Anal. Chem. 1990, 62, 2457-2460
response is strong and inverted). Note that any element that should happen to have the same response ratio as manganese at the two wavelengths could theoretically produce the same effect; however, the probability of this occurring is remote. Beyond MMT in gasolines, such dual-channel differential methodologies can be used to analytical advantage in a wide variety of samples containing FPD-active elements.
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(7) Hob, M. C. B. ARernathres to Lead in Gasoline; The Royal Society of Canada, Commission on Lead in the Environment, Minister of Supply and Services Canada: Ottawa, Ontario, 1988. (8) kngenese; EnvkonmentalHealth Crlterla 17; World Health Organhation: Geneva, Switzerland, 1981. (9) Meggers, W. F.; Corliss, C. H.; Scribner, B. F. Tabks of Spectfal-Line Intensities, 2nd ed.; NBS Monograph 145; U.S. Government Printing Office: Washington, DC, 1975. (IO) Sun, X.-Y.; Aue, W. A. J . Chromtogr. 1989, 467, 75. (11) Brcdy, S.S.;Chaney, J. E. J . Gas Chromtogr. 1988, 4 , 42.
LITERATURE CITED (1) Crompton, T. R. comprehensive Crgmometallic Analysis; Plenum Press: New York, 1907; pp 418-423, 763-785. (2) Smith, G. W.: Palmby, A. K. And. Chem. 1959, 31, 1798. (3) DuPuls, M. D.; Hill, H. H., Jr. Anal. Chem. 1979, 57, 292. (4) Qulmby, B. D.; Uden. P. C.; Barnes. R. M. Anal. Chem. 1978, 50, 2112. (5) M e n , P. C.; Barnes. R. M.; DiSanro. F. P. Anal. Chem. 1978, 50, 852. (6) Coe, M.; Cruz, R.; vanloon, J. C. Anal. Chim. Acta 1980, 120, 171.
RECEIVED for review May 9,1990. Accepted August 13,1990. This study was supported by NSERC Operating Grant A9604. Excerpts from this study were presented at the 72nd CIC Conference (Victoria, BC, June 1989) and the 20th Ohio Valley Chromatography Symposium (Hueston Woods, OH, June 1989). This material forms part of the doctoral thesis requirements of X.Y.S.
Indirect Inductively Coupled Plasma Atomic Emission Determination of Fluoride in Water Samples by Flow Injection Solvent Extraction Jamshid L. Manzoori' and Akira Miyazaki* National Research Institute for Pollution and Resources, 16-3 Onogawa, Tsukuba, Zbaraki 305,Japan
An indirect determination of fluorlde in water by Inductively
coupled plasma atomic emissbn spectrometry combined with flow InJectlon coupled with solvent extraction Is reported in this paper. A manlfokl for rapkl determination of fluoride has been designed that uses a single coil for complex formation and extraction. The method involves the formatlon of ianthanum/akarln compkxone/tluorlde complex and its extraction Into h e x a d contahrlng N,N-dlethyianHlne. The concentration of fluorlde is determined indirectly by Introduction of the organic layer Into the plasma and measurement of the emlsrlon intensity of the La I1 333.75-nm line. The optknwn experimental conditions for the determination are described. A coiled groove phase separator fitted with a grid and PTFE porous membrane was used In this work. The sampling rate was 36 samples per hour and the caiibratlon graphs were bear from 0.09 to 1.3 WmL. The relatlve standard devlatkn found was 2.16% for 290 pL of 1 pg/mL of fluorlde. The method Is selective and has been applied satisfactorily to the determination of fluoride In water samples.
INTRODUCTION In recent years there has been a growing trend toward the application of flow injection analysis (FIA) to the determination of fluoride. FIA systems for fluoride determination by ion-selective electrodes (1-31,spectrophotometry with cerium or lanthanum alizarin complexone (La-AC) (4,5), and microwave induced plasma (6)have been developed. Among these methods ion-selective electrodes in FIA offer remarkable detection limits, but their applicationto real samples is limited because of interference effects. Other methods lack sensitivity Present address: Department of Chemistry, Faculty of Science, University of Tabriz, Tabriz, Iran. 0003-2700/90/0362-2457$02.50/0
and simplicity; thus further efforts to develop simple and sensitive methods appear to be worthwhile. Since the introduction of liquid-liquid extraction based on the flow injection principle by Karlberg and Thelander (7) and Bergamin et al. (8)several papers have been published on this topic (9-12),but its application to inductively coupled plasma atomic emission spectroscopy (ICP-AES) has been limited and few papers concerning solvent extraction in FIA with ICP-AES have appeared in the literature (13,14). The direct determination of fluoride by ICP-AES is difficult since its resonance line appears at 95.5 nm; consequentlywork with fluoride has utilized nonresonance lines, which leads to poor detection limits. However, the application of indirect methods seems to be promising. Miyazaki and Bansho (15) have proposed an indirect method for the determination of fluoride based on ICP-AES measurement of La-AC/fluoride complex (La-AC-F). We recently described a useful extension of FIA combined with ICP-AES to the determination of total phosphorus and phosphate (16). The aim of this work is to develop a flow injection solvent extraction combined with ICP-AES for the determination of fluoride as an alternative to the manual method reported by Miyazaki and Bansho (15).The method involves the formation of La-AC-F and extraction into hexanol containing N,N-diethylaniline and determination of La I1 333.75-nm emission in the organic layer by ICP-AES.
