Anal. Chem. 1980, 52, 117-120
of the supplementary material from this paper on microfiche (105 X 148 mm, 24X reduction, negatives) may be obtained from the Business Operations Office, Books and Journals Division, American Chemical Society, 1155 16th St., N.W., Washington, D.C. 20036. Remit check or money order $6.50 for photocopy or $3.00 for microfiche referring to code number ANAL-80-JAN.
LITERATURE CITED (1) Wester, P. 0.; Brune, 0.; Samsahl, K. Int. J . Appi. Radiat. Isot. 1963, 75, 59-67. (2) Guzzi, G.; Pietra, R.; Sabbioni, E. €URATOM(Refs.) EUR 5282e, 1974. (3) Tjioe, P. S.; de Goeij, J. J. M.; Houtman, J. P. W. J . Radioanal. Chem. 1973, 76, 153-164. (4) Schumacher, J.; Maier-Borst, W.; Hauser, H. J . Radioanal. Chem. 1977, 37, 503-510. (5) Girardi, F.; Sabbioni, E. J . Radioanal. Chem. 1968, 7 , 169-178. (6) Torok, G.; Scheienz, R.; Fisher, E.; Diehl, J. F. Fresenius' 2. Anal. Chern. 1973, 263, 110-115. (7) Van der Sloot, H. A. Thesis, Free University, Amsterdam, 1976. (8) Massee, R.; Van der Sloot, H. A.; Das, H. A. J . Radioanal. Chem. 1977, 35, 157-165. (9) Van der Sloot. H. A.; Wais, G. D.; Das, H. A. Anal. Chim. Acta 1977, 90, 193-200. (10) Wijkstra, J.; Van der Sloot, H. A. J . Radioanal. Cbem. 1978, 4 6 , 379-388. (11) Van Eenbergen, A.; Bruninx, E. Anal. Chim. Acta 1978, 98, 405-406. (12) NBS certificates SRM 1571, 1570, 1573, 1575, and 1577.
117
(13) Schelenz, R.; Diehl. J. F. "Accuracy in Trace Analysis: Sampling Sample Handling, Analysis", Voi. 11; Natl. Bur. Stand. ( U . S . )Spec. Pubi. 422; U.S. Government Printing Office: Washington, D.C., 1976, pp 1173-1 180. (14) Nadkarni, R. A.; Morrison, G. H. Anal. Chem. 1973, 45, 1957-1960. (15) Bowen, H. J. M. J . Radioanal. Chem. 1974, 79, 215-226. (16) Nadkarni, R. A. Radiochem. Radioanal. Lett. 1977, 30, 329-340. (17) Heydorn, K. "Accuracy in Trace Analysis: Sampling, Sample Handling, Analysis", Vol. I; Natl. Bur. Stand. (U.S.) Spec. Pub/. 422; U S . Government Printing Office: Washington, D.C., 1976, pp 127-139, (18) Tjioe, P. S.; de Goeij, J. J. M.; Houtman, J. P. W. J . Radioanal. Chem. 1977, 37 51 1-522. (19) Gaudry, A.; MaziBre, B.; Comar, D. J . Radioanal. Chem. 1976, 29. 77-67. (20) Behne, D.; Jurgensen, H. J . Radioanal. Chem. 1978, 42, 447-453. (21) Nagy, L. G.; Torok, G.; Feuer, L. J . Radioanal. Chem. 1977, 37, 23 1-242. (22) Lievens, P.; Versieck, J.; Cornelis, R.; Hoste, J. J . Radioanal. Chem. 1977, 37, 483-496. (23) Laui, J. C.; Rancitelli, R. A. J . Radioanal. Chem. 1977, 38, 461-476. (24) Laul, J. C.; Nielson, K . K.; Wogman, N. A. Proc. Conf. Nuclear Methods in Environmental and Energy Research, Columbia, Mo., 1977, (CONF771072) 198-209. (25) Hoede, D.; Van der Sloot, H. A,, Anal. Chim. Acta, in press.
