nism, as these factors were not studied in the simulation experiments. From knowledge of the principles and specifications of the various pumping systems, one can conclude that many of the currently available units have performance deficiencies for use in high performance GPC for the calculations of molecular weights as described here. (The reader is reminded that qualitative information is usually obtained without serious bias and does not fall under the described restrictions.) Most modern solvent delivery systems are limited to pumping stabilities of 0.5-1.0% or greater. Design and fabrication of sophisticated pumps which will directly deliver solvents with variations of 0.3% or less is difficult and expensive. Therefore, a more practical approach might be to operate a less expensive pump in conjunction with a very precise flow-measuring device with feedback control to the pump to ensure the desired short- and longterm flowrate precision. Another option is to interact flowrate measurements with data acquisition software to correct for flowrate aberration. During the preparation of this manuscript, a paper was published by Patel (19) describing the use of "oligomeric" internal standards to compensate for flowrate variation. The technique appears promising. In addition to the errors in molecular weight measurements caused by flowrate variation in high performance GPC, additional errors due to factors associated with the very efficient columns (>lO,OOO theoretical plateslmeter) also can be significant. Studies are now under way in this laboratory to determine the effect of column and extra-col-
umn peak variances (band broadening effects) on molecular weight measurements by high performance GPC. LITERATURE CITED (1) D. D. Bly, "Recent Advances in Size Exclusion Chromatography," FACSS, First National Meeting, Atlantic City, N.J.. November 20, 1974, Paper No. 72. (2) J. J. Kirkland, J. Chromatogr. Sci.. I O , 593-599 (1972). (3) R. J. Limpert, R. L. Cotter, and W. A. Dark, Amer. Lab., 6 (5). 63 (1974). (4) K. Unger, R. Kern, M. C. Ninow, and K.-F. Krebs, J. Chromatogr.. 99, 435-443 (1974). (5) M. J. Telepchak, J. Chromatogr., 83, 125-134 (1973). (6) W. W. MacLean, J. Chromatogr., 99,425-433 (1974). (7) "Chromatography Notes," IV (2), Waters Associates, Milford, Mass.. June 1974. (8)W. W. Yau, H. L. Suchan, and C. P. Malone, J. folym. Sci., fart A-2, 6, 1349-1355 (1968). (9) A. R. Cooper and J. F. Johnson, Eur. folym. J., 0, 1381-1391 (1973). (10) A. C. Ouano and J. A. Barker, Separ. Sci., 6, 673-699 (1973). (11) H. A. Swenson, H. M. Kaustinen. and K. E. Almin, folym. Led.. 9, 261268 (1971) or (J. Polym. Sci., Parts). (12) J. S.Fok and E. A. Abrahamson, Chromatographia, 7,423-431 (1974). (13) H. E. Pickett. M. J. R. Cantow., and J. F. Johnson.,~J. ADO/. Polvm. Sci... , I O , 917-924(1966). H. E. Pickett, M. J. R. Cantow, and J. F. Johnson, J. folym. Sci., Pari C, 21, 67-81 (1968). S.T. Balke. A. E. Hamielec, 9. P. LeClair, and S. L. Pearce, lnd. fng. Chem., Prod. Res. Develop., 8,54-7 (1969). T. D. Swartz. D. D. Bly, and A. S. Edwards, J. Appl. folym. Sci., 16, 3353-3360 (1972). D. D. Bly, "Progress in Liquid Exclusion Chromatography," "Du Pont Innovation", 5 (2), 16-20, Winter 1974. D. D. Bly, "Gel Permeation Chromatography in Polymer Chemistry" in "Physical Methods in Macromolecular Chemistry", Vol. 2, Benjamin Carroll, Ed., Marcel Dekker, New York, 1972, Chap. 1, pp 16-25. G. N. Patel, J. Appl. folym. Sci., 18,3537-3542 (1974). ~~~~
rr
~~
RECEIVEDfor review April 30, 1975. Accepted June 11, 1975.