EXPERIMENTAL SECTION Apparatus. A FIA Star 5020 Analyzer (Tecator,Sweden) with two pumps and a FIA Star 5102-001 variable volume injector was used. A schematic diagram of the flow injection system is shown in Figure 1. Aqueous solutions were introduced into the system by peristaltic pumps fitted with Tygon pump tubes. A double plunger micropump (NP DX-2, Nihon Seimitsu Kagaku, Japan) was used for the organic solution. A T-segmentor (Sanuki Kogyo Ltd., Japan) in which the aqueous phase flows straight through and organic phase at right angles was used for mixing organic and 0 1990 American Chemical Society
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ANALYTICAL CHEMISTRY, VOL. 62, NO. 22, NOVEMBER 15, 1990
UI \
W
W
Figure 1. Schematic diagram of flow injection system: C, carrier solution (distilled water); B, acetate buffer solution (pH = 4.7); R, reagent (La-AC); 0, organic solvent (Hexanol contahlng N , N d + ethylamine);PI, peristalk pumps; P,, dooMe plunger pump; S,sample (200 w l ) ; See, segmentor (T connector); FtEC, reactkm-extraction coil (300 cm, 1 mm 1.d.); PS, phase separator (coil grooved); W, aqueous
waste.
ammonia (1+ 10) and 4 mL of ammonium acetate (20% (w/v)), solution 1. In another container, 41 g of sodium acetate trihydrate was dissolved in 400 mL of water and 24 mL of acetic acid was added, solution 2. Solution 1and solution 2 were mixed and 400 mL of acetone was added while mixing, solution 3. A 0.163-g portion of lanthanum oxide was dissolved in 10 mL of dilute hydrochloric acid (1 + 5) and was added to solution 3. The resulting solution was diluted to 1L with water. This solution was stored in a refrigerator and protected from light and remained stable for at least 3 weeks. One liter of buffer solution contained 110 g of sodium acetate trihydrate and 98 mL of acetic acid. The organic solvent was prepared by mixing 960 mL of hexanol with 40 mL of NJV-diethylaniline. Procedure. With the manifold described above and under optimum instrumental conditions, sample or standard solutions with a volume of 200 gL were injected into the system by the carrier stream which were delivered at a flow rate of 2 mL/min. Buffer and reagent (La-AC)solutions were introduced into the system with a flow rate of 0.2 and 0.4 mL/min, respectively. The aqueous stream and a stream of organic phase (1.6 mL/min) were segmented in the solvent segmentor, resulting in a regulator pattern of alternate aqueous and hexanol segments. The mixture then passed through a reaction-extraction coil where La-AC-F complex formationand extraction process took place. The solution was then conducted to the membrane phase separator and impinged on the membrane and a fraction of the organic phase penetrated instantly. The aqueous and the remaining organic phase were guided away from the center of the membrane in a coiled groove. The separated organic phase was passed through a second separator and the remaining aqueous phase was separated. Pure organic phase was transferred to the ICP and emission from La I1 333.75 nm was measured.
RESULTS AND DISCUSSION
Figwe 2. Diagram of phase separator: 1, aqueous and organic solutions mixture; 2, aqueous waste; 3, separator donor haff; 4, " b a n e (pore size 0.45 pm); 5, grid; 6, separator reclpiint hak 7, organic phase.
aqueous phases. Complex formation and extraction took place in a reaction coil (300 cm, 1 mm i.d.1 fixed in a water bath thermostated at 60 "C. For phase separation, the separator units of two FIA Star 5105 extraction modules were used. Each unit consists of donor and recipient chambers, a membrane (pore size 0.8 pm), and a grid (Figure 2). A 27.12-MHz radio frequency (rf) generator (Shimadzu ICPS-PH) and a Shimadzu ICP spectrometer (GEW-170P) were employed in combinationwith a multirange recorder (Servocorder type SR 6221 Graphtec Corp. Japan). The output of the ICP detector was connected through the recorder to the FIA analyzer, which made the digital readout of the signal intensity on the microprocessor of the analyzer and automatic injection of the sample possible. The plasma was operated at a rf power output of 1.5 kW (reflected power
