Table of Contents
INTRODUCTION
Colour measurement on Lovibond scale is useful for determining the quality of oils and in the refining processes. Measurement of colour serves to check the bleaching processes also.
PRINCIPLE
This method determines the colour of oils by comparison with Lovibond glasses of known colour characteristics.
The colour is expressed as the sum total of the yellow and red slides used to match the colour of the oil in a cell of the specified size in the Lovibond tintometer.
REQUIREMENTS
- Apparatus
- Lovibond Tintometer or Colorimeter
- Glass Cells – The Lovibond cell designations namely, ¼”, ½”, 1” and 5¼” are recommended.
- Filter Paper
PROCEDURE
- Melt the sample, if it is not already liquid, and filter through a filter paper to remove any impurities and the last traces of moisture.
- Make sure that the sample is absolutely clear and free from turbidity.
- Clean the glass cell of the desired size with carbon tetrachloride and allow it to dry.
- Fill it with the clear filtered sample and place the cell in position in the tintometer.
- Place alongside it such red, yellow, blue, or neutral Lovibond glass slides or any combinations of these as are necessary to match the color shade of the oil, observing the colors of the oil and of the combination of the glass slides through an eyepiece.
CALCULATION
The dimensions of the cell used and the mode of expressing the colour reading for different oils shall be as follows:
Colour reading in (*) cell = (aY + 5 b R ) or ( a Y + 10 b R) *Size designation of the cell used,
where,
a = the sum total of the various yellow (Y) slides used, and
b = the sum total of the various red (R) slides used.
RESULTS AND INFERENCE
The difference between the results of two determinations carried out simultaneously or in rapid succession by the same analyst (repeatability) shall not exceed 0.2 units for each colour.
The maximum colour intensity of commonly used edible refined oils in Lovibond scale is given below.
| Type of Oil | Y+5R Unit | Type of Oil | Y+5R Units |
| Coconut oil | 2 | Safflower oil | 15 |
| Cottonseed oil | 10 | Sunflower oil | 5 |
| Groundnut oil | 3 | Soybean oil | 20 |
| Mustard oil | 15 | Rice bran oil | 20 |
| Sesame oil | 2 | Palm oil | 50 |
PRECAUTIONS
• Fat should be melted and any oil or fat that is cloudy should be filtered at a temperature not more than 60°C.
• Colour readings need to be taken within a comparatively.
• Lamp should not be used continuously for a long time.
• During matching, the sample should be at room temperature for oils or not more than 10°C above the melting point.
• Do not strain your eyes for a long time, allow to relax from time to time.