Chromatographic methods online detection

In recent years, those methods that do accept original samples (e.g., from soils or water) without major treatment and concentration have gained importance due to the small degree of denaturing and of added pollutants. This section will focus on the methods that are suited to characterize the organic matter in its dissolved state. Powerful methods are also in use for online detection of chromatographic or otherwise obtained fractions. 

IPC-MS combined methods must be optimized with respect to separation and compatibility with online detection involving the constraints detailed in Table 12.2 regarding the composition and volatility of the mobile phase. The major concern of chromatographers who deal with this combined technique is the reduced signal caused by source pollution of non-volatile IPRs. Moreover, the efficiency of droplet development, which in turn affects the number of charged ions that ultimately reach... 

Chiron, S. and Barcelo, D., Determination of pesticides in drinking water by online solid-phase disk extraction followed by various liquid-chromatographic systems,/ Chromatogr., 645, 125-134, 1993. Sundaram, K. M. S. and Curry, J., High-performance liquid-chromatographic methods for the analysis of aminocarb, mexacarbate, and some of their At-methylcarhamate metabolites by postcolumn derivatization with fluorescence detection, J. Chromatogr. A, 672, 117-124, 1994. 

Countercurrent chromatography (CCC) is a chromatographic method that separates solutes that are more or less retained in the column by a stationary phase (liquid in this case) and are eluted at the outlet of the column by a mobile phase. Two treatments of column effluent have been used up to now in CCC. Either the column outlet is directly connected to a detector commonly used in HPLC (online detection) or fractions of mobile phase are collected and analyzed by spectropho tome trie, electrophoretic, or chromatographic methods etc. (off-line detection). 

The online coupling between TLC and MS provides a powerful combination for the detection and identification of substances separated by a planar chromatographic method. The online coupling between these two methods... 

Another important application of hyphenated NMR methods is to provide insights into processes that affect the separation. Eor example, online NMR detection of the water chemical shift was used to noninvasively probe intracapillary temperatures in CE separations with subsecond temporal resolution and spatial resolution on the order of 1 mm [111]. Lacey et al. [112] followed up this report with a second NMR study using a novel 2-turn vertical solenoidal coil to measure temperature increases of more than 50 C in a chromatographic frit of the type used in CEC. Insights into the mechanisms underlying cITP have also been investigated utilizing online NMR... 

Because of the variety of interfaces and the low detection limits, hyphenated mass spectrometers are among of the fastest growing markets for scientific instrument manufacturers in the 1990s and beyond. Every available type of chromatographic separation has been analyzed by mass spectrometry from desorption methods for TLC plates26 to online CE-MS.27,28 Not all techniques are routinely used for the characterization of small organic molecules of pharmaceutical interest (Table 4). The two workhorse instruments for the characterization of small molecules are GC-MS and... 

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