Multilayer columns

BDE 17, 28, 47, 66, 85, 99, 100, 153, 154 183 Palm oil Palm oil Extraction by dialysis in hexane using a semi-permeable membrane. Purification thorugh multilayer column filled with neutral silica, silica modified with sulfuric acid (44%, w/w), and silica modified with KOH. Gas Chromatography (VF-5MS Factor Four, Varian) IT-MS 0.07-1.3 pg (instrumental limit of detection) [42]... 

Cleanup of sediment samples. The extracted sediment samples were cleaned up using a multilayer column. The multilayer glass column consisted of the following materials (from top to bottom) 1 cm water-free sodium sulfate, 1 g silica, 7 g 44% sulfuric acid on silica, 1 g silica, 2 g 33% sodium hydroxide on silica, 1 g silica, 1.5 g 10% silver nitrate on silica, and a small piece of silanized glass wool. After addition of each layer, the column was compacted by tapping... 

Countercurrent Chromatography Procedure. The entire column (pair of coiled multilayer columns connected in series) was filled with the stationary phase. The apparatus was then rotated counterclockwise at 600 rpm in planetary motion while the mobile phase was pumped into the inlet of the column at a flow-rate of 2.2 mL/min (head to tail elution mode). Maximum pressure at the outlet of the pump measured 80 psi. After a 1-hour equilibration period, the sample was loaded into the Rheodyne injector loop and injected. Effluent from the outlet of the column was continuously monitored with a Shimadzu UVD-114 detector at 312 nm and fractions collected with a Gilson FC-lOO fraction collector to obtain approximately 8.8 mL of eluant in each tube (during a 4-min interval). Retention of the stationary phase was estimated to be 930 mL (74%) by measuring the volume of stationary phase eluted from the column before the effluent changed to mobile phase (330 mL) and subtracting this volume from the total column capacity of 1260 mL. 

Method a PCBs were recovered by Soxhlet extraction with acetone and subsequently with a hexane/acetone (60 40) mixture. The extracts were combined, dried over sodium sulfate anhydrous, and solvent was exchanged to -hexane. Cleanup was performed on a multilayer column filled with silica gel and alumina. A further cleanup was carried out by gel permeation. 

Method b sample was Soxhlet extracted with toluene. Cleanup of the extract was performed on an open silica column followed by HPLC fractionation. A further cleanup was carried out on a multilayer column containing sulfuric acid impregnated silica, potassium hydroxide impregnated silica, and water deactivated silica. 

Organic solution was cleaned up by chromatography in a multilayer column filled with Florisil and alumina. PCBs were eluted with n-hexane. Elutes were concentrated under a gentle nitrogen stream before GC analysis. 

SPMD extracts were cleaned up on a multilayer column filled with phosphoric acid/silica gel, potassium silicate, and silica gel using 4% methyl tert-butyl ether in hexane as eluent. A second purification was carried out on Florisil using methyl tertbutyl ether hexane (75 25) mixture as eluent. PCBs were isolated with a fined fractionation on a silica gel column by elution with hexane. 

Major matrix components or other trace organic compoimds, such as polycyclic aromatic hydrocarbons (PAH) and pesticides, are coextracted with PCBs and might cause interference to the instrumental response, thus they should be eliminated by suitable cleanup procedures. The cleanup is generally performed by column chromatography on suitably activated or deactivate silica [24,54,68,97,128,138,146], sulfuric acid impregned silica [131], alumina [9,14,15,90-92,142], or Florisil (synthetic magnesium silicate) [24,44,67,83], and styrene-divinylbenzene resin [121]. Multilayer columns are frequently utilized. The retention of analytes in the column should be checked by standard solutions in order to find both the best solvent or mixture of solvents and the optimum volume to be used to selectively elute PCBs and leave interferents in the column. n-Hexane and dichloromethane are the most widely used solvents to elute the PCBs from the stationary phase. In addition, special treatments are very often used to eliminate specific interfering substances. For instance, activated copper powder with [23] or without mercury [14,49,81,87,151] or tetrabutyl ammonium sulfite [4] is used to remove elemental sulfur and sulfuric acid is used to remove lipids [107]. 

