Separation of alkylnaphthalenes by preparative liquid chromatography using column switching systems

Summary The paper describes the separation of the mixture of alkynaphthalenes from distillation cuts of a pyrolysis oil, by preparative liquid chromatography on silica. The design of the system permits the connection of the columns to form multicolumn systems.The samples were first separated on a single column. The mixtures were further separated using two-column chromatography systems.The obtained fractions were analyzed by capillary gas chromatography. In most cases a substantial increase in the concentrations of the individual components was achieved. In several cases, pure compounds have been obtained. Separation efficiency increases in the following order: single column, two directly coupled collumns, two-step switching chromatography, heartcutting.     

High-throughput preparative process utilizing three complementary chromatographic purification technologies

A high-throughput process was developed in which wells in plates generated from parallel synthesis are automatically channeled to an appropriate purification technique using analytical data as a guide. Samples are directed to either of three fundamentally different preparative techniques: HPLC with UV-triggered fraction collection, supercritical fluid chromatography (SFC) with UV-triggered fraction collection, or HPLC with MS-triggered fraction collection. Automated analysis of the analytical data identifies the product compound mass and creates work lists based on chromatographic properties exhibited in the data so that each preparative instrument cherry picks the appropriate list of samples to purify when a preparative-scale plate is loaded.     

Optimization of throughput in preparative column luquid chromatography by column overloading and partial fractionation of the effluent

Summary The criteria for the optimization of preparative chromatography are sample throughput and product purity. It is shown for column liquid chromatography that the throughput has been maximized for a given purity by column overloading and appropriate fractionation. The size and position of the fraction must be determined by chemical analysis, since overlapping peaks under overloading conditions are usually distorted compared to the peaks of the same amounts of pure compounds. With overloading of the column larger particles can be used as column packings without reduction of the separation effect.     

Computer simulation of non-linear preparative chromatography processes

Summary A theory of non-linear chromatography based on the mass balance equation is presented. The model is a system of partial differential equations and it includes axial dispersion in the mobile phase, flow in the mobile phase and mass transfer between phases. In the case of the injection of a mixture competition between components for places in the stationary or the mobile phase is taken into account. In the paper are discussed: numerical calculations of concentration and volume overloading and the effect of the mutual influence of the components of the injected mixture on the process of mass transfer between phases. Additionally, results of experiments for convex and concave adsorption isotherms are presented. In both cases the results obtained qualitatively confirm the theoretical analyses.     

Twin column chromatography for industrial-scale decontamination processes

A frontal chromatographic unit was devised consisting of a column-detector-column array. The unit is either equipped with identical columns (identical twins) or with columns of varying length (fraternal twins). Due to the finite nature of the columns, a prerun is formed at the column walls following the same regularities as the main stream. These regularities are used for the identification of the process termination below the detection limits of the monitor. For the implementation, a clear preference is given to the employment of fraternal twins, as the feed assay can be integrated into the separation process.     

Direct preparative resolution of racemic amino-acids using ligand exchange chromatography (chirallec)

Summary Preparative resolutions of racemic amino-acids by ligand-exchange chromatography are described. Base-line resolution of multigram quantities of many racemic solutes was obtained using very simple equipment (open tubular column).     

Use of the sol-gel technique to prepare capillary columns coated with a macrocyclic dioxopolyamine for open-tubular capillary electrochromatography

Summary Columns for open-tubular (OT) capillary electrochromatography (CEC), coated with 1,4,7,10-tetraazacyclotridecane-11,13-dione (dioxo[13]aneN₄) by use of the sol-gel technique, have been investigated for the first time. Dioxol[13]aneN₄ was reacted with 3-(2-cyclooxypropoxy)propyltrimethoxysilane and the product was then mixed with tetraethoxysilane (TEOS) and water to form a glass matrix as a network in which the stationary phase (dioxo[13]aneN₄) was incorporated. In comparison with OTCEC columns prepared by the sol-gel process with TEOS only, the sol-gel-derived macrocyclic dioxopolyamine columns enabled better separations of a mixture of isomeric nitrophenols and benzenediols, a mixture of isomeric aminophenols and diaminobenzenes, and a mixture of four biogenic monoamine neurotransmitters. High efficiencies (60 000—340 000 plates m⁻¹) were achieved for isomeric benzenediols, aminophenols, nitrophenols, and diaminobenzenes. Migration time and theoretical plate number reproducibility was satisfactory;RSD was <2% for one column and <8.5% from column to column.     

