Table IV. Determination of Copper in Chalcopyrite and in Beryllium Chloride
Taken, Cu(II), Found, Sample FeCuSZa
BeC1,b
g L
bg
7c
0.4 0.4 0.4 0.4 0.4 0.4
0.223 0.235 0.215 0.220 0.221 0.216
32.2 32.9 30.2 30.8 30.9 30.2 31.3
0.4
0.07
0.22 0.21
hle t hod length length length
weight weight weight extraction spectrophotometry length
extraction spectrophotometry a 0.375 g of chalcopyrite was dissolved i n concd HNO, a n d diluted to 100 mL w i t h water. 7.99 g of BeCI, was dissolved in HCI a n d diluted to 1 0 0 mL with water. The standard deviation was 1.4 (with t h e length method) a n d 0.37 (with the weight method). chromatography” or “candle chromatography” by judging from the mechanism of this chromatography or the shape of t h e chromatograms which is similar to the flame of a candle. A similar phenomenon was observed in the precipitation chromatography of several metal ions such as Hg(II), Ag(I), P d ( I I ) , C u ( I I ) , Bi(III), Cd(II), Zn(II), and Fe(II1) with thiooxine impregnated filter paper (16).
Application of the Proposed Thin-Layer Chromatograph>,. T h e possibility of the direct quantitative determination of copper(I1) has been investigated by measuring t h e length of tailing on t h e plate or weighing the paper equal to the area
of tailing drawn on a millimeter-graph sheet. T h e calibration curves thus obtained are shown in Figure 8. T h e length of t h e tailing or the weight of t h e area equivalent t o t h e graph sheet depends on the amount of copper(I1) initially taken. By using these calibration curves, t h e separation and t h e determination of a few micrograms of copper(I1) in chalcopyrite and in beryllium chloride of commercial reagent grade were achieved on the plate of the STT’A-impregnated cellulose. The results are shown in Table IV. These values were in quite good agreement with those obtained by t h e extraction spectrophotometry of copper(I1) with STTA in cyclohexane.
LITERATURE CITED M. Cox and J. Darken, Coord. Chern. Rev., 7, 29 (1971). S. E. Livingstone, Coord. Chem. Rev., 7 , 59 (1971). T. Honjo and T. Kiba, Bunseki Kagaku, 21, 676 (1972). T. Honjo, S. Yashima, and T. Kiba, Bull. Chem. SOC. Jpn.. 46, 3772 (1973). (5) M. Chikuma. A. Yokoyama, Y. Ooi, and H. Tanaka, Chern. Pharrn. Bull., 23 (3), 507 (1975). (6) R. K. Y. Ho, S. E. Livingstone, and T. N. Lockyer, Aust. J . Chern., 21, 103 11968). T. Honjo and T. Kiba, Bull. Chern. SOC. Jpn.. 45, 185 (1972). S. Ohashi, Bull. Chern. SOC.Jpn., 28, 645 (1955). T. Kiba, I.Akaza, and S. Taki, Bull. Chern. SOC.Jpn., 30, 482 (1957). V . M. Shinde and S. M. Khopkar, Anal. Chem., 41, 342 (1969). M. Deguchi and M. Yashiki, BunsekiKagaku, 20, 317 (1971). T. Braun and G. Ghersine, “Extraction Chromatography”, Elsevier Scientific Publishing Company, Amsterdam, The Netherlands, 1975. L. S.Bark, G. Duncan and R. J. T. Graham, Analyst(London), 82, 31, 347 (1967). R. W. Murray and R. J. Passarelli, Anal. Chern., 39, 282 (1967). H. Irving and R. J. P. Williams, J . Chern. S O C . ,1953, 3192. H. Nagai, T. Deguchi, and N. Narahara, BunsekiKagaku, 24, 184 (1975).
(1) (2) (3) (4)
RECEI~XD for review April 26,1977. Accepted August 23,1977.
