Relative Methods

A certain analytical method has a relative sampling variance of 0.40% and a relative method variance of 0.070%. Evaluate the relative error (a = 0.05) if (a) you collect five samples, analyzing each twice and, (b) you collect two samples, analyzing each five times. 

As expected, since the relative method variance is better than the relative sampling variance, a sampling strategy that favors the collection of more samples and few replicate analyses gives the better relative error. 

Gel permeation chromatography (GPC) or size exclusion chromatography (SEC) has been routinely used to estimate die molecular weight of die polymers. The molecular weight measured by GPC is relative to a polymer standard, typically polystyrene GPC is dius a relative method rather than an absolute one. For those polymers whose structure is very different from polystyrene, GPC molecular weight values could significantly differ from the real ones. In those cases, GPC values should only be regarded as a reference. 

The experimental approaches described above are examples of relative methods, wherein a thermochemical property is measured with respect to that of a standard, or an anchor. The quality of these measurements ultimately depends on the quality of the anchor. Alternatively, there are methods of determining thermochemical properties, in which the energy for a chemical process is measured on an absolute basis. Among the more common of these are the appearance energy measurements, in which the threshold energy for formation of an ionic fragment from an activated precursor is measured. There are mauy differeut methods of activation that can be used. Some of these are discussed here. 

The parameter c can be easily determined by using viscometric measurements, which yield a relative number, or by performing, for example, light scattering measurements, which yield absolute values of c. Viscometric measurements are most commonly used because results are obtained quickly. However, this relative method is not equivalent to the absolute value of c LS and only absolute determination methods such as light scattering result in correct values of c. ... 

Demonstrating equivalence of the two approaches does not infer that one is right and the other wrong. One of the unique attributes of dissolution analysis is that there is no right or wrong approach as long as tests can be validated. It is a relative method that is a function of the apparatus and... 

Relative Methods solution viscosity, melt viscosity, size-exclusion chromatography... 

Knowledge of the molecular weight and of the molecular-weight distribution of a polymeric material is indispensable for scientific studies as well as for many technical applications of polymers. They effect the solution and melt viscosity, the processability, and the resulting mechanical properties tremendously. Therefore, we will give a short introduction into methods that allow us to determine the required information. Roughly, the methods developed for the determination of molecular weights are subdivided into absolute and relative methods ... 

Relative methods measure properties that depend clearly on molecular weight, for example, the hydrodynamic volume of the polymer coils (GPC, vis-cosimetry) or their solubility as a function of chain length. However, these measurements can only be evaluated with respect to the molecular weight of the mac-... 

The architecture of hypeibranched polymers and dendrimers is connected with difficulties in determining molar mass. Many of the common characterization techniques—e.g. size exclusion chromatography (SEC)—used for polymers are relative methods where polymer standards of known molar mass and dispersity are needed for calibration. Highly branched polymers exhibit a different relationship between molar mass and hydrodynamic radius than their linear counterparts. 

In addition to the relative method, Harkins and Jura have also developed an absolute method for surface area measurement which is independent of... 

GPC is a relative method, especially for UV and refractive index (RI) detectors, and must be calibrated using polymer standards whose molecular weight has been determined using absolute methods such as intrinsic viscosity or light scattering. Consequently, the accuracy is relative to the calibration. 

Absolute determinations of V are extremely difficult. For routine measurements relative methods have been worked out29 31, in which the experimental material is compared directly with a standard liquid ([Pg.58]

Meyer HW (2001) A review of the paleoelevation estimates from the Florissant flora, Colorado. In Fossil Flora and Stratigraphy of the Florissant Formation, Colorado. Evanoff E, Gregory-Wodzicki KM, Johnson KR (eds) Proc Denver Museum Nature Sci ser 4 no 1 p 205-216 Mosbrugger V (1999) The nearest living relative method. In Fossil Plants and Spores Modern Techniques. Jones TP, Rowe NP (eds) Geol Soc London, p 233-239... 

Mass spectrometry MALDI-MS (also high generations), ESI-MS, and FAB-MS (low generations) relative methods... 

SEC relative method non-availability of suitable size standards can frequently lead to inaccuracies... 

Compared to the simplicity of the relative method, with its simple measurement equation, there is a hidden complexity in the k0 method complex algorithms, dedicated software for reactor neutron fluxes and gamma ray measurement efficiency and many problems associated with spectrum deconvolution. The method relies on a complex set of written standards which are not always fully understood by the average user. It uses non-transparent instrumentation and measurement processes. In short the method becomes, forgive the terminology, non-traceable to the user and this is, I believe, worse than non-traceable to SI units. 

Determination of the amount of substance is thus in direct relation to basic units of the SI system and does not need a RM for comparison. The Faraday constant is one of the fundamental constants (it can be expressed as the product of the electron charge and the Avogadro constant). It enables the attainment of high precision and accuracy and is independent of the atomic weights of the elements in the sample. Its drawback is lower selectivity, a feature common to titration methods. This makes coulometry especially suitable for determination of relatively pure substances used as standards by other (relative) methods. The Faraday constant has been proposed as an ultimate standard in chemistry [3],... 

Strictly speaking gravimetry belongs to the relative methods. The only difference is in the position of the RM in the measurement process the weighed product itself serves as an RM - usually with the a priori assumption, that its purity is 100% and stoichiometry is correct. The mass fraction of the weighed substance should be taken into account in the equation used. Problems associated with the formation of solid phase [4], e.g. surface adsorption effects (ionic species and water [5]) are significant in analyses aiming at relative uncertainties at about 10 4. 

The situation is seldom favourable enough to enable the use of a single method for establishing a link to the SI system. The information on the content of impurities (by means of relative methods) is needed in most cases. Except for coulometry, determination of molar weight... 

The major products of the photolysis of glycolaldehyde are HCHO and CO, methanol and OH production was also observed. Photolysis of glycolaldehyde was used as the OH source to measure the reaction rate constants of OH with a series of dienes by the relative method and to identify and quantify the oxidation products of the OH-initiated oxidation of propan-2-ol. HCHO is observed to be the major product of the OH-initiated oxidation of glycolaldehyde. The results indicate that the OH reaction and photolysis can compete as tropospheric sinks for glycolaldehyde.218... 

Relative methods By comparing signals from analytes in die model sample and in die examined sample die calibration stage is necessary... 

The factors which influence the reproducibility of retention in HPLC have been studied [55]. The conclusion is that the relative method of re-... 

The kinetic method [42,43] is a relative method for thermochemical data determination which is based on measurement of the rates of competitive dissociations of mass-selected cluster ions. This method was introduced by Cooks [44] for proton affinity determination. Later, an extension of this method was proposed by Fenselau [45]. 

Gaschromatographie GC-Retentionsdaten auf unpolaren Trennphasen, relative Methode... 

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