Table 11. Determination of Total Iodide in Iodide-Iodate Mixturesa,* Fraction of
Table 111. Determination of KI in Commercial Iodized Salt Method
KI, 46
This work AOAC Titrimetric Method
1.11 X lo-' 1.15 x lo-'
Total I , u g / m i
Std deviation, %
m o l e s of t o t a l I Present as IO
1 .oo 0 -80 0.50 0 -20 0 -00
3
Taken
Found
101 101 101 101 101
102 103 103 104 102
*
a No added salts other than sodium sulfite. Determinations made using standard curve for 1 0 3 - described in t e x t .
curve which was constructed with potassium iodide standards. An additional bit of evidence for complete reduction of iodates in iodate-iodide mixtures is provided by a series of determinations of total iodide concentrations in mixtures whose compositions ranged from pure iodate to pure iodide. All of the experimentally determined total iodide concentrations are in close agreement with the calculated total iodide concentrations (Table 11). One final indication of the utility of the new analytical method was obtained when it was applied to the determination of iodide in iodized table salt. The results obtained by the new method were comparable to those obtained by the AOAC iodometric method (see Table 111).
CONCLUSIONS In conclusion, it should be mentioned that the new technique is quite rapid. Sample preparation for a single sample took approximately four minutes. Samples which are turbid may be handled without difficulty. Since bromide, sulfate, and chloride are the major anions present in some brines which carry iodide (15),the method can probably be adapted to the determination of iodide in that type of sample. The method could also be applied in a qualitative fashion to the rapid detection and identification
0.03 X 0.01 x
of small quantities of iodide or iodate in solid salts and brines.
ACKNOWLEDGMENT The author thanks Kristine Chadwick for her help in the preparation of the manuscript. Ted Mueller helped to prepare the illustrations, and his assistance is appreciated. The author gratefully acknowledges the donation of laboratory space and chemicals by Union Sugar Division/Consolidated Foods Corporation. LITERATURE CITED (1)K. Kodama, "Methods of Quantitative Analysis", Interscience Publishers, New York. NY, 1963,pp 440-447. (2)D. F. Boltz in "CRC-Critical Reviews in Analytical Chemistry", L. Meites and E. H. Campbell, Ed.. CRC Press, Cleveland, Ohio, 1973, pp 147199. (3)M. J. Fishman and E. P. Robinson, Anal. Chem., 41, 323R (1969). (4)M. J. Fishman and D. E. Erdmann, Anal. Chem., 43, 356R (1971). (5) M. J. Fishman and D. E. Erdmann, Anal. Chem., 45, 361R (1973). (6)E. J. Poziomek and D. W. Reger, Anal. Chim. Acta, 58, 459 (1972). (7)R. A. Mackay and E. J. Poziomek, J. Am. Chem. SOC..92, 2432 (1970). (8)A. T. Balaban, M. Mocanu, and 2.Simon, Tetrahedron, 20, 119 (1964). (9)T. C. Chadwick, Anal. Chem., 45, 985 (1973). (10) T. C. Chadwick, Anal. Chem., 46, 1326 (1974). (11) K. Kanai, M. Umehara, H. Kitane, and K. Fukui, Nippon Kagaku Zasshi, 84, 432 (1963);Chem. Abstr., 59, 139349 (1963). (12)K. Dimroth, G. Arnoldy, S.von Eicken, and G. Schiffler, Justus Liebigs Ann. Chem., 604, 221 (1957). (13)William Horowitz, Ed., "Official Methods of Analysis of The Association of Official Agricultural Chemists", 9th Ed., Association of Official Agricultural Chemists, Washington, DC, 1960,pp 461-462. (14)H. K. Biswas and E. M. Mandal, Anal. Chem., 44, 1636 (1972). (15)F. W. Clarke, "Data of Geochemistry, Fifth Ed.", U.S. Geol. Survey Bull,, 770,233 (1924).
RECEIVEDfor review September 3,1974. Accepted January 23, 1975.
