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Chromatography is a laboratory technique for the separation of a mixture. The mixture is dissolved in a fluid called the mobile phase, which carries it through a system on which is fixed a material called the stationary phase. The different constituents of the mixture have different affinities for the stationary phase. The different molecules stay longer or shorter on the stationary phase, depending on their interactions with its surface sites. So, they travel at different apparent velocities in the mobile fluid, causing them to separate. The separation is based on the differential partitioning between the mobile and the stationary phases. Subtle differences in a compound's partition coefficient result in differential retention on the stationary phase and thus affect the separation.
In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen bonds. Due to carbon's ability to catenate, millions of organic compounds are known. The study of the properties, reactions, and syntheses of organic compounds comprises the discipline known as organic chemistry. For historical reasons, a few classes of carbon-containing compounds, along with a handful of other exceptions, are not classified as organic compounds and are considered inorganic. Other than those just named, little consensus exists among chemists on precisely which carbon-containing compounds are excluded, making any rigorous definition of an organic compound elusive.
Spectrophotometry is a branch of electromagnetic spectroscopy concerned with the quantitative measurement of the reflection or transmission properties of a material as a function of wavelength. Spectrophotometry uses photometers, known as spectrophotometers, that can measure the intensity of a light beam at different wavelengths. Although spectrophotometry is most commonly applied to ultraviolet, visible, and infrared radiation, modern spectrophotometers can interrogate wide swaths of the electromagnetic spectrum, including x-ray, ultraviolet, visible, infrared, and/or microwave wavelengths.
In the physical sciences, a partition coefficient (P) or distribution coefficient (D) is the ratio of concentrations of a compound in a mixture of two immiscible solvents at equilibrium. This ratio is therefore a comparison of the solubilities of the solute in these two liquids. The partition coefficient generally refers to the concentration ratio of un-ionized species of compound, whereas the distribution coefficient refers to the concentration ratio of all species of the compound.
Archer John Porter Martin was a British chemist who shared the 1952 Nobel Prize in Chemistry for the invention of partition chromatography with Richard Synge.
Dimethylformamide is an organic compound with the formula (CH3)2NC(O)H. Commonly abbreviated as DMF (although this initialism is sometimes used for dimethylfuran, or dimethyl fumarate), this colourless liquid is miscible with water and the majority of organic liquids. DMF is a common solvent for chemical reactions. Dimethylformamide is odorless, but technical-grade or degraded samples often have a fishy smell due to impurity of dimethylamine. Dimethylamine degradation impurities can be removed by sparging degraded samples with an inert gas such as argon or by sonicating the samples under reduced pressure. As its name indicates, it is a derivative of formamide, the amide of formic acid. DMF is a polar (hydrophilic) aprotic solvent with a high boiling point. It facilitates reactions that follow polar mechanisms, such as SN2 reactions.
Gas mixtures can be effectively separated by synthetic membranes made from polymers such as polyamide or cellulose acetate, or from ceramic materials.
Ion chromatography separates ions and polar molecules based on their affinity to the ion exchanger. It works on almost any kind of charged molecule—including large proteins, small nucleotides, and amino acids. However, ion chromatography must be done in conditions that are one unit away from the isoelectric point of a protein.
Ion-mobility spectrometry (IMS) is an analytical technique used to separate and identify ionized molecules in the gas phase based on their mobility in a carrier buffer gas. Though heavily employed for military or security purposes, such as detecting drugs and explosives, the technique also has many laboratory analytical applications, including the analysis of both small and large biomolecules. IMS instruments are extremely sensitive stand-alone devices, but are often coupled with mass spectrometry, gas chromatography or high-performance liquid chromatography in order to achieve a multi-dimensional separation. They come in various sizes, ranging from a few millimeters to several meters depending on the specific application, and are capable of operating under a broad range of conditions. IMS instruments such as microscale high-field asymmetric-waveform ion-mobility spectrometry can be palm-portable for use in a range of applications including volatile organic compound (VOC) monitoring, biological sample analysis, medical diagnosis and food quality monitoring. Systems operated at higher pressure are often accompanied by elevated temperature, while lower pressure systems (1-20 hPa) do not require heating.
