724
Anal. Chem. 1985, 57, 724-729
Preconcentration of Cadmium from Highly Acidic Saline Solutions and Direct Determination of Bismuth, Cadmium, Mercury, Antimony, Tin, and Thallium in Highly Acidic Aqueous Solutions with Electrically Vaporized Thin Gold Film Atomic Emission Spectrometry Stephen W. Brewer Chemistry Department, Eastern Michigan Uniuersity, Ypsilanti, Michigan 48197
Richard D. Sacks* Department of Chemistry, Uniuersity of Michigan, Ann Arbor, Michigan 48109
Corroslon-reslstant Au thln fllms are routlnely produced for analysis of hlghly acldlc solutions by electrlcally vaporized thln fllm atomic emlsslon spectrometry. Dlrect determlnatlon of BI, Cd, Hg, Sb, Sn, and TI from 2 M HCI Is posslble, wlth detectlon llmlts ranglng from 0.085 to 6.5 mg/L, useful concentratlon ranges of about 2 decades, and relatlve errors of 4-5.7 % to -26 %. Slmple batch separatlon/preconcentratlon of Cd( I I ) wlth a mlcrobead strong base anion exchange resln allows determlnatlon of Cd In complex acldlc solutions near the 10 ng/mL (10 ppb) concentration level wlth relatlve errors of around 8 %. The method Is not expensive; materlals cost for a slngle cadmlum determlnatlon Is about $12, Including preparatlon of the analytlcal curve. Materials cost for preparation of the analytical curve plus flve cadmlum determinatlons Is about $20.00.
The determination of traces of toxic heavy metals in very acidic or saline aqueous solutions has long been of interest (1-3). Seawater, other brines, acid mine waters, and plating bath liquors are among these solution types. Seawater, -0.5 M in NaCl, contains trace levels of a number of toxic heavy metals (I). The presence of high concentrations of group 1 and 2 salts can make determination of trace heavy metals difficult. Concomitant effects among trace metals have been reported in determinations by atomic absorption spectrometry with electrothermal atomization, a widely used method (4,5). Recent work (6-12) on electrically vaporized thin metal films as alternative vaporization and excitation sources for atomic emission spectrometry has shown their utility in analyses of refractory powder samples and ground solids such as coal, flour, dried spinach, and river sediments. In these investigations, using -350 pg Ag thin films, Goldberg and Sacks (12) found that aqueous solutions could be used as standards. They noted, however, that aqueous standards containing more than 500 ng of the element of interest were difficult to vaporize completely, because thick salt crusts formed when the solution droplets dried. Samples of more than 100 pg of particles suspended in 2-propanol were also not easy to vaporize. Goldberg and Sacks (12) also found that slightly acidic (-0.1 M HC1) aqueous solutions eroded Ag films badly. A number of the problems in determinations of trace heavy metals in acidic aqueous solutions of high salt content have been addressed in the present investigation. First, acid-resistant Au films have been developed. Second, optimum analysis wavelengths and radiation integration time intervals (12) have been selected for determination of Bi, Cd, Hg, Sb,
Table I. Conditions for Short and Long Discharges support gas
long (12) short (9) 60% Ar/40% O2 60% Ar/40% O2
pressure capacitance, pF charging voltage, kV inductance, p H ringing frequency, kHz energy, J peak current, kA
atmospheric 30 8.0 1200 0.830
960 1.0
atmospheric 22.5 4.0 residual 15.5 180 7.9
Sn, and TI. Third, direct sequential determinations of four metals, Bi, Cd, Hg, and T1, dissolved together at widely varying (0.35-35 mg/L) concentrations in 2 M HCI have been performed, showing no significant interelement effects, and showing promise for future simultaneous determinations of these elements.
