Spraying procedures layer preparation

Suspensions of fine-grain adsorbents can be evenly spread on carriers using commercial sprayers. The uniformity of the layer depends however on the skill of the operator when the spraying apparatus is hand operated-more so than in the other procedures. Sutter s proposed TLC with the spraying procedure [303] utilises a spray pistol in which the suspension is prepared in a container using an air current a spray chamber, like a fume cupboard, containing a grating and a spirit level and a compressor to develop the necessary pressure of 1 — 1.5 atmosphere (Firm 73). 

The unvulcanized rubber sample is extracted with isopropanol to remove accelerators and antioxidants. Isopropanol is removed and the residue dissolved in chloroform and applied to a thin-layer plate. Development with a range of solvent mixtures separates the components which are then detected with a range of spray reagents. Calibration is achieved by applying the procedure to prepared pure standard solutions. 

Surface coating using sol-gel technology is mainly used for the preparation of oxide or organofunctional siloxane layers on solid materials. In this case, the material is dipped or spun in the TEOS sol. This procedure leads to the formation of multilayered coatings of irreproducible thickness. Since this type of coating may only be used for axially or radially symmetric materials, alternatives have been developed. Those include spraying, electrophoresis, thermophoresis and ultrasonic pulverization.63 However, these are not of interest in powder modification. 

The impregnation of the layer is performed by immersing the plate in a solution of the silver salt in methanol, acetone or acetonitrile or by spraying the plate with one of these solutions. Preparative plates are usually treated with 1-20% silver nitrate solutions. For analytical Ag TLC, the concentration of silver nitrate varies in the range 0.5-10%. The impregnation procedures must be standardized to provide reproducible separation. Plates are left in the air for the solvent to evaporate and are usually activated prior to use (between 5 min and 1 h depending on the purpose) by heating at 110°C. 

SAM Formation. SAMs of 11-MUA were prepared ex situ in 1-3 mM ethanolic solution of 11-mercaptoundecanoic acid, which was purchased at Sigma Aldrich. Two different substrates were used Au(lll)/mica and recrystallized gold foils. Typically, substrates are cleaned in piranha solution. This procedure was not possible for Au( 11 l)/mica, because it led to a separation of the gold layer from the mica substrate. Therefore, both substrates were cleaned in a UHV chamber by Ar+ -sputtering, followed by short annealing at 800 K to get a smooth surface. After removal from the vacuum chamber, it was immediately immersed into the solution. Typically samples remained for 48 h in the solution. After removal out of solution, the samples were rinsed with ethanol and dried with C02 - spray. 

An overpressured layer chromatographic procedure, with photodensitometric detection for the simultaneous determination of water-soluble vitamins in multivitamin pharmaceutical preparations, was developed and evaluated. HPTLC on silica gel plates with 1-butanol-pyridine-water (50 35 15 vol/vol) as mobile phase was used. The quantitation was carried out without derivatization [vitamin B2 (Rf value 0.30), vitamin Bg (Rf value 0.64), folic acid (Rf value 0.37), nicotinamide (Rf value 0.80), and vitamin C (Rf value 1.02)] or after spraying ninhydrin reagent [calcium panthothenate (Rf value 0.72)] or 4-demethylaminocin-namaldehyde [vitamin B12 (Rf value 1.84) and biotin (Rf value 0)]. 

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