2502
Anal. Chem. 1986, 58,2502-2504
ais: Phlbdelphla, 1983; ASTM STP 623, pp 10-17. (6) Galloway, J. N.: Cosby, B. J.. Jr.: Likens, G. E. J. Oceanogr. 1079. 24, 1161-1165. (9) Landsberg, H. Arch. Meterol., Geophys. B/ok/imato/.,Ser. A 1054, 7 , 219-226 (10) Ruzlcka, J.: Hansen, E. H. Anal. C h h . Acta 1985, 173, PP 3-21. (11) Fed. Reg. 1984, 49(209), 11. (12) ~ossetti,E. J. ROSSO~~I, H. J . Chem. EdUc. 108s. 42, 375-378. (13) Perrin, D.: Dempsey, B. Buffers for pH and Metal Ion Control; Chapman and Hall: London, 1974. (14) Beech, W. F. Fibre-Reactive Dyes: Logos Press Limited: London, 1970: pp 218-225.
c.:
(15) Kubelka, P.; Munk, F. 2. Tech. Phys. 1031, 12, 593. (16) Nelsius, K. H. U S . Patent No. 4029597. (17) Neisius, K. H. US. Patent No. 4029598.
R ~ E for~review D January 3, 1986. Accepted M~~ 16, 1986. This work was supported in part by NSF Grant No. ATM8318028. We also wish to thank the University of Washington Graduate Research Fund for providing funds to purchase the pH meter used in this work.
Preconcentration of Copper in Water Samples with 2-Mercaptobenzothiazole on Naphthalene Masatada Satake* and Koichi Ishida Faculty of Engineering, Fukui University, Fukui 910, Japan Bal Krishan Puri Department of Chemistry, Indian Institute of Technology, Hauz Khas, New Delhi 110016, India Shiro Usami Department of Industrial Chemistry, Faculty of Engineering, Toyama University, Toyama 930, Japan
A soltd chelating materlal, 2-mercaptobenrothlazde (P-MBT), on naphthalene provides a rapid and hlghly selective means of preconcentratlon of copper from natural water samples. Copper Is quantkathrdy retained on 2-MBT-napMhalene In the pH range 5.5-7.5 and at a flow rate of 5 mumin. The metal complex-naphthalene Is dissolved from the column wlth 10 mL of n -butyiamlne-dimethytformamlde (5100 v/v) and measured by an atomic absorption spectrophotometer at 324.7 nm. Beer's law is obeyed In the concentratlon range 2.0-80.0 pg of copper in 10 mL of the flnai solutlon. Ten replicate analyses of 40 pg of copper gave a mean absorbance of 0.190 wlth a relatlve standard devlatlon of 1.0%. The sensltlvlty for 1 % absorptlon Is 0.093 pg/mL (0.133 pg/mL for the dlrect AAS method from the aqueous solution). The method has been employed for the determlnatlon of copper in varlous standard reference materials and natural water samples.
the nonaqueous organic solvents (7, 8). The only difficulty is the filtration, i.e., handling of a small amount of naphthalene, which may result in an error in the determination. In the present communication, a chromatographic method has been developed for the selective preconcentration of copper from a large volume of the aqueous phase using 2mercaptobenzothiazole (2-MBT)-naphthalene as an adsorbent. The method is very convenient (no need to filter the metal complex-naphthalene), rapid, and sensitive. The adsorbed metal in the column is not eluted even on washing with water but can be dissolved with a suitable solvent like n-butylamine-dimethylformamide from the column along with naphthalene and can be determined directly by atomic adsorption spectrophotometry. Various parameters have been evaluated and the method has been employed for the determination of copper in different standard reference materials and natural water samples and may be employed for various environmental and biological samples.
The usual liquid-liquid extraction method cannot be employed directly for the extraction of metal ions that form complexes with the complexing reagent at a high temperature ( I , 2). This difficulty can be overcome with the method of solid-liquid separation after liquid-liquid extraction developed by Fujinaga and co-workers using naphthalene as an extractant ( 3 ) . Although this method has many advantages over the usual liquid-liquid extraction (4,5),it is inconvenient since the operation is carried out at a high temperature and cannot be applied for the extraction of metal ions that form thermally unstable complexes. In order to overcome these drawbacks a second method, solid-liquid separation after adsorption of metal chelates on microcrystalline naphthalene, was developed (6). The method is very convenient (carried out a t room temperature), rapid (no need of heating naphthalene), sensitive, and economical (hardly 0.4 g of naphthalene is needed), can be applied to many types of the complexes, and is especially useful for metal complexes that have low solubility in
EXPERIMENTAL SECTION Reagents. Copper sulfate solution was prepared in double distilled water from its analytical reagent grade sample and standardized (9). A more dilute solution ( 5 ppm) was prepared by taking the appropriate amount of the standard solution. Buffer solutions were prepared by mixing 1 M acetic acid and 1 M ammonium acetate solution for pH 3-6 and 1M aqueous ammonia and 1 M ammonium acetate solution for pH 8-11. N-Butylamine-dimethylformamide solution was prepared by mixing 5 mL of the amine with 100 mL of DMF. Naphthalene, 2mercaptobenzothiazole (2-MBT), DMF, and all other reagents were of analytical reagent grade. Preparation of Loaded 2-Mercaptobenzothiazole-Naphthalene Mixture. Naphthalene (20 g) and 2-MBT (3 g) were completely dissolved in 100 mL of acetone. This solution was transferred to 300 mL of water in a fast stream and stirring magnetic stirrer-hot plate arrangement at 50 "C. Naphthalene coprecipitated along with 2-MBT waa filtered through filter paper by suction, washed with water, dried in air for 2 days, and then stored in a bottle. Apparatus. A Toa-Dempa HM-5A pH meter and a PerkinElmer, 403 atomic absorption spectrophotometer were used. A
