amount of smoke would have corresponded to 100-800 ppm SO2 (5-4096 of chart)-even more if the mean particle size were submicron-since the mean wavelength of the opacity monitor was much larger than t h a t of the SO2 instrument.
man and R. L. Rizer of Ohio Edison Company, J. W. Wright and A. A. Barasch of Toledo Edison, G. T. Welch of Westvaco, and J. D. Homolya of EPA, Research Triangle Park, N.C., who arranged the test a t Duke Power.
CONCLUSION
(1) I. Rubeska and B. Moldan. “Atomic Absorption Spectroscopy,”Chemical Rubber Co., Cleveland, Ohio, 1969. (2) R. 0. Gumprecht. Ph.D. Thesis, University of Michigan, Ann Arbor, Mich., 1952. (3) H. E. Rose, “The Measurement of Particle Size in Very Fine Powders.” Chemical Publishing Company, New York, N.Y., 1954. (4) R. A. Dobbins and G. S. Jizmayian, J. Opt. SOC. Amer., 56, 1345 (1966). (5) Milton Kerker, “The Scattering of Light and Other Electromagnetic Radiation,” Academic Press, New York. N.Y.. 1969. (6) P. Warneck, F. F. Marmo. and J. W. Sullivan, J. Chem. Phys., 40, 1132 (1964). (7) W. L. Paterson. Rev. Sci. lnstrum., 34, 1311 (1963). (8) J. N. Giles, Ed., ”Linear Integrated Circuits Applications Handbook,” Fairchild Semiconductor,Mountain View, Calif., 1967. (9) G. N. Theon, G. G. DeHaas, and R. R. Austin, Tappi, 51, 246 (1968). (10) M. L. Robinson and R. R. Austin, U S . Patent No. 3,180,132, April 27, 1965. (1 1) J. Brown and G. Burns, Can. J. Chem., 41, 4291 (1969).
The present instrument concept appears well suited to in-situ measurement. Its embodiment as an SO2 analyzer is reasonably accurate and stable, even without continual on-line zero and range checks. Freedom from particulate interference is both a theoretical and practical reality. Compensation for aging of both phototubes and both lamps is also provided. Accuracy seems to be within the precision of corroborating measurements provided account is taken of residual long-term calibration drift, which amounts to perhaps 5% in three weeks.
ACKNOWLEDGMENT The authors are indebted to their then immediate supervisors, H. P. Markant of B&W Research and R. A. Murzyn of Bailey Meter Company, for continued encouragement and support. Our field test program could not have been successful without the generous cooperation of R. S. Bau-
LITERATURE CITED
RECEIVEDfor review December 7, 1973. Accepted September 30, 1974. Presented a t the 167th National Meeting, American Chemical Society, Los Angeles, Calif., March 31-April 5, 19’74.
Arsenic Determination in Tobacco by Atomic Absorption Spectrometry H. R. Griffin, M. B. Hocking, ‘and D. G. Lowery Department of Chemistry, University of Victoria, Victoria, British Columbia V8W 2 Y 2
A safe wet-ashing technique has been used to put the arsenic content of tobacco into solution without loss. The arsenic( V) obtained was converted to arsine and frozen out in a packed U-tube with liquid nitrogen. Aspiration of the arsine into a conventional atomic absorption spectrometer, using the 193.7-nm As line, gave detection limits for arsenic of 0.2 pg. Determination of arsenic at concentrations of 50 ppb or lower could readily be achieved by use of larger sample sizes. The relative arsenic levels determined in this way for several domestic and foreign tobaccos is given and discussed in the light of earlier results.
The determination of the arsenic content of tobaccos from a number of widely separated areas was approached with the premise that more frequent applications of arsenical pesticides in the developed areas would show up as higher arsenic concentrations in tobacco from these areas. While the Marsh, Gutzeit, and Reinsch procedures of arsenic determination have historically demonstrated reliable and reproducible results, i t was thought desirable to apply a modern instrumental technique. Neutron activation analysis has successfully been applied recently t o this problem ( I , 2 ) , but on a limited rang61 of samples. This work sought to substantiate the recent arsenic levels established by neutron activation analyses and to broaden the geographical Author to whom correspondence should be addressed.
range of samples for which the arsenic content was known, with data obtained by an independent atomic absorption (AA)-based procedure. The procedure evolved adopted all those most desirable published features of AA which could feasibly be incorporated to give a combination best suited for the determination of arsenic in tobacco.