Extraction and Separation Studies of Chromium(V1) from Nitric Acid Solutions Using 4-( 5Nonyl)Pyridine Mohammad lqbal and Mohammad Ejaz' Nuclear Chemistry Division, Pakistan lnstitute of Nuclear Science and Technology, P. 0.Nilore, Ra waipindi, Pakistan
Information on the use of high molecular weight heterocyclic pyridine amines as extractants is unavailable in literature. In a previous communication, we reported the separation of technetium(VI1) from uranium and some fission products using symmetrical 4-(5-nonyl)pyridine from nitrate media (1).In the present investigation the extraction of trace and weighable quantities of chromium(V1) by this reagent has been reported from nitric acid solutions. The extractant appears to behave as a liquid anion exchanger. Compared with pyridine and its methyl-substituted derivatives, this extractant has several advantages, e.g., higher boiling point and the much lower solubility of water in it. This latter property leads to lower uptake of impurity salts l A u t h o r t o whom correspondence should be addressed.
936
ANALYTICAL CHEMISTRY, VOL. 47, NO. 6, MAY 1975
from the aqueous phase and gives very clean phase separations which cannot be achieved from acid solutions by pyridine and its methyl substituted derivative.
EXPERIMENTAL Apparatus, Reagents, and Nuclides. T h e equipment used for general alpha assay was: a n argon gas-flow proportional counter, H a r w e l l type 3-7/11558 in conjunction w i t h a n EKCO fast scaler, t y p e N 530 F. H i g h voltage was taken f r o m the scaler; a n d a Nuclear Chicago Corporation alpha scintillation counter, M o d e l D S - S Serial 1709. Solid beta-emitting samples were assayed w i t h t h e a i d of a n end window Geiger Assembly equipped w i t h G.E.C. tube EHM 2/S. Gamma-ray count rates were determined using a Nuclear Chicago single channel analyzer, M o d e l 872 coupled w i t h a 3-in. X 3-in. t h a l l i u m doped sodium iodide well-type gamma-ray scintillation
s
L"' Y
10
I,
I
Id7
,
.
. ,
I...
10.'
I
1
1 N i t r i c acfd I M )
.
,
. . . . .I
-
10
Figure 2. % Extraction of Cr(VI) into 4-(5-nonyl) pyridinelbenzene as a function of nitric acid concentration 10.l
10.'
1
"0,
10
IM 1
Figure 1. Distribution of Cr(VI) between 0.1M NPylbenzene as a function of nitric acid Concentration. 0
loT8 MCr(V1) 0 5 X
MCr(VI)
counter. y-Spectra were taken with a Nuclear Data ND-4410 computer system 512/1024 multichannel analyzer, Model 2560. The detector used with this analyzer was a 4-X 3-in. NaI(T1) crystal. Analytical grade reagents were used throughout without further purification. 4-(5-Nonyl)pyridine (NPy) was obtained from K&K Labs Inc., Plainview, NY and was purified by vacuum distillation before use. The NPy is a pale yellow oily liquid and has bp of 94 OC a t 0.8mm Hg, refractive index rz? of 1.485 and density d Z o of 0.9208 g/cm3. The reagent does not have the pungent odor that is characteristic of the lower members of the homologous series. Solubility of the reagent in water was found to be 1.2 g/l. Purity of the reagent was checked by a Varian Aerograph Chromatography unit, using a 10% carbowax 20M column a t 220 "C, which showed a single peak. The detector employed was an alkali flame ionization type. Enriched chromium-51 as Cr042- was prepared as reported ( 2 ) . 233Uwas obtained from the Radiochemical Centre, Amersham, and was purified by solvent extractions (3) before use (the concentration of uranium in the initial aqueous phases was mole 1-l) 234Thwas milked from natural uranium ( 4 ) and 230Th was isolated ( 5 ) from a pitchblende mineral sample of South Alligator River, Australia. 99mTcwas separated from its parent 66.6-hour99Mo by solvent extraction according to the method of Faddeeva et al. (6). lg8Au, 99Mo, and 64Cu were obtained by neutron activation of the respective reagent grade stable salts, AuC13, MoO3, and CuO in the research reactor of this Institute The Ig7Pttracer was obtained by neutron irradiation of platinum sponge. A period of four hours has elapsed since the tracer was formed, so that all of the lg9Pthad decayed to lg9Au which was separated before use. T h e other radioisotopes used in this work were obtained from the Radiochemical Centre, Amersham, and were pure enough t o meet the catalog specifications. Measurement of Distribution Coefficients. The distribution coefficient of Cr(V1) between equal volumes of aqueous and organic phases (equilibrated previously with aqueous solution of the same composition as the solution from which chromium was extracted) was found by contacting the phases for 5 min. This was sufficient time for equilibration. T o avoid errors due to loss of the radioactive material, the material balance was checked, with those points having a balance of less than 90% being repeated. The distribution coefficient, D,is defined as: (j'Cr activity in the organic phase)/(jlCr activity in the aqueous phase).
