Applications

Spin trapping electron paramagnetic resonance (EPR) method is a method that combines the spin-trapping technique with the EPR technique to detect short-lived free radicals.     Why Use Spin Trapping Technology?Free radicals are atoms or groups with unpaired electrons formed by the covalent bonding of compound molecules under external conditions such as heat and light. They are widely found in nature.With the development of interdisciplinary disciplines such as biology, chemistry, and medicine, scientists have found that many diseases are associated with free radicals. However, due to their active and reactive nature, the free radicals generated in the reactions are often unstable at room temperature and difficult to be detected directly using conventional EPR spectroscopy methods.    Although short-lived free radicals can be studied by time-resolved EPR techniques or low-temperature fast-freezing techniques, their lower concentrations for most free radicals in biological systems limit the implementation of the above techniques. The spin trapping technique, on the other hand, allows the detection of short-lived free radicals at room temperature through an indirect method.     Fundamentals of Spin Trapping Technology   In a spin-trapping experiment, a spin trap (an unsaturated antimagnetic substance capable of trapping free radicals) is added to the system. After adding the spin trap, the unstable radicals and the trap will form more stable or longer-lived spin adducts. By detecting the EPR spectra of the spin adducts and processing and analyzing the data, we can invert the type of radicals and thus indirectly detect the unstable free radicals.     Figure 1 Principle of spin capture technique (DMPO as an example)     Selection of Spin Trap   The most widely used spin traps are mainly nitrone or nitroso compounds, typical spin traps are MNP (2-methyl-2-nitrosopropane dimer), PBN (N-tert-butyl α-phenyl nitrone), DMPO (5,5-dimethyl-1-pyrroline-N-oxide), and the structures are shown in Figure 2. And an excellent spin trap needs to satisfy three conditions.   1. Spin adducts formed by spin traps with unstable free radicals should be stable in nature and long-lived. 2. The EPR spectra of spin adducts formed by spin traps and various unstable radicals should be easily distinguishable and identifiable. 3. Spin trap is easy to react specifically with a variety of free radicals, and there is no side reaction. Based on the above conditions, the spin trap widely used in various industries is DMPO.     Figure 2 Schematic chemical structure of MNP, PBN, DMPO   Table 1 Comparison of common spin traps     Common Types of Spin-trapping Free Radicals   In spin trapping experiments, the most common ones are O- and N-centered radicals, such as reactive oxygen species (ROS) and reactive nitrogen species (RNS), but not all ROS and RNS are free radical...

The electron paramagnetic resonance (EPR or ESR) technique is the only method available for directly detecting unpaired electrons in samples. Among them, the quantitative EPR (ESR) method can provide the number of unpaired electron spins in a sample, which is essential in studying the reaction kinetics, explaining the reaction mechanism and commercial applications. Therefore, obtaining the unpaired electron spin numbers of samples by electron paramagnetic resonance techniques has been a hot topic of research.  Two main quantitative electron paramagnetic resonance methods are available: relative quantitative EPR (ESR) and absolute quantitative EPR (ESR).     Relative Quantitative EPR (ESR) Method   The relative quantitative EPR method is accomplished by comparing the integrated area of the EPR absorption spectrum of an unknown sample with the integrated area of the EPR absorption spectrum of a standard sample. Therefore, in the relative quantitative EPR method, a standard sample with a known number of spins needs to be introduced. The size of the integrated area of the EPR absorption spectrum is not only related to the number of unpaired electron spins in the sample, but also to the settings of the experimental parameters, the dielectric constant of the sample, the size and shape of the sample, and the position of the sample in the resonant cavity. Therefore, to obtain more accurate quantitative results in the relative quantitative EPR method, the standard sample and the unknown sample need to be similar in nature, similar in shape and size, and in the same position in the resonant cavity.   Quantitative EPR Error Sources     Absolute Quantitative EPR (ESR) Method   The absolute quantitative EPR method means that the number of unpaired electron spins in a sample can be obtained directly by EPR testing without using a standard sample. In absolute quantitative EPR experiments, to obtain the number of unpaired electron spins in a sample directly, the value of the quadratic integral area of the EPR spectrum (usually the first-order differential spectrum) of the sample to be tested, the experimental parameters, the sample volume, the resonance cavity distribution function and the correction factor are needed. The absolute number of unpaired electron spins in the sample can be directly obtained by first obtaining the EPR spectrum of the sample through the EPR test, then processing the EPR first-order differential spectrum to obtain the second-integrated area value, and then combining the experimental parameters, sample volume, resonant cavity distribution function and correction factor.   CIQTEK Electron Paramagnetic Resonance Spectroscopy   The absolute quantification of unpaired electron spins of the CIQTEK EPR (ESR) spectroscopy can be used to obtain the spin number of unpaired electrons in a sample directly without the use of a reference or standard sample. The resonant cavity distribution funct...

