a04
Anal. Chem. 1980. 52,804-807
multicomponent utility of systems showing matrix effects could be exploited as long as the cross terms either did not dominate the equations and/or varied functionally as reaction conditions were changed. This data treatment would probably be necessary if this method were to be extended to systems of more than two analytes, as accuracy would decrease to unacceptable levels if such cross-term matrix effects were ignored. There may also exist CL systems in which the cross-terms dominate and need to be considered in a first approximation in order to effect multicomponent utility. The exploitation of the gallic acid CL system described here is an example of a general type of study which this automated CL instrument makes feasible. Since the reagent dilution system drastically reduces the time required to optimize a CL system toward a specific analyte (about 2 h) and enables plots such as appear in Figures 2-4 to be constructed in less than an hour, not only is long-term irreproducibility due to reagent solution decomposition minimized, but new experiments with t h e reactant concentrations are easily designed by simple program changes. As a consequence of this more flexible approach to CL reactant concentration selection, the future application of CL reactions to analytical chemistry could be done with more thought as to the nature of the CL systemanalyte interactions. This approach has been hampered primarily by the complexity of CL reactions, and not by a lack of interest in such studies on the part of analytical chemists (8,14,19-23). In the gallic acid system, we have related the selectivity to the complexing ability of gallic acid (8). It would be fruitful to explore the possibilities of tailoring CL reactions so t h a t the rate determining step is affected by known interactions with the analyte. Most mechanistic studies are now applied after the fact and not used in the planning stage of
CL methods development. Such knowledge of CL systemanalyte interactions would help put CL methods on a firmer chemical footing such as is enjoyed by other reaction rate methods.
LITERATURE CITED Stieg, S. W. Ph.D. Thesis, University of Illinois, Urbana, IiI., 1979. Seitz, W. R.; Hercules, D. M. I n "Chemiluminescence and Bioluminescence", Cormier, M. J., Hercules, D. M., Lee, J., Eds.; Plenum: New York, 1973, pp 427-49. Kalinichenko, I. E. Ukr. Kbim. Zh. 1968, 34, 307. Hartkopf, A.; Deiumyea, R. Anal. Lett. 1974, 7 , 79. Neary. M. P.; Seitz, W. R.; Hercules, D. M . Anal. Lett. 1974, 7, 583. Delumyea, R.; Hartkopf, A. V. Anal. Chem. 1978. 48, 1402. Montano. L. A.; Ingle, J . D. Anal. Cbem. 1979, 51, 926. Stieg, S.; Nieman, T. A. Anal. Chem. 1977, 49, 1322. Stieg, S.;Nieman, T. A. Anal. Chem. preceding paper in this issue. Dubovenko, L. I.; Khotinets, E. Ya. Ukr. Khim. Zb. 1970, 36, 379. Dubovenko, L. I.; Guz, L. D. Ukr. Kbim. Zh. 1970, 36, 1264. Dubovenko, L. I.;Tovmasyan, A. P. Ukr. Kbim. Zb. 1971, 37, 845. Babko, A. K.: Dubovenko, L. I.; Terietskaya, A. V. Ukr. Khim. Zh. 1988, 3 2 , 1326. MacDonald, A.; Chan, K. W.; Nieman, T. A. Anal. Chem. 1979, 51, 2077. Isacsson, U.; Wettermark, G. Anal. Chim. Acfa 1978, 8 3 , 227. Stieg, S.; Nieman, T. A. Anal. Cbem. 1978, 50, 401. Morgan, S. L.; Deming, S. N. Anal. Cbem. 1974, 46, 1170. Routh, M. W.; Swortz, P. A.; Denton, M . B. Anal. C k m . 1977, 49, 1422. Montano, L. A.; Ingle, J. D. Anal. Chem. 1979, 51, 919. Slawinska. D.; Slawinski. J. Anal. Cbem. 1975, 4 7 , 2101. Burdo. T . G.; Seitz, W. R. Anal. Cbem. 1975, 47, 1639. Delumyea, R. Ph.D. Thesis, Wayne State University, Detroit, Mich., 1974. Veazey, R . L.;Nieman. T. A. Anal. Cbem. 1979, 51, 2092.
RECEIVEDfor review August 14, 1979. Accepted January 28, 1980. This research was supported by t h e donors of the Petroleum Research Fund, administered by the American Chemical Society, and by the National Science Foundation (CHE 78-01614).
