Detectors thin layer chromatography

We studied conditions for the determination of tiametoxam (TM), the active component of the fungicide Actai a (Syngenta, Switzerland) by the method of thin layer chromatography with use of the Perkin-Elmer liquid chromatograph combined with spectrophotometric detector. The 250 mm-long and 4.6 mm in diameter steel column filled with Silasorb was used. 

Thin-layer chromatography (TLC) is used both for characterization of alcohol sulfates and alcohol ether sulfates and for their analysis in mixtures. This technique, combined with the use of scanning densitometers, is a quantitative analytical method. TLC is preferred to HPLC in this case as anionic surfactants do not contain strong chromophores and the refractive index detector is of low sensitivity and not suitable for gradient elution. A recent development in HPLC detector technology, the evaporative light-scattering detector, will probably overcome these sensitivity problems. 

Most often the sterols have been collected by liquid-liquid extraction using petroleum ether and ethyl acetate [408], chloroform and methanol [409], -hexane [410,411] or chloroform [412,413]. After concentration, gas chromatography was generally used for the final separation and determination, although thin-layer chromatography has also been employed. The extra sensitivity of the electron capture detector could be used by reacting the concentrated sterols with bromomethyldimethylchlorosilane (BMDS) before separation and measurement [414],... 

Padley FB. The use of flame-ionization detector to detect components separated by thin-layer chromatography. J. Chromatogr. 1969 39 37—46. 

GC = gas chromatography GPC = gel permeation chromatography ECD = electron capture detector MS = mass spectrometry MSD = mass selective detector SFE = supercritical fluid extraction TLC = thin layer chromatography... 

Furthermore CE and thin layer chromatography (TLC) have the advantage to detect retained substances in the original injection zone. In CE, either pressure can be applied or the EOE itself transports uncharged or slow molecules past the detector. In this case, a blank sample solvent injection should be compared with the sample to elucidate whether the peaks are caused by the injection plug itself or are compound-related. 

Following extraction and cleanup, nitrofurans are separated by thin-layer or liquid chromatography and measured by spectrophotometric, fluorometric, electrochemical, or mass spectrometric detectors (Table 29.5). Thin-layer chromatography has been carried out on commercially available silica gel plates. Nitrofurans were separated using various solvent mixtures as mobile phases and subsequently detected after spraying with pyridine, using spectrophotometric (29) or fluorometric (158, 159) detectors. 

Confirmatory analysis of suspected liquid chromatographic peaks is usually accomplished by a photodiode array detector that continuously collects spectral data during the chromatographic separation and further compares the spectrum (200-550 nm) of the eluted suspected compound with that of a standard (37, 38, 66, 161, 163, 166-168, 178, 180, 181). Online absorbance ratio techniques combined witlr off-line thin-layer chromatography have been also reported (171). Although tliese confirmation techniques are relatively simple, their sensitivity is not generally adequate to identify trace levels of residual nitrofurans in edible animal products. 

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