Extractions with Metal-Dithiocarbamates as Reagents Armin Wyttenbach and Sixto Bajo Swiss Federal Institute for Reactor Research, 5303 Wurenlingen, Switzerland
The metal-dithlocarbamates Ho(DDC)~, Ag(DDC), Ni( DDC)2, Cu( DDC)2, Sb( DDC)3, Te( DDC)4, Se( DDC)3, II~(DDC)~,As( DDC)3, Cd( DDC)2, Zn( DDC)2, Co( DDC)3, Fe(DDC)3, and TI(DDC) have been tested as reagents for the extraction of 12 different metals from 0.1N H2SO4 and from solutions of pH 5 into CHC13. These reagents show excellent selectivity for the extraction of metals with higher conditional extraction constants. In the majority of all cases, extraction is complete within 2 minutes; Se(DDC)4, Co( DDC)3, and Fe( DDC)3, however, react only slowly and in some cases incompletely or not at all. The successive extraction of a sample with several different reagents yields a series of organic fractions that contain dlfferent metals. As an example, the application of these reagents to a neutron activated biological sample is given, where the resulting organic fractions can be directly submitted to y-spectrometry without any further chemical treatment.
The diethyldithiocarbamate anion (C2Hs)zNCSz- (in the following denoted by DDC) forms complexes extractable into organic solvents with many metals. If the reagent is added in excess as water soluble NaDDC to an aqueous phase containing several metals, and if the complexes formed are subsequently extracted, selectivity may be achieved by the choice of pH andlor the addition of mask-
ing agents. Because of the fast decomposition of DDC in this time acid solutions ( I ) , the pH should not lie below 4; problem can be considerably eased by applying the reagent in a form that is soluble in the organic phase, Le., as Zn(DDC)2, in which case decomposition in contact with acid solutions even of [HI = 1 is slow enough to allow extraction times up to 1 hour before DDC decomposition is substantial. Alternatively, selectivity can be achieved by the application of the substoichiometric principle ( 2 ) , which uses quantities of reagent sufficient to extract only part of the metal to be separated. Beside the necessity to remove any metal with a higher conditional extraction constant beforehand, application of substoichiometry is greatly complicated in the case of DDC by the formation of mixed C1-DDC complexes ( 3 , 4 )with many metals. As another possibility, we propose the application of different metal-DDC complexes as reagents to achieve selectivity. This paper gives the principle of the method, screens the behavior of 14 metal-DDC complexes in the extraction of 14 ions from the aqueous phase, and gives some representative applications. It should be noted that this mode of operation is somewhat similar to the method proposed by Elek et al. (5-7) for substoichiometric multielement separation with dithizone. However, in using solutions of metalDDC complexes as reagents, the need to employ exactly measured amounts of metals and chelating agent to fulfill
ANALYTICAL CHEMISTRY, VOL. 47, NO. 11, SEPTEMBER 1975
0
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(A) + [A(DDC)mIorg= {AI (7) n[B(DDC)nIorg + m [A(DDC)mIorg= n IB(DDC)nlorg (8) When the metal in the aqueous phase is C, A has to be replaced in Equations 5, 7 , and 8 by C. Equations 6 to 8 will hold only if there is no substantial competition of H+ for the ligand, Le., if the pH is not too low. Provided that the reagent B(DDC), is used in excess relative to all A, metals present, i.e., n {B(DDC)nI> Em, {All
Figure 1. Fraction extracted of an A3+-metal ( F A )and a C3+-metal (Fc) by the reagent B(DDC)2 as a function of the ratio of the respective conditional extraction constants K' (a) (A) = iO-5M, ( b ) IC) = 10-5M. ( c ) (C) (B(DDC)*)is iO-3M in all three cases
=
iO-5M, { A } = 7 X iO-5M.
(9)
and if the K'A, K'B, and K'c values are not too similar, then, after attaining equilibrium, all of A will be complexed by DDC; B is only partially complexed, since the amount of DDC not reacted with A is now substoichiometric to B; C will not be complexed at all. One therefore expects complete extraction of A, into the organic phase, distribution of B between the two phases, and no extraction of C,. By combining Equations 5 to 8, the fraction extracted, i.e.,
the necessary conditions is avoided. The method proposed here is therefore much simpler to apply.