Multielement Preconcentration of Trace Heavy Metals in Water by Coprecipitation and Flotation with Indium Hydroxide for Inductively Coupled Plasma-Atomic Emission Spectrometry Masataka Hiraide, Tetsumasa
Ito, Masafumi Baba, Hiroshi Kawaguchi, and Atsushi Mizuike"
Faculty of Engineering, Nagoya University, Nagoya 464, Japan
Microgram quantities of Cr(III), Mn(II), Co, Ni, Cu(II), Cd, and Pb In 1200-mL samples are quantitatively coprecipitated wlth indium hydroxide at pH 9.5. After adding ethanolic solutlons of sodium oleate and dodecyl sulfate, the precipitates are floated with numerous tiny nitrogen bubbles to the solution surface, and then collected in a small sampling tube. The procedure is simple and rapid, and suitable for operation at sampling spots. The heavy metals in the dlssolved preclphates are determined by inductively coupled plasma-atomic emission spectrometry. The concentrations of the heavy metals are Increased 240-fold, and those of alkali and alkaline earth metals in artificial seawater are reduced to '/50-1/20 for Na and K, and ca. for Mg, Ca, and Sr.
T h e concentrations of most heavy metals in natural water and seawater are too low to be determined directly by inductively coupled plasma-atomic emission spectrometry 0003-2700/80/0352-0804$0 1 .OO/O
(ICP-AES). Ion exchange, liquid-liquid extraction, and coprecipitation can be used as multielement preconcentration techniques, but sometimes they are time-consuming or troublesome, especially for large volume samples. Previously, we proposed a simple and rapid coprecipitation and flotation technique, in which traces of heavy metals were simultaneously coprecipitated with aluminum hydroxide by p H adjustment with aqueous ammonia, and then floated to the solution surface by a stream of tiny nitrogen bubbles ( I ) . However, the recovery of cadmium in 1000 m L of seawater was 20-50%, and 20-30 mg of magnesium coprecipitated, which increased the quantity of precipitates and therefore the final solution volume. By using sodium hydroxide solution instead of aqueous ammonia to adjust the pH, cadmium was nearly completely recovered, but much larger quantities of magnesium were coprecipitated. We have surveyed various metal hydroxide precipitates to solve this problem, and found that indium hydroxide, which has not been used as a gathering precipitate to date, is most 0 1980 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 52, NO. 6, MAY 1980 0 5 cm U
NITROGEN +
Table I. ICP-AES Instruments and Operating Conditions spectrometer
computer ICP source Ar flow wavelengths, nm observation height
NITROGEN
A
B
Figure 1. Flotation cells and sampling tube
suitable. Cadmium in 1200 mL of artificial seawater is quantitatively collected, and only 3-4 mg of magnesium coprecipitated. Thus the final solution volume was minimized and hence the concentrations of the desired heavy metals were increased 240-fold. In separating the flocculent precipitates of indium hydroxide from the mother liquor, flotation is more rapid and convenient t h a n filtration or centrifugation, and it is suitable for operation a t sampling spots. This preconcentration technique has been successfully applied to the simultaneous determination of microgram quantities of chromium(III), manganese(II), cobalt, nickel, copper(II), cadmium, and lead in 1200 mL of water and artificial seawater by ICP-AES.
EXPERIMENTAL Flotation Cells a n d Sampling Tube. A flotation cell for 200-mL samples is shown in Figure 1A. For 1200-mL samples, a 1000-mL graduated cylinder was used as a flotation cell (Figure 1B). A bubbler was made of a sintered-glass filter (porosity-4), which produced numerous tiny nitrogen bubbles (diameter below 0.5 mm) in 0.5% (v/v) ethanol. A sampling tube was an Allihn filtering tube (porosity-4)containing vitreous-silica wool to prevent the sintered-glass disk from clogging with the precipitates. A silicone rubber stopper with a tapered bent glass tubing was fitted into the sampling tube. The sampling tube is convenient for transporting the precipitates to laboratories for the determination of the heavy metals after the coprecipitation and flotation at sampling spots. ICP-AES Apparatus. Main instruments and their operating conditions are given in Table I. Atomic Absorption and Flame Photometry Apparatus. A Nippon Jarrell-Ash Model AA-1 Mark I1 atomic absorption/flame emission spectrophotometer with an SA-61 slit burner was employed under the following conditions: wavelengths (in nm) Mn 279.5, Co 240.7, Ni 232.0, Cu 324.7, Cd 228.8, Pb 217.0, In 451.1, Na 589.0, K 767.0, Mg 285.2, Ca 422.7, and Sr 460.7; air 8.0 L/min, acetylene 2.5 L/min. Reagents. An indium solution (100 mg In/mL) was prepared by dissolving 10.0 g of indium metal (99.9999% purity) in 40 mL of 14 M nitric acid and diluting to 100 mL with water. Standard solutions of heavy metals (1 mg metal/mL, in 1 M hydrochloric or nitric acid) were prepared from chromium, manganese, cobalt, nickel, copper, cadmium, and lead metals, and diluted to appropriate concentrations with 0.1 M hydrochloric or nitric acid immediately before use. Ionic surfactant solutions were prepared by dissolving sodium oleate (Nakarai Chemicals), sodium dodecyl sulfate (Nakarai Chemicals), or benzalkonium chloride (Tokyo