Solvent Effect on the Liquid-Liquid Distribution of Monothiothenoyltrifluoroacetone and Its Metal Chelates of Copper(II), Cobalt(II), and Zinc(I1) Takaharu Honjo,
Ryumon Honda, and Toshiyasu Kiba
Department of Chemistry, Faculty of Science, Kanaza wa University, Marunouchi, Kanaza wa, Ishika wa 920, Japan
The solvent effect on the liquid-liquid distribution of S l T A (monothiothenoyltrifluoroacetone) and its metal chelates of copper(II), cobalt(II), and zinc( 11) is investigated. The correlation between the distribution coeff iclent of S l T A ( PHA) and the distribution ratio of tts metal chelates ( DM)expressed 4- constant at a fixed pA is valid in nine by log DM = nlog PHA solvents for all chelate systems except for the Co-SlTA system. The difference of the relationship for oxygen containing solvents from that for Inert solvents is also discussed. The data for l T A and its metal chelates of copper(II), cobalt(II), and zlnc(I1) are also reported for comparison.
T h e organic solvents play an important role in the distribution of extractable species; however, t h e theoretical treatment of t h e solvent effect has not yet been fully elucidated. Recently, the regular solution theory ( I ) has been found useful for interpreting the solvent effect on the chelate ex2246
*
ANALYTICAL CHEMISTRY, VOL. 49, NO. 14, DECEMBER 1977
traction systems such as the liquid-liquid distribution of TTA (thenoyltrifluoroacetone),its zinc(I1) chelate and adduct with T B P ( 2 ) ,oxine derivatives and their copper(I1) chelates ( 3 , 4, and nickel(I1) dimethylglyoxine chelate ( 5 ) . T h e viscosity of dilute solutions of chromium(II1) acetylacetonate in organic solvents was also explained by this theory (6). T h e following empirical equation derived from t h e regular solution theory has been found t o be established in various P-diketones and their metal chelates a t a fixed pA (7):
+
log D, = n l o g PHA constant where n is the ratio of the molar volume of the metal chelate to t h a t of t h e chelating agent, DMis t h e distribution ratio of metal chelate, and P H A is t h e distribution coefficient of t h e chelating agent, respectively. In the present paper, the effect of t h e solvents on t h e liquid-liquid distribution of S T T A (monothiothenoyltrifluoroacetone) and its metal chelates of copper(II), cobalt(II), and zinc(I1) is examined with t h e use of the equations derived from the regular solution theory. The
equilibrium of STTA. It should be noticed that a little error can accompany this, owing to the decomposition of STTA during the shaking. The P H A value was calculated by using the equation
0
I
Y
d
/
07
06
I
20
5
3
2
I
I
0 HCI
I
I
l
l
I
3
1 EtOH
Flgure 1. Molar absorptivity, t , of STTA in the solutions containing 1 M hydrochloric acid and 9 9 . 5 % ethanol in various ratios. ( 0 )STTA solutions after standing for 2-3 min. (0)STTA solutions after standing for 17 h
data for T T A and its metal chelates of copper(II), cobalt(II), and zinc(I1) are also presented for comparison. EXPERIMENTAL Materials. The STTA was synthesized by the reaction of hydrogen sulfide with TTA in absolute ethanol in the presence of hydrogen chloride (8). The TTA of the guaranteed-grade reagent was supplied from Dojindo Co., Ltd. The chlorides of radioisotopes of ' W o and "Zn were purchased from New England Nuclear Corporation ( U S A ) and The Radio Chemical Centre (England). Organic solvents were of the highest purity commercially available, and were purified further in the ordinal manner if necessary. Other reagents used were all of guaranteed-grade materials. Apparatus. The visible and ultraviolet spectra were scanned