V O L U M E 2 4 , N O . 1, J A N U A R Y 1 9 5 2
_-
+
-~
f i e uency approaches ( 1 / 2 x ) d , ( C 1 C2)/LClC2. I n the intermeliate regions, where the two impedances are the same order of .magnitude, the frequency varies nionotonically with concentration between these two limits The equivalent circuit of Figure 2 explains quantitatively data obtained with both kinds of instruments. The concentration corresponding to maximum absorption may be derived as a function of frequency from the circuit of Figure 2, and the relation is the same as that obtained using Falkrnhagen’s equation for the rela\;:ition time of ionic solutions APPLlCATION TO TITRATIONS
A desirable situation exists when an unloading of the oscillator takes place during titration ( 4 ) due to the formation of un-ionized or insoluble substances, follo\ved liy an increase in loading caused by :in excess of titrating agent beyond the end point. The choice of the titrating agent which produceE an insoluble substance frequently presents problems, in that the precipitate must be quickly :tiid quantitatively fornied and must show low ahsorption properties. Many oscillating circuits :ire not respousive t o clianges in heavily loading solutions, whem the ion concentrations are high, as i n niarine maters. Modificatioiis m:ty he niade so that the response varies linearly with c*onc.ciitr:rtionin these cases, The titration of c:~lciumn.ith st:tiid:~i~(lsoap solution vas disAlso presented were preliminary data on the saponification of ethyl acetate t o shovi the feasibility of following r e a d o n rates by the high frequency method. Readings of concentration changes nixy be made instantaneouply as reactmionproceeds. APPLICABILITY O F HIGH FREQUENCY METHODS TO ORGANIC S Y S T E M S
1Iaiiy organic solutions do not sholv the decreasing sensitivity nit11 increasing concentratioti th:rt ionic. solutions do ( I , 2 ) . For
199
such noncouducting solutions, where the impedance of R is always much greater than that of Cp, examination of Figure 2 shows that the response is inherently simpler than that of conducting systems, for all changes are essentially capacitive. If the particular instrument, temperature, and volume of solution are held constant, the frequency change upon insertion of any particular substance is a fixed property of that substance, and is measurable (1). This property, called the frequency change, may he handled in the course of analysis as though it were additive for ideal solutions. Ideality and a linear response are not necessary for analysis, however (1, 2 ) . By use of a working curve, it is possible t o determine the lvater content of alcohol (1). The composition oi‘ o-xylene in p-xylene may be determined with an accuracy of 1% (1). Even ternary systems may be so analyzed .4n example is ~vater-benzene-methyl ethyl ketone. The frequency change upon removal of water by almorption in calcium chloride is dependent only upon the water content, and independent of the benzenemethyl ethyl ketone ratio. The remaining binary system is analyzed as described above (1). By forming a condenser of two semicircular plates wrapped around the bottom of a chromatographic adsorption column, the high frequent>- method ma^ be used to detect the passage of colorless substances down the column. Solutions of aniline, acetone, phenol, ethanol, and methanol were consecutively developed on the same Fluoroqil column (1). REFERENCES
(I) Burkhalter, T. S.,reported i r i meeting. 12) Elving, P. J., Flom. D. G . , and Coleman .\, I . , reported i n meet-
ing. (3) Hare, George, reported iri meeting. (4) Jensen, F IT., reported in meeting. ( 5 ) Jensen, F. K,, and Parrack, A . I,., 1x1).1,:si:.C’tIE>f.3 .-IN.
