five consecutive elutions can be obtained before significant breakthrough occurs. Small quantities of uranium are eliminated effectively during the subsequent separation. When a significant breakthrough appears certain during a n additional elution, elute the uranyl chloride from the column with 2 or 3 liters of water. Evaporate the solution t o dryness, dissolve the uranyl chloride cake in 500 ml. of 9.6M hydrochloric acid, and p u t the uranium back on the column after xashing the latter with 9.6M acid. Place the combined hydrochloric acid effluents containing the thorium234 tracer in a 4-liter beaker, add 2 or 3 boiling chips, and evaporate the solution to about 25 ml. Transfer the solution t o a 250-ml. Erlenmeyer flask and rinse the beaker with a little concentrated hydrochloric acid to reccver most of the activity. Add the rinses t o the flask but do not transfer the boiling chips. Add 3 ml. of concentrated sulfuric acid carefully around the sides of the flask and evaporate the solution to fumes. When nearly t o fumes, add a few drops of nitric and perchloric acids t o oxidize a small quantity of organic matter from the resin. Add 2 grams of anhydrous sodium sulfate and heat the flask over a blast burner with continuous swirling
until a clear pyrosulfate fusion is obtained. Cool the flask, and add 25 ml. of water, 0.2 ml. of a ferric perchlorate solution containing 1 mg. per ml. of iron, and 2 drops of 30% hydrogen peroxide. Heat the solution to boiling and add 8M sodium hydroxide until the solution becomes alkaline, as indicated by the precipitation of ferric hydroxide and a few drops in excess. Boil the solution for 2 or 3 minutes to dissolve any lead sulfate that might be present and to decompose excess hydrogen peroxide, but ignore the typical flocs of silica that will generally be present from the resin. Transfer the solution to a 40-ml. conical centrifuge tube and centrifuge at 2000 r.p.m. for 2 minutes. Discard the supernate. Add 1 ml. of 72% perchloric acid and 15 ml. of water to the centrifuge tube. Warm the solution if necessary to dissolve the precipitate and filter the solution through a 2.5-cm. hardened paper in a small Hirsch funnel to remove the silica. Wash the tube and filter paper with a little water. The resulting solution will contain approximately 2 X lo7 c.p.m. (gamma) from 1 pound of uranyl nitrate hexahydrate containing thorium234 in equilibrium. Half this quantity can be obtained every 24 days. Prepare a working solution containing about 2 X lo5 c.p.m. per milliliter or less by appropriate dilution of the stock solution in 1% perchloric acid.
Improved Determination of Strontium-90 in by an Ion Exchange Method SIR: During analysis of several thousand Public Health Service milknetwork samples with the procedure previously reported (C), two useful modifications were developed which are described here. The procedure consists of storing the milk samples with formaldehyde preservative for the ingrowth of the yttrium-90 daughter of strontium-90, adding yttrium carrier, and then passing the milk consecutively through cation and anion exchange resin columns. The alkaline earth ions in milk are replaced by sodium ions in the cation exchange column, after which the yttrium is retained as an anionic complexprobably of citrate-in the anion exchange column. The effluent milk is discarded and the yttrium complex on the anion exchange resin is destroyed with hydrochloric acid. The yttrium, eluted with the acid, is precipitated as the oxalate, and the radio-yttrium is measured with a low-background beta counter. One modification in the original procedure is the inclusion of solvent extraction after the yttrium elution to remove 676
ANALYTICAL CHEMISTRY
Standardization. Although generally not necessary for tracer work, the solutions can be standardized by gamma counting after determining t h e counting efficiency for a given set of conditions as follows. Dissolve 1 gram of pure uranium metal or U3O8 at least several months old in the appropriate acid, add 1.0 ml. of 6.6% barium chloride dihydrate solution, and evaporate to dryness. Fuse with 3 grams each of anhydrous sodium and potassium sulfates and 3 ml. of concentrated sulfuric acid. Reprecipitate, wash, and dissolve the barium sulfate in alkaline diethylenetriamine pentaacetic acid as described in another publication ( 2 ) , and count under the desired conditions. Calculate the counting efficiency by dividing the observed counting rate per gram of natural uranium by 7.36 X lo5,the activity of uranium-238 and therefore of thorium234 per gram of natural uranium in secular equilibrium. LITERATURE CITED
S. S., McKinney, L. E., Bednas, M. E., Talanta 4, 153 (1960). (2) Sill, C. W., Willis, C. P., ANAL. CHBM.36, 622 (1964). CLAUDE w.SILL U. S. Atomic Energy Commission Idaho Fulls, Idaho (1) Berman,
Milk
