677
V O L U M E 20, NO. 7, J U L Y 1 9 4 8 Table 11.
Concentrations of Carbon \\Ionoxide in Eight Carbon >Ionoxide-Air Samples
(Deteririined by Beckman-hfcCullough method in order of analysis compared rvith 1 2 0 6 reference method) Analysis 1 9 0 5 h l e t hod
JIlU.
Carbon 90 5 1 8 4 . 0 44 8 40 95 184 54 202 96 42 215 9" 49 204 102 44 195 103 42 201 93 50 201 101 47 92 169 44 182 95 192 43 YO 95.9 1 9 4 . 3 4 5 . 5 103 204 .54 40 92 169
A r. Mas. Slin.
Per 106.0 113.8 101.7
Bechman.\lcCullo11 method
hv. Ala-..
Monoxide, P a r t s per Million 360 2 4 4 . 7 2 3 . 8 66 2 1 3 7 . 8 1 3 7 . 8 155 215 261 26 128 56 142 2i9 2 14 55 119 23 281 25 146 61 197 119 149 25 278 57 123 21 149 60 269 117 '2 146 57 122 208 264 152 65 17 127 220 206 159 55 27 208 201 121 12'2 216 266 60 ... 214 119 ... 61 276 270 212 '24.2 5 8 . 7 1 2 1 . 7 1 4 8 . 5 279 220 27 65 128 155 261 197 21 55 119 142
;;
Cent Recovery of Carbon llonoaide 1 0 5 . 4 1 0 1 . 6 8 4 . 4 8 6 . 6 9 3 . 8 8 8 . 7 8 8 . 7 107.6 110.5 120.5 8 7 . 2 9 0 . 0 1 0 4 . 7 9 8 . 2 Y2.Y 112.5 82.9 8 9 . 3 81.6 8 0 . 5 8 1 . 4 8 3 . 1 8 6 . 4 1 0 3 . 0
prepared, the traces on both sides nieasuied, and the ten resulting values averaged. PERFORIIAhCE
The accuiacy of the instrument may be judged from the data given in Tables I and 11. Table I shoss typical re- ilts obtained in the authors' laboratories in the calibration of five lots of selenium sulfide test papers. The data in Table I1 were obtained during comparative tests ( 3 )of five methods for the determination of carbon monoxide in air a t S a v a l Medical Research Institute. Table 11,which is taken directly from Consolazio's report, com-
pares the results obtained with the mercuric oxide instrument with those obtained n i t h an iodine pentoxide train. The mean deviation of the instrument values from those obtained by the iodine pentoxide method is S.S%, which is good a t these low concentrations. Some of the deviation is without doubt due to errors in the iodine pentoxide method, which was said by the author of the report to be perhaps as high as 5%. That the instrument error is almost entirely in the selenium sulfide step is shown by the high accuracy of the gravimetric method based on the mercuric oxide reaction ( 1 ) . Instrument accuracy is high enough for many laboratory and most field requirements and the instrumrnt has the distinct advantages of speed and simplicity. In over five hundred determinations with one of these instruments in the writers' laboratory in the calibration of papers no servicing of the instrument n as required. LITER.4TURE CITED
(1) Beckman, A . O., hIcCullough, J. D., and Crane, R. .1.,Report
PB 5921, Office of Publication Board, Department of Cornmerce, Washington 2 5 , D. C. (2) Campbell, T. W., and McCullough, J. D., J . Am. Chem. Soc., 67, 1965 (1945). ( 3 ) Consolaeio. W. V.. and eo-workers. Remaort 5 . Proiect X-417,
h'aval Medical Research Institute, Naval Medical Center, Bethesda, Md., 1944. (4) McCullough, J. D., Crane, R. A., and Beckman, 9.O., ,1N.4L. CHEM.,1 9 , 9 9 9 (1947). ( 5 ) h'ordlander, B. W., Ind. Eng. Chem., 19, 518 (1927). (6) Sanger, C. R., and Black, 0. F., Proc. Am. Acad. Arts Sci., 43, 295 (1907-8). RECEIVED October 27, 1947. Based on research done for the Office of Scientific Research and Development under Contract KO. OEMsr 674 with Arnold 0. Beckman.
Argentometric Microdetermination of Organic Chlorine KEIITI SISIDO AND HIROSI Y.AGI Depurtment of Industria: Chemistry, Fuculty of Engineering, Kyoto Cnicersity, Iiybto, Japan A sample containing about 2 mg. of chlorine is digested with an excess of metallic sodium in butyl or amyl alcohol according to the method of Stepanow. The resulting chloride ion is titrated with 0.01 ,V silver nitrate solution and bromophenol blue is used as an adsorption indicator.
