400
Anal. Chem. 1983, 55,400-403
Table IV. Analyses of Olefin Blend before and after One Hour of Reaction ( w t %) olefin C6 c7 C8 c9 c10
c11
c12 C13 C14
Table V. GLC Analysis of the Liquid from the Self-Metathesis Reaction of lJ3-Tetradecadiene
before reaction after reaction
olefin
16.3 48.0 52.0
Composition of Gas Phase c2 91 c3 9 c4
13.9 1.0 30.5 0.9 29.7 0.3 7.4
the rhenium oxide catalyst. Analysis of the liquid after 1 hour of reaction gave the results shown in Table 111. Also included are the results of the GLC analysis of the 4-nonene sample. For pure 4-nonene, the mole ratio of CS/ClO should be 1.00 and the value from the data in Table I11 is 0.95. These results indicate this sample to be at least 95% 4-nonene. (3) The third example describes the determination of the isomer purity of the symmetrical olefin 5-decene. Because of the symmetry of the 5-decene, the FCM predicts only one product, 5-decene. As a tool for analysis of symmetrical molecules such as 5-decene, an equal mole amount of a nonsymmetrical olefin is mixed with the symmetrical compound to be analyzed. I t has been found advantageous to use 1octene which, on metathesizing with the 5-decene, will yield according to the FCM four olefins, a C2, C6, C12, and C14 olefin. One possible impurity in 5-decene is 4-decene which on metathesizing with the 5-decene/l-octene mixture will yield, according to FCM, five additional olefins, a C5, C7, C9, C11, and C13 olefin. Hence a comparison of the amount of even-carbon-number olefins with the amount of odd-carbonnumber olefins in the product will indicate the isomer purity of 5-decene providing the major impurity is 4-decene. Forty grams of the blended olefins were metathesized over 20 g of the rhenium oxide catalyst. Analyses of the blended olefins before the run and after 1h of reaction time are given in Table IV. These results indicate the isomer purity of the 5-decene to be about 95% with about 5% 4-decene. The results of this analysis are also useful in emphasizing the necessity of keeping the reaction time to a minimum. There are at least six different olefins resulting from the initial reactions all capable of undergoing further metathesis reactions yielding still more different olefins. (4) The fourth example describes the analysis of the isomer purity of a sample of 1,13-tetradecadiene. FCM predicts for this analysis that the products should be ethylene and 1,13,25-hexacosatriene,a 26 carbon triene. On metathesization of 35 g of the tetradecadiene over 20 g of the rhenium oxide catalyst for 1h, the results given in Table V were obtained.
amt, wt %
Composition of Liquid Phase C24 c25 6.7 C26 91.6 C27 1.7 These data indicate the isomer purity of the 1,13-tetradecadiene to be approximately 95%, The major impurity was probably 1,12-tetradecadiene. The accuracy of the data given in the preceding four examples is believed to be about 1to 2% which is about the same accuracy of most of the GLC results. Since the metathesis reaction is stoichiometric, the accuracy can be improved if more care is taken in the GLC analyses and by using higher purity olefin samples.
CONCLUSIONS The preceding four examples demonstrate the flexibility and versatility of a method based on the metathesis reaction for the determination of the location of olefinic bonds in and the isomer purity of olefins. The method is simple, using only readily available equipment, and rapid. Only about 1h of total time was required for each of the four analyses described in this report. In conclusion it is worthwhile to point out that while the four examples in this report. were selected to illustrate different applications, they were also selected because they are examples of practical applications of this method. The purpose of each example was as follows: (1)check isomer purity of 1-octene feed to a metathesis reactor unit, (2) determine isomer purity of a 4-nonene sample for a potential customer, (3) check isomer purity of 5-decene, typical of a number of analyses of symmetrical olefins which are produced by the metathesis reaction of commercially available a olefins, and (4) test a hypothesis that the two olefinic bonds in the tetradecadiene were conjugated. Registry No. 1-Octene, 111-66-0; 4-nonene, 2198-23-4; 5decene, 19689-19-1;1,13-tetradecadiene, 21964-49-8. LITERATURE CITED (1) Bradshaw, C. P. C.; Howman, E. J.; Turner, L. J . Catal. 1967,7,269. (2) Heckelsberg, L. F. U.S. Patent 3676520,July 11, 1972.
RECEIVED for review June 25, 1982. Accepted November 8, 1982.