805
computer-controlled programmable monochromator ( 2 ) , Nippon Jarrell-Ash JE-50; grating: 1180 lines/mm, 1.6 nm/mm; slit width: 20 pm; number of accumulation: 2500; measuring time for each element: 25 s HITAC 10-11, 8-kW Nippon Koshuha, 27.12 MHz, 1.2 kW regulator: Kojima GM-2A; coolant: 1 2 L/min; plasma: 0 L/min; carrier: 1 L/min Cr(I1) 283.56, Mn(I1) 257.61, Co(I1) 228.62, Ni(I1) 231.60, Cu(1) 324.75, Cd(1) 228.80, Pb(I1) 220.35 14 mm above load coil
Kasei Chemicals) in 70% (v/v) ethanol. Artificial seawater was prepared by the formula of Lyman and Fleming (3). Water was purified by ion exchange. All reagents used were of reagent grade, except for surfactants (extra pure reagents). Recommended Procedure. Place 1200 mL of water or seawater in a flotation cell (Figure lB), add l mL of indium solution, and adjust the pH to 9.5 with 0.3 M sodium hydroxide solution while stirring with a magnetic stirrer. Place a bubbler in the flotation cell, and add 2 mL of sodium oleate solution (1mg/mL) and 1 mL of sodium dodecyl sulfate solution (4 mg/mL). While gently stirring, pass nitrogen for 3-5 min to obtain complete mixing and flotation of the precipitates with the aid of numerous tiny bubbles (diameter below 0.5 mm). Suck the precipitates which have become mixed with foam into a sampling tube. Add 1 mL of sodium dodecyl sulfate solution (4 mg/mL) to the water sample, pass nitrogen, and suck the precipitates once more as described above. From the sampling tube, remove the silicone rubber stopper and the tubing connected to the aspirator. Wash the lower end of the sampling tube with 7 M nitric acid followed by water, and set it on a bell jar for suction filtration. Add two 1-mL portions of 99.5% (v/v) ethanol to break down the foam, and suck off the filtrate. Wash the precipitates with three 1-mL portions of water, and suck off the washings. Add 2 mL of 14 M nitric acid to dissolve the precipitates, collect the filtrate in a 5-mL volumetric flask, wash the sintered-glass disk and vitreous-silica wool with water, and dilute to the mark. Determine heavy metals in the solution by ICP-AES. Construct calibration curves using the solutions prepared by taking diluted standard solutions containing 0-30 pg of heavy metals, 1 mL of indium solution, and 2 mL of 14 M nitric acid in a 5-mL volumetric flask and diluting to the mark with water.
RESULTS AND DISCUSSION Flotation of I n d i u m Hydroxide Precipitates. The optimal conditions for flotation were examined as follows. Indium hydroxide was precipitated at different pHs from 200 mL of water or artificial seawater containing 20 mg of indium, and floated with the aid of ethanolic solutions of surfactants by 10-30 s of nitrogen bubbling. The precipitates on t h e solution surface were sucked into a sampling tube, and indium was determined by flame photometry after dissolving t h e precipitates. Figure 2 shows the indium recovery as a function of pH. The percentage of indium precipitated was obtained by filtering the solution through a 1.2-pm filter paper (Toyo Roshi No. 5C) after p H adjustment and determining indium in the filtrate. For both water and artificial seawater, satisfactory flotation was achieved with sodium oleate plus sodium dodecyl sulfate (anionic surfactants). The precipitates were completely floated and supported on the solution surface by a stable foam layer over the pH range 7.8-10.5 for water and 5.8-10.1 for artificial seawater. With sodium oleate only, flotation was successful for water, but redispersion of the precipitates during collection of the precipitates occurred for artificial seawater because a stable surface foam layer was not formed. With
806
ANALYTICAL CHEMISTRY, VOL. 52, NO. 6, MAY 1980 100
Table 11. Coprecipitation and Flotation of 0 . 1 p g of Cadmium at pH 9 . 5 sample, indium 115rnCd 1200 mL added, mg recovered, % water watera artificial seawater
100 100
1
91 99 91 95,97
::1
a 5 p g each of Mn(II), Fe(III), Ni, Cu(II), Zn, and Pb were added.
