Anal. Chem. 1983, 55, 1103-1107
Rearranging terms, eq 11 becomes eq 6. TI. Derivat,ion of the Saline Oxygen Solubility Coefficient. By mass balance the following equation is given for the saline/saline mixture:
FB~SPCMT) = (FB + Fs)Wo2(s)
(12)
where Po2(T)is the oxygen partial pressure in tonometer I1 and the rest of the parameters are described in the text. Mass balance for the saline/water mixture i s given by FBxWP02(T)
= (FBAW
FSh3)P02(W/S)
(13)
(Note: The tested assumption of linearity made above in Appendix I is ,also implied in this equation.) Dividing eg 12 by eq 13 we have
_ --
(FB
+ FS)xSP02(S)
(FBxW + FS)POz(W/S)
(14)
Dividing the numerator and the denominator of the right hand side of eq 14 by Xs and rearranging terms, eq 9 is produced. Registry No. Oxygen, 7782-44-7.
LITERATURE CITED (1) Van Slyke, D. D.; Nelll, J. M. J. Blol. Chem. 1924, 61, 523-573. (2) Nevllle, J. R. J. AppE. Physiol. 1960, 15,717-722.
1103
(3) Laver, M. B.; Murphy, A. J.; Seifen, A.; Radford, E. P.,Jr. J. Appl. Physioi. 1965, 20, 1063-1069. (4) Kllngenmaier, C. H.; Behar, M. G.; Smith, T. C. J. Appl. Physlol. 1969, 26. 653-655. (5) Bates, D. V.; Harkness, E. V. Can J . Blochem. Physiol. 1961, 39, 991-999. (6) Clerbaux, Th.; Gerets, G.; Frans, A. J. Lab. Clin. Med. 1973, 82, 342-348. (7) Baumberger, J. P. Am. J. Physiol. 1940, 129,308. (8) Clark, L. C.,Jr. Trans. Am. SOC. Artif. Intern. Organs 1956, 2 , 41-48. (9) Llnden, L. J.; Ledsome, J. R.; Norman, J. B r . J. Anaesth. 1965, 3 7 , 77-88. (IO) Tazawa, H. J. Appl. Physlol. 1970, 29 (3), 414-416. (11) Malmstadt, H. V.; Pardue, H. L. Anal. Chem. 1961, 33, 1040-1047. (12) Blaedel, W. J.; Hlcks, G. P. Anal. Chem. 1962, 3 4 , 388-394. (13) Blaedel, W. J.; Laesslg, R. H. Anal. Chem. 1965, 3 7 , 1255-1260. (14) Sendroy, J., Jr.; Dlllon, R . T.; Van Slyke, D. D. J. Blol. Chem. 1934, 105,597-632. (15) Altamn, P. L.; Dlttmer, D. S. “Biological Handbooks: Respiration and Circulation”; Federation of Amerlcan Societies Experimental Biology: Bethesda, MD, 1971; pp 16-18. (16) Wallace, W. D.; Clark, J. S.;Cutler, C. A. Anal. Chem. 1961, 53, 2313-231 a. (17) Harabln, A. L.; Farhi, L. E. J. Appl. Physlol.: Respir., Environ. Exerclse Physlol. 1978, 44 (5), 818-820.
RECEIVED for review August 10, 1982. Resubmitted January 31, 1983. Accepted March 3, 1983. This research was supported by National Heart, Lung and Blood Institute, Grants HL-20351 and HL-21445.
Kinetic Spectrum Method for Analysis of Simultaneous, First-Order Reactions and Application to Copper(I I) Dissociation f rom Aquatic Macromolecules Dean L. Olsoin and Mark S. Shuman* Department of Environmental Sciences and Engineering, School of Public Health, University of North Carolina, Chapel Hiii, North Carolina 27514
A nonllnear dlfferential rate method tlhat requires no prior knowledge of rate constants, lnltlal concentrations, or number of components Is developed to analyze multicomponent, flrst-order or pseudo-flrst-order reactlone. The method glves a klnetlc spectrum with peak maxlma correspondlng to rate constants and peak areas equal to inltlal concentratlons of components. Complete resolutlon of two components requires a rate constant ratio greater than about 40. The method was applied to a study of Cu( I I ) dlssoclatlon from estuarlne humlc material In whlch a Cu(I1)-humic mixture was reacted wlth a colorlmetrlc reagent and absorbance followed from 50 ms to 1835 s. The klnetlc spectrum showed bound Cu(I1) dlstrlbuted In two regions over a wide range of rate constants. About 43 % of the total Cu( I I ) dlssoclated In times greater than 50 ms correspondlng to rate Constants 5 4 0 s-’.