Industrial Hygiene Personal Sampling of 2-Ethylhexanol and Determination by Flame Ionization Gas Chromatography Joseph Russo' and Shane S. Que Hee" Department of Environmental Health, University of Cincinnati Medical Center, 3223 Eden Avenue, Cincinnati, Ohio 45267
2-Ethylhexanol (2-EH) is the most important and widely used synthetically produced higher aliphatic alcohol (1). It is used principally as an intermediate in the manufacture of 'Presently at Badische Corp., Kearny, N J 07032.
plasticizers, the major one being bis(2-ethylhexyl) phthalate, commonly called dioctyl phthalate (DOP) (2). It is also used in the manufacture of wetting agents, synthetic lubricants, and 2-ethylhexyl acetate, as well as a solvent of nitrocellulose, urea resins, enamels, alkyd varnishes, and lacquers ( 1 , 2).
0 1983 American Chemical Society 0003-2700/83/0355-0400$01.50/0
ANALYTICAL CHEMISTRY, VOL. 55, NO. 2, FEBRUARY 1983
2-EH is a moderate (dermalirritant, a severe eye irritant, a central nervous system1 depressant, and a moderate irritant of the respiratory tract but does cause slight hemorrhaging in the lung ( 3 ) . T h e acute oral LDEOis around 3730 mg/lcg (3). There are no federal standards or even recommended ones for 2-EH. The most similar chemical for which a TLV-TWA (8 h) is available is isoamyl alcohol for which the TLV-TWA is 50 ppm (4). There are no published industrial hygiene personal sampling and analytical techniques for 2-EH. The evolution of such techniques was the aim of this study.
EXPERIMENTAL SECTION Reagent Purity. 2-EH (Fisher Scientific) was found to be 98.4 f 1.9% pure by gas-liquid chromatography (GC) with a Perkin-Elmer 881 chromatograph. The column was a 1.5 ft (1.83 m) X 0.079 in. (200 mm) i.d. iethinless steel column packed with 0.2'% Carbowax 1500 on 80/100 mesh Carbopack C (Supelco). The helium carrier flow rate was 25.0 i 0.3 mL/min, and the injector, column and flame ionization detector temperatures were 250,170, and 250 "C, respectively. The hydrogen and air flow rates to the detector were 30 and 400 mL/min, respectively. The choice of this column was made after evaluation of many moderately polar and polar column packings contained in 6 ft X 0.125 in. (id.) glass and stainless steel columns. The column packed with 0.2% Carbowax 1500 on Carbopack C evidenced a long retention time (>30 min) but with superior peak shape compared with the other packings. The short 1.5 ft column of this packing material exhibited excellent 2-EH peak shape and constant retention times. Its chromatographic characteristics at 170 "C were as follows: separation factor, 43.5; resolution (2-EH/acetone), 3.4; solvent efficiency,256; capacity factor, 51.2; minimum number of required theoretical plates, 37.7; number of theoretical plates, 151; height equivalent of a theoretical plate (HETP), 3.0;"I minimum length of column required for adequate resolution, 11.6 cm. Temperature programming GC (hold 95 "C (1 min), then 4 OC/min to 170 "C for 9 min) revealed only one substantial peak. The purity was assessed by area integration of all peaks on the isothermal chromatogram on a Perkin-Elmer Sigma 1 analyzer. The major impurity appeared to be 2-ethylhexenal(O.4%). The infrared spectrum of the alcohol was identical with that reported in the Aldrich catalog (5). Generation of Test Atmospheres. Teflon gas bags (Cole Parmer) each of 7 L capacity and equipped with a stainless steel inlet/outlet valve and a Teflon septum port were utilized to contain the 2-EH atmospheres. The latter were generated by injecting the calculated amount of 2-EH via a 10-pL Hamilton syringe through a gas chromatographic septum contained in a brass injection port heated to 193 "C (the boiling point of 2-EH is 185 "C ( I ) ) and allowing the vaporized compound to be swept by organic-free air into the bag. The flow rate of this airstream (20 psi) was monitored by a calibrated Fisher Porter rotameter (10 A-1338) with a range of 1.0-6.8 L/min. A small piece of Tygon tubing was utilized to make a butt-to-butt connection between the gas bag inlet valve and the injection port outlet. The concentration of 2-EH in the bag was determined from the known mass injected assuming EI 2-EH density of 0.834 g/mL a t 20 "C ( I ) and measuring volumes before and after injection and bag volume (flow rate multiplied by time). The concentrations generated were 12, 25, 50, 70, and 120 ppm corrected to standard conditions (760 mmHg, 25 "C). Triplicate bags were always utilized for each concentration. Bags were filled and emptied three times at the desired concentration to assure the adsorbing sites on the walls were filled before the bags for the test atmosphere were prepared. Gas bags filled with air delivered at the Sam15 conditions as 2-EH showecl no gas chromatographic peaks. Adsorption to the Tygon around the butt-to-butt joint was standardized by the filling and emptying procedure. There were no memory effects from the 'l'ygon as shown by sampling the gas bags filled with air. Negligible wall desorption/adsorption cycles occurred with this technique since the readings of a Century OV-A portable gas chromatograph, utilizing a flame ionization detector were constant over a half an hour of monitoring. Sampling Media and 2-EH Recovery. Thirteen solid Sam.