I
W
> 0 U
O
z
80
5 -
Table 111. Coprecipitation and Flotation of Cadmium and Copper(I1) with 100 mg of Indium at pH 9 . 5 sample, 1200 m L
water artificial seawater
heavy metals
added,
found,a lig
E
4.0 4.0
4.0 4.0
60
Cd cu
5.0 5.0
4.5 4.9
40
-
Cd
i cu i Cd cu
4.0 4.0
3.6 4.0
20
-
4.0 4.0
4.5 4.2
Cd cu
10.0 10.0
9.2 9.3
Cd cu
10.0 10.0
9.2 9.5
a By atomic absorption spectrometry. tion and flotation at pH 9.0.
,
I
I
8
I
9
10
11
12
I
I
r
-I I
Pg
’1
I i
I
p ’ , 6 7
i
SEAWATER
ARTIFICIAL
0
0-3
I
I
.
I
.
Coprecipita-
sodium dodecyl sulfate only, 100% of indium was recovered from water a t p H 9.5, but the recovery fell to 7% for artificial seawater. Flotation with benzalkonium chloride (cationic surfactant) was possible over the pH range 10.5-12.0 for water, b u t impossible for artificial seawater. Therefore, combined use of sodium oleate and sodium dodecyl sulfate is most recommended for flotation. Coprecipitation a n d Flotation of Traces of C a d m i u m and Copper(I1). The p H where coprecipitation and flotation
are carried out must be selected from standpoints of complete coprecipitation of the desired heavy metals, minimization of the magnesium coprecipitation, and successful flotation. For example, the percentage of cadmium coprecipitated with indium hydroxide from 50 mL of water containing 1Fg of labeled cadmium and 10 mg of indium was 82% at p H 8.0, but greater than 96% over the p H range 9.0-10.0 (96, 97% at pH 9.0; 100% a t p H 9.5; 96,100% at p H 10.0). In the same pH range, complete coprecipitation of other heavy metals can
Table IV. Multielement Preconcentration and Determination of Heavy Metals in Water and Artificial Seawater heavy metals, p g sample, Mn Ni cu Pb cr co 1200 mL noes water
artificial seawater
Cd
1
added found
3 4
3 3
3 3
3 4
1 1
1 1
1 1
2
added found
10 11
10 11
10 11
10 10
3 4
3 3
3 3
3
added
found
30 30
30 31
30 30
30 33
10 11
10 10
10 10
added found
3 4
3 4
3 3
3 3
1 1
1
1
1
1
5
added found
3 3
3 4
3 3
3 3
1 1
1 1
1 1
6
added
10 10
10 10
10 10
10 9
3 3
3 3
3 3
30 18
30 29
30 30
30 27
10 10
10 9
10
found added foundb
10 9
10 10
10 10
10 11
3 N. D.C
3 3
3 3
4
found 7
8
added
a The following quantities of Al and Fe(1II) were added: 1 0 p g each for nos. 4 and 5; 30 pg each for nos. 1, 3, and 7 ; 300 p g each for no. 2. By atomic absorption spectrometry.
10
each for nos. 6 and 8; 100 N o t determined.
pg
807
Anal. Chem. 1980, 52. 807-812
be expected from the results for coprecipitation with aluminum hydroxide (1). Because lower pHs are preferred for the separation from magnesium, pH 9.5 was selected for coprecipitation and flotation. The recoveries of cadmium and copper(I1) by the recommended preconcentration procedure were examined radiochemically or by atomic absorption spectrometry. Table I1 shows t h a t 0.1 pg of llSrnCdlabeled cadmium in 1200-mL samples (optimal volume for easy collection of the floated precipitates) was recovered in greater than 90% yields with 50-100 mg of indium a t p H 9.5. For water, a better recovery of cadmium was obtained in the presence of traces of other heavy metals. Table I11 shows that cadmium and copper(I1) a t the low pg/L level were quantitatively recovered with 100 mg of indium over the pH range 9.0-9.5. The blank values through the whole procedure were below the lower limits of determination (0.2 pg for cadmium, 0.5 pg for copper). For artificial seawater, alkali and alkaline earth metals accompanying the desired heavy metals, determined by flame photometry or atomic absorption spectrometry, were 1-3 mg for sodium, 3-4 mg for magnesium, 1-1.5 mg for calcium, 0.05-0.1 mg for potassium, and 0.03-0.04 mg for strontium. Therefore, initial concentrations of these metals were reduced to 1/&/20 for sodium and potassium, and ca. ' / z for alkaline earth metals. Multielement Preconcentration and Determination of Traces of Heavy Metals. Heavy metals a t the low pg/L level in water or artificial seawater were simultaneously preconcentrated and determined by the recommended procedure.