RECEIVED for review June 29, 1979. Accepted September 10, 1979.
Determination of Manganese in Seawater by Flameless Atomic Absorption Spectrometry after Pre-concentration with 8-Hydroxyquinoline in Chloroform Gary P. Klinkhammer Graduate School of Oceanography, University of Rhode Island, Kingston, Rhode Island 0288 7
A method is described for determining manganese in a seawater matrix for concentrations ranging from about 30 to 5500 ng/L. The samples are extracted with 4 mM 8-hydroxyquinoline in chloroform and the Mn-oxinate in the organic phase is then back-extracted into 3 M "0,. The manganese concentrations are determined by flameless atomic absorption spectrophotometry. The blank of the method is about 3.0 ng/L and the precision from duplicate analyses is f9 % ( 1u).
With our instrumentation, manganese concentrations down
to 100 ng/L can be detected by direct injection into a graphite furnace. The quinolinol extraction method described here decreases the effective detection limit at least 250 times. This pre-concentration step is necessary in marine studies since most open ocean waters have manganese concentrations less than 50 ng/L. For example, in a recent study of distributions in t h e Pacific Ocean ( I ) , 1200 samples were analyzed for manganese. Ninety percent of these samples had Mn concentrations below the detection limit of direct injection. This paper demonstrates that this extraction technique is precise a n d accurate (f9%) and generates a blank of only 3 ng/L. T h e nonselectivity of 8-hydroxyquinoline (quinolinol or oxine) has made possible a wide range of analytical applications (2). Moeller (3)was the first to present systematic results using 8-hydroxyquinoline in chloroform to extract metals from aqueous solutions b u t his work did not include manganese. Later, Gentry and Sherrington ( 4 ) used 1 % solutions of quinolinol in chloroform to extract a number of elements from 0003-2700/80/0352-0117$01.00/0
laboratory solutions including manganese. A comprehensive study of metal oxinates was presented by Stary ( 5 ) . He found that, by varying t h e pH, 32 metals could be separated from water using 8-hydroxyquinoline in chloroform. Stary determined that 0.01 M solutions would extract 1005'0 of the Mn(I1) from aqueous solutions if the p H was maintained between 6.7 and 10. The lack of selectivity that makes 8-hydrox>quinolinesuch a versatile chelate for extractions from simple matrixes accounts for its limited use in seawater analyses (6). Quinolinol-chloroform extraction has been used t o separate uranium ( 7 ) and other trace elements (8, 9) from seawater but with limited success. The method discussed in this paper was used to make t h e first comprehensive studies of t h e distribution of manganese in seawater ( I , IO).
EXPERIMENTAL Cleaning Plastics. Most seawater has a manganese concentration of about 30 ng/L ( I O ) . At these levels the cleaning of storage bottles and labware becomes a critical aspect of the analysis. By adhering to the following procedure, storage blanks become undetectable. Use only hard linear polyethylene plasticware. For reasons not understood, samples stored in soft plastic bottles cannot be extracted cleanly. Rinse all containers with deionized water and do an initial acid wash by swirling a small volume of concentrated HN03. Then fill the bottles with deionized water and let this dilute acid work overnight. Discard the acid and rinse each container thoroughly with deionized water. Rinse the collection bottles three times with the sample before filling. Open ocean water should be acidified to pH 2 with ultra-pure HCl as soon as possible after collection to prevent adsorption. If the samples contain high amounts of organics, additional experiments S 1979 American Chemical Society
118
ANALYTICAL CHEMISTRY, VOL. 52, NO. 1, JANUARY 1980
