may be compared with a maximum K + to N a + selectivity of about 30:1 for the best available glass electrode. Fur thermore, the valinomycin electrode has an 18000:1 selectivity for K + with re spect to H + ; this means that the elec trode should be usable in strongly acidic media, where cation-sensitive glass electrodes lose their effectiveness. The nonactin electrode, on the other hand, shows an interesting selectivity for N H 4 + over hydrogen ion and the alkali metal ions and may be of con siderable practical value in this con nection. I t is too early to say whether anti biotic electrodes will be of general util ity and give rise to a broad new class of ion electrodes; however, there is no question but that electrodes based upon the synthetic organic analogs of such compounds are worthy of serious in vestigation. Pedersen (18) recently synthesized a whole series of cyclic polyethers, so-called "Crown" com pounds, which bind (19) alkali metal ions selectively. These compounds can be tailor-made to display desired ion binding and transport properties; thus, they should play a major role in the development of new ion-selective elec trodes. Two U. S. manufacturers have recently announced potassium ion-selec tive, liquid-membrane electrodes. A K + to Na+ selectivity of about 5000:1 is claimed for one of these. New directions for ion-selective elec trodes are not limited, of course, to the development of electrodes. Novel and imaginative applications are of equal importance. Electrode development and application mutually stimulate one another, however, so that the present vigorous pace of research in this area assures ion electrodes a major place in modern measurement science.
Literature Cited (1) G. A. Rechnitz, Chem. Eng. News, 43 (25), 146 (1967). (2) G. Eisenman, (Editor) "Glass Elec trodes for Hydrogen and other Cat ions," Marcel Dekker, New York, Ν . Υ., 1966. (3) R. A. Durst, (Editor) U. S. Bureau of Standards Monograph on Ion-Selec tive Electrodes, Government Printing Office, Washington, D . C., 1969.
a portable FURNACE
(4) G. Eisenman, ANAL. C H E M . , 40, 310
(1968). (5) M. J . Brand and G. A. Rechnitz, ibid., 41, 1185 (1969). (6) F . A. Schultz, A. J . Petersen, C. A. Mask, and R. P . Buck, Science, 162, 267 (1968). (7) G. A. Rechnitz and Τ . Μ . Hseu, ANAL. C H E M . , 41, 111 (1969).
(8) J. W. Ross, paper presented at meet ing of the Electrochemical Society, New York, M a y 1969. (9) T. M. Hseu and G. A. Rechnitz, ANAL. C H E M . , 40, 1054 and 1661 (1968).
(10) G. A. Rechnitz and N . C. Kenny, Anal. Letters, 2,395 (1969). (11) J. W. Ross and M. S. Frant, ANAL. C H E M . , 41, 967 (1969).
(12) J. Kummer and Μ. Ε. Milberg, Chem. Eng. News, 47 (20), 90 (1969). (13) G. G. Guilbault and J. G. Montalvo, J. Am. Chem. Soc, 91, 2164 (1969). (14) G. G. Guilbault and J. G. Montalvo, Anal. Letters, 2, 283 (1969). (15) G. G. Guilbault, R. K. Smith, and J. G. Montalvo, ANAL. C H E M . , 41, 600
(1969). (16) L. A. R. Pioda and W. Simon, Chimia, 23, 72 (1969). (17) W. Simon, paper presented at meet ing of the Electrochemical Society, New York, Ν . Υ., M a y 1969. (18) C J. Pederscn, J. Am. Chem. Soc, 89,7017 (1967). (19) R. M . Izatt, J. H . Rytting, D . P . Nelson, B. L. Haymore, and J. J. Christensen, Science, 164, 443 (1969).
Type 1400 furnace
FAST HEAT For schools, shops or labs to 1650°F (899°C) in 4 0 minutes.
PORTABLE Weighs only Ι ό lbs.; plugs into ordinary outlets.
STEPLESS CONTROLS To
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BASED on a lecture presented at the Ana lytical Summer Symposium, Athens, Ga., June 1969.
ELEMENTS EMBEDDED Exclusive refractory plates avoid sag and damage.
QUALITY CONSTRUCTION
COMMENTARY
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Τ \ κ . RECHNITZ'S ESSAY on this subject
-L-' is most stimulating and should convince analysts that continued re search and development of ion selective electrodes is a fertile field. What has been accomplished so far is impressive and very useful, but, as he has pointed out, the possibilities are almost unlimit ed. Dr. Rechnitz and his associates continue to contribute heavily to the subject and this discussion combines en thusiasm with extensive experience. It seems quite certain that a host of useful systems can be developed for in-
organic, organic, or biological systems. We are not too happy about the pres ent state of knowledge of the electrical behavior of selective ion electrodes. For example, what is the equivalent cir cuit of such systems? How are poten tial, current, capacitance, and resis tance related and how do they combine to account for the observed behavior? If this query reeks too much of the electrical engineer's "black box," it still seeks to get a practical answer. Knowledge about the attainment of equilibrium at the electrode is unsatis-
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Catalog
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VOL. 41, NO. 12, OCTOBER 1969 • 113 A
