a stirrer. T h e absolute sample size could then be reduced.
only about 3 to 4%, b u t this is normallv adequate at such low concentrations.
SUMMARY ACKNOWLEDGMENT
The electrade is easily reproducible, no pretreatment of any kind is necessary, and calibration values can be maintained over a long period of time. I n contrast to other systems, interaction between mixtures of deposited metals is minimized and resolutions of mixtures can be accomplished which are not possible by conventional polarography. The sensitivity of the method is high and solutions as dilute as 0.001 y per ml. can be analyzed. On the other hand, the precision of the method is
This research was supported b y the United States Air Force, through the Office of Scientific Research of the Air Research and Development Command. This support is gratefully acknowledged. LITERATURE CITED
(1) Arthur, Paul, Komyathy, J. C., Maness, R. F., Vaughan, H. W., ANAL.CHEM. 27, 895 (1955). (2) Delahay, Paul, “New Instrumental
Methods in Electrochemistry,” p. 233, Interscience, New York, 1954. (3) Gardiner, K. W., Rogers, L. B. , ANAL.CHEM.25, 1393 (1953). (4) Johnston, R. J., Ubbelohde, A. R., Proc. Royal SOC.(London) A206, 276 (1951). \----,Kolthoff, I. M., Tanaka, Kobuyuki, ANAL.CHEX 26, 632 (1954). Lord, S. S.,O’Neill, R. C., Rogers, L. B., Ibid., 24, 209 (1952). Rosie. D. J.. Cooke. W. D.. Ibid.. 27, 1360 (1955). Sevcik, A., Collection Czechoslov. Chem. Commun. 13, 349 (1948). Streuli, C. A., Cooke, W. D., ANAL. CHEM.25, 1691 (1953). Zakhar’evskil, M. S., Khim. Referat. Zhur. 2, 84 (1939). ,
I
RECEIVED for review November 17, 1956. Accepted January 16, 1957.
Determination of Traces of Potassium in Reagent Chemicals by Sodium Tetraphenylboron and Sodium Cobaltinitrite W. K. KINGSLEY, G. E. WOLF, and W. E. WOLFRAM J. T. Baker Chemical Co., Phillipsburg, N. J.
Determination of traces of potassium by turbidimetric sodium cobaltinitrite and gravimetric sodium tetraphenylboron methods was investigated as well as the influence of excess sodium on accuracy. The recoverability and reproducibility of each method were evaluated when applied to reagent grade sodium salts and sodium hydroxide. Results were compared with flame photometric values.
T
increasing demand for chemicals of higher purity emphasizes a need for more accurate methods for determination of trace metals. This paper is primarily concerned with the comparison of the turbidimetric sodium cobaltinitrite ( 1 ) and gravimetric sodium tetraphenylboron methods for determination of trace amounts of potassium in reagent grade chemicals. The sodium cobaltinitrite gravimetric method is included only to sholy a direct comparison between two grarimetric procedures. Gravimetric and volumetric methods using sodium tetraphenylboron have been described extensively in the literature ( 3 ) . The authors chose the gravimetric method for simplicity and accuracy. Solutions containing known amounts of potassium mere prepared and the potassium content was determined grarimetrically with sodium cobaltiniHE
trite aiid bodium tetraphenylboron. X turbidimetric determination of potassium was also made n ith sodiuni cobaltinitrite and read on an electrophotometer for greater ac’curacy. known aniount of sodium ion was added to the solution and the potassium content agaiii deterniined to shon the msrked influence of excess sodiiini on the turbidimetric determination. Seven sodium salts and sodium hydroxide conforming to ACS specifications ( I ) , TI-hich require a potassium determination, were analyzed for potassium turbidimetrically with sodium cobaltinitrite and gravimetrically with sodium tetraphenylboron. The results n-ere compared n itli flame photometric
Table I.
values (Table I). Potassium in sodium acetate was determined by the first two of these methods. Known amounts of potassium were added in order to determine the rerorerability of pot,:wiuni by both methods, in the presence of the large amount of sodium ion in t l ! ~salt. APPARATUS AND REAGENTS
ELECTROPHOTOVCTER, Fisher dcicw tific Co. AC Model, equipped nit11 :I 6 5 0 - m ~filter. SPECTROPHOTOJICTER, BecLniaii blodel DU with flame attachment
SODIUM COBALTIKITRITE TESTSOLU-
Dissolve 25 grams of sodium nitrite ( S a S O 2 ) in 50 nil. of watcr, add 5 ml. of glacial acetic acid and 3 gram?
