Thin-layer quantitative

The comparison of flow conductivity coefficients obtained from Equation (5.76) with their counterparts, found assuming flat boundary surfaces in a thin-layer flow, provides a quantitative estimate for the error involved in ignoring the cui"vature of the layer. For highly viscous flows, the derived pressure potential equation should be solved in conjunction with an energy equation, obtained using an asymptotic expansion similar to the outlined procedure. This derivation is routine and to avoid repetition is not given here. 

To determine the phosphoHpid and fatty acid compositions chromatographic methods (28) like gas chromatography (gc), thin-layer chromatography (tic), and high performance Hquid chromatography (hlpc) are used. Newer methods for quantitative deterrnination of different phosphoHpid classes include P-nmr (29). 

Analysis. Dilute aqueous solutions of hydroxyhydroquiaone turn blue-green temporarily when mixed with ferric chloride. The solutions darken upon addition of small amounts, and turn red with additions of larger amounts of sodium carbonate. Derivatives used for identification are the picrate, which forms orange-red needles (mp of 96°C), and the triacetate (mp 96—97°C). Thin-layer chromatography and Hquid chromatography are well suited for the quahtative and quantitative estimation of hydroxyhydroquiaone (93,94). 

Gas-flow counting is a method for detecting and quantitating radioisotopes on paper chromatography strips and thin-layer plates. Emissions are measured by interaction with an electrified wire in an inert gas atmosphere. AH isotopes are detectable however, tritium is detected at very low (- 1%) efficiency. 

Chromatographic methods including thin-layer, hplc, and gc methods have been developed. In addition to developments ia the types of columns and eluents for hplc appHcations, a significant amount of work has been done ia the kiads of detectioa methods for the vitamin. These detectioa methods iaclude direct detectioa by uv, fluoresceace after post-column reduction of the quiaone to the hydroquinone, and electrochemical detection. Quantitative gc methods have been developed for the vitamin but have found limited appHcations. However, gc methods coupled with highly sensitive detection methods such as gc/ms do represent a powerful analytical tool (20). 

High Pressure Liquid Chromatography. This modem version of the classical column chromatography technique is also used successfully for separation and quantitative analysis of dyes. It is generally faster than thin-layer or paper chromatography however, it requires considerably more expensive equipment. Visible and uv photometers or spectrophotometers are used to quantify the amounts of substances present. 

The new way of quantitative determination of the ascorbic acid (AC) by means of ion-pair thin layer chromatography (TLC) in organo-aqueous mobile phases containing cetyltrimethylammonium bromide (CTAB) has been alaborated. 

Commercially available pre-coated plates with a variety of adsorbents are generally very good for quantitative work because they are of a standard quality. Plates of a standardised silica gel 60 (as medium porosity silica gel with a mean porosity of 6mm) released by Merck have a specific surface of 500 m /g and a specific pore volume of 0.75 mL/g. They are so efficient that they have been called high performance thin layer chromatography (HPTLC) plates (Ropphahn and Halpap J Chromatogr 112 81 1975). In another variant of thin layer chromatography the... 

Dispersion equations, typically the van Deemter equation (2), have been often applied to the TLC plate. Qualitatively, this use of dispersion equations derived for GC and LC can be useful, but any quantitative relationship between such equations and the actual thin layer plate are likely to be fraught with en or. In general, there will be the three similar dispersion terms representing the main sources of spot dispersion, namely, multipath dispersion, longitudinal diffusion and dispersion due to resistance to mass transfer between the two phases. 

A bulk sample is the last choice and the least desirable. It should be submitted "for laboratory use only" if there is a possibility of contamination by other matter. The type of bulk sample submitted to the laboratory should be cross-referenced to the appropriate air samples. A reported bulk sample analysis for quartz (or cristobalite) will be semi-quantitative in nature because (1) The XRD analysis procedure requires a thin layer deposition for an accurate analysis. (2) The error for bulk samples analyzed by XRD is unknown because the particle size of nonrespirable bulk samples varies from sample to sample. 

It is only since this method has come into use that the precise quantitative analysis of thin-layer chromatograms has become possible. For the increased... 

Getz, M. E., in J. C. Touehstone, D. Rogers Thin-Layer Chromatography Quantitative Environmental and Clinical Application. J. Wiley Sons, New York-Chiehester-Bris-bane-Toronto 1980. 

The first part of the book eonsists of a detailed treatment of the fundamentals of thin-layer ehromatography, and of measurement techniques and apparatus for the qualitative and quantitative evaluation of thin-layer ehromatograms. In situ preehromatographie derivatization teehniques used to improve the selectivity of the separation, to inerease the sensitivity of deteetion, and to enhanee the precision of the subsequent quantitative analysis are summarized in numerous tables. 

Bohrer, I. M. Evaluation Systems in Quantitative Thin-Layer Chromatography, 126,95-118 (1984). Boekelheide, V. Syntheses and Properties of the [20] Cyclophanes, 113, 87-143 (1983). 

Ebel, S. Evaluation and Calibration in Quantitative Thin-Layer Chromatography, 126, 71-94... 

The present chapter is largely concerned with HPLC, together with a summary of developments in quantitative thin-layer chromatography, but a brief account of the various types of liquid chromatography is given first together with a guide to the choice of appropriate separation mode. 

The purpose of the experiment is to illustrate the elution technique for the recovery of pure substances after their separation by thin-layer chromatography. The experiment can be readily extended to include the quantitative determination of the recovered substances. 

W E Court, Quantitative thin-layer chromatography using elution techniques. In Quantitative Paper and Thin-Layer Chromatography E J Shellard (Ed) Academic Press, New York, 1968, p 29... 

J C Touchstone (Ed), Quantitative Thin-Layer Chromatography, Wiley, New York, 1973... 

The multiplicity of responses makes thin-layer chromatography not particularly suited for pyrethrum analysis, either qualitative or quantitative. It did confirm, however, that the crude oleoresin contains several pyrethroid compounds in substantial quantity, as previously shown by gas chromatography work. 

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. 

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