The Principle of UV spectrophotometer

The Lambert-Beer law is used to figure out how much something is by using spectrophotometry. That is, the amount of a substance that can be absorbed at a given concentration is proportional to how thick the medium is that can absorb it. The electronic structure of a substance is linked to how it looks.

When radiation (photons) causes electronic transitions that move molecules (or ions) from the ground state to the excited state, the molecules (or ions) will absorb light in the visible or ultraviolet range. The molecule’s normal electronic structure is changed in a way that makes the color happen or change. Radiation can change the electron energy of a molecule if it has one or more chromogenic genes, which are groups of atoms with broken bonds.

Difference between a Spectrophotometer and a UV spectrophotometer

A visible spectrophotometer’s wavelength range is usually between 350nm and 1100nm, and an ultraviolet-visible spectrophotometer’s wavelength range is usually between 190nm and 1100nm. Because of this, the range of wavelengths that can be used is different. From 190 to 350 nm, there are more waves. Because of this difference in ultraviolet light, it is clear that there are some differences in the way their instruments are put together, such as:

1) Different light sources: The visible spectrophotometer usually only has one light source, a tungsten lamp. The UV-Vis spectrophotometer, on the other hand, has two light sources: a tungsten lamp and a deuterium lamp, and there are extra parts to switch between the two. This is because the tungsten lamp gives off most of its light in the visible to near-infrared range, while the deuterium lamp gives off most of its light in the ultraviolet range.

2) Different devices that use light: Since glass can absorb UV waves and is good at letting light through from the visible end to the near-infrared end, it can be used in some optical parts of the visible spectrophotometer but not in the UV-visible spectrophotometer. Glass parts generally use quartz optical parts. At the same time, this is why different cuvettes are used for different things. Visible spectrophotometers can use glass cuvettes, while quartz cuvettes are most often used in UV-Vis spectrophotometers.

Visible UV spectrophotometer vs. Atomic Absorption spectrophotometer

1) Principle

Atomic absorption looks at how electrons move around in the atomic orbitals of the elements (atoms) that make up the material. Molecular absorption, on the other hand, looks at how electrons move around in the molecular orbitals of the molecules that make up the material. They are both the same and different.

Quantitative analysis works the same way, but the amount of light needed to measure is different. Atomic absorption is a ray with a lot of energy that can move electrons from a low orbit to a high orbit. UV-visible absorption is the absorption of ultraviolet light and visible light with a small amount of energy. There are only electrons that can be excited so that they can move from a molecular orbital to a lower (or next lower) empty orbital.

In simple terms, the atomic absorption spectrophotometer burns the sample at a higher temperature to turn it into atoms. The ground state atoms are then excited by the characteristic radiation, and the energy is absorbed. The energy difference is then used to figure out the concentration.

The UV-Vis spectrophotometer reacts with our measured element through a color developer. The reactant molecule has a certain color, and it is put in front of a molecular absorption deuterium lamp (ultraviolet region) or a tungsten lamp (visible region) to absorb the energy given off by the lamp and figure out the concentration based on the energy difference.

2) Structure

There are two different kinds of light sources. The UV-Vis spectrophotometer uses a tungsten lamp or a deuterium lamp to give off a continuous spectrum, while the atomic absorption spectrophotometer uses a hollow cathode lamp to give off sharp light with characteristic wavelengths, and the selectivity will be better. The two detectors don’t work the same way. UV-visible spectrophotometers usually find things by using photocells. Photomultipliers are used in atomic absorption spectrophotometers because they are more accurate than photocells.

3) Application: Atomic absorption spectrophotometers are part of the atomic spectrum, while UV-visible spectrophotometers are part of the molecular spectrum. Both types of spectrophotometers follow the Lambert-Beer law, but an atomic absorption spectrophotometer has a low detection limit, while a flame atomic absorption method can have a high detection limit. If the UV-Vis spectrophotometer gets to the ppb level and the color developer is different, the detection limit will be different, but each color developer will also cause a different amount of interference.

The atomic absorption spectrophotometer’s standard solution can be kept for a long time at 4 °C and can be used normally once it has been brought to room temperature.

Atomic absorption spectrophotometers are easy to use and can analyze samples quickly. It can measure 5 or 6 elements at the same time in dozens of samples in half an hour. Because of how the UV-Vis spectrophotometer makes colors, it takes a short amount of time to measure and is hard to use.

How to Choose a UV-Vis Spectrophotometer

UV-Vis spectrophotometers come in many different styles. There are three types of spectrophotometers based on how they are built: a single-beam spectrophotometer, a double-beam spectrophotometer, and a dual-wavelength spectrophotometer.

1) Single-beam spectrophotometer: The light from the light source is split by a monochromatic to form a monochromatic beam of light.After going through the absorption cell, the light always hits the detector in the form of a beam. This type of spectrophotometer is simple and cheap, but it is not very accurate because stray light and changes in the light source affect it a lot.

2) The monochromatic light that comes from the light source and is emitted by the double beam spectrophotometer is split by the monochromator and split into two beams of equal intensity by the mirror (light cutter). The reference solution and the sample solution each pass through one of the beams.