RESULTS AND DISCUSSION The dependence of the degree of extraction of chromium(V1) on the nitric. acid concentration was found for trace and macro amounts of the metal. Figure 1 presents the variation of the degree of extraction of chromium(V1) from lo-* to 10M nitric acid with 0.1M NPy solution in benzene. T h e form of the extraction curves is approximately the
1O-l
u 10.'
10.l
NPy ConcenlrationlM)
Figure 3. Dependency of the trace Cr(VI) distribution ratio on the NPy concentration in the organic phase.
same for both the concentrations with a maxima a t 0.25M "03. The detrimental effect of the increased acid concentration is considered to be due to an exchange of anions in the extracted adduct between chromium species and the mineral acid. The data describing the percentage chromium extracted (% E ) by 0.1M NPy/benzene from nitric acid solutions is shown in Figure 2. The concentration of Cr(V1) in the initial aqueous phases was 2.55 g/l. The effect of the amine concentration on extraction of trace amounts of chromium from 0.25M "03 was studied using benzene as a diluent. The slope of the resulting straight line, as shown in Figure 3 is close to two. Presumably doubly-charged complexes (Cr0d2-) are extracted and/or the singly-charged chromium complexes of the type HCr04- may be extracted by either of the following mechanisms: 2NPy (PyN.
+
HNO, e (PyN ,
. . H . . . NPy)+N03-
. . H , . . NPy)+N03' + HCr0,- i ( P y N . . . H . . . NPy)+HCrO,-
(1) (2)
or through the formation of the mixed quadrupoles formed by the association of the free amine nitrate with the chromium species to give (NPyH)+N03- (NPyH)+ HCr04either as dipole-dipole head to tail association of NPyH+ Nos- with NPyH+ HCr04- or as having two NPyH+ cations hydrogen bonded with one nitrate anion. Since in trace amounts of Cr(V1) the concentration of HCrz07- and
-
-
ANALYTICAL CHEMISTRY, VOL. 47, NO. 6, M A Y 1975
-
937
-
1o1
A
lo' r 0.25 M " 0 ,
3.00 M HNQ, 5.00 M "0,
16' IO-'
lo-?
10.' A q u e o u s s a l t IM)
l
lo"
j
l oI'
l
C",,",,
1!3/1;
Figure 4. Extraction isotherms in the systems 0.1M NPy in benzene/ 0.25M, 3M, 5MHN03 4- variable Cr(VI)
Flgure 6. Extraction of Cr(VI) by 0.1 M NPy solutions in benzene as a function of the initial concentrations of the fluoride, chloride, and SUIfate ions from 3 M nitric acid
mately two and the reaction may be expected to proceed as follows:
+ HN03 e (NPyH)+NO3(4) (NPyH)+N03' + HCr,O,- ===(NPyH)*HCr207- (5) NPy
+ 0 . 2 5 M HNC+ + 3 O O M WNC+
-+ 5 O O M
16'
1
"0,
10
A q u e o u s n i l r a l ~IMI
Figure 5. Distribution ratio of Cr(VI) as a function of sodium nitrate concentrations from different molarity nitric acid solutions
Cr20T2- is negligibly small (7), there is no possibility for their extraction. The influence of the concentration of chromium (VI) on the extraction from 0.25, 3, and 5M nitric acid by 0.1M NPy/benzene was studied. The results are shown in Figure 4. The concentration of the metal in the aqueous phase was varied from 0.51 to 204 g/l. From 0.25M "03, the maximum obtainable Cr(V1) concentration in the organic phase corresponds to 3.7 g Cr(VI)/l. when the original aqueous concentration of Cr(V1) was 5.1 g/l. This indicates the extraction of a mixture of compounds which contain one or two molecules of the extractant, probably as (2BH+, and (BH+,HCr04-). The loading capacity of 0.1M NPy/benzene decreases when the original aqueous chromium(V1) concentration exceeds 5 g/l. The possible explanation is that the large Cr(V1) amounts in the aqueous phase lead to polymeric species (8): 2HCr04Cr,07*- f H,O (3) With a subsequent decrease in the hydrogen ion concentration of the aqueous phase such that stability of the amine salt of the type (NPyH)+is considerably decreased. Similar results were obtained from the corresponding hydrochloric and sulfuric acid systems. From 3 and 5M nitric acid, the saturation of the organic phase corresponds to 9.2 g Cr(VI)/l. This indicates that, a t high Cr(V1) concentrations, the Cr/NPy ratio is approxi938
ANALYTICAL CHEMISTRY, VOL. 47, NO. 6, MAY 1975
