are shown in Table 111. Also shown are results obtained with ZnO which had been calcined in oxygen, and a special zinc oxide before and after calcination in oxygen. The results of this study show that Zn in ZnO can be determined in samples of 500 mg or even smaller to levels of about 10 ppm, and even lower zinc levels can be measured
if samples of 1 gram or more are available. The precision of the proposed procedure is better than 10% (relative), which at this level of impurity is usually satisfactory.
RECEIVED for review August 6, 1970. Accepted December 20, 1970.
Integral Spectrophotometric Titrations Using Eosin for the Determination of the Critical Micelle Concentration of AI kyldimethylbenzylammonium Chlorides Downloaded by UNIV OF CALIFORNIA SAN DIEGO on September 3, 2015 | http://pubs.acs.org Publication Date: May 1, 1971 | doi: 10.1021/ac60301a040
John W. Ledbetter, Jr., and James R. Bowen Department of Biochemistry, Medical Uniuersity of South Carolina, Charleston, S. C. 29401
THEFOLLOWING PROCEDURE represents an improvement over an earlier method for obtaining the critical micelle concentration of several alkyldimethylbenzylammonium chlorides ( I ) . In the spectrophotometric dye method, eosin was used to minimize pH fluctuations which were encountered earlier with fluorescein. In order to further minimize experimental problems, the titration apparatus was designed as an integral part of the spectrophotometer.
‘t
0.9
EXPERIMENTAL
The preparation of the alkyldimethylbenzylammonium chlorides and the titration procedure of Corrin and Harkins as employed by the authors have been previously described (1). The sodium salt of eosin was obtained from K & K Laboratories and was used without further purification. The absorbance measurements were recorded with a Cary Model 14 Recording Spectrophotometer at 528 nm utilizing a titration apparatus designed as an integral part of the spectrophotometer. The dye solution was titrated from a class A Kimax buret into a 500-cc funneled glass reservoir (made from a separatory funnel) which connected via a rubber coupling to a 1.00-cm glass stoppered sample cell. The (1) J. W. Ledbetter and J. R. Bowen, ANAL.CHEW,41,1345 (1969).
1I 11
0.21
,
,
,
,
,
,
0.4
0.8
12
1.6
2 .o
2.4
28
M a IO3
Figure 2. Determination of CMC for myristyldimethylbenzylammonium chloride 1.00 X lO+M and 5.00 X 10WM eosin
reservoir and cell were mounted in a vertically extended sample compartment with laboratory clamps to a ‘/2-inch steel rod bolted to the floor of the sample compartment. The extension to the sample compartment was constructed of a light metal alloy. Satisfactory mixing was obtained by a high speed stirrer which was constructed from a stainless steel welding rod and which extended through the reservoir and just into the top of the cell. The titration was performed in a nitrogen atmosphere in the sample compartment to minimize the absorption of C o n . RESULTS AND DISCUSSION
0.5
3.0
3.5
4.0
4.5
5.0
M a 10’
Figure 1. Determination of CMC for lauryldimethylbenzylammonium chloride 1.00 X 10-5M and 5.00 X 10WM eosin
The results of the titrations, in terms of absorbance of the eosin dye as a function of surfactant concentration, are shown in Figures 1, 2, 3, and 4. It was possible in these titrations to plot concentrations linearly and obtain well defined inflection points at the CMC. With fluorescein log M was used to obtain the inflection points. In the data recorded here, the CMC is taken as the point at which the plot deviates from linearity on decreasing surfactant concentration. These CMC’s are tabulated in Table I along with results from the spectrophotometric dye method employing fluorescein and from the surface tension method. ANALYTICAL CHEMISTRY, VOL. 43, NO. 6, MAY 1971
773
t
From the figures and the table, it is observed that improved inflection points were realized with eosin over fluorescein. This undoubtedly led to the improved results with the cetyl and stearyl derivatives. A CMC for the stearyl derivative was unobtainable from the fluorescein titration. Furthermore, the concentration of the dye had no observable effect on the CMC. The integral spectrophotometric titration method proved to be an improvement over the earlier pumping procedure. It allowed for a more rapid titration, better control of the NZ atmosphere, and a reduction in procedural errors due to the direct coupling of the titration reservoir and sample cell. Both the instrument design and the choice of dye further minimized absorbance and p H fluctuations.
