sulphate in water to make 100 of solution.

0.1 N Ferrous ammonium sulphate (FAS solution)

Dissolve 39.2 gm of ferrous ammonium sulphate in water adding 20 ml of conc. H₂SO₄

To make 100 ml of solution. Standardise the solution as follows:-

Weigh accurately about 150 mg of potassium dichromate (AR  grade) previously dried at 1100 C for one hour. Dissolve in about 20 ml water and add 10 ml of conc. Sulphuric acid. Cool, add few drops of ferroin indicator and titrate with ferrous ammonium sulphate solution.

Normality = Wt. Of K₂Cr₂O₇ (mg)

Vol. Of FAS used X 49.03

Procedure

Take 20 ml of sample in a 250-500 ml COD flask. Add to it, 20 ml of 0.25 N K₂Cr₂O₇ solution and a pinch of silver sulphate and mercuric sulphate. Add 40 ml conc. Sulphuric acid and a few glass beads to avoid bumping. Fix a Friedrich condenser o the neck of the flask and reflux it for 2 hours on a hot plate. Wash the condenser with about 100 ml of distilled water. Cool to room temperature. Add few drops of Ferroin indicator and titrate with 0.1 N ferrous ammonium sulphate. Similarly, run a blank with distilled water same quantity of the chemicals.

Calculation

COD (ppm)  =   (b-a) x N x 1000 x 8

                                       V

Where :

a =  Vol. Of ferrous ammonium sulphate used with sample

b =  Volume of ferrous ammonium sulphate used with blank

V =  Volume of sample ammonium sulphate used.

N =  Normality of ferrous ammonium sulphate used.

NOTE : 

Dilute and volume of sample to be taken can be adjusted depending upon its expected COD value which can be judged from the solution before reflux.

Analysis of Purified Water PDF Notes

 Analysis of Purified Water PDF Notes

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