TION.
Per Cent Potassium in Reagent G r a d e Chemicals
XCS specifications Sodium acetate (NaCZH3023HzO) 336 Sodium bicarbonate ( NaCH03) 338 Sodium carbonate, anhydrate (r\’a&Oa) 346 Sodium carbonate, monohydrate ( Na2C03 HaO) 350 Sodium chloride (NaC1) 354 Sodium hydroxide ( NaOH) 364 Sodium nitrite (NaNO2) 369 Sodium oxalate ( Ka2C204) 372 a
Method Sodium Sodium tetraFlame cobalti- phenyl- photomnitrite boron eter 0 005 0 004 0 005 0 005 0 002 0 002 0 005 0 0009 0 002 0 004 0 003 0 003 0 001 0 0008 0 001 0 01 0 001 0 002 0 002 0 0008 0 001 0 005 0 001 0 002
S o . refers to page ( 1 ) .
VOL. 29, NO. 6, JUNE 1957
939
oi cobalt nitrate [Co(XO& 6HzO] dissolved in 15 ml. of water, and dilute to 100 ml. Make a fresh solution for each set of tests ( 2 ) .
SODIUMTETRAPHEXYLBORON TEST SOLUTION.Dissolve 1.2 grams of sodium tetraphenylboron in 100 ml. of water and shake with 0.5 gram of alkali free aluminum oxide (!L~~O~)for 5 minutes. Filter; refilter the initial portions if they are turbid (6). POTA4SSIUJl SOLUTIONA. Dissolve exactly 5.000 grams of 99.95% reagent grade potassium biphthalate in a minimum amount of water and dilute to eyactly 250 nil. Each 10-ml. aliquot contains 38.2 nig. of potassium ion. POT.~SSIUJI SOLUTIOSB. Dissolve 0.5224 gram of 99.95% reagent grade potassium biphthalate in a minimum of water and dilute to 1 liter. One niilliliter contains 0.1 mg. of potassium ion.
SODIUMTETRAPHEXYLBORON ITASH
SOLUTION. Dilute 10 ml. of sodium tetraphenylboron test solution to 100 ml. SODIUMSOLUTION. Dissolve 35.676 grams of reagent grade anhydrous sodium acetate in a minimum amount of water and dilute to 100 ml. One milliliter of the solution contains 100 nig. of sodium. EXPERIMENTAL
Gravimetric Sodium Cobaltinitrite Procedure. Exactly 10 ml. of potassium solution A was diluted t o 100 ml. with mater, 25 nil. of sodium cobaltinitrite test solution was added, and t h e solution was warmed t o 70" C. It was cooled and filtered through a tared Gooch crucible. The precipitate was washed with water, dried a t 100" C. for 2 hours, cooled, and weighed. This same procedure was repeated, adding 5ml. aliquots of sodium solution to each 10 ml. of potassium solution A. The results are shown in Table 11. Gravimetric Sodium Tetraphenylboron Procedure. Exactly 10 ml. of potassium solution A was diluted t o 100 nil. with water; 2 ml. of 1 t o 1 acetic acid and 25 ml. of sodium tetraphenylboron test solution were added ivith stirring. T h e solution was allowed to stand for l hour, filtered through a tared Gooch crucible, and washed with three 5-ml. portions of sodium tetraphenylboron wash solution. The precipitate was dried for 2 hours a t 110" C., cooled, and weighed as potassium tetraphenylboron. This same proccdurc was repeated adding 5 nil. of sodium solution to each 10 nil. of potassium solution -1. The results are shown in Table 11. Turbidimetric Sodium Cobaltinitrite Procedure. A series of standards was prepared containing 5 to 20 p.p.ni, ( 7 ) of potassium solution B. The standards nere diluted to 20 ml. with water, and 5 nil. of sodium cobaltinitrite test solution war added. The solutions were diluted to exactly 50 nil. with ethyl alcohol with stirring and read with an electrophotometer using a 650-ni~filter, This same procedure \vas repeated, adding 5 ml. of 940
ANALYTICAL CHEMISTRY
Table II.
