Determination of misoprostol free acid in human breast milk and serum by gas chromatography/negative ion chemical ionization tandem mass spectrometry

To study an expected transition of misoprostol from human blood into breast milk, a novel method for the determination of its active metabolite misoprostol acid (MPA) was developed. MPA was determined in serum and breast milk samples by an isotope dilution assay using gas chromatography/negative ion chemical ionization tandem mass spectrometry (GC/NICI-MS/MS). After addition of (15S)-15-methylprostaglandin E(2) (15-methyl-PGE(2)) as an internal standard, MPA was extracted from both matrices using a reversed-phase cartridge. The prostanoids were derivatized with O-2,3,4,5,6-pentafluorobenzylhydroxylamine hydrochloride (PFBHA) and 2,3,4,5,6-pentafluorobenzyl bromide (PFBB) to the pentafluorobenzyl oxime (PFBO)-pentafluorobenzyl ester (PFB) derivatives. The sample was subjected to thin-layer chromatography with ethyl acetate-hexane (1 : 1 (v/v)) as the developing solvent. The corresponding zone was extracted. After derivatization to the trimethylsilyl ether, MPA was determined by GC/NICI-MS/MS using the [molecule (M) - pentafluorobenzyl (PFB)](-) ([P](-)) ions as precursor in the negative ion chemical ionization mode. The product ions used for quantification were [P - 2TMSOH - C(6)F(5)CH(2)OH](-) (MPA) and [P - 2TMSOH - C(6)F(5)CH(2)OH - CO(2)](-)(15-methyl-PGE(2)), respectively. The limit of quantification for MPA was approximately 1 pg ml(-1) in breast milk and serum samples. The correlation coefficients of the calibration curves for MPA were r > 0.997 in the 0.5-2000 pg ml(-1) range for both tested matrices.     

Influence of Resolution of Rasterized Geometries on Porosity and Specific Surface Area Exemplified for Model Geometries of Porous Media

Rasterized representations of geometrical structures are commonplace in science and engineering. They are used in analysis and design of complex geometrical structures; however, the introduced errors for volume and surface estimation are often not considered in detail. To provide insight and information on these effects, in this study model geometries of porous media (simple cubic, body-centered cubic, face-centered cubic) are used to investigate the influence of resolution (voxels per length) on volume and surface approximation. The numerically obtained results are compared with analytical solutions for porosity and specific surface area. Small deviations from the real volume are found for the rasterized geometry at reasonable resolution. For the estimated surface area, in contrast, when using marching cubes considerable deviations from the analytically calculated surface area are found even at relatively fine resolutions. These findings are especially important for the use of rasterized voxel data as input for engineering correlations to estimate characteristic physical transport properties such as pressure drop or effective heat transport.