Graphical extrapolation and multiple proportions are the two differential reaction rate methods frequently used for kinetic analysiri of mixtures (1,2). These methods are commonly applied to binary systems and are occasionally extended to kinetic analysis of rnore than two components. Graphical extrapolation requires that one component react nearly to completion before the other component reacts significantly, and the method of multiple proportions requires an inde-
pendent estimate of the rate constants. These methods cannot be readily adapted to the analysis of mixtures for which neither the number of components nor the rate constants are known. Graphical extrapolation is sometimes used in such cases, but fitting data to straight line segments becomes rather arbitrary without prior knowledge of the number of components and the relative values of the rate constants. Dissolved organic materials in natural waters are poorly characterized, polydisperse macromolecules possessing multiple metal binding sites. Estimation of the metal dissociation rate constant for each of these sites reduces to the problem of analyzing a multicomponent mixture for which the dissociation mechanisms, relative rate constants, and the nature and number of binding sites are unknown. Cu(I1) dissociation rate constants have been estimated electrochemically with a rotated electrode (3-5), but this technique has a rather narrow experimental time range. The photometric method described here was developed to broaden the time range and is based on monitoring the appearance of a colored complex, Cu(PAR),, where PAR is the reagent 4-(2-pyridylazo)resorcinol. PAR was chosen because it forms a strong, water-soluble Cu(I1) complex of simple stoichiometry with a large molar absorptivity (6). The rate of Cu(PAR), appearance depends on the rate of Cu(I1) dissociation from multiple sites on the macromolecules. A “kinetic spectrum” method was used to plot the distribution of binding sites which gives a series of peaks with
0003-2700/83/0355-1103$01.50/0 -. A 0 1983 Amerlcan Chemical Soclety
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ANALYTICAL CHEMISTRY, VOL. 55, NO. 7, JUNE 1983
peak maxima located at abscissa values corresponding to the dissociation rate constants of the individual binding sites and peak areas equal to the initial concentration of Cu(I1) bound to these sites. The mathematical model is similar to that used for analyzing the relaxation spectra of viscoelastic materials (7,8). It has superficial similarities to Connors' kinetic spectra methods (9,lO) but is developed from a completely different conceptual and mathematical viewpoint.
KINETIC MODEL Consider an aqueous mixture of n components in which each component, designated CULL, undergoes simultaneously with all other components a first-order or pseudo-first-order reaction
to form a common product, P, which in this case is C U ( P A R ) ~ Reaction 1 is written in terms of Cu(I1) and Lj, where Lj represents the ith Cu(I1) binding site on an organic macromolecule, although the model pertains as well to any system of simultaneous, first-order reactions in which either reactant or product concentration can be monitored over time. The sum of the concentrations of all dissociating components a t time t is
The distribution function, H ( k , t ) ,is obtained graphically by numerical differentiation of experimental concentration vs. In t data and has important, useful properties. Note that
x I H ( k , t ) d In k =
(2)
i=l
where Cio is the initial concentration of CuLj, the ith component. If the rate constant is considered the variable of integration, the summation can be replaced by the integral
C(k,t) = l m0 F ( k , t ) e - k tdk
(3)
where F(k,t) is a continuous decay function whose value at time t depends only on the rate constants and initial concentrations. The mathematical form of F(k,t) is determined by the form of C(k,t). In eq 3, C(k,t)is the Laplace transform of F(k,t). This expression must be inverted to obtain F(k,t), the required function. Inversion can be accomplished with the Post-Widder equation ( 1 2 , 12)
lim Fm(k,t) (4)
m-m
where m is an integer. The notation C ( m / k )for C(k,t) is to indicate that t corresponds to m / k for any computed value of F(k,t). The error decreases with increasing m (8),but values of m > 2 lead to the use of higher order derivatives which is unwarranted with the usual accuracy of experimental data (7). The second-order ( m = 2) approximation gives
