scatter via small differences from sample to sample in nebulization or light interference effects. Deck and Kaiser (22) separated the aqueous extract from the oil by filtering the mixture through 18.5-cm Whatman No. 40 filter paper. We found that 100 ml of fresh extractant filtered picked up 0.6 f 0.1 pg of copper and 3.6 f 0.3 kg of zinc from the filter papers themselves. Such contamination is appreciable for analysis of oils with metal content as low as those listed in Table I. Suitable procedures to avoid this contamination are to pre-extract the filter papers or eliminate filtering by carefully pipetting out the aqueous layer underneath the oil. A few fats and oils present unique difficulties for metal analysis by acid extraction. We found a crude menhaden oil would not reflux with the aqueous extractant without violent bumping. Extraction of inorganic salts from some oils may cause light scattering interference in the atomic absorption flame. Willis encountered this in nitric acid extracts of butter and corrected for it by subtracting background absorbance (21). The data show that the acid extraction method gives nearly quantitative recovery of added copper and zinc standard from oils in the range of 0.03-0.35 ppm of metal. Even where metal recoveries dropped to about 90% within this range, the reproducibility was good, with RSD's of 2-3. Detection limits determined from measurement of precision a t blank levels indicate the method is useful for analysis of oils with metal content down to about 0.010 ppm. The char-ashing method though sensitive below 0.010 ppm of metal, requires 3-4 days for complete analysis. Acid extraction of oils requires 4 hours; thus, several samples a day can be analyzed using simultaneous reflux extractions. As with char-ashing, the acid-EDTA extraction method is apparently applicable to the determination of a variety of trace metals in both liquid oil and solid fat or shortening samples.
LITERATURE CITED (1) C. D. Evans. A. W. Schwab. H. A. Moser. J. E. Hawley, and E. H. Melvin, J. Amer. OilChem. SOC.,28, 68 (1951). (2) G. R. List, C.D. Evans, and W. F. Kwolek, J. Amer. Oil. Chem. SOC.,48, 438 (1971). (3) A. J. DeJonge, W. E. Coenen, and C. Okkerse, Nature, (London), 206, 573 (1965). (4) S.Koritala and H. J. Dutton, J. Amer. Oil Chem. Soc., 43, 556 (1966). (5) S. Koritala, J. Amer. OilChem. SOC.,47, 106 (1970). (6) K. J. Moulton, D. J. Moore, and R. E. Beal, J. Amer. Oil Chem. SOC.,46, 662 (1969). (7) Anon, "Vital Statistics of the United States, 1967. Mortality." U S . Department of Health, Education, and Welfare, Washington, D.C., 1969, Vol. 2, part A, Tables 1-7. (8) A. Keys, Ed., "Coronary heart disease in seven countries," Cirwlation, 41, 42; Suppl. I, 1 (1970). (9) D. S. Fredrickson and R. I. Levy, "Familial hyperlipopro~lnemia." in "The Metabolic Basis of Inherited Disease," 3rd ed., J. B. Stanbury, J. B. Wyngaarden, and D. S. Fredrickson. Ed., McGraw-Hill, New York, N.Y., 1972, p 545. (10) L. M. Klevay, Amer. J. Clin. Nutr., 26, 1060 (1973). (11) Analytical Methods committee, Analyst, (London), 85, 649 (1960). (12) R. P. Taubinger and J. R. Wilson, Analysf, (London),90, 429 (1965). (13) Analytical Methods Committee, Analyst, (London), 98, 459 (1973). (14) C. Feldman, Anal. Chem., 46, 1609 (1974). (15) Official, J. Amer. Oil Chem. SOC.,49, 432A (1972). (16) B. Piccolo and R. T. O'Connor, J. Amer. Oil Chem. SOC.,45, 789 (1968). (17) A. Prevot, Rev. Fr. Corps Gras, 18, 655 (1971). (18) A. Prevot and M. Gents, Rev. Fr. Corps Gras, 20, 95 (1973). (19) M. K. Kundu and A. Prevot, Anal. Chem., 46, 1591 (1974). (20) C. D. Evans, G. R. List and L. T. Black, J. Amer. 01Chem. SOC.,48, 840 (1971). (21) J. B. Willis, Aust. J. Diary Tech., 1964, 70. (22) R. E. Deck and K. K. Kaiser, J. Amer. Oil Chem. SOC.,47, 126 (1970). (23) I. S. Rombauer and M. R. Becker, "Joy of Cooking," Bobbs-Merrill, Indianapolis, Ind., 1964, p 511.
