1504
ANALYTICAL CHEMISTRY, VOL. 50, NO. 11, SEPTEMBER 1978
Chromatography of Metal Ions with a Thioglycolate Chelating Resin Richard J. Phillips" and James S. Fritz Ames Laboratory-Department
of Energy and Deparfment of Chemistry, Iowa State University, Ames, Iowa 5001 1
The synthesis and properties of a chelating resin containing a thioglycoloyloxymethylfunctional group are described. This resin retains silver( I ) , bismuth(111), tin( I V ) , antimony(III), mercury(11), and gold(111) from 0.1 M acid and cadmium(11), lead(II), and uranium(V1) from pH 3.5 solution. On a column containing this resin, separations of several of these metal ions are obtained by elution with acetate and hydrochloric acid eluents. Application to real samples is demonstrated by the successful analysis of NBS samples for antimony, and of acidic brine solutions for traces of mercury( 11).
Synthesis T
Recent work has shown that chelating ion-exchange resins can be synthesized that are highly selective for certain groups of metal ions (1-4). T h e resins can be used to concentrate certain metal ions from aqueous solution and for columnchromatographic separations. The hexylthioglycolate resin developed by Moyers and Fritz ( 1 ) has been shown to be specific for silver(I), mercury(II), bismuth(III), and gold(II1) in 0.1 M acid. This resin is a diester formed by stepwise reactions of l,&hexanediol and thioglycolic acid with a carboxylic acid group on XAD-4, a macroporous styrenedivinylbenzene copolymer. The synthesis involves several steps and the final resin contains unreacted carboxyl groups which impart general ion-exchange properties. Thus, the hexylthioglycolate resin exhibits strong selectivity toward metal ions only in highly acidic solutions. This paper reports the synthesis and analytical applications of a resin containing the thioglycoloyloxymethyl chelating group (-CH20CO-CH2SH) attached to the benzene ring of a polystyreneDVI3 resin. Synthesis of this resin is more direct than that of the hexylthioglycolate resin, and the new resin is useful both in strongly acidic and in less acidic aqueous solutions. We report the retention behavior of a number of cations in acetate buffers, and demonstrate the separation of zinc(II), cadmium(II), and lead(I1). In addition, the retention behavior of silver(I),bismuth(II1). mercury(II), tin(IV), and antimony(II1) in hydrochloric acid is described. The results are compared with those of Moyers and Fritz using the hexylthioglycolate resin. Analytical applications are demonstrated by analyzing NBS standards for antimony and a simulated chlor-alkali brine for mercury(I1) using liquid chromatography with automatic detection.
The starting material was Rohm and Haas XAD-4. The resin was rinsed with methanol, and dried by suction filtration. It was ground immediately, sieved, and dried overnight at 60 "C. 1.3 g of resin, 0.3 g paraformaldehyde, 4 mL acetic acid, and 1 mL acetic anhydride were added to a 25mL Erlenmeyer flask. The contents were mixed for a few minutes by magnetic stirring, 1.5 g zinc chloride was added, and the flask was closed with a ground glass stopper. A4ftera few more minutes, the stirring was stopped, and the flask was heated overnight at 60-70 "C. The product was isolated by suction filtration, and rinsed with methanol. The acetylated intermediate was heated at reflux for 1 h in a mixture of 10% concentrated hydrochloric acid and 90% methanol. The product was isolated by suction filtration and dried for 2 h at 60 "C. This was treated with 5 mL thioglycolic acid, and a few drops of concentrated hydrochloric acid. A stream of dry nitrogen was introduced to remove water and prevent oxidation. The mixture was heated overnight at 60-70 "C. The product was isolated by suction filtration, rinsed with water, 1 M HC1, and methanol, and dried at 60 "C. Characterization. The sulfur content of the final product was determined by an oxygen flask method ( 5 ) . The batch capacity for silver(1) was measured by adding 100-200 mg resin to a small beaker containing 0.5 mmol silver nitrate dissolved in 10 mL of 0.1 M nitric acid. The mixture was allowed to stand in the dark for 1 h, and was then filtered. The resin was washed with two 10-mL portions of 0.1 M nitric acid, and the filtrate and wash were titrated with 0.1 M potassium thiocyanate, using a saturated solution of ferric ammonium sulfate as the indicator. Solutions, Detection of Metal Ions. Metal ion solutions were prepared and standardized using standard analytical procedures. The antimony(II1) solution contained 2 M hydrochloric acid. Bismuth(II1) was made up in 0.1 M acid with enough tartaric acid to prevent hydrolysis. Metal ions in effluents from gravity ion-exchangecolumns were determined by atomic absorption or by standard spectrophotometric procedures. Automatic detection with the liquid chromatograph was accomplished in two ways. Zinc(II), cadmium(II), and lead(I1) were detected at 520 nm using a solution of 4-(2-pyridylazo)-resorcinolin pH 9.0 tris(hydroxymethy1) aminomethane buffer in the dye circuit. The preparation of this solution has been described in an earlier paper (3). Polyethylene glycol (PEG 400),0.5% vjv, was added to solubilize the reagent and its complexes. Silver(I), bismuth(III), mercury(II), antimony(III), tin(IV), and arsenic(II1)were detected at 225 nm using 2-12 M hydrochloric acid in the dye circuit (6). The first four ions mere adequately detected with 2 M hydrochloric acid, but tin(IV), and particularly arsenic(II1). required more concentrated
EXPERIMENTAL Liquid Chromatograph. The system for liquid chromatography with automatic detection has been described previously ( 3 ) . Sample loops of 50, 200, or 1000 pL were used depending on the concentration of the ion of interest. A 10 cm by 2 mm i.d. column was used for the separation of zinc, cadmium, and lead and a 5 cm by 2 mm i.d. column was used for separations involving antimony, bismuth, and mercury. The resin used in these columns was taken from the