with a Hitachi 323 Type automatic recording spectrophotometer and a Hitachi 239 Type digital spectrophotometer. Radioactivity was counted with a Kobe Kogyo NaI(T1) well-type scintillation counter, Mount Model EA-14, connected to a scaler, SA-250 and t o a Dual Timer, TM-2. A Hitachi-Horiba M-5 pH meter was employed for the pH measurement. A Iwaki KM shaker was used for the agitation (54 strokes/min) of aqueous and organic phases. Distribution of STTA. An equal volume of M STTA organic solution and 1 M hydrochloric acid solution was equilibrated by shaking both phases for 30 min. After centrifugation, the absorbance of the hydrochloric acid solution was measured, and the concentration of the neutral STTA in an aqueous phase was determined spectrophotometrically by using the molar absorptivity of STTA of e = 9.89 X lo3 at 375 nm. This value was estimated by extrapolation of the plots of t values of mixtures of 1 M hydrochloric acid and 99.5% ethanol in various ratios as is shown in Figure 1. As can be seen from Figure 1, STTA may be decomposed relatively fast in higher concentrations of hydrochloric acid, and the above procedure was carried out as quickly could also as possible. The distribution coefficient of STTA, PHA, be determined by using the equation,
PHA=
C [HAIorg. init.-
where D, is the distribution ratio of STTA calculated on several points on the extraction curves. K , is an acid dissociation constant of STTA. Although the pK, value is reported to be 3.96 (9),4.05 (9), and 4.31 ( I O ) , the value of 4.00 was adopted in this study. Distribution of Copper(I1). Ten milliliters of an aqueous solution containing M copper(I1) in the region of pH 0-5 were shaken with the equal volume of M STTA in an organic solvent. A shaking time of 30 min was enough to attain equilibrium. After extraction, a 5-mL portion of the organic phase was furthermore shaken with an equal volume of boric acid buffer of pH 10-10.5 for about 30-40 min t o remove the excess of the chelating agent from the organic phase. In order to check the extractability of copper(II), 5-mL portion of the aqueous phase was taken out, adjusted again to pH 3-5, and shaken with an equal volume of M S T T A solution to extract copper(I1) completely. In these experiments, the aqueous buffer solution consisted of 0.01 M sodium acetate (in the acidic region, pH 4-7) or 0.01 M boric acid (in the basic region pH 7-10). The STTA in cyclohexane, carbon tetrachloride, chloroform, and benzene was confirmed to be almost stripped out from the organic phase by shaking it with the solution of pH 1C-10.5; however, the chelating reagent could only be stripped out as far as about one third of the total amount from the MIBK (methyl isobutyl ketone) solution. When the higher pH solution was used for stripping the excess chelating reagent, decomposition of copper chelate occurred; therefore, pH 1C-10.5 seemed to be the limit to remove the excess of STTA from organic solvents as well as MIBK. After centrifugation, the distribution of copper(I1) was determined by measuring the absorbance of the wavelength in the vicinity of the maximum absorption of the copper chelate in each solvent. The distribution of copper(I1) with 10-1 IvI TTA in organic solvents was also determined by the same procedure. Distribution of Cobalt(I1) a n d Zinc(I1). Ten milliliters of 0.01 M acetate buffer solution containing 65Znand 6oCoin a trace amount M) adjusted to an adequate pH were shaken with 10 mL of the organic solution of M STTA for about 40-50 min. After centrifugation, 3-mL portions were taken from both phases, and the y-activity was counted by a scintillation counter to