I
S T E R E S T in organic chlorine compounds has made necessary the establishment of a suitable method for the determination of chlorine. llost of the micromethods listed in testbooksPregl-Roth ( 11 ), Siederl-Siederl ( 9 ) , and Ochiai-Tsuda (10)as well as in the literature could not be performed because of the postwar shortage of equipment. Even the Carius micromethod, which is perhaps the most universal, could not be carried out because of the lack of suitable glass tubing and fuel gas for sealing the Carius tubes and heating the Carius oven. Other methods required special equipment or rare reagents or were too coniplicatcd or time-consuming. In the authors' laborator?, carbon and hydrogen analyses are performed by specialists and the research chemist need only purify and submit the saniplr. Sulfur and halogen determinations must always be done by the research chemist himself. .Xccording to the prcn-ar literature available to the authors, no simple method of analysis exists. In order to determine the chlorine in organic combination, it must first be converted into the ionic form. For this purpose, chlorine compounds with the exception of hydrochlorides and alkyl chloride addition products of organic bases (13, 16) must be decomposed by the Carius, oxidation, reduction, combustion, fusion, or other method. The Stepanow method ( l q ) , in which the compound is digested
15 ith metallic sodium to convert the chlorine to chloride ion, dispenses with special apparatus, is free from explosion, and is rapid and as in the Kjeldahl method for nitrogen, many analyses can be carried out in parallel a t the same time. As the result of recent developments, the method is now improved in accuracy and reliability. Indeed, the analysis of a compound, for which even the Carius method failed to give a correct value, has been successfully carried out (1, S, 4,5, 6,8, 12, 16). Chloride ion is best determined by means of the silver salt. Both volumetric and gravimctric procedures are used. illthough Rauscher (12), in modifying the Stepanow method, emplo! ed gravimetric analysis on a micro scale, a volumetric modification is preferred because of its simplicity, even though it is less accurate than the gravimetric procedure. The errors aie attributable to the buret and to the indicator. The backtitration (of the Volhard method), which doubles the largest error, must be avoided and the nature of the color change must be carefully studied. The original Stepanow method and many of its improvements, in nhich the Volhard back-titration is used, are unsatisfactory \Then applied to microanalysis. iinother objection to the Volhard method is the fact that the reddish brown color of ferric thiocyanate often becomes indistinguishable from that of the solution titrated and is influenced by tempera-
678
ANALYTICAL CHEMISTRY
ture, and that silver chloride reacts ith ferric thiocyanate and thiocyanate ion. Table 1. Results 0.01 s DifferWhen an adsorption indicator is used, Conivound Forinula Sample .4g?;Os Factor Found Calcd. ence only one standard solution, silver niCI Mg. M1. 70 % trate, is needed and the indicator underHexachloroethane GCla 2.050 5.25 0.9900 89.90 89.87 + O 08 2.290 5 . 8 9 90.29 + 0 .42 goes not only a color change but also a p-Dichlorobenzene hexaC6H4C18 2.976 6.71 0.4887 79.04 78.89 -0.13 chlorides change in fluorescence. The end point 3.165 7.10 78.64 -0.35 Benzene hexachloride= CaHaC16 2.925 6.33 0.9523 73.07 73.20 -0 13 is therefore more clearly recognized. 2.640 5.71 73.03 -0.17 DDTa C14HoClj 4,166 6.34 0.94.51 51.00 51 23 -0.23 This kind of procedure must be ap4,383 6.70 51.22 -0.01 1,2-Dichloro-1,1,2,b-tetra-&H%Clr 11.432 plied in order to avoid the faults of 5.88 0.4433 ’ 17.20 17 6.3 -0 43 phenylethanea the Volhard method. This modificap-Dichlorobenzene C6HaC11 4.001 6 38 0 8.590 48.57 48.29 +0.28 4.574 7 29 48.54 ‘0.25 tion has been described by Feldmann a Substances synthesized recent1:in authors laborator:and analyzed by 3Iih. l I r i a y 6 for their and Powell ( 5 ) in a macrodeterminacarbon and hydrogen content5 to confirm the purity. tion of halogens, but is not applicable ___ _~ ___ as it stands on a micro scale. Simple calculation shows that in order to which hinders the easy distinction of the color change of t,hr inobtain the usual analytical arcuracy with niilligi~aiiiquantitit~s, dicator. centinormal solutions must be used. PROCEDURE Ifre need therefore to investigate anew the concentration of .1sample containing about 2 mg. of chlorine is weighed out in a chloride that can be titrated and the kind’of indicator that can manner analogous to the Dumas micromethod and t,ransferred to be used. Bromophenol blue ( 7 , 15) has been used with success. the flask. A volume of 3 ml. of alcohol or less is added to dissolve the sample. If the sample is not easily soluble in alcohol Tetrabromophenolphthalein ester, according to Sakaguti (13) it is dissolved in an appropriate solvent containing no halogen gives excellent results. and t’hen the alcohol is added. Ll sample containing about 2 mg. of chlorine