EXPERIMENTAL SECTION Discharge Circuit. The discharge circuit, chamber, film holding cassette, and gas flow conditions used to vaporize thin films have been described in detail (9, 10, 12). Two types of discharge, called “short” and “long” were investigated for their analytical utility. Table I shows conditions and characteristics of each discharge type. Thin Film Production. Thin Ag films on polypropylene substrates were prepared with the apparatus described by Clark and Sacks (9). Thin Au films were prepared with the same vacuum system and substrate holder. A tungsten boat, coated with A120,, was used for melting and evaporating gold. A special brass die was constructed to put sample-holding dimples into plastic substrate strips before they were coated with Au. Optical and Electrical Monitoring. Goldberg and Sacks (12)have described optical and electrical monitoring techniques and apparatus. In earlier work with Ag films, photographic detection was used. In later work with Au films, photoelectric detection, with 80 pm entrance and exit slits, was used. As in Goldberg and Sacks’ work (12)the discharge chamber was placed 68 cm from the entrance slit, without ancillary optics. Experimental Procedure. Thin films of Ag were prepared according to Clark and Sacks’ procedure (9). Thin films of Au were prepared on the same plastic substrate material. Chunks of Au weighing from 1 to 2 g were cut from a solid bar, then hammered flat and thin enough to cut with scissors. The thin foil was cleaned in concentrated HCl, washed with distilled water, and dried in air. Then 0.2500 f 0.0007 g batches were weighed, mass control being important (7). For each evaporation, 0.25 g was placed in the alumina-coated tungsten crucible. The substrate material was cleaned in an ultrasonic bath with 75% 2propanol/25% H20 (v/v), and cut into 7.3 X 1.6 cm strips. Two cylindrical dimples, each centered 2.44 cm from an end of the strip, each 0.85 cm in diameter and 0.16 cm deep, were pounded into
0003-2700/85/0357-0724$0 1.5010 0 1985 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 57, NO. 3. MARCH 1985
725
Table 11. Characteristics of Thin Films Deposited on Polypropylene Substrates Ag (12)
substrate dimensions, cm
7.3
film dimensions, cm vaporized surface area, cm2 film thickness, A cylindrical dimple dimensions, cm
7.3 X 1.6 7.9 400 none
film mass vaporized, pg resistance, R
X 1.6 X
350 5.0-10.0
Au
0.05 7.3 X 1.6 X 0.5 7.3 X 1.6 7.9 230 2 dimples, each 0.85 diameter by 0.16 deep, centered 2.44 em from ends 350 16.WO.O
each strip with a brass die and rubber mallet. The strips were cleaned again and attached to the substrate holder with transparent tape, with dimples concave downward toward the crucible. Stripsof Al foil were placed on top of the plastic strip and secured to the metal holder to conduct heat away from the plastic and prevent its melting. The evaporation chamber was evacuated to a nominal 2 x lo" torr. The crucible was heated to white heat in -5 s with a 250-A current and held at white heat until all the Au was observed to evaporate, a process that took -10 s. The evaporation chamber was brought up to atmospheric pressure, and the plastic strips, coated with thin Au films, were removed. Films with resistances between 15 and 40 R gave good results. Film and substrate properties are summarized in Table 11. Standard solutions for direct determinations were prepared by dissolving reagent-grade metal salts in demineralized waterHCI solutions, usually 2 M HCI. Drops of 5 to 200 pL were placed in dimples of Au films and dried with a heat lamp. Because of the volatility of ShCI,, Sb(II1) solutions were air-dried. A strong base anion exchange resin was used for isolation and preconcentration of cadmium. Two methods were tried for isolation and preconcentration. In the first method, 20-mg batches of resin were placed in plastic viala and equilibrated with 20-mL samples of solutions of Cd(I1) in 2 M HCI or 1.5 M HC14.5 M NaCl for 1 h with stirring. Then 10-mL aliquots of the suspension were placed in conical centrifuge tubes and spun for -10 min at -2100 rpm. The Supernate was drawn off, and the resin beads were resuspended in demineralized water. Aliquots of 50 p L were placed on Ag films in 10 roughly equal drops and dried under a heat lamp. The resin beads, of 9 2 pm diameter, were left on the film surface. In the second method, 50-mg batches of the anion exchanger were wuilihrated with 50-mL samnlea of Cd(I1) and other metals in~2~M~'HCI. In 2 M HC1-0.5 M N h . or 2 M HC14.43 M "0, for 1 h with stirring. Twenty milliliters of the suspension was filtered through a polycarbonate filter of 47 mm diameter and 1 pm pore rine. The center of the filter, containing the resin. was cut out and put into a conical centrifuge tube. One milliliter of demineralized water was added tn the tube to remove the metal from the resin. The tube was placed in a sonic bath for 5 min to break the resin away from the filter. To ensure equilibration, the tube was stirred on a vortex mixer for 1 min. The tube was centrifuged at -2100 rpm for -10 min, and one 50-pL drop of supernate was placed in each dimple of an Au film. Five films were prepared from each solution. Solutions from HCI-HNO, mixtures were air.dried u) minimize erosion of the Au film; so. lutions from HCI or HCI-NaCI mixtures were dried with a heat lamp. Five films were vaporized for the blank and for each different metal concentration. Intensities were record4 photoelectrically with a 1P28 photomultiplier tube and the gated integrator deacrihed in ref 12. The integration interval extended over the entire discharge. Materials and Reagents. Silver films were made from high-purity (99.999%) 100-mesh Ag needles. No purity figures were available for the surplus Au used to make films, but pho-
*
UNERODED-ic
6 'i i
. . . .
