Porphyrinogen fragmentation profiles by ultra-high-performance liquid chromatography/electrospray ionisation tandem mass spectrometry

An ultra-high-performance liquid chromatography/electrospray ionisation tandem mass spectrometry system is described for the separation and characterisation of uroporphyrinogen, heptacarboxylic acid porphyrinogen, hexacarboxylic acid porphyrinogen, pentacarboxylic acid porphyrinogen and coproporphyrinogen. The separation was carried out on a 100 mm × 2.1 mm Thermo-Hypersil BDS column (2.4 μm average particle size) by gradient elution with a mixture of acetonitrile, methanol and 1 mol/L aqueous ammonium acetate buffer, pH 5.16, as eluent. The fragmentation pattern of each compound was established by collision-induced dissociation tandem mass spectrometry. The most characteristic fragmentation was ring opening at one of the four methylene bridges of the protonated porphyrinogen molecule followed by further cleavages of methylene bridges linking the four pyrrole rings at various points to give product ions with methylenepyrrolenine, methylene-dipyrrolenine and methylene-tripyrrolenine structures.     

Analysis of furanocoumarins from Yemenite Dorstenia species by liquid chromatography/electrospray tandem mass spectrometry

A series of prevailing prenylated furanocoumarins from leaves of Dorstenia gigas and Dorstenia foetida (Moraceae) were investigated by liquid chromatography/electrospray tandem mass spectrometry. The mass spectral behavior of the furanocoumarins under positive ion electrospray conditions is discussed using both an ion trap and a triple quadrupole system. It is demonstrated that both methods represent valuable tools not only for the rapid classification of this type of compounds, but also with respect to their substitution pattern.     

Detection and quantitation of a pheomelanin component in melanin pigments using pyrolysis-gas chromatography/tandem mass spectrometry system with multiple reaction monitoring mode

Here, we describe the reliable method for the detection and quantitation of a pheomelanin component in melanin pigments. Synthetic melanins with various contents of pheomelanin-type structural units were thermally degraded, and the multiple reaction monitoring mode was applied to detect the pheomelanin markers in the pyrolysates by GC/MS/MS. The method allowed the specific detection and quantitation of a pheomelanin component in melanin with the incorporation of pheomelanin-type units as low as 0.05%. Considering highly universal character of the pheomelanin markers, the method could be applied for structural studies of natural melanin pigments being mixtures of eumelanin and pheomelanin.     

Isotope ratio monitoring gas chromatography/Mass spectrometry of D/H by high temperature conversion isotope ratio mass spectrometry

Of all the elements, hydrogen has the largest naturally occurring variations in the ratio of its stable isotopes (D/H). It is for this reason that there has been a strong desire to add hydrogen to the list of elements amenable to isotope ratio monitoring gas chromatography/mass spectrometry (irm-GC/MS). In irm-GC/MS the sample is entrained in helium as the carrier gas, which is also ionized and separated in the isotope ratio mass spectrometer (IRMS). Because of the low abundance of deuterium in nature, precise and accurate on-line monitoring of D/H ratios with an IRMS requires that low energy helium ions be kept out of the m/z 3 collector, which requires the use of an energy filter. A clean mass 3 (HD(+.)) signal which is independent of a large helium load in the electron impact ion source is essential in order to reach the sensitivity required for D/H analysis of capillary GC peaks. A new IRMS system, the DELTA(plus)XL(trade mark), has been designed for high precision, high accuracy measurements of transient signals of hydrogen gas. It incorporates a retardation lens integrated into the m/z 3 Faraday cup collector. Following GC separation, the hydrogen bound in organic compounds must be quantitatively converted into H(2) gas prior to analysis in the IRMS. Quantitative conversion is achieved by high temperature conversion (TC) at temperatures >1400 degrees C. Measurements of D/H ratios of individual organic compounds in complicated natural mixtures can now be made to a precision of 2 per thousand (delta notation) or, better, with typical sample amounts of approximately 200 ng per compound. Initial applications have focused on compounds of interest to petroleum research (biomarkers and natural gas components), food and flavor control (vanillin and ethanol), and metabolic studies (fatty acids and steroids). Copyright 1999 John Wiley & Sons, Ltd.     

