Chromatographic procedures/techniques

Several gas-Hquid chromatographic procedures, using electron-capture detectors after suitable derivatization of the aminophenol isomers, have been cited for the deterrnination of impurities within products and their detection within environmental and wastewater samples (110,111). Modem high pressure Hquid chromatographic separation techniques employing fluorescence (112) and electrochemical (113) detectors in the 0.01 pg range have been described and should meet the needs of most analytical problems (114,115). 

Affinity chromatographic procedures have been widely accepted for purification of biological macromolecules48). This technique is also one of the most convenient... 

The major difference between HPLC and the old column chromatographic procedures is the pressure applied to drive the mobile phase through the column. This requires a number of improvements in the equipment, materials used for separation, and the application of the theory. HPLC offers major advantages in convenience, accuracy, speed, and the ability to carry out difficult separations. Comparisons to and relative advantages of HPLC over classical LC and GC are given below (see Sections 15.1 and 15.2) to provide the reader a better appreciation of this technique. The readers are encouraged to look up an excellent classical text on HPLC by Snyder and Kirkland [2]. A short review of... 

The objectives of each theoretical approach are not only the explanation of the experimental results or failures of practice but also the prediction of new possibilities to increase the sensitivity, separation capacity and velocity of the chromatographic procedure under investigation. Numerous theoretical reviews deal with the problems of the CE separation technique. In recent years the methods to enhance the precision in CE by the modification of operational parameters [113], the theory and methodological improvements of sample stacking of cationic and anionic solutes in CE [114-116], and the results and difficulties of the application of conductivity detection in CE technologies [117] have been reviewed. 

A procedure for estimating hexamethylene l,6-bis[l-(5-p-chloro-phenyl)biguanide] ( chlorohexidine") in the presence of anesthesine in tablets has been described (617). Nt,NiAnhydro[bis(p-hydroxyethyl)]-biguanide (616) and other biguanides (137) have been determined by spectrophotometric (137, 616) (including infra-red (563)) techniques. Chromatographic procedures have also been described (26, 449, 467). 

Content, as well as impurity determinations, are done by chromatographic procedures such as gas chromatography (GC), high pressure liquid chromatography (HPLC) [831], capillary electrophoresis (CE) [832], and by spectroscopic techniques (UV, IR, MS, and NMR) [833, 834]. 

Derivatization After Desorption. Alkanolamines, highly polar basic compounds, present a difficult analytical problem. Although direct gas chromatographic separations can be achieved, this technique is not applicable to trace analysis due to sorption problems at trace concentrations. A derivatization/gas chromatographic procedure has been developed for the determination of alkanolamines in air as low as 100 ppb (54,55). The samples are collected on activated alumina and desorbed with an aqueous solution of 1-octanesulfonic acid. The... 

The techniques used to demonstrate selectivity will depend on the intended objective of the analytical procedure. The selectivity of a procedure may be confirmed by obtaining positive results from samples containing the analyte, while obtaining negative results from blank samples. For chromatographic procedures, representative chromatograms should be used to demonstrate selectivity and individual components should be appropriately labeled. Similar considerations should be given to other separation techniques. 

Coupling chromatographic procedures with immunochemical techniques can also provide a very sensitive and specific analytical system for either determinative or confirmatory analysis. If the antibody used is very specific for the analyte of interest and the antibody reactivity is known to be sensitive to small variations in the structure of the analyte tested, positive reactions with the method are strongly indicative that an analyte of defined structural characteristics is present in the sample. Full rigorous confirmation, however, would depend on further analysis by mass spectrometry, which is the method of choice in confirmatory analysis. Mass spectrometry gives specific information on the identity and structure of the compound of interest. Coupled with chromatographic techniques it becomes a very powerful confirmatory tool for both quantitative and qualitative assessment of drug residues in foods. 

The first step in the development of a gas chromatographic procedure is to establish the performance characteristics of the drug in the absence of any matrix. Of principal importance is the selection of some portion that may serve as a standard. As was pointed out earlier, the analyst must be careful in his or her judgment of a chemically pure standard. Purity should be established by independent techniques which will reinforce confidence in structural integrity before any GC is attempted. 

Roughly 10 years ago, an ion-pair HPLC was introduced for the determination of sulfites in foods (32). The method combined the chemical approach of the Monier-Williams technique for liberating the sulfite from the matrix with ion chromatography. The ion chromatographic procedure... 

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