THEORY In the following, the reagent used will be denoted by B(DDC), and the metals in the aqueous phase by Ai and Ci; the distributiqn of the differe_nt metals into the groups Ai and C, is given by the condition 1 1 1 m n m where m and n are the numbers of DDC ligands in the complexes A(DDC),, B(DDC),, and C(DDC),, and K' is the conditional extraction constant of the respective complexes. This quantity is defined by
- log K'A > - log K'B > - log K'c
In Equation 2, terms in brackets denote equilibrium concentrations in the organic phase (subscript org) and in the aqueous phase (no subscript); (Me) is the concentration of all forms of the metal in the aqueous phase. Unlike the extraction constant K
(3) which is a true constant for a given organic solvent, K' will vary with the actual composition of the aqueous phase. K' and K are related by
K' = K l a
(4)
where Ringbom's a-coefficient is defined as a = (Me)/[Me]. a can be calculated if the stability constants of all metal complexes formed in the aqueous phase are known. In the present experiments, where an aqueous phase containing the metal A (or C) is extracted with the reagent B(DDC),, there will be competition between A (or C) and B for the ligand DDC. The resulting distribution can be obtained by combining the two expressions for K'A (or K'c) and for K'B:
From the material balance and the stoichiometry of the reaction, it follows (assuming equal volumes for the organic and the aqueous phases, and denoting the concentrations before extraction by terms in { ) braces):
1014
can be calculated for any given initial condition. The results for one case are represented in Figure 1 as a function of K ' ~ l l ~ l ~K l' / and " K ' ~ l ~ ~ l K ' gExtraction ll~. of elements of the A group is quantitative (FA > 0.99) even for KlA1/m K'g'l" (curve l a ) . If there are no A metals present, K ' ~ l l ~ l K 'must ~ l l ~be less than 2 X to suppress completely the extraction of C metals (Fc < 0.01) (curve I b ) . The situation for the C metals is more favorable if there are A metals present too; in this case, K ' ~ l l ~ l K ' & < ~5 X will be sufficient to prevent extraction of any C metals (curve IC). It follows from the preceding that the correct choice of the reagent B(DDC), for a given separation problem requires knowledge of the K' values of all metals involved, However, in practice, this will be difficult in many cases due to lack of the necessary a and K values. As a first-order approximation in judging the feasibility of a separation, we therefore have to resort to the so-called order of extraction; this order gives, for a specified system, not the absolute values, but the sequence of the K'll" values of different metals. The order of extraction (as far as ions considered in this work are concerned) has been established by Bode and Tusche (8) for pH 11 and 8.5 as Hg2+, Ag+, Cu2+, Ni2+, Bi3+, PbZ+, Co2+, T1+, Zn2+, In3+, Sb3+, Fe3+, Te4+; by Wickbold (9) for pH 9 and 1 2 as Hg2+, Ag+, Cu2+, Ni2+, Co2+, Pb2+, Bi3+, Cd2+, Sb3+, Zn2+, Fe3+; by Eckert (IO) for pH 5-6 as Hg2+, Ag+, Cu2+, Ni2+, Bi3+, Pb2+, Cd2+, Fe3+, Zn2+,As3+; and by Wyttenbach andeBajo ( 3 )for 0.1N HzSO4 as Hg2+, Ag+, Cu2+, Ni2+, Bi3+, Sb3+, Te4+, Mo6+, Se4+, Ins+, As3+, Cd2+, Zn2+,Co2+,Fe3+, T1+. The order of Kiln given by Stary and Kratzer ( 1 1 ) is Hg2+, Ag+, Cu2+, Ni2+, Bi3+, Pb2+,Ins+, Cd2+, Zn2+, Co2+,Fez+,T1+. Major differences in these orders exist mainly for easily hydrolyzable metals like Fie4+, Te4+,As3+, Sb3+, and Mo6+, which reflects the pronounced effect of pH on the K' values in these cases. N
EXPERIMENTAL Reagents. The different Me(DDC), were prepared by precipitation of aqueous solutions of Men+ with NaDDC; the precipitates were washed, dried, and dissolved in CHC13. An equal volume of CzHbOH was added. Preferential evaporation of CHC13 from this solution a t room temperature yielded crystallized Me(DDC),, which were filtered off and dried. Analysis of these products for their metal content was carried out by complexometric titration after their destruction in "03. The results confirmed within the experimental error of 1%the fol-
ANALYTICAL CHEMISTRY, VOL. 47, NO. 11, SEPTEMBER 1975
Table 11. Extraction of Different Metals (Ordinate) by Different MeDDC Reagents (Abscissa) from a Citrate Buffer (pH 5)
Table I. Extraction of Different Metals (Ordinate) by Different MeDDC Reagents (Abscissa) from HzS04 0.1N
0
000000
0000
( m ) extraction complete within 2 min. ( A ) extraction complete within 15 min. (v) extraction complete within 60 min. (v) extraction is only partial within 60 min. (0) there is no extraction within 15 min.
