tends to flatten in 6 or 8 hours of continuous operation. With the pump pressure plate removed, Solvaflex will return to shape overnight. The sensitivity of the determination is greatly affected by the quality of the methylthymol blue reagent. Weight of methylthymol blue and barium chloride is critical. Fresh methylthymol blue should be prepared daily. Certain cations, notably calcium, even in low concentrations, interfere with the methylthymol blue-barium reaction. An ion exchange column of Dowex 50W-X8 (Dow Chemical Company) has proven satisfactory for cation removal. The optimum length of the column should be determined experimentally and must be sufficient to remove the highest calcium concentrations experienced. Fourteen inches of 2-mm i.d. glass tubing is sufficient to remove all apparent interferences a t Coweeta where the calcium con-
centration never exceeds 7.0 mg/l. Since the cation exchange column tends to slow the response time, a longerthan-necessary column should be avdided. Received for review December 17, 1973. Accepted March 3, 1974. Research supported in part by the Eastern Deciduous Forest Biome, US-IBP, funded by the National Science Foundation under Interagency Agreement AG 199, 40-193-69, with the Atomic Energy Commission-Oak Ridge National Laboratory, and in part by the U. S. Forest Service, Southeastern Forest Experiment Station. Contribution No. 151 from the Eastern Deciduous Forest Biome, US-IBP. Mention of commercial products and sources does not constitute an endorsement of such products, to the exclusion of others equally acceptable, by the Forest Service or the Department of Agriculture.
Titrimetric Analysis of Carboxylic Acid-Anhydride Mixtures with Tetrabutylammonium Hydroxide C. A. Lucchesi, L. W. Kao, G. A. Young, and H. M. Chang Department of Chemistry, Northwestern Unrversity. Evanston. I / / . 60207
The majority of methods for the analysis of admixtures of an anhydride and its parent carboxylic acid are titrimetric in nature ( I , 2), and most of these involve the determination of small amounts of acid in the anhydride sample ( 3 ) .Essentially all of the methods reported for the determination of both the acid and the anhydride contents over the entire concentration range require two separate titrations with either two standardized titrants or one titrant in a two-step procedure. The oldest and probably still the most widely used procedure is that described by Smith and Bryant ( 4 ) . In this procedure, one portion of a sample is titrated for total acidity with sodium hydroxide after it is hydrolyzed with water in the presence of a pyridine catalyst. A second portion of the sample is titrated with sodium methoxide in methanol. The equivalent difference between the two titrations yields the anhydride content, and through calculation the acid content is found. Since the anhydride and acid concentrations are derived from the difference between two large numbers, the precision is poor-particularly, a t very low and very high acid concentrations. Other two-step methods also suffer from the same disadvantage and are even more excessively time-consuming. The purpose of the work reported here was to develop a simple and rapid single titration procedure applicable to a wide variety of anhydride samples over an extended concentration range. A number of investigators have demonstrated that anhydrides behave as monobasic acids when titrated with sodium methoxide in nonaqueous solvents ( 5 - 7 ) . PatchorSiggia. "Quantitative Organic Analysis via Functional Groups," John Wiley. New York, 1967, p 187. (2) R D Tiwari and J P. Sharma, "The Determination of Carboxylic Functional Groups." Pergamon Press, Oxford, 1970. p 68. (3) E. J Greenhow and R. L. Parry Jones. Analyst (London) 97, 346 (1) S.