should be performed since acidification can flocculate Mn with organic material (11). Two experiments were performed to determine the effectiveness of this cleaning technique. The effects of any adsorption or desorption were determined by periodically measuring the Mn concentrations in aliquots of a Sargasso Sea water sample. The water was collected in June 1974 (10) and was analyzed the first time in December 1975. Aliquots of this sample were analyzed 13 times during the following two years. The mean manganese concentration was 30 ng/L. One standard deviation about the mean of these determinations was 3 ng/L but there was no systematic change in the concentration over the two-year period. At the end of this two-year experiment, a 1-L aliquot of this Sargasso Sea sample was poured into a recently cleaned bottle. Aliquots of this 1-L sample were analyzed for Mn after 1 week and after 6 months. The mean and range of these determinations was 31 A 3 ng/L. Since the uncertainty of this measurement, determined from 59 duplicate analyses of seawater, is f9% (I), these experiments demonstrate that no measurable adsorption or desorption of Mn occurs in bottles cleaned with this procedure. A tracer experiment supported the contention that adsorption was insignificant. A 1-L seawater sample was spiked with 54Mn and 1-mL aliquots were counted at 1-week intervals for 17 weeks. The measured activity, in counts per min per mL, at the initiation of the experiment was 259 A 8 (16). The predicted activity a t the initiation of the experiment calculated from the activity in the undiluted spike was 271 cpm/mL. The measured activity a t the end of the 17-week period, corrected for decay, was 269 A 12 cpm/mL. These experiments demonstrate that, if adsorption of Mn occurs at pH 2, this process must be so slow that it has no measurable effect ( > 5 % ) on the concentration. Reagents. Hydrochloric Acid. We use G. Frederick Smith (GFS) 6 M HC1 (without further distillation) to acidify samples. The maximum Mri concentration of this acid is between 280 and 550 ng/L. Since 2 mL are required to acidify 1 I, of seawater, the acidification can add 1.0 ng of Mn/L of sample. This acid blank was similar for redistilled acids used to acidify samples drawn during the Geochemical Ocean Section Study (1). " M n Tracer. Carrier-free, isotopically pure "Mn in dilute HC1 was obtained from New England Nuclear. This solution was diluted so that the activity of 1 mL in the well of a NaI detector was about 1500 counts per 10 min. The uncertainty of counting at this level is typically f 3 % , The Mn blank resulting from tracer addition is less than 0.5 ng/L of sample. A m m o n i u m Hydroxide. Starting with G. Frederick Smith ultra-pure ammonium hydroxide, "*OH is fluxed between 2 Teflon bottles. One bottle contains GFS reagent and is warmed with a heat lamp. The other bottle contains deionized water and is water cooled. This refluxed "*OH is about 6 M and has a manganese concentration of 140 ng/L. Typically, 4 mL of this reagent are required per liter of sample to bring the pH up to 9. This NH40H addition can contribute 0.5 ng/L to the manganese concentration. 8-Hydroxyquinoline in Chloroform. GFS chloroform is extracted by shaking 500 mL in a separatory funnel for 2 min with 200 mL of 3 M HNOJ. The CHC13 is taken into a Teflon bottle with 0.3 g of GFS 8-hydroxyquinoline. This solution is 4 mM in quinolinol and has a shelf life of several weeks, if stored in the dark, The quinolinol reagent has a Mn concentration of about 17 ng/L and 80 mL are required to extract 1 L of seawater. This addition can result in a Mn blank of 1.4 ng/L. Procedure. Reagent Addition. The methods outlined in this section are for 250- and 15-mL sample volumes. The volumes given in parentheses are for the smaller sample size. Approximately 250 mL (15 mL) of sample at pH 2 are weighed into a linear polyethylene container. One milliliter of the 54Mn tracer is added and the sample is shaken, and allowed to equilibrate overnight. Another milliliter of the tracer solution is pipetted into a counting vial and serves as the standard. An experiment was performed to ensure that the equilibration of the tracer with the sample was complete. Twenty-six samples were divided into two aliquots. One aliquot was spiked with the tracer and extracted less than 24 h later. The other aliquot was allowed to equilibrate at least 4 days before being extracted with oxine. Manganese concentrations in 86% of these duplicates agreed within the analytical uncertainty (la) of the measurement.