dk = C ( k , t ) N JmF2(k,t)e-kt n Jm(
$)-e-kt
dk (5)
Equation 5 can be rewritten as
where
(7) Substituting l / d In t for t / d t in eq 7 gives
-m
(9)
and
Lm
x I k 2 t 2 e - k td In k = t2
&kt
dk = 1
(10)
where the integral is evaluated by recognizing that the Laplace transform of k is l / t 2 . Equation 9 then reduces to
which indicates that the area under the graphical distribution curve is equal to the sum of the initial reactant concentrations. Also, since H ( k , t ) is symmetric in k and t
dH(k,t) --dH(k,t) --
n
C ( t ) = CCioe-kit
5 Ci0Jmkzt2e-"' d In k
i=l
dlnk
(12)
dlnt
and
x I H ( k , t ) d In k = S m H ( k , t )d In t = ?Cjo (13) -m
i=l
Equation 13 indicates that the distribution function is identical when plotted vs. either In k or In t. The In k data are not directly available from the experiment, but since t corresponds to 2 / k , In 12 can be calculated from In ( 2 / t ) . A peak-shaped curve results for each component with the area under the peak equal to the initial concentration of the component, Cio, and with the peak maximum appearing at In k j = In ( 2 / t ) . The maximum value of H ( k , t ) for a single component is found by setting dH(k,t)/d In k equal to zero and solving for t in terms of hi. Substituting the result, t = 2 / k i , into the right-hand side of eq 8 yields H(k,t),,, = 4C,0e-2 indicating that the peak height is dependent only on the initial component concentration. The peak width at half-height, H(k,t),,/2, is found iteratively to have the value (A In k ) l p = 1.6973 and is independent of ki and Ci". It is convenient to plot H ( k , t ) vs. log k instead of In k . As a result, the half-width (A log k ) , j 2 = 0.7371. Also, the area under the curve must be multipled by 2.3026 to yield the concentration. A Numerical Example. The two-component system
+
C ( t ) = 2e4.1t (14) where the initial concentrations CIo = 2 and Czo = 8 are in arbitrary concentration units, was chosen as a numerical example to illustrate the characteristics of the model. Graphical extrapolation would require In C ( t ) to be plotted vs. t as in Figure la. Figure l b shows C ( t ) plotted vs. log t for analysis by the kinetic spectrum method. Pairs of C ( k , t ) ,log t data are entered into a computer program that calculates H ( k , t ) vs. log k . The result (Figure IC)gives rate constants, initial concentrations, peak heights, and half-widths with their expected values and correctly indicates the number of components. The numerical example was also used to examine the effect of noisy data and smoothing on the appearance of the distribution function. Smoothing was required for noisy data and caused a decrease in peak height and an increase in half-width. Peak area was the best measure of concentration, but with smoothing, the area overestimated the concentration
ANALYTICAL CHEMISTRY, VOL. 55, NO. 7, JUNE 1983
1105
on the log t axis, and where w1and w 2are the base line peak widths. When the base line width is defied at 5% of the peak height, the calculated width is (A log k)0.05= 1.63. Since this width is the same for all peaks, w1 = w2 and
R = -x 2
A
r
lo
8 -
6
C (k,t) 4
2
0
- x1
1.63 It is usually necessary to have R 2 1for complete resolution, which requires that k 2 / k l 2 42.7. An R 2 1 may be unnecessary to reasonably resolve two peaks for some Czo/CIoratios. In a numerical example where Czo/Cl0 = 9 and k 2 / k , = 10 (R = 0.61), the rate constants were estimated to within 0.2% of their expected values, C20 to within 10% and Cl0 to within 30%. The two areas representing the concentrations were time (sec) defined by drawing a vertical line through the minimum beI tween the two peaks. This example indicates that the resolving abilities of the distribution function are somewhat limited but in some cases are comparable to the abilities of the graphical extrapolation method as described by Mark and Rechnitz (1). Complete analysis of even a multicomponent system could be handled quite easily if resolution was sufficient. For a poorly resolved system, graphical extrapolation would probably be inadequate, but the kinetic spectrum method could still estimate the number of components.