401
pling media and two recovery solvents were evaluated in this study (Table 111). Two of the sampling media were commercially available 20/40 mesh activated charcoal (Environmental Control) and 20/40 mesh silica gel (SKC). For the rest of the sampling media (Table 111), 100 mg was packed into 6 mm 0.d. (4 mm id.) Pyrex tubing via a vibrator (10 s) with nonsilanized glass wool plugs a t each end. The tubes were sealed by glass-blowing until use. Acetone and carbon disulfide (0.5,l.O mL) were utilized to effect 2-EH recovery before GC analysis. T o find the most suitable sampling medium and recovery solvent, we performed the following experiments: (a) 2-EH (1pL) was spiked onto the sampling medium in the tubes; 12 L of air was then drawn through at 500 mL/min; the tubes were held overnight at 10 "C, and 2-EH was recovered by the three solvents above, and analyzed by GC, comparing the peak areas to that of 1 pL of 2-EH, in the corresponding volume of solvent. Recovery was accomplished by placing the spiked sampling medium in a 5 mL volume 1cm diameter polyethylene tube, adding the solvent, and shaking periodically for 30 min. The GC calibration curve covered the range 0.5-16 pg using five different injected masses in triplicate. This screening procedure allowed the most promising sampling medium/recovery solvent combinations to be selected using the criterion of >90% recovery. (b) The promising sampling media (here, Porapak Q and Chromosorb 102) in triplicate were then filled with 50% acetone/water; 12 L of air was passed through a t 500 mL/min to evaporate the acetone; the sampling medium was thus saturated with water. The 2-EH spiking and analytical procedures given in (a) were then repeated by using the best recovery solvent(s) (in this case, acetone). This experiment was performed to select which of the test sampling media allowed best 2-EH recovery under conditions of water saturation of the sampling media. This simulates the effects of very humid atmospheres. Again, >90% recovery was used as the selection criterion. (c) The sampling media chosen from (b) (here, Chromosorb 102) were then similarly evaluated utilizing 2-EH atmospheres contained in the Teflon gas bags. Sampling in triplicate was accomplished with calibrated MDA Accuhaler Model No. 808 and MSA Model G pumps over the flow rate range 50-400 mL/min, using sample volumes of 6-18 L, the latter from multiple bags. Recoveries were calculated relative to 100% collection and recovery of the defined 2-EH concentration. (d) The sampling media chosen from (c) (in this case, Chromosorb 102) were then similarly evaluated for 2-EH vapor at 90% relative humidity. This humidity was obtained by the same means as utilized to generate the desired 2-EH concentrations at the known ambient conditions. This procedure allowed evaluation of the effects of relative humidity on the vapor-phase method. (e) The optimal sampling medium in triplicate (in this case, Chromosorb 102) was spiked with 1, 2, and 3 pL of 2-EH (corresponding to 13,26, and 52 ppm 2-EH in a 12-L air sample) under the analytical conditions in (a) and (b) to assess the recovery as a function of loading and to distinguish between sampling and recovery events. Sampling Capacity Estimation. The capacity of the optimum sampling medium was found in the following manner: a tube was packed with six sections of sampling medium (four 10 mg sections followed by two 20 mg amounts) separated by small portions of glass wool. This tube was utilized to sample a 100 ppm concentration of 2-EH in the presence and absence of 90% relative humidity in a gas bag at 200 mL/min for 95 min. The sections were individually analyzed to assess the extent of breakthrough. The saturating capacity for 2-EH was thus found, and calculated for a 100 mg tube in the absence and presence of 90% relative humidity. The duration of