Analytical Matrices Research Articles

Azide determination in protein samples by ion chromatography

Sodium azide is used as an anti-fungal agent in protein samples in the health related scientific community. Due to its toxic nature, monitoring of the azide level in proteins utsed in scientific research is necessary. Ion-exchange chromatography has been used to quantitate azide levels in protein samples. Anion-exchange methodology is described which allows for the separation of azide from various common anions found in analytical grade protein matrices. The analytical system described utilizes a polymer [Poly(styrene—dinivylbenzene)] stationary phase which has been surface sulfonated followed by the binding of the aminated latex bead active ion-exchange sites (Dionex, AS4A column). Sodium tetraborate is used as the weak anion-exchange mobile phase. A vendor ion-exchage column comparison is made along with eluent composition and selection studies. Method validation data are presented including: calibration plots for external standardization, limit of detection and method recovery. Various types of proteins are assayed using the described method.

Optical fibre chemical sensors

Optical fibre chemical sensors permit the determination of a wide range of anions, cations, gases and organic compounds in solution or gas phases. For in-line operation in complex or aggressive mixtures the requirements of selectivity, sensitivity, longevity and reproducible response impose great demands on the sensor reagents and protective membrane system. These demands will be alleviated by preceding the sensors with sample pretreatment and separation procedures and permit the best exploitation of their characteristics. For simpler analytical matrices, or those which are largely unchanging, tailored sensors provide a very useful means of specific determination. There is a clear need for high sensitivity and high selectivity of the reagent over as wide a range of conditions as possible — a demanding requirement.

The effects of post-seismic motions on the moment of inertia of a stratified viscoelastic earth with an asthenosphere

Summary. We give the analytical formulation for calculating the transient displacement of fields produced by earthquakes in a stratified, selfgravitating, incompressible, viscoelastic earth. We have evaluated the potential of viscous creep in the asthenosphere in exciting the Chandler wobble by a four-layer model consisting of an elastic lithosphere, a two-layer Maxwell viscoelastic mantle, and an inviscid core. The seismic source is modelled as an inhomogeneous boundary condition, which involves a jump condition of the displacement fields across the fault in the lithosphere. The response fields are derived from the solution of a two-point boundary value problem, using analytical propagator matrices in the Laplace-transformed domain. Transient flows produced by post-seismic rebound are found to be confined within the asthenosphere for local viscosity values less than 1OZoP. The viscosity of the mantle below the low-viscosity channel is kept at 1OZ2P. For low-viscosity zones with widths greater than about 100 km and asthenospheric viscosities less than lOP, we find that viscoelasticity can amplify the perturbations in the moment of inertia by a factor of 4-5 above the elastic contribution within the time span of the wobble period. We have carried out a comparative study on the changes of the inertia tensor from forcings due to surface loading and to faulting. In general the global responses from faulting are found to be much more sensitive to the viscosity structure of the asthenosphere than those produced from surface loading.

Improvement of a Large Analytical Model Using Test Data

A method has been developed which uses measured normal modes and natural frequencies to improve an analytical mass and stiffness matrix model of a structure. The method directly identifies, without iteration, a set of minimum changes in the analytical matrices which force the eigensolutions to agree with the test measurements. An application is presented in which the analytical model had 508 degrees of freedom and 19 modes were measured at 101 locations on the structure. The resulting changes in the model are judged to be small compared to expectations of error in the analysis. Thus, the improved model is accepted as a reasonable model of the structure with improved dynamic response characteristics. In addition, it is shown that the procedure may be a useful tool in identifying apparent measured modes which are not true normal modes of the structure. Nomenclature - analytical matrix = matrix of changes = identity matrix = full improved stiffness and mass matrices (n x n) = full analytical K, M matrices (n x n) = partitions of KA,MA corresponding to test coordinates = partitions of KA,MA corresponding to coupling elements = partitions of KA,MA corresponding to unmea- sured coordinates = number of measured modes = number of degrees of freedom in the model = measures of changes, Eqs. (15-17) = matrix norm, sum of the squares of all the elements = rectangular modal matrix, normalized (n x m) = /th mode, /th column of $ = measured and unmeasured partitions of ,- = diagonal matrix of measured natural frequencies (m xm) = natural frequency of /th mode = 12 17 = sum of the squares of all elements of matrix ( )