Analysis of compound mixtures

A reliable analysis of multicomponent mixtures is particularly difficult and the situation becomes more complicated and less meaningful with increasing mixture size. Nevertheless, the analysis of peptide libraries is possible by mass spectroscopic means.366-572 mixture size increases, the main aim of any analysis is to ensure that the vast majority of expected library members are represented in the mixture. The use of MS in conjunction with other analytical techniques (HPLC-MS, GC-MS, MS-MS) have been used successfully in library characterisation. 3.425.573 Electronspray-MS is a particularly mild method for ionisation. s Matrix-assisted Laser Desorption Ionisation - time-of-flight (MALDI-TOF) mass spectrometry is a tool of increasing importance in multicomponent analysis. Its reduced tendency to preferential ionisation results in an increased likelihood of observing ions from all components.5 575 

These robotic systems and workstations can be grouped into mainly three categories as schematically shown in Table 1.13  

Type of system Manual handling Type and complexity of library Library size costs building blocks 

1 manual devices intense focused libraries process development small (10-100) small 1-1 Og 

2 semi-automated workstations manual addressing of reagents possible focused libraries flexible adaptation of novel processes medium (100-500) medium lO OOO-lOO OOO US 10-50g 

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For library analysis of compound mixtures, reliable results are obtained by coupling mass spectrometry with HPLC or capillary electrophoresis (CE). In this arrangement, mixtures of several hundred compounds can be analyzed. A comparison of MS, CE, and NMR for library characterization has been made in [93]. It was concluded that existing analytical techniques can provide sufficient information about prepared libraries. 

Thus, synthetic combinatorial receptor libraries of high diversity are a prerequisite for further progress in the field of chemosensors. As yet, there are no specific receptors available for most of the analytes, but this can be overcome by the use of sensor arrays. A mathematical analysis by pattern recognition can lead to a successful analysis of compound mixtures which are exposed to an array of sensors with different selectivities ( bio-electronic nose ) [13,14]. 

An additional dimension to library analysis is introduced when mass spectrometry is coupled with common separation techniques, for example liquid chromatography (LC) and capillary electrophoresis (CE). While these couplings are compatible with spray ionization techniques such as ESI or APCI, they more or less exclude the use of the MALDI technique. Several contributions deal with LC-ES-MS [36, 37] and CE-ES-MS-coupling [38], For molecules with isobaric nominal masses, MS/MS-experiments are performed to confirm the identity of a library component. Separation and analysis of compound mixtures may also be performed by GC-MS [39, 40], As a supplement to the more common-... 

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