RECEIVEDfor review May 16, 1974. Accepted December 5, 1974. The authors wish to acknowledge partial support by the USDA Cooperative Agreement 12-14-100-11, 178 (61), Amend. 1. Mention of a trademark or proprietary product does not constitute a guarantee or warranty of the product by the U.S. Department of Agriculture, and does not imply its approval to the exclusion of other products that may also be suitable.
Response Surface and Atomization Mechanism in AirAcetylene Flames Kltao Fujlwara, Hlrokl Haraguchl, and Kellchlro Fuwa Department ofAgricultural Chemistry, University of Tokyo, Tokyo 1 13, Japan
The process of atomization in the flame has been studied by many workers, and they have considered such factors as chemical properties of the analyte elements, the condition of the flame, the effect of concomitant species and so on (1-9). The geometrical distribution of the atomic absorbance in the flame together with the condition of the flame is a useful method for the investigation of the atomization mechanism. In previous papers (10, II), the present authors have investigated the atomic distribution of cobalt and of its complexes, and concluded that the pyrolysis of the bonds between the central cobalt atom and the coordinating atoms in the ligands is the rate determining process of its atomization. In order to investigate and simplify those two major factors of atomization, ie., the geometrical distribution in the flame and the chemical nature of the flame, we found that the response surface plot of the atomic and molecular absorption in the axes of flame height us. fuel rate is most
convenient (1% 13). A similar expression has been suggested and tried by other workers also (1,14). Applying this expression to simple salts of many elements, the atomization mechanisms of the fundamental aquo complexes were investigated in this paper. EXPERIMENTAL Reagents. All reagents used in this experiment were analytical grade prepared by Wako Chemical Reagents Co. For the preparation of sample solutions, nitrates of Mn2+,Fe3+, Co2+, Ni2+,Cu2+, Zn2+, Ca2+, Cr3+, Cd2+, Ga3+, In3+, Pb'+, and chloride of Sn4+ were dissolved in distilled water containing 0.2% nitric acid. Ammonium molybdate and boric acid were dissolved in water. Concentrations of the analyte elements are listed in Table I. Apparatus. The Hitachi 207 atomic absorption spectrophotometer was used, the optics of which has been modified to the single light path with the light beam of two to three mm in diameter at the center of the flame (11). The light source for atomic absorption of the analyte element was a hollow cathode lamp made by Hitachi Ltd., except the one A N A L Y T i C A L CHEMISTRY, VOL. 47, NO. 4, APRIL 1975
743
Table I. Compounds, Concentrations and Analytical Lines Used in the Experiment Compound
Cd (NO,), * 8 H z 0 Ni(NO,), * 6 H z 0 Zn (NO,), .6H,O Cu(N03)2*3HzO Pb (NO, )z Co(NO,), *6H,O Mn (NO3),.4HZO Fe (N03),.7H,0 C r (NO,),*9HZO SnCI4*5H,O
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2288 3524 2138 3274 2833 2432 4030 2719 4274 2863 2874
for calcium was made by Hamamatsu TV Co. Ltd., the one for gallium by Westinghouse, and for tin by Varian Techtron Pty. Ltd., Australia. The light source for the molecular absorptions of InO, SnO, and OH was a 200-W deuterium discharge tube, model H S 200 DS made by Dr. Korn GmbH and Co. For the temperature measurement, a 150-W tungsten lamp, model KP-8 of Kondo Electrical Co. Ltd., a mechanical chopper for the light beam made by K. K. Ewig Co., and an optical pyrometer, model 201 N1 of Hokushin Electric Work were used. The burner was a 10-cm slot type for the air-acetylene flame. Procedure. The light beam was adjusted to pass through the center of the flame. The absorbance and the temperature of the flame were measured a t the spots above the burner with 2.5-mm interval by moving the burner vertically. The composition of the flame