Chromatography simulated

T. Hanai, Simulation chromatography of phenolic compounds using a computational chemical method,/. Chromatogr., A, 2003,1027,279-287. 

Along the same lines, a distillation can be simulated by gas phase chromatography. As in a refinery, distillation in the laboratory is very often the first step to be carried out, because it gives the yields in different cuts gasoline, kerosene, etc., and makes further characterization of the cuts possible. 

The simulated distillation method uses gas phase chromatography in conjunction with an apolar column, that is, a column where the elution of components is a function of their boiling points. The column temperature is increased at reproducible rate (programed temperature) and the area of the chromatogram is recorded as a function of elution time. 

In practice, simulated distillation by gas phase chromatography is used for the following objectives ... 

Finally, other methods are used to obtain simulated distillation by gas phase chromatography for atmospheric or vacuum residues. For these cases, some of the sample components can not elute and an internal standard is added to the sample in order to obtain this quantity with precision. 

True Boiling Point (TBP) jL Simulated distillation (gas chromatography) ... 

Distillation simulated by gas chromatography is a reproducible method for analyzing a petroleum cut it is appiicabie for mixtures whose end point is less than 500°C and the boiling range is greater than 50°C. The results of this test are presented in the form of a curve showing temperature as a function of the weight per cent distilled equivalent to an atmospheric TBP. 

Chromatography may also be advantageous when it is required to separate several pure products from a single feed stream. A simulated moving-bed system can yield only two weU-separated fractions from a single feed stream. 

Simulated TBP (gas chromatography) ASTM D 2887 Crude oil and petroleum fractions... 

An alternative to TBP distillation is simulated distillation by gas chromatography. As described by Green, Schmauch, and Worman [Anal. Chem., 36, 1512 (1965)] and Worman and Green [Anal. Chem., 37, 1620 (1965)], the method is equivalent to a 100-theoretical-plate TBP distillation, is veiy rapid, reproducible, and easily automated, requires only a small microliter sample, and can better... 

It is important to note that simulated distillation does not always separate hydrocarbons in the order of their boiling point. For example, high-boihng multiple-ring-type compounds may be eluted earher than normal paraffins (used as the calibration standard) of the same boiling point. Gas chromatography is also used in the ASTM D 2427 test method to determine quantitatively ethane through pentane hydrocarbons. 

These workers used binary solvent systems over a range of mole fractions to determine, for each solute, the constants a and b of equation (8.2). For methyl and phenacyl esters, TLC was used, while overpressured layer chromatography (OPLC) was used for dansyl amino acids. Nurok and co-workers (11) also evaluated how the quality of a simulated separation varies with changing solvent strength by using the inverse distance function (IDF) or planar response function (PRF), as follows ... 

W. Markowski and K. L. Czapiriska, Computer simulation of the separation in one- and two-dimensional tliin-layer chromatography hy isocratic and stepwise gradient development ,/ Liq. Chromatogr. 18 1405-1427 (1995). 

On that basis, crystallization is often used in combination with other enantiose-lective techniques, such as enantioselective synthesis, enzymatic kinetic resolution or simulated moving bed (SMB) chromatography [10, 11]. In general, when referring to crystallization techniques, the aim is to obtain an enantiomeric enrichment in the crystallized solid. However, the possibility of producing an enrichment in the mother liquors [12, 13], even if this is not a general phenomenon [14], must be taken into account. 

The competitive adsorption isotherms were determined experimentally for the separation of chiral epoxide enantiomers at 25 °C by the adsorption-desorption method [37]. A mass balance allows the knowledge of the concentration of each component retained in the particle, q, in equilibrium with the feed concentration, < In fact includes both the adsorbed phase concentration and the concentration in the fluid inside pores. This overall retained concentration is used to be consistent with the models presented for the SMB simulations based on homogeneous particles. The bed porosity was taken as = 0.4 since the total porosity was measured as Ej = 0.67 and the particle porosity of microcrystalline cellulose triacetate is p = 0.45 [38]. This procedure provides one point of the adsorption isotherm for each component (Cp q. The determination of the complete isotherm will require a set of experiments using different feed concentrations. To support the measured isotherms, a dynamic method of frontal chromatography is implemented based on the analysis of the response curves to a step change in feed concentration (adsorption) followed by the desorption of the column with pure eluent. It is well known that often the selectivity factor decreases with the increase of the concentration of chiral species and therefore the linear -i- Langmuir competitive isotherm was used ... 

Erancotte E., Richert P. (1997) Applications of Simulated Moving-Bed Chromatography to the Separation of the Enantiomers of Chiral Drugs, J. Chrotnatogr. A 769 101-107. 

Guest D. W. (1997) Evaluation of Simulated Moving Bed Chromatography for Pharmaceutical Process Development, J. Chromatogr. A 760 159-162. 

Zhong G., Guioehon G. (1996) Analytieal Solution for the Linear Ideal Model of Simulated Moving Bed Chromatography, Chem. Eng. Sci. 51 4307-4319. 

Mazzotti M., Storti G., Morbidelli M. (1997) Optimal Operation of Simulated Moving Bed Units for Nonlinear Chromatographie Separations, J. Chromatogr. A 169 3-24. 

Pais L. S., Loureiro J. M., Rodrigues A. E. (1997b) Modeling, Simulation and Operation of a Simulated Moving Bed for Continuous Chromatographie Separation of l,l -bi-2-naphthol Enantiomers, J. Chromatogr. A 169 25-35. 

Nieoud R. M., Euehs G., Adam P, Bailly M., Kusters E., Antia E, Reuille R., Sehmid E. (1993) Preparative Seale Enantioseparation of a Chiral Epoxide Comparison of Liquid Chromatography and Simulated Moving Bed Adsorption Teehnology, Chirality 5 267-271. 

Nieoud R. M., Seidel-Morgenstem A. (1993) Adsorption Isotherms Experimental Determination and Applieation to Preparative Chromatography Simulated Moving Bed Basics and Applications, R. M Nieoud (ed.), Institut National Polyteehnique de Lorraine, Naney, Pranee, p. 4-34. 

Preparative chromatography has been used for chiral separations for years, but examples of multi-kg separations (and hence larger ones) were rare until recently. The development of SMB techniques (both hardware and simulation software) has made major breakthroughs in this field. The ability of SMB as a development tool has allowed the pharmaceutical manufacturer to obtain kilo grams quantities of enantiopure drug substances as well benefit from the economics of large-scale production. 

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