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
Present
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A N A L Y T I C A L C H E M I S T R Y , VOL. 46, NO. 6, M A Y 1974
(2) C. W . Blount, D. E. Leyden, T. L. Thomas, and S. M . Guill, Ana/. Chem.. 45, 1045 (1973).
I' 0
Figure 1.
1.0 2.0 3.0 4.0 5.0 0 6.0 7.0 8.0 9.0 10.0'l ;O
lG0 l;O
2;)O 2;O
3 b 0 3 J O 4b0 4;O
5bO
Metal uptake on dithiocarbamate resin
polyurea resins, for the purpose of concentrating trace metals, were studied by Dingman et al. (3). Dithiocarbamates have been used to extract metal ions from solution ( 4 ) . It was felt that if a resinous dithiocarbamate were used, a "solid extraction" could be carried out which would have certain advantages over liquid extraction. Quantitative extraction with a solid is mechanically easier to perform than with a liquid, especially when a multiplate system is necessary, since a solid extractant can be used in a column. The advantage of the dithiocarbamate resin would be the ability to quantitatively concentrate a large number of trace elements simultaneously, while not complexing alkali and alkaline earth metals. Dithiocarbamates are prepared by reacting carbon disulfide with secondary amines. In ihis study, a polyaminepolyurea resin containing some available secondary amines was synthesized (3). The dithiocarbamate resin resulted when the amine resin was allowed to react with carbon disulfide.
-NH(CH&H2NH),CH&HZNH-
+ CH3C,H3(NCO),
--+
-[NH( CH2CHzNH),CH,CHzNHCONHCH,C,HLSIJHCO]j-5
-[NH(CHzCHzNCS2H),CH2CH~NHCONHCH&gH3NHCO] >An apparent problem is that long reaction times are necessary which may be due to the interfacial character of the carbon disulfide-amine reaction. Shorter times were tried but the extent of the reaction was small. Attempts were made to drive the reaction by refluxing; however, because of the thermal instability of dithiocarbamates, it is likely that rearrangement to thioureas may have occurred ( 5 ) . Parameters such as the amount of resin, solution volume, resin contact time. temperature, degree of crosslinking, and amount of agitation were similar to those found most favorable for the polyaminepolyurea resin ( 3 ) .
Table I. Capacity of Resin at 9970 Uptake Capacity, mg Mn' gram
Metal
Ag Hg2
cu2 Sb3 Pb2-
+
Cd3-
Uptake
99+% +3% >90 % 99+% *3% 99+% +3% 99% 1 3 % 99+% 1 3 %
resin
200 54 21 4 0 3 9 1 0
Reagents. T h e solvents dioxane and isopropyl alcohol were technical grade. Dioxane was dried over KOH pellets before use. Pyridine, toluene-2,4-diisocyanate, and carbon disulfide were reagent grade chemicals. The polyethyleneimine, molecular weight 1200, (PEI-12) was obtained from Dow Chemical Company. The metal ion stock solution was prepared lo00 ppm in the metal ion from acetate salts and stored in polyethylene bottles. Test solutions were made by appropriate dilution of the stock solution with distilled de-ionized water. Procedure. Resin Synthesis. The polyamine-polyurea (PEI12/TDI) was prepared by reacting 9.08 grams of toluene-2,4-diisocyanate with 9.96 grams of PEI-12. The reaction was carried out in 2 liters of dioxane. The resin was stirred overnight, washed five times with alternate charges of isopropanol and water, then filtered and dried. The dithiocarbamate resin was synthesized by the reaction of 18 grams of PEI-lP/TDI with a carbon disulfide (35 ml), pyridine (25 ml), isopropanol (65 ml) mixture. The resin was stirred for three weeks then washed, filtered, and air dried. The dried resin was ground to 60-80 mesh. Analysis for Metal Uptake. A batch equilibration technique was employed for investigation of the metal uptake by the resin. The method involved equilibrating 50 f 0.5 mg of resin with 10 ml of a metal ion test solution. Small polyethylene bottles were used as containers. The solutions were agitated for 24 hours a t room temperature, then centrifuged. The supernatant liquid was diluted to fall into the linear range suggested for determination of each metal by atomic absorption. After this preparation of the sample solutions, a standard curve was prepared from which unknowns could be determined. A back calculation indicated the resin uptake.
