Reference values ‘standards

Table 3.7 Values of pH(RVS) for the reference value standard of 0.05 mol kg-1 potassium hydrogen phthalate at various temperatures... 

P. R. Mussini,T. Mussini, and S. Rondinini, Reference value standards and primary standards for pH measurements in D2O and aqueous-organic solvent mixtures New accessions and assessments. Pure Appl. Chem. 69 (1997), 1007-1014. 

Operational standards (OS) are also defined which are traceable to the Reference Value Standard (RVS). Values are assigned by means of the operational cells I and II where the Uquid junctions are the free diffusion type reproducibly formed in 1 mm vertical capillary tubes. These operational standards are not restricted in number provided certain preparation criteria are met, and pH(OS) values for 16 solutions are given in Table 4. These OS represent an alternative procedure and are in no way to be regarded as inferior to the primary standards. As a consequence of their definition, all pH(OS) values fall on the line with slope given by the slope factor value forthe appropriate temperature in Table 1. Any ddference in liquid junction potential between the solutions of cells I and II and KCl is subsumed into the assigned value of pH(OS). 

D normalized standard deviation given by d=(x-u)i(suifn), X average value of three independent measurements, U reference value, su reference value standard deviation and n square root of the number of independent measurements. 

Table 8.17 Standard Reference Values pH for the Measurement of Acidity in...

B is the potential of the reference electrode, without whose identification the potential U is undefined. Potentials are conveniently calculated against a standard reference value. Section 3.2 contains further details on reference electrodes and conversion factors. Section 3.3 describes practical methods for measuring potential in the case of flowing currents. 

Primary calibration standard A calibration standard based on direct measure of a reference value. 

C 0.5012 mol 2 at 15°C). It is clearly unwise to associate a pH meter reading too closely with pH unless under very controlled conditions, and still less sensible to relate the reading to the actual hydrogen-ion concentration in solution. For further discussion of pH mea.surements, see Pure Appl. Chem. 57, 531-42 (1985) Definition of pH Scales, Standard Reference Values, Measurement of pH and Related Terminology. Also C E News, Oct. 20. 1997. p. 6. 

One form of comparative analysis is direct comparison of the acquired data to industrial standards or reference values. The International Standards Organization (ISO) established the vibration severity standards presented in Table 43.2. These data are applicable for comparison with filtered narrowband data taken from machine-trains with true running speeds between 600 and 12,000 rpm. The values from the table include all vibration energy between a lower limit of 0.3x true running speed and an upper limit of 3.0X. For example, an 1800-rpm machine would have a filtered narrowband between 540 (1800 x 0.3) and 5400rpm (1800 x 3.0). A 3600-rpm machine would have a filtered narrowband between 1,080 (3600 x 0.3) and 10,800rpm (3600 x 3.0). 

Three types of reference-value comparisons are used to evaluate trend data baseline data, rate of change, and industrial standards. 

The IUPAC definition of pH39 is based upon a 0.05M solution of potassium hydrogenphthalate as the reference value pH standard (RVS). In addition, six further primary standard solutions are also defined which between them cover a range of pH values lying between 3.5 and 10.3 at room temperature, and these are further supplemented by a number of operational standard solutions which extend the pH range covered to 1.5-12.6 at room temperature. The composition of the RVS solution, of three of the primary standard solutions and of two of the operational standard solutions is detailed below, and their pH values at various temperatures are given in Table 15.4. It should be noted that the concentrations are expressed on a molal basis, i.e. moles of solute per kilogram of solution. 

A variety of procedures can be used to determine Z, as a function of composition.2 Care must be taken if reliable values are to be obtained, since the determination of a derivative or a slope is often difficult to do with high accuracy. A number of different techniques are employed, depending upon the accuracy of the data that is used to calculate Z, and the nature of the system. We will now consider several examples involving the determination of V,- and Cpj, since these are the properties for which absolute values for the partial molar quantity can be obtained. Only relative values of //, and can be obtained, since absolute values of H and G are not available. For H, and we determine H, — H° or — n°, where H° and are values for H, and in a reference or standard state. We will delay a discussion of these quantities until we have described standard states. 

