Measurement influence quantities

How to best describe this broadening we expect to occur One way is by analogy to random error in measurements. We know or assume there is a truly correct answer to any measurement of quantity present and attempt to determine that number. In real measurements there are real, if random, sources of error. It is convenient to talk about standard deviation of the measurement but actually the error in measurement accumulates as the sum of the square of each error process or variance producing mechanism or total variance = sum of the individual variances. If we ignore effects outside the actual separation process (e.g. injection/spot size, connecting tubing, detector volume), this sum can be factored into three main influences ... 

Molecular weight is an incorrect scientific term The numerical value being discussed, rather, is correctly known as a relative molecular mass. It is a mass, measuring a quantity of matter, not by the influence of an external gravitational field on that matter. It is a relative mass, not an... 

Surface viscosity has an important influence on the deformation of films and can also provide information about structure. Gaines [14] describes various methods of measuring this quantity. The damped torsion pendulum as developed by Langmuir and Schaefer [65] is probably the best device for making such measurements. Recent measurements of this type have been made by Buhaenko et al. [66]. Malcolm [67, 68] and Daniel and Hart [69] have carried out experiments which illustrate the important influence which viscosity has on the study of isotherms. 

The influence of the presence of an organic monolayer on the surface potential measured at the water surface can also provide interesting information. However, this information can be difficult to interpret as it depends on the dipole moments associated with both the upper and the lower ends of the molecules and also the surface double layer in the water immediately below the film. There are two different ways of measuring this quantity. Both, of course, involve a counter electrode below the water surface. 

Demonstrating, by validation, that the calculation and measurement conditions include all of the influence quantities that significantly affect the result, or the value assigned to a standard... 

Identifying the relative importance of each influence quantity - dictated by their quantitative effect on measurement results - in order to decide on the degree of control or calibration... 

The mercury coulometer has been employed chiefly for the measurement of quantities of electricity for commercial purposes, e.g., in electricity meters. The form of apparatus used is shown in Fig. 5 the anode consists of an annular ring of mercury A) surrounding the carbon cathode (C) the electrolyte is a solution of mercuric iodide in potassium iodide. The mercury liberated at the cathode falls off, under the influence of gravity, and is collected in the graduated tube Z). From the height of the mercury in this tube the quantity of electricity passed may be read off directly. When the tube has become filled with mercury the apparatus is inverted and the mercury flows back to the reservoir J . In actual practice a definite fraction only of the current to be measured is shunted through the meter, so that the life of the latter is prolonged. The accuracy of the mercury electricity meter is said to be within 1 to 2 per cent. 

Influence factor (quantity) Something that may affect a measurement result. For example, temperature, pressure, solvent, analyst. In calibration, influence quantities refer to quantities that are not the independent variable but that may affect the measurement. (Sections 4.2, 4.3, 5.3)... 

Before an analysis is performed using a particular method and instrument, there must be a measurement model, an equation that relates the quantities that are to be measured to the indication of the instrument and other influence quantities such as temperature and pressure. From this model we derive the calibration equation. Usually, the experiment is performed in such a way as to fix influence quantities and the calibration equation is determined in terms of the concentration of the measurand and some output of the instrument, which might be peak height, peak area, potential, current, absorbance, etc. A simple linear relation is... 

Influence of Feeding on the Quantity and the Composition of the Gastric Juice Secreted. — First of all, it has been established that there exists a very definite relation between the secretorial functions and the food absorbed. Thus Chigin, by measuring the quantity of gastric juice which flows after the ingestion of various foods, has found ... 

An important feature of this approach is that only the standards that realize the unit of length require a documentary chain of evidence that links to the definition of the meter. In a typical dimensional measurement, there are many influence quantities that contribute to the uncertainty associated with the end result, such as workpiece temperature and thermal expansion coefficient. If it were required that all such influence quantities themselves be metrologically traceable, then since each of the quantities depends on other quantities and so on, such a requirement would lead to an infinite regress. 

Resoles are formed in a mechanistically complex reaction dependent on the amount of catalyst, temperature, molar ratio of the starting materials, the purity of the taw materials, and the nature of the reaction vessel. A very complete study of this mechanism was published by Freeman and Lewis [75] who investigated the reaction between substituted phenols and methanal under the influence of sodium hydroxide at 30°C. The kinetics of this reaction system were exarttined by measuring the quantity of the different hydroxymethylated phenols formed as a function of concentration and reaction time. The concentration versus time profiles for the products formed in this system are shown in Figure 5. The data of Figure 5 allow the calculation of the rate constants for the formation of different methylol substituted phenols shown in equation 13. The rate constants are ... 

According to GUM, a measurement has imperfections which give rise to errors in the measurement result. A random error presumably arises from unpredictable or stochastic temporal and spatial variations of influence quantities. Although it is not possible to compensate for random error, it can usually be reduced by increasing the number of observations. Systematic error, like random error, cannot be eliminated but it too can often be reduced. Once the effect causing the systematic error has been recognized, the effect can be quantifled and a correction can be applied to compensate for the effect. The uncertainty of the result of a measurement reflects the lack of exact knowledge of the value of the measurand. 

After this step, uncertainties in influence quantities must be converted to uncertainties in the analytical results. In simple cases, when measurement equations involve one algebraic operation, the following rules apply if a quantity Xi is simply added to or subtracted from others to obtain the result y, the contribution to the uncertainty in y is simply the uncertainty u Xi) in Xi. In case of a division or multiplication, the contribution of the relative uncertainty in y, u y)/y, is the relative uncertainty u xi) jxi in Xi. These mles do not apply in compHcated cases with a... 

With the help of variance analysis, it is determined how far the variance of observed variable X can be traced back to suspected influence factors. These influence factors may be qualitative or quantitative variables. Variance analysis is based on the assumption that, in addition to data of the observed variable X, data on other suspected influence factors are also present in a measuring series, whereby these influence factors can be classified in such a way that each observed value of X can be associated to a class i. In the case of a simple variance analysis with one additional influence quantity, the following equation will result for X ... 

In a first step, influence quantities of isotope amount ratio measurements aiming at quantifying isotopic variations are discussed. In a second step, influence quantities also affecting isotope dilution measurements vill be taken into account. 

Single-collector instruments also prove very usefid for mass content determinations via isotope dilution, as carefiil estimation of all quantities that influence the uncertainty budget demonstrates that the precision on the isotope amount ratio is typically not the dominant factor for high-precision measurements. Often, the accuracy of a mass content measurement will hardly improve through the use of MC-ICP-MS instruments as other influence quantities, such as uncontrolled spectral interferences and sample inhomogeneities, typically deserve more attention. 

Clearly, further work is necessary to determine whether impurities are responsible for the prolonged emissions. The addition of limestone to a fluidized bed has no direct measurable influence on the combustion of coal so that carbon loss is independent of Ca/S ratio (Bonn and Richter, 1990). Because CO and CO2 are mostly dependent on combustion, it is expected that sorbent addition will not cause any change in the quantity of CO or CO2 emitted into the atmosphere. Further investigations are required to validate the point. 

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