(1972). (4) D M . Smith and W. M . D. Bryant. J. Amer Chem. SOC.. 58, 2452 (1936) (5) J . S. Fritz and N. M . Lisicki, Anal. Chem.. 23, 589 (1951) (6) A. Berger, M. Sela, and E. Katchalski. Anal. Chem.. 25, 1554 (1953). ( 7 ) A. Patchornik and S. E. Rogozinski, Ana/. Chem.. 31, 985 (1959)
nik and Rogozinski ( 7 ) reported the use of Triton B (trimethylbenzylammonium hydroxide) in pyridine as a titrant for anhydrides and presented data for the titration of acetic acid-anhydride mixtures. Their procedure required heating the sample in a dioxane-pyridine-water solution before titration, and two moles of Triton B were consumed for each mole of anhydride. Tiwari and Sharma (2) state that the anhydride content of an anhydride-acid mixture may be obtained from a total acidity determination by a simple calculation, but no data are given. In this paper, a method for the simultaneous determination of an anhydride and its parent carboxylic acid in binary mixtures is presented. The method involves a simple, room temperature indicator titration of a sample in pyridine with tetrabutylammonium hydroxide (TBAH) in benzene-methanol as the titrant. The indicator is either Thymol Blue or Azo Violet. Under these conditions. the anhydrides tested behave as monobasic acids. Data are presented for acetic, benzoic, maleic, phthalic, and succinic acid-anhydride binary mixtures.
EXPERIMENTAL Reagent. All the acids and anhydrides used were the best available. Most were analytical reagent grade obtained from .J. T. Baker (Phillipsburg, N.J.), Eastman Kodak (Rochester, N.Y.), Fisher (Fair Lawn. S . J . ) or Matheson, Coleman and Bell (Norwood, Ohio). The benzoic acid was NBS sample 140B. Except for acetic, all the acids were dried a t 110 "C for a t least 2 hours before use. The anhydrides were used as received or pulverized in a glove bag under dry nitrogen. The zone refined maleic and phthalic anhydrides were obtained from Aldrich (Milwaukee, Wis.). The pyridine (Eastman), acetone (Baker), and benzene (Fisher, spectranalyzed grade) were dried over 15% by weight of Linde (New York. N.Y.) molecular seives 4A before use. Absolute methanol (Baker) and 99% acrylonitrile (Aldrich) also were used as solvents, The TBAH titrant was made with silver oxide (Fisher) and tetrabutylammonium iodide (Eastman), and the TPA titrant was made with tripropylamine obtained from Eastman. The anhydrous barium perchlorate was from K and K Laboratories (Plain-
A N A L Y T I C A L C H E M I S T R Y , V O L . 46. NO. 9. A U G U S T 1974
* 1331
$Anhydride
Table I. Comparison of T B A H and T P A Titrations of A n h v d r i d e Samules Found b y TBAH, Anhydride sample
Acetic Benzoic I Benzoic I1 Maleic Phthalic Succinic S t d dev
7"
Acid found b y T P A ( 3 ) Acid found with Ba(ClOa)?, b y ?'PA
Anhydride
Acid
c.7 /o
98.0 97.7 82.1 82.6 94.0 94.2 98.5 98.1 95.7 96.0 96.9 96.4 0.27
2.0 2.3 17.9 17.4 6.0 5.8 1.5 1.9 4.3 4.0 3.1 3.6 0.27
2.1 2.0 18.1 17.9 5.5 5.6 ... 5.2 5.0 4.8 4.9 0.11
(IO),5%
... ...
... ... ... 1.0 1.1 5.0 5.1
(E) R H . Cundiff and P. C. Markunas, A n a / . Chem.. 28, 792 (1956) (9) J. Kucharsky and L. Safarik, "Titrations in Non-aqueous Solvents," Elsevier Publishing Co . Amsterdam, 1965
1332
(g - $)(-)(loo)E M
where B = net milliequivalents of TBAH, W = weight of sample in mg, E = equivalent weight of the acid, and M = molecular weight of the anhydride. The acid concentration is taken as the difference between 100 and the calculated per cent anhydride. The potentiometric TPA titrations of maleic and phthalic acids in the anhydride samples were carried out as described by Siggia and Floramo (10). Only maleic and phthalic acids were titratable by this procedure; both were monoprotic. The TPA titrations in the presence of barium perchlorate were carried out as described by Greenhow and Parry Jones ( 3 ) with the 0.W TPA titrant. A sample containing from 0.3 to 0.8 milliequivalent of acid was dissolved in 50 ml of acrylonitrile and 0.4 gram of anhydrous barium perchlorate was added to the solution. All of the acids studied were titratable by this procedure. Acetic, benzoic, and maleic acids were monoprotic; fumaric, phthalic, and succinic were diprotic.
