Temperature stationary phase

Reaction conditions 0.1 g of the zeolite Y modified catalyst, tested in a conventional glass microreactor with racemic butan-2-ol (7.35 x 10" mol h-1), prevaporized in a nitrogen diluent (6.2 -6.7 x 10" mol h-1). Products were analyzed using on-line GC with a 40m capillary y- cyclodextrin colimm with trifluoroacetyl stationary phase, temperature programmed from 25-70 "C with a split ratio of 120 1. 

C is not recommended and high-temperature LC has not been rigorously explored. With the advent of thermally stable phases such as zir-conia-based stationary phases, temperatures in excess of 150°C can now be utilized. Many zirconia-based phases are available, so the stability of stationary phases is less of an issue. 

For high-pH operation of any silica-based stationary phase, temperature should not exceed 40°C, organic buffers should be used instead of phosphate or carbonate, and methanol instead of acetonitrile should be the organic solvent. 

Stationary phase Temperature limit (°C) Solvent code Applications... 

Sulphonic acids and their salts are analysed by GC after esterification with diazomethane or after chlorination with thionyl chloride or phosgene [119]. Reaction with thionyl chloride proceeds according to Scheme 5.14. A 0.5-g sample of sulphonic acid or its salt is placed into a round-bottomed flask fitted with a magnetic stirrer and a reflux condenser, 0.5 ml of dimethylformamide and 20 ml of thionyl chloride are added and the mixture is refluxed for several minutes up to 2 h (according to the character of the sample) until the evolution of gas from the reaction mixture ceases (detection with the aid of a bubbler filled with chlorobenzene). If a salt is chlorinated, solid chloride produced in the reaction mixture must be removed by dilution with dichloromethane and by careful filtration through a fine glass filter. Excess of thionyl chloride and solvent is evaporated carefully under decreased pressure. The residue is dissolved in a suitable solvent (CCU) and analysed by GC (silicone stationary phase, temperature 160°C). 

Analyte Mobile Phase Stationary Phases Temperature Reference... 

Identify mobile-phase c-omposition. stationary phase, temperature and particle size which give the greatest separation factor of the product and the expected limiting impurity. 

In the design of the proce.ss, it is important to develop cut point strategies which lead to robust control of the product pool. Use of strategies which combine monitoring the elution volume and detector response can lead to robust control strategies which avoid the collection and analysis of fractions. The development of strategies which are sufficiently robust to accept the variability as.sociated with the feed composition, the degradation of the stationary phase, temperature variations, and mobile-phase composition, is not trivial and an important step in the development process. 

Several kinds of flavonoids are efficiently separated and analyzed using packed or capillary column supercritical fluid chromatography. The composition of mobile phase, stationary phase, temperature, and pressure aU affect the resolution. This article mainly focuses on the separation of polymethoxylated flavones, polyhydroxyl flavonoids, and flavonol isomers. 

Fig. 1 Analysis of underivatized cyclopeptidic alkaloids in chloroform extract using HT-HRGC. Condition fused-silica capillary column (6 m X 0.25 mm X 0.08 tm) coated with a LM-5 (5% phenyl, 95% polymethylsiloxane immobilized bonded phase) stationary phase. Temperature condition column at 200°C (1 min), increased by 4°C/min, then 300°C (5 min) inlet 250°C FID detector 310°C.

Then there are other parameters whose choice is not so compelling stationary phase, temperature, pH (or other ionic effects) and secondary chemical equilibria,... 

The gas chromatographic separation of chlorosilanes, methylchlorosilanes and their associated siloxanes have been reported404 on 11 different stationary phases. Temperature programming is necessary for the elution of the siloxanes but many of the stationary phases reported in the literature cannot be used under these conditions because of their high volatility at elevated temperatures. Among the liquids or gums which were used as stationary phases, the most effective were dimethyl, diethyl and dibutyl phthalates. 

Fig. 4. Chromatogram of separation on a silicone stationary phase of methyl esters of trifluoro-acetylated amino acids of hydrolysate of human fingernail. Sorbent silicone stationary phase. Temperature programme A, 100°C, isothermal B, heating from 100°C at 1.5°C/min C, heating from 116.5°C at 4°C/min D, 140°C, isothermal E, heating from 140°C at 6°C/min to 210°C. Peaks 1 = alanine 2 = valine 3 = glycine 4 = isoleucine 5 = threonine 6 = leucine 7 = norleucine 8 = internal standard 9 = proline 10 = asparagine 11 = glutamine 12 = phenylalanine 13 = tyrosine 14 = lysine. From ref. 13.

The development of a chromatographic procedure for an unknown sample (mixture) requires the selection of a variety of experimental conditions (type and composition of the mobile phase, characteristics of the column and the stationary phase, temperature, flow-rate, pressure, type of gradient, etc.). This problem was traditionally solved in an empirical way and with the aid of the vast literature on similar situations already dealt with. The last few years have seen attempts at the rationalization and automation of the optimization of chromatographic processes which have resulted In Interesting systematic approaches of great use. The monographs by Berridge [56], devoted to HPLC, and that by Shoenmakers [57], which deals with both HPLC and GC, represent the most systematic and complete compilations in this field at present. 

Figure 5.8 Column bleed, 25 m x 0.25 mm WCOT column dimethylsiloxane stationary phase, temperature programmed 50-350°C at 20°C min . ...

Since the distribution ratio, K, remains constant for a given stationary phase, temperature and carrier gas velocity the retention ratio, k, will vary directly with film thickness and inversely with the internal diameter dc = 2r). Retention times can therefore be manipulated by selecting alternative i.d. columns or a different film thickness, therefore retention time (i) increases as column i.d. decreases and (ii) increases as film thickness increases. 

Distillation was performed on a sample of 300 mg by addition of 0.5 mL H2SO4 (9 mol L ) in 20% KCl in H2O at a temperature of 145 °C distillation recovery was ca. 90%. Derivatization was by addition of 1% NaBEt4 in acetic acid. Separation was by gas liquid chromatography (column of 0.5 m length, internal diameter of 4 mm Chromosorb W AW-DMSC 60-80 mesh, loaded with 15% OV-3 stationary phase temperature of the injector of 500 °C, detector temperature at 20 °C column temperature of 100 °C He as carrier gas at 40 mL min ). Detection was by cold vapour atomic fluorescence spectrometry. Calibration was by calibration graph and standard additions using MeHgCl calibrant in Milli-Q water. 

Temperature increase always helps for a kinetic optimization of separations (it does, however, require prerequisites regarding the column thermostatting and stationary phase temperature stability). 

Fig. 6 Chromatogram of the separation of selected hydrocarbons on monomeric liquid-crystalline stationary phases. Temperature of capillary column 50°C. Time of separation 14 min. 1) hexane 2) heptane 3) octane 4) m-xylene 5) p-xylene 6) 0-xylene 7) m-ethyltoluene 8) p-ethyltoluene 9) m-diethylbenzene 10) O-diethylbenzene and 11) p-diethylbenzene.

Stationary phase (temperature of separation) Kovats trans- decalin Itrans index c/s- decalin Ids A/ //rans-/cfe First eluted isomer... 

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