I
EROOEO BY
. I *
SOLUTION
0 , "n I
Flgur 1. Secc&%y eleclmn hap (SEI)taken wlLh scanning e W m miu(SEM) of area on Ag min fib eroded by -pH 1 suspension of resin beads. Egpshaped objects are resin beads.
tographic spectra showed Ag, with a few weak lines,to be the major impurity. Some weak Cu lines were visible and may have come from Cu connections in the holder or from the Au. Aminex A-28 strong base anion exchanger, in acetate form, with a bead diameter of 9 2 pm, was bought from Bio-Rad Laboratories, Richmond, CA. National Bureau of Standards SRM 1643a, Trace Elements in Water, was the standard used. Polycarhnate membrane filters were suonlied bv Nucleoore COID..Pleasanton. CA. Tungsten evapora&n +ma&,catalog number.S35B-AC-W, were bughifrom R. D. Mathis Co., Long Beach, CA. RESULTS AND DISCUSSION Acid Resistant Films. A disadvantage of using either Ag or AI filmsis that they are easily eroded by even slightly acidic solutions. In Figure 1, a secondary electron image (SEI) obtained with a scanning electron microscope (SEMI shows a portion of an Ag f h eroded by an aqueous solution of -pH 1. The egg-shaped objects within the eroded area are resin beads. Erosion of the film increases its electrical resistance, makes the discharge harder to initiate, and may cause poorer sampling of the surface by the plasma. Au films are not eroded by 2 M HCI alone, nor by 0.5 M HNO, alone. If droplets containing both nitrates and chlorides in acidic solution are put on the films, however, they must be air-dried rather than lamp-dried, as hot acidic solutions of nitrates and chlorides will dissolve thin layers of Au. Despite the high cost of Au, thin films of it are inexpensive to make. Presently, each Au film costs 54 or less for raw materials. Corrosion resistance and low cost are desirable features of Au films. Optimum Analysis Wavelengths a n d Time Gates. Until the present work, no systematic study had been made of optimum analysis wavelengths in electrically vaporized thin filmspectrometry. For each of six elements, Bi, Cd, Hg, Sb, Sn, and TI, at least four spectral lines were examined for sensitivity and linearity. For each element at least one neutral atom resonance line was studied, and one neutral atom nonresonance line. Ion lines, resonance and nonresonance, were studied whenever possible because earlier work had shown the plasmas generated to be highly ionized (IO, I l l . Each spectral line was studied under two discharge conditions, short and long (see Table I), with radiation from each discharge being integrated over the duration of the discharge. Concentrations of each metal ranged from 2 to 800 mg/L in 10-pL samples, corresponding to metal masses ranging from 0.02 to 8 Wg. Fifty four analytical curves were generated. Six wavelengths, shown in Table 111, were selected for analysis. Long discharges were found to give the lowest detection limitsand best linearity, with the exception of thallium, for which a short discharge gave as good results as a long
726
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ANALYTICAL CHEMISTRY, VOL. 57. NO. 3, MARCH 1985
Table 111. Optimum Analysis Lines for Long Discharges detection limitb no of lines
element
studied
Bi Cd Hg Sh S” TI
in 10 pL sample
wavelength of best line, nm
line type“
306.772 226.502 253.652 217.589 283.999 377.572
atom, res ion, res atom, res atom, res atom. nonres atom. res
w 11
0.85 7.5
mg/L 1.1
0.085 0.75
log-lop slope
useful eonen range: mg/L
0.89 1.05
0.085-8.0
1.1-40.0
0.70
0.75-100
32. 20.0
3.2
0.73
3.2-800
2.0
0.77
2.0-400
65
6.5
0.79
6.5-800
OKey: atom, neutral atom; ion, singly charged positive ion; res, resonance line; nonres, nonresonance line. bConeentration that will produce a net signal intensity >3 times the standard deviation of blank intensity. ‘Concentration range over which a log-log plot is without curvature: above too concentration value done chances e.hharnlv to lower value. AU
SEI
CD
AU
CD
SEI
800
800
80 80
I mm
Figure 3. Au Ma. Cd Lm. and SEI photographs taken with SEM of residues left, after bng discharges, from 5-pL droplets of 800 and 80 mg/L Cd(I1) in 2 M HCI deposited on Au thin films and lampdried.