0003-2700/86/0358-2502$01.50/00 1986 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 58, NO. 12, OCTOBER 1986
Table I. Effect of Diver%eSalts and fonsa tolerance limit
salt or ion NaI, NaC104, KNO,, NaCl, CH3COONa.3Hz0, NH4Cl,Na2S04 KSCN, NH4Cl KHsPO4 sodium tartrate Na&O, sodium citrate, thiourea disodium EDTA MdII), Mn(I1) Ni(II), Zn(II), Fe(IIQb Mo(VI), W(VI), Pb(II), Al(III),' Bi(II1)' Ca(II), V(V), Pt(IV), Cd(II), Co(I1)
2g
Ig 500 h g 100 mg 50 mg 10 mg 100 Pg
10 mg 3 mg
2 mg 1 mg
"Cu(I1) amount was 40 jig, pH 6.0. *Masked with 250 mg of NH4F. 'Masked with 50 mg of sodium tartrate. Table 11. Determination of Copper in Natural Waters
sample hot spring water hot spring water river water lake water a
amt of comer founda present DDTC-MIBK method method 13 f 0.8
* *
8 1.0 6 f 1.3 5 1.2
15
* * *
1.0 7 1.2 7 f 1.1 4 1.0
Mean of five determinations.
hollow-cathode lamp for copper was obtained from Hamamatsu Photonics, Ltd., Japan. A glass tube of 150 mm length and 7 mm i.d. was used as a chromatographic column. It was fitted with quartz wool and then filled with 0.4 g of naphthalene loaded with 2-MBT. General Procedure. A portion of copper sulfate solution (2-80 rg) was taken in a 50-mL beaker and to this was added 2.0 mL of the acetate buffer (pH 6.0). The solution was diluted to 25-35 mL with water and then passed through the chromatographic column loaded with naphthdeneZMBT mixture at the flow rate of 5 mL/min. The column was aspirated if necessary. The column was washed with water and the colored naphthalene mixture was dissolved with 10 mL of n-butylamine-DMF solution. This solution was aspirated into an air-acetylene flame and the absorbance measured at 324.7 nm against reagent blank.
RESULTS AND DISCUSSION All the measurements were carried out a t the operating conditions given below: wavelength, 324.7 nm; slit setting, 4 (7 A); current, 8 mA; burner height from the top of the burner head, 11mm; acetylene flow, 35 (pressure 0.5 kg/cm2), and air flow, 55 (pressure 2.1 kg/cm2). Effect of pH. The adsorption is maximum and constant on naphthalene-2-MBT in the p H range 5.5-7.5. It is incomplete below and above this p H range. In subsequent study, the pH was maintained constant a t pH 6.0. Addition of 1.0-5.0 mL of the buffer (pH 6.0) caused virtually no
2503
variation in adsorption of the metal, and use of 2.0 mL was recommended. Effect of Flow Rate. The flow rate was varied from 1to 30 mL/min. It was found that up to 15 mL/min, the flow rate did not affect the adsorption. A flow rate of 5 mLJmin was recommended for convenience. Adsorption Capacity of the Adsorbent. The adsorption capacity of the loaded 2-MBT-naphthalene mixture was determined by the batch method. This experiment was carried out by taking 1mg of copper, 2.0 mL of the buffer (pH 6.0) and 0.2 g of the loaded 2-MBT-naphthalene mixture in a 100-mL separatory funnel. The solution was diluted to 30 mL and shaken well for 30 min. The maximum amount of adsorption was found to be 4 mg/g of the sample. Effect of Volume of the Aqueous Phase. The effect of volume of the aqueous phase on the adsorption of copper was studied by the general procedure. The adsorption remained constant and maximum when the volume of the aqueous phase did not exceed 200 mL and was best kept to 25-35 mL for convenience. Choice of Solvent. Various solvents were tried to dissolve out the naphthalene-copper-2-MBT mixture from the column. This material was found to be insoluble in many of the nonaqueous and water-miscible organic solvents but dissolved easily in binary solvents like n-butylamine-DMF (5 mL of n-butylamine 100 mL of DMF). Various volumes of these binary solvents were tried to dissolve the product. It was found that 8 mL of this solvent was enough for the purpose and 10 mL was recommended as an adequate amount. Linearity, Sensitivity, and Precision. With the optimum conditions described above, the calibration curve for copper was constructed a t 324.7 nm. It was linear over the concentration rar,ge 2.0-80.0 pg of copper in 10 mL of n-butylamine-DMF solution. Ten replicate analyses of 40 pg of copper gave a mean absorbance of 0.190 with a relative standard deviation of 1.0%. The sensitivity of 1% absorption is 0.093 rg/mL, while it is 0.133 pg/mL for the direct atomic absorption spectrophotometric method. Effect of Diverse Ions. Sample solutions containing 40 pg of copper and various amounts of different alkali metal salts or metal ions were prepared and the determination of copper was carried out by the general procedure. The tolerance limit (error