sampling and the optimal flow rates could then be varied depending on the concentrations of 2-EH actually encountered and the relative humidity of the atmosphere. Storage Characteristics. The storage ruggedness of the method was then evaluated. Sampling tubes were spiked in triplicate with 1, 2, and 3 pL of 2-EH. These tubes were stored a t room temperature. After 1, 14, and 40 days, the tubes were analyzed and the masses recovered compared with that found from a freshly spiked tube. Versatility of the Method for Other Alcohols. The suitability of the procedure for other alcohols was then evaluated
402
ANALYTICAL CHEMISTRY, VOL. 55, NO. 2, FEBRUARY 1983
Table I. Loading Capacity of Chromosorb 102 Sampling Medium (80/100Mesh)
section
weight, mg
amt of 2-EH found, mg
mg of 2-EH/mg of sampling medium a
1.3 1.6
0.13* 0.16* 0.13* 0.12* 0.09 0.10 0.12 i 0.02 0.14 i 0.02
10.0 2 10.1 3 12.6 4 11.9 5 20.8 6 20.0 av t std dev av* i std dev 1
1.6
1.4 1.9 2.0
Minutes
Asterisk indicates values used for the second average.
Flgure 1. Typical chromatogram for 2-EH estlmation. See the text for details.
Table 11. 'Recovery of 2-EH after Storage on Chromosorb 1 0 2 at Room Temperature storage duration, days
amt of 2-EH, p L
1 1 1
14 14 14 40 40 av i std dev
1
2 3 1
2 3
Table 111. Recoveries with Acetone (0.5 mL) for 2-EH (1pL) on Various Sampling Media
recovery, % 108 106 101 107 97 90 125 95 104 i 11
utilizing 1pL of 1-butanol, n-amyl alcohol, and n-octyl alcohol.
RESULTS AND DISCUSSION This study determined that air concentrations of 2-EH from 12 to 120 ppm in the presence or absence of 90% relative humidity (RH) can be quantitatively collected, using 80/100 mesh Chromosorb 102, and quantitatively recovered with 0.5 mL of acetone independent of water or relative humidity. The concentration (ppm)/efficiencies ( % ) a t 5% R H were (12.3 f 0.1)/(102 f 9), (24 f 1)/(97 f 5), (55 f 1)/(94 f 4), (70 f 1)/(91 f 4), and (116 A 2)/(102 f 6). The overall recovery was thus (87 f 7)%. At 90% RH, the values were 23.5 ppm/96% and 116 ppm/90%. The overall recovery a t 90% R H was thus (93 f 4)%. The capacity of Chromosorb 102 is (14 f 2.0) mg of 2-EH per 100 mg front section independent of relative humidity for a sample volume ranging from 6 to 18 L and sampling flow rates between 50 and 400 mL/min (Table I). The capacity may be dependent on vapor concentration. The storage recovery is also excellent, being (104 f 11%) over 40 days at room temperature (Table 11). A typical chromatogram is shown in Figure 1. In the initial set of experiments designed to rank the sampling media, carbon disulfide was utilized for recovery because of its universal use as a recovery solvent in industrial hygiene analysis. However, six of the sampling media were attacked by carbon disulfide, and the remainder showed low recoveries and precision for 2-EH. Acetone was chosen as a recovery solvent because it had been utilized to recover furfuryl alcohol from Porapak Q (6). Table 111shows the recovery efficiencies with acetone for 2-EH spiked onto the various sampling media. It is evident that Porapak Q and Chromosorb 102 were the best sampling media at 0 % RH. The experimental design involving the neat spike followed by passing through 12 L of air simulated the vapor phase sampling situation better than if the air were not passed through. Greater than 90% recovery implies that quantitative recovery is also possible with the
a
% recov-
% recov-
sampling medium (mesh)
ery i 2 std deva
ery i 2 std dev
alumina (30/60) charcoal (20/40) silica gel (20/40) Amberlite XAD-2 Amberlite XAD-7 Porapak Q (50/80) Porapak R (80/100) Tenax GC (60/80) Chromosorb 1 0 1 (80/100) Chromosorb 102 (80/100) Chromosorb 1 0 3 ( S O / l O O ) Chromosorb 104 (80/100) Chromosorb 106 (80/100)
54 5 1 2 39 i 1 2 50 3 5 78 i 5 70 i 4 92 i 2 54 i 3 4 f 0.4 0 92i7 9 i 15 80 i 3 70 i 11
At 0% RH.