8
1
mm
2. Au Mol. Cd La. and SEI photopaphs taken wim SEM of SpL droplets of 800. 80, and 8 mg/L Cd(1l) In 2 M HCI deposited on AU thin films and lampdried.
discharge. For Bi, TI, Hg, and Sh, neutral atom resonance lines gave the hest results. A neutral atom nonresonance line was best for Sn. and an ion resonance line for Cd. In most cases, log-log plots of relative intensity showed downward curvature above metal concentrations of 40 mg/L, corresponding to total metal masses of 0.40 pg in 10-pL samples. Detection limits ranged from a low of 0.85 ng of Cd to 65 ng of TI. log-log slopes ranged from a suhlinear 0.10 for Hg, to nearly linear values of 0.89 and 1.05 for Bi and Cd, respectively. Relative standard deviations of net relative intensities ranged from about 10% to about 50% near the detection limit. I t is probable that detection limits could he improved by simultaneous recording of background and signal radiation with a multichannel device. Time-gating of discharge radiation integrations improved neither linearity nor detection limits. Goldherg and Sacks (12) had concluded that sampling of aqueous solution residues hy the discharge is incomplete above sample sizes of about 0.50 pg. They noted that no enhancement of detection limits is possible with time-gating of radiation when residues this large are present. They ascribed the difficulty of sampling these residues to the formation of thick salt ridges formed on drying aqueous solutions. Duchane
and Sacks (7,8) had also observed these ridges. Figures 2 and 3 support these observations. Figure 2 shows photomicrographs of deposits of CdCI, from 5-pL droplets dried on Au film surfaces. The photographs were taken with an SEM having an energy dispersive X-ray spectrometer. In Figure 2, columns are labeled Au for Au M a X-ray maps, Cd for Cd La X-ray maps, and SEI for secondary electron images. Rows are laheled 800 for residues from 800 mg/L Cd solution (as CdCI, in 2 M HCI), 80 for residues from 80 mg/L Cd solution, and 8 for residues from 8 mg/L Cd solution. In the first row, labeled 800, a thick ridge of CdC1, is visible in the SEI. The CdC1, deposit is also visible in the Cd L a X-ray map. In the Au M a X-ray map, Au M a intensity is diminished in regions where the CdCI, crust is thickest, owing to absorption of Au M a radiation by cadmium and chlorine. Similar effects are seen in the second row of images, laheled 80,hut they are less pronounced than those in the first row, because the salt mass is IO-fold lower. In the third row, labeled 8, the ridge effect almost disappears. The photographs in Figure 3 show solution residues left on Au surfaces after sampling by long discharges. Row and column symbols are almost the same as those in Figure 2. Only the 8 mg/L row has been left out, because no traces of 8 mg/L droplet residues could he seen with the SEM after sampling by the discharge. The presence of CdCI, residues and Au film after discharge suggests incomplete vaporization of analyte material and may account for the downward curvature seen in most working curves beyond 0.40 pg of metal. Direct Determination of Bi, Cd, Hg, a n d TI. Direct determination of Bi, Cd, Hg, and TI mixed together in 2 M
ANALYTICAL CHEMISTRY, VOL. 57, NO. 3,MARCH 1985 727 Table IV. Direct Determination of Bi. Cd. Ag. and TI from 2 M HCI Solutions' concn found: element
concn taken? mg/L
mg/L
% re1 error
Bi Cd Hg TI
3.5
0.35 3.5 35.0
3.9 f 0.9 0.26 f 0.04 3.7 t 0.8
+11 -26 +5.7 -19.4
28.2 f 7.6
'Solutions studied each contained all four elements. 'Sample size was 100 pL. cPlus or minus values are estimates of standard deviation based on five determinations. Table V. Direct Determination of Cd from NBS SRM 16438 Major Constituents (Noncertified) element
concn, pg/g
mass on film,' pg
Ca Na
27 8
11.0
K
2
3 0.8
Recovery of Cd"
taken' found' re1 error, %
Cd concn, ng/g
Cd mass, ng
10fl 5.9 f 3.7
4.1 f 0.4 2.4 f 1.5 -41%
-41%
040C-rL sample. bPlusor minus values reported by NBS. 'Plus or minus values are estimate8 of standard deviation based on five determinations.