--
-i!.O
-1.0
0.0
1 .o
log t
-1.0
1 .o
0.0
2.0
log k
(a) Date from the numerical examlple plotted for analysis by the graphical extrapolation method. (b) Data from the numerical example plotted for analysis by the kinetic spectrum method. IC) Kinetic spectrum lrom the numerical example: (2.3026)(area I) = C,'; (2.3026)(area 11) = C20.
Flgure 1.
for the larger Czoand underestimated it for the smaller Cl0. With 1% normal random relative error (13)imposed on the ordinate of the data, tlhe smaller rate constant, kl, was underestimated l o % , but the larger constant, Itz, was underestimated less than 1%. With 5% random relative error, kl was still underestimated lo%, but k2 was overestimated 7%; both concentrations could sitill be estimated within 10% of their expected values. When 20% error was imposed on the data, little quantitative information was obtained, except the indication of a t least two components. The ability of the kinetic spectrum techmique to resolve two components can be examined by analogy with chromatographic techniques. Resolution for two components is commonly expressed (14)
where x1 and x 2 are the peak locations, in this case located
DATA COLLECTION AND ANALYSIS Kinetic measurements were made photometrically by monitoring the appearance of C U ( P A R ) ~ at 508 nm. A stopped-flow system was used from 20 ms to 50 s and consisted of a Beckman DU spectrophotometer, an Aminco-Morrow stopped-flow apparatus (15),and a circulating thermostating bath. Data acquisition, storage, and analysis were performed with a Charles River Data Systems, Inc., LSI-11 based microcomputer with 32K memory and a 16 bit A/D converter. Measurements from 50 s to 1835 s were made with a Cary 219 recording spectrophotometer after solutions were mixed in a stoppered cuvette. The stopped-flow method was employed over five different time ranges selected to give a continuous record with overlapping data between adjacent intervals. Absorbance values were taken from the Cary 219 recorder tracings every 5 s from 50 to 180 s, every 10 s from 180 to 420 s, and every 60 s from 455 to 1835 s. The result was 178 data points spaced in fairly regular intervals on the log t axis from -1.7 to 3.3. About 30-35 data points per decade was found adequate. A cubic spline was fitted to the C(k,t), log t data by an International Mathematical and Statistical Libraries, Inc. (IMSL) computer routine which provides continuous first and second derivatives and nonlinear, adjustable smoothing. The distribution function, H ( k , t ) ,was computed from the derivatives using the spline coefficients, and plotted vs. log k. Areas were determined from the integral of the fitted spline, and peak maxima were estimated from computer output, which was tabulated in 0.0087 log k increments to yield 12 values within 2% of each other. Smoothing was increased in small increments until minor variations disappeared from the graph of the distribution function and further increases had no significant effect on the major features of the plot. Because of the nature of the spline end condition, the spline oscillates at the beginning of the data set. Since this resulted in a poor fit from 20 to 50 ms, H(k,t) output from this region was discarded. Final output covered 4.6 orders of magnitude from k = 0.001 s-l to 40 s-l. ENVIRONMENTAL APPLICATION The chemistry of Cu(I1) in natural waters is affected by the binding of Cu(I1) to polydisperse organic macromolecules collectively termed humic materials (HM). These materials are thought to originate from decaying vegetation and mi-
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ANALYTICAL CHEMISTRY, VOL. 55, NO. 7, JUNE 1983
crobial synthetic activity (16). Although HM has been investigated extensively, no single structural model has emerged. As a consequence, the concentration of HM is usually expressed simply as milligrams per liter of dissolved organic carbon (DOC). Phenolic and carboxylic functional groups appear to be the major binding sites for Cu(II), though other groups present in smaller abundance may bind significantly when the metal/HM ratio is small. The kinetic model was developed to study the dissociation reaction I
