One-dimensional chromatography

The values of n and the corresponding N which are necessary to resolve 50-90% of the constituents of a mixture of 100 compounds are listed in Table 1.5, thus making clear the limitations of one-dimensional chromatography. For example, to resolve over 80 % of the 100 compounds by GC would require a column generating 2.4 million plates, which would be approximately 500 m long for a conventional internal diameter of 250 p.m. For real mixtures, the situation is even less favourable to resolve, for example, 80 % the components of a mixture containing all possible 209 polychlorinated biphenyls (PCBS) would require over lO plates. 

Detection, and the GC calibration process for the pesticide Fenvalerate constitutes a major focus of this paper. Though relatively simple compared to possible higher dimensional cases, it is representative of a large and basic class of problems (calibration in one-dimensional chromatography and spectroscopy), and it exhibits already some of the difficulties with assumption validity. 

Since one-dimensional chromatography is very often insufiScient to permit separation of the many tryptophan or indolic compounds and their degradation products occurring in urine, Dalgliesh (D4) worked out a two-dimensional method suitable for routine analysis and reported a map of spots. Urine extracts were prepared by absorption of aromatic metab-... 

Using one-dimensional chromatography on alumina, polyamide, and silica gel, difficulties are encountered in resolving Leu/Ile and Glu/Asp pairs as well as other combinations of PTH-amino adds (e.g., Phe/Val/Met/Thr). The most common solvents used on polyamide plates are n-heptane-n-butanol-acetic add (40 30 9), toluene-n-pentane-acetic acid (60 30 35), ethylene chloride-acetic add (90 16), and ethylacetate-n-butanol-acetic add (35 10 1), and... 

No solvent system resolves all the Dns-amino acids by one-dimensional chromatography and, also, TD chromatography requires more than two runs for a complete resolution. The most common used eluents on polyamide layers are benzene-acetic acid (9 1), toluene-acetic acid (9 1), toluene-ethanol-acetic acid (17 1 2), water-formic acid (200 3), water-ethanol-ammonium hydroxide (17 2 1 and 14 15 1), ethylacetate - ethanol- ammonium hydroxide... 

When many substances are to be separated or when the Rf values of the constituents in a given solvent are smilar, straight-forward one-dimensional chromatography gives incomplete separation, and use of two-dimensional paper partition chromatography becomes necessary to achieve satisfactory separation of the given mixture into its components. In this variation of the technique the initial spot is placed near one comer of a square sheet, and developed in the usual way... 

A common method for chemical identification in one-dimensional chromatography is to define retention-time windows for peaks of interest. Under repeatable, reproducible, and tightly controlled chromatographic conditions, the peaks for target compounds will fall reliably within fixed retention-time windows. However, narrow windows may be required for peaks with nearby neighboring peaks (to avoid false positives), and, with narrow windows, even... 

Peak deconvolution in one-dimensional chromatography using a two-way data approach. Journal of Chromatography A, Vol.958, No.1-2, 0une, 2002), pp. 35-49, ISSN 0021-9673... 

Spot aliquots (2 jl1) on PEI cellulose thin-layer sheets and dry. Develop with 1 M LiCl by one-dimensional chromatography. 

In this article, the role of the detector has not been discussed. At the minimum the detector operates and is chosen exactly as that in a one-dimensional chromatography experiment. Whilst it was alluded... 

In some cases, the chemistry within a given column can be insufficient to separate some analytes. It is possible to direct a series of unresolved peaks onto a second column with different physico-chemical (Chemical classification) properties. Since the mechanism of retention on this new solid support is different from the first dimensional separation, it can be possible to separate compounds that are indistinguishable by one-dimensional chromatography. The sample is spotted at one comer of a square plate,developed, air-dried, then rotated by 90° and usually redeveloped in a second solvent system. 

Complex lipid mixtures cannot always be separated by one-dimensional chromatography. In that case, either a preliminary fractionation on a column (to give, say, neutral, glycolipid and phospholipid fractions) or two-dimensional thin layer chromatography can be used. An example of the separation of lipid extracts from a variety of tissues by TLC is given in Figure 2.1. 

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