the strontium-90 parent of yttrium-90. Although no yttrium-91 has been found, a decay measurement. is performed on every sample to discover possible contamination. ACKNOWLEDGMENT
Acknowledgment is made of the valuable support given by Melvin W. Carter, and the laboratory assistance rendered by Estie Pepper, Ann Etrong, and Johnnie Johnson. Ursula MOSS,
LITERATURE CITED
(6) Radiological Health Data 3, 48 (1962).
(1) Goldin, A. S.J Velten~ R. J.1 ANAL. CHEM.33,149 (1961). ( 2 ) Hahn, p. I Baratta, E. J.I Northeastern
MENTIONof several commercial products used in connection with the work reported in this article does not constitute an endorsement by the U. S. Public Health
Radiological fhalth Laboratory, WinChester, Mass., personal communication, 1963. (3) Lamana, A., Levine, H., Rockville Radiological Health Laboratory, Rockville, Md. personal communication,
1963. (4) Porter, C. R., et al., ANAL. CHEY. 33,1306 (1961). (5) Pyzell, E. , Southwestern Radiological
Health Laboratory, Las Vegas, Nev. personal communication, 1963.
service.
CHARLES R. PORTER BERNDKAHN Southeastern Radiological Health Laboratory, Montgomery, Ala., and Robert A. Taft Sanitary Engineering Center, Cincinnati, Ohio Division of Radiological Health U. S. Public Health Service
Determination of Nonionic Ethylene Oxide Adduct in Some Commercial Products SIR: Published methods for the determination of poly(ethy1ene oxide) and related compounds may be classified under the three main headings: gravimetric, spectrometric, and volumetric. A gravimetric method by Oliver and Preston (3) is based on the precipitation of the phosphomolybdic acid complex in a barium chloride-hydrochloric acid medium. Stevenson (7) described a colorimetric method based on precipitation of phosphomolybdate followed by determination of the molybdenum content of the precipitate colorimetrically. A routine volumetric method by Schonfeldt (6) involves precipitation of the ethylene oxide adducts with an excess of potassium ferrocyanide and titration of the unused reagent with zinc sulfate solution. Another volumetric method, reported by Uno and Miyajima ( 8 ) , uses sodium tetraphenyl borate as titrant and congo red as an indicator. Van der Hoeve (9) showed that polyethylene oxide forms a blue precipitate with ammonium cobaltothiocyanate. Brown and Hayes (1) based a method on this reaction but used a modified version of Van der Hoeve's Table I. Typical Results on Eight Lots of a Commercial Product' by Two Methods
Phosphomolybdic Cobaltothiocyanate Found Relative Found Relative 70 error %* 70 error q;j* 0.345 -1.4 -1.1 0.347 -0.9 +8.0 0.341 -2.6 -7.4 0.342 -2.3 -7.1 0.310 -2.9 -8.6 0.347 -0.9 -0.3 0.353 +0.9 +1.1 0.341 -2.6 -6.9 Label Claim 0.35070. Error relative to Label Claim.
0.346 0.378 0.376 0.325 0.320 0.351 0.354 0.326
*
678
ANALYTICAL CHEMISTRY
reagent (200 grams of ammonium thiocyanate plus 30 grams of hydrated cobalt nitrate). They extracted the complex into chloroform and measured the absorbance of the solution a t 620 mp or 318 mp, with the latter having a higher sensitivity. Morgan ( 2 ) developed a modified version of this colorimetric method, with greater sensitivity in the visible region by extracting the complex into benzene, then decomposing the cobaltothiocyanate complex with water and determining the cobalt as its nitroso-R salt complex at 500 mp. I n any of these methods, the presence of ionic surfactants would interfere with the determination of the nonionic agents. Rosen (4) reported the separation of nonionic surface active agents from ionic by the batch ion exchange method. Dowex 1-X2 (200 to 400 mesh) was used as the ion exchange resin. Smith (6), in a comprehensive review of surfactant analysis, has suggested the use of a mixed-bed resin which removes all of the ionic surfactants as well as the inorganic material present as builders, softeners, or as impurities. An example of this resin in Amberlite MB-1. We have investigated a procedure for the rapid separation of nonionic surfactant (Triton X-100) from ionic surfactant, with mixed-bed resin and subsequent determination of the nonionic fraction by a modification of the method of Brown and Hayes, (1). Several other nonionic surfactants were also investigated. EXPERIMENTAL
Apparatus. Absorbance measurements: Beckman D U spectrophotometer or Evelyn colorimeter. For scans of absorbaiice us. wavelength: Beckman model DK-2 double-beam recording instrument.
