The use of photoionization at atmospheric pressure shows great potential for the mass analysis of large apolar or hydrophobic peptides. Mass spectra that were obtained using this technique showed mainly singly charged ions. While polar peptides spectra do not produce fragment ions, others lead to B-type or C-type in-source fragmentation. These dissociation reactions, which could involve electron capture dissociation processes in the case of the C-type ions, are observed for hydrophobic peptides. Both the compatibility of this ionization mode with reversed- or normal-phase liquid chromatographic separation and its sensitivity allow liquid chromatography coupling to both mass spectrometry and tandem mass spectrometry for the analyses of hydrophobic peptide mixtures. Atmospheric pressure photoionization seems to be an interesting alternative method to study hydrophobic peptides that are not easily ionizable by more classical ionization techniques such as electrospray ionization and matrix-assisted laser desorption/ionization.

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SUMMARYThe equations describing the mechanical behaviour of intervertebral disc tissue and other swelling porous media are three coupled partial differential equations in which geometric and physical non-linearities occur. The boundary conditions are deformation-dependent. To solve the equations for an arbitrary geometry and arbitrary boundary conditions, we use the finite element (FE) method. The differential equations are rewritten in an integral form by means of the weighted residual method. The domain of the integral is defined via a set of shape functions (i.e. finite elements). By applying the Gauss theorem and rewriting with respect to the reference state (total Lagrange), non-linear equations are obtained. These are solved by means of the Newton-Raphson technique. In order to get a finite set of equations, the weighted residual equations are discretized. The shape functions are chosen as weighting functions (Galerkin method). This discretization results in a non-symmetric stiffness matrix. A general description is given for the elements implemented into the commercial FE package DIANA (DIANA Analysis B.V, Delft, Netherlands). The numerical results of unconfined compression of a schematic intervertebral disc with varying proteoglycan concentration are given.

Uniaxial confined compression and swelling experiments on cylindrical specimens taken either in an axial or in a radial direction from a canine lumbar annulus fibrosus are presented. The loading protocol consisted of a combination of stepwise mechanical and chemical loading. Swelling and consolidation curves of normalized displacement versus square root of normalized time did not show a dependence on site or orientation of the specimen. All stages in which height increases, namely, conditioning, swelling, and desolidation show only slight differences in these normalized curves. Consolidation is initially faster, and later slower. The transport coefficient for axial specimens is higher than for radial specimens, for consolidation e.g., 3.14 ± 1.56 10−10 m2s−1 and 1.11 ± 0.33 10−10 m2s−1 respectively, the biphasic aggregate moduli are 1.01 ± 0.31 MPa and 0.66 ± 0.30 MPa, respectively.