Solid-phase extraction, biomarkers

Surface enhanced laser desorption/ionization (SELDI) is a distinctive form of laser desorption ionization where the target plays an active role in the sample preparation procedure and ionization process [49]. Depending on the chemical or biochemical treatment, the SELDI surface acts as solid phase extraction or an affinity probe. Chromatographic surface is used for sample fractionation and purification of biological samples prior to direct analysis by laser desorption/ ionization. SELDI is mainly applied for protein profiling and in biomarker discovery by comparing protein profiles from control and patient groups. 

The final sulfur mustard urinary biomarker to be discussed is also a reaction product of sulfur mustard with glutathione 1,1 -sulfonyl-bis-[2-S-(V-acetylcystein T)ethane. Using solid-phase extraction for sample cleanup and analyte concentration followed by analysis with negative ion electrospray LC-MS-MS, Read and Black (2004b) were able to achieve detection limits of 0.5-1.0 ng/mL. Methods for the analysis of urine samples for sulfur mustard verification are summarized in Table 19.5. 

For biomarker identification, it is also possible to separate out substances of interest from a complex biofluid sample using techniques such as solid phase extraction or HPLC. For metabolite identification, directly coupled chromatography-NMR spectroscopy methods can be used. The most powerful of these hyphenated approaches is HPLC-NMR-MS [24] in which the eluting HPLC peak is split with parallel analysis by directly coupled NMR and MS techniques. This can be operated in on-flow, stopped-flow, and loop-storage modes and thus can provide the full array of NMR and MS-based molecular identification tools. These include MS-MS for identification of fragment ions and FT-MS or TOF-MS for accurate mass measurement and hence derivation of molecular empirical formulae. 

Barfi, B., A. Asghari, M. Rajabi, A. Barfi, and I. Saeidi. 2013. Simplified miniaturized ultrasound-assisted matrix solid phase dispersion extraction and high performance liquid chromatographic determination of seven flavonoids in citrus fruit juice and human fluid samples Hesperetin and naringenin as biomarkers, f. Chromatogr. A 13H(l) 30-40. 

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