EXPERIMENTAL Apparatus. An atomic absorption spectrometer, Perkin-Elmer 403, was used for metal determination. (3) J . Dingman, Jr., S. Siggia, C. Barton, and K. Hiscock, Anal. Chem.. 44., 1353 (1972). . ~ . -, ( 4 ) G . A . Thorn, and R. A. Ludwig, "The Dithiocarbamates and Related Compounds," Elsevier, New York. N . Y . , 1972. ( 5 ) F . E. Critchfield and J . E. Johnson, Anal. Chem., 28, 430 ( 1 9 5 6 ) . \
~
RESULTS AND DISCUSSION The resin was analyzed for elemental sulfur to determine the extent of the carbon disulfide-amine reaction. The result was 9.5% sulfur by weight, indicating that apA N A L Y T I C A L C H E M I S T R Y , VOL. 46, NO. 6 , M A Y 1 9 7 4
775
~~~~~
~
~~~
~
~~
~
Table 11. Effect of pH on Metal U p t a k e Buffered (pH 9.7) Cd2+b
Zn2+a Concn, ppm
Capacity, mg Zn2T/gram resin
5 10
1 .o 2 .o
Capacity, mg Cd2+/gram resin
Concn, ppm
70 Uptake
99+% 1 3 % 99+% + 3 %
50 70
70 Uptake
14
99+% + 3 % 99+% *3%
0.41 1 .o
99+% * 3 % 96% 1 3 %
11
Unbuffered ( p H 4.5)
0.3 0.5 0.7
0.045 0.081 0.10
75% i 3 %
81% = t 3 %
5 10
71% + 3 %
a For Zn2- (buffered solution), a concentration range from 5-200 ppm was studied. At concentrations greater than 10 pprn Zn2+, less than 99% uptake was observed. For Cd2- (buffered solution), a concentration range from 50 to 500 ppm was studied. At concentrations greater than 70 ppm, less than 99% uptake was observed.
proximately one in every four amines had undergone reaction to the dithiocarbamate. During the course of the metal-resin study, a color change was observed for Cu2+ and Ag+. In the former case the resin became increasingly more blue as the test concentrations increased from 100 ppm Cu2+ to 800 ppm CUP+. In the latter, the resin color was yellow at lower test concentrations (100 ppm Ag+) and dark brown a t high test concentrations (1200 ppm Ag+). No color change was observed for any of the other metal ions tested. The uptakes for ten metals are given in Figure 1 and summarized in Table I. From these data, it may be concluded that, with respect to the capacity of the resin for the metals tested, the capacity proceeded as follows: Ag+ > Hg2‘ > Cu2+ > Sb3’ > Pb2+ > Cd2+ > NiZ+ > Zn2+ > Co2+, and Ca2+ was not taken up. It has been stated that one of the advantages of a chelating resin is its preferential complexation of cations according to the stability constants of the cation complex formed by the resin. The order reported ( 4 ) for the 1:2 diethyldithiocarbamate complex is Hg2+ > Ag+ > Cu2+ > Ni2+ > Co2+ > Pb2+ > Cd2+ > Zn2+. In general, the bonding of metal ions to diethyldithiocarbamates has been described as an equilibrium between the 1:l and the 1:2 complex with the 1:2 complex predominant (6); however, due to the steric limitations imposed by the polymeric structure of the resin described herein, the possibility of the formation of the 1:2 complex may be lowered considerably and the 1 : l complex may predominate. The order of stability for the 1:l dithiocarbamate complex has not been reported.
