High-peak-capacity

When John Phillips, in 1991, presented the practical possibility of acquiring a real comprehensive two-dimensional gas chromatographic separation (33), the analytical chemists in the oil industry were quick to pounce upon this technique. Venkatramani and Phillips (34) subsequently indicated that GC X GC is a very powerful technique, which offers a very high peak capacity, and is therefore eminently suitable for analysing complex oil samples. These authors were able to count over 10 000 peaks in a GC X GC chromatogram of a kerosine. Blomberg, Beens and co-workers... 

Comprehensive two-dimensional GC has also been employed for the analysis of pesticides from serum, which, although not strictly a forensic analytical problem , provides an example of the promise of this technique to forensic applications, such as the analysis of drugs of abuse (40). Two-dimensional gas chromatograms of a 17-pesticide standard and an extract from human serum are shown in Figure 15.13. The total analysis time of about 5 min, high peak capacity and the separation of all... 

It is seen that a high peak capacity was available but, as a gradient program was used, the isocratic peak capacity is not pertinent. The mobile phase program started with a solvent mixture containing 20% v/v of ethyl acetate in n-hexane and ended with pure ethyl acetate. 

The greatest strength of 2D planar methods is that they distribute components widely over a 2D space of high peak capacity. 

The greatest strength of 2D planar methods is that they distribute components widely over a 2D space of high peak capacity. Multidimensional TLC development has the advantages of requiring simple equipment is compatible with scanning densitometry for solute identification and quantitation and enables exploitation of the spot reconcentration mechanism. 

Polymer monolithic columns with small diameter have been successfully employed for proteome analysis. Karger and coworkers reported MALDI-TOF of separated fractions spotted on a plate from a polymeric reversed-phase column that showed high peak capacity (Chen et al., 2005). Huber and coworkers reported separation and detection of about 200 peaks within 5 min by using a PSDVB column (Premstaller et al., 2001). 

In two-dimensional separations, as in any other form of chromatography, it is desirable to generate very high peak capacity in as short a time as possible. In reality, some compromise between speed and resolution must be made, the specifics of which depend on the nature of the sample to be analyzed. A relatively new technique known... 

UHPLC for LC x LC High Speed Versus High Peak Capacity... 

As yet, the number of applications is limited but is likely to grow as instrumentation, mostly based on existing CE systems, and columns are improved and the theory of CEC develops. Current examples include mixtures of polyaromatic hydrocarbons, peptides, proteins, DNA fragments, pharmaceuticals and dyes. Chiral separations are possible using chiral stationary phases or by the addition of cyclodextrins to the buffer (p. 179). In theory, the very high efficiencies attainable in CEC mean high peak capacities and therefore the possibility of separating complex mixtures of hundreds of... 

It should be pointed out that capillary GC is more suitable for the separation of some volatile enantiomers in a complex matrix, such as essential oils, where high peak capacity and hence high column efficiency is required [69, 70]. Approximately 50 components including enantionmers in the natural peppermint oil were separated using a GC method [70]. Eight pairs of volatile lactone emantiomers were resolved by GC with a y-cyclodextrin-based column [71]. 

The advantage of the use of CE for identification screening is based on the high peak capacity of the system and the separation ability to identify substance mixtures. Due to variations in the electroosmotic flow, the migration times in CE are less stable as in a HPLC system. Therefore, the identification tests in CE are based on the principle of calculating the... 

Based on the high peak capacity of CE, the separation speed, and the availability of numerous chiral selectors and the simplicity of the systems, chiral CE is superior to chiral HPLC separations. This is as well reflected by the high number of publications on chiral CE in recent years. Chiral HPLC is suffering from low peak capacity (broad peaks), system stability (often normal phase systems), pressure sensitivity of columns (often cellulose-based column materials), and as a consequence long separation times. 

For separations in the ng/mL-to-pg/mL range and solutes that absorb in the UV/visible portion of the spectrum, optimize the detector wavelength. The optimal wavelength is usually in the low-UV portion of the spectrum. Using LC, the UV cutoff of the mobile phase often prevents such low wavelengths from being employed. Limits of detection usually approach 10"6 M without heroic measures. The downside of low-UV detection is a loss of selectivity, since more solutes will absorb there. This is countered in part by the high peak capacity of CE. In some cases, appropriate sample preparation may be required for selectivity. 

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