FIa me
Spec t ro photometric Dete rminuti o n of Cesium and Rubidium in Oil Field Waters A. GENE COLLINS Bureau o f Mines, U. S. Department o f the Interior, Petroleum Research Center, Bartlesville, Okla.
b Knowledge of the cesium and rubidium content of oil field waters i s useful in water analyses correlations. These correlations aid in resolving the origin of waters and oils, exploring for petroleum and other minerals, finding casing leaks, discovering water pollution sources, and augmenting the knowledge of geologic formations. These metals are valuable, and reserves of cesium especially are being sought b y National Aeronautics and Space Administration as a fuel supply for spacecraft. A flame spectrophotometric method for determining cesium and rubidium in oil field waters, with a sensitivity permitting detection of less than 0.05 mg. per liter, was developed. Several solvents possessing high dielectric constants were evaluated for their ability to extract the tetraphenylboron complexes of cesium and rubidium from oil field waters and for their emission characteristics. Nitroethane was selected and used for the extractions and flame spectrophotometric determinations. Radiotracer methods using cesium-137 and rubidium-86 were used to estimate the extraction efficiency.
R
OF CESIUM are being sought by SASA because it is used as a fuel supply in ion-type rocket engines for interplanetary travel. Other uses for cesium as well as rubidium are as plasmas in thermionic converters to convert heat to electricity and for heat tran>fer mediums in nuclear powerplants. Gast (8) and Conipston and Jeffery ( 4 ) used a rubidium-strontium method to determine the age of rocks. A similar method should prore useful in determining the age of waters. The determination of strontium in oil field waters has been described (3). Several methods for the determination of cesium and/or rubidium are described in the literature. Borovik-Romanova (1) and Smales and Webster (18) have determined rubidium in sea water. Smales and Salmon (f7) determined cesium and rubidium in sea mater. Zyszczynska-Florian and Chomik (21) analyzed some Ciechocinek oil field brines with paper chromatography and found traces of rubidium but no cesium. ESERVCS
1258
ANALYTICAL CHEMISTRY
Some of the other methods that were investigated are: Ion exchange bj Ishibashi (11) and Smit (19); chromatography by hlagee ( 1 3 ) ; solvent extraction by Fix ( 7 ) ; radiochemical by CabeIl (b), Finston ( 6 ) ,Smalea (17, 18); colorimetric by Hara (10); spectrographic by Glendening (9)and Taylor (20) ; flame spectrophotometric by Kick (12) and Shellenberger (16); ionophoresis by Pompowski ( I d ); flotation by Rylov ( 1 5 ) ; and spot test by Dean ( 5 ) . The method debcribed in this paper can be completed more rapidly than most of the above methods and is more accurate for the determination of trace amounts of cesium and rubidium than most of them, with the exception of the radiochemical methods. The method should be suitable for determining cesium and rubidium in oil field waters and fresh waters. EXPERIMENTAL
Apparatus. -4 modified recording Beckman DU flame spectrophotometer equipped with a Farnsworth 6836; FW118 multiplier phototube. and acetylene and oxygen was used. -4 R I D L model 49-31 radiation counter equipped with a sodium iodide well crystal was used to determine the estraction efficiency. Reagents. Standard solutions of cesium. rubidium, potassium, and ammonium mere used. -4synthetic oil field water was prepared by dissolving 61 grams of sodium chloride, 19 grams of calcium chloride, 12 grams of magnesium chloride, 5 grams of strontium chloride. 5 grams of potassium chloride, and 0.4 gram of sodium bicxrbonate in a liter of matpr. The buffer solution was prepared by adjusting the pH of a 1.V sodium citrate solution to 6.6 with 0.511 nitric acid. The emission characteri5tice of 10 mg. per liter each of cesium and rubidium in 407, ethyl alcohol solutions were tested with small, medium, and large bore Beckman burncrs:. The cesium and rubidium peaks at 780.0, 794.8. 832.1, and 894.4 nip w r e .scanned automatically. The methods which were tested most extensively for the concentration and separation of cesium and rubidium from oil field brines were ion exchange and solvent extraction. Some of the ion exchangers used m r e the BIO-RAID resins (BIO-REX 40, -IMP-1, and ZP-1)
