Content1. What is circular dichroism spectrometer?
1.1 Working principle of circular dichroism spectrometer
1.2 Feature of circular dichroism spectrometer
1.3 Function of circular dichroism spectrometer
1.4 Application of circular dichroism spectrometer2. Use of circular dichroism spectrometer
2.1 Circular dichroism spectrometer (CD) sample requirements
2.2 Precaution of circular dichroism spectrometer3. How to buy circular dichroism spectrometer?
What is circular dichroism spectrometer?
The instrument designed according to the principle of circular dichroism and test requirements is called circular dichroism spectrometer. Nowadays, circular dichroism and its instruments have been widely used in organic chemistry, biochemistry, coordination chemistry and medicinal chemistry, and it has become an important method to study the stereo-configuration of organic compounds.
Working principle of circular dichroism spectrometer
Light is a transverse electromagnetic wave, which is a ray that vibrates in all directions. Its electric field vector E is perpendicular to the magnetic field vector H and is perpendicular to the direction of light wave propagation. Because the electric field vector is the main role in producing light sensitivity, the vibration vector of a light wave is usually the electric field vector. The plane formed by the electric field vector and the direction of propagation of the light wave is called the vibrating surface of the light wave. If the vibrating plane does not change with time, then the light is called plane-polarized light, and its vibrating plane is called the polarization plane. Plane polarized light can be decomposed into two circularly polarized lights with the same amplitude and frequency and opposite directions of rotation. The electric vector rotating in the counterclockwise direction is called left-rotating circularly polarized light, and the electric vector rotating in the clockwise direction is called right-rotating circularly polarized light. With two beams of the same amplitude and frequency, the direction of rotation of the oppositely polarized light can also be synthesized into a beam of plane-polarized light. If the amplitude (intensity) of the two polarized beams are not the same, then the synthesis is a beam of elliptically polarized light.
The difference between the absorption rates of left and right circularly polarized light of an optically active substance is called circular dichroism (Al - Ad). The plane-polarized light propagating through the substance becomes elliptically polarized due to the presence of circular dichroism, and is only observed at the wavelength where the absorption occurs. The difference between the absorption of left- and right-hand circularly polarized light by an optically active substance, ΔA (Al - Ad), is called the circular dichroism of the substance. The plane-polarized light propagating through the substance becomes elliptically polarized due to the presence of circular dichroism, and is only observed at the wavelength where the absorption occurs.
According to the Lambert-Beer law, the ellipticity can be proved, and the circular dichroism spectral curve
is measured as the relationship between theta (or Δε) value and wavelength λ at different wavelengths. If there is no characteristic absorption of the measured substance in this spectral curve, it means that the value of Δε is very small and the characteristic circular dichroism spectrum cannot be obtained. When εl is larger than εd, a positive circular dichroism spectral curve is obtained, which means that the measured substance is right-handed; if εl is smaller than εd, then a negative circular dichroism spectral curve is obtained, which means that the measured substance is left-handed.
Feature of circular dichroism spectrometer
a. Dual light source design provides an unmatched signal-to-noise ratio. The technology has been upgraded to eliminate errors in the solid sample itself when measuring solid samples and to acquire IR spectra and vibrational circular dichroism spectra simultaneously. Digital signal processing of circular dichroic spectra without locking or electronic filtering. The independent infrared light source interface and the constant temperature of PEM can obtain the baseline without warp time change.
b. The optical axis is controlled with high precision, and the device is optimized by controlling artifacts and warp time changes. The circular dichroic spectrum
is detected by the DSP locking function that is suitable for the VCD algorithm, and the signal-to-noise ratio is greatly improved.
c. The optical system, sample chamber and detector can be purged, and the measurement can be stable without the influence of the atmosphere. Circular dichroism spectroscopy
is mainly used for the study of chiral optically active substances. It can be used for organic stereochemistry, purity testing of optically active substances, quantitative analysis of drugs, natural organic chemistry, biochemistry and macroscopic macromolecules, metal complex chemistry, polymer chemistry, protein folding studies, protein conformation studies, physical chemistry, etc.
d. Instead of correcting linear anisotropy artifacts, the auto-alignment system directly eliminates them.
e. High-intensity ceramic light source, long life and high energy, the use of ten years.
f. Optional accessories are used for automatic sampling.
g. Digital signal processing is used to make the sensitivity enhanced.
h. A thermally stabilized modulator system is used to take the baseline drift out of the equation.
i. Operation of the oversized Dewar bottle for up to 15 hours is allowed without refills.
