Jozef Hodyl PhD Thesis - Theses - Flinders University

APPENDIX BDETERMINATION OF STOICHIOMETRY BYTHE METHOD OF CONTINUOUSVARIATIONThe method of continuous variation (or isomolar solutions) is also known as Job'smethod as it was first suggested by P. Job in 1928. 165, 246 It is popularly employed todetermine the stoichiometry of a system containing two species that are likely tointeract with one another to form a complex comprised of both species atequilibrium, for example.H n + G mH n G mThe general procedure for the method of continuous variations requires thepreparation of a series of solutions in which the total molar concentration H n + G m iskept constant while the ratio (χ) H n :G m is varied incrementally such that a fixedvolume is maintained. A range of molar concentrations is established so that0 ≤ G m /(H n + G m ) ≤ 1A measurable quantity such as the change in chemical shift ∆δ of one of theconstituent species is monitored and plotted in the normalised form χ∆δ as a functionof the χ of that species to give a curve that is commonly known as a Job's Plot,195, 197, 198Figure B.1.0.5 Maximumwhere χ G = m/(m + n)χG∆δFigure B.1m nχ GJob's Plot showing the correlation between the stoichiometry of the host-guest complexH n G m formed and the molar fraction χ of one of the constituent species, in this case theguest, G. 195, 198157