and the Duolite resins (C-3, C-10, S-30. and CS-100). We tested solvent extraction of the cesium and rubidium tetraphenylboron complexes with water-immiscible solvents possessing high dielectric constants, such as nitrobenzene, nitroethane, nitromethane, 1-nitropropane, 2-nitropropane, amyl acetate, and amyl alcohol. The optimum p H for the extraction proved to be about 6.6. An acetate buffer and a citrate buffer were tested to determine which would give the better results. The extraction of cesium and rubidium tetraphenylboron complexes into 10 ml. of nit,roet,hane was evaluated with cesium-137 and rubidium-86. This v a s done by adding carrier-free cesium137 and rubidium-86 to solutions of distilled ivater, potassium, ammonium, and synthetic brine. The concentrations of the synthetic brine, potassium, ammonium. and the sodium tetraphenylboron were varied. Procedure. An aliquot of brine containing 0.005 t800.05 mg. of cesium and rubidium was transferred to a 100ml. beaker. Citrate buffer solution (25 nil.) was added and the p H was adjusted to 6.6 by adding sodium hydroxide or hydrochloric acid. The volume of this solution was adjusted to 100 ml. and transferred to a 125-ml. Teflon stoppered separatory funnel. Two milliliters of 0.05-11 Saa4B solution and 10 ml. of nitroethane were added, and the mixture was shaken vigorously for 2 minutes. The phases were alloned to separate for 30 minutes, then the aqueous phase was witlidran-n. The nitroethane phase then 11-as filtered quickly through l17hatnian S o . 4 filter paper, using vacuum. (This m-as done by placing a piece of TTIiatman S o . 4 filter paper on a coarke fritted glass filter.) The cesium and rubidium emib>ion intensities n-ere d&rniined by burning the nitroethane pha.se in the flame al,cct,rophotonieter and automatically scanning the 780.0, 794.8. 852.1, 894.4 nip lines. The amount of cesium and rubidium in the sanipk was calculated from a calibration curve prepared in :i similar manner. RESULTS A N D DISCUSSION
Figure 1 indicates the sensitivitea obtained with the small, medium, and large bore burners. Because the large bore burner allowed the greatest sensitil ity. it was used in the experimental work. 3lo.t of the resin5 tested gave good
Beckman burner
Beckman burner
Y4040
Y4030 Medlum bore LO Ibs 02 5 Ibs % H 2
Small bore 15 lbs 02 4 5 ibs C2H2
aeckrncr burnEr # 4090 Large bore IO lbs 02
NITROBENZENE
NITROETHANE
I- NITROPROPANE
2-NITROWANE
6 Ibs C2H2
ll
Figure 1. Relative intensities of 10 mg./liter of cesium and 10 mg./liter of ruhidium in 40% ethyl alcohol using 3 different Beckman burners
separations of cesium and rubidium from the other c o n k t u e n t s in oil field waters, but the eluting reagents ammonium chloride, amrnonium nitrate, or ammonium carbonate interfered in the flame spectrophotometer. The column effluents were concentrated by evaporation, and this also concentrated the eluting reagents which in turn clogged the aspirat,or of the flame spect'rophotometer. Another dkadvantage of the ion exchange method was the langthy time necessary for separation. Figure 2 illustrates the relatix-e crnision intensities obtained with resiuiii and rubidium in nitrobenzene, nitrnet'liane, l-nit'ropropa;ie, and 2-nitropropane. Fifteen milliliters of each of