Reagents. AMBERLITEMB-1, 20 t o 50 mesh, (Rohm and Haas Co.) may be used or a substitute may be made as follows: mix in a water slurry equal volumes of strong cationic resins (either Dowex 50-X4 or Amberlite IRA-120) and anionic resin (Amberlite IRA-400). -khfhfOYIUM COBALTOTHIOCYANATE REAGEI~T.Dissolve 178 grams of ammonium thiocyanate and 28 grams of cobalt nitrate hexahydrate in n-ater and dilute to 1000 ml. with water. The reagent is stable stored in a polyethylene bottle. STAXDARDSOLUTION. Keigh accurately about 2 grams of Triton X 100 and dissolve in 100 ml. of ethanol, then dilute to 1000 ml. with 50% v./v. aqueous ethanol. Procedure. The column of mixedbed resin, in a layer about 4.5 cm. high (1- to 1.5-cm. diameter) between two small pledgets of glass wool, is washed first with 25 ml. of water, then with 16 ml. of 5OY0 v./v aqueous ethanol. The sample solution is prepared containing about 0.2 mg. per ml. of the surfactant in 507, v./v. aqueous ethanol. The sample is added to the column in 8-ml. aliquots, and the eluent obtained while adding the third aliquot is collected. Pipet into a 50-ml. polypropylene centrifuge tube, (Silicone-coated glass centrifuge tubes may be used), 2 ml. of the eluent, 5 ml. of cobaltothiocyanate reagent, and 20 ml. of ethylene dichloride. In other Table II.
Trade name Igepal CO 990 Brij 52 Brii 76 Brij 98 Tween 60
Reaction of Various Surfactants
Av. absorbance" 0.323 0.283 0.922 0.943 0.788 0.346 0.550
Glycosperse TS20 Triton X-100 These values are temperature dependent. (1
tubes, pipet 2 ml. of lhe standard solution and, for the blarlk, pipet 2 ml. of 50% v./v. of aqueous ethanol. All tubes are shaken on a mechanical shaker for about 2 rrlinutes, then centrifuged for 30 seconds a t about 1500 r.p.m. The aqueous layer is aspirated off, and the absorbance is measured a t 620 mp against the rcagent blank. RESULTS A N D DISCUSSION
Accuracy. Result.; obtained with this method on commercial products are listed in Table I and compared with results obtained by the gravimetric method of Oltver and Preston (3) (phosphomolybdic acid method). All samples had both ionic surfactant and Triton X-100. An empirical correction factor mas wed in the gravimetric method, based on a separate assay of the ionic surfxtant. Precision. Replicate determinations of Triton X-100 by this method on a commercial product with a label claim of 0.35091, gai'e a n average of 0.355% for 10 deterininations, and a The range of 0.345 to 0.360%. standard deviation was +0.00469, with a relative standard deviation of 2~1.3491,. D a t a on prepared samples indicated t h a t the method shows no significant bias. Discussion. All of the published methods which depend on quantitative precipitation are somewhat time consuming. The cobaltothiocyanate
colorimetric methods (1, 2 ) require quantitative extraction of the complex which adds several steps to the method. Brown and Hayes (1) found the extraction to be temperature-sensitive. This variation was overcome by running a standard with each group of samples. Thus, by the use of a single extraction by partitioning rather than total extraction, the analytical time was reduced to 30 minutes as compared to 60 minutes by the method of Brown and Hayes (1). The method is fairly general for nonionic surfactants containing ethylene oxide adducts. Fifteen different surfactants were tested for color formation and extraction with ethylene dichloride. Table I1 lists seven surfactants run in triplicate. The alcohol concentration of the sample had to be adjusted to give a homogeneous solution which is necessary for column separation. The columns were prewashed with the same concentration of aqueous alcohol as the sample (between 5091, v./v. and 957, v./v.). Morgan (2) encountered difficulty with extraction of the complex of some surfactants in chloroform. We found ethylene dichloride extracted all surfactants tested which were extractable by benzene. Qualitative tests were run on Igepal DhI 210, Igepal DM 530, Igepal DM 730, Igepal CO 880, Igepal CO 530, Brij 35, Rfyrj 51, and Tween 40. Only Igepal D M 210 produced a color complex which was not extracted by ethylene dichloride or benzene.