RESULTS
0.1
view, N.J.) and dried a t 140°C. for a t least 2 hours before use. The Thymol Blue (Baker) indicator used was a 0.3% (w/v) solution in absolute methanol. The Azo Violet indicator was a saturated solution of p-nitrobenzeneazoresorcinol (Fisher) in dry benzene. Dry, high-purity nitrogen gas (Linde) was used. Apparatus. A conventional potentiometric titration set-up with a 10-ml buret (0.02-ml divisions) and a 250-ml electrolytic beaker with a cork cover was used. The cork had holes for electrodes, buret tip, and nitrogen inlet and outlet. The buret was fitted with a drying tube containing Drierite. Beckman glass electrodes (No. 41263) were used with Beckman ceramic junction calomel electrodes (No. 39402) in which the aqueous salt bridge was replaced with methanol saturated with potassium chloride (8). All titrations were magnetically stirred and the emf's were read with a Beckman Expandomatic pH/millivolt meter. Before use in a given solvent, the electrodes were presoaked in the solvent for a t least 48 hours and stored thereafter in the same solvent ( 3 ) . The indicator titrations were carried out with a 10-ml microburet fitted with Driertie on top and a one-hole rubber stopper attached to the tip. The titration vessel was either a 125- or 250-ml iodine flask. Indicator solutions were added with a 1-ml tuberculin syringe. Procedure. Standardizations. The 0.1F TBAH solution in 10 t o 1 (v/v) benzene-methanol was prepared as described by Cundiff and Markunas (8, 9) and standardized against NBS benzoic acid. From 0.05 to 0.1 gram of benzoic acid was weighed (to the nearest mg) into a dry iodine flask. About 20 ml of pyridine was added, the air displaced with dry nitrogen, and the flask covered with a glass stopper. When the acid was completely dissolved, about 0.2 ml of Thymol Blue indicator was added with the syringe. The flask was then placed under the rubber stopper at the buret tip, and the solution was immediately titrated with the 0.1F TBAH to the blue end-point color of the indicator. The volume of titrant was recorded and later corrected by the volume of titrant required for a blank. A typical blank titration for the pyridine solvent was 0.04 ml. The 0.2F tripropylamine (TPA) titrant in dry acetone was standardized as described by Greenhow and Parry .Jones ( 3 ) by potentiometric titration against KBS benzoic acid. A 0.1F TPA titrant was prepared by dilution of the 0.2F solution with acetone and standardized against maleic acid which was previously assayed by titration with standardized TBAH. Titration. The TBAH titrations of the acid, anhydride. and acid-anhydride samples were performed with an amount of'sample (weighed to the nearest 0.1 mg) that would require from 0.5 to 0.9 milliequivalent of titrant. The determinations were done in the same way as the standardization above except that two drops of Azo Violet were used for succinic acid and for the succinic acid-anhydride samples. All the acids except succinic are monoprotic in this procedure; succinic is diprotic. Each anhydride has an equivalent weight equal to its molecular weight. The anhydride content of the acid-anhydride mixtures may be calculated with the following equation:
=
Typical results obtained with the TBAH titration for a number of anhydride samples are compared with results obtained with the TPA methods (3, 10) in Table I. The anhydride samples were purchased as pure substances. Several had been in the laboratory for some time in containers which had been opened before use in this study; .some were new and not previously opened. The precision of the method for a single determination, as measured by the standard deviation of the six sets of duplicates ( I I ) , is 0.27%. It was necessary to use the Siggia method (10) for determining the maleic acid in the maleic anhydride sample because with the Greenhow method ( 3 ) maleic acid is not titrated in the presence of maleic anhydride. In Table I1 are given the recovery data for the five acidanhydride systems studied. The concentration of acid in the binary acid-anhydride mixtures covered the range from about 5 to 90% and showed an overall average recovery of 100.6%. Over the corresponding concentration range, the average anhydride recovery was 99.7%. In no case was the recovery lower than 93% nor higher than 108%. The theoretical values in Table I1 were obtained by taking into account the purity of the anhydride samples on the assumption that only impurity in the anhydride sample was the parent carboxylic acid.