CuHM
kl
Cu2+
0.01
+ HM
(17)
+ PAR-
k k-2
CuPAR+
(18)
Rate constants were determined under conditions of 10 pM Cu(I1) and 100-130 pM PAR and found to be k z = 2.6 X lo6 M-l s-l and kZ= 85 s-l. With PAR in sufficient excess, the condition kz[PAR] >> kl[HM] holds and the overall reaction CUHM + 2PAR--
Cu(PAR)Z
I
'
-2.0
'
'
8
-1.0
'
0.0
'
'
1 .o
I '
log k
where CuHM represents the Cu(I1) bound to various sites on the HM, and k-l and k, are the observed dissociation and association rate constants, respectively. Equation 17 is a general statement of the reaction in which electrochemical neutrality is neglected since the charge on CuHM varies with the extent of metal binding. PAR forms both 1:l and 1:2 complexes with Cu(I1). The method of continuous variations showed a CU(PAR)~ complex when [CuZ+]/[PAR-]< 0.2, a mixture of complexes when 0.2 I [Cuz+]/[PAR-] I0.5, and a 1:l complex when [Cu2+]/ [PAR-] > 0.5. The formation of the complexes was studied under pseudo-first-order conditions with Cu(I1) in excess for CuPAR formation and PAR in excess for CU(PAR)~ formation. Rate constants were determined by varying the concentration of the excess reactant which indicated that the rate-determining step for C U ( P A R )formation ~ was Cu2+
-3.0
+ HM
(19)
is assumed irreversible. An 8-10-fold molar excess of PAR over Cu(I1) was found sufficient, since experiments a t 80100-fold excess gave nearly identical results. Cu(I1) in the CuHM mixture is bound to multiple sites, all of which dissociate simultaneously at a rate that depends on the nature of the functional group, its position on the macromolecule, and the residual charge. If the rate-limiting step in reaction 19 is assumed to be the dissociation of CuHM, then
The concentration of the CuHM mixture, C(k,t) (see eq 2) is measured photometrically as Cu(I1) by monitoring the formation of Cu(PAR)*over time. The formation reaction of CU(PAR)~ without HM present is complete in about 20 ms under experimental conditions. Though this is quite rapid, it theoretically limits observation of the fastest dissociation reactions. Since data from 20 to 50 ms were discarded, 50 ms was the practical lower limit of these kinetic measurements; this corresponds to a dissociation rate constant k 5 2/0.050 s = 40 s-'. The CU(PAR)~ complex has an absorbance maximum at 508 nm, obeys Beer's law when [Cu2+]/[PAR] C 0.2, and has a molar absorptivity 6 = 57 470 M-l cm-l. PAR has an absorbance maximum at 413 nm and E = 36 740 M-l cm-l. The PAR dihydrate disodium salt was obtained from the Eastman Kodak Co. All experiments were conducted at 25 "C and adjusted to 0.1 M ionic strength with NaN03, buffered with 1 mM NaHC03, and adjusted to pH 7.5 with 1 N H N 0 3 or 1N NaOH. A stock solution of Cu(I1) was prepared by dis-
Flgure 2. Kinetic spectrum of the dissociation of Cu(I1) from a sample of estuarine humic material.
solving 1 g of metal with 7 mL of concentrated H N 0 3 and diluting to 1L. All chemicals were reagent grade. Dissolved HM from the Ogeechee River estuary near Savannah, GA, was concentrated by membrane ultrafiltration (5) and organic carbon was measured with a Dohrmann/Envirotech DC-54 carbon analyzer. Kinetic experiments were performed by first adding Cu(I1) to a solution of HM. This solution was allowed to equilibrate for about 12 h and was then mixed 1:l with a solution of 200 pM PAR. Absorbance was measured as AA = A, - A,, the difference between the absorbance of CU(PAR)~ at long time and at time t. A mixture of only HM and PAR was used as a blank to make relatively small corrections in AA and to correct for HM and PAR absorbance. The corrected AA was used to compute the total concentration of bound Cu(I1) at time t, C(k,t),from the formula C(k,t) = AA/cb, where b was the path length, 1 cm. A sample of HM was adjusted