Figure 5 illustrates the extraction of the metal from 0.25, 3, and 5M nitric acid by 0.1M NPy solution in benzene in the presence of sodium nitrate. The overall concentration of to 5M. In the case the nitrate ions was varied from 5 X of 0.25M HN03, the D values decrease with increase of sodium nitrate concentration in the aqueous phase. From 3 and 5M nitric acid, the partition coefficients remain virtually constant. I t is possible that a t low acid loading of the organic phase (Le., when the aqueous acid concentration is 0.25M) the total extracted acid is in the form of ionized species and the extraction of chromium anions takes place by the exchange of the nitrate anions with the anions of chromium and when an excess of nitrate ions is present the competition between nitrate and chromium species for association with the amine cation results in the decrease of D value. At comparatively high nitric acid concentrations (3 and 5M), the acid may be extracted in its associated molecular state only and the extraction of chromium species (possible oxymetal acid) may be resulting by the exchange of the nitric acid with the oxymetal acid in its associated molecular state, salted out by the supporting acid and thus avoiding the competition of the nitrate and oxychromium anions for the protonated amine. The effect of sodium chloride, sodium sulfate, and ammonium fluoride on the extraction of 0.05M Cr(V1) by 0.1M NPy/benzene was studied from 3M nitric acid (Figure 6). In the case of the sulfate and fluoride ions, the D values decrease a t high salt concentrations, probably because of the formation of some inextractable complexes. In the case of chloride ions, the D value increases with the increase of chloride ions in the aqueous phase. Such an increase in D values was also observed in the corresponding sulfuric acid system. The addition of ammonium acetate, potassium oxalate, sodium citrate, and potassium bitartarate to 3M nitric acid solution decreases the D values. Figure 7 shows the decrease varying in the sequence: Tartarate > oxalate > citrate > acetate. In the case of oxalate, the color of the aqueous phase changed into violet above 0.1M. In the case of EDTA (Figure 8 ) , the extraction decreases with increase of its concentration in 3M nitric acid solution. The color of the aqueous phase became violet above
IO ,
IHIOSULFAIE
- -?I
10
10.'
10.' A q u e o u s sail I M
1
10
I
I
10
Figure 7. Distribution of Cr(VI) as a function of the concentration of
oxalate, citrate, tartarate, and acetate ions from 3M nitric acid by 0.1M NPyIbenzene
I
l d
10
Aqueous salt 1M
1
I
Figure 9. Effect of reducing agents on the extraction of chromium from 3 M HN03 by 0.1 M NPy/benzene
Table I. Distribution Coefficient of Various Metal Ions between 0.1M 4-(5-Nonyl)pyridine/Benzeneand 3M Nitric Acid Amount present in the initial aqueous Metal ion
phase
99mT~
\
9
9
~
10 < 10-3 < 10-3 < 10-3 < 10-3 < 10-3 < 10-3 < 10-3 0.02
C. F.Carrier-free
sumed that the contribution of the reagent toward the reduction of Cr(V1) is negligible. Back-Extraction of Chromium(V1). Figures 1 and 4 show that it is possible to back-extract macroamounts of chromium(V1) from the solvent phase with very low acid concentrations. It is also possible to back-extract by stirring the organic phase with a reducing agent. Ascorbic acid, hydrazine hydrochloride, and thiosulfate will reduce chromium(V1). Dilute ammonia was also found suitable for back-extraction. The selectivity of the extraction of chromium(V1) was checked from 3M nitric acid. Figure 1 suggests that the optimum nitric acid concentration is 0.25M. Yet the decontamination studies were made using 3M nitric acid because the chromium(V1) uptake by the reagent a t this acid concentration was double the amount taken up from 0.25M nitric acid. It is also evident from Figure 4 that 0.25M nitric acid cannot be used for the extraction of chromium(V1) ANALYTICAL CHEMISTRY, VOL. 47, NO. 6, MAY 1975
939
products was carried out and chromium was back-extracted with 0.01M nitric acid. Ruthenium did not accompany chromium through extraction and stripping. Clear separation was achieved. This is shown by the y-spectra in Figure 10. Since iron, cobalt, nickel, and manganese(I1) are also inextractable, the separation of chromium from steel can also be effected. The decontamination factor would improve considerably when the extraction process is carried out in a manner such that there is a high degree of saturation of the organic phase with Cr(V1).