Alcohol sulfates commonly have free alcohol and electrolytes as impurities. Other hydrophobic impurities can also be present. A method suitable for the purification of surfactants has been proposed by Rosen [120]. Consequently, commercial products have CMCs that deviate from the accepted reference values. This was demonstrated by Vijayendran [121] who studied several commercial sodium lauryl sulfates of high purity. The CMC was determined both by the conductimetric method and by the surface tension method. The values found were similar for both methods but while three samples gave CMC values of 7.9, 7.8, and 7.4 mM, close to the standard range of 8.0-8.2 mM, three other samples gave values of 4.1, 3.1, and 1.7 mM. The sample with a CMC of 7.9 mM was found to have a CMC of 8.0 mM with no detectable surface tension minima after purification and recrystallization. This procedure failed in all other cases. 

Mixed solvent systems containing water are included below even in case water is only a minor constituent. Details are given only if relevant for the stated value of she-All data refer to standard (room) temperature T = 298 K if not stated otherwise. 

To do this, one particular half-reaction has to be selected as a reference reaction with zero potential. Once a reference half-reaction has been selected, all other half-reactions can then be assigned values relative to this reference value of 0 V. This is necessary because an experiment always measures the difference between two potentials rather than an absolute potential. The standard potential of 1.10 V for the Zn/Cu cell, for example, is the difference between the E ° values of its two half-reactions. 

Defining a reference value for the SHE makes it possible to determine E ° values of all other redox half-reactions. As an example. Figure 19-14 shows a cell in which a standard hydrogen electrode is connected to a copper electrode in contact with a 1.00 M solution of C U . Measurements on this cell show that the SHE is at higher electrical potential than the copper electrode, indicating that electrons flow from the SHE to the Cu... 

Many calculations using Equation refer to standard temperature, 298.15 K. Furthermore,. eq often has a very large or very small value that is expressed using power-of-ten notation. For such values, calculations using the logarithm to base 10 (log) rather than In are more convenient log X-2.302 585 In X. We can substitute these values and the value for F and then evaluate the multiplier for the log term at standard temperature ... 

The National Institute of Standards and Technology (NIST) released certified standard materials of a baby food composite (SRM 2383) and an infant formula (SRM 1846) containing carotenoids however, the relative uncertainties of certified values are considerably high, ranging Irom 20% for P-carotene (cis + trans) to 28% for lutein (including esters) and to a 47% for free lutein reference value in SRM 2383. ... 

Thus, in order to improve the behavior of the parameter estimates, Watts (1994) centers the temperature factor about a reference value T0 which was chosen to be the middle temperature of 375°C (648 K). The parameters estimates and their standard errors are given in Table 16.19. 

Now the origin of the scale must be defined, i.e. a pH value must be selected for a standard (as close as possible to the value expected on the basis of definition 1.4.46). A solution of potassium hydrogen phthalate with a molality of 0.05 mol kg-1 has been selected as the reference value pH standard (RVS). 

Covington, A. K., R. G. Bates and R. A. Durst, Definition of pH scales, standard reference values, measurement of pH and related terminology, Pure Appl. Chem., 57, 531 (1985). 

QCC contain - as quality target values Q - standard or reference values, x0, resp. optimum values as well as their limits. The inner pair of limits are called warning limits and the outer pair control limits (action limits). When... 

Comparison of test values with a conventional true value ( reference value ) of a (certified) reference material (RM, CRM). In method development and validation of analytical procedures, the comparison of experimental results with standards of diverse kind (laboratory standards, certified reference materials, primary standards) plays an essential role. The decision as to whether an experimental result hits the reference value depends not only from the result itself but also from its uncertainty interval. 

In case (i), the comparison of an experimental result, xexp, with the reference value, xRM, of a high quality standard is simply carried out by a specified f-test according to Eq. (4.45) ... 

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