After equilibration, about 1.0 mL (60 pL) of refluxed NH40H are added. The pH is checked a t this point to ensure that it is between 8 and 9.5. The sample is poured into a separatory funnel and extracted with 20 mL (3.0 mL) of quinolinol reagent by shaking for 1.5 min. The organic phase is taken into a small Teflon bottle with 1.0 mL (100 pL) of ultra-pure 3 M "OB. The Teflon bottle is rinsed with deionized water and shaken dry before the 3 M HN03 is pipetted into it. This rinsing serves two purposes: it rinses out the previous sample and ensures that the volume of the aqueous phase will be somewhat greater than 1.0 mL (100 pL). The Mn-oxinate is then back-extracted into the acid by shaking for 1min. The separation is complete in a few minutes and exactly 1.0 mL (100 pL) of the aqueous phase is removed from the surface of the chloroform with a pipet and dispensed into a clean plastic vial. Extraction Efficiency. The overall efficiency of the two extractions is calculated by counting the 835-keV y activity of "Mn in the 1.0 mL (100 pL) acid concentrate and comparing this activity with the activity in the 1.0-mL standard. If the standard and concentrates are counted in the well of a NaI detector, any change in counting efficiency created by the difference in volumes between the 1.0-mL standard and the 100-pL concentrate is insignificant. This observation was made by evaporating a 1.0-mL standard to dryness and counting the activity at increments of 0.1 mL from 0 to 1.2 mL. The activity did not change during the experiment outside a A470 counting uncertainty. The theoretical yield of the method is less than 100% since only 80-90% of the aqueous phase is removed after the backextraction. This loss is tolerated in order to maintain an accurate concentration factor and does not affect the precision since the loss is corrected for by counting the "Mn activity in the 3 N HN03 concentrate. The average recovery from twelve hundred 250-mL samples was 69.5 A 7.8% (la) while the efficiency from forty-eight 15-mL samples was 61.7 f 12.2% (la). Since the efficiency is measured for each concentrate, the uncertainty in the yield for any particular sample is reduced to counting statistics (f3%). Manganese Concentrations. After y counting, the manganese concentration in the concentrate is measured by comparing its atomic absorption signal with the response of a standard in 3 M HN03. A Perkin-Elmer 603 Spectrophotometer, 2100 Graphite Furnace, and Deuterium Arc Background Corrector were used for this study. The drying, charring, and atomization temperatures were set at 100,1100, and 2500 "C, respectively. The output signal was amplified up to 10 times. The sample concentration is calculated by dividing the AA concentration by the efficiency times the concentration factor (i.e. 250/1.0 = 250 or 15/0.1 = 150). One of the potential problems with atomic absorption measurements (especially in the graphite furnace) is uncertainty due to salt effects. Two observations suggest that matric effects are not serious problems in this method. First the major cation in seawater is sodium at 435 mM, but the sodium levels measured in 45 randomly selected 3 M "OB concentrates was 1.8 f 1.4 mM. This level is an order of magnitude below the sodium concentrations of solutions for which detectable matrix effects for manganese were found by Segar and Contillo (12). Second, the manganese concentrations determined after extracting standards in a seawater matrix agree reasonably well with values reported by the EPA (Table I). Blanks. The reagent blank expected from adding the HC1, ",OH, and quinolinol reagents is about 3 ng/L. This blank does not include any contribution from labware, dust, or any other random sources of contamination during the analysis. The total blank (including random sources) was measured by re-extracting samples after re-adding the reagents but without further tracer addition. That is, after a sample had been extracted, the stripped water was acidified with the same amount of HC1 added initially, then the pH was adjusted back to pH 9 with "*OH. Finally, the quinolinol reagent was added and the stripped water was extracted as usual. The 3 M HNOBconcentrate from this blank was counted and the Mn was measured by AA. Using this scheme, the total blank or the blank due to reagents plus random contamination during the analysis can be calculated from the following equation (if MnB is less than Mns). blank =
MnB - (EB/Es)Mns CF X E
ANALYTICAL CHEMISTRY, VOL. 52, NO. 1, JANUARY 1980
110
Table I. Comparison of Methods manganese, ng/L sample
ref.
no.