HCI showed no apparent interelement effects. Relative errors in recovery of these elements were the same as would be expected if the elements were determined unmixed by the method used. Solutions for analytical curves were made up to contain 8 to 40 mg/L TI(III), 0.8 to 4.0 mg/L Bi(II1) and Hg(II), and 0.08 to 0.4 mg/L Cd(I1). A solution 35 mg/L in TI(III), 3.5 mg/L in Bi(II1) and Hg(II), and 0.35 mg/L in Cd(I1) was used for recovery study. Results are summarized in Table IV. Relative errors in recovery ranged from +5.7% for Hg to -26% for Cd(I1). These errors were about the same as could be expected if the "I,Hg, Bi, and Cd were not mixed, but isolated in 2 M HCI. It should also be noted that Cd was determined in a solution with a 100-fold excess of T1 and 10-fold excesses of Bi and Hg. Relative errors could possibly be reduced if line and background intensities were measured simultaneously. Direct determination of Cd in a still more complex matrix, with great excesses of group 1and 2 salts, near the detection limit for Cd, is just possible. NBS SRM 1643a. Trace Elements in Water, was chosen as the more complex matrix. Table V shows masses of major group 1and 2 constituents in SRM 1643a present on the film surface prior to discharge. The concentration of Cd found showed -41% relative error from the certified value. The relatively large masses of Ca and Na salts on the film may have impaired the accuracy of the determination through formation of crusts. Two other difficulties may be considered. First, droplets of 200 pL are not as easily applied and dried as 50-pL droplets. Second, the concentration of Cd in NBS 1643a was very near the detection limit for this set of experimental conditions. Separation and preconcentration of Cd have overcome these problems. Separation/Preoonoentration of Cd from Brine and Complex Mixtures. More accurate results were seen when Cd in brine and complex mixtures was determined after a separation/preconcentrationstep. Aminex A-28 was chosen for batch separation of Cd(I1) from highly acidic, high chloride
0.1
mm
Flgure 4. SEI taken with SEM of resin suspension deposited on Ag thin Rlm after attempt to separate suspension from 0.5 M NaCl soluton. Cubic clystak are NaCI. Spheres are resin beads. Erosion of Ag thin film is
visible.