is decomposed by A piece of clean sodium weighing 0.03 to 0.05 gram is added. reduction with metallic sodium in amyl or butyl alcohol. Thc The sodium need not be weighed every time, but the amount must be judged by the eye as const’ant as possible in order to sodium chloride produced is now dissolved in about 10 ml. of keep thr error produced by the impurities within t,he allowable water and titrated with 0.01 iY silver nitrate solution. The color limit. change of the bromophenol blue is sharp even in the presence of After the condenser is att,ached, the flask is shaken a t room alcohol and decomposition products. temperature until the react’ion ceases. Then t’he vessel is heated gradually during 10 minutes and finally the refluxing is conAlthough the authors did not investigate cornpouiicls continued rTith strong heat,ing for 10 to 15 minutes, taining nitrogen, it is \Yell known that the nitrogen is converted The flask is allowed to cool and about 10 ml. of water are added to ammonia by metallic sodium and escapes from the reaction to dissolve the sodium chloride. After addition of 1 to 2 drops of niist urr . the bronioplienol blue solution, the contents of the flask are neutralized with 10% acetic acid until the color of the indicat’or Kimura (6) and Bobranski (2) have sliown that the dccombecomes yellow. The p H of the solution is therefore about 3.0. position with sodium and the titration with an adsorption inThe solution is then t,itrated with a 0.01 silver nitrate soIution. dicator clan be carried out, on a semimicro scale using 20 mg. or Before arriving a t the end point the color changes slowly,’from more of sample n-eighccl on an ordinary chemical balanccs and an yellow t,o blue-green, but this is not the true end point’. The end point is sharply and clearly seen when one drop of the titrat’ordinary buret with a 0.05 S d v e r nitrate solution. Ethyl ing solution changes the color from blue-green to violet. This alcohol can be used as solvent if the chlorine is not firmly attached point is also approximately distinguished by the mode of forniato the nucleus or to an unsaturated carbon. tion of the silver chloride mass. The time required for the analysis, including the ~reighingof The same procedure is repeated without the sample, but adding, after the digestion, 5.00 ml. of the 0.01 S sodium chloride the sample, digestion with sodium, and titration is less than an solution. The factor of the silver nitrate solution is t,hus deterhour. It is much more rapid than the Carius and combustion mined. methods. The errors are as large as i n previous methods. The 1.00 ml. of 0.01 .\- si1vc.r nitrate corresponds to 0.35457 nig. of only apparatus necessary is a buret and digestion flask with chloritic,. ACKNOW LEDGBZEYT ground-in reflux condenser. h test tube used as a cold finger can be used to replace the condenser. The indicat,or, also used The writers wish to thank AIiss Yasuko Ileizyi3 for her coas a pH indicator, is easily available. operation in this nork. This method is believed to be useful in microanalysis for reLITERATURE CITED search purposes as well as semimicroanalpis in industrial work. Bacon, .J. A m . Chem. Soc.. 31,49(1909). Bobranski, A., 2 . a n d . Chem., 84,225 (1931). APPARATUS Cook and Cook, IXD.ESG. CHEW,ANAL.ED.,5, 186 (1933). Drogin and Rosanoff, J . Am. Chem. Soc., 38, 711 (1916). A 50- to 100-ml. flask with a ground-in reflux condenser-i.e., Feldmann and Powell, ISD. ENG.CHEM.,ASAL. ED., 11, 89 an acetylation flask. If a ground joint is not available, a flask (1939). fitted with a cold finger may work equally well. Kimura, J . Soc. Che7n. I n d . J a p a n , S u p p l . bindirLy, 37, 5YO A microburet with 0.05-ml. graduations. (1934). Kolthoff, Z . a n a l . Chem., 71, 235 (1927). REAGENTS Landis and Wickmann, ISD. ESG. CHEM.. .%SAL E D . , 2, 3 9 4 ~
~~
Sodium chloride, 0.001 S , used as a standard. Silver nitrate, 0.001 S. Bromophenol blue solution, 0.1%. Bromophenol blue is mixed with the eauivalent amount of sodium hvdroxide solution and diluted to 0.l-9%. Acetic acid, lo%.Metallic sodium. Ailthounh metallic sodium often contains sodium chloride as an impuGty, this need not be considered, as the error produced can be eliminated by the blank test. %-Butyl alcohol, isobutyl alcohol, or amyl alcohol. The alrohol must be digested with metallic sodium to remove aldehydes and distilled; otherwise the aldehydes polymerize by the artion of sodium and give to the solution a brown coloration
(1930).
Xiederl and Niederl, “Alicroniethods of Quantitative Organic Elementary Analysis,” New York, John Wiley & Sons, 1938. Ochiai-Tsuda, “Yfiki Birj-6 Sqbry6 Teiryb Bunsekihb,” 31d ed., 1942. Pregl-Roth, “Die quantitative organische Mikroanalyse,” 4th ed., Berlin, Julius Springer, 1935. Iiauscher, 1h.D. ENG.CHEW., d X . k L . E D . , 9, 296 (1937). Sakaguti, J . P h a r m . Soc. J a p a n , 62, 121 (1942). Stepanow, B e y . . 39,4056 (1906). Uyeo and Sakamoto, J . P h a r m . Soc. J a p a n , 58,219 (1938). Walker and Rae, J . A m . Chem. SOC.,33, 598 (1911). R ~ C E I V EJuly U 9, 1947
