Mobile Phase Gradient
Mobile Phase Gradient - Related Videos
08:40
Using a Cyclic Ion Mobility Spectrometer for Tandem Ion Mobility Experiments
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Cited by 3 •
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Ion mobility spectrometry (IMS) is an interesting complement to mass spectrometry for the characterization of biomolecules, notably because it is sensitive to isomerism. This protocol describes a tandem IMS (IMS/IMS) experiment, which allows the isolation of a molecule and the generation of the mobility profiles of its fragments.
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What is an Electrochemical Gradient?
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Adenosine triphosphate, or ATP, is considered the primary energy source in cells. However, energy can also be stored in the electrochemical gradient of an ion across the plasma membrane, which is determined by two factors: its chemical and electrical gradients.The chemical gradient relies on differences in the abundance of a substance on the outside versus the inside of a cell and flows from areas of high to low ion concentration. In contrast, the electrical gradient revolves around an ion’s...
02:15
Density Gradient Purification of Cyanobacterial Plastoglobules
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Source: Shivaiah, K., et al. Plastoglobule Lipid Droplet Isolation from Plant Leaf Tissue and Cyanobacteria. J. Vis. Exp. (2022).This video demonstrates the isolation of plastoglobules from cyanobacteria using sucrose density gradient centrifugation, highlighting their lipid-rich, low-density nature and ensuring their structural preservation for downstream analysis.
08:42
Density Gradient Ultracentrifugation
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2023
Density gradient ultracentrifugation is a common technique used to isolate and purify biomolecules and cell structures. This technique exploits the fact that, in suspension, particles that are more dense than the solvent will sediment, while those that are less dense will float. A high-speed ultracentrifuge is used to accelerate this process in order to separate biomolecules within a density gradient, which can be established by layering liquids of decreasing density in a centrifuge tube. The...
08:32
Directional Solidification and Phase Stabilization
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2023
Source: Sina Shahbazmohamadi and Peiman Shahbeigi-Roodposhti-Roodposhti, School of Engineering, University of Connecticut, Storrs, CT Directional solidification zone melting is a metallurgical process in which a narrow region of a crystal (usually in the form of bar) is melted. The furnace moves along the rod shape sample, meaning that the molten zone is moved along the crystal and the molten zone is moved from one end of the bar to the other. This mechanism is widely used in alloys, however...
FAQs
Increasing or decreasing solvent strength changes how strongly analytes interact with the stationary phase. Molecules that remain retained under weaker conditions can be released as the mobile-phase composition shifts, while less strongly retained compounds elute earlier. This controlled change helps establish an ordered separation and can improve recovery of molecules that would otherwise remain in the column.
Polarity and solvent composition influence the balance between analyte retention and movement through the column. Adjusting these properties progressively changes the conditions experienced by proteins, peptides, nucleic acids, or metabolites. A suitable profile can separate compounds with different properties more effectively, producing more distinct elution behavior than a single unchanged solvent composition.
Changes in pH can alter analyte interactions with the stationary phase, particularly for biomolecules whose behavior depends on their chemical properties. Incorporating pH changes into the gradient therefore provides another way to release retained compounds in a controlled sequence. This can support improved separation of complex biological samples containing molecules with differing properties.
Constant-composition elution keeps the mobile phase unchanged throughout the separation, whereas a gradient varies its composition to modify analyte retention over time. The changing conditions can release strongly retained molecules more efficiently and may shorten the run. Gradient operation also offers a way to optimize resolution, retention time, peak shape, and target-fraction collection.
A useful gradient should account for the properties of the molecules being separated and the desired balance among resolution, retention time, peak shape, and collection of target fractions. Researchers adjust the proportions of mobile-phase components, and when relevant, solvent strength, polarity, or pH. These choices determine how progressively retained biomolecules are released from the column.
Researchers can assess the resulting retention times, resolution between compounds, and peak shapes. They can also determine whether the gradient releases the target molecules in a sequence that supports collection of useful fractions. These outcomes show whether the selected composition changes are adequately distinguishing the sample components and whether further optimization is needed.
Gradient operation is particularly valuable for complex biological mixtures containing proteins, peptides, nucleic acids, metabolites, or other biomolecules with different retention behavior. It helps researchers separate components progressively, improve resolution and efficiency, and collect target fractions. The approach is also relevant when constant-composition elution would produce long runs or insufficient release of strongly retained molecules.