ANALYTICAL CHEMISTRY
1356
DISCUSS103
Table I.
Comparison of End Points i n Aqueous Media thiosulfate, 0.001290 N. diluted t o 0.0002580 N , was used t o
(Sodium titrate 25-ml. asmples containing 0.00300 me. of potassium iodate) Me. of ThioSample MI. at Visual M1. a t Starch MI.at Dead sulfate Used So. E n d Point E n d Point Stop E n d Point a t Dead Stop 11.550 0.00298 1 7.50 10 80 11.625 0.00300 2 6.80 11.10 11.600 0.00300 3 6.50 10 i o .\v. 6 90 i:0.40 10.90 = 0.17 11.592 zk 0.028
Table 11. Comparison of Visual and Dead Stop End Points in Semiaqueous Media (Titration of 0.00456 me. of Tetralin peroxide in 2 ml. of benzene soliltion with 0 0002.580 .\-sodiritii thiosulfate) 1\11. a t Dead hfe of Thiosulfate Sample 311 a t Visual End Point Stop End Point Csed at Dcad Stoli NO. 1 14.00 I6 600 0.00428 2 14.30 16 550 0 00426 3” ,... 16.600 0.00428 a 111the presence of lo-‘ JI (lh-e (,zinc salt of terraphen?Iporphi~~t‘).
of the 0.001290 .V thiosulfate \vas cari,icd Out, using the dead stop end point. T?ble I1 illustrat.es the heh:tvior of the dead stop end point fur peroxide analysis in semiaqueous media. Even under condit,ions o i extrc~melgsmall peroxide content and titrant concentration thc nietliod i p quantitative and the error i.* I c w t,han 0.5%.
A method has been out.lined for the quantitative dctcriiiiiiutioii of organic peroxides iodometrically using the dead stop tcc.linique. The technique works very well in semiaqueous i n d i d and has several distinct advant,ages over the visual end point technique. It is by far more sensitive and strictly quantitative, with an error of less than 0.5% even for peroxide content of the order of 0.005 me. Furthermore, it is applicable in highly colored solutions or in the presence of insoluble material under which condit.ions the visual end point is useless. It has also been found to function satisfactorily in emulsions if sufficient time is allowed near the end point for partition of the iodine into the more aqueous phase. LITERATURE CITED (1) 1)cl:ihay. P,, d r r c r l . Chim. A d n . . 4, 638 (1950). (2) Foulk, c‘. JV., and Rawdeli. A. T., .I. A m . Chem. Soc., 48, 2045 (1926). ( 3 ) IIock, H., :md Sueeniihl, \\-., Rer., 66, 61 (1933). (4) \\.itgner, C. D., Smith, K. H., and Peters, E. D., I x u . €:si:. CHEY., AN.II.. ED., 19, 976 (1947).
R E L ~ : I I - Efor D review Deceiiibpr 6 , 1931. Accepted April 29, 1952. JVork done in connection with projrcts supported by the Reoearcli Corp., K e w Tork. N , I-., and the C. S. rZtoiriic Ent-rgy Conimirsion, Contract S o . .iT(30-1)-820.
Conversion of Hydrogenic Materials to Hydrogen for Isotopic Analysis JdCOB BIGELEISEN, M. L. PERLMAN, AND H. C. PROSSER’ Rrookhnretc Yational Luboratory, C ptotL. Lorag Zslurtd, .V. Y . isotopic analysis of hydrogen by mass spectrometry is complicated by the fact that water, obtained by combustion ( ~ fhydrogenic materials, is strongly adsorbed onto the walls of conibust,ion trains and vacuum systems. Thus, large “memory” effects are observed when Fater is introduced into conventional mass spectrometers. This has been overcome by conversion of \v:tter to hydrogen by t,he action of hot magnesium (6) or zinc (j, II), by equilibration of water with hydrogen of known coniposition ( 3 , 7j, and by conversion of water to hydrocarbons (4, I O ) . Each of these methods has some liniit,ation; the ease of conversion, the size of sample required, the fact that an accurately knovm equilibrium state must be attained, the interference of foreign gmes present in the sample or spectrometer, the coniplexity of ion pattern. Theso !imitations may 1)c minimized for a variety of hyclrogeI ~ O ~ compounds IE by their reactions with hot uranium to produce pure hydrogen ( 8 ) ,which g:ti may he analyzed mass spectrometricall!. by comparison Kith standards (1,9). The results given here were obtained by use of the urariium reaction carried out in the apparatus shown in Figure 1. Cranium metal turnings, which were cleaned in concentrated nit,ric acid and then rinsed and dried a t room temperature, were placed in the silica U-tube. Direct contact of the metal with the silica was prevented by copper gauze sleeves and copper wool plugs as shon-n in the diagram. The uranium was maintained at a temperature of 400’ to 700” C. by a small electric furnace manually controlled. The use of turnings rather than powder was dictated by the requirement that all the uranium be held in the heated zone in order t o avoid formation of uranium hydride. This substance exchanges rapidl:. with elementary hydrogen evexi xt room temperature (2j. The measured sample of gas or liquid for analysis was condensed into trap A from the bulb, C. With proper manipulation of the stopcocks the gas flowed into the E-tube, where reaction occurred. The extracted hydrogen, after passage through the refrigerated trap, B , for removal of any unreacted gas, was slowly expanded into the Toepler vessel, from which it was compressed into a receiving hulb. By careful operation of the Toepler it was easily ~~