Frank Henry Westheimer was an American chemist. He taught at the University of Chicago from 1936 to 1954, and at Harvard University from 1953 to 1983, becoming the Morris Loeb Professor of Chemistry in 1960, and Professor Emeritus in 1983. The Westheimer medal was established in his honor in 2002.
Countercurrent distribution is an analytical chemistry technique which was developed by Lyman C. Craig in the 1940s. Countercurrent distribution is a separation process that is founded on the principles of liquid–liquid extraction where a chemical compound is distributed (partitioned) between two immiscible liquid phases according to its relative solubility in the two phases. The simplest form of liquid-liquid extraction is the partitioning of a mixture of compounds between two immiscible liquid phases in a separatory funnel. This occurs in five steps: 1) preparation of the separatory funnel with the two phase solvent system, 2) introduction of the compound mixture into the separatory funnel, 3) vigorous shaking of the separatory funnel to mix the two layers and allow for mass transfer of compounds in and out of the phases, 4) The contents of the separatory funnel are allowed to settle back into two distinct phases and 5) the two phases are separated from each other by draining out the bottom phase. If a compound is insoluble in the lower phase it will distribute into the upper phase and stay in the separatory funnel. If a compound is insoluble in the upper phase it will distribute into the lower phase and be removed from the separatory funnel. If the mixture contains one or more compounds that are soluble in the upper phase and one or more compounds that are soluble in the lower phase, then an extraction has occurred. Often, an individual compound is soluble to a certain extent in both phases and the extraction is, therefore, incomplete. The relative solubility of a compound in two phases is known as the partition coefficient.
Micellar liquid chromatography (MLC) is a form of reversed phase liquid chromatography that uses an aqueous micellar solutions as the mobile phase.
Thermospray is a soft ionization source by which a solvent flow of liquid sample passes through a very thin heated column to become a spray of fine liquid droplets. As a form of atmospheric pressure ionization in mass spectrometry these droplets are then ionized via a low-current discharge electrode to create a solvent ion plasma. A repeller then directs these charged particles through the skimmer and acceleration region to introduce the aerosolized sample to a mass spectrometer. It is particularly useful in liquid chromatography-mass spectrometry (LC-MS).
Field-flow fractionation, abbreviated FFF, is a separation technique in which a field is applied to a diluted suspension in a fluid or to a solution pumped through a long and narrow channel, perpendicular to the direction of the field, in order to cause the separation of particles present in the fluid, depending on their differing "mobilities" under the force exerted by the field. It was devised and reported by J. Calvin Giddings in 1976. Giddings, credited for the invention of FFF, was professor of chemistry and specialist of chromatography and separation techniques at the University of Utah. The FFF method is unique to other separation techniques because it can separate materials over a wide colloidal size range while maintaining high resolution. Although FFF is an extremely versatile technique, there is no "one size fits all" method for all applications.
The history of chromatography spans from the mid-19th century to the 21st. Chromatography, literally "color writing", was used—and named— in the first decade of the 20th century, primarily for the separation of plant pigments such as chlorophyll and carotenoids. New forms of chromatography developed in the 1930s and 1940s made the technique useful for a wide range of separation processes and chemical analysis tasks, especially in biochemistry.
Partition chromatography theory and practice was introduced through the work and publications of Archer Martin and Richard Laurence Millington Synge during the 1940s. The process of separating mixtures of chemical compounds by passing them through a column that contains a solid stationary phase that was eluted with a mobile phase was well known at that time. Chromatographic separation was considered to occur by an adsorption process whereby compounds adhered to a solid media and were washed off the column with a solvent, mixture of solvents, or solvent gradient. In contrast, Martin and Synge developed and described a chromatographic separation process whereby compounds were partitioned between two liquid phases similar to the separatory funnel liquid-liquid separation dynamic. This was an important departure, both in theory and in practice, from adsorption chromatography.
Binding selectivity is defined with respect to the binding of ligands to a substrate forming a complex. Binding selectivity describes how a ligand may bind more preferentially to one receptor than another. A selectivity coefficient is the equilibrium constant for the reaction of displacement by one ligand of another ligand in a complex with the substrate. Binding selectivity is of major importance in biochemistry and in chemical separation processes.