Hudson River
13
Sargasso Sea Pacific Ocean Pore Water Deep Two EPA
10
27 S 26 S -10 B 135
salt,
14
9 10 1104
15
7BC20B1 9BC26B3
14
8-3 1 2
3
OIiw
direct injection
0.89
900
1.03 30.7 36.3
1900 6810 < 200
34.7 34.7 34.7 34.7 34*7
7 40 4870 9 30 7 30
36,3 36.3 36.3
2880
110
4290 4730
The Chelex-100 method used for these analyses is given in ( 1 3 ) . determinations given in parentheses. MnB and Mns are the manganese concentrations determined by atomic absorption in the blank concentrate and sample concentrate, respectively. E B and Es are the ratios of the "Mn activity in the blank or sample divided by the activity of the same standard. (The first term in the numerator is the Mn concentration in the blank concentrate measured by AA which includes the total blank; the second term is the concentration expected if the blank is zero.) CF is the conce_ntrationfactor which is common to the sample and the blank. E is the average efficiency of the separation (Le. 69.5%). The total blank was calculated using the above equation from 110 sampleblank pairs and the average value is 2.5 ng/L. These calculations demonstrate that the total blank is not statistically different from the reagent blank alone (3.0 ng/L); that is, random sources of contamination were negligible. Since reagent concentrations vary and the maximum blank expected is only 10% of the lowest sample concentration, data are not corrected for a blank.
RESULTS AND DISCUSSION Three types of comparisons are presented in this report as a further test of the analytical technique. First, the manganese concentrations in the same samples were determined with the quinolinol technique described here and by direct injection into the graphite furnace. Second, the manganese concentrations of four samples were measured by AA after separation with quinolinol and with Chelex-100 ion-exchange resin (13). Third, seawater dilutions of trace metal standards obtained from the environmental agency (EPA, Environmental Monitoring and Support Laboratory, Quality Assurance Branch, Cincinnati, Ohio) were extracted with quinolinol-chloroform. The accuracy of this method was determined by comparing the quinolinol results with values reported by the EPA. These data are presented in Table I. Twelve samples of various types were analyzed by both direct injection and quinolinol extraction. The atomic absorption signals from direct injection were calibrated vs. standard concentrations in Sargasso Sea water while the absorbances of the quinolinol concentrates were compared with 3 M H N 0 3 acid standards. The natural samples were collected from the Hudson River (13),the Sargasso Sea (IO),and the Pacific Ocean ( 1 4 , 15). T h e direct injection and quinolinol results agree within a coefficient of variation of 5.1 7%. This precision is within the uncertainty of f 9 % found by analyzing 59 seawater duplicates ( I ) . This agreement has important implications. First, quinolinol extraction of samples which have been acidified to p H 2 captures a t least 90% of the total manganese (defined as atomizable at 2500 "C). Since none of the seawater samples were filtered prior to acidification, this total includes par-
Chelex-100 resina 1200 2100 5820
150
reported
___
--__.
___
quinolinol extractionb 1010
2300 5880
l5Oi lO(4) 7 5 0 + 1.00 ( 2 ) 4730 i 1.6 ( 2 ) 1170 510 115
2940 4260 4410
i
140 (2)
i
I70 (2) 770 ( 2 )
i
The limits given are l o based on the number of
ticulate matter. Second, the Hudson River results demonstrate t h a t the method works over a wide salinity range in samples containing a variety of pollutants (13). Third, the method is applicable over a wide range of concentrations. To compare the quinolinol method with these other techniques, the data presented in Table I are for samples which contain more manganese than deep ocean water (50 ng/'L). Still, there is good agreement between quinolinol and Chelex or direct injection for the two samples containing only 100 ng/L (the Sargasso Sea and Deep Tow samples). T h e separation of trace elements with Chelex-100 has become a popular technique in seawater analyses 16). The theory and mechanics of ion exchange are so different from solvent extraction that a comparison of these two methods is an important experiment. T h e differences in Mn concentrations determined by the two methods (Table I) is within analytical uncertainty. This agreement was found even though the samples cover wide ranges of salinities, concentrations, and environmental settings. The three trace metal standards prepared by the EPA provide a measure of the accuracy of this method, at least for samples in the mid-concentration range of natural waters. The mean value of duplicate determinations of these standard seawater solutions agrees with the reported concentrations with a coefficient of variation of 4.9%. These results demonstrate that the accuracy of the quinolinol method is comparable to the precision ( f 9 % ) . T h e pre-concentration of manganese from natural waters with 8-hydroxyquinoline followed by quantitative analysis by flameless atomic absorption spectrophotometry provides a precise and accurate (f9W) method for determining the concentration of this element. T h e blank of the method is about 3 ng/L. If a seawater sample is acidified to p H 2 but not filtered, this method accounts for at least 90% of the "total manganese". The method is applicable over a wide range of sample volumes and concentrations.