ACKNOWLEDGMENT M. Saeed and Riaz Joseph gave valuable assistance with the measurement/counting of radioactive samples and the calculations on D values. LITERATURE CITED
when the original aqueous Cr(V1) concentration exceeds 10 g/l. The extraction of a number of metal ions including the important fission products was checked a t this acidity. The data presented in Table I show that Cr(V1) can be separated from a number of elements. Separation of spiked W r ( V 1 ) (the concentration of chromium in the initial aqueous phase was 2.55 g/l) from four-month-old fission
(1) M. lqbal and M. Ejaz, J. Radioanal. Chem., 23, 51 (1974). (2) H. M. A. Karim, Int. J. Appl. Radiat. /sot., 24, 599 (1973). (3) A. S. Solovkin, M. I. Konarev. and D. P. Adaev, Zh. Neorg. Khim. 5, 1861 (1960). (4) M. Ejaz, Radiochim. Acta, in press. ( 5 ) M. Ejaz, Radiochim. Acta, in press. 16) M. S. Faddeva. O.N. Panlov. and V.V. Bakunina. 2%. Neora Khim.. 3, 165 (1958). (7) J. Ying-Peh Tong and E. L. Prue, J. Am. Chem. SOC.75, 6180 (1953). (8)G. P. Haight, D. C.Richardson, and N. H. Coburn, horg. Chem. 3, 1777 11964\ -- I \
(9) K. A. Muirhead, G. P. Haight, Jr., and J. K. Beattie, Inorg. Chem., 12, 1116 (1973). (10) I. Baldea and G. Niac, Inorg. Chem., 9, 110 (1970).
RECEIVEDfor review July 10, 1974. Accepted January 14, 1975.
Extraction and Spectrophotometric Determination of Vanadium(V) with N-Phenyl-2-naphthohydroxamic Acid Y. K. Agrawal' Department of Chemistry, Indian Institute of Technology, Bombay, Powai, Bombay 400 076, India
Hydroxamic acids are the potential reagents for the determination of vanadium(V) (1-20). The parent acid Nphenylbenzohydroxamic acid (PBHA) (I) is a selective and
H
- N-OH I
@J-c=o @-!-OH e c
N-OH
@ - L O
= o (I)
sensitive reagent for vanadium(V) having a maximum absorbance a t 530 nm; t = 4650 of chloroform extract of vanadate complex ( 4 ) . However, Zr, Ti, Mo, and W interfere in the determination of vanadium with PBHA. Several other acids such as N-phenylcinnamo- ( 5 ) ,disubstituted (9) and unsaturated (6, 7) hydroxamic acids have been reported for the determination of vanadium. Bass and Yoe have proposed 2-naphthohydroxamic acids(II), as a reagent for vanadium which gives in methanol an intense red-orange color with vanadium(V) a t a wavelength of 450 nm ( c not reported) (10). Sometimes an introduction of substituent group in the ring increases the reactivity of the reagent. Present address; E n v i r o n m e n t a l Studies Section, H e a l t h P h y s ics Division, B h a b h a A t o m i c Research Centre, T r o m b a y , B o m b a y 400 085. India.
940
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a-I
ANALYTICAL CHEMISTRY, VOL. 47, NO. 6, MAY 1975
With this object in view, a new acid has been synthesized by replacing the H atom from 11, by a benzene ring (111). In the present communication, N-phenyl-2-naphthohydroxamic acid (P-2-NHA) (III), is shown to be the most selective and sensitive reagent, surpassing 2-naphthohydroxamic acid. I t gives an intense violet colored complex with vanadium (extracted with chloroform from 3-8M HC1) molar absorptivity being 7.1 X lo3 a t 545 nm. The advantage of the proposed reagent lies in the fact that a satisfactory separation from many common metal ions is easily accomplished and it can be used for the extraction of trace amounts of vanadium. The effects of acidity, reagent concentration, and diverse ions on the absorbance of the vanadium(V)-P-2-NHA system have been studied. An attempt has been made to elucidate the stoichiometry of the extracted species.
