There are some obvious differences in the nature of the loss of cadmium relative to the loss of mercury from aqueous solution during storage. Losses of mercury occur for all types of containers and even in highly acidic solutions (1, 2 ) . The loss of cadmium by adsorption takes place only on the walls of glass containers and at a pH greater than 7. Since polymer surfaces do not interact with cadmium in aqueous solution, sampling for cadmium would be better done in plastic containers. To prevent losses of cadmium by adsorption to the walls of glass containers, water samples should be acidified with nitric acid. If such pre-
cautions are taken, losses of cadmium from water samples during storage may be minimized.
ACKNOWLEDGMENT We wish to thank R. K. Tucker and R. A. Porter for helpful discussion. Received for review August 27, 1973. Accepted December 10, 1973. This work was supported in part by funds made available through the Research Council of the University of Idaho and Idaho State Office of Higher Education.
Fusion Methods for the Determination of Intractable Organic Compounds (Including Polymers) Sidney Siggia and David D. Schlueter D e p a r t m e n t of C h e m i s t r y , U n i v e r s i t y of M a s s a c h u s e t t s , A m h e r s t , M a s s . 0 1002
In organic analysis, we are often confronted with the quantitative determination of functional groups or compounds which react very slowly when solution methods are used. With solution methods, one is limited as to reagent concentration by the solubility of the reagent, reagentsample-solvent compatibility, and reaction temperature which is dictated by the reflux temperature of the solvent. Therefore, the application of fusion methods was obvious. With fusion, one uses pure reagent or thereabouts; the reaction is run at about melt temperature and can be raised to just below the thermal decomposition temperature of the sample components. Hence, for most organic compounds, fusion temperatures of up to 300-350 "C are common. Few compounds can remain unreacted under these conditions. Two factors control the resistance of a given chemical compound to chemical reaction. One is the inherent stability of the bonds of the molecules; the other is the steric configuration of the molecule. For example, amides, especially tertiary, are quite resistant to hydrolysis, yet caustic fusion brings about complete hydrolysis of these compounds in less than 30 minutes ( 1 ) . Polymeric esters, where the ester groups are pendant from a hydrocarbon polymer chain, are often very difficult to saponify in solution. Yet fusion with potassium hydroxide proceeds quite rapidly. For example poly(methy1 methacrylate) saponifies in solution only to the extent of 30% with 1N potassium hydroxide in amyl alcohol (bp 137 "C) after 90 hours a t reflux; by fusion with potassium hydroxide at 360 "C this compound is completely saponified in 0.5 hours ( 2 ) . Most chemists look on fusion reactions as being crude and somewhat akin to pyrolysis. This is not the case; fusions can be clean, quantitative, stoichiometric reactions as long as the fusion temperature is kept below the pyrolysis temperature of the compound under test. This is usually easy to accomplish since most fusion reactions take place between 200-350 "C and most decompositions in an oxygen-free system do not start until the temperature is above 400 "C. Fusion methods are far from being new. Alkali fusion reactions, dating as far back as 1840, have been used extensively in organic synthesis and degradation. Literature surveys of this important field have been published by ( 1 ) S . P. Frankoski and S. Siggia, Anal. Chem.. 44, 2078 (1972) (2) S . P. Frankoski and S Siggia, Anal. Chem.. 44, 507 (1972).
Weedon (3) and Nara ( 4 ) . Unfortunately, the analytical application of these reactions to organic analysis has not, until recently, been explored to any great extent. Fusion Reagents. These fall into four categories at present: bases, acids, reductants, and oxidants. In the case of the bases, sodium and potassium hydroxides have been the most widely used ( I , 2, 5-11) although lithium, rubidium, and cesium hydroxides have also been employed (11). Potassium hydroxide is generally preferred because of its lower melting point and the fact that more organic compounds dissolve in it. It has been found that a clean, homogeneous melt is almost always mandatory. The water (usually about 15% by weight) contained in commercial potassium hydroxide is essential in the fusion reagent, since many of the reactions are hydrolysis reactions. In addition, the water lowers the melting point to about 125 "C. Pure potassium hydroxide melts a t 360 "C. Only one acid fusion reagent has been successfully used to date (12). This is sodium hydrogen sulfate monohydrate (mp 58.5 "C). The water associated with the acid is needed with this reagent, as it was above, since hydrolysis is the reaction of interest. The amount of water as well as the melt temperature can be regulated by applying a VBCuum to the salt for a sufficient length of time. A number of hydrazines and hydrazides have been investigated as possible reducing agents in fusion reactions (13). Carbohydrazide was found to be the most promising because it is solid, easy to obtain, degrades slowly to evolve hydrogen and hydrazine, both of which effect re(3) E. C. L. Weedon. "Elucidation of Structures by Physical and Chemical Methods," Vol. XI, Part 2, in "Technique of Organic Chemistry," A. Weissberger, Ed., Interscience, New York, N.Y., 1963, Chapter X I I . pp 655-705. (4) K. Nara, Kagaku To Kogyo (Osaka), 43 ( l o ) , 539 (1969): ( 1 1 ) . 605; Chem. Abstr.. 73, 8 7 1 3 6 ~(1970). (5) S. Siggia, L. R. Whitlock, and J. C. Tao, Ana/. Chem., 41, 1387 (1969). (6) S. Siggia, L. R. Whitlock. and J. E. Smola, Ana/. Chem., 44, 532, (1972). ( 7 ) D. D. Schlueter and S. Siggia, in press. (8) M. G. Voronkov and V . T. Shemyatenkova, I z v . Akad. Nauk SSSR. Otd. Khim. Nauk, 1961, 178; C . 6. Trans. 164-5: Chem. Absfr.. 5 5 , 16285b (1961). (9) J. H. Wettersand R. C. Smith, Anal. Chem., 41, 379 (1969). (10) C. L. Hansonand R. C. Smith.Ana/. Chem., 44, 1571 (1972). (11) T. Kakagawa, K. Miyajima, and T. Uno, J . Gas Chromatogr.. 6 , 292 (1968). (12) Work in progress in our laboratory. (13) P. C. Rahn and S. Siggia. Ana/. Chem., 45, 2336 (1973). A N A L Y T I C A L C H E M I S T R Y , V O L . 46, NO. 6, M A Y 1974