these solvent. was w e d to estract 0.1 mg. each of cesium and rubidium tetraphenylboron compleseR from aqueousolutioiis. The organii: phases then were aspirated directly into the flame, and the peaks were scanned automaticall\-. CTood resolut.ion was obtained with a 0.01-mm. slit width. Amyl alcohol also Iyas tested, and it gave poorer results than nitrobenzene. Figure 3 illustrates the relative emis.sion intensit'ies of 0.1 mg. per ml. each of potassium, rubidium, and cesium in 50% ethyl alcohol solutions. The figure is also indicative of the resolution obtainable li-ith this flame spect,rophotometer. Table I illustrates some of the result? obtained n-ith the twi buffer I t indicates that slightly superior resilks were obtained 1Yit;h the citrate buffer. It was pos,sible to extract 8700 of the cesium-137 and 58% oi the rubidium-86 from distilled water solutions with 10 ml. of nitroethane Rhen the N a a J 3 molarity was 0.008, Pot'aspium affected the estract'ahility of 130th cesium and
Figure 2. Emission peaks obtained b y burning organic solvents containing tetraphenylboron complexes of cesium and rubidium
rubidium, especially when high molar concentrations of Ka@4B, such as 0.008, were used. For example, when 52 mg. of potaqgium was preqent the cesium
and rubidium recoveries were 44 and 30%, respectively. However, when the N a a 4 B molarity was dropped to 0.0002, the cesium and rubidium recoveries were 20 and loyo,respectively, in the absence of potassium and 19 and 10% in the presence of 52 mg. of potassium. Possible interference from ammonium ion? also was tested, but they did not interfere appreciably. Table I1 illustrate. some of the recoveries obtained. The data in Table 111 indicate that consistent results were obtainable when the molarity of the Sa94B was 0.001. At this molarity any visible precipitation in the presence of 20 mg. of potassium was low. Obviously, the low cesium and rubidium recoveries were caused by the heavy precipitation and subsequent occlusion of cesium and rubidium in the presence of relatively high concentrations of X a a J 3 and potassium.
Table 1. Comparison of Emission Intensities Obtained with Nitroethane Extractions of Cesium and Rubidium Tetraphenylboron Complexes Using Acetate and Citrate Buffers
Figure 3. Relative intensities of 0.1 mg./mI. of potassium, rubidium, and cesium in 50% ethyl
Acetate buffer Citrate buffer RuRUCesium bidiu,m Cegium bidiu.m emission emission emission emission intenintenintenintensit)-, sity sity, sity, mm . mm. mni. mm.
alcohol solution VOL. 35, NO. 9, AUGUST 1963
1259
Table It. Recovery of Cesium-1 3 7 and Rubidium-86 as Tetraphenylboron Complexes from Aqueous Solutions with 10 MI. of Nitroethane
Cesium-13T Rubidium-86 extracted, extracted, .c
Ta@qB molarity
c-
( -
20 "0 19 21
0 0 0 0 0 0
'3
10 10 10 19 1s
41
Synthetic brine, ml.
0002 0002 0002 0002
nig.
mg.
0
0
0
"0 "0 20
0 52
0 0 "0 0
40 ~. 40 39
"0
001 001 0.001
38 30 40
19 18
0.001 0.001
30
0.002
"0 "0 20 0
57
0.008
20
19
YS
0
0 0 0 13 ~. 52 156 0
0
10 60 ~~
n nni
19
Potassium, Ininioniuni,
J
0.001
0 0 I)
0
0 20
Table 111. Flame Spectrophotometric Emission Intensities of Cesium and Rubidium Extracted as Tetraphenylboron Complexes from Aqueous Solutions with 10 MI. of Nitroethane Mg: each of cesiiiiii and
rubidiuni 0 01 0 (1 0 0
Cesium emission intensity,
Rubidium emission intensity,
0 0.5 0 90 1 00 1 .00 2 25 2.20 2 15 2.20 6 00 5 95 6 .05 6 00
1 05 1 10 1 .OO
mm.
01
01 01
03 0 03 0 03 0 03 0 .05 0.05 0 .05 0.05
nim.
1.05 2.45 2.45 2 .-in 2.40 6.90 5,95 6.90 6.85
Table IV. Results Obtained b y the Flame Spectrophotometric Method for Determining Cesium and Rubidium
Cesium, mg." 0.011
0.010
0.010
0.010
nin
012
(I
0 011
0 009 0 010
n
0 011
0 010 0 011
Rubidium, mg." 0.009 0.011
o.010 0 010 0 012 0 010
0.009
0.010 0.010 0 011 0 011 0 009
Duplicates.
