Below detection, limit resolution between

In comparison with NMR, mass spectrometry is more sensitive and, thus, can be used for compounds of lower concentration. While it is easily possible to measure picomoles of compounds, detection limits at the attomole levels can be reached. Mass spectrometry also has the ability to identify compounds through elucidation of their chemical structure by MS/MS and determination of their exact masses. This is true at least for compounds below 500 Da, the limit at which very high-resolution mass spectrometry can unambiguously determine the elemental composition. In 2005, this could only be done by FTICR. Orbitrap appears to be a good alternative, with a more limited mass range but a better signal-to-noise ratio. Furthermore, mass spectrometry allows relative concentration determinations to be made between samples with a dynamic range of about 10000. Absolute quantification is also possible but needs reference compounds to be used. It should be mentioned that if mass spectrometry is an important technique for metabolome analysis, another key tool is specific software to manipulate, summarize and analyse the complex multivariant data obtained. 

The mobile phases consisting of acetonitrile/methanol [16] or acetoni-trile/methanol/water [18] in different ratios with a few drops of ammonia solution were found to discriminate between two enantiomers of these three -blockers in one-dimensional (ID) ascending development mode. The mobile phase composition and values of chiral separation factor a are listed in Table 11.3. The zones of separated antipodes were detected using iodine vapor and the detection limit of both alprenolol and propranolol racemates was 2.6 ng, while that of metoprolol was 0.26 /rg [16]. The effects of temperature on the separation of these three jS-blockers were also investigated [16]. It was observed that no resolution of atenolol racemate was achieved at the temperatures higher than 15" C, as well as below 8°C. The best resolution of propranolol and metoprolol racemates was achieved at 22°C. Increase of the temperature above 22°C led to the tailing, while a decrease up to 6°C had little or no effect on the quality of resolution. 

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