SOP for the determination of Turbidity

Principle

This method is based on comparison of the intensity of light scattered by the sample under defined conditions with the intensity of light scattered by a standard reference suspension under the same conditions. The higher the intensity of scattered light the higher the turbidity. Formazin polymer is used as the primary standard reference suspension.

Table of Contents

Interference

Dirty glassware and the presence of air bubbles give false results.

Apparatus

Turbidity Meter, Beakers

Reagents

Turbidity-Free Water

Pass distilled water through membrane filter having a pore size not greater than 0.45 µm, if such filtered water shows a lower turbidity than the distilled water. Discard the First 200 ml collected. Otherwise use distilled water.

Hexamethylene Tetramine Solution

Dissolve 10.0 g hexamethylene tetramine in demineralised water and dilute to 100 ml.

Hydrazine Sulphate Solution

Dissolve 1.000 g hydrazine sulphate in demineralised water and dilute to 100 ml.

Turbidity Standard Suspension I ( Formazin)

In a 100 ml volumetric flask mix 5.0 ml hydrazine sulphate solution with 5.0 ml haxamethylene tetramine solution. After 24-hour standing at 25 ± 3 deg C, dilute to 100 ml with demineralised water and mix well. Prepare fresh monthly.

Turbidity Standard Suspension II

Dilute 100 ml turbidity standard suspension I to 100 ml with DM water, The turbidity of this suspension is defined as 40 Jackson Turbidity units (JTU). Prepare fresh weekly. This suspension may be diluted as required to prepare more dilute turbidity standards.

Procedure

Calibration and Measurement

Calibration to be done as per manufacturer instructions General method is as follows.

Switch on the instruments and keep it on for some time.
Select appropriate range depending upon the expected turbidity of the sample.
Set zero of the instruments with turbidity free water using a blank solution and adjust 000 with set zero knob.
Now in another test tube ,take standard suspension just prepared as described in
Gentle agitate sample. Wait until air bubbles disappear and pour sample into cell.
Take its measurement and set the display to the value of the standard suspension with calibrate knob.
Take measurements of any solution of unknown concentration.

Note:

Turbidity Less Than 40 Unit – shake the sample to disperse the solids. Wait until air bubbles

Disappears. Pour sample into turbidimeter tube and read turbidity directly from the instrument scale or from Calibration Curve.

Turbidity Greater Than 40 Unit — In case turbidity values are greater than 40 units, dilute the

Sample with turbidity-free water to bring the values within range. Take readings of diluted sample.

Compute the turbidity of the original sample from the turbidity of the diluted sample and the dilution factor.

Calculation

Calculate the turbidity of diluted samples, using the following equation:

Turbidity unit = A x (B+C)

Where,

A= Turbidity unit found in diluted sample

B= Volume in ml of dilution water used

C= volume of sample in ml taken in dilution

Safety guidelines

Proper safety & health precaution are taken while doing the analysis by using safety goggles, apron, safety shoes & using fume chamber for fume generating chemicals.

Reference

IS 3025 (Part-10): 1984 RA-2012