88.0
i
20
113+6
Tubes presaturated with water.
solvent utilized, in spite of a sampling medium of relatively high affinity for 2-EH. When the effect of water on the recoveries from the two sampling media was investigated ((b) in Sampling Media and Recovery in the Experimental Section above), the results in the third column of Table I11 were found. The efficiencies for Chromosorb 102 were higher and more precise than for Porapak Q, although Porapak Q was still an acceptable sampling medium. When Chromosorb 102 was further evaluated using vapor phase 2-EH in gas bags, the results quoted above were obtained, confirming that Chromosorb 102 collected 2-EH independent of relative humidity up to 90% RH, without any decrease in recoveries. It might be noted that when Porapak Q was utilized for vapor-phase 2-EH estimation a t 0% RH, the recoveries were 92.1, 89.1, and 79.5% a t 23.4 55.6, and 116 ppm of 2-EH, respectively. These figures imply a limited loading capacity compared with Chromosorb 102, but are still nevertheless acceptable so that Porapak Q can also be used to sample for 2-EH, at least under dry conditions. When the recoveries for 2-EH were found for 1, 2, and 3 p L of 2-EH spiked onto Chromosorb 102, the average recovery was 101 f 3% (mean A 2 standard deviation). It appears, therefore, that Chromosorb 102 (80/100 mesh) is the optimal sampling medium to collect 2-EH vapor from work-place atmospheres. As to how general the method is, the recoveries of 1 pL of 1-butanol, n-amyl alcohol, and n-octyl alcohol from Chromosorb 102 were 12,11, and 114%, respectively, using acetone. As 2-EH has the same number of carbon atoms as n-octyl alcohol, the result for n-octyl alcohol is not surprising. It is evident a more polar solvent like acetonitrile or even methanol
403
Anal. Chem. 1983, 5 5 , 403-405
may have to be used to recover the shorter chain alcohols. Nevertheless, long chain alcohols 2C8 should be quantitatively collected and recovered by using the above procedure. The method has been tested in the field and appears to produce satisfactory results. The methodology given here can be applied to evolve a personal collection, recovery, and analytical method for most compounds with vapor pressures >lo5mmHg. The use of gas bags to contain known atmospheres of interest is a relatively cheap and quick way to test a potential method. The methodology allowing some discrimination of humidity effects via water presaturation of the sampling medium is novel, as is the manner in which the most suitable sampling medium under dry conditions is selected. Registry No. 2-EH, 104-76-7;Chromosorb 102, 9003-70-'7.
LITERATURE CITED (1) Treon, J. F. "Industrial Hygiene and Toxicology Vol 11: Toxicology", 2nd ed.: Patty, F. A., Ed.; Wiley: New,,York, 1963: pp 1462-1463. (2) Kirk, R. E., Othmer, P. F., Eds.; Encyclopedia of Chemical Technology", 3rd ed.; Wlley: New York, 1978; Vol. I, p 716. (3) Scala, R. A,; Burtis, E. G. Am. Ind. Hyg. Assoc. J . 1979, 3 4 , 493. (4) Amer. Conf. Governmental Industrial Hygienists, TLVs (Threshold Limit Values) for Chemical Substances in Workroom Air adopted by the A. C.G.I.H. for 1980, A.C.G.I.H., Cincinnati, 1980. (5) Pouchert, C. J. "The Aldrlch Library of Infrared Spectra", 2nd ed.; Aldrlch Chemical Co.: Milwaukee, WI, 1975; p 67. (8) Taylor, D. J., Ed. "NIOSH Manual of Sampling Data Sheets", Supplement to 1977 Ed.; DHEW (NIOSH): Cincinnati, OH, 1978; Publication Number 78-189.
RECEIVED for review March 22, 1982. Accepted October 28, 1982. We gratefully acknowledge the financial support of NIH-ES-00159.