the lanthanum-I40 daughter of barium140. These fission products, being so short-lived that they are usually detected in the environment only within one-half year after their formation, were not in milk when the procedure was first developed and applied. They were identified in milk soon after the resumption of atmospheric nuclear testing in September 1961 (6). At yttrium-90 and lanthanum-140 levels much higher than those occurring in milk, the two radionuclides may be distinguished from each other by their different halflives (64 us. 40 hours, respectively) and types of radiation (lanthanum emits gamma rays whereas yttrium does not). At the low levels encountered in milk, however, differentiation by decay properties is inaccurate. Solvent extraction from 14N nitric acid into 100% tributylphcsphate was utilized because effective lanthanum removal n i t h little yttrium loss had been demonstrated (1). The procedure was further modified to obtain higher yttrium yields. Initially, the maximum yttrium yield was 65% and average yields were 5570. Yttrium retention OII the resin was
improved from 80 to 99% by adding sodium citrate to the milk. The per cent eluted in 35 ml. of hydrochloric acid was increased from 81 to 967& by decreasing the amount of anion exchange resin and by thoroughly stirring the resin during elution. Other losses were minimized by small procedural changes, so that the overall average yield was increased to 86%. EXPERIMENTAL
Reagents and Apparatus. Use ion exchange resins and apparatus described in the original procedure (4), except for the following changes in dimensions: upper rolumn is 5 cm. in diameter and contains 170 ml. of Dowex 50W-X8 resin; lower column is 1.9 cm. in diameter and contains 15 ml. of Dowex 1-X8 resin. Prepare yttrium carrier by dissolving 25.5 grams of yttrium oxide in 100 ml. of concentrated nitric acid. Add water, adjust t o pH 2 with XHdOH, and dilute to 2 liters. Measure concentration of yttrium in carrier solution as yttrium oxalate. Prepare strontium carrier by dissolving 50 grams of strontium nitrate in water, adding 1 ml. of concentrated
nitric acid, and diluting to 2 liters. Prepare barium carrier by dissolving 40 grams of barium nitrate in water, adding 1 ml. of concentrated nitric acid, and diluting to 2 liters. Prepare equilibrated reagent grade kributyl phosphate (TIiP) by washing 300 ml. with 150 ml. 3f 0.5N sodium carbonate, and then with 150 ml. of water. Equilibrate thrice with 150-ml. portions of 14N nitric acid. Prepare citrate solution by dissolving 200 grams of reagent grade citric acid in 500 ml. of distilled water. Adjust p H t o 6.5 with approximately 220 ml. of 12N sodium hydroxidi’. Dilute t o 1 liter. Procedure. Place I liter of milk, stored under refrigeration (32’ to 34” F.) for two weeks, in a glass reservoir. Combine 1 ml. each of yttrium, strontium, and barium carr ers, and 10 ml. of citrate solution, transfer quantitatively to milk, and mix. Let milk flow through the t w o r3sin columns a t 10 ml. per minute. Displace milk on columns with 300 ml. 3f warm water. Separate the columns. .Ittach a separatory funnel containing 60 ml. of 2‘V hydrochloric acid to the top of the anion column. Let acid flow at 2 ml. per minute. Discard effluent until pH drops to 2 ( a f t x 10 to 20 ml.). Collect the next 5 ml. of effluent, stop flow of acid, and remove separatory funnel. Stir the anion resin thoroughly with a glass stirring rod. Wash the stirring rod with a small amount of 2147 hydrochloric acid and :tdd the acid to the resin column. Connect the separatory funnel and complete elution with 30 ml. of 2 S hydrochlor c acid. Add 5 ml. of 2‘V oxzilic acid to the eluate and adjust its pH to 1.5 with concentrated ammonium hydroxide to precipitate yttrium oxalate. Stir, heat t o near boiling, cool in ice bath, centrifuge, and discard supernatant liquid. Pipet 10 ml. of Concentrated (68%) nitric acid t o dissolve the precipitate. Transfer from centrifuge tube to separatory funnel. R a s h centrifuge tube with 10 ml. of equilibrated T B P and add T B P to separatory funnel. Shake vigorously for 2 minutes, allow phases to separate, and discard the acid phase. Wash the T B P phase h i c e with 15 ml. of 1 4 s nitric acid, and discard the acid phases. Remove the yttrium from the T B P phase by shaking with 15 ml. of water for 2 minutes. Drain the aqueous phase into a 40-ml. centrifuge tube. Repeat the yttrium re-extraction with 15 ml. of 0.1N nitric acid and combine the aqueous phitses. Precipitate yttrium oxalate as before with 5 ml. of 2 5 oxalic acid a t p H 1.5. Take up precipitate in 10 ml. of cold water and filter on tared 2.5-cm. diameter membrane filter (Millipore mem. brane filter No. OH, ?Jillipore Filter Corp., Bedford, Mass.), Wash precipitate on membrane filter with a 10-ml. portion of cold water, and dry with alcohol and ether. Weigh filter with precipitate, calculate weight of precipitate, and compute chem cal yield. Count precipitate in beta counter (having background of approximately 1 c.p.m.) for 50 minutes. Subtract
background count. Correct for yttrium90 decay in time interval between its separation from strontium-90 on the cation resin column and counting. Correct for chemical yield. Wash columns to regenerate resins. Reconnect reservoir and columns. Use cation resin elutriant to measure barium140, strontium-89, and calcium concentrations in milk. RESULTS AND DISCUSSION