1 Present address. Department of Cheinistry. Stanford University, Stanford, Calif.
possible to have the gas enter at auch a rate as to undergo quarititative reaction in a single passage. The apparatus is designed to permit recirculation of unreacted substance. The results obtained for several substances are summarized in Table I. The test for “memory” in the case of water was made by the converbion, in succession, of 25-pl. samples of tap water, 99% deuterium oxide, and then tap water again. The hydrogen of the second tap TI ater sample contained 0.5% deuterium. Smaller samples showed larger fractions of carry-over. The result indirates that a smaller conversion apparatus would decrease the To PUMPS
bRA*IIUM TURNINGS IN COPPER G A U Z t S E E
Figure 1.
Table I.
com~,ouu~l HnO SH1
PHs HzS C2HaOH CsHa
Apparatus for. Extraction of Hydrogen from Compounds
Percentage Hydrogen Extracted from Various Compounds U-Tube Hydrogen Temp., Yield,
c.
%
400
100 =t1 100 I 1
400 600 700
700 700
100 i. 1 100 i. 1 96 =t1 93 + 1
Remarks 0 5 % memory with 2.5-cu. mrn. sample 0 OYOmemory 0 0% memory Soiiie cracking on hot siirface
1357
V O L U M E 2 4 , NO. 8, A U G U S T 1 9 5 2 carry-over effect. K O carr>--over w:td observed in similar tePts made with ammonia and phosphine. The mass spectrometer was flushed with a sample of gas to be analyzed if the sample differed markedly from the previous one. The time required for convtarsiori of R $ample was 15 t o 30 niinutes. The conversion of propune required that the uranium be maintained at a temperature higher than that needed for water or ammonia. At 400' C. with propane the met.al became coated with a protective lager which inhil)itcri reaction not only with that gas but with many othcrs also. Trwtnient tTith nitric acid restored t,he activity of the metal.
( 2 ) Higeleisen, .J.. and Kant, .I.. unpublished data.
(3) Chenouard, J., Geuron, J.. and Roth, E., with technical collaboration of Paoli, O., and Lecomte, J., Commission for
Atomic Energy, France, Rept. 87, 1951. (4) Friedman, L., and Irsa, .I.P., ASAL. CHEM.,24, 876 (1952). (5) Giaff, J . , and Rittenberg. D.. I b i d . , 24, 878 (1952). ( 6 ) Kamen, M.D., "Radioactive Tracem in Biology," p. 131, Sew
York, Academic Press, 1948. ( 7 ) Kirshenbaum, l., "Physical Properties and Analysis of Heavy Water," Chap. 4, Section 5, Ne-iv Tork, hicGraw-Hill Book 1951 (8) Xewton, -4.. 8., Manhattan District, Declassified Docitment 724 (January 1947). ( 9 ) Sier, A. O., Inghram, M. G., Stevens, C . .i.,and Rustad, B., Ibid.. 197 (1947). (10) Orchin, & I . , Wender, I., and Friedel, R. -I., ANAL.CHEX..21, 1072 (1949). ( 1 1 ) Sprinson, D. B., and Rittenberg, D., C-. S.. T a d M e d . Bu12. (Supplement), 115, S9 (1948).
co.,
RECEIVED for review February 6, 195?.
.iccepted . i p r i I 29, 1962.
