Authors:Bernd Spangenberg and Karl-Friedrich Klein
In-situ densitometry for qualitative or quantitative purposes is a key step in thin-layer chromatography (TLC). It is a simple means of quantification by measurement of the optical density of the separated spots directly on the plate. A new scanner has been developed which is capable of measuring TLC or HPTLC (high-performance thin-layer chromatography) plates simultaneously at different wavelengths without damaging the plate surface. Fiber optics and special fiber interfaces are used in combination with a diode-array detector. With this new scanner sophisticated plate evaluation is now possible, which enables use of chemometric methods in HPTLC. Different regression models have been introduced which enable appropriate evaluation of all analytical questions. Fluorescent measurements are possible without filters or special lamps and signal-to-noise ratios can be improved by wavelength bundling. Because of the richly structured spectra obtained from PAH, diode-array HPTLC enables quantification of all 16 EPA PAH on one track. Although the separation is incomplete all 16 compounds can be quantified by use of suitable wavelengths. All these aspects are enable substantial improvement of in-situ quantitative densitometric analysis.
Authors:Bernd Spangenberg, Klemens Lorenz, and Steffen Nasterlack
In-situ densitometry for qualitative or quantitative purposes is a key step in thin-layer chromatography. It offers a simple way of quantifying by measuring the optical density of the separated spots directly on the plate. A new TLC scanner has been developed which is able to measure TLC plates or HPTLC plates, at different wavelengths simultaneously, without destroying the plate surface. The system enables absorbance and fluorescence measurements in one run. Fluorescence measurements are possible without filters or other adjustments.The measurement of fluorescence from a TLC plate is a versatile means of making TLC analysis more sensitive. Fluorescence measurements with the new scanner are possible without filters or special lamps. Improvement of the signal-to-noise ratio is achieved by wavelength bundling. During plate scanning the scattered light and the fluorescence are both emitted from the surface of the TLC plate and this emitted light provides the desired spectral information from substances on the TLC plate. The measurement of fluorescence spectra and absorbance spectra directly from a TLC plate is based on differential measurement of light emerging from sample-free and sample-containing zones.The literature recommends dipping TLC plates in viscous liquids to enhance fluorescence. Measurement of the fluorescence and absorbance spectra of pyrene spots reveals the mechanism of enhancement of plate dipping in viscous liquids — blocked contact of the fluorescent molecules with the stationary phase or other sample molecules is responsible for the enhanced fluorescence at lower concentrations.In conclusion, dipping in TLC analysis is no miracle. It is based on similar mechanisms observable in liquids. The measured TLC spectra are also very similar to liquid spectra and this makes TLC spectroscopy an important tool in separation analysis.
Authors:Juan Zhang, Feng-Tian Hu, Qian-Qian Liu, Xin Zhao, and Shou-Qing Liu
, CA, USA) was used for the separation of intermediates formed in the photo-Fenton process. It was coupled to an Agilent 6220 Accurate-mass Time-of-Flight (TOF) mass spectrometer for the detection of these intermediates for compoundidentification, the
Authors:K. Alloun, O. Benchabane, M. Hazzit, F. Mouhouche, A. Baaliouamer, A. Chikhoune, and A. Benchabane
with electron ionization at 70 eV over a scan range of 30–550 atomic mass units.
The oils components were identified by matching their recorded mass spectra with the data bank mass