The yttrium yield for the combined solvent extraction, washing, and reextraction steps was 9597& while O.lycof the initially present lanthanum was found in the final yttrium precipitate, for tracers added to the milk 24 hours before analysis. Yttrium carrier yields for the analysis of actual samples confirm the tracer values. Lanthanum-140 concentrations in actual milk samples were too low to permit radioactive recovery measurements on single samples, but the order of magnitude of the decontamination was confirmed by gamma counting 20 combined yttrium precipitates and comparing this value with the lanthanum-140 levels in the milk samples, measured by beta counting barium-140. The criterion for satisfactory lanthanum-140 decontamination-that the highest encountered lanthanum-140 activity be decreased to less than the equivalent of the 1 picocurie per liter (pc./l,) detectability limit of yttrium-90-is met by the modified procedure. I n combination with the decrease in activity resulting from the decay of the 12.8-day barium-I40 during the milk storage period, 1000 pc. of lanthanum-140 per liter would be reduced to undetectable levels. The highest barium-140 concentration in milk-network samples was 200 pc /I. ( 5 ) , corresponding to 230 pc./l. of lanthanum-140 a t equilibrium. Quantitative retention of yttrium on the anion exchange resin was achieved by increasing the citrate concentration of milk to 0.02N from its normal level of 0.01JJ. [This effect was observed simultaneously at 2 other laboratories. (2, $1. The enhanced retention is attributed to the increased complexing of yttrium by citrate in the more concentrated citrate solution. Increased complexing of the alkaline earths also occurs, as shown by the appearance of calcium and strontium-90 in the cation exchange resin effluent after passage of one-half liter of milk. The presence of the alkaline earths in the influent to the anion exchange resin interfered with the retention of yttrium by the resin, but was decreased to negligible proportions by increasing the volume of the cation exchange resin from 140 to 170 cc. As little as 12 cc. of anion exchange resin retain the yttrium quantitatively; to provide a margin of safety, 15 cc. are used.
Upon adding 2N hydrochloric acid to the anion exchange column, yttrium appears in the elutriant as soon as the pH decreases to approximately 2, indicating the destruction of the yttrium citrate complex. The elution was not as prompt as was expected for a cation on an anion exchange column; whereas 80% of the yttrium appeared in the first 35 ml. of acid elutriant, another 100 ml. was required for quantitative elution. By stirring the resin after acidification, the resin was brought into better contact with the acid, and recovery was increased to 96% in the first 35 ml. of acid elutriant, and 99% in another 25 ml. Approximately 1% of the yttrium was discarded with the initially appearing neutral effluent. The procedures were tested for reproducibility and compared with each other by analyzing 32 milk-network samples in quadruplicate-twice by the improved method and twice by the original one. Maximum, median, and minimum strontium-90 concentrations were 58, 32, and 13 pc./l., respectively, and no barium-140 or lanthanum-140 was found in these samples. The measured standard deviation for the values obtained by the improved method was equal to the computed statistical counting error, indicating a relatively insignificant analytical error. The standard deviation for the samples ranged from 0.6 pc./I. a t 13 pc./l. to 1.2 pc./l. a t 58 pc./l. For the original method, the counting error was larger by the inverse ratio of the square root of the yield-(0.86/0.55)”* on the average-and the standard deviation exceeded the counting error by approximately 25%. The smaller analytical error of the improved method is attributed to higher yields, which were between 80 and 94%, with an 86% average. Analytical results by the improved and the original methods agreed within their estimated errors. As discussed previously (4), 57-day yttrium-91 in recently produced fission products would not be separated from yttrium-90 in this procedure. Hence, this method can be utilized only because the feeding habits or metabolism of the cow results in the transmittal of very little yttrium-91 from the environment to the milk. To confirm this, 32 yttrium precipitates were combined, stored for 36 days to remove by decay 99.99% of the yttrium-90, and then beta counted for 100 minutes. Despite self-absorption and decay, as little as 0.01 pc. of yttrium-91 per liter would have been detected in samples whose strontium-89 (which has a similar halflife and fission yield) content was approximately 100 pc./l. S o vttrium-91 was detected, indicating a t least a 10,000-fold greater discrimination by the cow against yttrium-91 than against VOL. 36, NO. 3, MARCH 1964
677
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 a b o u t 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 t h e 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. I n 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
