SOP Of Determination of Oil and Grease in Water

How to Determine the Quantity of Oil and Grease in Water by Liquid-Liquid Partition Gravimetric Method

Introduction

Oil and grease are common contaminants in water, and can be harmful to human health and the environment. This method describes how to determine the quantity of oil and grease in water using a liquid-liquid partition gravimetric method.

Principle

This method involves extracting the oil and grease from water using hexane. The hexane extract is then evaporated, and the residue is weighed to determine the quantity of oil and grease.

Apparatus

• Separating funnel
• Distillation flask
• Water bath
• Filter paper
• Centrifuge
• Centrifuge tubes
• Desiccator
• Glass funnel
• Vacuum pump
• Distilling adapter
• Ice bath
• Waste receptacle

Reagents

• Hydrochloric acid
• n-hexane
• Sodium sulfate
• Acetone
• Hexadecane
• Stearic acid

Procedure

1. Transfer the acidified 1000 ml sample to a separating funnel. Carefully rinse the sample bottle with 30 ml of hexane and add the solvent washings to the separating funnel.
2. Shake vigorously for about 2 min. However, if it is suspected that a stable emulsion will form, shake gently for 5 to 10 min. Let the layers separate.
3. Drain aqueous layer and a small amount of organic layer into the original sample container.
4. Drain the solvent layer through a funnel containing filter paper and 10 g Na₂SO₄, both of which have been rinsed with the solvent, into a clean tared distillation flask.
5. If a clear solvent layer cannot be obtained and an emulsion of more than 5 ml exists, drain emulsion and solvent layers into a glass centrifuge tube and centrifuge for 5 min at approximately 2400 rpm.
6. Transfer the centrifuged material to separating funnel and drain solvent layer through a funnel containing filter paper and 10 g Na₂SO₄, both of which have been rinsed with the solvent, into a clean, tared distillation flask.
7. Put the separated aqueous layer into the separating funnel again. Extract two more times with 30 ml of solvent each time, but first rinse the sample container with the solvent.
8. Collect the extracts in tared distillation flask and wash filter paper with an additional 10 to 20 ml of the solvent.
9. Distil solvent from distillation flask over a water bath at 85 °C. To maximize solvent recovery, fit distillation flask with distillation adapter equipped with a drip tip and collect solvent in an ice-bath cooled receiver.
10. When visibly all the solvent has been distilled off, remove distillation adapter and draw air through the distillation flask with applied vacuum for one minute.
11. Remove the flask from water bath and wipe it dry from outside. Cool in a desiccator until the flask obtains a constant weight.

Calculation

The quantity of oil and grease in the water sample is calculated as follows:

Oil and grease (mg/L) = (mass of residue / initial sample volume) * 1000

Safety Guidelines

• Wear safety goggles, an apron, and safety shoes when performing this analysis.
• Use a fume hood when working with hydrochloric acid and hexane.
• Dispose of the solvents and waste materials in accordance with local regulations.

Reference

IS 3025 Part 39: 2021

Keywords

oil and grease, water, liquid-liquid partition gravimetric method, hexane, hydrochloric acid, sodium sulfate, acetone, hexadecane, stearic acid, safety guidelines, IS 3025 Part 39: 2021