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ANALYTICAL CHEMISTRY, VOL. 50, NO. 9, AUGUST 1978
Preparation and Chromatographic Applications of an Amide Resin Gene M. Orf and James S. Fritz" Ames Laboratory-U.S.
Department of Energy and Department of Chemistry, Iowa State University, Ames, Iowa 500 1 1
Synthetic routes are discussed for incorporation of a tertiary aliphatic amide group in a macroporous polystyrene-divinylbenzene resin. The amide resin retains uranium(VI), thorium( I V ) , and zirconium(I V ) selectively from aqueous solution, pH 3.0. A liquid chromatographic separation scheme using the resin is given and quantitative results are obtained for uranium in synthetic and actual samples, and for thorium in synthetic samples. Gold(II1) and palladium(I1) are selectively retained by the resin from aqueous solutions containing hydrochloric acid. The resin has a capacity for gold of 1.7 mmol/g.
Incorporation of a chelating group of known selectivity into a resin is likely to result in a chelating ion-exchange resin of predictable selectivity. For example, isooctylthioglycolate is known t o extract silver(I), gold(III), bismuth(IIJ), copper(II), and mercury(I1) selectively from acidic aqueous solution (1). A resin containing the thioglycolate functional group retains selectively all of the above metal ions except copper(I1) from acidic aqueous solution (2). The success of liquid amides in extracting uranium(VI), and t o a lesser extent thorium(1V) and zirconium(IV), from aqueous nitrate solutions ( 3 ) has inspired us to introduce an amide group into a polystyrene-DVJ3 resin. The resulting resin does indeed sorb selectively uranium, thorium, and zirconium from aqueous solution. It also retains gold(II1) and palladium(I1) strongly from aqueous chloride solutions.
EXPERIMENTAL Chromatography. The liquid chromatograph used has been previously described ( 4 ) . A resin column 6.0 cm X 0.6 cm was used for all separations. Uranium(VI), thorium(1V). and zirconium(1V) were determined automatically after addition of an Arsenazo I11 solution to the eluent stream at pH 0.5. Gold(II1) was detected by collecting fractions and analyzing by ICP emission spectrometry. Resin Synthesis. First, an amide group was introduced into silica gel or Porasil by the following sequence ~ ~ ~ -cSiOH a }
t
ICH30)3S~CH2)3NHCH3---)
The starting material for resins I1 and 111 was Amberlite XAD-4 resin, a macroporous styrene-divinyl-benzene copolymer supplied by Rohm and Haas Co. The resin was Soxhlet extracted with methanol, ground, and sieved. before use. Resin I1 was prepared by the following reaction sequence:
@ + XAD-4
0003-2700/78/0350-1328$01 .OO/O
The first product of the synthesis of resin I11 was prepared as described by Falbe, Paatz, and Korte ( 5 ) . This was accomplished by stirring 28 mL of y-chlorobutyryl chloride into a solution of 84 mL of dibutylamine in 150 mL of petroleum ether which had been cooled in an ice bath. The reaction mixture was stirred for 2 h in the ice bath and then allowed to stand overnight. The salt was then filtered off and washed with petroleum ether The ether was distilled from the product by rotovaporization and the product was purified by vacuum distillation at 150 "C, 0.001 mm Hg. The IR and NMR spectra confirm the structure of the first product. The final resin was prepared by slowly adding 15 mL of the first product to a mixture of 9 g of XAD-4 which had been dried in a vacuum at 120 "C for 24 h, 2 1 g of anhydrous aluminum chloride, and 200 mL of carbon disulfide. The reaction mixture was then poured into an ice bath and the resin was finally filtered and washed with dilute hydrochloric acid and acetone. CI(CH~)~COC + I B q N H -* CI(CH~)SCDNB%?
_L
XAD-4
The presence of an amide group on the resin was confirmed by an IR spectra of the final product. The nitrogen content of the resin was determined by the Dumas method. This showed the resin to contain 2.88% nitrogen, which indicates 2.05 mequiv of amide functional group per gram of resin.