0ID.9
t
0,3
I
'
6
20
1.0
3.0
4 .O
50
6.0
RECEIVED for review September 23, 1970. Accepted February 3,1971.
M a IO'
Downloaded by UNIV OF CALIFORNIA SAN DIEGO on September 3, 2015 | http://pubs.acs.org Publication Date: May 1, 1971 | doi: 10.1021/ac60301a040
Figure 3. Determination of CMC for cetyldimethylbenzylammonium chloride 1.00 X 10-6Mand 5.00 X 10-BMeosin
Correct ion Photon Activation Analysis In this article by George Lutz [ANAL.CHEM.43, 93 (1971)l there are several errors in the references. In the final stages of setting the manuscript in pages an unfortunate decision was made to renumber the original alphabetical listing in chronological order. The corrected references are listed below.
0.9c
Reads Ibid., 710 Ibid., 714 Zbid., 88, 52 (1967)
Should Read Ibid., 87, 710 (1966) Ibid., 87, 714 (1966) S. Abe, Nippon Kagaku Zasshi,
88, 52 (1967)
"t 1
I
I
OD
0.e
1
1.0
I
1.2
1.4
I
1.8
1.6
Ibid., 87, 1057 (1966) Y . Oka and T. Kato, Nippon Kagaku Zasshi, 87,1057 (1966) Y. Oka, T. Kat0 and Y . Oka, T. Kat0 and K. Nomura, Nippon Kagaku Zasshi, 87, 147 K. Nomura, ibid., 20
87, 147 (1966). Ibid., 84, 588 (1963)
Malo'
Figure 4. Determination of CMC for stearyldimethylbenzylammonium chloride
Ibid., 86, 612 (1965)
1.00 X 10-6Mand 5.00 X 10-BMeosin
Table I. Critical Micelle Concentrations of Alkyldimethylbenzylammonium Chlorides CMC, M
Method Eosin, 5.00 X 10-6M Eosin, 1.00 X 10-6M Fluorescein,n5.0 X Fluorescein,a 1.0 X 10-6M Surface tensiona a Reference 1.
774
Lauryl Myristyl 3.8 3.8 3.8 3.8 3.8
1.5 1.5 1.5 1.5 1.5
x
103
Cetyl
Stearyl
0.34 0.34 0.35 0.34 0.34
0.10 0.10 ... ... 0.093
ANALYTICAL CHEMISTRY, VOL. 43, NO. 6, MAY 1971
T. Azuma, Y. Sato, J. Tsurugi, R. Miki Y . Kondo, J. Yoshda and K. Yamamichi, ibid., p. 50 G. Goldstein, ANAL. CHEM.,35, 1620 (1963) A. Pradzynski, W. W. Sulin and H. C. Witozenc, Nukleonika 13, 581 (1968) P. Meijers and A. H. W. Aten, Jr., Radiochirn. Acta 11, 60 (1969)
(1966) Y . Oka, T. Kat0 and M. Sasaki, Ibid., 84, 588 (1963) Y . Oka, T. Kat0 and M. Sasaki, Nippori Kagaku Zasshi, 86, 612
(1965) T. Azuma, Y. Sato, J. Tsurugi, R. Miki,Y. Kondo, J. Yoshido, and K. Yamamichi, Ann. Rep. Radiat. Center Osaka Perfect,
8, 50 (1967) G. Goldstein, ibid., 35, 1620
(1963) A. Pradzynski, W. W. Sulin and H. C. Witozenc, ibid., 13, 581 (1968) P. Meijers and A. H. W. Aten, Jr., ibid., 11, 60 (1949)
