is at its lower practical limit. The reagent solution for chelation a t p H 4.5. is made by dissolving 20 mg. of PAX in 35 nil. of glacial acetic acid, adding 61 grams of sodium acetate t,rihydrate, and making to 100 ml. with water. It may be necessary to warm this solution before use to obtain a homogeneous solution. Bromine will oxidize vanadyl to pervanadyl a t low p H and this procedure was used in most cases. The excess bromine mu;t be removed because it destroys the PAX molecule. Because the solution of pervanatlyl ion is yellow, it is not possible to observe wlien the cxccs3 bromine has been renioyed. Extended boiling is required to ensure its coniplete removal. Potassium permanganate ill oxidize vanadyl to pervanadyl a t low pH. A small excess of permanganate dors not interfere. It therefore can act as its own indicator. If a large quantity of permanganate is required to complete the oxidation, hydrated manganous oxide precipitates when the pEI is adjusted to 3.5 to 4.5. If a visible amount precipitates, the results will be low, Oxidation with permanganate gives hetter results on ferrovanadimn. tlfter removal of iron froni an aliquot of the
ferrovanadirim solution by Iij-droriric precipitation, tlic solution was adjusted to pH 1.5 ~ i t hhydrochloric acid. A fen drops of potassium permanganate were added to givo a permanent pink color. Thr, pII was then adjusted to 4.5 and excess of the PI€ 4.5 PAS solution added. IYhatcvcr 1iII is choscn, 3.5 to 4.5, should be rcproduced within i O . l pH for ssmples and standards. The sensitivity varies with pH. The method is applicable to a considerable range of vanadium conccntrations and to different types of samples. The technique is simple and should be feasihle in routinr: nork. The method is sensitive and is made specific by the hydroxide separation of interfering ions, Traces of iron left are readily compensated for or corrrcted for. Other metals, chclatable by PAK) n.hich are left show no particular interference a t 615 mp. Most of t h ~ i rabsorbances occiir a t S5O to 570 m u . LITERATURE CITED
(1) Cheiig, Ti. L., Bray, R. II , ANAL. CIIERI. 27, 782-5 (1055). (2) Crouthamel. C. E., Hjeltc, B. E , Johnson, C E., I h i d . , 27, 5?&13 (1955):
Goldstein, CicIsld, SIannirig, D. I>,, h1enis, Oscar, fhid.,31, 1!J2 (1059\. (1) Hiliebrand, \V. I;., Lundcll, ti. E,I;.. Bright, l1. A . , Hoffmnn: J . I . , “Applietl Inorganic An:ilysis,” 2nd ed., p . 341, JJ-iiey, S e w York, 1953. (5!, Latimer, \V, h l . , Hildebrarid, J . 5 , Principles of Chinistry 2nd Iteference Hook of Inorganic Chemistry,” 4th ed., 11. 3-11, hTacmillnrl, Srw York, 19-12, (6) Lingan?, J. J . , “E1ectronn:tlytical Chemistry,” p. 122, IntersciencP, Ne\\. York, 1953. (7) Lundell, C;. E. F., FIoffmsn, -1. I., “Outlines of hIetliods of Chcmic:II Analysis,” p. 81, \ViIey: iVe\v Ynrl;, 1038. (8) Siwerts, A , Llilller, E. €1 , %. nnorg. t i . a l ~ g c r n .Chem. 173, 313-23 (1928). (9) TnlViti?, ?rT. A , , ANAL. CllE?,f. 2 5 , (:3)
604-i (1953). (10) Treadwell, F. l’., Hall, \V. ’I\., “Analytical Chemistry,” L’ol. 11, 9 t h eti , p. 240. Wiley, Kew York, 1942.
(11) Willard, H. H., Martin, E. 1, Feltham, Robert, A N A L . CHEM 25, 1863-5 (1953). (12) Killard, H . H., Young, Philena, ~
Ind. Eng. Chem. 20, 768 (1028).
(13) Wright, E. R., hIellon, hf. G . , TND. EXC.
CHElr.,
A N A L . E D . 9,
37.5 (1937,.
I ~ O C E I F Kfor D review April 6, 1959 Accepted September 14, 1959. Research supported by the United States Air Force under Contract No. .4F 33(616)-3964, monitored by the Aeronautical Research Laboratory, Wright Air Devclopment Center
Polurographic Determination of Aliphatic Aldehydes and Ketones as Imines MAYNARD E. HALL The Chemstrand Corp., Decafur, Ala.
b Methods have been developed for the polarographic determination of aldehydes and ketones as imines. The carbonyl compounds are converted to imines b y reaction with diamines, and the imino group i s reduced a t the dropping mercury electrode. The diffusion current obtained i s directly proportional to the concentration of carbonyl compound present. The effect of pH and diamine concentration on the conversion to imine i s discussed. Aldehydes can be distinguished from ketones, as their corresponding imines are reduced at different voltages. Aliphatic carbonyl compounds can b e determined with an average error of 1.5% in the 0 to 20% concentration range. The imine compound does not have to be isolated for analysis. The time required per analysis i s approximately 20 minutes.
T
application of polarography to the determination of aliphatic carHE
bony1 compounds has been ostensive, illy to nldrh~-dcs,as t1ic.y rcadily rcclucc at voltages just I~elow the reduction voltages of the more coninion supportiiig elcctrolytes. The direct retluctioii of :iliphatic ketoncs, hon.c,ver, is difficult :tntl troublesonic b e c a u x they reduce a t voltages as high as - 2 . 4 volts cs. S.C.F.j n.1iere ill-defined w v c s nrr often obtnineil. Conscquently, v.orkers in the ficltl of 1)nlnrography 11aw resorted to indirect methods or t o c:irl)onyl derivativcs for the tleterniination of ketoncs and, in many cases, aldchj~!cs. Ketoncs have been determined by the rctluction of the sulfur dioxide current of a n acid solution of sodium 1)isulfitc when ketones are added to tlie solution ( 2 ) . Ketones :rnd aldehydes also havc bcc.11 converted to liydrazoncs and their concentrations rneasurcd polarographically (3, 4). 12ecent :inalytical studies on polarographic nicthods for acetone have shon 11 that con-
APPARATUS A N D REAGENTS
Po1arogral)hic measiirmicnts ivcrc made with a Lectls ant1 Sortfirup T ~ . l v E Elrctrochernograpli. II-tyl~epolarcigraphic cells w r e used wliicl~containmi a saturated calomel ref(wncc7 elcctrotl!. separated from the solution c,oml!artVOL. 31, NO. 12, DECEMBER 1959
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