Reference values transferability

Standardizing the predicted values is a simple, useful choice that ensures smooth calibration transfer in situations (a) and (b) above. The procedure involves predicting samples for which spectra have been recorded on the slave using the calibration model constructed for the master. The predicted values, which may be subject to gross errors, are usually highly correlated with the reference values. The ensuing mathematical relation, which is almost always linear, is used to correct the values subsequently obtained with the slave. 

ADDITIONAL TOPICS Transferability of Reference Values The determination of refiable reference values for each test in the laboratory s repertoire is a major task and is often far beyond the capabilities of the individual laboratory. It would therefore be convenient if reference values generated in another laboratory could be used. This is especially important when ethical considerations limit the number of available individuals (e.g., when producing pediatric reference values). Then, cooperative establishment of reference values may be necessary. 

A major prerequisite for transfer of reference values is that the populations be homogeneous (i.e., there should be no major ethnic, social, or environmental differences among them). 

The verification of transferred reference values or intervals is both important and problematic. The comparison of a locally produced, small subset of values with the large set produced elsewhere using traditional statistical tests often is not appropriate because the underlying statistical assumptions are not fulfilled and because of the unbalanced sample sizes. Alternative methods using nonparametric tests or Monte Carlo sampling have been described. 

International Federation of Clinical Chemistry, Expert Panel on Theory of Reference Values. Approved recommendation on the theory of reference values. Part 1. The concept of reference values. J CUn Chem Clin Biochem 1987 25 337-42 Part 2. Selection of individuals for the production of reference values. J Clin Chem Clin Biochem 1987 25 639-44 Part 3. Preparation of individuals and collection of specimens for the production of reference values. J Clin Chem Clin Biochem 1988 26 593-8 Part 4. Control of analytical variation in the production transfer and application of reference values. Eur J CUn Chem Clin. Biochem 1991 29 531-5 Part 5. Statistical treatment of collected reference values Determination of reference limits. J Clin Chem... 

In addition, for value transfer, multiple weight-corrected dilutions of the reference (e.g., CRM 470) and the target material should be assayed in multiple runs, with the dilutions of each material calculated to be within the same section of the assay range. If possible, for optimal results, one material should be used as the cafibrator and the other as the test sample to avoid the introduction of a third material and increased imprecision. ... 

In this expression, a represents the transfer coefficient (assumed to be equal to 0.5) and i is the dimensionless initial concentration (in this example equal to 1.0). The symbols Cw and w represent the concentration and the potential at the catalyst wall, respectively. The boundary conditions for the potential include a reference value at X = 0, and Ohm s law at the catalyst wall. These expressions along with the continuity of potential at distances far from the reaction site are represented as follows ... 

It has been demonstrated that the partial-transfer velocities, and k, can be estimated in terms of reference values obtained by experiment. Extensive studies of the evaporation of water have shown that, under static conditions, fea = 0.3 cm s, which would give a value of 0.9 cm for Za, given for water in air is... 

Values for Da and D can also be estimated in terms of reference values for water in air and oxygen in water (Dx = Dref[MWref/MWx] ). The exponents have been estimated from experimental observations. It is now possible to estimate evaporation rates under static conditions by first estimating molecular diffusion coefficients, deriving values for the partial transfer velocities and calculating fctot-The data summarized in Table 4.6 use some laboratory observations listed in Tables 4.3-4.5 to evaluate this model. Reasonable agreement is observed between the calculated and observed values, considering possibilities for experimental error and uncertainties in the values for Henry s law constant, and so on. 

Any cell reaction can be considered to be an electron transfer between two coupled half-cells. The measured potential corresponds to the difference of the electron energy. The arbitrary definition of a reference electrode raises the question of whether the electrochemical potential scale can be correlated with energy scales of electrons in surface physics. If measuring work functions or electron affinities, the reference value is the free electron in vacuum. Mehl and Lohmann calculated for the electron affinity of a hydrogen electrode —4.5 eV using the following Bom-Haber process... 

As mentioned previously, molecular mechanics force fields use redundant internal coordinates. In a tetrahedrally coordinated center such as Si04, all six bond angles Aa, , Aog are used, but only five of them are independent. Thus correlations exist between the force constants and the reference values of the coordinates, and this poses a problem in the fitting process because there is no unambiguously optimal set of parameters. Hence, parameters fitted to redundant coordinates may not be transferable and also may lack a well-defined physical meaning. 

ELDAR contains data for more than 2000 electrolytes in more than 750 different solvents with a total of 56,000 chemical systems, 15,000 hterature references, 45,730 data tables, and 595,000 data points. ELDAR contains data on physical properties such as densities, dielectric coefficients, thermal expansion, compressibihty, p-V-T data, state diagrams and critical data. The thermodynamic properties include solvation and dilution heats, phase transition values (enthalpies, entropies and Gibbs free energies), phase equilibrium data, solubilities, vapor pressures, solvation data, standard and reference values, activities and activity coefficients, excess values, osmotic coefficients, specific heats, partial molar values and apparent partial molar values. Transport properties such as electrical conductivities, transference numbers, single ion conductivities, viscosities, thermal conductivities, and diffusion coefficients are also included. 

To validate the standardization parameters, independent samples should be measured in the prediction step. Depending on the retained approach, either the resulting spectra should be transferred, or the transferred calibration model should be applied to the spectra. Standardized predictions are obtained and these predictions must be compared either with the reference values (this implies that the standardization samples have been analyzed by the reference method), or with the predictions obtained in the calibration step (this implies that the standardization samples have been measured in the calibration step). This procedure verifies the standardized predictions are in good statistical agreement with either the reference method or the original calibration model. 

The metal-like orbital in the reduced species, M, is expected to be more diffuse than M or M (e.g., due to radial atomic orbital expansion)23, Accordingly, we may generally expect the unconstrained result for Hif in eq 14 to be larger in magnitude than the 1-electron reference value (eq 16), since the anticipated increase in magnitude of the 1-electron transfer integral, hj4 j4j. enhanced spatial... 

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