dered by the polymeric configuration of the resin. The uptakes of Ag+ by the resin were much higher than expected. Initially photolytic reduction was suspected; however, atomic absorption monitoring of the solutions indicated that such large uptakes could not be completely explained by photolytic reduction. In addition, care was taken to keep all test solutions wrapped and covered during equilibration. No particulate matter, characteristic of reduction to the metal ion, was observed. For Ag+, a monovalent ion, the 1:l dithiocarbamate complex may be greatly favored and thus only half as many dithiocarbamate ligands are necessary for complexation. Mercury was of particular interest because of its biological significance. A standard curve from 10 to 300 ppm Hg2+ was prepared; however, no signal was observed for less than 30 ppm because of the insensitivity of atomic absorption spectroscopy for mercury. After the 24-hour batch equilibration, no signal was observed for any of the test solutions. Absence of an output signal indicated that for a test solution initially at 300 ppm, less than 30 ppm Hg2+ remained. Therefore the ‘70 uptake for mercury by the dithiocarbamate resin was at least 90%. All metal solutions were prepared by simple dissolution of the acetate salts and thus were slightly acidic. Since natural water systems exhibit a pH of up to 11, some information on metal removal from basic solutions was sought. Two metals, Cd2+ and Zn2+, were studied in an ammonia solution buffered at pH 9.7. Results showed markedly increased uptakes for both metals as may be seen in Table 11. The base may make the dithiocarbamate more available for complexation as follows:
S R,N&
+
OH-
+
&NCRS
‘SH d
‘S-
+
H20
1:1
1:2
Antimony and silver were studied in order t o determine the resin’s affinity for a trivalent and a monovalent ion. The results for Sb3+ were lower than expected on the basis of its theoretical affinity for sulfur ligands. These results may be explained sterically. Sb3+, a trivalent ion, would require an orientation of sulfurs which may be hin( 6 ) T. E. Cullen,Ana/. Chem.. 36,221 (1964).
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One of the advantages of the polyamine-polyurea resin studied previously was that metals could be selectively removed by acidification ( 3 ) .The dithiocarbamate resin did not exhibit this behavior. The metal uptakes were unaffected by acid at a pH of 2 or greater, but below this pH the resin decomposed. Decomposition due to acid is a well documented property of dithiocarbamates (7), but is not an important disadvantage since the pH of natural water ranges from 4-11. Selective removal may not be so important since the goal of this research is to quantitatively remove metal ions from solution for analysis. ( 7 ) K . I . Aspila, C. L. Chakrabarti, and B. 363 (1973)
S. Sastri, Ana/. Chem.. 45,
CONCLUSION
ACKNOWLEDGMENT
The results of the metal uptake studies indicate that quantitative uptakes are achieved for Ag+, Hg2+, Cu2+, Sb3+, Pb2+, and Cd2+. The uptakes for Ni2+, ZnZ+, and C d + are expected to increase when columns are used since more plates will be present. Alkali metals and alkaline earths should not interfere since they are not complexed by the dithiocarbamate resin.
We wish to thank G. Dabkowski and P. Oles for their assistance in this study.
Received for review July 11, 1973. Accepted December 26, 1973.
Microdetermination of Hydrazine Salts and Certain Derivatives with N-Chlorosuccinimide M. 2 . Barakat, .M.Abou-El-Makarem, and M. Abd El-Raoof Biochemistry Department, Faculty of Medicine, Azhar University, Madina Nasr, Cairo, Egypt
Previous methods for the determination of hydrazine salts include titrimetric (I, 2 ) , colorimetric ( 3 ) , and potentiometric ( 4 ) methods. The oxidation of hydrazine has been extensively employed as the basis of techniques for its determination ( 5 - 7 ) . Of these, the titrimetric methods are the most widely used but either show certain defects (8, 9) or seem to be unreliable (5, 10). More recently, Nbromosuccinimide has been reported as a titrant for determining amounts as low as 0.5 mg of hydrazine salt or l mg of hydrazine derivative (11). The present work describes a new method for the microdetermination of amounts as low as 100 k g of hydrazine salts and certain derivatives by the use of standard Nchlorosuccinimide solution. EXPERIMENTAL