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Determination of chloride, sulfate and nitrate in drinking water

Determination of chloride, sulfate and nitrate in drinking water

Nitrate testing in water giving below three methods. (What are the different types of water testing?)

Sources of impurities in water 

• Fertilizers and manures

• Decayed vegetable and 

• Animal feedlots

• Municipal wastewater and sludge disposal to lands

• For Industrial discharges

• Leachates from refuse dumps

• Septic systems 

• N-fixation from the atmosphere by bacteria and lightning.

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Methods for Nitrate Estimation

Determination of nitrate in water by the ultraviolet spectrophotometry.

• Useful for uncontaminated natural waters and potable water supplies that have low organic contents

• Follows the Beer’s law up to 11 mg/L as N

• Interferences

 Dissolved Organic Matter


 Nitrite and Hexavalent Chromium


 Filter the sample

 Add 1 ml of 1N HCl per 50 ml of sample

 Read absorbance or transmittance at 220 nm and 275 nm

 Set 0 absorbance or 100% transmittance with distilled water

Determination of nitrate in water by Electrode Method

• Useful for a Nitrate concentration range of 0.14 to 1400 mg/L NO3-N

• Interferences

 Chloride and bicarbonate with weight ratios to NO3-N >10 or >5 respectively

 NO2, CN, Sulphide, Br, I, Chlorite, and Chlorate

Phenoldisulphonic Acid (PDA) Method

• Nitrate reacts with Phenoldisulphonic acid to produce nitro derivatives that in alkaline solution rearranges its structure to form a yellow-colored compound with characteristics that follows

Beer’s law

• Chloride interferes seriously which can be overcome by precipitation of chloride with Ag+ as AgCl

Determination of chloride in water by titration

Methodology: Argentometric Method

• Principle

Chloride determined in a natural or slightly alkaline solution by titration with standard silver nitrate, using potassium chromate as an indicator. Silver chloride are quantitatively precipitated before red silver chromate is formed.

Chloride mg/L = (A-B) x N x 35.45 x 1000/ml sample

Where A = ml AgNO3 is required for sample

B = ml AgNO3 required for blank

N = Normality of AgNO3 used

Standard analytical procedure for water analysis

Note=How to make AgNO3  Standard Solutions

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