High-performance liquid chromatography fillers can be classified into inorganic matrix fillers and organic matrix fillers, and inorganic matrix fillers include silica gel, alumina, zirconia, hydroxyapatite, nitride, and activated carbon. In addition, the composite material, that is, the inorganic-organic spherical hybridization sphere prepared by the fine regulation technology, is chemically derivatized, and is prepared to be highly effective for drug analysis and screening, and is resistant to pH 2-8 and low adsorption. filler.
1, silicone
The most important of the inorganic matrix materials is the appearance of silica gel, particulate silica gel, which promotes the occurrence and development of high performance liquid chromatography. Synthetic chromatography is distinguished from natural crystalline silica by silica gel, and is also distinguished from quartz capillary used in chromatography and electrochromatography between crystalline form and amorphous type. As a chromatographic filler, amorphous silica is used. Silica gel adsorption chromatography is a classic in chromatography. Silica gel is still the main material for preparing packed columns in chromatography. The water content of silica gel particles from 250 mesh to 400 mesh (ie 40 μm to 63 μm diameter) directly affects the activity, and its activity varies with water content. The increase is lowered. When the water content is close to 20%, the silica gel has substantially no adsorption activity; if the activity is too high, irreversible adsorption and tailing occur, and even the molecular structure of the isolate changes. The process of chemical modification and polymer coating will be highlighted below.
Silica gel can be used as a chromatographic matrix material because its surface has an important reactive group of silanols, ie free silanols, or isolated silanols. Since free silanol is the main cause of chromatographic peaks, especially alkaline solute tailing, the tailing technology for silanol is very important in the synthesis of reversed-phase chromatography materials. For example, a C18 column, after bonding octadecyl groups, is also required to be blocked by a small molecule silylating agent (for example, trimethylchlorosilane) to minimize the polarity of the silicon hydroxy group. The overall appearance of non-polar column effects, such as silicone hydroxyl exposure, incomplete sealing, will inevitably affect the retention time and chromatographic peak shape of reversed-phase chromatography.
The modification of the surface of the silica gel is carried out by the reactive group, and the surface of the silica gel is modified by various silylating agents to obtain an alkyl reverse phase packing including an alkane and an aromatic hydrocarbon. In addition to chlorosilanes and alkoxysilanes, commonly used silylating agents are also alkyl silazanes. For example: a octadecyl group bonded to a siloxyl group can be used to prepare a C18 column (ODS) commonly used in a liquid chromatography column; an amino group, a carboxyl group, and a sulfonic acid group can be modified to obtain an ion exchange filler; By modification, a hydrophobic filler can be obtained.
2, alumina
The alumina used as the adsorbent material and the chromatographic filler matrix is ​​mainly γ-alumina. The chemical modification of γ-alumina surface is more difficult than that of silica gel. Therefore, alumina is mostly used for the separation of some small molecular organic compounds for normal phase and ion. In exchange chromatography and reversed-phase high performance liquid chromatography, it is used less in biochemical separation. The chemical modification of alumina can be achieved by reaction of aluminum hydroxy groups or by coating techniques. The alkylated alumina which is stable in a wide pH range and is applied to reverse phase chromatography can be obtained by reacting an alkyl group such as C4, C8 and C18 with an active hydroxyl group on the surface of alumina by an aluminum hydroxy reaction. The surface coating can produce a strong hydrophobic composite such as polystyrene-divinyl, polybutylene or octadecylsilane.
In the adsorption preparative chromatography, the adsorption capacity of alumina is stronger than that of silica gel, and the sample volume of alumina is larger than that of silica gel. According to the water content (0% to 15%), in most cases, the water content to be controlled is 6% to 10%, the corresponding activities are the third and fourth grades. According to the acidity and alkalinity, the alumina used in the adsorption chromatography is divided into neutral, acidic and basic alumina, and the pH of the neutral alumina water extract is 7.5, which is suitable for aldehydes, ketones, oximes, certain Separation of unstable compounds such as esters and lactones in glycosides and acid-base solutions is therefore widely used. In most cases, the alkaline alumina aqueous extract has a pH of 9 to 10, which is often used for the separation of hydrocarbons. It is often used for the separation of hydrocarbons, the removal of oxygenates from hydrocarbons, and The removal of oxygenates from hydrocarbons can also separate certain pigments, steroids, alkaloids, alcohols, and other neutral and basic materials. The alumina water extract has a p H value of 4 to 4.5 and is suitable for the separation of natural and synthetic acidic pigments and certain aldehydes and acids.