to 84 mg/L DOC and 28.4 pM Cu(I1). The initial metal/HM ratio was only about 14% of the binding capacity of HM for Cu(II),which was estimated in separate experiments by cupric ion selective electrode titrations as 2.5 pmol of Cu(II)/mg of DOC. The sample was analyzed from 50 ms to 1835 s by the kinetic spectrum method and the distribution function, H ( k , t ) ,was plotted vs. log k in Figure 2. The average squared difference between the fitted spline and the ordinate values was 0.00016. The completeness of reaction 19 was indicated by the recovery of 90% of the initial Cu(I1). The assumption that reaction 19 was first order or pseudo first order in CuHM was verified by doubling the initial concentrations of Cu(I1) and HM which doubled the total area under the curve but had no effect on the overall appearance of the distribution curve. The reproducibility of the total area was estimated at &2%. The analysis resolved at least two dissociating components in this environmental sample and revealed how the bound Cu(I1) was distributed over the range of rate constants. The total area under the curve in Figure 2 yields 6.1 pM Cu(I1) bound as CuHM that dissociated with rate constants 540 s-'. This was only 43% of the total added Cu(II), indicating that a large portion of the Cu(I1) reacted in less than 50 ms with rate constants >40 s-l. Other estuarine samples gave similar results. This finding raises questions about the ability of dissolved HM to decrease the bioavailability of Cu(I1) and suggests that binding capacity may be a poor indicator of Cu(I1) reactivity. The greatest advantage of this method of kinetic analysis is that it requires no prior knowledge of the rate constants, initial concentrations, or number of components; it does require that the reactions under study be first order or pseudo first order. The method provides useful information on how the concentration of the reactants is distributed over values of k and always gives the total initial concentration of reactants over the measurable range of rate constants. The technique
Anal. Chem. 1983, 55, 1107-1111
yields useful information from the analysis of multicomponent systems. A copy of the computer program used for data analysis is available upon request.
LITIERATURE CITED (1) Mark, H. B., Jr.; Rechnitz, G. A. "Kinetics in Analytlcal Chemlstry"; Intersclence: New York, 1968; Chapter 7 (2) Mottola, H. A. CRC Crit. Rev. Anal. Chem. 1974, 4 , 229-280. (3) Shuman, M. S.;Mlchael, L. C. I n "International Conference on Heavy Metals In the Envlronment: Symposium Proceedings"; Hutchinson, T. C., Ed.; Toronto, Canada, 1975; Vol. I , pp 227-248. (4) Shuman, M. S.;Michael, L. C. fnviron. Sci. Techno/. 1978, 72, 1069- 1072. (5) Shuman, M. S.;Collins, 6. J.; Fitzgerald, P. J.; Olson, D. L. I n "Aquatic and Terrestrial Humic Materials"; Chrlstman, R. F., Gjesslng, E. T., Eds.; Ann Arbor Press: Ann Arbor, M I , 1983; pp 349-370. (6) Shlbata, S. I n "Chelates in Analytical Chemistry, Vol. 4"; Flaschka, H. A,, Barnard, A. J., Jr., Eds.; Marcel Dekker: New York, 1972; p 116.
1107
(7) Ferry, J. D. "Viscoelastlc Properties of Polymers", 3rd ed.; Wiley: New York, 1980; Chapter 4. (8) Schwarzl, F.; Staverman, A. J. Physica (Amsterdam) 1952, 7.9, 791-798. (9) Connors, K. A. Anal. Chem. 1975, 4 7 , 2066-2067. (10) Connors, K. A. Anal. Chem. 1979, 57, 1155-1160, (11) Widder, D. V. "The Laplace Transform"; Princeton University Press: Princeton, NJ, 1946. (12) Bellman, R.; Kalaba, R. E.; Lockett, J. "Numerical Inversion of the Laplace Transform"; American Elsevier: New York, 1966. (13) Beck, J. V.; Arnold, K. J. "Parameter Estlmation in Engineering and Science"; Wiley: New York, 1977; p 126. (14) Karger, B. I-.;Snyder, L. R.; Horvath, C. "An Introduction to Separation Science"; Wlley: New York, 1973; p 147. (15) Reich, R. M. Anal. Chem. 1971, 4 3 , 85A-97A. (16) Saar, R. A.; Weber, J. H. Environ. Sci. Techno/. 1982, 76,510A517A.
RECEIVED for review November 4,1982. Accepted February 7, 1983.