Electron spin sensors have high sensitivity and can be widely used to probe various physicochemical properties, such as electric field, magnetic field, molecular or protein dynamics, and nuclear or other particles. These unique advantages and potential application scenarios make spin-based sensors a hot research direction at present. Sc3C2@C80 has a highly stable electron spin protected by a carbon cage, which is suitable for gas adsorption detection within porous materials. Py-COF is a recently emerged porous organic framework material with unique adsorption properties, which was prepared using a self-condensing building block with a formyl group and an amino group. prepared with a theoretical pore size of 1.38 nm. Thus, a metallofullerene Sc3C2@C80 unit (~0.8 nm in size) can enter one of the nanopores of Py-COF.   A nanospin sensor based on metal fullerene was developed by Taishan Wang, a researcher at the Institute of Chemistry, Chinese Academy of Sciences, for detecting gas adsorption within a porous organic framework. The paramagnetic metal fullerene, Sc3C2@C80, was embedded in the nanopores of a pyrene-based covalent organic framework (Py-COF). The adsorbed N2、CO、CH4、CO2、C3H6 and C3H8 within the Py-COF embedded with the Sc3C2@C80 spin probe were recorded using the EPR technique ( CIQTEK EPR200-Plus).It was shown that the EPR signals of the embedded Sc3C2@C80 regularly correlated with the gas adsorption properties of the Py-COF. The results of the study were published in Nature Communications under the title "Embedded nano spin sensor for in situ probing of gas adsorption inside porous organic frameworks".     Probing gas adsorption properties of Py-COF using molecular spin of Sc3C2@C8     In the study, the authors used a metallofullerene with paramagnetic properties, Sc3C2@C80 (~0.8 nm in size), as a spin probe embedded into one nanopore of pyrene-based COF (Py-COF) to detect gas adsorption within Py-COF. Then, the adsorption properties of Py-COF for N2、CO、CH4、CO2、C3H6 and C3H8 gases were investigated by recording the embedded Sc3C2@C80 EPR signals. It is shown that the EPR signals of Sc3C2@C80 regularly follow the gas adsorption properties of Py-COF. And unlike conventional adsorption isotherm measurements, this implantable nanospin sensor can detect gas adsorption and desorption by in situ real-time monitoring. The proposed nanospin sensor was also used to probe the gas adsorption properties of metal-organic framework (MOF-177), demonstrating its versatility.     Relationship between gas adsorption properties and EPR signals     Effect of gas pressure on EPR signal     EPR signal line width analysis   Spin-based sensors have attracted considerable attention owing to their high sensitivities. Herein, we developed a metallofullerene-based nano spin sensor to probe gas adsorption within porous organic frameworks. For this, spin-...

Hydrogen energy is the clean energy that drives the transformation from traditional fossil energy to green energy. Its energy density is 3 times that of oil and 4.5 times that of coal! It is the disruptive technology direction of the future energy revolution. The hydrogen fuel cell is the key carrier to realize the conversion of hydrogen energy into electric energy, and countries around the world attach great importance to the development of hydrogen fuel cell technology. This has put forward higher requirements on materials, process technology, and characterization means of hydrogen energy and hydrogen fuel cell industry chain. Gas adsorption technology is one of the important methods for material surface characterization, and plays a crucial role in the utilization of hydrogen energy mainly in hydrogen fuel cells.   Application of gas adsorption technology for characterization in the hydrogen production industryHow to produce hydrogen is the first step in harnessing hydrogen energy. Hydrogen production from electrolytic water with high purity grade, low impurity gas, and easy to combine with renewable energy sources is considered the most promising green hydrogen energy supply in the future [1].To improve the efficiency of hydrogen production from electrolytic water, the development and utilization of high-performance HER electrode catalysts is a proven way.  Porous carbon materials represented by graphene have excellent physicochemical properties, such as rich pore structure, large specific surface area, high electrical conductivity, and good electrochemical stability, which bring new opportunities for the construction of efficient composite catalytic systems. The hydrogen precipitation capacity is enhanced using co-catalyst loading or heteroatom doping [2].   In addition, a large number of studies have shown that the catalytic activity of HER electrode catalysts depends largely on the number of active sites exposed on their surfaces and the more active sites exposed, the better their corresponding catalytic performance. The larger specific surface area of porous carbon material, when used as a carrier, will to a certain extent expose more active sites to the active material and accelerate the reaction of hydrogen production.   The following are examples of the characterization of graphene materials using CIQTEK V-Sorb X800 series specific surface and pore size analyzer. From Figure 1, it can be seen that the surface area of graphene prepared by different processes has a large difference of 516.7 m2/g and 88.64 m2/g, respectively. Researchers can use the results of the specific surface area test to make a judgment of the basic catalytic activity, which can provide a corresponding reference for the preparation of composite catalysts.     Fig. 1 Test results of the specific surface area of graphene synthesized by different processes   In addition, many researchers have improved the electrocatalytic ac...