DISCUSSION The titration system consisting of the TBAH titrant in methanol-benzene and the pyridine solvent is generally readily available in laboratories engaged in the nonaqueous titration of organic acids and was chosen over other possible systems primarily for this reason. The pyridine is not only a good solvent for the tetraalkylammonium salts of weak acids, but it serves also as a catalyst in anhydride esterification and hydrolysis reactions. Titration of each of the anhydrides studied showed that 1 mole of quaternary base is consumed per mole of anhydride in reaching the end point in the titration. This is the same stoichiometry involved in the titration of anhydrides with sodium methoxide ( 7 ) , and since the so-called quaternary hydroxide is known to consist of equimolar amounts of methoxide and hydroxide (12), the following reaction is suggested. (RC0)zO + [ B u ~ N ] [ O C H ~ ] RCOOCH3 + [Bu~N][RCOO] If this is the reaction, then as the initially present meth( 1 0 ) S . Siggia and N. A . Floramo, Anal. Chem.. 25, 797 (1953) (11) W J Youden, "Statistical Methods for Chemists." J o h n Sons, Inc.. New Y o r k . N Y , 1951. p 16. (12) M L Cluett. Anal. Chem.. 31. 610 (1959).
A N A L Y T I C A L CHEMISTRY, V O L . 46, N O . 9, A U G U S T 1974
Wtley and
Table 11. Recovery Data for TBAH Titration of Acid-Anhydride Mixtures Theoretical"
-~
Acid-anhydride mixture
Acetic A Acetic B Acetic C Acetic D Acetic E Benzoic A Benzoic B Benzoic C Maleic A Maleic B Maleic C Maleic D Maleic E Phthalic A Phthalic B Phthalic C Phthalic D Phthalic E Succinic A Succinic B Succinic C
~~
~~
~~~
~
Acid ~~
~~
m
~~~
~
~~
~
~
~~
Found
~
Anhydride ~~~
~
1 ' /'
~~
~~
...
~~
Acid,
~
'10
lllg
Anhydride,
< r
-
Recovery,
Acid
(,;
~~~
Anhydride
/O
(/" 1
4.7 15.3 18.6 43.0 52.9
5.5 23.9 48.6 75.2 86.7
81.3 48.6 19.7 14.2 8.1
94.5 76.1 51.4 24.8 13.3
5.1 24.1 46.6 74.1 86.3
94.9 75.9 53.4 25.9 13.7
92.7 100.8 95.9 98.5 99.5
99.7 103.9 104.4 103.0
14.2 42.0 73.3
15.3 45.0 90.8
78.8 51.3 7.4
84.7 55.0 9.2
14.7 44.9 91.4
85.3 55.1 8.6
96.1 99.8 100.7
100.7 100.2 93.5
12.8 48.2 87.3 2.4 9.1
10.6 38.3 85.3 5.3 11.2
108,l 77.7 15.1 42.5 71.9
89.4 61.7 14.7 94.7 88.8
11.1 39.2 85.1 5.6 11.8
88.9 60.8 14.9 94.3 88.2
104.7 102.3 99.8 106.0 105.0
99.4 98.5 101.4 99.6 99.3
15.2 37.7 95.3 4.2 8.7
15.2 41.7 91.3 5.1 11.1
84.9 52.7 9.1 78.4 69.8
84.8 58.3 8.7 94.9 88.9
16.0 41.2 91.8 5.5 11.8
84.0 58.8 8.2 94.5 88.2
105.3 98.8 100.5 107.8 106.3
99.1 100.9 94.3 99.6 99.2
13.6 28.3 48.7
13.5 39.5 90.9
87.4 43.3 4.9
86.5 60.5 9.1
12.6 38.3 91.5
87.4 61.7 8.5
93.3 97.0 100.7
101.0 102,o 93.4
100, '1
Purity of the acids and of the anhydrides are accounted for in the theoretical values given.
