Abstract
In an equilibrium system, there are some chemical species to be separated unsatisfactorily. Accordingly, in order to study the chemical species in such an equilibrium system, it is necessary to determine them without separation.
This paper describes a method whereby the absorption spectra and the concentration of the chemical species in an equilibrium can be evaluated without separation by complementary tristimulus method. (CTSmethod)
For this purpose, Qr and E which are the important parameter of the CTS-method are obtained by a graphical method and by a calculation, respectively.
In CTS-method, absorption spectra are divided into three portions which are named " range ". A series of absorbance are measured at a regular mμ interval in each of the three ranges, and the sum of the absorbance in each range is represented by U, V or W, respectively, and the total amount of U, V and W is represented by J.
Qr is the generic name of Qu, Qv and Qw and corresponding to U/J, V/J and W/J, respectively. E equals to J of 1 mol solution. Qr of a chemical species in an equilibrium, can be obtained from the Qr plot in which two kinds of Qr among three are coordinates of a point on the graph, and its value could be determined from the intersection of the two lines which represent two chemical dissociation in succession.
The values obtained by this graphical method agree well with those obtained by a complicated mathematical maticel, method.
To determine the analytical concentration of A and B by CTS-method in a two components equilibrium system in which the component A is satisfactorily, separable but B is not, the values of Qra, Qrb, Eb and Eb must be known either by measurement or calculation.
Here, Qra, Qrb, Ea and Eb represent Qr and E of A and B, respectively.
The values of Qra and Ea can be obtained from the solution of its pure component, and that of Qrb from the graphical method mentioned above. The value of Eb is calculated from the following equations by substituting the values of Qra, Qrb and Ea into them.
Um = Qua·Ea·Ca+ Qub·Eb·Cb
Vm =Qva· Ea· Ca+Qvb· Eb·Cb
Wm =Qwa· Ea·Ca+ Qwb·Eb·Cb
Um, Vm and Wm represent the sum of the absorbance of the mixture in the u-range, v-range and w-range, respectively, and Ca and Cb the analytical concentration of A and B component, respectively, and the sum of them are always constant.
Qua, Qva and Qwa are the values of Qra in the u-range, v-range and w-range, and Qub, Qvb and Qwb are that of Qrb in the corresponding ranges.
By this method, it is possible to determine a series of dissociation constants of colorants and molar fraction of mixture of two kinds of colorants.