A?
lowing formulas: TlDDC; Ni(DDC)Z, Cu(DDC)z, Zn(DDC)z, Cd(DDC)*, Pb(DDC12, Fe(DDC13, Co(DDC13, In(DDCh, Tl(DDC)3, Bi(DDC13. Extractions. Aqueous Phase. One hundred ml containing 100 kg of the metal under investigation; this metal was marked with an appropriate y-emitting isotope The aqueous phase was either 0.1N HzS04 or contained a citrate/NaOH buffer of p H 5 . Organic Phase. Thirty ml Me(DDC),, 1.7 X 10-3M in CHC13. The amount of DDC was thus roughly 100 times the theoretical amount necessary for quantitative extraction of the metal from the aqueous phase. The extraction vessel was mechanically shaken a t ambient room temperature (22 f 2 “C). Shaking amplitude was 6 cm and frequency was 6 sec-’; an increase of the shaking frequency had no influence on the extraction rates. Activity Measurements. The amount of metal extracted into the organic phase after 2, 15, and 60 min was determined by withdrawing an aliquot of the organic phase and measuring its activity with a NaI well-counter.
RESULTS
mately 30%) by all reagents up to and including As(DDC)3 and not extracted at all with the other reagents. T13+ (which has a high l/n log I(’ value) and Tl(DDC)3 are not included, since experiments indicate that Tl(DDC)S is not stable in CHC13; there is evidence for a partial transformation into TlDDC. The results of the extraction experiments from solutions of pH 5 are given in Table 11. The order chosen for the arrangement of the metal ions and the reagents had to be changed relative to the one from Table I; this reflects the different effect of pH on the a-values of the different metals. The changes are the following: Mo6+ and Se4+ had to be dropped because these elements do not extract at all at p H 5; As3+, Sb3+, and Te4+ had to be moved down and to the right. Obviously the U-values of these 5 ions increase faster with increasing pH than do the a-values of the other metals. The order thus arrived a t roughly coincides with the order given by Eckert (IO) for pH 5-6.
The results of the extraction experiments from 0.1N H2SO4 are given in Table I; the results are coded to indicate the extent of the extraction as well as the time necessary to obtain the specified extraction. F > 0.99 is taken as complete extraction, F < 0.01 as no extraction, and 0.01 < F < 0.99 as partial extraction. The order chosen for the metal ions (left hand side, from top to bottom) corresponds to the order of decreasing I/,, log K f e Xvalues as determined by substoichiometric extractions from 0.1N H2S04 ( 3 ) ;the same order was kept for the arrangement of the different Me(DDC), reagents (top, from left to right). There are no experiments with Ni2+ because Ni extracts notoriously slowly a t high acidities ( I O ) ; missing experiments with Mo02(DDC)2 are due to the fact that we could not prepare this product by the procedure given above. Not included in Table I are As5+, Sb5+, Se6+, and Te6+, which are not complexed by DDC. T c (in carrier-free form from the decay of 99Mo) is only partially extracted (approxi-
DISCUSSION The discussion will first concern the extractions from 0.1N HzS04. The arrangement of Table I is: if the intersection of a given metal (aqueous phase) with a given reagent (organic phase) lies below the diagonal line, the metal belongs to the Ci group for this particular system; if the intersection lies above the diagonal, the metal belongs to the Ai group. The expectations are therefore: no extraction of the metal from the aqueous phase below and complete extraction above the diagonal. These expectations are met by the majority of all combinations; exceptions are discussed below. Unexpected partial extractions occur with Bi3+ Cu(DDCI2, Te4+ + Sb(DDC)3, and Cd2+ In(DDC)$. In all these cases, the metals in the aqueous phase belong to the Ci group, and their partial extraction must be due to an insufficient difference in the l/,, log K’ values. This differ-
The results are coded as in Table I.