RESULTS AND DISCUSSION Resins. Resin I retains uranium, thorium, and zirconium at p H values greater than 4.0 when nitrate or perchlorate salts are in relatively high concentration. However, unreacted hydroxyl groups on the silica prevented clean elution of the retained metal ions. Attempted deactivation of the hydroxyls by silanization improved the situation only slightly. Resin I1 retained uranium, thorium, and zirconium only when 2.0 M (or greater) sodium nitrate or sodium perchlorate was added to the aqueous solution. It is possible that the 1,4-dichlorobutane may have caused some cross-linking between phenyl groups that would hinder complexation of metal ions by the amide groups. Since three different chemical reactions were performed before obtaining the final product, there is the possibility of undesirable functional groups remaining from incomplete chemical reactions. Resin I11 was much the most successful. At least two different batches of the resin were prepared successfully. This resin was used for all of the work reported in this paper. Separation of Uranium(VI), Thorium(1V) and Zirconium(1V). Uranium, thorium, and zirconium are taken up by a column of the resin from p H 3.0 perchloric or nitric arid solutions. The method chosen for the separation of uranium, thorium, and zirconium from each other and from several other heavy metals was as follows. A sample containing uranium, thorium, zirconium, and foreign ions is injected into an eluent stream of p H 3 perchlorir acid. Under these conditions, most foreign ions are eluted and the three ions of interest are retained. T h e uranium is then eluted with p H 2 perchloric acid, the thorium is eluted with p H 0.5 perchloric acid, and the zirconium is eluted with 1 M sulfuric acid. Zirconium could be eluted with any mineral acid with a 0 1978 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 50, NO. 9, AUGUST 1978
Table I. Determination of Uranium in the Presence of Foreign Ions % recovery, av of foreign ions two trials M Fe3+,A13+,and Co2+ 99.1 M Mg”, Pb”, and N i 2 + 99.5 M Z n z + ,Cuz+,and Cd2+ 99.5 M V”, 5 x 10” M Th4+,and Zr4+ 100.0 lo-’ M HgZ+,5 X lo-’ M T h 4 + ,and Zr4+ 99.0 10-3M NO,-, 5 x lo-’M T h 4 + ,and Zr4+ 91.9 M Cl-, 5 x lo-’M T h 4 + ,and Zr4+ 100.0 M SO, :-, 5 X l o - ’ M Th4+,and Zr4+ 99.4 M tartrate 91.5 lo-’ M citrate 76.0 lo-: M phosphate 99.2
0
5
IO 15 20 MINUTES
Figure 1. Separation of 5 X zirconium(1V)
Table 11. Determination of Thorium in the Presence of Foreign Ions % recovery, av of foreign ions two trials M Fe, Al, Co, 5 x lo-’M U, and Zr 97.2 M Mg, Pb, Ni, 5 x 10.’ M U, and Zr 99.4 98.9 l o - , M Zn, Cu, Cd, 5 X 10‘’ M U, and Zr 10.’ M tartrate, 5 x l o - ’ M U, and Zr 94.6 10.’ M citrate, 5 x lo-’ M U, and Zr 85.6 lo-’ M phosphate, 5 x M U, and Zr 0 lo-, M Ho, 5 x M U, and Zr 83.3 M Ce, 5 x M U, and Zr 90.7 M U , and Zr 92.6 M Gd, 5 x M V, 5 X lo-’ M U, and Zr 97.2 M Sn, 5 X l o - ’ M U, and Zr 77.6 M Hg, lo-’M U, and Zr 100.0 M sulfate, 5 x 10.’ M U, and Zr 127.0 M nitrate, 5 x M U, and Zr 104.0 M chloride, 5 x 10.’ M U, and Zr 98.2 concentration of 1M or greater, but the sharpest elution was obtained with sulfuric acid. A chromatographic separation is shown in Figure 1. Separations of standard solutions of uranium, thorium, and zirconium of various concentrations gave linear calibration curves (peak height vs. l g of metal ion) for uranium and thorium. However, zirconium could not be determined quantitatively, possibly because of polymerization or lack of complete, reproducible reaction with the color-forming detection reagent. Uranium and thorium were determined quantitatively in the presence of 20-fold molar excesses of several foreign metal ions and as much as a 200-fold excess of some anions. All separations were performed on a 6.0 cm X 0.6 cm resin column with an eluent flow rate of 1.2 mL/min and a color-forming reagent flow rate of 0.8 mL/min. The sample loop was 54 pL. The results in Tables I and I1 show the method to be quite selective. Rare earth salts and citrate cause major interference for both uranium and thorium. Phosphate interferes with thorium but not with uranium.
