High performance liquid chromatography summarized

Full acceptance of HPLC/MS methods by the US EPA OPP as enforcement methods occurred between 1998 and 2001. For example, in 1998, the EPA OPP accepted HPLC/MS (without MS/MS) methods as primary enforcement methods, and high-performance liquid chromatography/tandem mass spectrometry (HPLC/MS/MS) only was suitable for confirmatory methods. However, in 2001, HPLC/MS/MS methods also became acceptable for primary enforcement. Table 4 summarizes the types of methods that were validated by the EPA OPP method validation program, for both food tolerance enforcement methods and environmental chemistry methods. 

Other kinds of bloassays have been used to detect the presence of specific allelochemical effects (8), effects on N2 fIxatlon (9), the presence of volatile compounds (10) and of Inhibitory substances produced by marine microalgae (11). Putnam and Duke (12) have summarized the extraction techniques and bioassay methods used In allelopathy research. Recent developments In high performance liquid chromatography (HPLC) separation of allelochemlcals from plant extracts dictates the need for bloassays with sensitivity to low concentrations of compounds contained In small volumes of eluent. Einhellig at al. (13) described a bloassay using Lemna minor L. growing In tissue culture cluster dish wells that maximizes sensitivity and minimizes sample requirements. 

Optical purity(0.P.) of grown parts of the crystals were analyzed by high performance liquid chromatography. Experimental conditions for growth tests are summarized in Table I. 

In the next section, the term "complex polymers" is defined, the effects of polymer complexity on conventional SEC analysis are examined, and attempts to analyze ccanplex polymers by utilizing SEC detector technology are summarized. High performance liquid chromatography (HPLC) attempts to accomplish the task are then described. This is followed by a summary of the theoretical development of OC, experimental results of OC analysis, complications which emerged, and finally a summary of the status of OC in light of recent developments. (1) and (2) provide reviews of OC. 

The separation nf the poly saccharide components utilizes their different solubilities, polar groups, extents of branching, molecular weights, and molecular flexibilities and may he accomplished batebwisc or with easily automated column techniques such as column ur high performance liquid chromatography. These pmcedures have been summarized in several reviews. 

Direct determination of urea pesticides by high-performance liquid chromatography has been widely reported in the literature (10,32-36,127-130). Ultraviolet detection has often been used (32,33,35,36,60,127) with usually acceptable sensitivity, although this detector is nonspecific and the sensibility is, in general, low. To overcome this problem, several techniques have been assayed, such as precolumn enrichment (60), postcolumn derivatization (34,10), and the use of other detection techniques such as the electrochemical (129), photoconductivity (128,130), and fluorescence detectors (9,10,34). Table 9 summarizes representative papers using these techniques in HPLC analysis. 

An overview and discussion is given of literature methods published after 1989 devoted to the ion-interaction chromatographic determination of inorganic anions. Seventy references are quoted. Ion-interaction chromatography makes use of commercial reversed-phase stationary phase and conventional high-performance liquid chromatography instrumentation. The basis of the technique, the modification of the stationary phase surface, the choice of the ion-interaction reagent as well as the dependence of retention on the different variables involved are discussed. Examples of application in the fields of environmental, clinical and food chemistry are presented. The experimental conditions of stationary phase, of mobile phase composition as well as detection mode, detection limit and application are also summarized in tables. 1997 Elsevier Science B.V. 

The most popular method used for the assay of aspartame is that of high performance liquid chromatography. A large number of methods and studies have been reported, and the reported conditions used for these analyses since 1980 are summarized in Table 4. 

One of the most important features of the capillary electrophoresis instrument is the detection system. Several of the detection methods commonly used in high-performance liquid chromatography have been somewhat adapted for capillary electrophoresis. Currently, the most popular detection methods developed for capillary electrophoresis are summarized in Table III. 

Strege summarized the technique of high-performance liquid chromatography-electrospray ionization mass spectrometry (HPLC-ESI-MS) in dereplication of natural products. In contrast to earlier electron impact ionization (El), ESI technique is applicable to virtually any ion in solution with a soft ionization process. A comparison of ESI with fast atom bombardment (FAB), matrix assisted laser desorption ionization (MALDI), atmospheric pressure chemical ionization (APCI) and other techniques demonstrates its superior sensitivity, compatibility and reliability when coupled with HPLC [51]. 

Other high performance liquid chromatography methods reported for the determination of acetylcholine are summarized (together with their conditions) in Table 3 [4, 117, 147-193],... 

Table 1 summarizes substances considered as possible uremic toxins. Fig. 1 illustrates the chemical structures of some of the most important uremic toxins that are determined by high-performance liquid chromatography (HPLC). In this paper, some of the most important uremic toxins are discussed (concerning their chromatographic determination). 

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