ACKNOWLEDGMENT The trace metal samples were provided by the Environmental Protection Agency, Cincinnati, Ohio. Technical assistance was provided by Frank DiMeglio, Mike Doyle, Ron Stevens, and the rest of the staff at the Rhode Island Nuclear Science Center.
LITERATURE CITED (1) Kiinkhammer, G. P.; Bender, M. L. Earth Planet. Sci. Lett. in press. (2) Holiingshead, R. G. W. "Oxine and Its Derivatives"; Butterworths Scientific Publications: London, 1954; Vois. I-IV. (3) Moelier, T. Ind. Eng. Chern., Anal. Ed. 1943, 75. 346-349. (4) Gentry, C. H. R.; Sherrington, L. G. Analyst(London), 1950, 75, 17-21.
120
Anal. Chem. 1980, 52, 120-124
(5) Stary, J. Anal. Chim. Acta 1963, 28, 132-149. (6) Riley, J. P.; Robertson, D. E.;Dutton. J. W. R.; Mitchell, N. T.; Williams, P. J. "Chemical Oceanography", Riley, J. P.,Skirrow, G., Eds., Academic Press: London, 1975; Vol. 111, Chapter 19. (7) Milner, G. W. C.; Wilson, J. D.; Barnett, G. A,; Smales, A. A. J . Elecfroanal. Chem. 1961, 2, 25-38. (8) Brooks, R. R. Talanta 1965, 12, 511-516. (9) Armitage, B.; Zeitin, H. Anal. Chim. Acta 1971, 53, 47-53. (IO) Bender, M. L.; Klinkharnmer, G. P.; Spencer, D. W. Deep-sea Res. 1977, 2 4 , 799-812. (11) Sholkovitz, E. R. Geochim. Cosmochim. Acta 1976, 4 0 , 831-845.
(12) Segar, D. A.; Cantillo, A. Y. "AnaMicai Methods in Oceanography", Gibb, T. R. P., Jr., Ed., ACS: Washington, D. C., 1975; Chapter 7. (13) Kiinkhamrner, G. P.; Bender, M. L., submitted for publication in Esfuar. Coast. Mar. Sci. (14) Klinkhammer, G. P., submitted for publication in Chem. Geol. (15) Klinkhammer, G. P., submitted for publication in Earth Phnet. Sci. Lett.
RECEIVED for review July 30,1979. Accepted October 10,1979. Work supported by the NSF under contract OCE 77-05184.
Determination of Silicon and Aluminum in Biological Matrices by Inductively Coupled Plasma Emission Spectrometry F. E. Lichte' and S. Hopper Environmental Trace Substances Research Center, University of Missouri, Columbia, Missouri 6520 1
T. W . Osborn" The Procter & Gamble Company, Miami Valley Laboratories, P.O. Box 39175, Cincinnati, Ohio 45247
An analytical method for the determination of silicon and aluminum in blood, urine, feces, and animal feed is described. The samples were ashed, fluxed wlth sodium carbonate, and dissolved in hydrochloric acid. The solutions were analyzed by Induction Coupled Plasma-Atomic Emission Spectrometry (ICP-AES). The 251.6mm emission line was used to measure silicon, and the 394.4-emission line was used to measure aluminum. The method was tested by analyzing samples to which known quantities of silicon and aluminum had been added. The method was further tested by analyzing pure water samples to which known quantities of silicon and aluminum were added. The precision of the method was limited by the instability and heterogeneity of the biological samples.