+
+
ANALYTICAL CHEMISTRY, VOL. 47, NO. 11, SEPTEMBER 1975
-
1815
6 $ 2
3
I, I
*
k."
500
Figure 2.
y-Spectrum of the organic phase from the extraction with
Bi(DDC)3 (decay time: 38 hr, measuring time. 1 hr) The assignment of the lines 203Hg(4)
IS
64Cu (6). lgsAu (5).Ig7Hg(1,2),lslrnHg (3),
The assignment of the lines is: "Mo (3,4, 8, 18,20),'15Cd (5,6,7, 1 1 , 12), 24Na (22),40K (23).65Zn (21),69mZn (9),la7W (1, 2, 10, 15, 16, 17, 19), lZ2Sb(14)
Table 111. Extraction of Bi with Cu(DDC)z Fgi,
Initial conditions
~.
C a l c u l a t e d with simplifying assumptions (see text) Found
70 0.5
25 0.6
ence has been determined for Cd-In in the present conditions to be 0.8 (3); there are no values available for the Te-Sb case, whereas for the Bi-Cu case, a first-order approximation can be gained by inserting the K values for a cc14 system for Cu and 1016.s for Bi ( 1 1 ) into Equation 5 . The result (see Table 111) does indeed indicate a substantial extraction of Bi by Cu(DDC)2. Equations 5 to 8 further predict a very considerable reduction of the extraction of Bi if the system contains an excess of uncomplexed Cu, which has also been verified experimentally. Thus, in these three exceptional cases, it is sufficient to introduce some uncomplexed metal B to the system in order to arrive at a clean separation. Partial or no extraction of A, metals is seen to occur, especially with Se(DDC)4, In(DDC)3, Co(DDC)3, and Fe(DDC)3, and can be attributed to the kinetic inertness of these reagents. These compounds obviously liberate DDC only very slowly into the aqueous phase, thus leading to a slow extraction or even to no extraction a t all. The inertness of these reagents is most pronounced in the extraction of metals which by themselves do not show a large extraction rate. The rate of extraction 0.f the individual metals diminishes roughly in the order Hg2+,Ag+, Bi3+, Sb3+,Cu2+, Te4+, Cd2+, Mo6+, Se4+, As3+, and In3+; this leads for instance in the case of the In(DDC)3 reagent to a fast extraction of Hg2+,Ag+, and Bi3+; to a slower extraction of Cu2+ and Sb3+; and to only partial extraction within 15 min of Te4+, Mo6+, and Se6+. I t should be noted that in all cases where the extraction could be followed as a function of time, the reaction is first-order with respect to the extracted metal, e.g., log (1 - F A ) depends linearly on the extraction time; the question of extraction kinetics in these systems will be dealt with in a separate publication. The arrangement of Table 11, which shows the results of the extractions at pH 5 , is analogous to Table I. Again, the expectations for complete or for no extraction are met in the majority of all cases. Unexpected partial extractions occur with Cd2+ + In(DDC)3, Sb3+ Cd(DDC)2,and Co2+ Zn(DDC)2. In all these cases, the metals in the aqueous phase belong to the 1816
y-Spectrum of the organic phase from the extraction with Zn(DDC)Z after reduction (decay time: 40 hr, measuring time: 45 b.
