2 As two different light sources are needed to scan both the UV and visible wavelengths, the light source in the instrument must switch during measurement. Xenon lamps are, however, associated with higher costs and are less stable in comparison to tungsten and halogen lamps.įor instruments employing two lamps, a tungsten or halogen lamp is commonly used for visible light, 2 whilst a deuterium lamp is the common source of UV light. A single xenon lamp is commonly used as a high intensity light source for both UV and visible ranges. Justin Tom.Īs a light-based technique, a steady source able to emit light across a wide range of wavelengths is essential. Whilst there are many variations on the UV-Vis spectrophotometer, to gain a better understanding of how an UV‑Vis spectrophotometer works, let us consider the main components, depicted in Figure 1.įigure 1: A simplified schematic of the main components in a UV-Vis spectrophotometer. How does a UV-Vis spectrophotometer work? Therefore, light can be described by its wavelength, which can be useful in UV-Vis spectroscopy to analyze or identify different substances by locating the specific wavelengths corresponding to maximum absorbance (see the Applications of UV-Vis spectroscopy section). 1 UV light has wavelengths shorter than that of visible light to approximately 100 nm. Humans are able to see a spectrum of visible light, from approximately 380 nm, which we see as violet, to 780 nm, which we see as red. This is why the absorption of light occurs for different wavelengths in different substances. Electrons in different bonding environments in a substance require a different specific amount of energy to promote the electrons to a higher energy state.

A specific amount of energy is needed to promote electrons in a substance to a higher energy state which we can detect as absorption. Thus, shorter wavelengths of light carry more energy and longer wavelengths carry less energy. Light has a certain amount of energy which is inversely proportional to its wavelength. Since this spectroscopy technique relies on the use of light, let’s first consider the properties of light. This property is influenced by the sample composition, potentially providing information on what is in the sample and at what concentration. UV-Vis spectroscopy is an analytical technique that measures the amount of discrete wavelengths of UV or visible light that are absorbed by or transmitted through a sample in comparison to a reference or blank sample.

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