Considerable interest has developed concerning the behavior of trace elements in biological systems (1-3). Two elements of current interest are silicon and aluminum, ubiquitous elements t h a t represent major fractions of the lithosphere. Silicon is an essential trace metal ( 4 ) ,although in some specific forms it may produce toxic reactions (5,6). Aluminum may be a n essential trace metal, although some of its compounds can cause toxic reactions ( 7 ) . I n pharmacokinetic or toxicology studies, the preferred way t o find out how animals absorb, distribute, and excrete a n element is to use a radioisotope of the element. Unfortunately, t h e radioisotopes of silicon and aluminum have such short half-lives or low specific activities that they are not suitable for biological studies. Therefore, we sought a method of analysis t h a t could be used for tracing the absorption, distribution, and excretion of silicon and aluminum without using radioisotopes. Techniques t h a t measure single elements, such as nitrous oxide flame emission (8) dc arc or spark emission spectrometry (9),graphite furnace atomic absorption ( I O ) , and colorimetry (I1,12) have been used for t h e determination of silicon and aluminum. However, we needed a method that would measure both elements a t once, because we anticipated analyzing a Present address, U.S.Geological Survey, Branch of Analytical Laboratories, Mail Stop Lakewood, Colo. 80225. 0003-2700/80/0352-0120$01.00/0
great many samples, some of which are not large enough to carry out two separate determinations. Inductively coupled radio-frequency plasma-atomic emission spectrometry (ICPAES) was chosen as the analytical technique most likely to meet the analysis requirements (13). ICP-AES is a multielement technique that is relatively free of chemical interferences. It possesses high sensitivity and is particularly useful for the determination of refractory elements such as silicon and aluminum. This paper describes t h e application of ICP-AES for the determination of silicon and aluminum in urine, feces, blood, and animal feed.
EXPERIMENTAL Apparatus. Figure 1 is a block diagram of the po;ychromator and associated equipment. The plasma was viewed axially (14) with the center of the plasma focused onto the entrance slit. Other features of the system are given in Table I. The analytical methods and optimization of the operating parameters will be discussed below. Reagents. All reagents were Analytical Reagent grade or better and included concentrated HCl, Na2C03,NaOH, Na202,NaCl, and deionized/distilled/deionized water. Silicon reference solutions were prepared from both pure quartz and from Fisher certified solution (Lot 2755125-12). The aluminum reference solutions were prepared from Fisher certified solution (Lot 0753439). All dilutions were made on a weight basis in polyethylene to eliminate contamination from glassware. Samples. Samples were obtained from a variety of animal species. The excreta samples were collected from animals housed in stainless steel metabolism cages. Plastic fecal cups were used to prevent contamination of urine samples by feces. The cages were kept in a room with air filters to keep dust from them. The cages and sample collection apparatus were washed with triple distilled water. Animal personnel wore talc-free plastic gloves, hair nets, and protective clothing to reduce the possibility of contaminating the samples. Blood samples were collected using a stainless steel needle and a polyethylene syringe. The samples, after collection,were stored in acid washed, screw-cap polyethylene bottles until they were analyzed. Sample Preparation. The tissues and excreta were prepared for analysis in a Class 100 horizontal laminar flow work station (Contamination Control, Inc.). Samples were weighed into nickel or platinum crucibles. Liquid samples were evaporated to dryness on a hot plate. The crucibles were then covered with the lid and ashed in a muffle furnace for 1 h at 200 "C, 1 h at 400 "C, and 4 h at 600 "C. The platinum crucibles were found to be superior 1979 American Chemical Society
