A double beam spectrophotometer irradiates organic matter with UV visible light, causing valence electrons to transition and be selectively absorbed. A group of spectra whose absorbance changes with wavelength, showing the properties of the sample.
In the ultraviolet and visible ranges, the degree of absorption is proportional to the sample’s component concentration. Therefore, the absorption spectrum can be qualitatively examined and compared to a standard sample. Quantitative analysis can also be performed if the concentration is known.
The difference between a double wavelength spectrophotometer and a double beam spectrophotometer
1) double wavelength spectrophotometer
The main feature of a double wavelength spectrophotometer is that light from the same light source is split into two beams, which then go through two monochromators to get two monochromatic lights with different wavelengths (1 and 2). The frequency then alternately shines on the same absorption cell, passes through the photomultiplier tube and the electronic control system, and then the display shows the difference in absorbance at the two wavelengths.
double-wavelength spectrophotometry can often improve the sensitivity and selectivity of a method when it is used to analyze mixtures with more than one component, turbid samples (like fluids from biological tissue), and situations where background interference or interference from other components is present. Using a spectrophotometer with two wavelengths, a derivative spectra can be obtained.
2) double beam spectrophotometer
After the monochromator splits the light, the mirror decomposes it into two beams of equal intensity. One beam travels through the reference cell and the other via the sample cell. The photometer automatically compares beam intensity. This ratio is the sample’s transmittance, which is then turned into a logarithm and recorded as a function of wavelength.
double beam spectrophotometers auto-record absorption spectra. Since the two beams of light pass through the reference cell and sample cell at the same time, errors caused by changes in light intensity are automatically avoided.
Difference between double beam spectrophotometer and Single Beam Spectrophotometer
- doublebeam spectrophotometer
double beam spectrophotometers examine samples by passing two light beams through them and a reference solution. This approach can detect sample changes over time and overcome light source instability and contaminant interference.
- Single beam spectrophotometer
Single-beam spectrophotometers use a light beam travelling through a monochromator to detect light intensity.
The double-beam spectrophotometer’s complicated structure allows for automatic scanning of the absorption spectra, expansion of the wavelength application range, and elimination of light source intensity fluctuations. It measures precisely and quickly, making it ideal for structural research.
double beam light intensity and detector sensitivity fluctuate with time. When only the sample light is measured, the light source’s intensity and the detector’s sensitivity will vary between the baseline and sample measurements, causing inaccuracies. The reference light monitors and corrects for variance.
The two-beam system can make steady measurements even if the light source intensity and detector sensitivity fluctuate. Single-beam devices are affected by light source intensity and detector sensitivity. After turning on a single-beam device, wait for the light source and detector to stabilize before doing baseline correction and automatic zero point correction to reduce oscillations.
Buying a double-light speed spectrophotometer requires several considerations.
1) Photometric accuracy
Photometric accuracy is the difference between the photometric reading that was actually taken and the real value. It can directly show how accurate the instrument’s test data is, which is what the user wants directly from the instrument.
Users pay attention to stability as one of the signs.
The lower limit of the concentration of the tested sample is the main thing that affects noise or limits what it can do.
4) Wavelength precision and repeatability
At a certain wavelength, each value of the instrument is measured. At a certain wavelength, each value of the instrument is measured. If the displayed wavelength is thousands of miles off from the actual wavelength, how can the measured value match the true value.
5) Stray light
Stray light is light that comes in from a different direction than the light that is being absorbed. In other words, light is shining where it shouldn’t. It figures out the range of concentrations of the sample that the instrument is analyzing, especially the maximum concentration.
6) Bandwidth in the spectrum
Refers to the width of the spectral band at half the height of the monochromator’s intensity profile curve for a single spectral line. According to Beer’s Law, the spectral bandwidth should be as small as possible. But if the instrument’s light source is weak and the optical sensor is not sensitive enough, the spectral bandwidth is small and you can’t get the best measurement result. Because of this, the instrument must be chosen and used with care.
double Beam UV-Vis Spectrophotometer Options
1) Select from wavelength range
It is decided whether the required wavelength range is in the ultraviolet range (190nm–340nm), the visible range (340nm–1100nm), or both the ultraviolet and visible ranges.
