Determination of Chloride, Sulfate and Nitrate in Drinking Water

Nitrate testing in water giving below three methods.

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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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


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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