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1. COLORIMETERS AND SPECTROPHOTOMETERS
Colorimeters are electrically powered instrument that are used to measure the concentration of the colored solution
Components of a Colorimeter
All types of colorimeters consist of the following:
- The light source consisting of ordinary bulb
- The filter used to produce monochromatic light
- Wavelength selector
- Cuvettes to hold the colored solution being investigate
- Galvanometer and absorptiometry.
How to use a Colorimeter
- Switch on the colorimeter and let it warm for a duration that have been recommended by the manufacturer. These is important for optimum performance of filters and light detectors
- Set the wavelength to the correctwavelength or simply insert the correct filter for the substance to be tested
- Arrange the blank, standard and the test solution in the test tube rack
- Clean the cuvettes using soft material e.g. Lens cleansing tissue or cotton gauze to avoid scratching them. Do not touch the sides of the cuvettes with fingers. instead hold them by the groundsides or sides which do not face the direction of light
- Transfer the blank solution into the cuvette and place it into the cuvette chamber with its aides facing the light path. close the cuvette chamber and set the absorption to zero
- Remove the cuvette from the chamber , pour the blank solution back into the test tube then pour the standard solution into the cuvette and record the absorbency
- Repeat with the test solution and also record the absorbency
- Rinse the cuvette with distilled water , drain off and wipe with the sort material and store carefully in small boxes to avoid scratches and dust
- Calculate the concentration of the test solution as :
Conc. of test sol = Abs of test sol X Conc. std sol
Absorbency of standard sol
Sources of error in Colorimetry
Colorimetry is subject to some errors which may be due t
- Use of faulty techniques e.g. failure to mix the solutions adequately, inaccurate pipetting etc.
- Use of wrong filters for solution being tested
- Contamination of the reagents , standards or samples
- Use of scratched or dirty cuvettes
- Wrongly placing of the cuvettes in the cuvette chamber
- Use of cuvettes that are not recommended by the manufacturer
- Incomplete color development due to reading results early or fading of color due to prolonged delay
- Reading solutions containing air bubbles
- Obtaining readings from colorimeters whose cuvette chambers are open
Care and Maintenance of Colorimeters
- Keep them away from direct sunlight and near a power source
- Switch off the colorimeter after use.
- Clean the cuvettes and store carefully.
- Cover the colorimeter with a plastic cover to prevent dust and lock it in a cupboard .Keep the cuvette chamber closed at all times.
- Protect the optical components from dirt and fingerprints.
- Wipe away immediately any liquid spilled on the colorimeter using a clean gauze or tissue paper.
- Do not use organic solvent e.g., xylene, acetone, ether alcohol etc. to clean detachable filters instead use lens tissue .Store detachable filters in a box or polythene bags.
- Replace the bulb carefully using the manufacturer’s instruction. All servicing should be left to qualified experts.
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