M uranium(VI), thorium(IV), and
Low grade ores were analyzed for uranium and thorium to see if the resin had a practical use for the determination of trace amounts of the metals in real samples. Carnotite samples of 0.1 g were digested in 20 mL of concentrated hydrochloric acid and then digested to dryness in a solution of 15 mL of concentrated hydrochloric acid and 15 mL of concentrated nitric acid. The residue was then dissolved in 100 mL of distilled water. Uraninite samples of 0.1 g were digested in a solution containing 15 mL each of concentrated sulfuric and nitric acids and also diluted to 100 mL. The samples were analyzed in the same way as all previous samples. The results are shown in Table 111. Attempted analysis of a monazite sample for uranium and thorium was not successful. Separation of Gold(II1). The amide resin sorbs gold(II1) strongly from aqueous hydrochloric acid solutions. The capacity of a resin column for gold was fairly constant from 0.5 M to 4.0 M hydrochloric acid and averaged 1.7 mmol/g. This compares with column capacities of only 0.08 mequiv/g for uranium and 0.04 mequiv/g for thorium under the conditions described earlier. Column studies with 1.0 M and 5.0 M hydrochloric acid showed that gold(II1) and palladium(I1) are taken up strongly, but rhodium(III), platinum(IV), and silver(1) are not retained. It is difficult to elute gold and palladium from the resin column with most reagents tried, but elution is readily accomplished with 0.1 M sodium cyanide. Gold(II1) added to deionized water and also to seawater at approximately 1 ppm concentrations was quantitatively recovered after passing 1 L of water through a 6.0 cm x 0.6 cm resin column at 5 mL/min and subsequently eluting with 0.1 M sodium cyanide. Many resins that are selective for gold(II1) cause partial reduction of the gold(III), perhaps t o the metal. This does not occur nearly so readily on the amide resin, although the yellow gold band on the resin column does turn black if left for a long period of time. Even then, the black band is removed by elution with cyanide and the resin can be used for many sorption and elution cycles.
Table 111. Analysis of Low Grade Uranium and Thorium Ores %
sample Uraninite (International Atomic Energy Survey Reference Sample No. S4) Carnotite (USERDA Reference Materials Section, New Brunswick, N.J., Carnotite Sample N o . 4 )
1329
species determined u30,
found 0.371 i 0.053
u30,
0.19
%
i
0.02
previously found 0.375 0.18
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ANALYTICAL CHEMISTRY, VOL. 50, NO. 9, AUGUST 1978
LITERATURE CITED
(5) J. Falbe, R. Paatz. and F. Korte, Chem. Ber., 97, 2544 (1964).
(1) J. S. Fritz, R . K. Gillette, and ti. E . Mishmash, Anal. Chem., 38, 1869 (1966). (2) E. M. Moyers and J. S. Fritz, Anal. Chem., 48, 1117 (1976). (3) J. S. Fritz and G. M. Orf, Anal. Chem., 47, 2043 (1975). (4) M. D. Arguello, Ph.D. Thesis, Iowa State University, Ames, Iowa, 1977.
RECEIVED for review December 19, 1977. Accepted May 12, 1978. This work supported by the U. S. Department of Energy, Division of Basic Energy Sciences.
Characterization of the Ion-Exchange Membrane Detector for Liquid Chromatography and Its Application to the Separation of Quaternary Ammonium Compounds John G. Dorsey, Mark S. Denton,’ and T. W. Gilbert” Department of Chemistry, University of Cincinnati, Cincinnati, Ohio 4522 I
An LC detector which operates by measuring dimensional changes of a strip of ionexchange membrane has been further characterized and is shown to be useful for the detection of quaternary ammonium ions. The detector has a precision of better than 1 % standard error and a h e a r range for choline and acetylcholine of at least 2.5 orders of magnitude.