Function of circular dichroism spectrometer
Circular dichroism spectrometer is an effective analytical instrument for the study of molecular structural asymmetries, allowing the following measurement functions.
a. Circular dichroism (CD)
b. Optical Rotatory Dispersion (ORD)
c. Line dichroism (LD)
d. Fluorescent circular dichroism (FDCD)
e. Magnetic circular dichroism (MCD)
Application of circular dichroism spectrometer
Circular dichroism spectrometers are widely used in the following industries.
a. Structure determination of optically active compounds.
b. Conformational studies of proteins, peptides, and nucleic acids.
c. Reaction kinetics.
d. Thermal and chemical denaturation studies.
e. The study of the absolute conformation of compounds.
f. Circular dichroism for biomolecule research, protein secondary structure, etc.
Use of circular dichroism spectrometer
Circular dichroism spectrometer (CD) sample requirements
a. A blank solvent is required for the test as a control background, with at least 5 ml of sample and solvent each. The sample must maintain a certain level of purity without light-absorbing impurities, and the solvent must have no absorption interference at the measurement wavelength. The sample can be completely dissolved in the solvent, forming a homogeneous and transparent solution.
b. The concentration of the sample and solvent has a strong influence on the test and should not be too high or too low. If the concentration is too high, the voltage will be exceeded and the data will be inaccurate, while if the concentration is too low, there will be no signal. The optimum concentration is different for different substances, so the concentration should not be explored during the test.
c. Control of nitrogen flow.
d. Buffers and solvents are individually checked for absorption interference or formation of precipitates and gels in the measurement wavelength range before preparing the solution. In protein measurements, the phosphate with excellent transparency is often chosen as the buffer system.
e. If the samples are different, the measured circular dichroism spectral range is different, and the selection of the cell size (optical diameter) and the concentration requirements are different. Protein CD spectroscopy measurements are generally performed in relatively dilute solutions.
Solid CD sample preparation requirements
a. 10-20 mg of solid CD is required, preferably powdered samples, special samples can be communicated specifically.
b. If the sample penetration is not good, it is recommended to use integrating sphere mode.
c. Before sending the sample, please note the storage temperature of the sample and whether ice packs or dry ice are required to prevent deterioration of the sample during the sample preparation process and to prevent the test results from being affected.
Precaution of circular dichroism spectrometer
a. Instrument failure should be reported to the technician in time to deal with. When an abnormality occurs in the instrument, the operator should immediately turn off the power, protect the site and report it in time.
b. The operator shall not enter any procedure other than that specified in the operating procedures, and shall not press any function key other than that specified. The operator should be careful when removing the sparking plate to prevent scratches on the inner surface. The operator should be careful when taking out the round quartz spacer and glass casing inside the spark chamber to prevent them from breaking due to improper operation.
c. The clamp should be vertical when pressing the sample. Do not press the excitation button while the sample is not clamped. Do not touch or lift the sample clip when excited.
d. After the excitation of the sample in the spark table to produce black deposits will lead to a short circuit between the electrode and the spark table, so the spark table should be cleaned regularly.
e. Non-post personnel is not allowed to enter the machine room, smoking and eating food are prohibited in the machine room.
f. If the operator encounters a sudden power failure, he should first turn off the total, and then turn off the other power supplies, wait until the call comes, and then operate the machine according to the terms of the regulations.
How to buy circular dichroism spectrometer?
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