Titration, deducing stoichiometry

The chemical compositions of the samples, obtained from chemical analyses are reported in Table 1. In order to check the chemical analyses, the mother and washing liquors were collected, analysed and their acidity was titrated. In all cases, the alkaline cations were detected only as traces. The acidimetric titration allowed us to determine the HPA amount remaining in the solution. On the other hand, the samples separated after precipitation and washings were weighted in order to calculate the precipitate yields. The results are reported in table 1 where the samples are designated as MxY (M being the alkaline or ammonium cation, Y the heteroatom, x the stoichiometry deduced from chemical analyses. 

A stock solution of trypsin (Sigma T-8642 or equivalent) is first standardized using the substrate p-nitrophenol-p -guanidobenzoate HCl (Sigma N-8010). By the initial burst principle (5) one can titrate the active site of trypsin and c culate the uM amount of active trypsin introduced into the rSLPI inhibition assay. By knowing the molecular weight of the trypsin (source dependent) the uM amount of rSLPI present can be deduced from the 1 1 stoichiometry of the reaction. 

Stearic acid titration is performed by a potentiometric method in dimethylformamide and in the presence of tetra-n-butyl ammonium hydroxide (7). The consumption of carboxylates vs. time is deduced from chloride and stearic acid titration according to the stoichiometry of Reaction 1 where Me is Zn or Ca and R is the stearic group. 

From titration of solutions b) and c), the author deduced the existence of the species Zr2(OH)) and Zr(OH)4 and their corresponding stability constants from the potentiometric equivalence points corresponding to the neutralisation of 1.5 and 2 protons per Zr atom. However, the stoichiometry of these species can only be deduced from these data if the speciation of Zr in the initial solution is known. Uncertainties in the speciation of the initial solution result in equivalent uncertainties in the stoichiometries of the observed hydrolysis reactions. For example, in case of tetramer formation, titration end point data could equally well be explained by formation of and Zr4(OH)i6(aq). 

Titration curves for rosmarinic acid in (he presence of different concentrations of iron ions indicate a stoichiometry of 1 to 1 for the complex. These data were confirmed by elemental analysis and inductively coupled plasma emission spectrometry (70. This 1 to 1 complex seems to be the only absorbent species in the reaction media. Support of this assertion come from graphical analysis of the consecutive spectra according to Coleman et al. (Jd) and from HPLC analysis of the reaction media (Figure 6). From this figure, it can also be deduced that, under the assay conditions, almost all rosmarinic acid is forming part of the complex, since absorbance at 333 nm for the expected retention time of rosmarinic acid is very low. 

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