content, aqueous solutions for two remns. First, similar resins have high distribution coefficients for Cd(I1) and other heavy metals in 2 M HCI, so that small batches of resin could remove significant amounts of anionic chloro complexes of Cd(1I) from solution, leaving group 1 and 2 metals behind. Second, the beads' size offered the possibility of easy direct vaporization in a discharge. Early experiments with Ag films, involving direct application of suspended beads to the films, and photographic detection yielded mixed results. Preconcentration of Cd with single batch extractions from 2 M HCI and from 1.5 M HC1-0.5 M NaCl was efficient, giving DG values of 1400 and 1560, respectively. Dr, values, where
D -
(1)
were measured for batch extractions with atomic absorption. When separation of Cd from NaCl solutions was tried, some NaCl was carried with the resin beads onto the film surfaces, as the SEI in Figure 4 shows. The spheres in Figure 4 are resin beads, and the cubic crystals are NaCl. Although their small diameters suggested easy vaporization (E?),resin beads were not completely vaporized in long or short discharges. Figure 5 shows SEI'Sof beads left on Ag films after short and long discharges. Beads left after short discharges appear to be undisturbed, and those left after long discharges appear to be charred. NaCl crystals were not much vaporized by either type of discharge. Separation of Cd(I1) from saline solutions was improved when the resin beads, after equilibration with solution, were filtered and equilibrated with distilled water. A significant fraction of the Cd(I1) was released from the resin so that the water, with relatively few beads and little NaCI, could be applied to films and dried. Table VI shows the analytical results of separation and preconcentration of Cd(I1) by the latter procedure, from solutions of 0.5 M NaC1-2 M HCI, 2M HCI, and 0.43 M HN03-2 M HCI (SRM 1643a with added
728
ANALYTICAL CHEMISTRY, VOL. 57. NO. 3. MARCH 1985
Flgure 6. SEI'S taken with SEM of Au thin films with no separationloreconcentration (a) before discharm and (b) after lono discharm and &h separatim/pr&ncenImMn (c~betore'dmhargeand (d) a& long discharge.
01 rnm Figure 5. SEI'S taken with SEM of resin suspensions deposited on Ag thin films and subjected lo (a) long and (b) shorl discharges. Note charred appearance of beads after long discharge. and undisturbed appearance 01 beads after short discharge.
Table VI. Determination of Cd after Separation/Preconcontration solution
0.5 M NaC1-2 M HCI" 2 M HCI" NBS 1643a (0.43 M
cmcn taken. cmcn found.' % re1 ng/mL (ppb) ng/mL (ppb) error 11.5 11.5 8.4 f 0.8*
15.8 f 4.6 12.4 i 1.3 1.0 i 2.3
+31.4 +1.8 -7.7
HNO,-2 M HCI)
'Solution also contains 115 ng/mL Bi and Hg and 1150 ng/mL TI. bCorrected for density and dilution with HCI. Plus or minus values reported by NBS. 'Plus or minus values are estimates of standard deviation based on five determinations. HCI). With the preconcentration step, 50-rL drops could be used, and very little excess salt was loaded onto the film. An attempt was made to determine Cd directly from 0.5 M NaCI-2 M HCI without preconcentration, but large crystal residues of NaCl (-1.5 mg of NaCl per 5O-pL drop) prevented efficient vaporization of the analyte. In Figure 6, SEI photomicropraphs of residues taken directly from 0.5 M NaCI-2.0 M HCI solutions and of residues left after preconcentration from these solutions are shown to emphasize this point. Large crystals of NaCl are visible before (a) and after (b) vaporization of the film when no preconcentration was done. When preconcentration was done, separation was not quite complete,
as Figure 6c shows that some resin beads and some NaCl were transferred to the film surface. Little evidence of residues of such beads and crystals after preconcentration and discharge is visible in Figure 6d. The small number of crystals and beads were not difficult to vaporize but may have impaired the accuracy of Cd determination from 0.5 M NaCI-2 M HCI, relative error being about +37.4%. More accurate results, as Table VI shows, were obtained from application of preconcentration to 2 M HCI and to SRM 1643a, with relative errors in Cd determination of +7.8% and -7.7%. respectively Goldberg and Sacks (12) pointed out some advantages enjoyed by the application of electrically vaporized thin film spectrometry to analysis of solid powders. The method appears to be applicable to determination of heavy metals in complex aqueous solutions as well. It should be stressed that the method is inexpensive even when Au films are used. A single determination of Cd in solution reported here, including preparation of the analytical curve, for example, costs about $12.00 for f h materials, support gas, and resin. The Au films cost only about $2.00 of that total. Materials cost for preparation of the analytical curve plus five cadmium determinations is about $20.00. Simultaneous multielement determinations at minimum materials cost are a definite prospect and may offer improved measurement statistics. ACKNOWLEDGMENT Photomicrographs were taken by L. Marcotty, W. Wagner, and B. Winter of the Electron Microbeam Analysis Laboratory at the University of Michigan, Ann Arbor, MI. Registry No. Bi, 7440-69-9; Hg, 7439-97-6; Sb, 7440-36-0; Sn, 7440-31-5: TI, 7440-28-0; Cd, 7440-43-9; Au, 7440-57-5. LITERATURE CITED (1) Brooks. R. R. Anafysst(London) 1980. 85. 745-748. (2) Leyden. D. E.; Palterson. T. A,; Alberts. J. J. Anal. Chem. 1975. 4 7 ,
733-735. (3) Buchanan. A. S.;Hannaker. P. Anal. Chem. 1984. 56. 1379-1382. (4) Syty. A CRC Crif. Rev. Anal. Chem. 1974. 4 . 155-228.