min)
1 . 7 x 10-3M Cu(DDC),, 100 pg Bi3+ The same plus 0.6 mg Cuz'
+
Figure 3.a. y-Spectrum of the organic phase from the extraction with Zn(DDC)* before reduction (decay time: 64 hr, measuring time: 1 hr)
+
The assignment of the lines is: 75As (2,5, 6,9, 10, ll),lZ2Sb(3,8),i24Sb (4),24Na(12).42K (13),g g m T(~l ) ,le7W(7)
Ci group, and again their extraction must be due to an inlog K' values. sufficient difference in the Partial or no extraction of A; metals occurs mainly with the reagents Co(DDC)3, Fe(DDC)3, and As(DDC)3, and is again most pronounced in the extraction of metals which by themselves do not show a large extraction rate. The rate of extraction of the individual metals diminishes roughly in the order Hg2+, Ag+, Bi3+, Cu2+, Cd2+, I$+, Sb3+, Zn2+, Te4+, Co2+, As3+, Fe3+. If this order of rate is compared with the one found for 0.1N HzSO4, it is seen that As3+, Sb3+, and Te4+ have shifted toward lower extraction rates, while the order stays the same for Hg2+, Ag+, Bi3+, Cu2+, Cd2+, and In3+. This is thought to be due to a faster increase in the cy-values with increasing pH for As3+, Sb3+, and Te4+ than for the rest of the metals; e.g., it is known (12) that As3+ and Sb3+ in solutions of [HI = 0.1 are present in substantial fractions as cationic species, whereas a t pH 5 they are predominantly present as neutral species. This decrease in the concentration of the metal ions in the aqueous phase not only decreases the value of their conditional extraction constant K', but also decreases a t the same time the observed extraction rate.
APPLICATIONS Extractions with MeDDC as reagents can be applied in many situations. A particularly interesting application represents activation analysis, where small activities have often to be measured which are completely masked by the major activities in the y-spectrum of the untreated sample. Selective extractions can provide an easy way around this problem. This was demonstrated by the analysis of a standard plant material, which for many days after the irradiation showed mostly y-lines of 24Na,42K, and s2Br, thus preventing the detection of any other activities of comparable half life. The procedure used was the following: 200 mg of kale powder (13) was irradiated for 14 hours at 3.5 X 1013 n/ cm2sec. Then, 36 hours after the irradiation, the material was dissolved in a mixture of 5 ml "03 (69%), 1 ml H2S04 (96%), and 1 ml HC104 (60%) with the addition of
ANALYTICAL CHEMISTRY, VOL. 47, NO. 11, SEPTEMBER 1975
inactive carriers (100 Mg of each metal). The solution was heated to the appearance of SO3 fumes and diluted with water to 100 ml, giving [HI 0.1. This solution was first extracted with Bi(DDC)B and then with Zn(DDC)2. Thereafter, the aqueous phase was reduced by adding 0.5 g KI and 1.5 g ascorbic acid, heated for 15 min to 90 OC and, after cooling, extracted once more with Zn(DDC)2. All three extractions were made only once with an extraction time of 10 min and with 30 ml of reagent (1.7 X 10-3M in CHC13). The organic phases were drained and measured without washing. The resulting y-spectra are shown in Figures 2, 3a, and 3b. Extraction with Bi(DDC)3 (Figure 2) shows only activities attributed to isotopes of Au, Hg, and Cu, which is in perfect agreement with the data from Table I [Au3+ was not included in our study, but it is known to have a log K value larger than Hg2+ (14)]. Extraction with Zn(DDC)2 before reduction (Figure 3a) shows the expected activities g9Mo and I15Cd. IB7Wis also extracted; it was not included in our study because of its erratic behavior. 24Na results from a carry-over from the aqueous phase; its contribution is very low, the activity being the same order of magnitude as 40K which belongs to the counter background. 65Zn is only partially extracted (-6%) because the acidity is too high for its complete extraction. lzZSbis not expected in this extraction because S b is supposed to be in the 5+ state; however the quantity present in this fraction is only 1%of the total amount of lz2Sb in the sample. Extraction with Zn(DDC)2 after reduction (Figure 3b) shows the expected activities from 76As and 122J24Sb,these ions having been reduced to their 3+ state. Very small other activities are 24Na and 42K (carry-over from the ~ IB7W(erratic behavior). aqueous phase), and 9 9 m Tand These examples show that extractions with MeDDC as reagents can give fractions with clear-cut separations from a very complicated sample with a minimum of chemical op-
-
erations and within a very short time. The method can be adopted to the special circumstances of a given sample, since the sequence followed above could easily be replaced by others; for instance, replacing the extraction with Zn(DDC)2 after the reduction of the sample by an extraction with In(DDC)S would yield a fraction containing only Sb, and a subsequent extraction with Zn(DDC)2, then one with only As. Another typical application is the determination of traces of metals in ancient silver coins by neutron activation analysis ( 1 5 ) . In this case, the signals from the impurities in the y-spectra of the entire sample are completely hidden by the large activities of IlornAg,Ig8Au,and 64Cu;extraction of the dissolved sample with Bi(DDC)3 removes these three activities completely from the aqueous phase and allows the interference-free determination of all other activities, which stay quantitatively in the aqueous phase.
