in black and white
Main menu
Share a book About us Home
Biology Business Chemistry Computers Culture Economics Fiction Games Guide History Management Mathematical Medicine Mental Fitnes Physics Psychology Scince Sport Technics

Chromatographic scince series - Cazes J.

Cazes J. Chromatographic scince series - Marcel Dekker, 1996. - 1098 p.
ISBN 0-8247-9454-0
Download (direct link): сhromatography1996.pdf
Previous << 1 .. 419 420 421 422 423 424 < 425 > 426 427 428 429 430 431 .. 601 >> Next

Complex formation is another possibility for detection of some OP insecticides. PdCVHCl (8,55,154) or K2PdClj (155) were applied in this reaction, where ligands formed from sulfur-containing OP insecticides after cleavage of the P-S bond.
Some other complexes, e.g., pentacyano-aminoferrate, were also applied for the detection of nitrofen (82).
2. Color Reactions of Organochlorine Insecticides
Use of silver nitrate spray with UV irradiation has been widely used for the detection of insecticides with a sensiti vity of 0.001 jag. 2-phenoxyethanol (2) or ammonia (51,156) has been added to silver nitrate to improve the stability of the reagent. A more sensitive detection and effective separation was achieved when silver nitrate was incorporated into the slurry of silica gel or aluminum oxide. These plates gave better resolution, but their storage caused problems. According to an earlier study, primary aromatic amines detect chlorinated pesticides (157). The noncarcinogenic reagent 3,5,3',5'-tetramethylbenzidine made visible chlorinated pesticides with a detection limit in the microgram range (48). Chlorinated agrochemicals such as a-chlordane and 14 other pesticides were detected with o-tolidine at the same level (49). Another possibility for detection of DDT and DDE in water samples involves the immersion of developed HPTLC plates into 0.1% diphenylamine containing ethanolic solution and UV irradiation. In situ fluorimetric measurement was carried out with the Camag TLC/HPTLC scanner at 366 nm coupled to a Shimadzu Chromatopac Integrator. Linearity was observed between 20 and 200 ng in the case of DDT and DDE (53).
1,4-dihydroxybenzene was introduced as a specific visualization reagent for /'-DDT, allowing microgram-level detection. No color reaction was observed with o/?'-DDT, pp'-DDE, '-DDD, and polychlorinated biphenyls (158).
3. Color Reactions of Organophosphorus Insecticides
Organophosphorus (OP) insecticides containing phosphorus and sulfur atoms offer a large variety of chemical color reactions. There are also some commonly used methods based on the chlorine content of these insecticides, but these methods are not as specific for the OP pesticides. Further amine-specific reactions can also be applied for the visualization of these insecticides in certain cases. Comparing the sensitivities of these methods and enzyme inhibition (see Section V.B), the latter is two or three orders of magnitude better.
Palladium chloride detects phosmethylan (55) with 0.5 |Xg/spot sensitivity. This reaction was used for quinalphos (7), phosphamide (8), and methamidophos in food samples (154) as well. Malathion residues were studied in pharmaceutical preparations by dipping plates into a 0.1 % solution of palladium chloride in hydrochloric acid, yielding yellow spots that could be quantitatively determined by scanning at 400 nm (159).
Phosmethylan also reacts with p-dimethylaminobenzaldehyde (55). This reaction is specific for primary aromatic amines. Methaphos gives the same reaction in acetic acid medium (8).
Potassium iodide o-tolidin is a common chromogenic reagent for the detection of secondary amines, but primary amines also react with it after chlorination. This method was applied in a metabolism study of the broad-spectrum, nonspecific insecticide phosmethylan (55).
Some OP pesticides were detected with pinacryptol yellow (61) and UV light, and 0.01% thioacridone in dichloromethane solution made visible some other OP insecticides with a detection limit of 0.1-1.0 (ig/spot (62).
Silver nitrate was used as a detecting agent in OP pesticide analysis using quite different conditions. Dimethoate, its oxygen analog, dioxathion, disulfoton, fonofos, fonofos oxygen analog, and oxydemetonmethyl were detected by spraying with ammoniacal silver nitrate solution in acetone followed by exposure to longwave UV light (60). Dicrotophos, ethion or phorate, fensulfothion, oxydemetonmethyl, fosmet, phosphalon, and trichlorfon were also detected by this method (64).
Chlorpyrifos and its metabolites were determined in tapwater by densitometric scanning after AgN03 spray detection (6). Dimethoate, diazinon, malathion, ethion, parathion, and methylparathion were detected with a combined spray of silver nitrate-tetrabromosulfophthalein (148). Another possibility is the impregnation of Silufol plates with silver nitrate, which was used successfully for the analysis of gardona. No interference was observed between this compound and DDT, HCH, or chlorophos (9). The sulfur content of the OP insecticides gave another possibility for their detection. These pesticides react in acidic conditions with KI03, and the liberated free iodine gives a blue color with starch. In alkaline medium the color is intensified, so the sensitivity was also higher (about 1 (ig) (ISO). and carbamate insecticides or OP compounds without any sulfur atoms failed to give a positive response.
Previous << 1 .. 419 420 421 422 423 424 < 425 > 426 427 428 429 430 431 .. 601 >> Next