Effect of Sodium on Gravimetric Methods
SIg. IC Found in Presence of 500 Mg. of Naa
Mg. K Found"
Sodium cobaltinitrite 3'7.9
38.2 38.3
Sodium tetraphenylhron 38.2 38.1 38.1
Sodium cobaltinitrite 10 3 40 5 40.4
~
Sodium tetraphenylhoroii 38.2 38.1 38.2
K calcd., 38.2 mg.
sodium solution to each staiidard. The results are plotted in Figure 1. Table 111. Potassium Recoverability in Procedures for Sodium Salts and Sodium Acetate Sodium Hydroxide. The salts analyzed are listed in Table I. Sodium Cobaltinitriten TURBIDIMETRIC, SODIC31 COBALTINg. K Ng. K NITRITE. The sodium compounds were added recovered Difference checked for potassiuni content by ACS 0 0 02 specificatioiis (1). 0 02 -0 01 GRAVIMETRIC, SODIUM TETRAPHENYL- 00 01 05 0 07 0 BOROX DETERMINATIONS. All of the 0 10 0 10 -0 02 compounds, except sodium chloride, were Sodiiitu Tetraphenylboron* converted to the chlorides by dissolving 10 grams in a minimum amount of water, 0 0 02 adding 10 ml. of hydrochloric acid, and 0 01 0 03 0 evaporating to drpncqs. (The conver0 05 0 07 0 sion to the chlorides nas essential for 0 10 0 11 -0 01 three of the salts and sodium hydroxide a Sensitivity = 0.02 mg. per gram. whose alkaline solutions will precipitate Scn3itivitj = 0.01 mg. per gram sodium tetraphenylboron. Sodium nitrite may interfere by breaking down the phenyl group of tetraphenylboron.) The residue was dissolved in 10 ml. of 1 to 1 hydrochloric acid, re-evaporated Standards were prepared a t 2.0, 1.5, 1.0, to dryness, and dissolved in 25 nil. of and 0.5 p.p.ni., and a graph was prewater. The potassium content was depared from results obtained from these termined gravimetrically with sodium standards. tetraphenylboron The reqults are POTBShIUJI RECOVERABILITY IF-ITH shown in Table I. SODIUM COBALTINITRITE. One gram Of FLAME PHOTOMETRIC. Ten grams sodium acetate was dissolved in 5 ml. of each of the salts and sodium hydroxide water. Five milliliters of sodium cowere converted to the chlorides. The baltinitrite and 10 ml. of ethyl alcohol final residue was diluted to exactly 100 were added with constant stirring. The nil. The potassium content was deterturbidity of the sample was compared mined by the flame photometer a t a wave with 0.01-, 0 OS-, and 0.10-mg. standlength of 769 mp with the slit set a t 0 3 ards. KnoiT-n amounts of potassium mm. and the selector switch a t 0.1 mm. solution B were added to the sample, the above procedure was repeated, and the turbidity m s again compared with the standards. The results are shown in Table 111. POTAWL-JI RECOVERABILITYWITH SODIUM TETRAPHENYLBORON. Ten grams of sodium acetate was run according to the above gravimetric sodium tetraphenylboron procedure. Knon n amounts of potassium were added and the procedure was repeated. The results are shown in Table 111. RESULTS AND DISCUSSION
0
I
I
5
I
10
I
15
I
20
P A R T S P E R M I L L I O N OF POTASSIUM
Figure 1 . Interference of sodium in determination of potassium by sodium cobaltinitrite method
The sodium cobaltinitrite method for the determination of potassium produces results that vary in the presence of certain cations, such as sodium. The marked influence of sodium ion can readily be seen in Table I1 and Figure 1. The graph shows the effect of sodium ion on the size and amount of the cobaltinitrite precipitate. Transmittance decreases in respect to the increased concentration of the potassium ion more rapidly in tlie presence of the added
sodium ion. Since the sodium cobaltinitrite method for potassium provides no correction for the sodium ion, the results are inaccurate. T h e influence of sodium on the potassium determination with sodium tetraphenylboron shows little or no effect (Table 11). Other ions that also interfere with the sotliuni cobaltinitrite method are iron, aluminum, calcium, magnesium, and copper ( 4 ) . However, t’hese elements :IS well as manganese, c>obnlt: nickel, mlfate. and phosphate do not interfere wit’li the sodium tetraphenylboron n1ethod ( 6 ) . The determination of potnssium in tlie sodium salts and sodium hydroxide 1))- the sodium tetraplienylboron nietliotl gives results in closer agreement x i t h the flame photometric findiiigs than results obtained with the turbidimetric sodium robaltinitrite method. I n general, t’lie wriation in tlie two methods is greatest when the sodium ion concentration of the reagent is over 40%. Thus, good agreement \vv:is realized by each method for sodium carbonate monohydrate having a sodium content of 37%, whereas the anhydrous salt having R sodium content
of 43.4y0 gave poor agreement. Sodium hydroxide, with a sodium content of 57.5%, showed the greatest variance. The potassium recoverability of the sodium cobaltinitrite method is only half as sensitive as the sodium tetraphenylboron method and is limited in range from 10 t o 20 p.p.ni.I a s shown in Table 111. The salts of the sodium tetraphenylboron complex are well defined, the potassium salt corresponding exactly to the formula KB(C6H5)4.The cobaltinitrite precipitate is usually a mixture of monopotassium disodium cobaltinitrite and dipotnssiuni monos.odium cobaltinitrite ( 7 ) .