was changed by varying the acetylene flow rate by 0.5 1./ min., keeping the flow rate of the air constant at 13 l./min. Sample solution was aspirated into the flame a t the rate of 3 ml/min. The analytical lines for the atomic absorptions of the elements are shown in Table I; 2730 A and 3323 A were used for the absorption measurements of monoxides of indium and tin, respectively (15, 16). The absorbance of OH radical was measured a t 3048 and 3064 8, with the beam from a deuterium lamp source and with distilled water aspirated into the flame us. a reference with no flame. Temperature of the flame was measured by the sodium 5889-8, line reversal method (27, 18).Two pinholes were used, one for the production of a very narrow light beam from the tungsten light source, and the other, behind the flame, for excluding the emission of the flame. The current of the tungsten lamp was adjusted by the autotransformer, and the temperature of the tungsten filament was measured by the optical pyrometer at the reversal point of sodium absorption and emission. The precision of the measurement was within 10 "C. For the accuracy check of the measured temperature, the indium two-line atomic absorption method (19) was employed which gave a few hundred degrees higher values. Such discrepancies of the flame temperature by different methods were recently discussed by Reif et al. (20). Absorbance and temperature are plotted in the figures with the acetylene flow rate in the abscissa and the height above the burner in the ordinate. The spots in the figure which give the same absorbance or temperature form contour lines or iso-absorbance lines at intervals of 0.012 and iso-temperature lines a t intervals of 25 "C. The area which is covered with the maximum iso-absorbance or iso-temperature lines is hatched in the figure, for the convenience of comparison. A 3.0 l./min acetylene flow rate in the regular measurement corresponds to a C2Hz:Oz ratio of 3:2.6. The region where the acetylene flow rate is larger than the normal condition of ordinary experiments is conventionally referred to as the acetylene-rich, and the region less than that as the acetylene-lean, respectively.
RESULTS AND DISCUSSION The temperature distribution in the flame with water being aspirated is shown in Figure 1. The spot of the high744
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ANALYTICAL CHEMISTRY, VOL. 47, NO. 4 , APRIL 1975
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decomposition of the oxides in the flame. A clue to the redox potentials of the flame can be seen by OH radical distribution, Figure 2. This radical is considered to be oxidative radical in the flame (23),enriched, therefore, a t the fuel-lean region, and, hence, further supports the chemical decomposition reaction of oxides of some elements. Indium and tin are the elements sited a t the extreme ends in the series of Figure 5 . The maximal spot of indium atoms locates at the lower part of the acetylene-lean region and its monoxide increases gradually in the region above the maximal spot, as can be seen in Figure 3, Part 1. Indium first atomizes at the early stage of the flame reaction, and this process is almost independent of the distribution of the reducing component except for the very acetylenelean flame. Then the formation of monoxide follows after the atomization according to the recombination of the indium atom and oxygen, right above the atomic maximum. Another appearance of the absorption maximum of I n 0 in the acetylene-rich region, Figure 4, suggests the formation of I n 0 at the lower temperature below 2000 "C. Contrary to the case of indium, the absorption maximum of the tin atom locates above that of tin monoxide, both of which stay a t the rather fuel-rich region, Figure 3, Part 2. It has been recognized that the equilibrium between free atoms and monoxides is most important at the post reaction zone of the flame (4, 6, 7,23-28). For instance, Koirtyohann et al. (28) calculated the free atom fraction from the equation, assuming that the sum of the fractions of free atom and monoxide equals one. Considering this assumption, the present results suggest that at the center of the flame, indium may atomize quickly and then combine with