2) Select from wavelength bandwidth
Different industries have different needs when it comes to the UV-Vis spectrophotometer‘s wavelength bandwidth. The performance of an instrument is better when the bandwidth is narrow, but the price goes up as the bandwidth gets narrower. Not every industry needs to have a narrow bandwidth, but if users can choose based on their needs, that’s fine as long as it works. When discussing bandwidth, it is necessary to mention stray light. When the bandwidth is narrow, there is usually less stray light. A spectrophotometer does, in fact, use stray light as its main technical indicator.
3) Choose from the extra features
double-beam UV-Vis spectrophotometers often have extra features like full wavelength scanning and kinetic scanning (time scanning).
Full wavelength scanning is the process of looking at the whole range of wavelengths, from the smallest to the largest. On the scanning spectrum, the instrument can automatically show the spectrophotometry or transmittance of each set wavelength point, and it can also show the ways in which the sample absorbs light at different wavelengths.
The brand of the photometer shows not only that the equipment is widely used and well-known but also, to a large extent, that the quality of the instrument is professional and stable. This is why it is important to choose a well-known double beam spectrophotometer.
Choose a high-quality photometer by looking at the manufacturer’s technical production appraisal and technical inspection report. Then, make sure that the equipment’s specific parameters, such as frequency range, frequency accuracy, scanning speed, transmittance, resolution, etc., meet your needs.
6) After-sales support
You should know that after-sales photometers are also very careful and helpful when it comes to fixing problems with instruments and keeping them in good shape. Some merchants with good service offer professional instrument training and other services. Choosing a well-sold photometer is also an important part.
This is how to choose a double beam spectrophotometer. In general, there are many things to think about when choosing a good instrument. We can choose high-quality double beam spectrophotometers based on our needs, the brand, the quality, the service after the sale, etc.
What are the optical paths of the double beam UV-Vis spectrophotometer?
The external optical path system of a double-beam UV-Vis spectrophotometer consists of a light source, a reflector, and a lens. The light source consists of a deuterium lamp and a tungsten lamp (a tungsten halogen lamp) and a lamp holder. Some instruments’ external optical paths use lenses or cylinders. These mirror images of the light source onto a single-shot slit. The light source concentrates and uniformly illuminates the monochromator’s entrance slit. The light source filament and incident slit are sometimes considered to be object-images.
1) The deuterium and tungsten lamps are mounted on the concave reflector. The quasi-double-beam UV-Vis spectrophotometer switches light sources via motor-driven mirror vibration.
2) The concave reflector moves while the deuterium and tungsten lamps are fixed. Motor-driven concave mirrors swap light sources.
3) The concave reflector, deuterium light, and group seat are fixed. Motor-driven movement of the deuterium lamp and tungsten lamp group seat switches the light source.
4) If a deuterium-tungsten lamp is used in the double-beam UV-Vis spectrophotometer, the lamp is on the left or right side of the concave mirror. The mirror is fixed, and the light source is seen through the mirror on the entrance slit.
How many photoelectric converters does the double beam UV-Vis spectrophotometer have?
double beam UV-Vis spectrophotometers have two light beams, two cuvettes, and two photoelectric converters. double-beam UV-Vis spectrophotometers use photomultiplier tubes as photoelectric converters (PMTs).
1) Two photoelectric converters
Using a double-beam UV-Vis spectrophotometer with two photomultiplier tubes, light source fluctuations, stray light, and electrical noise may be offset. Thus, photometric accuracy is good in fixed-point measurement, but the construction is more difficult and the price is higher. Due to mismatched photomultiplier tube spectral response characteristics, this double-beam UV-Vis spectrophotometer is not used for scanning. Because one beam is split into two, each beam’s energy is low and the signal-to-noise ratio is lower than with a single beam UV-Vis spectrophotometer.
2) A photoelectric converter meter
double-beam UV-Vis spectrophotometers have superior technological indicators. Due to two light beams, light source fluctuations, stray light, and electronic noise can be partially offset, reducing stray light and photometric noise. double-beam UV-Vis spectrophotometers provide good photometric accuracy. double-beam UV-Vis spectrophotometers with photoelectric converters have this advantage. Splitting a monochromatic beam into two halves, each beam’s energy double-beam UV-Vis spectrophotometers with one photoelectric converter have a worse signal-to-noise ratio than single-beam models. Since the two beam routes cancel noise, sensitivity is still high.
double-beam UV-Vis spectrophotometers with two photoelectric converters are unusual, and most instruments with a photoelectric converter, notably double-beam UV-Vis spectrophotometers, are all analog.