3, zirconia
Zirconium oxide, like silica gel, has excellent mechanical strength, a suitable pore structure and an active site that can be used to bond other functional groups, as well as a broader pH tolerance range and better temperature resistance. The zirconia porous pellets can withstand an environment of pH 0-14, can work at temperatures up to 900 °C for a long time without deformation and the structure is not damaged. Carbon eighteen-bonded zirconium dioxide (ODZ) can be used in the range of pH 2-12. The polybutadiene-coated zirconium dioxide composite filler is stable over the full pH range and is resistant to a column temperature of 200 °C.
4, composite filler
Composite fillers, in general, the silica matrix chemically bonded phase is stable in the range of pH 2-8, it is difficult to tolerate a wider pH range, and the silica matrix will dissolve under alkaline conditions, so people will have lower mechanical strength. The polymer which is apt to swell in the organic solvent is introduced into the silica matrix filler to form an organic-inorganic composite filler, that is, a coated filler or a coated filler. Silica gel, alumina, zirconia, etc. have been used as matrix materials for coated fillers, the most important of which are silica gel and zirconia. The high polymer used for coating the inorganic matrix filler is polystyrene, polyethyl styrene-divinyl benzene, polybutadiene, polyethylene oxide, polysiloxane, agarose, polychloroform. Styrene-diethoxymethylvinylsilane, vapor deposited carbon, and the like.
The preparation of the early coated filler adopts the physical coating method, and the obtained pore structure of the composite is not controllable and the reproducibility is poor. In the later stage, a chemical bonding or a composite coating method is employed. The method first uses an inorganic matrix surface modification technique to bring a suitable amount of reactive groups on the surface of a substrate such as silica gel, alumina or zirconia, for example, a double bond, an epoxy group, an amino group or a carboxyl group which can undergo an addition reaction. Then, the monomer, the crosslinking agent and the like required for preparing the high polymer are applied to the surface of the substrate, and then the chemical bonding or copolymerization reaction is initiated by adding an initiator, temperature control, etc., thereby obtaining a compact and compact composite chromatography. filler. However, due to incomplete polymer coating, the exposed inorganic matrix will adsorb Lewis basic substances, especially adsorbing proteins and causing peak shape deterioration. This adsorption can expose the pyrolytic carbon to the naked body by organic hot vapor chemical vapor deposition. The inorganic substrate is coated. Of particular note in the bonded stationary phase are chiral separation stationary phases for chiral resolution of drugs, acids, and amides. The polymer-based sphere used in the chiral stationary phase is usually a monodisperse glycidyl methacrylate-ethylene dimethacrylate copolymer microsphere, a one-pot prepared monodisperse polymethacrylamide sphere, Polysiloxane, optically active polyurethane and polystyrene. Various types of chiral stationary phases such as Pirkle type (brush type), polysaccharides, cyclodextrins, crown ethers, and calixarene have been developed by covalent bonding or coating.
5. Graphitized carbon filler
Silica gel has poor chemical stability and can only work in pH=2~8 environment. However, in many cases, extreme pH conditions are required. For this reason, people have vigorously developed matrix materials with better chemical stability such as polymer microspheres, alumina, and zirconia. However, it is difficult to have a material that fully satisfies the requirements of a liquid chromatography matrix. For example, polymer microspheres undergo some swelling in an organic solvent, so it is difficult to apply to a gradient elution with a mobile phase containing an organic solvent; although alumina and zirconia have better chemical stability than silica gel, However, surface modification and bonding are difficult. Therefore, a carbon material with good chemical stability is naturally considered as a matrix for the chromatographic packing.
Carbon material has excellent chemical stability and can withstand a wide range of pH=1~14; high temperature resistance, graphitized carbon can withstand high temperatures above 3000°C without damage; properly processed carbon materials can have very high Good mechanical strength, excellent electrical conductivity, thermal conductivity and electromagnetic shielding properties. What is more commendable is that the porous carbon material has good adsorption and selectivity due to its structural characteristics. It is these properties of carbon materials that make them expect special use in the field of chromatography.