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duction, and all decomposition products are readily volatilized. As possible oxidative fusion reagents, the following materials are presently being investigated in our laboratory: potassium metaperiodate (mp 582 "C), sodium metaperiodate (dec 300 "C), lead tetraacetate (mp 174 "C), potassium dichromate (mp 398 "C), sodium dichromate (mp 357 "C), and chromium trioxide (mp 196 "C). Fluxes. Fluxes are used for two purposes; one is to control the melting point of the fusion reagent. If a reagent melts too high causing some thermal decomposition to take place along with reaction, an added flux can depress the melting point to a more desirable temperature. A flux can also raise the fusion temperature if enough is added, and if the melting point of the flux is higher than that of the fusion reagent. Fluxes can also be used to help dissolve samples in the melt to achieve homogeneous reactions. This facilitates reaction completeness in minimal time and enhances precisiori. A number of fluxes have been tried in caustic fusion ( 1 , 2, 5 ) ; sodium acetate (mp 324 "C) was found to be the most useful. A prefused potassium hydroxide-1% sodium acetate reagent melts around 100 "C. Details on its preparation have been given elsewhere (2, 5 ) . The properties of a good flux are: proper melting point; stability toward the fusion reagent, sample components, and products of fusion reaction; and solubility for samples of interest. Requirements for Fusion. Temperature control of fusion is mandatory. However, coarse control (A20 "C) is generally all that is required, and in some cases A50 "C is adequate. One must completely react the materials to be reacted without pyrolyzing them or their reaction products. Closed systems and inert atmospheres are required in most cases since the fusions are hot and oxidation of sample Components and/or reaction components can occur. Measuring Approaches Usable after Fusion. The approach taken in analyzing the reaction products depends upon the system being studied and the originality of the investigators. The use of a gas buret (8) was perhaps the first measuring approach used for the quantitative analysis of volatile fusion products. Nonvolatile products have been measured gravimetrically ( 9 ) , colorimetrically (6, 9 ) , and by volumetric titration ( 5 ) .
The most popular measuring approach to date has been gas chromatography (1, 2, 5-7, 10, 11, 13-15). One important advantage of the gas chromatographic measurement is the ability to analyze systems where mixtures of reaction products are evolved upon fusion. Hence, isomers, polyfunctional species, homologs, and general mixtures can be resolved and measured. In addition, only small amounts of sample (several micrograms to a few milligrams) are required. This shortens fusion time and minimizes heat transfer and pyrolysis problems. Rather than carrying out the fusion externally, as is commonly done in reaction gas chromatography, the reaction chamber has been interfaced to the gas chromatograph via a cold trap. The reaction apparatus which is commercially available from Perkin-Elmer (Norwalk, Conn.) is designed to hold six samples ( 5 ) but has recently been enlarged to accomodate as many as thirteen (7). The fusion reaction always takes place in an inert atmosphere, usually helium, and the reaction products are liberated as they are formed and concentrated in the trap. Upon completion of the reaction, the trapped products are thermally volatilized and swept into the gas chromatograph as a slug. A detailed diagram and description of the apparatus is given in references 2 and 5 . In cases where the functional group reaction occurs almost instantaneously, it is possible to eliminate the trap. It was recently demonstrated that 0.01-0.10 pmole amounts of sample can be quantitatively reacted in a reaction tube positioned in the injection port of the gas chromatograph. Materials Measured Using Fusion. Silicones (8-1 0), sulfonates (5, 6, 11, 13, 14), esters ( 2 ) , amides ( I ) , ureas ( I ) , nitriles ( I ) , carbamates (15),imides (7), azo (13),and nitro (23) compounds have been successfully measured in monomeric and polymeric systems which were difficult, if not impossible, to handle by reaction in solution. Received for review September 4, 1973. Accepted December 7, 1973. This work has been supported by National Science Foundation Grant GP37493X. (14) S. Nishi, BunsekiKagaku, 14, 917 (1965). (15) A . S. Ladas and T. S. Ma, Mikrochim. Acta (Wien). 1973, 853.
Concentration of Heavy Metals by Complexation on Dithiocarbamate Resins Joseph F. Dingman, Jr.,' Kenneth M. Gloss, Ellen A. Milano, and Sidney Siggia University of Massachusetts, Arnherst, Mass. 01002
The purpose of this study was to synthesize a resin containing dithiocarbamate groups and determine its applicability for concentrating trace metals from aqueous media. Other resins have been studied for this purpose but none have achieved quantitative removal for such a large number of metals as the dithiocarbamate resin.
Dithizone on a cellulose base was synthesized by Carritt for concentrating metals from sea water ( I ) . Blout, Leyden, Thomas, and Guill used Chelex 100, an ion exchange resin, for trace analysis of cobalt, nickel, and bismuth. The metals were concentrated on the resin, then pelletized, and analyzed by X-ray fluorescence (2). Polyamine(1) D. E. Carritt,Ana/. Chem., 25, 1927 (1953).
address, Noxell Corporation, 11050 York Road, Baltimore. Md. 21203. 1
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(2) C. W . Blount, D. E. Leyden, T. L. Thomas, and S. M . Guill, Ana/. Chem.. 45, 1045 (1973).
