motion by a precision screw for use as the input to the ball and disk integrator. The time function was supplied b y a synchronous motor. The output of the integrator was displayed on a high speed Veeder-Root G5l-28 counter. This vounter gives a digital read-out directly proportional to the quantity of silver ion generated during a titration. EXPERIMENTAL RESULTS
-4 series of titrations was run using Kational Bureau of Standards 2-chlorohenzoic acid sample number 144. This compound theoretically contains 22.65% rhlorine. The sample size used in these cxperiments ranged from 0.5 t o 1 mg., n eighcd in a platinum combustion boat on an Ainsu-orth microbalance. The oxygen flow rate was 30 cc. per minute and the furnace temperature was 800” C. The combustion was carried out automatically in approximately 10 minutes. ,4n E. H. Sargent (Model S21 580) automatic combustion apparatus \\as used t o burn the samples. The titration cell was attached to the end of the combustion tube b y a ball and
Table 1. Coulometric Determination of Chloride in 2-Chlorobenzoic Acid
EsperiThco- mental Run Sample, retical Result, Error, so. Mg. % c1 % CTO +0 13 1 0 505 22 65 22 78 -0 11 2 0 529 22 6.5 22 54 3 1 048 22 6,5 22 48 -0 17 4 0 522 2‘2 65 22 7+ +O 09 5 0 567 22 65 22 7 3 t O 08 15 4“ 1.5 15 -0 25 6 1 047 -0 28 7 0 894 2’2 6-5 2’1 J7 -0 19 8 0 514 22.65 22 46 a Methyl-3- amino- 3-deosy - a - 1)-altropyranoside hydrochloride.
socket connection. Fiftcetl per cent water in glacial acetic acid was used as a n electrolyte in the titration cell. The neighed sample wab plaiwi in the conibustion tube and the sample wvss burned in oxygen automatically. The eluted gases from the combustion tube were passed into the titration ccil, \\here chloride ions were titrated by coulomet-
rically generated silver ions. Tlit. total current used for the titration na? proportional to the digital output of the intfgrator, thus the quantity of chloride in the sample nas obtained from a simple calculation. The integrated values represent coulombs divided by Faraday’s constant. When this value is multiplied b y the equivalent n eight of chloride, the product is the weight of chloride in the sample. The results of light consecutive runs are shou n in Table I. ACKNOWLEDGMENT
The authors are indebted to S a n c y Vitteborn for assistance in obtaining experimental data. LITERATURE CITED
(1) Linganc, J. J., ;ISAL.CHEII. 26, 622
(1954). (2) Sundberg, 0. E., Craig. H. C., Parson, J. S., l b z d . , 30, 1842 (1958).
RECEITED for review hlarch 21, 1960. Accepted July 5,1960.
Determination of Molybdenum in Nitrilotriacetic Acid Medium by Derivative Po arography Application to Solutions of Mixed Tho i u m-Ura niu m Oxides D. L. MANNING, R. G. BALL,’ and OSCAR MENIS* Oak Ridge National laboratory, Oak Ridge, Tenn.
b A supporting electrolyte composed of 0.1 5M nitrilotriacetic acid (NTA) at a pH of 3.0 was utilized for the determination of molybdenum b y derivative polarography. The method i s applicable to the determination of molybdenum in thorium oxide samples which also contain uranium. Major interferences include chromium(Vl), copper(ll), tin(lV), and nickel(l1); however, 80 to 100 pg. of these ions can b e tolerated a t the 7 0 - p g . molybdenum level. It i s postulated that the molybdenum waves which occur a t half-wave potentials of -0.22, -0.35, and -0.48 volt vs. S.C.E. are due to the reduction of molybdenum (VI) species, whereas the wave at -0.65 volt vs. S.C.E. i s caused b y the reduction of molybdenum(V) a t the dropping mercury electrode.
I
polarographic determination of molybdenum in the presence of uranium it is necessary to utilize a complexing medium to separate the reduction waves of the two elements. Complexation in both basic and acidic N THE
media presents certain difficulties. I n basic complexing media the molybdenum waves are generally poorly defined and the p H is critical. On the other hand, with acidic chrlating agents uranium is complexed less strongly than molybdenum, which ~icccssitates the measurement of t l v tliffusioii current of molybdenuni supchiposed on a large diffusion cui,rc’nt from uranium. To minimize this difficulty a wide separation of the two viaws 1.4 dcsi1~al)le. T o separatr th(. two waws, either (ethylenedinit d o ) tctraawtic acid (EDTA) or niti,ilnti,iacetic acid ( S T A ) appeared to lx suitahli. supporting electro!ytca. I’wsok a i d Sawyer ( 7 ) ohser\-d twn :i~olyf)iIen~t~ii rpduction waves in ErYrA with half-nave potentials of -0.17 and -0.G8 volt us. the S.C.E.‘!‘hw~ woikci~s point out, however, that a carcful control of ligand concentratioii and pH is necessary for the satisfactory determination of molybdenuni by this mc4hod. The polarography of molyhdcnum in an acetate-buffered solut~ionof ST.4 (pH 4) was investigated by Sinyako1.a and
Glinkina (91, n h o reportrd two leduction waves having half-\\ avc’ poteiitials of approximately -0.55 and -0.65 volt us. S.CC. In comparison, the ieduction of uianium(T’1) in E D T A and STA occui 5 a t half-m-ave potentials of -0.31 and -0.23 volt us. S.C E., respectively. I n this ctudy utilizing d e n \ at11 e polarography ( 3 ) ,four reduction aari nerc obsericd in :tn KTA medium :it p H 3 5 or IC-