6. Cross-flow chromatography packing
Cross-flow chromatography is a new method of chromatographic separation developed in the late 1980s and early 1990s. On the filler, there are usually micropores or macropores, for example, micropores of 50 to 150 nm, and pores having a pore diameter of about 600 to 800 nm penetrating through the entire particle. This through-hole allows for the mobile phase to pass directly into the interior of the filler particles and through. Thus, the diameter of the filler particles is greatly reduced, that is, the filler is divided into a plurality of finer particles by the through holes, and the micropores on the small particles are so short that they do not significantly hinder the mass transfer process. Therefore, on this cross-flow chromatography packing, the mass transfer resistance is already very small. At the same time, the linear velocity of the mobile phase in the through-hole is proportional to the velocity of the mobile phase in the column, that is, the mass transfer process has changed from diffusion mass transfer to convective mass transfer. This means that, within a certain range, increasing the mobile phase speed in time will not reduce the separation efficiency of the column. Since the filler has a usual porous structure at the same time, its specific surface area does not greatly decrease with the occurrence of the through holes.
Therefore, the sample loading on this packing does not decrease as the flow rate increases. Moreover, the through hole of 600~800nm ​​on the filler greatly increases the permeability of the column, so that the operating pressure of the column does not need to be high even when operating at a high flow rate. Therefore, this cross-flow column can simultaneously feature high flow rates, high efficiency, high sample loading and low operating pressure.
7, the overall column
The monolithic column, also known as the whole stationary phase, rod column, continuous bed, etc., is a continuous monolithic structure which is polymerized or immobilized in situ in the column tube. The surface of the whole material can be derivatized according to the needs, which is a new type. A porous medium for separation analysis or as a reactor. A monolithic column having an ideal pore size distribution is obtained by controlling the polymerization conditions. The space in the monolith consists of pores in the polymer particles and gaps between the particles, which occur as the sample flows through the pore structure. You can reduce the difference and vertical expansion of the path.
The advantages of the monolithic column include: it can be prepared in situ, the preparation of the packing and the packing is omitted, or the polymer particles can be prepared in the same manner and then the column is assembled; the polymer is easy to prepare, and the length and diameter of the column are not limited to some extent; The monomers in the reaction mixture can be flexibly selected to give a suitable matrix and properties; they are readily derivatized in the column to give a column with suitable properties; the properties of the pores can be optimized by controlling the conditions of the polymerization.
Full Automatic Video Measuring Instrument
The fully automatic image measurement instrument is an artificial intelligence modern optical non-contact measurement instrument developed on the basis of the digital image measurement instrument (also known as CNC image instrument). The fully automatic image measuring instrument inherits the excellent motion accuracy and motion control performance of digital instruments, integrates the design flexibility of machine software, and belongs to the forefront of optical size detection equipment today.
The full-automatic anime image measuring instrument is based on the CCD digital image, relying on the computer screen measurement technology and the powerful software capability of spatial geometry operation. After installing specialized control and graphic measurement software, the computer becomes the measurement brain with the soul of the software and is the main body of the entire device. It can quickly read the displacement value of the optical ruler and obtain the desired result instantly through software module operations based on spatial geometry; And generate graphics on the screen for the operator to compare the images and images, so as to visually distinguish possible deviations in the measurement results. All of this is done in real-time in front of powerful computer computing power, and the operator himself cannot detect it. This kind of precision instrument that can use CCD digital image, through computer software operation, to meet the needs of complex measurement is the real image measuring instrument, anime.
The fully automatic image measuring instrument has a wide range of applications in precision electronics, wafer technology, cutting tools, plastics, precision parts, springs, stamping parts, connectors, molds, military industry, two-dimensional reading, drawing, engineering development, hardware and plastic, PCB board, conductive rubber, powder metallurgy, screws, clock parts, mobile phones, pharmaceutical industry, fiber optic devices, automotive engineering, aerospace, higher education institutions, research institutes, and other fields.
Full Automatic Video Measuring Instrument,Automated Video Measuring Machine,Vmm Video Measuring Machine,Automatic Video Measuring Instrument
Zhejiang dexun instrument technology co., ltd , https://www.dexunmeasuring.com