Did you know that light can create sound? In the late 19th century, scientist Alexander Graham Bell (considered one of the inventors of the telephone) discovered the phenomenon of materials producing sound waves after absorbing light energy, known as the photoacoustic effect.   Alexander Graham Bell Image Source: Sina Technology   After the 1960s, with the development of weak signal detection technology, highly sensitive microphones and piezoelectric ceramic microphones appeared. Scientists developed a new spectroscopic analysis technique based on the photoacoustic effect - photoacoustic spectroscopy, which can be used to detect substances of samples and their spectroscopic thermal properties, becoming a powerful tool for physicochemical research in inorganic and organic compounds, semiconductors, metals, polymer materials, etc.     How can we make light create sound?As shown in the figure below, a light source modulated by a monochromator, or a pulsed light such as a pulsed laser, is incident on a photoacoustic cell. The material to be measured in the photoacoustic cell absorbs light energy, and the absorption rate varies with the wavelength of the incident light and the material. This is due to the different energy levels of the atomic molecules constituted in the different materials, and the absorption rate of light by the material increases when the frequency ν of the incident light is close to the energy level hν. The atomic molecules that jump to higher energy levels after absorbing light do not remain at the higher energy levels; instead, they tend to release energy and relax back to the lowest ground state, where the released energy often appears as thermal energy and causes the material to expand thermally and change in volume.When we restrict the volume of a material, for example, by packing it into a photoacoustic cell, its expansion leads to changes in pressure. After applying a periodic modulation to the intensity of the incident light, the temperature, volume, and pressure of the material also change periodically, resulting in a detectable mechanical wave. This oscillation can be detected by a sensitive microphone or piezoelectric ceramic microphone, which is what we call a photoacoustic signal.   Principle Schematic     How does a lock-in amplifier measure photoacoustic signals?   In summary, the photoacoustic signal is generated by a much smaller pressure signal converted from very small heat (released by atomic or molecular relaxation). The detection of such extremely weak signals necessarily cannot be done without lock-in amplifiers.   In photoacoustic spectroscopy, the signal collected from the microphone needs to be amplified by a preamplifier and then locked to the frequency signal we need by a lock-in amplifier. In this way, a high signal-to-noise ratio photoacoustic spectroscopy signal can be detected and the properties of the sample can be measured.   CIQTEK has launc...

Spin trapping technique has been widely used in biology and chemistry because it can achieve the detection of short-lived radicals. For spin trapping experiments, many factors such as the time of trapping agent addition, trapping agent concentration, system solvent and system pH can affect the experimental results. Therefore, for different radicals, it is necessary to select the trapping agent and design the experimental scheme reasonably to achieve the best experimental results.   1.Trapping Agent and Solvent Selection   The common O-center radicals are hydroxyl radicals, superoxide anion radicals, and singlet oxygen.   Hydroxyl radicals (∙OH)   For hydroxyl radicals, they are usually detected in aqueous solutions and captured using DMPO, which forms adducts with DMPO with half-lives of minutes to tens of minutes.   Superoxide anion radicals (∙O2-)   For superoxide anion radicals, if DMPO is chosen as the trapping agent, the detection needs to be performed in a methanol system. This is because the binding ability of water and DMPO is higher than that of superoxide radicals to DMPO. If superoxide radicals are detected in water, the binding speed of water to DMPO will be greater than that of superoxide radicals to DMPO, resulting in superoxide radicals not being easily captured. Of course, if the superoxide radicals are produced in large amounts, they may also be captured by DMPO. If one wants to trap superoxide radicals in aqueous solution, BMPO needs to be chosen as the trapping agent because the half-life of adducts formed by BMPO trapping superoxide radicals in aqueous solution can be up to several minutes.   Single-linear state (1O2)   For single-linear state oxygen detection, TEMP is usually selected as the capture agent, and its detection principle is shown in Figure 1. Single-linear state oxygen can oxidize TEMP to form TEMPO radicals containing single electrons, which can be detected by electron paramagnetic resonance spectrometry. Since TEMP is easily oxidized and prone to background signal, TEMP needs to be tested before detecting single-linear state oxygen as a control experiment. Figure 1 Mechanism of TEMP for detecting singlet oxygen     Table 1 Common O-center radical detection trapping agent and solvent selection   2、Addition Time of Trapping Agent         In photocatalytic reactions, when light irradiates the catalyst, the valence band electrons are excited to the conduction band, producing electron/hole pairs. Such experiments generally require the addition of the trapping agent before the light irradiation, and in combination with the in situ light system, the variation of the radical signal with the light irradiation time can be studied, as shown in Figure 2, with different light irradiation times, the ∙OH content generated varies.   Fig. 2 Results of CIQTEK in-situ illumination experiments   In the warming reaction, if the reaction temperature...