Some aspects of the preparative separation of enantiomers on chiral stationary phases

Summary In preparative column liquid chromatography, it is necessary to work with conditions of mass overload to obtain high throughput per unit time. The influence of sample mass and of eluent composition on the separation of R,S-1-(1-naphthylethyl)propylamide on chiral 3,5-dinitrobenzoylphenylglycine-silica (Pirkle type stationary phase) was investigated. At a sample load of 200μg of racemate per gram of stationary phase, the column becomes overloaded. At higher sample loads the peaks become triangular; therefore the first peak is always pure up to loads of 10mg g⁻¹, although resolution is low. The purity of the second peak depends on sample mass, but not on the strength (polarity) of the mobile phase. This is due to the effect that peak width, as well as resolution, decrease as the polarity of the eluent increases. In certain cases the polarimeter, used as a detector, can give more information on peak purity than the UV detector.     

A new non-synchronous preparative counter-current centrifuge—the next generation of dynamic extraction/chromatography devices with independent mixing and settling control,which offer a step change in efficiency

A new and significantly more robust design of non-synchronous coil planet centrifuge is introduced where the degree of mixing between two immiscible phases can be changed independently from the “g” field required to separate out the phases. A hypothesis that an optimum ratio between the speed of the bobbin and the speed of the rotor can be found to optimise the efficiency of the separation for a given force field is upheld for an intermediate polarity phase system. This paves the way for extensive further research to find the optimum non-synchronous conditions for a range of different phase systems that are desirable for the separation of large molecules, proteins and biologics but can tend to emulsify in the standard “J” type centrifuge systems currently available and routinely in use for aqueous organic phase systems. A step change of up to 30% in resolution and 90% in plate efficiency is demonstrated.     

Planar electrochromatography Part 1. Planar electrochromatography on non-wetted thin-layers

Summary Planar electrochromatographic separations of test substances were performed on non pre-wetted, commercially available, thin-layer plates. The behavior of different layers and solvents was studied in an applied electric field of up to 2000 V cm^–1. Evident electrokinetic effects, electroosmosis and electrophoresis were observed only on silica gel and polyamide layers developed with polar solvents. The selectivity of separation of nonionic and ionogenic compounds was greatly enhanced. Although experimental conditions were controlled to a certain extent, results obtained with the same solvents were reproducible within 5%.     

Mass overload in preparative liquid chromatography: Choice of column dimensions and optimum working conditions

Summary This paper deals with a theoretical study which makes it possible to calculate column dimensions (length and inner diameter) and to select working conditions (particle diameter of the column packing, elution flow rate, run number) with regard to purity, recovery ratio and amount of pure substance that is to be isolated. These determinations take into account the pressure limitation and pumping capacity of the available chromatograph.     

Magnetically immobilized frits for the preparation of packed columns used in capillary electrochromatography

Fabrication of porous frits to retain stationary phases is a critical issue in column preparation for capillary electrochromatography (CEC). In this work, porous frits were prepared by applying an external magnetic field to magnetically responsive particles placed inside a fused-silica capillary. Three batches of uniform magnetite spheres with particle diameters of 0.3, 0.4, and 0.6 μm and saturation magnetization values of 73.03, 74.41, and 77.83 emu/g, respectively, were used as frit particles and octadecyl- and phenyl-bonded silica gels were packed successfully into frit-containing capillaries. The performance of the resulting magnetically immobilized frits and packed columns was evaluated. The electroosmotic mobilities in capillaries containing outlet frit only were found to be reduced by 2–4% whereas the plate heights of an unretained marker increased by 30–50% as compared to those in open capillaries. These variations are believed to be associated with the inhomogeneities of the packed structure of the frits. The magnetically immobilized frits showed adequate mechanical strength to withstand the flow drag force, allowing separation in capillaries packed with 5-μm stationary phases up to 10–15 cm, thus rendering column efficiency and reproducibility comparable with those obtained with sintered frits. Taken together, retaining frits made of uniform magnetite particles serves as a viable alternative to sintered frits for column preparation, which offers several distinct advantages such as ease of preparation, improved durability as compared to sintered frits where the removal of the polyimide coating makes the packed column susceptible to breakage, and use of large-bore capillaries for semipreparative separations.     