Calibration curves for manganese, nickel, copper, and lead were linear up to at least 30 pg, and the scattering of the points was less than 1 pg. For chromium, cobalt, and cadmium, calibration curves were linear up to a t least 10 pg, and the scattering of the points was less than 0.5 pg. Five mg of sodium, 5 mg of magnesium, 2 mg of calcium did not interfere with the determinations. Table IV shows the results obtained for seven heavy metals in 1200-mL samples. For water, blank values through the whole procedure were zero for nickel, copper(II), lead, chromium(III), cobalt, and cadmium, and 1 pg (1, 1, and 2 pg) for manganese(I1). The addition of salts for the preparation of artificial seawater increased blank values for two metals as follows: 3 pg (3, 3, and 4 pg) for manganese(I1) and 4 pg (4,4, and 5 pg) for lead. The heavy metals a t the low pg/L level in water and artificial seawater were determined with satisfactory results, but for sample no. 7 a lower value was obtained for manganese(I1). The same phenomenon was observed in coprecipitation and flotation with aluminum hydroxide precipitates (I). The time required for the preconcentration was ca. 40 min.
LITERATURE CITED (1) Hiraide, M.; Yoshida, Y.; Mizuike, A. Anal. Chim. Acta 1976, 87, 185. (2) Kawaguchi, H.; Okada, M.; Ito, T.; Mizuike, A. Anal. Chim. Acta, Comput. Techniques Optimization 1977, 95, 145. (3) Sverdrup, H. U.; Johnson, M. W.; Fleming, R. H. "The Oceans: Their Physics, Chemistry, and General Biology"; Prentice-Hall: Englewood Cliffs, N.J., 1942; p 186.
RECEIVED for review October 15,1979. Accepted January 17, 1980.
Matrix Effects on the Raman Analytical Lines of Oxyanions A. G. Miller" Research Department, Rockwell Hanford Operations, Richland, Washington 99352
J. A. Macklin Department of Chemistry, University of Washington, Seattle, Washington 98 195
The characteristics of Raman analytical lines are frequently affected by changes in the chemical environment of the vibrating molecule. Aqueous solutions containing pairs of the following anions, alumlnate, C104-, Cr042-, NO3-, POP-, SO4*-, and NO,- have been studied as a function of increasing Na' concentration. Typical effects noted are line broadening and a blue shift of the A, lines of high-symmetry oxyanions with Increasing sodium content. Spectral changes are generally Interpreted In terms of contact ion pair formation with sodium. Analytical ratios derived from the analytical lines of analyte and internal standard oxyanions are evaluated in terms of matrix independent character. The classical peak area ratio is not necessarily the best analytical measure of concentration.
The quantitative measurement of Raman intensities is frequently complicated by varying background, changes in band shapes with changing matrix, and the lack of absolute intensity measurements. Irish and Chen (I) have outlined the principles of quantifying the Raman signal and reviewed some of the varied applications of laser Raman spectroscopy 0003-2700/80/0352-0807$0 1.OO/O
(LRS) in analytical chemistry. The conventional technique in quantitative LRS is to relate analyte peak areas to that of an internal or external standard. The use of peak areas is preferred because chemical influences may alter the shape of the Raman band. The internal standard, if practicable, cancels difficult-to-control factors such as index of refraction and variations in source brightness. Many of the analytical applications reviewed by Irish and Chen were to oxyanions for which LRS is particularly well suited. In later work, A. L. Marston ( 2 ) applied LRS to the determination of oxyanions in high salt, nuclear chemical waste solutions. Peak heights were used rather than areas. The advantages of LRS are best revealed in a similar application a t Rockwell Hanford Operations, where up t o six oxyanions can be simultaneously determined ( 3 ) . Peak heights have also been used in this laboratory for the following reasons: (1) peak heights could be manually measured much more rapidly and accurately than the associated arear; and (2) peak heights are less subject to spectral interferences than the area technique because of the smaller spectrum segment necessary in the measurement. One peak height inaccuracy due to matrix effects was noted: the relative molar intensity of nitrite 6 1980 American Chemical Society