Since the two beams of light pass through both the reference solution and the sample solution at the same time, errors caused by changes in the intensity of the light source can be automatically fixed. The double-beam spectrophotometer can usually record the absorption spectrum curve automatically, and it is sensitive. However, its structure is more complicated, and it costs more.

3) Light from the same light source is split into two beams in a dual-wavelength spectrophotometer.Each beam passes through two monochromators to make two beams of monochromatic light with different wavelengths. Then, a light cutter is used to make two beams of monochromatic light with different wavelengths. You could also shine light on the same solution at a certain frequency and then send it through the photomultiplier tube and electronic control system.

Dual-wavelength spectrophotometry gets rid of some background interference and interference from components that are already there. This makes the analysis more sensitive. The dual-wavelength spectrophotometer can be used to measure turbid samples like biological tissue fluids that can’t be measured by regular spectrophotometers. It can also be used to measure samples with a lot of different components mixed together.

When choosing a UV spectrophotometer, you should first decide if the experiment is a qualitative or quantitative analysis. You should also think about the state of the sample being tested (liquid, gas, or solid). The price difference between models is, of course, the most important thing to consider. If you have enough money, choose a spectrophotometer with good sensitivity. When choosing a lab, you should think about what your lab needs and what it will be used for. There are a lot of things to think about, including the structure and source of light in the optical system, the ways in which the light is picked up, and how the data is processed.

1) Optical structure

In general, there are two types of UV-Vis spectrophotometers: those with a single beam and those with a double beam. The single-beam type, as the name suggests, mostly uses a single beam of light to measure. To get the absorbance result, a beam of light with a certain wavelength goes through a control object and then through the sample solution.

The double beam type splits one beam into two beams, one for measuring the control sample and one for measuring the actual sample. You can cut down on optical drift and measurement time. Because they can measure things more quickly, dual-beam spectrophotometers are good for studies that look at how some solutions change over time.

2) The source of light and its detection

Another important thing to think about is the spectral range of the spectrophotometer. Researchers in the lab usually want to buy specialized tools for a low price so they can measure the growth of nucleic acids, proteins, or bacteria. If researchers need more options, they might think about getting a high-performance, broad-spectrum instrument that can program both ELISAs and colorimetric assays.

UV spectrophotometers usually measure wavelengths between 190 nm and 380 nm. They are usually lit with a deuterium lamp. There are special tools that can be used for research in photonics and semiconductors.

Some instruments have UV, visible, and even infrared light sources (780 nm to 3,000 nm). Tungsten and halogen lamps usually only light up what can be seen (approximately 380 nm to 800 nm). The xenon lamp can work with both UV and visible light.

The width of the monochromator’s slit has a lot to do with how wide a spectrophotometer’s measuring range is. Spectra can be shown exactly how the experiment needs them to be shown. The instrument can measure the absorbance of complex mixtures with high resolution because it has a narrow bandwidth. Because the monochromator slit width can be changed, a spectrophotometer can be used for a wide range of experiments.

Photomultiplier tubes and photodiodes are often used in spectrophotometers to measure absorbance. Photomultiplier tubes respond quickly, are sensitive, and can be tuned to a certain part of the UV spectrum. The photodiode has a wide dynamic range, which means that all spectral measurements can be made in seconds.

3) Data management

Most spectrophotometers that work on their own have software that runs the instrument and keeps track of the data. Most of the time, high-performance instruments are used with a PC, and users can also choose to upgrade the software to fit their needs.

Other important factors

1) Photometric accuracy: This is the difference between the actual measured photometric reading value and the real value, which is what the person using the instrument needs.

2) Stray light: This is the main reason why spectral measurements are often wrong. Of course, the value should be as small as possible.

3) The spectral bandwidth is defined as half the height of the monochromatic spectral line intensity profile curve from the monochromator. Describe how well the instrument can separate different colors. In Beer’s law, the spectral bandwidth should be as small as possible. If the instrument’s light source isn’t very bright and the optical sensor isn’t very sensitive, the spectral bandwidth isn’t very wide. This means that the ideal measurement result can’t be reached.

4) Stability: One of the most important indicators for users is stability.

5) Noise: Noise is one of the most important signs of a good instrument.

It talks about how the instrument can be used to make diluted solutions. The better this is, the smaller this number is.

6) Wavelength accuracy and repeatability: Each instrument value is measured at a specific wavelength. If the wavelength shown on the screen is very different from the real wavelength, the measured value and the real value will be very different.


Why doesn’t the UV spectrophotometer send out a signal that it has found something?

There is a chance that none of the beams of light hit the sample chamber. We can set the wavelength to 530nm, open the slit as wide as possible, put a piece of white paper at the light window of the sample room in a dark room, and see if there is an image of a green light spot on the paper. Check to see if the light source mirror is on and if the double-beam instrument’s light-cutting motor is turning (the sound of the motor rotating can be heard by the ear)

Negative numbers for a long time or loud noises on the UV spectrophotometer’s full screen?

It’s possible that the motor that feeds the filter is “out of step,” which would cause the gear to be in the wrong place. We can get the machine to work again in many ways. We can start it up again, or we can open the monoc