Reagents. A 0.02hr solution of standard Ar-chlorosuccinimide (NCS), B.D.H., (mol wt 133.54) was freshly prepared by dissolving 133.54 mg of NCS in hot distilled water, allowing it to cool, and diluting t o 100 ml with water in a volumetric flask. A fivefold dilution yields 0.004N solution. A 0.02N solution of standard -V-bromosuccinimide (NBS), B.D.H., (mol wt 178) was freshly prepared by dissolving 178 mg of NBS in hot distilled water, allowing it to cool, and diluting with water to 100 ml in a volumetric flask. Standardization of either titrant was done iodometrically ( 1 2 ) . Action of N-Chlorosuccinimide on Hydrazine Sulfate. A 1,3013-gram portion of hydrazine sulfate (0.01 mol) was dissolved in 20 ml of distilled water, and 2.6708 grams of N-chlorosuccinimide (0.02 mol) were dissolved in 200 ml of hot distilled water. The N-chlorosuccinimide solution was allowed t o cool and then was added gradually with shaking to the cold hydrazine sulfate solution. During the addition, a strong effervescence was observed because of evolution of nitrogen. The presence of hydrochloric acid was detected by treating 10 ml of the colorless reaction solution with nitric acid and 10'7~sil-
ver nitrate solution. A white precipitate of silver chloride was deposited and dissolved in ammonium hydroxide. T h e presence of sulfuric acid was established by treating 10 ml of the colorless solution with hydrochloric acid and 1070 barium chloride solution. A white precipitate of barium sulfate was formed. Succinimide was isolated by distilling in uucuo the remaining 200 ml of the colorless solution and crystallizing the solid residue from benzene. I t was identified by melting point (125 "C) and mixed melting point determinations with an authentic sample showing no depression. Stoichiometry of t h e Reaction. When the recommended procedure was used, hydrazine sulfate (10 to 100 pmol), phenylhydrazine hydrochloride (10 to 100 l m o l ) , or p-nitrophenylhydrazine (10 to 100 pmol) reacted with exactly two equivalents of N-chlorosuccinimide. Procedure. To a n accurately measured volume--e.g., 5 ml of t h e hydrazine sulfate or hydrazine derivative solution in a 100-ml stoppered Erlenmeyer flask-add a n equal volume of dilute sulfuric acid, 1 ml of 10% potassium bromide solution, and 2 drops of Methyl Red indicator solution. Titrate the mixture with standard N-chlorosuccinimide solution (0.02N or 0.004N solution) added dropwise from a microburet with shaking after each addition. When the red color of the indicator fades, another drop is added, and the titration is continued until the red color just disappears. This is the end point and the volume of the titer is noted. A blank experiment is done simultaneously and the reading is subtracted from the titer before calculation. Calculate the hydrazine sulfate content or the hydrazine derivative content of the unknown solution from the expression as follows:
Hydrazine sulfate content (mg or p g j = 130.13 133.54 X 2 Phenylhydrazine content (mg or p g ) = 144.61 133.54 x 2 p -Nitrophenylhydrazine content (mg or p g) =
t2)
153.14 133.54 X 2
(3)
I . M .Koithoff, J. Amer. Chem. SOC..46, 2009 (1924). 8. Singh and A. Singh, Anal. Chim. Acta, 9, 22 (1953) M . G. Bapat and S. V. Tatwawadi. J. Sci. Res. Banaras Hindu
Univ., 7, 235 (1956-57). H . T. S. Britton and M . Konigestein. J. Chem. SOC.(London), 673 (1940).
Jilek and J. Brandstetr, J. Chem. Zvesti, 7, 611 (1953) P. Endroi, Magyar Kem. f o l y . , 59, 211 (1953); Chem. Abstr., 48,
A.
SO5 (1954), B. Suseela. Ber., 88, 23 (1955). I . M . lssa and R. M. Issa, Anal. Chim. Acta, 14, 578 (1956). R. C. Paul and A. Singh, J. lndian Chem. SOC.,32, 599 (1955). R . A. Penneman and I. F. Audrieth, Anal. Chem., 20, 1058 (1948). M . 2. Barakat and M . Shaker, Analyst (London),88, 59 (1963) M 2. Barakat and M. F. A. El-Wahab, Anal. Chem., 26, 1973 (1954).
(lj
where V = volume of standard A'-chlorosuccinimide solution used in the reaction and C = concentration of ?i-chlorosuccinimide in mg or p g per 1 ml of solution.
RESULTS Each result recorded is the average of at least two determinations. Microdetermination of Hydrazine Sulfate. A stock aqueous solution containing 0.1 gram/100 ml of hydrazine sulfate was prepared. The hydrazine sulfate content was ANALYTICAL CHEMISTRY, VOL. 46, NO. 6 , MAY 1974
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