determine the distribution of the metals. The pH of the aqueous solution was checked again after extraction. The distribution of cobalt and zinc with lo-' M TTA in organic solvents was also determined by the same procedure. In all experiments described above, the aqueous phase was maintained a t an ionic strength of 0.10 with NaClO.,. All investigations were carried out a t room temperature (25 "C). RESULTS AND DISCUSSION T h e values of the distribution coefficient of STTA, PHA, between an aqueous solution and various organic solvents obtained from the two methods are given in Table I together with those of TTA. It was found that the distribution coefficient of STTA was larger t h a n t h a t of T T A , and the solvents having higher dielectric constant gave larger distribution coefficients. T h e interaction between STTA and the more polar solvents, e.g., the hydrogen bonding or the dipole-dipole interaction may take place in the solution (IO). When the metal chelate in the aqueous phase seems t o be in negligible amount, the distribution ratio of divalent metal ion can be expressed as
[HAIHcI)/[HAIHcI
where [HA] mit. is the initial concentration of chelating reagent in the organic phase, and [ m ] H C I is the concentration of chelating reagent in 1 M hydrochloric acid solution after equilibrium, respectively. The distribution coefficient of STI'A in some organic solvents was obtained by another method in which the extraction curves of STTA were determined spectrophotometrically. The shaking time of 30 min was enough to reach the distribution
where p2 is overall stability constant of metal chelates, PM is the distribution coefficient of metal chelates, K , is a n acid dissociation constant of the chelating agent HA, and the suffix "org" is an organic phase, respectively. T h e plots of the log D M of Cu(II), Co(II), and Zn(I1) vs. p H for regular extraction ANALYTICAL CHEMISTRY, VOL. 49, NO. 14, DECEMBER 1977
2247
Table I. Distribution Coefficients of STTA and TTA Solvent
1
Cyclohex me Carbon tetrachloride Chloroform Benzene Methyl isobutyl ketone Isopropyl ether n-Butyl ether Ethyl acetate n-Butyl acetate
2 3
4 5 6
7 8
9 a
Dielectric constant
No.
Solubility parameter
2.1 2.2 4.8 2.3
8.2 8.6 9.3 9.2 8.8 7.0 7.6
13.1
3.9 3.1 6.0 5.1
STTA
TTA ( 2 , 7, 1 2 , 1 3 )
3.10, 3.44a 3.49Q 4. 2ga 4.30a
1.30
0.56 1.73 1.62 2.30 1.51 1.29 2.27 2.22
4.00
3.58 3.74 3.35 3.65
9.1
8.5
Values obtained from the distribution curves.
Table 11. Distribution Ratios of STTA and TTA Chelates of Copper(II), Cobalt(II), and Zinc(I1) a t a Fixed pA log D M STTA
-~ - __
No.
Solvent Cyclohexane Carbon tetrachloride Chloroform Benzene Methyl isobutyl ketone Isopropyl ether n-Butyl ether Ethyl acetate n-Butyl acetate
1
2 3 4
5 6 7 8 9
3
TTA
___
Cu(II), pA 10.0
Co(III), pA 6.0
Zn(II), pA 6.0
CU(I1), pA 7 . 0
CO(111, pA 4.0
WII), pA 4.0
- 0.80
0.84 2.19 -0.30 1.65 2.57 1.86 2.34
-1.95 -0.17 0.51 0.24 1.46 0.19 0.40 0.36 0.47
- 1.20 - 0.08
-
2.80
-2.77 -0.93
0.84 0.76 0.78 -0.60
- 0.03
1.41
I
'2t l
I
Cu- S T T A
/
I
1
CD-STTA PA= 6 0 7 0 5 0
2
Jj
0:
P
7 i
I 3
4
0 6
b/
/
.I
/
i Li
I
II
I
I
I
2
3
4
t
i
.I
0 4
09
cD-TT/ 'PO6
t
L
I
3.39 1.35 1.30 2.48 2.60
Zn- S T T A pA=6 0
'0
-3
-0.11 - 0.36
-0.50 2.80 0.85 1.12 2.65 3.31
~A'4.c
t pA=lO.O
-2
0.94 0.76 2.64
1. CU-TTA PA=7.0
- 1.82 - 1.38
/
O S
&
/ I
2
3
4
log PHA
Figure 2. Correlation between the distribution coefficients of STTA and TTA, and the distribution ratios of their metal chelates of copper(II),cobaR(II), and zinc(I1) at a fixed P A . (0)Inert solvents: 1, Cyclohexane; 2, Carbon tetrachloride; 3,Chloroform; 4, Benzene (0)Oxygen containing solvents: 5, Methyl isobutyl ketone: 6 , Isopropyl ether: 7, n-Butyl ether; 8, Ethyl acetate: 9, n-Butyl acetate
