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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
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The modern multiresidue TLC methods are based on sample preparation and cleanup by SPE and a computer-assisted AMD-HPTLC determination of the pesticides. These procedures allow the determination of 30-50 or more pesticides on one TLC plate.
A Cjg cartridge was used for the SPE of s-triazines, metabolites, and ureas from water samples (Table 11), and the pesticides were determined with a 25 step universal gradient elution. The screening gradient elution was carried out with a solvent system based on dichloromethane, and the second gradient on ferf-butyl methyl ether in case of a positive result in the screening procedure (Table 11) (134a). The Manual of Pesticide Residue Analysis contains several examples for determination of OP pesticides by the AMD-HPTLC procedure, using their color reaction with 4-(4'-nitro-benzyl)pyr-idine and tetraethylene pentamine (134b). Two other examples describe the determination of numerous pesticides using alkaline, neutral, and acidic components in a gradient elution system (134c,d). The HPTLC plates were evaluated at five different UV wavelengths. According to another AMD-HPTLC method, amitrol residues were determined in water samples (134e) after a diazo-coupling reaction (Table 11).
More than 20 pesticides were investigated in water samples by AMD-HPTLC method using multiple and stepwise development combined with UV/VIS detection and determination (134f) (Table 11).
The optimization of the AMD-HPTLC method was investigated (134f). Thin layers (100 ) enhance the sensitivity of UV detection by a factor of 2 to 3. No effect was observed in the visible spectrum or in fluorescence measurements. Sample preparation is of great importance. Various phthalate esters can interfere with several pesticides, such as parathion, trifluralin, vinclozolin, and pendimethalin. The determination of polar substances is hindered by humins if present in high concentration. In this case, other AMD gradients should be used. Despite these limitations and drawbacks, the AMD-HPTLC method offers very sensitive quantitative determination of numerous pesticide residues in water samples (134g) (Table 11).
H. Polycyclic Aromatic Hydrocarbons
This and the following section cover nonpesticidal compounds that have been determined as residues in environmental and food samples.
Polycyclic aromatic hydrocarbons (PAHs) are produced through the incomplete combustion of various materials. Air-suspended particulates adsorb PAHs so air and subsequently soil and sand will also be contaminated. PAHs generally exhibit strong carcinogenic and mutagenic activity. For example, benzo[a]pyrene (B[a]P) is known as a carcinogenic compound. Synchronously excited fluorescence spectrometry has provided a multicomponent analysis of PAHs (135). After ultrasonic extraction of PAHs, e.g., B[a]P benzo[k]fluoranthene (B[k]F), chrysene (Chry), benzo[a]anthracene (B[a]A), pyrene (Py), perylene (Pery), and benzo[ghi]perylene (B[ghi]pery), from soils, they were separated by TLC on kieselguhr G layers mixed with 26% acetylated cellulose (135). Twelve PAHs
Table 11 AMD-HPTLC
Compound Stat. phase Mobile phase Rf x
Atrazine HPTLC 25 step gradient
Desethylatrazine 60 elution
Desisopropylatrazine i'2S4 ten isocratic
(Merck) steps
Isoproturon CH2CI2, n-hexane
Terbutylazine CH3CN
Phenmedipham /er/-butyl methyl
Metamitron ether
Carbetamide
Chloridazon
Chlortoluron
Carbofuran
Metribuzin
Omethoate HPTLC CS2, CH,C12
Carbendazim Silica gel Diisopropyl ether
Triadimenol 60 Methanol
Metamitron (Merck no. Ammonia solution
Triadimefon 5641) Formic acid
Methabenzthiazuron
Azinphos-methyl
Azinphos-ethyl
Parathion
Azinphos-ethyl HPTLC Acetonitrile
Azinphos-methyl Silica CS2
Bitertanol gel 60 Dichloromethane
Carbofuran Diisopropyl ether
Metamitron Ammonia solution
Methabenzthiazuron Formic acid
Parathion Screening and
Triadimefon confirmative
Triadimenol gradient elution
Bromacil
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