Table V. Results Obtained by the Flame Spectrophotometric Method for Determining Cesium and Rubidium Rubidium, nig."Cesium, mg.4 0.049 0.051 0.050 0.048
0.050 0.051 0.050 0.050
0.050 0.051
0.051
0.051
0.050 0.052 0.049 0.050 0.052 0.050
Duplicates.
1260
ANALYTICAL CHEMISTRY
0.050
0.051 0 050 0.050
0.051 0.050
Sa@4,B molarity 0 001 0 001
Synthetic brine, ml. 0 20
0.001
0.001 0.001
0.001 0 001
0.001 0.001 0.001
0.001 0.001
"0 20 0
n
20 "0 0
Potassium, mg. 0 0 32 0 0 0 52 0 0 0 52 0
.~lllllllJ-
niuni, mg. (I
0
Samples containing cesium and rubidium in the 10- to 5O-,ug. rangc \\-ere used because the extraction coefficients were the same in this range as tho.se obtained with the carrier-free niet,al ions. The emission intensities of ,samples containing higher amounts of cesium and rubidium also were too high to w e without fear of self-absorption. The data in Table I1 are not representative of data which should be used in the preparation of a calibration curve, because the gas pressure.: and other variables were not rigorously standardized between runs in obtaining these d a h . The intensity of emission rises fairly rapidly with the a,mount of cesium and rubidium and will vary with multiplier phototubes. If self-absorption is evident, smaller samples should be used. The weights of the metals, as given in all of the tables, were in the original aqueous solutions. The data in Table IV were obtained by analyzing duplicate samples of synthetic brines containing 0.01 mg. each of cesium and rubidium. The standard deviation was 10.0008 mg. for cesium
and +0.0007 nig for rubidium in the 0.01-mg. range. These data were obtained by preparing a calibration curve when nitroethane extracts of synthetic brines were used to which standard amount.; of cesium and rubidium were added. The amount of potassium was 20 nig. in each. The data in Table i7 were obtained by analyzing duplicate samples of q n thetic brines containing 0.05 mg. each of cesium and rubidium. The standard deviation was 10.0008 mg. of cesium and 10.0006 nig. of rubidium in the 0.05-mg. range. The accuracy of this method was dependent' upon exactly follon-ing the procedure for the preparation of t,he calibration curve and analysis of the sample. Sitroethane is slightly soluble in water; therefore, the ratio of the nitroetIrvine, J. X., Jr., .\fuss. lnst. P'echnol., L a b . .Yiicl. Sei., Ann. Progr. Re@., June 1, 19j5 to May 31, 1956. ( 8 ) Gast, P. lY.>=Inn. S. I'. A C C JSci. ~. 91, 181 (1,961). (9) Glendening, B. I,., Parrish, D. B., Schrenk, IV. G., hs.i~.CHEM. 27, 1554 (1955). (10) Nara, T., Bull. Inst. Chem. Xes., Kyoto GniuPrsity 27, 139 (1959). (11) Ishibashi, Fujinaga, T., Iioyania, J . , Saito, T., Buirseki Kuyaku 10, 116 (1961). ( 1 2 ) Kick, H., 2. P$unzenc.rnuhr. D..; I n a h s t
80, 37 (1955). (18) Pnides, A. .4., Rebster, R. K., Geochznz. Cosmochzii~. d c t a 1 1 , 139 (1957). (19) Smit, J. Van R., Robh, \T., Jacobs, J. J , J . Inorg. Sucl. Chem. 12, 104 (1959). (20) Tal-lor, J. lI., rlEC Res Dezel. Rept. HT17-45964,1956. (21) Z y s z c z j nska-Florim, B., Chomik, T.,
Roczntki Pnmtwowego Zakladu 10, 87 (1959).
Hig.
RLCEIVED for review Februarv 13, 1963. hcc