The absorbance of the triplicates were averaged and the per cent deviation for the seven surfactants were grouped and plotted on a bar graph, which showed no significant difference from that obtained for Triton X-100. The standard used must be of the same surfactant being determined, since the absorbance of the cobaltothiocyanate complex depends on the number of ethylene oxide units present (1). LITERATURE CITED
( 1 ) Brown, E. G., Hayes, T. J., Analyst 80,755 (1955). ( 2 ) Morgan, D. J., Ibid., 87, 233 (1962). (3) Oliver, J., Preston, C., Nature 164, 242 (1949). (4) Rosen, M. J., ANAL.CHEM.29, 1675 (1957). ( 5 ) Schonfeldt, X., A'ature 172, 820 (1953). (6) Smith, W. B., Aiialyst 84,77 (1959). ( 7 ) Stevenson, D. G., Zbid., 79, 504 (1954). (8) Uno, T., Miyajima, K., Chem. Pharm. Bull. (Tokyo) 1 1 , 75 (1963). (9) Van der Hoeve, J. A . , Rev. T r a n . Chim. Pays-Bas 67, 649 (1948).
JOSEPH R. WEBER ELMERF. DEGNER KHALID5.BAHJAT~
Quality Control Laboratories Miles Laboratories, Inc. Elkhart, Ind. Elevent,h Detroit Anachem Conference, October 22, 1963 Present address, Quality Control Laboratory, Xerox Corp., Webster, X. Y.
Increasing Slensitivity of 3-Methyl-2-Benzothiazolone Hydrazone Test for Analysis of Aliphatic Aldehydes in Air SIR: Numerous methods have been employed to determir e aliphatic aldehydes in the atmosphere (S), and concentrations up to 1 p.p.m. by volume have been found in the ambient air of some large cities (9) I n most procedures aliphatic aldehydes are reported as formaldehyde since it has been shown that fornialdehyde is not only fairly stable in air (8) but is also the predominant aldehyde in polluted air ('7). The sensitivities obtained with various procedures used to determine formaldehyde have been compared (5) and by far the most ;sensitive is the 3methyl-2-benzothiazolme hydrazone (MBTH) test (6). dliphatic aldehydw react with MBTH in the presence of ferric chloride to form a blue catioric dye in acidic media. This relatively new test has been applied to analyses of aliphatic aldehydes in the ambient air of Los Angeles (2) and in ;synthetic photo-
chemical smogs (1). During color development in the MBTH procedure, a persistent water insoluble turbidity is encountered. To dissolve this turbidity, and give a homogeneous solution for colorimetric analysis, acetone must be added to the solution in at least equal volume. Because of this dilution, together with that caused by the addition of ferric chloride solution, only about one tenth of the potential sensitivity of the MRTH procedure is realized during the analysis of air samples (4, 5 ) . A modification of the 1 I B T H procedure is described in which the addition of sulfamic acid, in the oxidizing step of the reaction, gives a solution free of turbidity and cal)able of colorimetric analysis without dilution by acetone. -4reduction in the volume of the oxidizing agent originally added in this step further contributes to the concentration of the color. Although a comparison of this procedure with that
of Sawicki et al. (6) shows a loss in molar absorbance, the sensitivity of the method is increased approximately sixfold. This increased sensitivity easily permits the analysis of aliphatic aldehydes in the parts-per-billion range in ambient air. EXPERIMENTAL
Reagents and Apparatus. The 3methyl-2-benzothiazolone hydrazone hydrochloride was purchased from the Aldrich Chemical Co., Milwaukee 10, ]Vis. A 0.05% aqueous solution of this compound was used as the collecting solution; i t was filtered, if necessary, and was stable for a t least 1 week. The oxidizing agent was an aqueous solution containing 1.6% sulfamic acid and 1.0% ferric chloride. This solution was also filtered, if necessary. The stock formaldehyde solution was a 36 to 3801, ACS reagent purchased from Matheson, Coleman and Bell and VOL. 36, NO. 3, MARCH 1964
0
679
