The idea of using a chromatographic adsorbent in the form of a thin layer fixed on an inert rigid support seems to have been suggested by Izmailov and Shraiber in 1938. Meinhard and Hall[1] in 1949 developed this notion of an ‘open column’, and in 1951 Kirchner, Miller, and Keller[2] reported the separation of terpenes on a ‘chromatostrip’, prepared by coating a small glass strip with an adsorbent mixed with starch or plaster of Paris, which acted as a binder. The strips were handled in the same way that paper is handled in paper chromatography, and indeed the original object of the thin-layer technique was to apply the methods of paper partition chromatography to an adsorption system.

Thin Layer Chromatography

Polychlorinated biphenyls are widely dispersed in the global ecosystem, and are powerful inducers of hepatic enzymes which degrade oestradiol. Together with other chlorinated biocides, such as DDT, they could account for a large part of the aberration in calcium metabolism which has been observed in many species of birds since the Second World War.

Polychlorinated biphenyls in the global ecosystem.

The picture is complicated by the fact that we are not dealing with a single compound. The basic structure of PCBs is shown in Figure 1. Any of the positions marked with an x can be substituted by chlorine. Widmark (1968) has calculated that of the 210 possible combinations 102 are probable. His criteria for these limitations are those compounds containing five to eight chlorine atoms per molecule and the number of chlorine atoms per ring differing by not more than one. The commercially available Aroclors (Monsanto Company Trademark) are designated by numbers (Monsanto Technical Bulletins). The first two digits represent the molecular type: 12 chlorinated biphenyls; 25 and 44 blends of chlorinated biphenyls and chlorinated terphenyls (75% biphenyl and 60% biphenyl, respectively); 54 chlorinated terphenyls. The last two digits give the weight per cent of chlorine. Thus, Aroclor 1242 is a chlorinated biphenyl containing 42% chlorine. The biphenyls commercially available from Monsanto range from 21% to 68% chlorine. Mass spectrographic studies of Aroclor 1260 (Koeman et al., 1969a) show the presence of 11 isomers: five containing six chlorine atoms, five containing seven chlorine atoms, and one containing eight. Bagley et al. (1970), studying Aroclor 1254, found 18 compounds: one containing three chlorine atoms, four containing four chlorines, four containing five chlorines, five containing six chlorines, and four containing seven chlorines. Thus, the number of compounds present is, fortunately, much smaller than is theoretically possible. PCBs are chemically inert, are not hydrolyzed by water, and resist alkalies, acids, and corrosive chemicals. They have low volatility, their boiling points ranging from 278 C for Aroclor 1221 to 415 C for

Polychlorinated Biphenyls Another Long-Life Widespread Chemical in the Environment

Pentachlorophenol and its salts (primarily, the sodium salt) have many applications in industry and agriculture, with probably more varied uses than any other pesticide at this time. It has been used as a fungicide and/or a bactericide in the processing of cellulosic products, starches, adhesives, proteins, leather, oils, paints, and rubber; it has been incorporated into rug shampoos and textiles to control mildew problems; and it has been used in food processing plants to control mold and slime (Monsanto 1958, Dow 1962). It has also been added to fabrics for mothproofing, and derivatives, such as pentachlorophenyl laurate have been developed for this use because they have a greater resistance to dry cleaning and washing than pentachlorophenol and they are considered to have a lower toxicity risk to human beings (Hueck and La Brijn 1960, MOSS 1961). A recent United States patent granted the use of a mixture containing 80 percent of a pentachlorophenol fatty ester, one-to-ten percent of pentachlorophenol, and 0.5-to-ten percent of thymol for the protection of materials against biological attack (Read 1966). Pentachlorophenol has been used extensively in the construction and lumber industries and in homes to control mold and termite infestation, and for the control of powder post beetles and wood-boring insects (Monsanto 1958, Dow 1962, Carswell and Nason 1938, Carswell and Hatfield 1939). It has been applied in agriculture and around industrial sites as a weedicide and/or a preharvest desiccant (Monsanto 1958, Anonymous 1964) on pasture land (Grigsby and Farwell 1950), in the pineapple and sugarcane fields (Gordon 1956, Hilton 1966) and in the rice fields of Japan (Uede et al. 1962, Goto et al. 1963, Terai et al. 1964). A Japanese manufacturer added pentachlorophenol to soy sauce as a preservative Narahu et al. 1965 ) ; the practice was illegal according to the Japanese food laws (Suzuki 1963). Chloranil (tetrachloro-p-quinone), an oxidation product of pentachlorophenol, has been used as a fungicide under the trade name of “Spergon” to protect seeds and bulbs (Lane 1958).

Pentachlorophenol: a discussion of its properties and its occurrence as a residue in human and animal tissues.

Polychlorobiphenyls (PCB's) and their interference with pesticide residue analysis

Laboratory Culture of the Pink Bollworm on Chemically Defined Media

The effect of the column tubing composition on the recovery of chlorinated hydrocarbons by gas chromatography.

The experienced residue analyst is quite familiar with the indecisive and continuum-type curve produced by the pesticide toxaphene (a mixture of compounds described as "chlorinated camphene") when it is analyzed by gas chromatography and the concomitant problems involved in the interpretation of the analytical results obtained from a sample of an agricultural commodity that may be suspected of containing excess quantities (above legal tolerance limits) of this pesticide. The problem is enhanced if other pesticides, such as DDT, are present in the same residue mixture and it becomes acute in regulatory laboratories where the time factor between the receipt of the market sample and the required report of the chemical analysis may be no greater than twenty-four hours.

Herman Beckman

Papers

Laboratory Culture of the Pink Bollworm on Chemically Defined Media

The effect of the column tubing composition on the recovery of chlorinated hydrocarbons by gas chromatography.

A method for the determination of toxaphene in the presence of DDT.

A technique for the recovery of compounds from thin-layer chromatograph strips for infrared analysis.

Preparation and Detection of Derivatives of Temik and Its Metabolites as Residues