Carbon Paste Electrodes SIR: During an investigation of the properties of a dropping carbon electrode, a new paste electrode has been developed which possesses unique advantages in anodic polarography. This report concerns carbon-bromoform pastes used in a pool configuration. The paste is prepared by stirring together the carbon and organic liquid until the mass appears uniformlj, wetted. A typical mixture contained 1 gram of carbon and 7 ml. of bromoform (paste 1-7). This is a moderately thick paste, well suited for pool application. Varying consistencies may be prepared and used in a variety of electrode forms. The electrode proper was machined from a short Teflon rod. A well about 0.5 cm. in diameter and 3 inm. deep was drilled into the end of the rod. A heavy platinum wire ran through the rod to the bottom of the well for electrical contact. The paste was tamped into the well until the surface was smooth and flush with the \vel1 edges. Excess paste was trimmed with a small spatula. The rod was then inserted into the polarographic solution in ail inverted sense, so that the only electrical contact mas with the carbon pastc yurface. A conventional saturatctl valomel electrode completed the cell. All polarograms were run with a Leedq &, Sorthrup Electrochernograph. Peak polarograms, characteristic of pool electrodes, were obtained. The data are reported in terms of peah current, i,, and half-peak potential.. Ei,z. Tahle I sholvs typical data with paste
1-7 for the oxidation of ca. IO-jJI iodide ion in 1M sulfuric acid background. These seven runs were made on the same electrode with neither pretreatment nor any cleaning between runs. Four determinations with a representative organic compound S,.V’dimethyl-p-phenylenediamine,gave a mean deviation of =tl.6% for i, and 20.5% for E l l 2 . The electrolysis conditions used in the present study are far from ideal. S o care was exercised in arranging optimum diffusion conditions. Better sensitivity could be obtained with a faster voltage scan rate. Serertheless, the results are excellent in comparison with existing solid electrode data. While carbon rod electrodes have proved r e r y useful in anodic polarography, they require a rather trouble-ome \Tax impregnation for reproducible results ( I , 2 ) . I n contrast, carbon paste cslectrodes can be prepared. read>- for use, in about 5 minutes. Apparently they can be used repeatedly with precise results. With the proper organic liquid, it may be possible to dissolve and concentrate electrode reaction products for inechanisni studies. There appear to be no restriction. on srlection of the pasting medium, provided it is nonelectroactive and water-immiscible-e.g., carbon tetrachloride pastes give excellent results. A carbon tetrachloride paste used for iodide oxidation represents an interesting situation. The oxidation product. iodine, is highly qoluble in the organic pastc. This
Table I.
Run No. 1
2 :i 4
5
-
ij
1Ienn.
Typical Data
on Paste 1-7 E112 L I S . S.C.E., Volt
IP, P a .
46.0 49.8 49.9 50.0 51 2 50.4 51.1 49.8
+ 1.8
0.453 0,462 0.465 0.467 0.454 0.464 0.463 0.461
io. 0
le1 amalgam formation in mercury polarography of metal ions. Using more fluid carbon-bromoform pastes, a dropping carbon electrode wai devised. -4detailed report on this and other carbon paste electrodes !Till be presented in the near future. ACKNOWLEDGMENT
’I’hauthor islies t o thank thc Ilc3.cmc.h Corp. for financial a s k t n n c t in this n o r k . LITERATURE CITED
( 1 ) (&q.lor, T7. F., C o ~ i r a d.2. , I,.> Imidt~rl, J. H., . k s . q ~ CHEJI. . 29, 221 (1957). ( 2 ) Morris, J. B., Ph.U. thesis, PeIinsj-1vania Stat? Cniversitj-, 1956.
IIALPH S . .iU,i\fh
Ikpartment of Chemistry University of Kansas Lam-ence, Kan. RECEIVEUfor review Jul!.icwpted Jrdy 28, 1958.
7 ) 1958.
173. Tolbutamide JOHN W. SHELL The Upiohn Co.,Kalamazoo, Mich.
(The Upjohn Co. trade T name, Orinase) is a synthetic, orally active antidiabetic agent. Chemically. OLBUTAMIDE
1-butyl-3-p-tolylsulfonylurea. it is ( ‘rj.st:ils used for the present study were. grown from acetone solution, nlthouglI f he same form is produced by crystallization from a wide range of organic ancl aqueous solutions, and by sublimation. Forist and Chulski ( I ) have reportcd the pH-solubility relationships. 1576
ANALYTICAL CHEMISTRY
CRYSTAL MORPHOLOGI System and Class. Orthorhoiiibic i hombic pyramidal, 11112, a : b : c = 0.4504: Axial Ratio. 1:0.3864. Interfacial _Angle-. (101) ,i(101) = \ i o ; ( o i i ) ~ ( o i i= ) m0; (120).i(i20) = 96O. Habit. Tabular { O l O \ with { 101 j j 01 I } , jizo 1 . Supplementary twinning is coinnion. Iiut usually with the com~
position plane and re-entrant anglea I isible (Figure 1). Projections showing the various forms prevnt are presented in Figure 2 . The clinographic projection and its related orthogonal projeetion are hascd on :i gnomonic. projection vn n Iijyothpticnl (TO@) face.
