Thin-layer chromatography , water samples

Pelander, A., Ojanpera, I., Sivonen, K., Himberg, K., Waris, M., Niinivaara, K., and Vuori, E. 1996. Screening for cyanobacterial toxins in bloom and strain samples by thin layer chromatography. Water Research 30 1464—1470. 

To obtain reliable chromatograms in the final step of the determination of the analytes by LC or GC, it is important to remove interfering signals resulting from coelution of other compounds. To this end, a variety of techniques are applied for cleanup of the sample extract. The most effective procedures for sample cleanup for PAH measurements are partitioning between M, N-dimethylformamide/water/cyclo-hexane and LC on silica and on Sephadex LH 20. Other cleanup procedures include LC on alumina or XAD-2 and preparative thin-layer chromatography. 

Examine the sample by thin-layer chromatography, using silica gel G R as the coating substance. Dissolve 10 mg of the substance to be examined in 4 mL of water R as a test solution, and dissolve 10 mg of penicillamine reference substance in 4 mL of water R as a reference solution. Apply 2 pL of each solution separately to the plate. Develop over a path of 10 cm using a mixture of 18 volumes of glacial acetic acid R, 18 volumes of water R, and 72 volumes of butanol R. Dry the plate at 100-105 °C for 5-10 min, and expose to iodine vapor for 5-10 min. The principal spot in the chromatogram obtained with the test solution is similar in position, color, and size to the principal spot in the chromatogram obtained with the reference. 

An ingenious variation on the standard fluorescence methods was proposed by Red kin et al. [50]. Water samples were extracted with non-polar solvents, transferred into hexane and the hexane solution frozen at 77 K. At that temperature the normally diffuse luminescence emission bands are present as sharp emission lines, making identification of fluorescing compounds considerably simpler. In the case of a complex mixture, some separation by column or thin layer chromatography might be necessary. 

Mahel ova et al. [10] determined BHC isomers in soil by gas-liquid and thin layer chromatography after extraction with light petroleum. An air-dried, ground sample (18mesh) (20g) was deactivated by addition of 25% of water and set aside for 24h. Siloxid (active silica) was added to form a powdery mixture, which was extracted with 250ml of light petroleum... 

The question as to the potential availability of the requisite amphiphilic precursors in the prebiotic environment has been addressed experimentally by Deamer and coworkers, [143,145] who looked into the uncontaminated Murchison chondrite for the presence of such amphiphilic constituents. Samples of the meteorite were extracted with chloroform-methanol and the extracts were fractionated by thin-layer chromatography, with the finding that some of the fractions afforded components that formed monomolecular films at air-water interfaces, and that were also able to self-assemble into membranous vesicles able to encapsulate polar solutes. These observations dearly demonstrated that amphiphiles plausibly available on the primitive Earth by meteoritic infall have the ability to self-assemble into the membranous vesides of minimum protocells. ... 

TLC. Aliquots of samples and standards were run on silica-coated thin layer chromatography (TLC) plates in either n-butanol/acetic acid/water (4 1 1 by vol. (BUOH/HAC/H2O)) or n-propanol/concentrated ammo-nia/water (8 1 11, pre-equilibration). These eluents were previously described (Keller et ah, 1984) for the two-dimensional TLC-separation of elastin cross-links. 

Figure 9.29 Membrane formation by meteoritic amphiphilic compounds (courtesy of David Deamer). A sample of the Murchison meteorite was extracted with the chloroform-methanol-water solvent described by Deamer and Pashley, 1989. Amphiphilic compounds were isolated chromatographically on thin-layer chromatography plates (fraction 1), and a small aliquot ( 1 p,g) was dried on a glass microscope slide. Alkaline carbonate buffer (15 p,l, 10 mM, pH 9.0) was added to the dried sample, followed by a cover slip, and the interaction of the aqueous phase with the sample was followed by phase-contrast and fluorescence microscopy, (a) The sample-buffer interface was 1 min. The aqueous phase penetrated the viscous sample, causing spherical structures to appear at the interface and fall away into the medium, (b) After 30 min, large numbers of vesicular structures are produced as the buffer further penetrates the sample, (c) The vesicular nature of the structures in (b) is clearly demonstrated by fluorescence microscopy. Original magnification in (a) is x 160 in (b) and (c) x 400.

N-methylcarbamate and N.N -dimethylcarbamates have been determined in soil samples by hydrolyses with sodium bicarbonate and the resulting amines reacted with 4-chloro-7-nitrobenzo-2,l,3-oxadiazole in isobutylmethylketone solution to produce fluorescent derivatives [307]. These derivatives were separated by thin-layer chromatography on silica gel G or alumina with tetrahydro-furan-chloroform (1 49) as solvent. The fluorescence is then measured in situ (excitation at 436 nm, emission at 528 and 537 nm for the derivatives of methy-lamine and dimethylamine, respectively). The method was applied to natural water and to soil samples containing parts per 109 levels of carbamate. The disadvantage of the method is its inability to differentiate between carbamates of any one class. 

Sherma, J (1986). Determination of triazine and chlorophenoxy acid herbicides in natural water samples by solid phase extraction and quantitative thin layer chromatography. J. Liquid Chromatog., 9(16) 3433-3438. 

Thin layer chromatography is yet another means for determining identity of moxalactam materials. The mobility of the moxalactam sample must be identical to the mobility of the moxalactam reference standard which is run on the same TLC plate. The developing solvent for TLC consists of 42 parts ethyl acetate 14 parts glacial acetic acid 14 parts acetonitrile and 18 parts water. A silica gel type F plate is used and is viewed under short wavelength UV light to detect the position of the components on the developed plate. 

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