Equilibrium chemistry is concerned with systems in chemical equilibrium. The unifying principle is that the free energy of a system at equilibrium is the minimum possible, so that the slope of the free energy with respect to the reaction coordinate is zero. This principle, applied to mixtures at equilibrium provides a definition of an equilibrium constant. Applications include acid–base, host–guest, metal–complex, solubility, partition, chromatography and redox equilibria.
The Dumas method of molecular weight determination was historically a procedure used to determine the molecular weight of an unknown substance. The Dumas method is appropriate to determine the molecular weights of volatile organic substances that are liquids at room temperature.
Forced Rayleigh scattering (FRS) is an experimental method in physics and chemistry based on light scattering and is usually used to measure diffusion on length scales of roughly 10 µm. Many FRS experiments have been carried out on thermal and mass diffusion in liquids, and thermophoresis has been measured in polymer solutions.
References
- 1 2 3 Slabaugh, Michael R.; Seager, Spencer L. (2010). Introductory Chemistry for Today. Pacific Grove: Brooks Cole. ISBN 978-0-538-73430-1.
- 1 2 Giddings, J. C.; Seager, S. L.; Stucki, L. R.; Stewart, G. H. (1960). "Plate Height in Gas Chromatography". Analytical Chemistry. 32 (7): 867–870. doi:10.1021/ac60163a043.
- 1 2 "Faculty - Weber State University".
- ↑ Slabaugh, Michael R.; Seager, Spencer L. (2008). Chemistry for today: general, organic, and biochemistry. Australia: Thomson Brooks/Cole. ISBN 978-0-495-11282-2.
- ↑ "Organic and Biochemistry for Today, Spencer L. Seager, Book - Barnes & Noble".
- ↑ Slabaugh, Michael R.; Seager, Spencer L. (2007). Safety Scale Lab Experiments for Seager/Slabaugh's Chemistry for Today: General, Organic, and Biochemistry, 6th. Pacific Grove: Brooks Cole. ISBN 978-0-495-11269-3.
- ↑ Darweesh, Judith (1983). "Environmental Chemistry: Air and Water Pollution (Stocker, H.; Seager, Spencer L.)". Journal of Chemical Education. 60 (8): 686. Bibcode:1983JChEd..60..686D. doi: 10.1021/ed060p686.2 .
- ↑ Smith, Wayne L. (1976). "Energy: From source to use (Stoker, Steven H.; Seager, Spencer L.; Capener, Robert L.)". Journal of Chemical Education. 53 (6): A306. Bibcode:1976JChEd..53Q.306S. doi: 10.1021/ed053pA306.1 .
- ↑ "Rapid Determination of Gaseous Diffusion Coefficients by Means of Gas Chromatography Apparatus | Issue 5 - Journal of Chemical Physics".
- ↑ Seager, Spencer L.; Geertson, Lyle R.; Giddings, J. Calvin (1963). "Temperature Dependence of Gas and Vapor Diffusion Coefficients". Journal of Chemical & Engineering Data. 8 (2): 168–169. doi:10.1021/je60017a003.
- ↑ Giddings, J.Calvin (1964). "Plate height in coiled columns". Journal of Chromatography A. 16: 444–447. doi:10.1016/S0021-9673(01)82513-9. PMID 14265866. Archived from the original on 2013-02-02.
- ↑ Johnson, D. P.; Critchfield, F. E. (1960). "Colorimetric Determination of Low Concentrations of Primary and Secondary Alcohols". Analytical Chemistry. 32 (7): 865–867. doi:10.1021/ac60163a042.
- ↑ Giddings, J. C.; Seager, S. L. (1962). "Method for the Rapid Determination of Diffusion Coefficients. Theory and Application". Industrial & Engineering Chemistry Fundamentals. 1 (4): 277–283. doi:10.1021/i160004a009.
- ↑ Pagenkopf, Gordon K. (1977). "Environmental Chemistry: Air and Water Pollution (Stoker, H. Stephen; Seager, Spencer L.)". Journal of Chemical Education. 54 (3): A177. Bibcode:1977JChEd..54..177P. doi:10.1021/ed054pA177.2.
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