in t h e S T T A a n d T T A systems were approximately in agreement with the lines with the slope of 2 and the extracted species may be of M(STTA)2and M(TTA)* chelates except for t h e Co(I1)-STTA system in which t h e valence of cobalt changed from 2 to 3 to form C O ( S T T A )chelate ~ ( 1 0 , I I ) . The following relation between the distribution coefficient of the chelating agent and t h e distribution ratio of metal chelates at a fixed pA has been derived from the regular solution theory (2, 7):
+
log D, = n log PHA constant where n is t h e ratio of the molar volume of metal chelate t o 2248
ANALYTICAL CHEMISTRY, VOL. 49, NO. 14, DECEMBER 1977
t h a t of chelating agent. T h e pA = -log [A-] could be calculated by t h e equation
[A-] = (PHA
[HA],,,. init. + 1)["1/K, + 1
where A - is the concentration of anion of the chelating agent in an aqueous solution. It has been found that the distribution ratio of copper(II), cobalt(II), and zinc(I1) a t a constant pA is proportional t o t h e distribution coefficient of their metal chelates in each solvent, and t h e results are summarized in Table 11. T h e plots of log DMat a fixed pA vs. log PHAgave a straight line with a slope of about 2 except for the Co-STTA
system as shown in Figure 2. T h e results of t h e Zn-TTA system are in good agreement with those in previous papers (12, 13). I t is reasonable t h a t t h e ratio of t h e molar volume of the chelate t o t h a t of the ligand is about two, because two molecules of chelating reagent combine with a divalent metal ion. In t h e case of t h e Zn-STTA, Zn-TTA, and Co-TTA systems, the plots for polar solvents containing an oxygen atom are generally far apart from the lines for inert solvents as is shown in Figure 2. This may be due t o t h e solvation effect of polar solvents (13). T h e difference of the lines for oxygen containing solvents from those for inert solvents increased in the order of Cu(I1) < Zn(I1) < Co(II), showing the magnitude of t h e residual coordination power of a metal ion with polar solvent (14). T h e solvation effect concerning oxygen containing solvents in t h e T T A system is relatively larger t h a n t h a t in t h e S T T A system, as can be seen in Figure 2. This may be attributed to the enhancement of the stability of the metal S T T A chelates due t o t h e strong covalent bonding between metal and sulfur atoms such as dsr-dsr back donation,
and the participation of solvation t o the S T T A chelates may become relatively smaller.
LITERATURE CITED (1j J. H. HiMebrand and R. L. Scott, "The Solubility of Non-Electrotytes", Dover Publications, New York, N.Y., 3rd ed., 1964. (2) K. Akiba, N. Suzuki, and T. Kanno, Bull. Chem. SOC. Jpn., 42, 2537 (1969). (3) H. A. Mottola and H. Freiser, Talanta, 13, 55 (1966); 14, 864 (1967). (4) T. Wakabayashi, Bul!. Chem. SOC.Jpn., 40, 2836 (1967). (5) S. Oki, Talanta, 18, 1233 (1971). (6) H. M. N. H. Irving and J. S. Smith, J. Inofg. Nucl. Chem., 30, 1873 (1968). (7) T. Omori, T. Wakabayashi, S. Oki, and hi. Suzuki, J . Inorq. Nucl. Chem., 26, 2265 (1964). (8) T. Honjo and T. Kiba, Bull. Chem. SOC.Jpn., 45, 185 (1972). (9) E. Uhlemann and H. Muller, 2.Chem.. 8, 185 (1968). (10) T. Honjo, S . Yashima, and T. Kiba, Bull. Chem. Soc. Jpn., 46, 3772 (1973). (1 1) T. Honjo, M. Horiuchi, and T. Kiba, Bull. Chem. Soc. Jpn., 47, 1176 (1974). (12) N. Suzuki, K. Akiba, and H. Asano, Anal. Chim. Acta., 52, 115 (1970). (13) N. Suzuki and K. Akiba, J . Inorg. Nucl. Chem., 33, 1897 (1971). (14) T. Sekine and D. Dyrssen, J . Inorg. rVucr. Chem., 26, 1727 (1964).