Volume o f T B A H
Volume of T B A H
Figure 1. Titration curve for benzoic acid ( 1 ) benzoic anhydride ( 2 ) , and the acid-anhydride mixture ( 3 ) in pyridine solvent and T B A H titrant in benzene-methanol oxide is consumed, more is produced via reaction of the hydroxide with the methanol in the titrant. Another possible mechanism which gives the same 1 to 1 stoichiometry involves the reaction of the methanol in the titrant to give the methyl ester and the carboxylic acid followed by neutralization of t h e carboxylic acid with the quaternary base. The only known titration of acid anhydrides with a quaternary base (trimethylbenzylammonium hydroxide) was reported by Patchornik and Rogozinski (7) and required 2 moles of quaternary base to 1 mole of anhydride. In the Patchornik and Rogozinski method, it appears that the anhydride actually was hydrolyzed before titration with the quaternary base. The anhydrides and acids studied in this work were titrated potentiometrically to judge the best indicator for the visual titration and to determine the equivalent weight of each substance under the conditions of the visual titration. The equivalent weight of succinic acid is half its molecular weight when titrated to the Azo Violet end point. The equivalent weight of each of the other acids equals its molecular weight in the Thymol Blue titration. In all cases. the anhydride equivalent weight equals its molecular weight. In Figure 1 are shown the curves for the
Figure 2. Titration curve for maleic acid ( l ) , maleic anhydride ( 2 ) , and the acid-anhydride mixture ( 3 ) in pyridine solvent and T B A H titrant in benzene-methanol
I
-
Irnl
-
~
Volume of T B A H
Figure 3. Titration curve for succinic acid ( l ) , succinic anhydride ( 2 ) . and the acid-anhydride mixture ( 3 ) in pyridine solvent and T B A H titrant in benzene-methanol titration of benzoic acid, benzoic anhydride, and a mixture of the acid and the anhydride with TBAH titrant in pyridine solvent. In Figure 2 is shown the maleic system; in Figure 3, the succinic system. In the maleic and succin-
A N A L Y T I C A L C H E M I S T R Y , VOL. 46, N O . 9, A U G U S T 1974
1333
ic systems, it is possible to determine the acid and anhydride concentrations via the potentiometric titration curve. The same is true for the phthalic system. It should be clear that for all systems, it is possible to do a potentiometric titration instead of an indicator titration. It is worth mentioning that as part of the effort to determine the purity of maleic acid samples, it was found that fumaric acid is titrated as a diprotic acid in the TBAH-Thymol Blue method (8). It also was found that fumaric acid is not titrated in the straight TPA method of Siggia and Floramo (10). [As stated earlier, fumaric acid is a diprotic acid in the presence of the Ba(OC14)Z acidity enhancement salt (3) whereas maleic is a monoprotic acid under these conditions.] These properties provide the
basis for determining the maleic and fumaric acid contents of binary mixtures of the two. For example, one maleic acid sample which gave an apparent maleic acid content of 110.0% by the TBAH method was calculated to have 90.0 maleic and 9.96% fumaric via simultaneous equations with the assumption that the sample was a binary mixture of the two acids. Titration of the same sample with TPA without Ba(OC14)Z gave a maleic content of 90.17% and, by difference, a fumaric content of 9.83%. Received for review December 31, 1973. Accepted March 1, 1974. The authors wish to acknowledge the support of the National Science Foundation Undergraduate Student Program.
Simple Recovery of Plutonium, Americium, Uranium, and Polonium from Large Volumes of Ocean Water V. F. Hodge, F. L. Hoffman, R. L. Foreman, andT. R . Folsom Scripps institution of Oceanography, La d o h , Calif. 92037
Fallout plutonium concentrations in the world's oceans are extremely low-so low that if we are to understand the present distributions of this man-made element in order to predict the impact of future inputs, assays of many large volumes of sea water will have to be made. Moreover, as an increasing number of nuclear reactors locate on exposed sea coasts, and as plutonium makes its debut as a commercial nuclear fuel, many assays of coastal waters also will have to be made. Unfortunately, the two most widely used methods for extracting the small amounts of plutonium from large volumes of sea water, coprecipitation with ferric hydroxide or bismuth phosphate, are characterized by low and erratic recoveries of tracer plutonium and thus, presumably, environmental plutonium (1-4). However, we have found that plutonium can be consistently recovered from 50- and 200-liter volumes of coastal water in high yields simply by the partial precipitation of magnesium hydroxide and calcium carbonate by the addition of small amounts of sodium hydroxide. Morever, americium, uranium, and polonium can be concentrated likewise from sea water and easily purified for alpha spectrometric determination.