Anal. Chem. 1985, 57,729-733 (5) Cruz, R.; Vanloon, J. C. Anal. Chim. Acta 1974, 72, 231-243. (6) Duchane, D. V.; Sacks, R. D. Anal. Chem. 1978, 50, 1752-1757. (7) Sacks, R. D.; Duchane, D. V. Anal. Chem. 1978, 50, 1757-1765. (8) Duchane, D. V.; Sacks, R. D. Anal. Chern. 1978, 50, 1765-1769. (9) Clark, E. M.; Sacks, R. D. Specfrochlm. Acta, Part 6 1980, 358, 471-488. (10) Suh, S. Y.; Coltlns, R. J.; Sacks, R. D. A w l . Spectrosc. 1981, 35, 42-52. (1 1) Suh, S. Y.; Sacks, R. D. Spectrochim. Acta, Part 6 1981, 366, 108 1- 1096.
729
(12) Goldberg, J.; Sacks, R. Anal. Chem. 1982, 54, 2179-2186.
RECEIVED for review October 2, 1984, Accepted November 26,1984. This work was supported by the National Science Foundation through Grant No. CHE 78-25542 and by the (hduate School of Eastern Michigan University through the Research and Sabbatical Leaves Program.
Performance Studies under Flow Conditions of Silica- Immobilized 8-Quinolinol and Its Application as a Preconcentration Tool in Flow Injection/Atomic Absorption Determinations Monte A. Marshall’ and Horacio A. Mottola*
Department of Chemistry, Oklahoma State University, Stillwater, Oklahoma 74078
The use of silica-lmmoblllred 8-quinolinol prepared by an improved synthetic route has been evaluated as a preconcentratlon material for trace metal Ions In flow systems. Breakthrough capacitles were evaluated under different flow, temperature, and geometric characteristics of the preconceniratlng column. Mass transfer IlmHatlons under flow condltlons explaln the dependence of breakthrough capacltles on these variables. The capabllltles of this material for on-line preconcentration of copper( I I ) using flow Injection analysis (FIA) for sample processlng and atomic absorption spectrometry (AAS) for detection have also been evaluated. The relatively hlgh capaclties of these simply and reproduclbly prepared materials as well as the absence of swelllng complications afforded by the Inorganic slllca framework allow for their effective use In FIA/AAS by Implementation of rather slmple manlfolds. Results obtained for the determlnation of ng/mL levels of copper( I I ) in some EPA water samples agreed very well with reported values.
Bonded silicas, widely used in liquid chromatographic separations, have recently shown recognized potential for sample preconcentration or matrix isolation. The so-called “extraction columns”, employing bonded silicas, have become popular for sample preparation prior to chromatographic separations, virtually replacing the more laborious liquidliquid extraction procedures. In fact, bonded-phase sample preparation has been identified as a growing technological trend (1) and has received prevalent attention for the selective preconcentration of trace metal ions (2-7). The immobilization of reagents on silica supports offers some distinct advantages over immobilization on organic polymer supports. First, the silica is readily modified by a variety of silylating agents allowing for a myriad of functional groups to be immobilized. Second, since the bound group is a t the surface of the support, high exchange rates are generally observed (2, Present address: Monsanto Co., Corporate Research Center, 800
N. L i n d b e r g h Blvd., St. Louis, MO 63167.
4 ) whereas some highly cross-linked organic polymer matrices may require hours for equilibration (8). Third, silica offers excellent swelling resistance with changes in solvent composition having little effect on the support at pH