LITERATURE CITED (1) S. J. Joris, K. I. Aspila, and C. L. Chakrabarti, Anal. Chem., 41, 1441 (1969). ( 2 ) J. Ruzicka and J. Stary. "Substoichiometry in Radiochemical Analysis," Pergamon, Oxford, 1968. (3) A. Wyttenbach and S.Bajo, Anal. Chem., 47, 2 (1975). (4) A. Wyttenbach and S.Bajo. Helv. Chim. Acta, 56, 1198 (1973). (5) A. Elek, J. Bogancs. and E. Szabo, J. Radioanal. Chem., 4, 281 (1970). (6) A. Elek, J. Radioanal. Chem.. 16, 165 (1973). (7) A. €lek and E. Szabo. Proceedings International Solvent Extraction Conference (ISEC 71), Paper 167, The Hague, 19-23 April 1971: Society of Chemical Industry, London, 1971. (8) H. Bode and K.J. Tusche, 2.Anal. Chem., 157, 414 (1957). (9) R. Wickbold, 2. Anal. Chem., 152, 259 (1956). (10) G. Eckert, 2.Anal. Chem., 155, 23 (1957). (11) J. STARY AND K. Kratzer, Anal. Chim. Acta, 40, 93 (1968). (12) H. Shoji, H. Mabuchi, and N. Saito, Bull. Chem. SOC. Jpn, 47, 2502 (1974). (13) H. J. M. Bowen, J. Radioanal. Chem.. 19, 215 (1974). (14) F. Kukula and M. Simkova, J. Radioanal. Chem., 4, 271 (1970) (15) A. Schubiger and 0. Muller, private communication.
RECEIVEDfor review February 19, 1975. Accepted May 19, 1975.
Classification of Mass Spectra Using Adaptive Digital Learning Networks T. J. Stonham and 1. Aleksander' The Electronics Laboratories, The University, Canterbury, Kent, England
M. Camp, W. 1.Pike,2 and M. A.
Shaw
Unilever Research, Port Sunlight, Wirral, Cheshire, England
Digital learning networks of adaptive logic elements have been applied to the problem of automatic routine identlflcatlon of mass spectral data according to the functional groups present. The technique, which is an embodiment of the n-tuple method of pattern recognition is not limited solely to the classification of linearly separable data, and offers a saving In computer time and storage requirements over the discriminant analysis approach. The structure and mode of operation of the learning nets is discussed, and results Present address, Department of Electrical Engineering, Brunel University, Kingston Lane, Uxbridge, Middlsex, England. Present address, Proprietary Perfumes Ltd., Kennington Road, Ashford, Kent, England.
are given for three classification experiments. Finally, the separabilities of the 28 groups employed In the multicategory classification are considered, thereby enabling a comparison to be made between the digital learning net approach and the spectroscopist's Interpretation.
The interpretation of scientific data and, in particular, chemical data, has traditionally been based on theoretical analysis, and involves the detection of explicit relationships developed from previous experimentation and logically constructed models based on one's knowledge of chemistry. The advent of the computer made possible the development of large libraries of classified data such that interpre-
ANALYTICAL CHEMISTRY, VOL. 47, NO. 11, SEPTEMBER 1975
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