Chromatographic methods, disadvantages

A comparison of the two chromatographic methods shows that they have the following advantages and disadvantages ... 

Disadvantages Error levels still remain a concern, particularly with gradient systems and ionizable compounds. Systematic studies have not been published to date, but average errors in k for gradient systems can approach 30%. Also, both ChromSword and LC Simulator require a reasonable training set of compounds in order to characterize a chromatographic method for a particular compound. 

Two major disadvantages of dialysis and chromatographic methods, as well as ISE and ASV, are adsorption of interacting species and disturbing of complexation equilibria. Further, ISE and ASV are applicable adequately only to a limited typology of metal ions (e.g., Cu " ", Cd " ", Pb " ", and Zn-+). An important advantage of UF methods is that they do not take as much experimental time as does dialysis, and do not disturb the complexation equilibria. 

The main disadvantage is a certain lack of precision and reproducibihty and the use of different organic solvent systems, which renders the derivation of tc- or f-related scales (chapter 3.3) impossible. In addition, a chromatographic method is no equilibrium process (even if it results from distribution), leading to deviations, e.g. in the case of charged compounds [229]. 

As HPLC is the most widely used pharmaceutical analysis technique among current chromatographic methods, a short comparison of HPLC and CE should be very informative to the reader. Some comparisons will also be made to GC. This section will illustrate the advantages, disadvantages, and complementary natures of HPLC and CE. 

There are a wide variety of methods available for the analysis of alkaloids in tobacco. Each method is associated with certain advantages and disadvantages, but fills a certain niche for tobacco scientists. If the percent total alkaloids determined as nicotine suffices, then steam distillation or autoanalyzer are appropriate methods. When secondary alkaloids need to be quantitatively determined, then one of the chromatographic methods is more appropriate. 

As has been previously said, 2,3-butanodione (diacetyl) is an important aroma of alcoholic beverages, it has not been studied and measured extensively in the past because of analytical difficulties in the quantitation caused by its highly volatile nature, chemical instability, and interference of other compounds. Colorimetric methods to measure diacetyl have been widely used in the past. These methods involve steam distillation to isolate diacetyl from the matrix. However, distillation has the disadvantage of incomplete isolation of diacetyl from other closely related compounds that will result in an overestimation of its concentration. A fluorometric method was developed to improve upon the lengthy distillation methods that involve derivatization. Although acetaldehyde and its acetal can be determined by direct injection GC-FID in spirit drinks (EU reference method for spirits), most chromatographic methods for minor aldehydes implicate also derivatization. While a very sensitive and accurate method based on SMPE without derivatization and MS detection has been developed, it requires the use of... 

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