under field conditions. A moderate number of potassium-containing particles is in the air, the greatest amount being in the medium size range (Figure 3). ACKNOWLEDGMENT
The help of H. R. Byers of this laboratory in discussions, and of J. P. Lodge, formerly of this laboratory, in
the statistical analyses is gratefully acknon ledged.
(4) Lodge, J. P., ROSS, H. F., Sumida, K., Tufts, B. J., h . 4 ~ .CHEJI. 28, 423
LITERATURE CITED
( 5 ) Pidgeon, F. W., Ihzd., 2 6 , 1832 (1954). ( 6 ) Tufts, B. J., Ibid., 31, 238 (1959). (7) Vittori, O., Cloud Physics Lahoratory, University of Chicago, Tech. xote (1956'*
(1) Gloss, G. H., Chemist Analyst 42, 50 (1953). ( 2 ) Lodge, J. P., A 4 ~ C ~m \~ x .. 26, 1829 (lgs4). (3) Lodge, J. P., APCA Proc. of Semiannual Technical Conference, San Francisco, Calif., Sovember 1957.
(1956).
RECEIVEDfor review February 7, 1958. Accepted September 17, 1958. This work supported by research grants No. RG-4521, No. S-l2(C), and S o . S-12(C2) from the Sational Institutes of Health, Public Health Service
Tetra ethy Ie nepe nta mine, a SeIect ive Titrant for Metal Ions Potentiometric End Point Detection CHARLES N. REILLEY and ALEXANDER VAVOULIS Department o f Chemistry, University o f North Carolina, Chapel Hill, N. C.
b Theoretical and practical considerations demonstrate that tetraethylenepentamine (tetren), as a selective titrant for metal ions, is superior to triethylenetetramine. The extent o f its reaction with mercury, copper, nickel, zinc, and cadmium is discussed quantitatively in relation to the effect of pH, complex formation, and hydrolysis. Potential-pH diagrams obtained using a mercury electrode offer a simple means o f predicting desirable titration conditions and detecting the relative effect o f competitive equilibria. Mercury, copper, nickel, zinc, and cadmium alone and in various mixtures were titrated using the mercury electrode for potentiometric end point detection. The alkaline earths, r a r e eurths, aluminum, bismuth, lead, and scandium d o not interfere. Mercury and copper can b e titrated a t low p H in the presence of nickel, zinc, or cadmium. In combination with EDTA, a large number of metal ions in multicomponent mixtures may b e readily estimated.
C
metal ions (such as cobalt, nickel, copper, zinc, cadmium, and mprcury) form more stable coordination bonds with nitrogen than n-ith ovygen (14). In ammoniacal solutions they form stable amnine complexes. I n contrast, other metal ions (such as alkaline and rare earths. aluminum, bismuth, lead, and scandium) either do not react or form hydrous oxide precipitates. Thus, reagents such as polyamines which have only nitrogens as coordinatERTAiS
ing atonis complex with a more restrictcd set of metal ions than reagents such as (ethylenedinitri1o)tetraacetic acid (EDTA) and consequently are useful as selecth-e titrants. Although this principle was recognizpd early by Schwarzenbach ( 4 ) , only recently has practical use been made of these reagents. Triethylenetetraminpj trien, H~S-C"~CH,-SI€-CH~ H2S-CH2CH2-SH-~H~ was first employed for practical titrations by Reilley and Sheldon (10. 11). Copper, zinc, mercury, and cadiniuni were selectirely titrated in the presence of calcium, magnesium, strontium, and barium, using metallochromic indicators (10). Copper at pH 5 was selectively titrated in the presence of nickel and the nickel then determined after the pH had been adjusted to 9 with ammonia ( 1 1 ) ; the mercury electrode served to detect the potentiometric end point. Nore recently Flaschka and Soliman (2) described the photometric titration of copper. Undoubtedly the lack of a source of purified trien contributed to the delay in its application; a n easy purification method (10) alleyiatcs this difficulty to some extent and the reagent is non con;niercially available (J. T. Baker Co.). Tetraethylenepentamine, tetren,
zinc, and cadmium, but does not react with the alkali and alkaline earth metals, aluminum, and the rare earths. Because tetren forms more stable metal complexes than trien, a theoretical and practical study of this new selectiye rcagent seemed worth FT hile. COMPARISON OF TRIEN AND TETREN
A cursory examination of the stability constants of trien and tetren (Table X) indicates that tetren forms complexes more stable by approximately 3 log K units than trien. The selective nature of trien and tetren is also indicated. Comparisons according to the log K values alone can be misleading, because
Table 1. Stability Constants of Trien Tetren, and EDTA Complexes
Netul Hg++ Cll + + Xl++
Zn++ Cd'+
Trien
Log I< Tetren
( 4 , 8)
(b)
25.0 20 1 14 1 11.9
27 7 22 9
10 8 10 4
1'1, + +
i\In H i + + + Iiegliqihle ++
17 S 15 4 14 0 10-11 7 0 a
'TH
H,X-CH,CH,--SH-CH,CH,/ like trien, forms very stable 1 to 1 complexes with mercury, copper, nickel.
..
16 4
16 4 1; 9
b
20°
13 8
