Spectroscopy

Introduction to Spectroscopy

• Spectroscopy is the study of the interaction between matter and electromagnetic radiation.

• Familiar constituents of the electromagnetic spectrum:

• High energy gamma rays → X rays → UV → Visible light → Infrared → Microwaves → Radio waves.

Absorption and Emission of Energy

• Molecules absorb specific parts of the spectrum, which is linked to their molecular structure.

• When electrons in a molecule absorb energy, they transition from a lower energy state to a higher energy state.

• Emission occurs when electrons fall back to lower energy states, releasing energy in quantized amounts.

• Instruments measure these energy transitions, revealing the types of compounds present in a sample.

• Applications include:

• Radio waves in MRI.

• Infrared for drug testing and compound identification.

Focus on UV-Vis Spectroscopy

• This experiment uses UV-Vis instrumentation to measure the concentration of sunscreens.

• Energy absorbed relates to the types of functional groups in a molecule.

• The visible spectrum ranges from:

• 700 nm (red light) to 380-400 nm (violet light).

• Human vision is limited to this range; wavelengths longer than violet move into ultraviolet (UV) light.

Ultraviolet Light Regions

• UV light is divided into:

• Near UV, Medium UV, and Far UV.

• Energy levels: UVA (lowest energy) < UVB < UVC (highest energy and most hazardous).

• Differences in human perception of color are subjective (illustrated through the "dress" phenomenon).

Quantifying Spectroscopy

• Objective quantification is necessary to avoid subjective perception.

• UV-Vis Spectroscopy allows definitive analysis using electromagnetic radiation.

• A UV-Vis spectrophotometer specifically measures the absorbance of UV and visible light by materials.

Working of a UV-Vis Spectrophotometer

• Light Source: Emits a broad spectrum across UV and visible ranges.

• Prism: Splits light into constituent wavelengths.

• Wavelength Selection: A slip allows only certain wavelengths to pass through to the sample (e.g., green light).

• Sample Cuvette: Contains the sample where the selected wavelength passes through.

• Detector: Measures the amount of light absorbed by the sample.

• Absorbance Measurement: The difference between light received and light expected is calculated to quantify absorbance (unitless).

• The next step will explore how to correlate absorbance data with concentration and other significant metrics for analysis.