Estimation of Pyrethrins on Coated Paper Bags FRED I. EDW-ARDS
AND
CIPRIANO CUETO
Bureau of Err torrroloz?. arid Plant Quarantine, U . S. Department of Agriculture, Beltsville, .Wd.
RESEST interest in the stoinge of foodstuffs in paper bags 'that have been treated Kith pyrethrum has necessitated the development of an analytical procedure for estimating the content of p-yrethrins in these bag coatings. both for control in nianufacture and for following the stal>ilit!- of the pyrethrins during s t n i q e of the bags.
2 3 Cm. LONG 0.0. 7rnm., FLARE, 0.D. I5mm., 4 cm. LONG
DISTRIBUTOR TUBE,
30cm.
-,-
/SIDE
'---BARREL,O.D. Figure 1.
A R M O.D. 15mm.
28mm.
F:xtraction ippiratus
Lord (a) has described a color reaction applicable t o the pyrethrins which has been adapted t o the estimation of the pyrethrin content of these paper bag coatings. The basic steps of this procedure are: reaction of pyrethrins and hydroxylamine to form a hydroxmic acid, formation of a colored complex by reac-
tion of the hvdroxaniic acid LT ith ferric chloride. and evaluation of thiq colored coniplev in a colorinieter PREPARATION O F STASDARD CURVE
Reagents. PTRETHRUJC COXCESTR.\TE.Select a 20"; concentrate which contains a pyrethrin I to pyrethrin I1 ratio of 1.16 f 0.1 to 1 [based on analysis following the method described in ( 1 ) . The pretreatment x i t h cold Skellysolve F must be carefully folloa-ed before analysis in all cases] , STAh-DARD S O L U T I O S , 0.1000 gram Of pyrethrins (based 011 f ) in 1000 ml. of et)hyl alcohol. 1 ml. = 0.1 m y . of pyrethrins. Hydrosylamine hydrochloride, 2 .If aqueous solution, to he made u p frefih weekly. Sodium hydroxide, 3.5 2V aqueouy solution. Hydrochloric acid, 4.0 S. Ferric chloride (c.P. anhydrous sublimed). 0.37 -\I i i i 0.1 S hydrochloric acid, t o be made u p fresh s-eekl!.. Ethyl alcohol, 95%. Skellysolve F, boiling point 30-60" c'. Sodium chloride, ACS grade. HvAo Super-Cel, a diatomaceous filtering aid. Apparatus. Nett-Summerson photoelectric colorimeter, Model 900-3, with 12.5-nim. calibrated test tubes and green filter having a transmittance peak a t 540 mp (any comparable coloi,iriieter may be used). Extraction apparatus, see Figure 1. Procedure. Aliquots of the standard aolution of pyrethrin3 are pipetted into 500-ml. separat,ory funnels; 5, 10, 15, 20, 25, and 30 ml., equivalent t o 0.5, 1.0, 1.5, 2.0, 2.5 and 3.0 mg. of pyrethrins, are used. Ethyl alcohol k added to each separatory funnel to bring the total volume t o 50 ml. Then 350 nil. of water. 15 ml. of Skellysolve F, and 7 grams of sodium chloride are added. The solution is shaken for 1 minute and allowed to separate, and the aqueous layer is transferred to a second separator) funnel. Ten milliliters of Skellysolve F is added to the second funnel, and the solution is again estractrd for 1 minute. Thir: extraction is repeated in a third wparatory funnel and th(, a q u e ous layer is then discarded. The three Skellysolve F extracts are combined, a minimum of olve F being used for the transfer. The conibined shed once with 5 ml. of water and filtered into a 50ml. volumetric flask through a small plug of cotton wet with Skellysolve F. Sufficient Skellysolve F is used in the transfer to bring the total volume to 45 nil. The Skellysolve F is then evaporated by immersing the flask in a water bath at 25' C . and passing a stream of nit,rogen into the flask. Three milliliters of ethyl alcohol are added and thp flask is swirled t o dissolve the residue. Six milliliters of alkaline h3-droxylamine solution (prepared within 30 minutes of use by mixing equal volumes of 2 h!J hydroxylamine hydrochloride solution and 3.5 N sodium hydroxide solution) are added and the flask is alloxved t o stand with intermittent shaking for esactly 10 minutes at 25" Ilt 5" C. At the end of this 10-minute period 3 ml. of 4.0 N hydrochloric acid solution are added, the flask is shaken thoroughly, and 3 ml. of the ferric chloride solution are added,
