Analysis time characteristics

High performance liquid chromatography (HPLC) is an excellent technique for sample preseparation prior to GC injection since the separation efficiency is high, analysis time is short, and method development is easy. An LC-GC system could be fully automated and the selectivity characteristics of both the mobile and stationary... 

Principles and Characteristics Extraction or dissolution methods are usually followed by a separation technique prior to subsequent analysis or detection. While coupling of a sample preparation and a chromatographic separation technique is well established (Section 7.1), hyphenation to spectroscopic analysis is more novel and limited. By elimination of the chromatographic column from the sequence precol-umn-column-postcolumn, essentially a chemical sensor remains which ensures short total analysis times (1-2 min). Examples are headspace analysis via a sampling valve or direct injection of vapours into a mass spectrometer (TD-MS see also Section 6.4). In... 

The method is essentially non-destructive, although in some circumstances a target may suffer radiation damage. For example the lattice site position of some dopants in semiconductors can be influenced by RBS analysis. With a typical analysis time of less than 30 min, it is a relatively quick method. Its most important characteristic is... 

Electronic noise, identified via rise-time characteristics, shown rising to 30 times background rate for 15-mL gas proportional counter. A tiny fraction of such noise, not identified by means such as pulse shape analysis, could invalidate results which presume that the background is stable to < 10%. 

The Raman spectra of heroin, morphine and codeine (Fig. 7.10) are highly characteristic because of the change in the bands due to the aromatic ring. The FT-IR spectra of these compounds are quite similar. Near-infrared Raman spectroscopy can provide a rapid method for characterising drugs with minimal sample preparation and analysis time. 

The separating power of a column varies as the square root of its length. Thus if a two-fold increase in resolution is required and a four-fold increase in column length would be required, this would result in a four-fold increase in analysis time. The increased resolution afforded by length can often be replaced with a decrease in temperature ensuring that more interaction with the stationary phase occurs, especially if the stationary phase has characteristics that enable it to select one analyte more than another. 

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