Gel Permeation Chromatography Column
2.Chromatographic Column (Rotation Type)
3.Chromatographic Column (Manual)
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Description
Technical Parameters
Gel Permeation Chromatography Column (GPC column for short) is the core component of gel permeation chromatography (GPC for short) technology. GPC, as an efficient liquid chromatography technique, was developed by J. in 1964 C. Since the success of Moore's research, he has played an important role in various fields of polymer science. It was in 1964, by J C. Moore was the first to successfully conduct research. Not only can it be used for the separation and identification of small molecule substances, but it can also be used to analyze polymer homologues with the same chemical properties but different molecular volumes (polymers are separated on a separation column according to their molecular fluid dynamics volume size).
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(1) All components are eluted before solvent molecule elution, with a short separation time.
(2) It can predict the elution time and allow for continuous injection.
(3) The separation process of gel chromatography does not rely on intermolecular forces.
(4) Short retention time, narrow chromatographic peak, easy to detect.
Generally, no strongly retained molecules accumulate in the chromatographic column, so the sample components will not be lost during separation, and the service life of the column will also be extended.
Parameter
Basic principles
Separation principle
Gel is chemically inert, gel permeation chromatography column does not have adsorption, distribution and ion exchange. Let the measured polymer solution pass through a chromatographic column with different pore sizes, where the pathways available for molecules to pass through the column include gaps between particles (larger) and through holes within particles (smaller). When the polymer solution flows through the chromatographic column (gel particles), larger molecules (larger than gel pores in volume) are excluded from the pores of particles, and can only pass through the gaps between particles at a faster rate; Smaller molecules can enter the small pores in particles at a much slower rate; Medium volume molecules can penetrate larger pores, but are hindered by smaller pores, falling between the two situations mentioned above. [1] After passing through a certain length of chromatographic column, molecules are separated based on their relative molecular weight, with those with higher relative molecular weight at the front (i.e. shorter elution time) and those with lower relative molecular weight at the back (i.e. longer elution time). The total volume of leachate received from the sample entering the column to being leached out is called the leached volume of the sample. After the instrument and experimental conditions are determined, the elution volume of solute is related to its molecular weight, and the larger the molecular weight, the smaller the elution volume.
(1) Volume exclusion
(2) Restricted diffusion
(3) Flow separation
Correction principle
A calibration curve is created in advance using a monodisperse standard polymer with known relative molecular weight, which corresponds to the elution volume or elution time and relative molecular weight. Almost no monodisperse standard samples can be found in polymers, and narrow distribution samples are generally used instead. Under the same testing conditions, a series of GPC standard spectra were created, corresponding to the retention times of samples with different relative molecular weights. The curve obtained by plotting lgM against t is called the "calibration curve". By correcting the curve, various required relative molecular weights and relative molecular weight distributions can be calculated from the GPC spectrum. There are not many types of polymers that can produce standard samples in polymers. Without standard samples, it is impossible to have calibration curves for polymers, and it is also impossible to obtain the relative molecular weight and relative molecular weight distribution of polymers using GPC methods. For this, the principle of universal correction can be used.
Universal calibration principle
Due to the fact that GPC separates polymers based on molecular fluid dynamics volume, which means that for the same molecular fluid dynamics volume, it flows out at the same retention time, resulting in the same fluid dynamics volume.
The fluid dynamics volume of two types of flexible chains is the same:
If the k and alpha values of the standard sample and the measured polymer are known, the relative molecular mass of the sample can be calibrated using a standard sample with known relative molecular mass
Experimental section
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Direct method:
Simultaneously measuring the viscosity or light scattering of the leachate concentration to determine its molecular weight.
Indirect method:
Using a set of monodisperse samples with varying molecular weights as standard samples, their elution volume and molecular weight can be measured separately to determine the relationship between the two.
instrument
Gel permeation chromatography column instrument consists of pump system, (automatic) sampling system, gel chromatographic column, detection system and data acquisition and processing system.
1.1. Pump system: including a solvent storage tank, a set of degassing devices, and a high-pressure pump. Its job is to make the mobile phase (solvent) flow into the chromatographic column at a constant flow rate. The working condition of the pump directly affects the accuracy of the final data. The more precise the instrument, the more stable the working state of the pump is required. The required flow rate error should be less than 0.01mL/min.
1.2. Column: The core component for separating GPC instruments. It is to add particles with different pore sizes as fillers into a hollow stainless steel tube. Each chromatographic column has a certain range of relative molecular weight separation and permeation limit, and there are upper and lower limits for the use of chromatographic columns. The upper limit for the use of chromatographic column is that when the size of the smallest molecule of the polymer is larger than the size of the largest gel in the chromatographic column, the polymer cannot enter the pore size of the gel particles, and all of it flows through the outside of the gel particles, which does not achieve the purpose of separating polymers with different relative molecular weights. Moreover, it is possible to block the gel pore, which will affect the separation effect of the chromatographic column and reduce its service life. The lower limit for the use of chromatographic columns is that when the maximum molecular chain size in the polymer is smaller than the minimum pore size of the gel pore, the purpose of separating different relative molecular weights is not achieved. Therefore, when using gel chromatograph to determine the relative molecular weight, it is necessary to first select the chromatographic column that matches the range of polymer relative molecular weight.
1.3. Filler (filler shall be selected according to the solvent used, and the basic requirement for filler is that the filler cannot be dissolved by solvent): cross-linked polystyrene gel (applicable to organic solvent, high temperature resistant), cross-linked polyvinyl acetate gel (up to 100 ℃, applicable to polar solvents such as ethanol and propanone) porous silicon ball (applicable to water and organic solvent), porous glass, porous aluminum oxide (applicable to water and organic solvent)
1.4. Column: Glass, Stainless Steel
1.5. Detection System: Universal Detector: Suitable for the detection of all polymers and organic compounds. There are differential refractometer detectors, ultraviolet absorption detectors, and viscosity detectors.
1.6. Differential refractometer detector: The refractive index of the solvent should be as different as possible from that of the sample being measured.
1.7. UV absorption detector: The solvent does not have strong absorption near the characteristic absorption wavelength of the solute.
1.8. Selective detector: suitable for high polymers and organic compounds that have a special response to the detector. There are UV, IR, fluorescence, conductivity detectors, etc.
operation
2.1. Selection of solvents: capable of dissolving various polymers; Cannot corrode instrument components; Match with the detector.
2.2. Combining laser light scattering with gel chromatograph: we can get not only the concentration spectrum, but also the spectrum of scattering light intensity versus leaching volume, so as to calculate the molecular weight distribution curve and various average molecular weights of the whole sample.
2.3. In laser light scattering experiments: gel permeation chromatography column is necessary to strictly remove dust from the sample. Dust in the solution can cause strong light scattering, seriously interfering with the measurement of light scattering in polymer solutions. Solution dust removal is the key to the success or failure of light scattering. Firstly, solvent dust removal is required. The solvent used to prepare the test sample should be distilled and filtered through a 0.2 μ m ultrafiltration membrane before use. The prepared solution should also be filtered through a 0.2 μ m ultrafiltration membrane. In addition, the instruments used in the test, such as syringes, should be soaked in detergent and vigorously rinsed with water before use.
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