Visible-ultraviolet spectrometer (UV-Vis)

UV-Vis Spectrophotometer

**A UV-Vis Spectrophotometer is an instrument used to measure the quantity of a substance based on how much electromagnetic radiation it absorbs. The material being analyzed in a spec is usually in liquid form. Using this method, substances that are colored and absorb light in the visible range, or those capable of absorbing ultraviolet light, are studied.**

**The light radiation in spectrophotometers is generated using a tungsten lamp for the visible region and a deuterium lamp for the ultraviolet region. Spectrophotometers are used for a wide range of applications in qualitative and quantitative material measurement in various laboratories and scientific research fields like chemistry, biochemistry, pharmaceuticals, materials science, and environmental studies.**

**There are two main types of UV-Vis spectrophotometers: the Single-Beam and the Double-Beam Spectrophotometer. The benefits of single-beam systems include their simplicity, compact size, and low cost. Their drawback, however, can be slight errors resulting from the sample environment.

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How the Instrument Works:

The amount of light absorbed by a sample is directly proportional to the concentration of the substance within it. In this method, if the sample is a solid, we first dissolve it in an appropriate solvent during the sample preparation process to create a uniform solution. To eliminate background absorption, a "blank sample" is typically prepared. This blank should ideally be similar to the actual sample but must not contain the analyte (the substance being analyzed). The absorption resulting from this blank sample is considered the background absorption from the sample matrix and is subtracted from the main sample's absorption to determine the true absorption of the analyte. It's important to note that before being placed in the instrument, samples are poured into glass or quartz sample cells (cuvettes). The type of cell depends on the analysis range. Glass absorbs UV light, so it can only be used for measurements in the visible region. Quartz cuvettes are necessary for measurements in the UV region.

Next, as light passes through the sample, the sample absorbs specific wavelengths, causing the intensity of certain wavelengths in the transmitted light beam to decrease. Every material has a set of absorption mechanisms, and each of these mechanisms can absorb a particular wavelength. In the UV-VIS analysis instrument, the light beam exiting the sample is dispersed by a prism, and then a sensor measures the intensity of each individual wavelength. The instrument's software compares the intensity of the output wavelengths with the baseline (reference) state and reports the absorption intensity at each wavelength as a graph. By identifying the absorbed wavelengths and knowing the sample type, one can determine which substance caused the absorption and confirm the presence or absence of that substance in the sample.

Instrument Components:

Light Source
Prism or Diffraction Grating
Monochromator
Detector
Processor

Applications:

Studying a substance's absorption and transmittance properties over a wavelength range.
Monitoring changes in absorption and transmittance at a specific wavelength over a period of time.
Examining the degree of absorption at several specific wavelengths.
Measuring the energy band gap.
Qualitative and quantitative identification of one or more specific species in a mixture.
Measuring solution concentration.