A discharge adaptor interface for use in liquid chromatography/mass spectrometry

A discharge adaptor, composed of a metal casing and platinum (Pt) wire needle, was directly attached to an electrospray ionization (ESI) probe tip, to transform the ionization into atmospheric pressure chemical ionization (APCI). Six generic drugs were analyzed with the developed discharge adaptor (DA) and two commercial interfaces. The DA interface produced more intense radical anions, [M]˙?, and less sodium adduct ions, [M + Na]?, than the ESI interface, whereas almost the same molecular ions were detected as the APCI interface. The effects of solvent and desolvation gas flow in the DA interface were similar to those in the ESI interface, but differed from those in the APCI interface. Better sensitivity of the tested drugs was obtained relative to the commercial APCI interface. For human plasma samples, the DA interface also demonstrated good tolerance to plasma matrices, linearity from 5 or 20 to 500 ng/mL (r2 > 0.99) and ruggedness.     

Determination of bakkenolide A in rat plasma using liquid chromatography/tandem mass spectrometry and its application to a pharmacokinetic study

A sensitive rapid analytical method was established and validated to determine the bakkenolide A (BA) in rat plasma. This method was further applied to assess the pharmacokinetics of BA in rats receiving a single dose of BA. Liquid chromatography tandem mass spectrometry in multiple reaction monitoring mode was used in the method, and costundide was used as internal standard. A simple protein precipitation based on methanol was employed. The combination of a simple sample cleanup and short chromatographic running time (2.4?min) increased the throughput of the method substantially. The method was validated over the range of 1-1000?ng/mL with a correlation coefficient?>?0.99. The lower limit of quantification was 1?ng/mL for BA in plasma. Intra- and inter-day accuracies for BA were 93-112% and 103-104%, respectively, and the inter-day precision was less than 15%. After a single oral dose of 20?mg/kg of BA, the mean peak plasma concentration (C(max) ) of BA was 234.7?±?161?ng/mL at 0.25?h. The area under the plasma concentration-time curve (AUC(0-24 h) ) was 535.8?±?223.7?h·ng/mL, and the elimination half-life (T(1/2) ) was 5.0?±?0.36?h. In case of intravenous administration of BA at a dosage of 2?mg/kg, the area under the plasma concentration-time curve (AUC(0-24 h) ) was 342?±?98 h?ng/mL, and the elimination half-life (T(1/2) ) was 5.8?±?0.7?h. Based on the results, the oral bioavailability of BA in rats at 20?mg/kg is 15.7%. Copyright ? 2012 John Wiley & Sons, Ltd.     

Identification and structural characterization of in vivo metabolites of ketorolac using liquid chromatography electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS)

In vivo metabolites of ketorolac (KTC) have been identified and characterized by using liquid chromatography positive ion electrospray ionization high resolution tandem mass spectrometry (LC/ESI-HR-MS/MS) in combination with online hydrogen/deuterium exchange (HDX) experiments. To identify in vivo metabolites, blood urine and feces samples were collected after oral administration of KTC to Sprague-Dawley rats. The samples were prepared using an optimized sample preparation approach involving protein precipitation and freeze liquid separation followed by solid-phase extraction and then subjected to LC/HR-MS/MS analysis. A total of 12 metabolites have been identified in urine samples including hydroxy and glucuronide metabolites, which are also observed in plasma samples. In feces, only O-sulfate metabolite and unchanged KTC are observed. The structures of metabolites were elucidated using LC-MS/MS and MS(n) experiments combined with accurate mass measurements. Online HDX experiments have been used to support the structural characterization of drug metabolites. The main phase I metabolites of KTC are hydroxylated and decarbonylated metabolites, which undergo subsequent phase II glucuronidation pathways.