Relative basicity, calorimetry

Several collaborating laboratories (usually five participating laboratories) test the proposed substance using a variety of techniques. The relative reactivity or relative absorbance of the impurities present in a substance must be checked when a nonspecific assay method is employed, e.g. by colorimetry or ultraviolet spectrophotometry. It is particularly important to quantify the impurities when a selective assay is employed. In such a case, it is best to examine the proposed substance by as many methods as practicable, including, where possible, absolute methods. For acidic and basic substances, titration with alkali or acid is simple but other reactions which are known to be stoichiometric may be used. Phase solubility analysis and differential scanning calorimetry may also be employed in certain cases. 

Nowadays, for a thermodynainicist, /pVT-calorimetry (further referred to as scanning transitiometry, its patented and commercial name ) is the most accomplished experimental concept. It allows direct determinations of the most important thermodynamic derivatives it shows how, in practice, the Maxwell relations can be used to fully satisfy the thermodynamic consistency of those derivatives. Of particular interest is the use of pressure as an independent variable this is typically illustrated by the relatively newly established pressure-controlled scanning calorimeters (PCSC). - Basically, the isobaric expansibility Op(p,T) =il/v)(dv/dT)p can be considered as the key quantity from which the molar volume, v, can be obtained and therefore all subsequent molar thermodynamic derivatives with respect to pressure. Knowing the molar volume as a function of p at the reference temperature, Tg, the determination of the foregoing pressure derivatives only requires the measurement of the isobaric expansibilities as... 

In the previous sections, the basic principles of the PN-N transition in LCEs and the experimental techniques were introduced to the reader. The issue of a smeared criticality observed in LCEs was introduced in Sect. 4. In this section, the experimental results providing an insight for the understanding of the PN-N transition are presented. These data were obtained by deuteron NMR and ac calorimetry on side-chain and main-chain LCEs. The distinct role of each parameter that affects the critical behaviour of the PN-N phase transition of LCEs will be demonstrated in different subsections. These parameters influence the relative strength of the locked-in mechanical field G and, as demonstrated in the previous sections, they may alter the order of the PN-N transition. 

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