oxygen, and tin may form monoxide first and then decompose to atoms. The lateral diffusion and the formation of a large amount of the third species other than atom and monoxide would cause errors in the atomization mechanism mentioned above. The lateral diffusion, however, does not seem to have a serious effect, as the flame widths with respect to temperature (2, 1 8 ) , flame components (29, 30) and metal atoms (3,29) do not greatly change in the crucial range of 5- to 20-mm burner height. I t was not confirmed in our experiment if the large amounts of the third species are formed. The formation of a higher oxide of tin, SnO,, or hydroxide may be possible in the acetylene-lean region, but it seems difficult in the acetylene-rich region because of high reduction potential and low concentration of OH. LITERATURE CITED (1)N. V. Mosshoider. V. A. Fassel, and R. N. Kniseley, Anal. Chem., 45, 1614 (1973). (2)J. B. Willis, Spectrochim. Acta, Part A, 23, 81 1 (1967). (3)J. B. Wiiiis, Spectrochim Acta, Part E, 25, 487 (1970). (4)V. A. Fassel. J. 0. Rasmuson. R. N. Kniseley, and T. G. Cowiey, Spectrochim Acta, Part 8, 25,559 (1970). (5) R . Smith, C. M. Stafford, and J. D. Winefordner, Anal. Chim. Acta, 42, 523 (1968). (6)P. J. Th Zeegers, W. P. Townsend. and J. D. Winefordner, Spectrochim. Acta, Part 5,24, 243 (1969). (7)C. L. Chakrabarti and S. P. Singhal. Spectrochim. Acta, Part 8, 24, 663 (1969). (8)T. J. Vickers, C. R. Cottreil, and D. W. Breakey, Spectrochim. Acta, Part 8,25,437 (1970). (9)A. Ando, K. Fuwa, and B. L. Vallee, Anal. Chem., 42,818 (1970). (10) K. Fujiwara, H. Haraguchi, and K. Fuwa. Anal. Chem., 44, 1895 (1972). (11) K. Fujiwara, H. Haraguchi. and K. Fuwa, Chem. Lett., 1973,461.
(12) K. Fujiwara, Masters thesis, The University of Tokyo, March 1972;K. Fujiwara, H. Haraguchi, and K. Fuwa, 21st Annual Meeting of Japan SOC.for Anal. Chem. at Sendai, Sept. 1972. (13) K. Fuwa, Fourth int. Conf. on Atomic Spectroscopy, Toronto, Canada, Nov. 2,1973. (14)R . K. Skogerboe, A. T. Heybey, and G. H. Morrison, Anal. Chem., 38, 1821 (1966). (15)H. Haraguchi and K. Fuwa, Chem. Lett., 1972,913:. (16) R. W. B. Pearse and A. G. Gaydon, "The Identification of Moiecuiar Spectra," Chapman and Hail, London, 1950. (17)B. W. Bailey and J. M. Rankin, Anal. Chem., 43,219 (1971). (18)W. Sneiieman, "Flame Emission and Atomic Absorption Spectrometry," J. A. Dean and T. C. Rains, Ed., Marcel Dekker, New York. N.Y.. 1969, p 213. (19)R . F. Browner and J. D. Winefordner, Anal. Chem., 44,247 (1972). (20)I. Reif, V. A. Fassel, and R. N. Kniseley, Spectrochim. Acta, Part 8, 29,
79 (1974). (21)A. G. Gaydon, "Dissociation Energies and Spectra of Diatqmic Molecules," 3rd ed,, Chapman and Hall, London 1968. (22)JANAF, Thermochemical Tables, Prepared by Dow Chemical Co., Midland, Mich. 1966,1967,1968. (23)D. R. Jenkins and T. M. Sugden, "Flame Emission and Atomic Absorption Spectrometry," J. A. Dean and T. C. Rains, Ed.. Marcel Dekker, New York, N.Y.. 1969,p 151. (24)C. Th. J. Alkemade, "Analytical Flame Spectroscopy," R. Mavrodineanu, Ed., Springer-Verlag. New York, N.Y.. 1970,p 28. (25)J. E. Chester, R. M. Dagnall, and M. R. G. Taylor. Anal. Chim. Acta, 51,
95 (1970). (26)T. G. Cowiey, V. A. Fassel, and R. N. Kniseley, Spectrochim. Acta, Part 6,23,771(i968). (27)V. K. Paday, Anal. Chim. Acta, 57,31 (1971). (28) S.R. Koirtyohann and E. E. Pickett, Spectrochim. Acta, Part B, 26, 349 11971) \ .I
(29)C. S.Rann and A. N. Hambly, Anal. Chem., 37,879 (1965). (30) S. Musha and S. Shimomura, "Atomic Absorption Analysis," Kyoritsu, Tokyo 1972,p 75.