EXPERIMENTAL Exploratory tests demonstrated that large fractions of plutonium, americium, uranium, and polonium were removed from sea water by the partial precipitation of calcium and magnesium on the addition of as little as 2.5 mmol NaOH/liter of sea water (Table I). However, from 3 to 4 mmol NaOH/liter of sea water gave volumes of precipitate that were convenient to transfer from the 50- and 200-liter sea water containers and subsequently re-
v. T. Bowen, K. M . Wong, and v. E. Noshkin. J. Mar. Res.. 29, 1 (1971). (21 T. lmai and M. Sakanoue. J. Oceanographical SOC. Jap., 29, 76 (1973) (3) H. D. Livingston, D. R Mann, and V. T. Bowen. in "Reference Methods for Marine Radioactivity Studies-Determination of Transuranic Elements, Radioruthenium and Other Radionuclides in Marine Environmental Samples," International Atomic Energy Agency, Vienna (1972) in press. (4) K . C . Pillai, ib/d. (1)
1334
sulted in relatively small volumes of 9M HCI, desirable for ion exchange. In general, unfiltered sea water was collected at the end of Scripps Pier, poured into polyethylene containers, and spiked with the appropriate tracers-approximately equal to the suspected environmental activities (see Table 11). However, somewhat larger spikes, 0.5 pCi, were used during the initial recovery tests of plutonium and americium from 1- and 50-liter samples. In subsequent assays of 50 and 200 liters of sea water, 0.05 pCi to 0.10 pCi of plutonium and americium tracers were added. Two to three hours were allowed for the tracer to mix thoroughly into the rapidly stirred solution. Then, 3.5 ml 1N NaOH/liter of sea water were added to 1- and 7-liter volumes, 10.5 ml of 50% NaOH (Mallinckrodt) to 50-liter volumes and 34 ml 50% NaOH to 200-liter volumes. The resulting milky mixture of hydroxides and carbonates was stirred for 1 to 2 hours and the fine precipitate allowed to settle overnight. The clear water was aspirated from above the precipitate leaving only enough for transfer of the precipitate to liter centrifuge tubes (cut off liter poly bottles). After centrifuging for 20 minutes a t 2500 rpm, precipitates from 50 liters of sea water occupied a volume of only about 100 ml (-10 gram dry salt). They are free of the large amounts of iron or bismuth that usually are employed. Isolation of Plutonium and Uranium. Precipitates were dissolved in the liter centrifuge bottles with concentrated hydrochloric acid and transferred to appropriate sized beakers. A volume of 12M hydrochloric acid, three times that of the dissolved material, was added to bring the acid strength to 9M; the final volume was adjusted to about 100 ml for 1-liter samples, 400 ml for 50-liter samples, and 750 ml for 200-liter samples. One drop of 30% H202 was added for each 10 ml of solution, and the solution was then heated just below boiling for 1 hour (5). After the solution had cooled, plutonium and uranium were isolated by the anion exchange techniques described by Talvitie (5) using the fact that plutonium-IV, uranium-VI, iron-111 and many other ions are strongly absorbed from 9M HC1 by Dowex 1-X2 (Bio-Rad AG 1-X2) ( 6 ) , while americium is not. The 9M HC1 effluent was saved for the americium assay. After the sample had drained and the column had been washed with 50 ml 9M HC1, iron ( a distinct yellow band) was eluted with 50 ml of 7.2M "08. Uranium was collected in the next 100 ml of ( 5 ) N. A. Talvitie. Anal. Chern., 43, 1827 (1971). (6) G. H. Coleman, "The Radiochemistry of Plutonium," Nat. Acad. Sci.-Nat. Res. Counc. Pub/.. NAS-NS 3058, 1965, p 92.
A N A L Y T I C A L C H E M I S T R Y , V O L . 46, NO. 9, A U G U S T 1974