An essential feature is the involvement of 6A, the additional area of multilayer exposed during the particular step as the group of pores loses its capillary condensate. 5A is calculated from the volume and radius of the group, using the geometry of the cylinder (column 15). The total area of multilayer which is thinned down during any step is obtained by summing the SA contributions in all the lines above the line of the step itself (column 16). 

Fig. 2.31. Chromatogram of crude lutein from the microalga Chlorella vulgaris by HPLC analysis, A = lutein. Conditions column reversed-phase C18 column (250 X 4.6 mm i.d., 5 pm) mobile phase methanol-dichloromethane-acetonitrile-water (67.5 22.5 9.5 0.5, v/v) flow rate l.Oml/min detection at 450 nm (a). Chromatogram of crude lutein from the microalga Chlorella vulgaris by preparative HSCCC separation, A = lutein. Conditions column multilayer coil of 1.6mm i.d. PTFE tube with a total capacity of 230ml rotary speed 800rpm solvent system ra-hexane-ethanol-water (4 3 1, v/v) mobile phase lower phase (ethanol-water) flow rate lml/min detection at 254 nm sample size 200 mg retention of the stationary phase 58 per cent (b). Reprinted with permission from H.-B. Li el al. [70].

Although the majority of chiral CEC—MS applications still involve packed columns, few reports on chiral OT-CEC-MS are found in recent literature. The feasibility of coupling OT-CEC (using a short Chirasil-Dex-coated capillary column) to MS and MS/MS for trace analysis of hexobarbital enantiomers in biological fluids was reported by Schurig and Mayer. More recently, Kamande et al. investigated polyelectrolyte multilayer (PEM) coating as a new medium for the separation of chiral analytes, and PEM-coated capillaries were successfully coupled to ESI/MS for the stereoselective analysis of five /1-blockers. 

Figure 3.17 Layout and dimensions of the integrated SPE-NCE with (b) photograph of the multilayer device (c) and (d) micrograph and diagram of the packed micro-SPE column between two shallow weirs [121].

XN = 30, and N = 20). Lines 1-3 concentric cylinder barrel phase at K= 0.01,0.02, and 0.03, respectively lines 4-6 sector column phase at K = 0.01, 0.02, and 0.03, respectively lines 7-9 complex multilayered sector column phase at K = 0.01, 0.02, and 0.03, respectively, (b) A sketch of morphology transition for a set of competing structures between the concentric cylinder barrel phase and the sector column phase in part (a), where sec means the sector column phase, and conVj means the concentric cylinder barrel structure with N ayer = n. 

Similar to the asymmetrical cylinder barrel structure, the asymmetrical square column is considered as a combination of the symmetrical multilayered structure with an asymmetrical one with half a period. The Helmholtz energy F of the asymmetrical concentric square column structure is separated into two parts one is the Helmholtz energy Fg are of symmetrical multilayered structure and another is the Helmholtz energy Fg aie of an asymmetrical one with half a period expressed by... 

In summary, it is clear that there are substantial effects that vary systematically with the wavelength of the multilayer due both to internal stresses and the microstructure of the coatings. It has also been seen that deformation can occur not just by dislocation flow, as the initial analyses have assumed, but by mechanisms such as lattice rotations and shear along column boundaries. In addition, the use of indentation complicates the deformation field, so that the assumption that equal strains in both layers are required need not be correct. These effects all influence the hardness but have not so far been included in analyses. 

The values of surface area, a(S, N2) and derived from the linear multilayer as-plots. As was pointed out in Chapter 6, if unrestricted multilayer adsorption has occurred, the specific surface area can be evaluated from the slope of the as-plot. The following equations have been developed for the adsorption of argon and nitrogen on alumina ... 

The separations are performed using a commercial high-speed CCC centrifuge equipped with a multilayer coil separation column(s). The column is first entirely filled with the stationary phase that contains the desired amount of chiral selector (CS). In order to prevent the contamination of CS in the eluted fractions, some amount of the CS-free stationary phase should... 

Fig. 7 shows a photograph of the most advanced model of the multilayer CPC, which holds a set of three multilayer coil separation columns symmetrically around the rotary frame. AU columns are connected in series with flow tubes which are supported by counterrotating pipes placed... 

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