Name: uv-vis spectrophotometer parts and samples
Uploaded: 2024-12-05T18:32:04.000Z
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High School

Chemistry

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Motion And Stability: Forces And Interactions

HS-PS2-6

UV&ndash;Vis Spectrometers

A UV&#8211;Visible spectrometer consists of a light source, such as a deuterium lamp for the UV region and a tungsten lamp for the visible region, a monochromator, a sample holder,&#160; and a detector.
Visible spectroscopy uses sample cells of glass or plastic, while UV spectroscopy uses cells of quartz.
The prism splits the beam of light into its component wavelengths, and a system of slits and filters focuses the desired wavelength on the sample cell.
The photodiode detector measures the intensity of light passing through the sample cell.
In single beam instruments, the monochromator placed between the source and the sample allows analysis of one wavelength at a time.
Alternatively, in a double beam instrument the monochromator is equipped with splitters and mirrors, which split the light into two beams. The sample beam passes through the sample cell, and the reference beam passes through the reference sample.
The two spectra are subtracted to remove contributions from the reference sample from the acquired raw spectrum.

uv&ndash;vis spectrometers

The absorbance of UV and visible (UV&#8211;visible) radiations is measured using a UV&#8211;visible spectrophotometer. Deuterium lamps, which emit UV radiation, and tungsten lamps, which produce radiation in the visible region, are used as light sources in UV&#8211;visible spectrophotometers. A monochromator or prism is used for diffraction grating, i.e., to split the incoming radiation into different wavelengths. A system of slits is used to focus the desired wavelength on the sample cell. Samples for UV&#8211;visible spectrophotometer must be in the liquid phase. Therefore, solid organic compounds should be dissolved in a suitable solvent prior to analysis. The sample is then placed in a sample holder known as a cuvette. Depending on the sample, and the radiation used, the cuvette may be made of quartz crystal, glass, or plastic. Glass or plastic sample cells are used in visible spectroscopy because their spectral cutoffs are around 350&#8239;nm&#8212;meaning they effectively transmit visible light but absorb UV. UV spectroscopy uses quartz cells with a lower cutoff of around 200&#8239;nm to allow transmission of UV light.
Since the solvent will also absorb light, a sample blank of the solvent alone is used prior to analyzing the actual sample. Selecting a suitable solvent for ultraviolet spectroscopy is critical for accurate absorbance measurements. Water, 95% ethanol, and hexane are the most commonly used solvents in UV&#8211;visible spectroscopy. A suitable solvent also helps get the fine structure of an absorption band. Nonpolar solvents do not form hydrogen bonds with the solute. As a result, the final spectrum of the solute will be similar to the spectrum observed in the gaseous phase, where fine structure is often present. In contrast, polar solvents do form hydrogen bonds with the solutes, which means that the fine structure of an absorption band will not be present.
A photomultiplier tube, charge-coupled devices, and photodiode or photodiode array are usually used as detectors. The intensity of the light passed through the sample cell is referred to as I. In a single-beam instrument, all of the light passes through the sample cell. In a double-beam instrument, the light is split into two beams; one beam is used as the reference, and the other beam is passed through the sample. In modern diode-array spectrophotometers, photodiode detectors are used to record the entire spectrum at once.

The absorbance of UV and visible (UV&#8211;visible) radiations is measured using a UV&#8211;visible spectrophotometer. Deuterium lamps, which emit UV ...

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Analytical Chemistry

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Introduction to Molecular Spectroscopy

KEY TERMS AND CONCEPTS

uv-vis spectrophotometer parts and samples

A UV-visible spectrophotometer measures how much UV and visible light a sample absorbs. It uses a light source, a wavelength selector, a sample holder, and a detector to build the spectrum. This makes it useful for checking liquid samples in the lab.

The light source depends on the region being measured. A deuterium lamp provides UV radiation, and a tungsten lamp provides visible radiation. A monochromator or prism acts as a diffraction grating and splits the incoming light into different wavelengths. Slits then focus the chosen wavelength on the sample cell.

Samples must be in liquid form before analysis. Solid organic compounds are first dissolved in a suitable solvent. The sample is placed in a cuvette, which is the small holder used in the instrument. Quartz crystal, glass, or plastic cuvettes may be used, depending on the sample and the radiation.

Glass or plastic cells are used for visible spectroscopy because their spectral cutoffs are around 350 nm. That means they transmit visible light but absorb UV light. UV spectroscopy uses quartz cells, which have a lower cutoff of about 200 nm and can transmit UV light. A blank made of the solvent alone is measured first, since the solvent also absorbs light.

Choosing the right solvent is important for accurate absorbance measurements in ultraviolet spectroscopy. Water, 95% ethanol, and hexane are common solvents in UV-visible work. The solvent can also affect fine structure in an absorption band. Nonpolar solvents do not form hydrogen bonds with the solute, so the spectrum can resemble the gaseous phase, where fine structure is often seen. Polar solvents do form hydrogen bonds, so that fine structure is usually not present.

The detector measures the light that passes through the sample cell, often written as I. Common detectors include photomultiplier tubes, charge-coupled devices, and photodiode or photodiode array systems. In a single-beam instrument, all of the light passes through the sample cell. In a double-beam instrument, the light is split into two beams, with one used as the reference and the other sent through the sample. Modern diode-array spectrophotometers use photodiode detectors to record the whole spectrum at once.

UV-Vis Spectrophotometer Parts and Samples

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A UV-visible spectrophotometer measures how much UV and visible light a sample absorbs. It uses a light source, a wavelength selector, a sample holder, and a detector to build the spectrum. This makes it useful for checking liquid samples in the lab. The light source depends on the region being measured. A deuterium lamp provides UV radiation, and a tungsten lamp provides visible radiation. A monochromator or prism acts as a diffraction grating and splits the incoming light into different...

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key terms and concepts

Learn how UV-visible spectrophotometers use lamps, cuvettes, solvents, and detectors to measure absorbance in liquid samples and record spectra.

UV-Vis Spectrophotometer Parts and Samples | JoVE K12

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UV-Vis Spectrophotometer Parts and Samples

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