Serially connected columns

The total retention of a given solute and the gas holdup time of an unretained solute eluting through two serially connected columns is the sum of the retentions in the individual column units, and thus we can write that... 

The trial and error approach to optinizing a separation using serially connected columns can be Very time consuming. 

Stationary phase optimized selectivity liquid chromatography basic possibilities of serially connected columns using the PRISMA principle. /. Chromatogr. A, 1157 (1-2), 122-130. 

In the DMSO-water system (90 10) with 0.05 M LiBr, three serially connected columns were used Gram 30, 100 and 3000 (PSS). The detector... 

In the DMSO-water system (90 10) with 0.05 M LiBr, three serially connected columns were used Gram 30, 100 and 3000 (PSS). The detector system consisted of a UV detector (PLLC 1200), and a RI detector (Shodex RI-71). The flow rate was 0.4 ml/min at 60 C. Molar masses were calculated from the viscosity and Rl-signals by universal calibration using pullulan standards. 

J. V. Hinshaw, Jr and L. S. Ettre, Selectivity tuning of serially connected open-tubular (capillary) columns in gas chromatography. Part 1 fundamental relationships , Chromatographia 21 561-572 (1986). 

In order to produce oxime 199 in greater quantities, the authors subsequently evaluated the use of DMF as the reaction solvent due to the increased solubility of the nitrite precursor 277 (36 mM). In conjunction with two serially connected microreactors, each containing 16 microchannels [1,000 pm (wide) x 500 pm (deep) x 1.0 m (length)] and eight black lights, the photochemical synthesis was performed continuously for 20h at a flow rate of 250 pi min 1 (residence time = 32 min). After an off-line aqueous extraction and silica gel column, 3.1 g of the oxime 199 was obtained equating to an isolated yield of 60% and successfully demonstrating the ability to use photochemical synthesis for the scalable preparation of pharmaceutically relevant compounds. 

A major advantage of modified-C02 pSFC is that due to the low pressure and similarity of the mobile phases used for structural and stereochemical separations, multiple stationary-phase columns can be connected in series, generating separations not achievable by other chromatographic methods. Multiple columns of the same phase have been serially connected to provide significantly amplified chromatographic efficiencies [1].A recent example chromatogram obtained by connecting four 250 X 4.6-mm Chiralpak AD columns in series is shown in Fig. 2 [6]. With the four columns in series, concurrent separation of the four stereoisomers of each of two structurally different compounds was achieved. 

Serial connection of different stationary phases provides some very interesting separations. The combination of different CSPs provides systems capable of resolving a wide range of enantiomers (Sandra et al. [2], Gyllenhaal [2]). Recent applications combining normal-phase bonded-silica (diol, cyano, amino) columns with CSPs in series, to provide concurrent structural... 

Packed column SFC stationary phases are very similar or identical to those used for HPLC. With neat CO2 mobile phases, polymer or polymer-coated silica stationary phases have typically been used. With modified-C02 mobile phases, bonded-phase silica columns are typically used. For structural separations, diol, amino, or cyano stationary phases are most often used. For stereochemical separations, derivatized polysaccharide-bonded silica columns are most often the stationary phases of choice. A powerful feature of modified-C02 pSFC is the ability to serially connect different stationary phases to obtain enhanced or mul-... 

GC xGC is based in the serial connection of two columns with different stationary phases. For this reason, peak size, width, and retention time have a similar meaning than in GC. As explained in Chapter 2, the modulation process divides the output from the first column into time slices, and focuses and reinjects them in the second column. However, adequate processing of the detector response allows separation of the contribution of the first and of the second columns in terms of retention time and of peak width to the final response, and it also makes it possible to present graphically the results in a two-dimensional plot. 

An interesting realization of continuous chromatography is simulated moving-bed (SMB) chromatography. Here, a serial connection of several chromatographic columns leads to a continuous simulated countercurrent process. In order to further explain the attribute simulated , first the idea of the true moving bed (TMB) is shown. 

Fig. 2-20. Different methods of connecting three columns in a quaternary mixture distillation unit. a)-d) Serial connections of columns e) Parallel connection F Feed...

The separation column was prepared by means of a pair of eccentric coil assemblies, which were made by winding a single piece of 1 mm l.D. polytetrafluoroethylene (PTFE) tubing onto 7.6 cm long, 5 mm O.D. nylon pipes forming 20 units of serially connected left-handed coils. 

After preseparation of the oil on a nonchiral stationary phase, the peaks of interest have to be transferred to a second capillary column coated with a chiral phase, a technique usually referred to as heart cutting. In the simplest case, two GC capillaries with different selectivities are serially connected, and the portion of unresolved components from the ef uent of the rst column is directed into a second column, for example, a capillary with a chiral coating. The basic arrangement used in 2D GC (GC-GC) is shown in Figure 2.3. By means of a valve, the individual fractions of interest eluting from the rst column are directed to the second, chiral column, while the rest of the sample may be discarded. With this heart-cutting technique, many separations of chiral oil... 

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