Fractional Separation of Organic and Inorganic Tin Compounds and Determination by Substoichiometric Isotope Dilution Ana Iysi:; Hisanorl Imura and Nobuo Suzuki" Department of Chemistry: Faculty of Science, Tohoku University, Sendal, 980 Japan
Tributyltln( IV), dibutylltln( IV), butyltln( IV), and lnorganlc tin( I V ) can be separated from each other by halide extraction with benzene. Dlbutylitin( IV), butyltln( IV), and inorganlc tin( I V ) are substoichiometrlcally determined vla complexatlon with sallcylldeneamino-2-thlophenoi in benzene. Trlbutyitln( I V ) can be determined by applylng the substolchiomeiry to one of the decomposlltlon products by bromine treatment of the mother compound. The subsiolchlometric determination of dlbutyltin( I V ) and biutyltln( I V ) In a commercial organotin chemical and B poly( vinyl chloride) sheet Is demonstrated. The reiatlve standard deviation of the substoichlometric determination is nearly 1% at the 0.1-1 mg level.
required. Simple measurement of the radioactivity of the substoichiometric extract is enough for the final determination. The substoichiometric isotope dilution method has been applied to the speciation of different valence states of antimony (4)and arsenic (5) and of methylmercury and inorganic mercury (6). We have already reported the substoichiometric determination of inorganic tin in environmental samples (7) and in various organotin compounds (8)via the complexation with salicylideneamino-2-thiophenol(SATP) in a nonaqueous medium. In this paper, a preliminary separation of butyltin(IV), dibutyltin(IV), and tributyltin(1V) and the substoichiometric isotope dilution analysis for these tin species are investigated and applied to a commercial organotin chemical and PVC sample.
Various orgaaotin compounds have been used in industry and agriculture; for instance, dibutyltin dilaurate is commonly used as a stabilizer for poly(viny1 chloride) (PVC), tributyltin polyacrylate (tributyltin polymer) in antifouling paints for ship bottoms, and bis(tributy1tin) oxide as a fungicide. These compounds on the market often contain other butyltin homologues with different numbers of butyl groups. Toxicity of the organotin compounds is remarkably different from one another depending on the number of alkyl groups. Speciation of individual organotin and inorganic tin should be developed. Only a few analytical methods (1-3) have been proposed for inorganic tin and a series of organotin compounds from monoto trialkyltin, but the following disadlvantages should be pointed out fo'r these methods: (a) decomposition and evaporation lose of tin compounds during the operation must be considered, (b) quantitative recovery of the compounds of interest must always be accomplished, and (c) calibration curves for all the compounds are required. Substoichiometry combined with the isotope dilution principle seems to be suitable for the speciation of alkyltin compounds by (consideringthe following advantages: quantitative recovery of each species and calibration curves are not
EXPERIMENTAL SECTION Materials and Apparatus. Radioactive Butyltin(IV) and Dibutyltin(1V). Carrier-free tin-113 produced by the nuclear reaction 1151n(p,3n)1'3Sn with 40-MeV protons at Tohoku University Cyclotron and Radioisotope Center was isolated from the irradiated indium oxide by an iodide-extraction method (7,8). Anhydrous tin(1V) chloride labeled with I13Sn was prepared by contacting purified '13Sn iodide with anhydrous tin(1V) tetrachloride. The labelling of different butyltin compounds was achieved by a redistribution reaction (9) under various conditions. Butyltin(1V) chloride labeled with l13Sn was prepared by stirring 0.4 mL of tetrabutyltin with 0.2 mL of labeled tin(1V) chloride for 3 h at 100-110 O C . Dibutyltin(1V) chloride labeled with I13Sn was prepared by the similar treatment except heating conditions were at 220 "C for 4 h. The labeled butyltin compounds were purified by halide extraction into benzene (cf. Figure 2). The purity of the labeled compounds was tested by silica gel thin-layer chromatography (IO) with a developing solvent of butanol-acetic acid-water (10:2:5). The carrier concentration of the labeled compound was accurately determined by the substoichiometric isotope dilution method developed here. Radioactive Tributyltin(IV). Radioactive tributyltin(1V) was prepared directly by the photonuclear reaction 11sSn(y,n)117mSn.
0003-2700/83/0355-1107$01.50/00 1983 American Chemical Society