for determination of traces of potassium in reagent chemicals. ACKNOWLEDGMENT
The authors wish to thank A. J. Barnard, Jr., E. F. Joy, and E. C. Larsen of the J. T. Baker Chemical Co. for their invaluable assistance in the preparation of this paper. LITERATURE CITED
CHEMICAL SOCIETY, “Reagent Chemicals, ACS Specifications,” 1955. Ibid.. n. 19. -hERICAX
CO NC L USI0 N
The recoverability of potassium and reproducibility of tlie sodium tetraphenylboron method demonstrate the suitability of this reagent as a replacement for odium cobaltinitrite. Good filtering char:wteristics, extremely low solubility of its potassium salt (2.25 x 10-8) ( 5 ) , and the simplicity of the gravimetric method make sodium tetraphenylboron an excellent reagent
Separation and Determi nation of by Liquid-Liquid Extraction
Gloss, G. H.,’Chemist h n a l y s f 42, 50-5 (1955). Snell, F. D., Snell, C. D., “Colorimetric Methods of Analysis,” Vol. 11, 3rd ed., p . 556, Van Nostrand, Yew Tork, 1949. RECEIVED for review October 4,1956. Accepted February 5 , 1957. Division of *4nalytical Chemistry, Fine Chemicals Symposium, 100th Meeting, ACS, Atlantic City, N. J., September 1956.
Neptu nium
FLETCHER L. MOORE Oak Ridge National laboratory, Oak Ridge, Tenn.
b A rapid and quantitative radiochemical method for the determination of neptunium-237 or neptunium239 tracer is based on the liquid-liquid extraction of neptunium(lV) into 0.5M 2 thenoyltrifluoroacetone - xylene. Neptunium is separated free from interferences, both radioactive and nonradioactive. The technique may b e adapted readily to remote control, and is very effective in the purification of neptunium tracer.
-
0
of nuclear reactors of increased neutron flux has stimulated interest in the isolation and determination of the long-lived neptuniuni237 alpha emitter (tliz = 2.2 X 106 years). A method ( I ) had been developed previously for the determination of the neptunium-239 beta, gamma emitter (tliz = 2.3 days); however, because this method allowed approximately 16% of the plutonium originally PERATION
present to follow through the procedure, it could not be used for the determination of neptunium-237. It was necessary to develop a method which would achieve a clean separation of neptunium from fission products, uranium, plutonium. americium, and curium. A carrier-free method was desired to eliminate alpha absorption errors. Experience accumulated in the development of a solvent extraction method for the determination of plutonium (4) using thc chelating agent. 2-thenoyltrifluoroacetone (TTA), suggested that an effective radiocheniical procedure for the determination of neptunium-237 could be devised through the use of this reagent. JIagnusson, Hindman, and La Chapelle ( 3 ) extracted neptunium-237 with 2-thcnoyltrifluoroacetonebenzene away from plutonium and uranium under suitable reducing conditions. It was a l w desirable to use the new method for the isolation and determination of neptunium-239.
Certain substituted, fluorinated betadiketones react with metal ions to form nonionized chelate compounds which are soluble in nonpolar solvents immiscible with water. Many of these ions can be separated from each other because of the strong dependence of the extraction of these chelate compounds in nonpolar solvents on the acid concentration. Thomas and Crandall ( 6 ) report that very few aqueous ions extract appreciably from 0.5X nitric acid. These ions are zirconium(IJ‘), plutonium(1T’) neptunium(IV), cerium(IV), uranium (IV), iron(III), and tin(1V). I n the determination of neptunium23i, the most difficult separation is that of neptunium from the plutonium and uranium which arc usually prescnt in the solutions to be analyzed. Previous workers ( 3 ) have shown that under suitable reducing conditions a solution may contain neptunium(IT’), plutonium(III), and uranium(VI), and the neptunium(1T’) may be extracted I
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