Chromatographic methods characteristics

Multidimensional chromatography has important applications in environmental analysis. Environmental samples may be very complex, and the fact that the range of polarity of the components is very wide, and that there are a good many isomers or congeners with similar or identical retention characteristics, does not allow their separation by using just one chromatographic method. 

Frames can be seen as structures where all relevant information about an object or a concept is collected. As an example the relevant information about a column in a chromatographic method can be represented by a dedicated general frame, COLUMN. Separate columns can be represented by so-called instantiations of this frame. Instantiations are copies of the general frame that contain the characteristics of a specific object, in this example the separate columns. 

Table 7.40 summarises the general characteristics of on-line SFC-MS. The method is potentially most useful for thermally labile and involatile compounds that are unsuitable for GC-MS. Because the MS instrument is the main source of information, the reproducibility of the retention and the separation selectivity are much less important than for other SFC applications. As a result, mass spectroscopists do not feel restrained by the limits on reproducibility, which slowed the uptake of SFC by chromatographers. Method development should not be underestimated. Practical problems are associated with interfacing and the effect of the expanding... 

Principles and Characteristics Of the chromatographic methods discussed in Chapter 4 essentially only SEC and HPLC are used to some extent for the analysis of dissolutions containing both macromolecular and additive components. SPE is a useful device for working... 

Table 13.1 summarizes the common chromatographic methods and the characteristics that differentiate them from other methods. In this list, HPLC... 

In choosing suitable methods to separate a given mixture of compounds, the general characteristics favouring a chromatographic method are ... 

On-line supercritical fluid extraction/GC methods combine the ability of liquid solvent extraction to extract efficiently a broad range of analytes with the ability of gas-phase extraction methods to rapidly and efficiently transfer the extracted analytes to the gas chromatograph. The characteristics of supercritical fluids make them ideal for the development of on-line sample extraction/gas chromatographic (SFE-GQ techniques. SFE has the ability to extract many analytes from a variety of matrices with recoveries that rival liquid solvent extraction, but with much shorter extraction times. Additionally, since most supercritical fluids are converted to the gas phase upon depressurization to ambient conditions, SFE has the potential to introduce extracted analytes to the GC in the gas phase. As shown in Fig. 13.8, the required instrumentation to perform direct coupling SFE-GC includes suitable transfer lines and a conventional gas chromatograph [162,163]. 

Before the ruggedness test could be contemplated it was essential to fully validate the method with respect to other method characteristics. Hence the following tests were carried out, specificity, spectral purity of chromatographic peaks, linearity of detector response, and repeatability over 100 injections. Satisfactory results were achieved for all these experiments before we continued to the ruggedness test. 

The final product specifications must contain a specific identity test. The full set of physical properties and physical constants that are characteristic of the substance must be measured and their appropriate values documented. And, very importantly, the purity of the final product must be demonstrated by a suitable chromatographic method. That chromatographic method must be able to measure the presence of impurities at concentrations of hundreds of a percent in order to be appropriate or acceptable for this purpose. Impurities present in the final product must be characterized. Those impurities which occur in final product at greater than 0.1% must be identified and tested for their biological properties, including toxicity, mutagenecity, etc. Ordinarily, impurities present in concentrations of 0.01 to 0.1% can be recorded as unidentified impurities, and impurities which occur at concentrations less than 0.01% are ordinarily just noted. 

ASTM D-2007. Standard Test Method for Characteristic Groups in Rubber Extender and Processing Oils and Other Petroleum-Derived Oils by the Clay-Gel Absorption Chromatographic Method. 

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