Desorption from matrix

The two most common temporal input profiles for dmg delivery are zero order (constant release), and half order, ie, release that decreases with the square root of time. These two profiles correspond to diffusion through a membrane and desorption from a matrix, respectively (1,2). In practice, membrane systems have a period of constant release, ie, steady-state permeation, preceded by a period of either an increasing (time lag) or decreasing (burst) flux. This initial period may affect the time of appearance of a dmg in plasma on the first dose, but may become insignificant upon multiple dosing. 

Nondestructive radiation techniques can be used, whereby the sample is probed as it is being produced or delivered. However, the sample material is not always the appropriate shape or size, and therefore has to be cut, melted, pressed or milled. These handling procedures introduce similar problems to those mentioned before, including that of sample homogeneity. This problem arises from the fact that, in practice, only small portions of the material can be irradiated. Typical nondestructive analytical techniques are XRF, NAA and PIXE microdestructive methods are arc and spark source techniques, glow discharge and various laser ablation/desorption-based methods. On the other hand, direct solid sampling techniques are also not without problems. Most suffer from matrix effects. There are several methods in use to correct for or overcome matrix effects ... 

Bemdt, P., Hobohm, U., and Langen, H. (1999). Reliable automatic protein identification from matrix-assisted laser desorption/ionization mass spectrometric peptide fingerprints. Electrophoresis 20, 3521-3526. 

Cain,T. Lubman, D. Weber, W. J. Differentiation of bacteria using protein profiles from matrix assisted laser desorption/ionization time of flight mass spectrometry. Rapid Comm. Mass Spectrom. 1994,8,1026-1030. 

C) and leave the solid matrix very quickly. An increase in temperature does not favour their vaporisation from the matrix to the gaseous phase, but causes their desorption from the fibre to the gaseous phase, which then becomes the major process [50,51]. 

Vinten et al. (1983) demonstrated that the vertical retention of contaminated suspended particles in soils is controlled by the soil porosity and the pore size distribution. Figure 5.8 illustrates the fate of a colloidal suspension in contaminated water during transport through soil. Three distinct steps in which contaminant mass transfer may occur can be defined (1) contaminant adsorption on the porous matrix as the contaminant suspension passes through subsurface zones, (2) contaminant desorption from suspended solid phases, and (3) deposition of contaminated particles as the suspension passes through the soil. 

The electrokinetic process will be limited by the solnbUity of the contaminant and the desorption from the clay matrix that is contaminated. Heterogeneities or anomalies in the soil wiU rednce removal efficiencies. Extreme pHs at the electrodes and the may inhibit the system s effectiveness. Electrokinetic remediation is most efficient when the pore water has low salinity. The process requires sufficient pore water to transmit the electrical charge. Contaminant and noncontaminant concentrations effect the efficiency of the process. 

Effect of Modifiers on Desorption of Alkaloidal Salts from Matrix 426... 

One of these methods is called kinetic calibration, in which analyte absorption from the sample to the liquid coating (PDMS) on the fiber is related to analyte desorption from the coating to the sample. The isotropy of absorption and desorption in the kinetic calibration has been described by Chen et al.31 In kinetic calibration, also called in-fiber standardization, desorption of a radio-labeled standard (preloaded on the fiber coating) into the sample is used to calibrate the extraction (absorption/adsorption in the case of a liquid/solid coating) of analyte from the sample into the fiber. This calibration approach considerably facilitates the use of SPME for the on-site field sampling of water, where the control of flow velocity or addition of a standard to the matrix is very difficult. 

Many potential applications have been proposed which involve the desorption of solutes from matrix using SCF solvents at elevated pressure these include activated carbon regeneration [1,2,3,4,5] and soil remediation [6,7,8] using supercritical carbon dioxide. 

If the most important determining step of the rate is the diffusion across the internal volume of the sample, the rate of extraction will be dependent upon the size of the particles contained in the sample. A pulverization will consequently increase the rate of extraction. The desorption from the surface of the matrix, as well as the diffusion across the boundary layer on the surface of the sample, can be significantly improved by adding a polar modifier such as MeOH. ... 

In preparation for the experiments, the library components were removed from the bead by exposing it to trifluoroacetic acid vapor for 30 min. After the cleavage reaction was complete an internal standard was added together with the matrix solution for the laser desorption. The matrix was formed around the bead within 15-30 min and MALDI-TOF analysis was performed directly from the sample well. Results are shown in Fig. 4 where a variety of peptides was monitored in addition to bradykinin, which acted as the internal calibrant. As for all MALDI experiments, it was critical that the right matrix be chosen for the analysis. After initial examinations of different matrices under a stereo microscope followed by the MALDI-TOF experiment, dihy-droxy-benzoic acid (DHP) was found to produce the largest crystals and the best results. 

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