Gel permeation chromatography or size exclusion chromatography (GPC/SEC) is the primary analytical tool commonly used for polymers, macromolecules and proteins. The most important reason is that it can quantitatively characterize molecular weight and molecular weight distribution data. The above analysis method is usually divided into two steps. Step 1: Separate the dissolved sample by molecular size/volume using a column containing appropriate characteristics of the microporous filling material; Step 2: Analyze the separated sample using a suitable testing instrument. In this article, Stephen Ball, product marketing manager from Malvern Instruments, will explain the detector technology that can be used and the potential for improved analytical efficiency.
The traditional configuration of the GPC/SEC system is to measure the concentration using a single refractive index (RI) detector, in which the relative molecular weight distribution data can be obtained using the reference calibration data. This is suitable for some common polymer materials and/or quality controls, but analysts are increasingly inclined to use a multi-detector combination GPC/SEC system with the following characteristics:
â— Obtain absolute data for all materials without column calibration
â— Greatly improve data processing results
There are many detectors available on the market for GPC/SEC. Since the analysis has a two-stage nature, there are many issues to consider when choosing the right system. A fully integrated single detector is advantageous, but I think it can only be described as a sub-optimal solution compared to choosing the best detector combination solution. Optimizing the choice of detector is a straightforward and efficient method with many advantages. For example, the characterization of molecular weight, hydrodynamic size and molecular structure can be obtained in only one experiment.
This raises the question: How can we find the best detector system for application-based? This issue is very broad, but it provides a good opportunity for us to understand the advantages of different detectors.
Starting with a viscometer, it can measure various viscosity parameters, and for a polymer solution, it can establish an association with the molecular weight of the sample. When used with the RI detector, the viscometer can be subjected to Platts calibration, eliminating the need to find a standard sample that is very close to the sample being tested, and improving the integrity of the molecular weight distribution data. Viscosity measurements can also determine structural aspects such as quantitative analysis of polymer branches.
Let's take a look at the static light scattering detectors, which measure the absolute molecular weight directly. The problem is starting to get complicated by the variety of detectors on the market, such as LALS, RALS and MALS. All of these detectors measure the molecular weight by measuring the energy of the scattered light, but the scattered light energy varies with angle. For example, a small angle light scattering detector (LALS) detects incident light at an angle of 7 degrees, and right angle light scattering ( RALS) Measure incident light at 90 degrees, in addition to multi-angle measurement light scattering (MALS).
The above instruments have their own advantages. This article does not discuss them one by one, but the key we need to understand is their respective characteristics? For macromolecules (>12 nm), the resulting change in scattered light intensity is a function of the angle of incident ray. The mathematical method for obtaining the molecular weight is to obtain the molecular weight by the sharp scattering equation using the scattered light intensity of the incident light at 0 degrees, and the scattered light at the 0 degree angle cannot be directly measured, so a method for detecting these macromolecules has been developed.
The LALS detector measures at an angle very close to the incident light, eliminating the need for extrapolation calculations. The MALS detector measures multiple angles and extrapolates the measured results to obtain the scattered light intensity at 0 degrees. Putting together technologies to explore has become a trend and preference in the industry. For example, SEC-MALS has become the standard method for protein characterization, and RALS is considered to be the best choice for molecular characterization based on molecular size.
Dynamic Light Scattering (DLS) further enriches the choice of light scattering detectors. It is a widely used particle size measurement method for determining nanometer particle size range and is very effective for some GPC/SEC users. The main application area of ​​this technology is protein analysis, which allows accurate measurement of the molecular radius of fluid mechanics. The DLS detector also enables static light scattering measurements, which opens up the possibility of molecular weight measurements.
Finally, there is an equally important technology to choose from, a single-wavelength or multi-wavelength detector based on UV technology. For samples containing chromosomes, the single-wavelength UV detector is a more accurate measurement method to measure the concentration instead of the RI (Refractive Index) detector. However, it can be combined with an RI detector to determine the proportion of specific components in each effluent component, which is of great value for evaluating monomer concentration. The ability of the PDA detector to measure multiple wavelengths further extends the flexibility and functionality of the detector.
This article is a brief summary of current GPC/SEC technology, two of which I believe are important for optimizing the application of the detector. It should first be recognized that the development of detector technology is critical to the potential value of GPC/SEC; secondly, to select a combination of detectors suitable for the company's application, it is important to gain some technical knowledge and adoption. A logical selection method. Establishing the right perspective on this aspect of GPC/SEC is key to improving long-term testing efficiency and collecting data in the most economical way.
(Author: Stephen Ball, Malvern Instruments Nano particle and molecular characterization Product Marketing Manager)
Striped Bonito,Sarda orientalis,Fresh Striped Bonito,Fresh Sarda orientalis
Zhoushan Boda Aquatic Products Co.,Ltd , https://www.baida-aquatic.com