RECEIVEDfor review May 9, 1974. Accepted December 5, 1974.
Determination of Methyl Alcohol in Wine by Gas Chromatography C. Y. Lee, T. E. Acree, and R. M. Butts Department of Food Science and Technology, Cornell University, Geneva, N.Y. 14456
Dietary methyl alcohol is derived in large part from fresh fruits and vegetables. It occurs as free alcohol or esterified with fatty acids, or as a product from the hydrolysis of methoxy groups on polysaccharides such as pectin. Methyl alcohol in alcoholic beverages is often of concern to the public because of its toxicity. The conventional colorimetric method for the analysis of methyl alcohol is tedious and time-consuming ( I ) . Dyer ( 2 ) analyzed methyl alcohol by gas chromatography using a polar Carbowax 1500 on Chromosorb W column described by Brunelle ( 3 ) .However, the separation of methyl alcohol from ethyl alcohol was marginal. Di Corcia et al. ( 4 ) achieved a greater separation of the two alcohols by using a column of polyethylene glycol 1500 on graphitized carbon. However, the retention time of acetaldehyde was very close to that of methyl alcohol. Recently, an ethylvinylbenzene polymer (Porapak) has been introduced to separate polar organic compounds. I t gives retention times which are a linear function of the molecular weights of the compounds ( 5 ) . Therefore, the common low molecular weight organic compounds found in alcoholic beverages, i.e. methyl alcohol, acetaldehyde, ethyl alcohol, ethyl acetate, etc., should be easily separated on this packing material. In this note, a simple gas chromatographic procedure using Porapak QS is introduced for the analysis of methyl alcohol in wine a t concentrations as low as 5 ppm by direct injection.
EXPERIMENTAL Apparatus. A Varian Aerograph 200 gas chromatograph equipped with a flame ionization detector was used. A coiled stainless steel column (2-m long X 0.2-cm i.d.) was washed thoroughly (6) and packed with Porapak QS (silylated ethylvinylbenzene polymer). New columns were conditioned at a temperature of 210 "C for 24 hours. The gas chromatograph operating conditions were as follows: the nitrogen carrier gas flow rate was 40 ml/min under a column head pressure 25 psig, the injector port and detector temperatures were 210 and 220 "C, respectively. The column was operated isothermally a t 115 O C . A Hamilton syringe (10 pl) was used to inject samples of 3 GI. Reagents. Methyl alcohol (reagent grade) obtained from Fisher Scientific Company and distilled water were used to prepare solutions of methyl alcohol of varying known concentrations. Procedure. Standard solutions were analyzed every day by injecting 3 pl of aqueous solutions of methyl alcohol of known concentrations in the range of 10 to 1000 ppm. A calibration curve was prepared by plotting the concentration in ppm vs. a response factor (peak height multiplied by the attenuation). T h e concentration of methyl alcohol in 3 p1 of an unknown sample was then determined by calculating the response factor and relating it t o calibration curve values.
RESULTS AND DISCUSSION A 2-m Porapak QS column gave good separation and resolution of the four important low molecular weight volatiles commonly found in alcoholic beverages. These compounds are methyl alcohol, acetaldehyde, ethyl alcohol, ANALYTICAL CHEMISTRY, VOL. 47. NO, 4, APRIL 1975
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