Colorimetry
Section 1: Understanding Colorimetry and Colorimeters
- Colorimetry: A scientific technique used to determine the concentration of a coloured compound in a solution by measuring its absorbance of light.
- Colorimeter: A device designed to measure the absorbance of light by a specific solution. Crucially, it allows the user to select the wavelength of light used.
- Components of a Colorimeter: Primary elements include a light source, a set of coloured filters, a sample holder (cuvette) and a light detector.
- Concept of Absorption: Key to understanding colorimetry is recognising that when light passes through a coloured solution, some wavelengths are absorbed while others are transmitted. The level of absorption or transmission can often reveal details about the solution itself.
Section 2: Using a Colorimeter
- Preparation and Use: Fill a cuvette with your sample solution. Slot it into the colorimeter following the instrument’s instructions. The device will measure the amount of light that passes through the sample and is detected on the other side.
- Readings: The colorimeter will provide readings in terms of absorbance or percent transmittance (%T). The higher the %T, the more light has passed through and less has been absorbed. Conversely, a low %T or high absorbance reading suggests the solution has absorbed a greater portion of the incident light.
- Constructing a Calibration Curve: By creating solutions of known concentrations and measuring their absorbance, you can generate a calibration curve. This curve can then be used to determine the concentration of an unknown sample, based on its absorbance.
Section 3: Care and Considerations for Colorimetry and Colorimeters
- Cuvettes: Use only clean, scratch-free cuvettes. Unclean or damaged cuvettes may interfere with light paths and lead to inaccurate readings.
- Calibration: For accurate results, you’ll need to zero or calibrate the colorimeter using a blank or reference sample. Usually, this is the solvent that the sample is dissolved in.
- Light Source Maintenance: Regularly check the light source to ensure it is working optimally. A weak light source can affect the accuracy of readings.
Section 4: Safety and Troubleshooting with Colorimeters
- Safety: Always wear appropriate lab safety equipment, such as goggles and gloves, when handling solutions.
- Troubleshooting: If you’re getting inaccurate or inconsistent results, check that the cuvette is clean and inserted correctly, that the colorimeter is calibrated, and that the relevant wavelength has been selected.
- Disposal: At the end of its life, dispose of your colorimeter as per local regulations and manufacturer guidelines.