Temperature-controlled chromatography

Temperature has often been suggested as a useful control variable for HPLC to make a changes and to speed equilibrations leading to faster separations. The problem has been that both bonded-phase hydrolytic cleavage and solubility of silica in aqueous solvents are accelerated at elevated temperatures. Mobile phase boiling within the column can cause bubble formation and vapor locking if the critical point of the solvent is exceeded. Finally, thermal-labile compounds can suffer degradation at elevated temperatures. 

HPLC A Practical User s Guide, Second Edition, by Marvin C. McMaster Copyright 2007 by John Wiley Sons, Inc. 

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For LC, temperature is not as important as in GC because volatility is not important. The columns are usually metal, and they are operated at or near ambient temperatures, so the temperature-controlled oven used for GC is unnecessary. An LC mobile phase is a solvent such as water, methanol, or acetonitrile, and, if only a single solvent is used for analysis, the chromatography is said to be isocratic. Alternatively, mixtures of solvents can be employed. In fact, chromatography may start with one single solvent or mixture of solvents and gradually change to a different mix of solvents as analysis proceeds (gradient elution). 

Many HPLC instruments are already furnished with temperature controls for the column. Unified chromatography requires a much wider temperature range than is currently practiced in HPLC. Until better defined by experience, a temperature range from about —60 to about 350°C seems reasonable as a specification. Since this is well in the range of a GC oven with subambient temperature capability, no new technology is required. 

Vanheukelem, L. et al., Improved separations of phytoplankton pigment using temperature-controlled high-performance liquid chromatography. Mar. Ecol. Prog. Ser., 14, 303, 1994. 

Hayakawa, K., Hirano, M., Yoshikawa, K., Katsumata, N, and Tanaka, T., Separation of phenylthiohydantoin-amino acids by temperature-controlled reversed-phase high-performance liquid chromatography, /. Chromatogr. A, 846, 73, 1999. 

Temperature control is important for the accurate measurement of retention data, and has to be used with refractometer detectors (Section 2.4.5). Increasing the temperature can increase the speed of the separation, especially in exclusion chromatography, and usually increases the efficiency of the column (though the gain in efficiency can be lost if the mobile phase is not properly equilibrated). Complicated separations can often be optimised by increasing the temperature, but this is done very much on a trial and error basis, and most work in hplc is still done without temperature control. 

Figure 7.4 Schematic diagram of a gas chromatography (GC) system. The carrier gas enters from the left, and the sample is injected into the gas flow and is carried through the capillary column inside a temperature-controlled oven where the components are separated. Detection here is by flame ionization, where the eluent increases the conductivity of the flame.

LKB 4151 Alpha Plus Alpha Plus is a fully automated and dedicated analyser, this turnkey system has been carefully designed to give a truly robust chromatography. Stepwise elution with up to five buffers plus flexible temperature control guarantees optimal separations from even... 

J.K. Swadesh, Temperature control in analytical high-performance liquid chromatography. In E. Katz (Ed.), Handbook of HPLC, Marcel Dekker, New York, 1998, pp. 607-615. 

GC Gas chromatography PI Pressure indicator PIC Pressure controller FIC Flow controller TIC Temperature controller... 

High-performance liquid chromatography (HPLC) is one of the premier analytical techniques widely used in analytical laboratories. Numerous analytical HPLC analyses have been developed for pharmaceutical, chemical, food, cosmetic, and environmental applications. The popularity of HPLC analysis can be attributed to its powerful combination of separation and quantitation capabilities. HPLC instrumentation has reached a state of maturity. The majority of vendors can provide very sophisticated and highly automated systems to meet users needs. To provide a high level of assurance that the data generated from the HPLC analysis are reliable, the performance of the HPLC system should be monitored at regular intervals. In this chapter some of the key performance attributes for a typical HPLC system (consisting of a quaternary pump, an autoinjector, a UV-Vis detector, and a temperature-controlled column compartment) are discussed [1-8]. 

Catalytic Experiments. Activities were performed in a 1 liter Parr reactor. A typical experiment was performed as follows at a temperature of 100 °C, 100 mg of the catalyst and 1.5 /. wt of (-)-carvone (Aldrich) in n-hexane solution (100 ml) were Introduced in a high pressure Parr reactor equipped with mechanical stirring and automatic temperature control. Before introducing the hydrogen the system was purged 2 or 3 times with Nz> The total hydrogen pressure was 21 atm. The reaction products were analysed by gas chromatography. NMR and Mass Spectrometry and identified as unreacted carvone, carvotanacetone, carvomenthone and three carvomenthol stereoisomers (axial-equatorial, equatorial-equatorial and equatorial-axial). 

Ultrasonic Mainly gases of low molar mass Hj, N2. COj, He. Ar. A quartz crystal transducer transmits a sound wave through a sample of gas with a similar crystal used as the receiver. The velocity of the sound wave is proportional to the square root of the molar mass of the sample. The phase shift of the sound signal is measured by comparison with a reference signal. Precise temperature control is required. 1-10 Gas chromatography... 

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