Analysis of High-Purity Graphite for Trace Elements by Inductively Coupled Plasma Atomic Emission Spectrometry after Chelating Resin Preconcentration Hlmansu S. Mahantl' and Ramon M. Barnes" Department of Chemistiy, GRC Towers, University of Massachusetts, Amherst. Massachusetts 0 1003-0035
Graphite is a critical material in nuclear reactors and has widespread industrial applications for which knowledge of the trace element content is essential. Both dc arc emission spectrometry (1-5) and neutron activation analysis (6-8) are the primary instrumental techniques employed for graphite analysis. Inductively coupled plasma atomic emission spectrometry (ICP-AES) only recently was adapted for the analysis of activated carbon after sample ashing followed by sodium peroxide fusion (9) and for the analysis of graphite after sample dissolution in ]perchloric and periodic acids (10). Although ICP-AES exhihits excellent powers of detection, the concentrations of most elements in high-purity graphite lie below the limits of quantitative determination obtained with ICP-AES. Therefore, a preconcentration step is required t o apply ICP-AES for graphite analysis. Recently two chelating resins were shown to be effective means to separate and concentrate trace elements from complex matrices prior to spectrochemical determinations (11-20). This paper describes the determination of six elements in high-purity graphite samples by sequential ICP-AES after the samples are ashed and dissolved and sought elements are concentrated by either a poly(dithi0carbamate) or poly(acrylamidoxime) resin.
EXPERIMENTAL SECTION Apparatus. Experimental facilities and operating conditions are listed in Table I, and analysis wavelengths are indicated in Table 11. Both conventional pneumatic nebulization and electrothermal vaporization (ETV) sample introduction are applied in these determinations. Prior to the ETV-ICP copper determination, the ETV graphite rod is coated first with pyrolytic graphite and then with tantalum (21). Operating conditions were determined for each element by Simplex optimization (22). For the determination of six elements, the ICP operating conditions are argon outer gas flow 16 L/min, nebulizer gas flow 0.8 L/min at a back-pressure of 24 psig, observation height above the in. duction coil 16 mm except for Si (14 mm), inonochromator slit widths, 50 pm, and power Al, Ti, V (0.7 kW), Cu and Fe (0.8 kW), and Si (0.5 kW). Sample Preparation. High-purity graphite (National SP-2 and TB-6, Union Carbide, New York) is dried in an oven at 100 'On leave from the Naliional Institute of Foundry and Forge Technology, Hatia, Ranchi-834003, India.
Table I. Instrumentation and Operating Conditions generator nebulizer plasma torch detection
electrothermal vaporizer
A. Instrumentation Plasma-Therm Model HFS-5000D, 40.68 MHz with three-turn ( in. copper) load coil Babington with double-barrel glass spray chamber Conventional 1 8 mm i.d. quartz with 1.5 mm i.d. injector orifice except 0.8 mm i.d. orifice for Si Minuteman monochromator, Model 310SMP, 1-m Czerny-Turner with 1200 groove/" grating; 1:1 image formed by quartz lens (Oriel A-11-661-37); RCA 1P28 photomultiplier (-700 V ) Keithley 411 Picoammeter, Heath EU201V log/linear recorder Varian carbon rod atomizer (CRA-90) with laboratory fabricated graphite rod electrode and enclosed quartz chamber (21 )
B. ICP-AES Operating Conditions for Cu with ETV-ICP 0.55 power, kW outer gas flow, L/min 16 intermediate gas flow, L/min 1 chamber flow rates, L/min inner 1.6, outer 4.6 observation height, mm 16 slit height, mm 5 monochromator slit widths, mm 0.05 temperature drying, 100 "C for 1 0 s ashing, 200 "C for 10 s vaporization, 2100 "C heating rate, "C/s 800 "C for 2 h. One to five grams of high-purity graphite is weighed into a platinum crucible, and 2 mL of 5% magnesium nitrate solution is added as an ashing aid, especially t o prevent volatilization loss of V. Prior to its use, the magnesium nitrate solution was purified by shaking for 24 h with 500 mg of the poly(dithiocarbamate) resin. The graphite sample is then dried on a hot plate and kept in a muffle furnace at 800 OC for 12 h until a complete ash is obtained. The ash is dissolved in 10 mL of hydrochloric and nitric acids (3:l) and diluted with distilled water to a final volume of 100 mL. Stock solutions are prepared from high-purity metal or reagent-grade chemicals, and high-purityacids and distilled, deionized
0003-270O/83/0355-0403$01.50/00 1983 American Chemical Society
