錯形成反応を利用した光度滴定へのコンプリメンタリートリスティミュラス法の応用

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The photometric titration is sensitive and accurate technique in the chelatometry, but in more dilute solution there are some problems to be resolved as described below. Considering the effects of a series of dissociations about the formed complexes, the exact equivalance point must be found stoichiometrically in dilute solution. The end point of titration must be decided without the theoretical error. The volume of sample solution in the course of titration must be corrected. The wavelength in which absorbances are measured without interferance from other chemical species must be selected. In order to eliminate the influence of dissociations about complexes, the titration was carried out under the excess and definite amount of titrant. Moreover, applying complementary tristimulus colorimetry (CTS method) to the photometric titration, we attempt to resolve the problems about the decision of the end point, the correction of volume and the selection of wavelength for measurement of absorbances without interferance of the other chemical species. In CTS method, absorption spectra are divided into three portions so as to represent their properties sufficiently, and the portions are named u, v and w range. In Cu(II)-PAN system, u, v and w range are settled on 420465 nm, 470515 nm and 520565 nm respectively. A series of absorbances are measured at a regular wavelength interval in each of three ranges and the sum of absorbances are represented by U, V and W respectively, and then the total sum of U, V and W is represented by J. Qu, Qv, and Qw are corresponding to U/J, V/J and W/J respectively, and Qr is the generic name of Qu, Qv, Qw and them. If two kinds of colored component a and b, are formed. in a titration, Qr-plot in the course of titration is represented in a graph where two kinds of Qr among three are coordinate, as a straight line connecting two fixed points Qra and Qrb. In the graph Qra and Qrb are Qr of the pure colored components a and b respectively, and molar fraction (q) of a in any state (m) of the titration can be evaluate from equation represented below. q=Eb(Qrb-Qrm)/Ea(Qrm-Qra)+Eb(Qrb-Qrm) Where Ea and Eb are sums of absorbances measured. at a regular wavelength interval with unit concentration of a and b respectively. In a state of chemical equilibrium M +L_??_ML, material balances of metal (M) and titrant (L) are shown as CM=[M]+[ML] and CL=[L]+[ML], and the conditional stability constant of ML complex is KML=[ML]/[M]·[L]. When two kinds of colored component are [L] and [ML] in the system, molar fraction is represented by q=[L]/([L]+ [ML]). Then total amount of metal (CM) can be derived as follow, CM=(1-q)(1/q·KML+CL) When an excess and definite amount (CL) of titrant is added and q is evaluated by CTS method, CM can be determined from the equation if KML is known previously. If KML is not known, the equation involving CL1, CL2 CM, q1 and q2 can be derived as follows. CM=(1-q1)
社団法人日本分析化学会の論文

錯形成反応を利用した光度滴定へのコンプリメンタリートリスティミュラス法の応用

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錯形成反応を利用した光度滴定へのコンプリメンタリー トリスティミュラス法の応用

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錯形成反応を利用した光度滴定へのコンプリメンタリートリスティミュラス法の応用