RECEI\-ED for review April 26, 1977. Accepted August 23,1977.
Determination of Trace Levels of Nitrates by an Extraction-Photometric Method Philip Baca and Henry Freiser" Department of Chemistry, University of Arizona, Tucson, Arizona 8572 1
Trace levels of nitrates may be quantitativeiy and selectively extracted as an ion pair with crystal violet using chlorobenzene. The results in the range of 60-720 ppb agree within a standard deviation of 28 ppb. The interference of bromide was substantially reduced by the use of hydrazine. It was surprising to learn that oxidation of bromide to tribromide under the mild extraction conditions will occur unless a reducing agent is added.
T h e most widely accepted methods currently available for analysis of nitrate ion generally involve either nitration of a phenol derivative, oxidation of an organic reagent, or reduction t o nitrite followed by production of a n azo dye ( 1 ) . These methods frequently give poor reproducibility because of t h e difficulty of maintaining proper control of the chemical reaction involved. Results may be affected directly by substances whose behavior is similar to that of nitrate or indirectly by substances which affect t h e reactivity of t h e reagents or the stability of the products, as well as by substances that react with nitrate under t h e reaction conditions used. Ion pair formation is another useful basis for nitrate analysis. The nitrate ion because of its size and relatively weak hydration readily forms extractable ion pair complexes with large organic cations. Although ions of similar charge a n d geometry interfere, very few such interferences occur in a t mospheric particulate samples. Yamamoto et al. ( 2 ) introduced a procedure based on the extraction of t h e ion pair complex between nitrate ion and the cation of crystal violet into chlorobenzene a t pH 5-7, which has a working range of 0.24 t o 1.20 p p m nitrate. When we examined t h e suitability of the method for analysis of nitrate in atmospheric particulate matter, we found it possible t o
substantially improve both the sensitivity and selectivity of t h e crystal violet method.
EXPERIMENTAL Apparatus. Absorbances were measured with a Gilford 2400 spectrophotometer using matched 1-cm path length glass cells. Reagents. Crystal violet chloride (Matheson Coleman and Bell) was used as received. Hydrazine sulfate (Fisher Scientific Company), potassium monobasic phosphate and chlorobenzene (Mallinckrodt Chemical Works) were reagent grade. Deionized water was used. Procedure. The following reagents were added to 50-mL volumetric flasks: 10.0 mL crystal violet chloride (1.3 X M aqueous solution), 4.0 mL potassium inonobasic phosphate (pH 6.0),5.0 mL of 1.4 X lo-' M hydrazine sulfate, and 1.0-12.0 mL of 3.00 ppm nitrate (prepared with KN03) working solution. Aliquots of 10.0 mL were transferred from each flask to separatory funnels, 10.0 mL of chlorobenzenewere added to each funnel, and the funnels were shaken for 2 min. Absorbances of the organic phase were measured at 595 nm against a chlorobenzene reference.
RESULTS A N D DISCUSSION A number of anions, including perchlorate, chlorate, a n d halides compete with nitrate for pairing with cations. Of these, only bromide ion and, t o a lesser extent, chloride ion, were expected t o present interference problems since t h e other interfering ions are not usually !present in atmospheric particulate samples. In the course of a bromide interference study, absorbances were observed t o continually increase with repeated shaking of t h e extraction vessels (Table I) or merely on prolonged contact (Table 11) of organic phases with aqueous phases containing bromide ion. In contrast, absorbances remained constant when bromide was not added t o t h e standard solutions. T h e results are consistent with atmospheric oxidation of bromide t o tribromide, a large and poorly solvated ion which ANALYTICAL CHEMISTRY, VOL. 49, NO. 14, DECEMBER 1977
2249