Preparative liquid chromatography: Choice of column dimensions and working conditions for occasional preparative separation

Summary This paper deals with a theoretical study which makes it possible to calculate column dimensions (length and inner diameter) and working conditions (particle diameter of the stationary phase, elution flow rate, run number) with regard to purity, recovery ratio and the amount of pure substance that may be isolated. This determination takes into account the pressure limitation and pumping capacity of the available chromatograph. The isolation of microgram amounts of a component is shown in order to illustrate the above-mentioned calculation method.Presented at the 14th International Symposium on Chromatography London, September, 1982     

Purification of thymine dimer from monomer solution in preparative liquid chromatography

Summary Cyclobutane pyrimidine dimers and monomers of thymine were separated on a C₁₈ reversed-phase high performance liquid chromatographic column. Using two mathematical models, the effect of the sample sizes on peak shapes in preparative liquid chromatography was investigated. One of these approaches is through a linear kinetic model, and the other is based on the non-linear adsorption isotherm. With the injection of small samples good agreement between the calculated value by the linear kinetic model and experimental, data were achieved. With increased sample size, this model is defective in its prediction of large concentration profiles of sample. However, the nonlinear model permits the accurate prediction of the location of the component band and the determination of the appropriate time to start and stop collection of the enriched fraction at higher concentrations of monomer and the lower concentrations of dimer. Therefore, extremely small amounts of dimer can be extracted from monomer solutions.     

Toward rapid preparation of capillary columns for electrochromatography use

CEC is a high performance electrodriving liquid phase separation technique. It does not need complex and sophisticated high pressure instrumentation for nanoflow driving. This is attractive for parallel multicolumn analysis. To this end, high throughput methods for column preparation are needed to support the use of multiple columns. In this study, we directly used CEC mobile phase solution as the packing solvent, and realized rapid preparation of capillary columns based on a single particle fritting technology. The method presented high preparation throughput compared with other reported methods based on various fritting technologies. The single particle fritting approach promoted column preparation throughput to 1 column/h, including all the fritting, packing and conditioning steps. The rapidly prepared columns showed consistently high efficiency of up to 150 000 plates per meter, and usefulness in reversed phase CEC of neutral, charged and biomolecules. With standard peptides as the sample, excellent long term reproducibility (better than 0.8%RSD, ten days, for retention times) was observed.     

Multiple preparative chromatography

Summary The capacity of different versions of single- and dual-stage separation of mixtures on a preparative scale is considered. It has been shown that dual-stage separation with intermediate condensation considerably enhances the capacity of the installation as compared with a single-stage process.     

Automated instrumentation for multidimensional preparative scale GC (PSGC)

Summary An automated instrument for preparative scale separations is described. The instrumental system, which does not include the general use of temperature programmed operation allows for the application of multidimensional techniques of carrier gas flow switching such as heart cutting, backflushing etc. in order to optimize the resolution within selected cuts taken from a preseparation, to enrich trace components or to shorten separation times at still sufficient sample capacity of the entire system. Typical applications of the instrument are discussed. Presented at the 15th International Symposium on Chromatography, Nürnberg, October 1984     

Instrumental developments in capillary electrochromatography

Summary An instrumental device for capillary electrochromatography (CEC) is described that permits conditioning of packed columns at pressures up to 100 bar, in or on-column fluorescence detection and electrokinetic sample injection. Capillaries with varying inner diameters (75, 100, 150 m) packed with octadecyl silica gel (3 m) are compared for efficiency and detection sensitivity. The influence of counter pressure on electroosmotic velocity and plate number is discussed.     

preparative liquid chromatography: History and trends-supplemental remarks

Summary Supplementing the paper of Geeraert and Verzele published in the November 1978 issue of this journal, the controversy between Tswett and Willstätter on preparative liquid chromatography, as well as the pilotscale applications for the isolation of rare earths and pure hydrocarbons are discussed.     

The preparative chromatographic enantioseparation of a racemic morphanthridine analog on a chiral stationary phase

Summary The preparative chromatographic enantioseparation of a chiral morphoanthridine analog has been performed on an analytical column using amylose-tris(3,5-dimethylphenylcarbamate) as chiral stationary phase. The racemate (100 mg) was resolved to baseline within 15 min. This paper describes the development of the method, estimation of the capacity of the chiral stationary phase and discussed the potential of the chromatography if performed under preparative conditions. From the results and calculations presented it seems likely that the resolution of 70 tons year⁻¹ could easily be achieved on 30 kg of stationary phase with a mobile-phase consumption of only 720 L day⁻¹.