Quaternary ammonium ions are commercially used as antiseptics, antistatic agents, in detergent formulations of fabric softeners, as a water treatment biocide, and in secondary-recovery oil wells. They are also prevalent in biological systems, and are of great biomedical interest. The commercial products are usually mixtures, and the determination of individual compounds in them has long been a troublesome analytical problem. Most often only the total tetraalkyl ammonium content is determined. Trace amounts have been determined in both commercial (1) and biological (2) samples by ion-pair extraction and colorimetry. Larger amounts may be determined and differentiated from amines by nonaqueous titration (3). Some degree of selectivity may be achieved by careful control of ion-pair extraction conditions followed by two-phase titration with lauryl sulfate ( 4 ) . However, closely similar quaternary ammonium ions cannot be differentiated by the latter procedure and, for those that can be differentiated, qualitative knowledge of the sample composition is required for proper adjustment of the conditions of extraction (5, 6). For the separation of closely similar quaternary ammonium ions, a chromatographic method is required. Thin-layer chromatography on alumina (7, 8) and high voltage electrophoresis (9) have been used, and quantitation has been accomplished by spraying with color-forming reagents. Gas chromatography has been applied to the analysis of choline and its esters but, because of the nonvolatility of the compounds, either prior derivatization or pyrolysis techniques must be used (10-13). GC-MS, both electron impact ionization and chemical ionization, is also useful (14, 15). Liquid chromatography would be the separation method of choice because of the poor volatility of the compounds. Unfortunately, the lack of useful UV-visible absorption bands has made the detection and quantitation of quaternary ammonium ions difficult. Ion-pair partition chromatography ‘Present address, Oak Ridge National Laboratories, P.O. Box X, Room B8, Building 4500N,O a k Ridge, Tenn. 37830. 0003-2700/78/0350-1330$01 .OO/O
using picrate as the anionic species has permitted the use of IJV detection (16). However, this method has a very limited concentration range because of changes in the distribution ratios of the individual cations with concentration. Various other methods, all involving collected fractions and subsequent analysis, are still widely used for the detection of quaternary ammonium ions. These include precipitation with sodium triphenylcyanoborate (I 7), I4C labeling of the compounds (18), NMR analysis (19),and color formation with periodide (18, 20). It is clear that a continuous means of detecting quaternary ammonium compounds is badly needed for such studies. Recently a new general purpose detector was developed in this laboratory for continuously monitoring the effluent from a liquid chromatography column (21). This detector utilizes a phenomenon which is associated with all ion-exchange processes-namely, the volume change of the resin matrix which accompanies all ion-exchange reactions. An osmotically induced volume change also occurs for nonelectrolytes which partition into the resin phase. Thus, i t is seen that insofar as only species which are capable of exchanging with the counterions, or partitioning into the resin are considered, the detector is completely general, giving a response for all species. The magnitude of the response will depend on the identity of the pair of ions in the exchange reaction, the physical properties of the resin matrix, and the composition of the external solution. The effluent flows through a low volume glass tube in which a strip of ion-exchange membrane is suspended and attached to a linear voltage differential transformer (LVDT) in a Du Pont Model 941 thermomechanical analyzer (TMA). Extremely small changes in the length of the ion-exchange membrane during sorption and desorption of ions cause the LVDT core to be displaced from its electrical center, resulting in a signal which is recorded on the Y axis of a strip chart recorder. This paper describes the application of this detector to the separation and determination of some simple quaternary ammonium ions, and of choline and its esters. The synthesis of an ion-exchange membrane with a greater sensitivity than commercially available membranes is reported. The precision, linearity of response, flow rate sensitivity, and detection limits of this new detector are discussed.
EXPERIMENTAL Chromatographic System. Delivery of the mobile phase was made with a Chromatronix Model CMP-2 chemically inert piston pump. Samples were introduced into the flowing mobile phase C 1978 American Chemical Society
