Gas chromatography/TLC

Progress of the reaction can be followed by gas chromatography, TLC (ethyl acetate/hexane 1 5) or 1H NMR. (Probe reactions can be carried out in CDCI3 in an NMR tube). 

Figure 2 Analytical methodologies for the determination of high-intensity sweeteners. NHDC, neohesperidine dihydrochalcone LC, liquid chromatography GC, gas chromatography TLC, thin-layer chromatography CE, capillary electrophoresis SP, spectropho-tometric EA, electroanalytical T, titrimetry G, gravimetry 1C, immunochemical. Source of information Chemical Abstracts (until January 2004).

Some OP insecticides were determined in green and dry tobacco leaves by TLC and gas chromatography. TLC detection required charcoal treatment, which diminished the recovery (88.5%) (59). Cardona content of fish tissues and water samples was established after chloroform or petroleum ether-chloroform extraction (9) (Table 3). Two solvent systems were reported for the separation of dimethoate, fonofos, and their oxygen analogs from disulfoton, fonofos, and oxydemeton meftiyl (60) (Table 3). Silica gel F254 or silica R (containing 5% 1102) layers were applied for the analysis of 10 OP insecticides (61). 

HPLC High liquid chromatography, ED electrochemical detector, ESI electrospray ionization, MS tandem mass spectrometry, LPT Liquid-phase sorbent trapping, TD Thermal desorption, GC Gas chromatography, TLC Thin layer chromatography, DAD Diode Array, FD Fluorescence detection, FTIR Fourier transform infrared spectroscopy, SPME Solid phase microextraction... 

Gas chromatography/TLC (GC/TLC), 940 Gentamicin, 457-US8 Glossary, 1079-1086 Glycolipids for lipid extractions, 691 one-dimensional solvent systems for TLC of, 693-694... 

FIG. 18 Determination of alkanesulfonates with thin-layer chromatography (TLC) and gas chromatography-mass spectrometry (GC-MS) clean-up procedure. 

An environmental protocol has been developed to assess the significance of newly discovered hazardous substances that might enter soil, water, and the food chain. Using established laboratory procedures and C-labeled 2,3,7,8-tetra-chlorodibenzo-p-dioxin (TCDD), gas chromatography, and mass spectrometry, we determined mobility of TCDD by soil TLC in five soils, rate and amount of plant uptake in oats and soybeans, photodecomposition rate and nature of the products, persistence in two soils at 1,10, and 100 ppm, and metabolism rate in soils. We found that TCDD is immobile in soils, not readily taken up by plants, subject to photodecomposition, persistent in soils, and slowly degraded in soils to polar metabolites. Subsequent studies revealed that the environmental contamination by TCDD is extremely small and not detectable in biological samples. 

The Window diagram method for the optimization of separation was developed by Laub and Purnell [73], and it has been used both for gas chromatography and HPLC. Recently it is applied in TLC and HPTLC [19,74—76]. 

PLC is used for separations of 2 to 5 mg of sample on thin-layer chromatography (TLC) plates (0.25-nun layer thickness) or high-performance TLC (HPTLC) plates (0.1-mm thickness). In these instances, the method is termed micropreparative TLC. The isolation of one to five compounds in amounts ranging from 5 to 1000 mg is carried out on thicker layers. PLC is performed for isolation of compounds to be used in other tasks, i.e., further identification by various analytical methods, such as ultraviolet (UV) solution spectrometry [1] or gas chromatography/mass spectrometry (GC/MS) [2], obtaining analytical standards, or investigations of chemical or biological properties [3]. 

SFE-GC-MS is particularly useful for (semi)volatile analysis of thermo-labile compounds, which degrade at the higher temperatures used for HS-GC-MS. Vreuls et al. [303] have reported in-vial liquid-liquid extraction with subsequent large-volume on-column injection into GC-MS for the determination of organics in water samples. Automated in-vial LLE-GC-MS requires no sample preparation steps such as filtration or solvent evaporation. On-line SPE-GC-MS has been reported [304], Smart et al. [305] used thermal extraction-gas chromatography-ion trap mass spectrometry (TE-GC-MS) for direct analysis of TLC spots. Scraped-off material was gradually heated, and the analytes were thermally extracted. This thermal desorption method is milder than laser desorption, and allows analysis without extensive decomposition. 

FID = flame ionization detection GC = gas chromatography HPLC = high performance liquid chromatography ITMS = ion trap mass spectrometry MS = mass spectrometry PNMR = proton nuclear magnetic resonance TLC = thin-layer chromatography... 

The minor alkaloid 21-oxogelsemine (3) was isolated from G. sempervirens by the combination of column chromatography, TLC, and preparative gas... 

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