Mass spectrometry/mass spectrometry of prostaglandins: Daughter ion spectra of derivatized and isotope-labeled E and D prostanoids

Abstract

Ohio 45239-8707The daughter ion spectra of parent ions produced by electron ionization of four derivatized prostaglandins (PG's) and eight deuteriated analogues have been obtained on a sector mass spectrometer of BE configuration (re versed-geometry magnetic sector/electric sector). Daughter ions were observed under unimolecular and colllslonally activated dlssocatkm conditions (6-keV laboratory energy) in the second field-free region. The various parent Ions showed two classes of fragmentation: (1) derivative-specific and (2) backbone-specific. The deuterium labels provided evidence for proposed fragmentation pathways of parent ions. Isotope labeling also resolved certain overlapping daughter ions obscured by kinetic energy release In the spectra of unlabeled compounds. Use of this Information to develop a systematic rationale for choosing parent Ion-daughter Ion pairs for selected reaction monitoring Of PG's In biological fluids by gas chromatography/mass spectrometry/mass spectrometry Is discussed.The trace analysis of arachidonic acid metabolites, namely prostaglandins (PG's), thromboxanes (TX's), and leukotrienes (LT's), continues to be analytically challenging. These assays are important for further understanding the pharmacology of this class of metabolites, as well as for developing new drug candidates to inhibit certain enzymatic reactions in the arachidonic acid cascade. Current methods of analysis rely on extensive sample purification by multiple solid-phase or liquid extractions, high-performance liquid chromatography (HPLC), and even immunoadsorption chromatography (1-5). Subsequent analysis by capillary gas chromatography/mass spectrometry (GC/MS) with selected-ion monitoring (SIM) often relies on the formation of a pentafluorobenzyl ester (PFB) derivative and on using electron-capture negative chemical ionization (EC-NCI) (5,6). This enhances both the sensitivity and selectivity of detection.Our initial studies of PGE2 quantitation in urine, by GC/MS/MS using electron ionization (7), showed that a small-scale (1-5 mL samples) organic extraction and/or reverse-phase minicolumn (0.5 cm i.d. X 2.5 cm) reduces the residues from biological samples quite adequately for GC/MS analysis. Further reduction of chemical noise was obtained by using MS/MS detection, a well-established technique, in the selected reaction monitoring (SRM) mode (8, 9). The detection was done under unimolecular conditions on an instrument of BE configuration (reversed-geometry magnetic sector/electric sector). Daughter ions were generated in the second field-free region. This approach has also been used for steroids on EB instruments (first field-free region) and referred to as metastable-ion monitoring (10).We have now studied the daughter ion spectra of several ions produced by electron ionization (El) of four derivatized * Author to whom correspondence should be addressed.

Ion trap tandem mass spectrometry of tryptamine. Tissue extracts and isotope dilution using combined radio frequency and direct current voltages

“…The ion of m/z 289 was chosen as the parent ion for an MS/MS assay because of its intensity, structural specificity for tryptamine, and m/z value (12). An RF/DC scan function was created for selected ion storage of m/z 289, as previously described for other compounds (7).…”

Derivatization in Mass Spectrometry—6. Formation of Mixed Derivatives of Polyfunctional Compounds

“…Hydroxyl, oxo and carboxyl groups are frequently present at the same time in prostanoid molecules. Usually, a sequence of three reactions is used for derivatization of prostaglandins A and E. For example, the mass spectrometric (GC/MS, SIM mode) quantitative determination of 6-oxo-PGF 1α as well as arachidonic acid metabolites was accomplished after successive methoximation, methylation and silylation (the EI mass spectrum is shown in Figure 9): [131][132][133] Attempts to derivatize the prostanoid following the conventional sequence by carrying out the methyl ester formation first, resulted in poor yield of the derivative. Quantitation was performed with the hexadeuterated analog as internal standard and GC/MS in SIM mode, monitoring the [M -Me 3 SiOH -CH 3 O] + fragment ion.…”

Quantification of fatty acid oxidation products using online high-performance liquid chromatography tandem mass spectrometry

“…Aside from exploring the bulk oxidation, many of these oxidized lipids and their associated oxidized fatty acids have activities of significant clinical interest[3–6, 10, 14, 18, 20, 22, 26–31]. Numerous GC, LC[32], and hybrid methodologies like GC/MS[3, 5, 14, 18, 20, 22, 31] and LC/MS[2–4, 8–10, 12, 19, 23, 27, 33] exist to quantify the levels of these compounds. These markers can be used clinically to ascertain the effectiveness of antioxidant therapies; however, there are no universal guidelines regarding the scale of the analyses required for the determination of lipid oxidation (and hence fatty acid oxidation) products in a large clinical study.…”