Thin-layer densitometry

The theoretical basis of thin-layer densitometry by transmission is the same as that for absorption in solution. The medium provides the main differences between the two processes. For example, in solution the effects of reflected and scattered light are at a minimum, whereas such effects are significant with samples adsorbed on layers. Also, the distribution of a compound in solution is homogeneous, while that of a spot on an adsorbent is not, neither vertically nor horizontally in the layer. Shibata [42] described the phenomenon of light striking a translucent material as... 

C7H7NO2, Mr 137.14, prisms, mp. 188-188.5 °C, D. 1.374, pKji 2.41, pKa2 4.85 (25°C), soluble in water. A. is easily oxidized, e.g., with Fe(III) salts a slight yellow to red discoloration occurs on exposure to air or light. Bacteria require A. as an essential growth substance for the synthesis of folic acid. Baker s yeast contains ca. 5-10 ppm 4-aminobenzoic acid. A. is not toxic to rodents LDjg 2850 mg/kg (mouse p.o.), 1830 mg/kg (rabbit p. o.). The biosynthesis starts from cho-rismic acid and glutamate. A. can be determined in urine by thin layer densitometry. ... 

Paesen, J., I. Quintens, G. Thoithi, E. Roets, G. Reybrouck, J. Hoogmartens, Quaternary ammonium antiseptics using thin layer densitometry, J. Chromatogr. A, 1994,677, 377-384. 

J C Touchstone and J Sherma (Eds), Densitometry in Thin-Layer Chromatography — Practice and Applications, Wiley-Interscience, New York, 1979... 

Thin-layer chromatography is employed in many areas of QC and routine monitoring of product quality [458]. Fluorescence scanning, densitometry or videodensitometry are used for quantification. Not all polymer additives are amenable to TLC analysis. Some fatty acid amides are virtually insoluble in organic solvents and cannot be isolated by thin-layer or column chromatography. 

Shriadah and Ohzeki [350] determined iron in seawater by densitometry after enrichment as a bathophenanthroline disulfonate complex on a thin layer of anion exchange resin. Seawater samples (50 ml) containing iron (II) and iron (III) were diluted to 150 ml with water, followed by sequential addition of 20% hydrochloric acid (100 xl), 10% hydroxyl-ammonium chloride (2 ml), 5 M ammonium solution (to pH 3.0 for iron (III) reduction), bathophenanthroline disulfonate solution (1.0 ml), and 10% sodium acetate solution (2.0 ml) to give a mixture with a final pH of 4.5. A macroreticular anion exchange resin in the... 

Shriadah et al. [516] determined molybdenum VI in seawater by densitometry after enrichment as the Tiron complex on a thin layer of anion exchange resin. There were no interferences from trace elements or major constituents of seawater, except for chromium and vanadium. These were reduced by the addition of ascorbic acid. The concentration of dissolved molybdenum (VI) determined in Japanese seawater was 11.5 pg/1, with a relative standard deviation of 1.1%. 

Corthout, J., Naessens, T., Apers, S., and Vlietinck, S. (1999). Quantitative determination of ginsenosides from Panax ginseng roots and ginseng preparations by thin layer chromatography-densitometry. /. Pharm. Biomed. Anal. 21,187-192. 

Bodart, P, Kabengera, C., Noirfalise, A., Hubert, P, Angenot, L. (2000). Determination of a-solanine and a-chaconine in potatoes by high-performance thin-layer chromatography/densitometry. J. AOAC Int., 83, 1468-1473. 

A number of compounds have been quantified by tic or high performance thin-layer chromatography (hptlc) using absorption or fluorescence scanning densitometry. 

Unlike densitometric determinations where absorption measurements are made by transmission through the surface of the thin layer, measurements of densitometry by reflectance are based on the diffusely reflected light from the surface of the layer. Thus, the light source and phototube are mounted on the same side of the absorbing surface. 

L. Zivanovic, S. Agatonovic, and D. Radulovic, Determination of diuretics in pharmaceutical preparations using thin-layer chromatographic densitometry, Pharmazie, 44 864 (1989). 

From a review of the available literature it is clear that methods based on thin layer chromatography are frequently being used by various workers in the field for the quantitation of pesticides. In the present paper the quantitative TLC technique using densitometry is described in detail for the determination of pesticides in various tissues pertaining to actual cases of poisoning. 

Argekar and Sawant [55] developed simultaneous determination of paracetamol and mefenamic acid in tablets by high performance thin layer chromatography method (HPTLQ. The procedure was performed on silica gel using toluene-acetone-methanol (8 1 1) as the solvent system. Detection and quantification of the substance was assayed by densitometry at 263 nm. The linearity ranges were 120-360 ng/pL and the RSD were between 0.41 and 0.78%. Limit of detection and limit of quantification were found to be 1.80 and 5.5 ng/pL, respectively. Recoveries were in the range of 95.50-103.60%. 

Thin layers of powdered cellulose, silica gel, alumina, ion-exchange or gel-permeation material supported on glass plates, plastic sheets or aluminium foil development tanks components sometimes examined by reflectance or transmittance densitometry or removed for spectrometric analysis. 

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