Ceramic capacitors, as a kind of basic passive components, are an indispensable member of the modern electronic industry. Among them, chip multilayer ceramic capacitors (MLCC) occupy more than 90% of the ceramic capacitor market due to their characteristics of high temperature resistance, high voltage resistance, small size, and wide range of capacitance, and are widely used in the consumer electronics industry, including home appliances, communications, automotive electronics, new energy, industrial control, and other application areas.   The use of CIQTEK SEM can assist in completing the failure analysis of MLCC, finding the origin of failure through micro-morphology, optimizing the production process, and achieving the goal of high product reliability.   Application of CIQTEK SEM in MLCC   MLCC consists of three parts: inner electrode, ceramic dielectric and end electrode. With the continuous updating of the market demand of electronic products, MLCC product technology also presents the development trend of high capacity, high frequency, high temperature and high voltage resistance, high reliability and miniaturization. Miniaturization means the need to use smaller-sized, more uniform ceramic powders. The microstructure of the material determines the final performance, and the use of scanning electron microscope to characterize the microstructure of ceramic powders, including particle morphology, particle size uniformity, and grain size, can help in the continuous improvement of the preparation process.      Scanning electron microscope imaging of different types of barium titanate ceramic powders /25kV/ETD   Scanning Electron Microscope Imaging Different types of barium titanate ceramic powders /1kV/Inlens   High reliability means that a deeper understanding of the failure mechanism is required, and therefore failure analysis is indispensable. The root cause of MLCC failure is the presence of various microscopic defects, such as cracks, holes, delamination, etc., either externally or internally. These defects will directly affect the electrical performance and reliability of MLCC products, and bring serious hidden danger to product quality. The use of scanning electron microscope can assist in completing the failure analysis of capacitor products, find the origin of the failure through the microscopic morphology, optimize the production process, and ultimately achieve the goal of high reliability of the product.   MLCC's internal is a multi-layer structure, each layer of ceramics whether there are defects, multi-layer ceramics thickness is uniform, whether the electrodes are covered uniformly, all of these will affect the life of the device. When using SEM to observe the internal multilayer structure of MLCC or to analyze their internal failures, it is often necessary to perform a series of pre-treatments on the samples before they can be tested. These include resin embedding, mechanical grinding, ...

Drug powders are the main body of most pharmaceutical formulations, and their efficacy depends not only on the type of drug, but also to a large extent on the properties of the powders composing the pharmaceutical formulations. Numerous studies have shown that physical parameters such as specific surface area, pore size distribution and true density of drug powders are related to the properties of powder particles such as particle size, hygroscopicity, solubility, dissolution and compaction, and play an important role in the purification, processing, mixing, production and packaging capabilities of pharmaceuticals. Especially for APIs and pharmaceutical excipients, parameters such as specific surface area are important indicators of their performance.   The specific surface area of API, as the active ingredient of a drug, affects its properties such as solubility, particle size and solubility. Under certain conditions, the larger the specific surface area of the same weight of API, the smaller the particle size, dissolution and dissolution rate is also accelerated. By controlling the specific surface area of the API, it can also achieve a good uniformity and fluidity, to ensure uniform distribution of drug content.   Pharmaceutical excipients, as excipients and additional agents used in the production of drugs and prescriptions, specific surface area is one of the important functional indicators, which is important for diluents, binders, disintegrants, flow aids, and especially lubricants. For example, for lubricants, the specific surface area significantly affects their lubrication effect, because the prerequisite for lubricants to play a lubricating effect is to be able to be uniformly dispersed on the surface of the particles; generally speaking, the smaller the particle size, the larger the specific surface area, and the easier it is to be uniformly distributed during the mixing process.   Thus, accurate, rapid and effective testing of physical parameters such as specific surface area and true density of pharmaceutical powders has always been an indispensable and critical part of pharmaceutical research. Therefore, the methods for the determination of specific surface area and solid density of pharmaceutical powders are clearly defined in the United States Pharmacopoeia USP<846> and USP<699>, the European Pharmacopoeia Ph. Eur. 2.9.26 and Ph. Eur. 2.2.42, as well as in the second additions of the physical and chemical analysis contents 0991 and 0992 to the four general rules of the Chinese Pharmacopoeia, 2020 edition.   01 Gas adsorption technique and its application   Gas adsorption technique is one of the important methods for material surface property characterization. Based on adsorption analysis, it can accurately analyze the specific surface area, pore volume and pore size distribution, true density and other parameters of APIs, pharmaceutical excipients and drug formulations. In turn, it can do some...