EXPERIMENTAL Apparatus. Digestion of tobacco samples was carried out in a n apparatus designed to maintain total retention of digest and condensable volatiles, similar in some respects to the Bethge apparatus, (as available from the G. F. Smith Chemical Co., Columbus, Ohio) and has been described earlier (3). Arsine generation was performed in the apparatus train depicted in Figure 1. The generator itself was a 3-necked, 250-ml flask fitted with a jam and leak-free swivel arm zinc doser, and a discharge tube for the arsine and hydrogen leading to a conventional drying tube. The drying tube was connected via a clamped ground glass ball joint to a Pyrex U-tube filled with 2-mm glass beads and placed in a liquid nitrogen-filled Dewar flask for condensation of arsine ( 4 - 6 ) . For reliable closure, this was fitted a t either end by spring-loaded stopcocks, and with a conventional syringe needle epoxied onto the outlet for aspiration into the AA burner. All joints were sealed with silicone high vacuum grease, and use of rubber components was eliminated to avoid the risk of “memory” effects. Instrumental Parameters. The Techtron Atomic Absorption Spectrophotometer Type AA5 with grating monochromator was fitted with an arsenic hollow cathode lamp (neon filler gas) operated a t 1 2 mA. A slit width of 300 pm on the 193.7-nm line was used. Atomization was via a single slot laminar flow high-tempera-
ANALYTiCAL CHEMISTRY, VOL. 47, NO. 2, F E B R U A R Y 1975
229
DRIERITE
SPRING-LOADED
\ -SYRINGE
NEEDLE
Table I. Effect of Waiting Period for Potassium Iodide Reduction on Quantitative Arsine Generation at Room Temperature
Zmm G L A S S B E A D S
’
e
ARSINE GENERATOR
Figure 1. Details of arsine generation and collection train
,/
I
I
I
I
I
I
2
4
6 p g ARSENIC
8
10
12
Figure 2. Standard caiibration curve obtained for arsenic
ture burner, Techtron Type AB40, fueled with acetylene (3-9 scfh), nitrous oxide (16 psi), and entrained air (15 psi). Readings were taken on 1-mV Westronix MT-21 strip-chart recorder, slew rate 1.6 mV/sec, connected to the galvanometer outlet so as to bypass the damping shunt on the standard meter readout of the instrument. Reagents a n d Standards. Reagent grade chemicals supplied by Baker and Adamson were used, except where otherwise stated. Digestions were carried out using concentrated nitric acid (1 ppb As) and 70-72% perchloric acid. A “20% HC1/5% H2S04”dilution mixture was prepared by adding 400 ml concd HC1 (Fisher, 10 ppb As) to 500 ml of distilled water, then adding 100 ml concd H2S04 (5 ppb As) and the whole brought to a volume of 2000 ml with distilled water. Stannous chloride (20%) was prepared by dissolving 20 g SnC12.2H20 (“max” 2 ppm As) in concd HC1. Macco reagent grade KI was used a t 20% strength in distilled water. The most suitable form of zinc for smooth arsine generation was 30-mesh material (Fisher, 2 ppb As). Standard arsenic in the + 3 oxidation state was prepared by dissolving 1.3203 g of As203 (98%) in 20 ml of 20% NaOH, and then diluting to a volume of 1000 ml with 20% HC1/5% H2S04 to give stock 1000 ppm As3+. In a like manner, but taking precautions t o avoid moisture uptake, 1.5495 g of As205 (99%) was made up to give a 1000 ppm solution of As5+. Procedures. Digestion. A 4.00-g sample of tobacco, was placed in the Kjeldahl flask ( 3 )rinsed in with 20 ml of concd “0.7. Then a mixture of 20 ml concd H N 0 3 with 20 ml70% HC104 was added (7-9) and the Kjeldahl flask strongly heated with an electric mantle a t 110 V. When the flask internal temperature reached 200 “C (about $ hr.), the mantle was removed and the contents allowed to cool to 80”. Forty milliliters of distilled water was added and strong heating again resumed (10) till the contents reached 200” (about y2 hr), and again allowed to cool to about 80”. Forty milliliters of distilled water and 4 ml of saturated aqueous ammonium oxalate (11, 12) was added and the same heating and cooling procedure followed. The Kjeldahl contents was then transferred to a 200-ml volumetric flask and brought to volume using 20% HC1/5% H2S04. Arsine Generation was conducted on a 50-ml aliquot of digestion solution or a suitably diluted aliquot of one or mixture of both standards placed in the 250-ml generator of Figure 1. Two milliliters of 20% KI was added, followed 15 minutes later by 2 further ml of 2046 KI and 2 ml of 20% SnClz (liquid additions performed through double stopcock fluid doser in center neck of generator or through opened neck of flask, quickly reclosed). Then the U-tube was immersed in liquid N2 and 5 g of zinc added to the generator to initiate arsine generation and collection. Most of the arsine was deposited as a white solid band in the first 2-3 minutes of generation but collection was continued until hydrogen evolution slowed (about 15 min). TIP stopcocks were then closed and the U-tube, still in coolant, was transferred to the adjusted spectrophotometer. 230
Absorbance
Arsenic found, pg
5 5 10
0.173 0.188
4.0 4.4 4.6 4.8 5.9
0.198
0.206 15 0.252 15 0.260 30 0.255 30 0.258 Each sample consisted of 3 pg As3-
10
a
0:
Waiting period, mina
+ 3 fig As5 -
6.2 6.0 6.1
The needle was then placed in the’aspirator of the spectrophotometer, and the liquid N2 Dewar was removed and stopcocks both opened smoothly to give the absorption trace. In this way, by running a series of digestions of standard samples and blanks, the standard calibration curve shown in Figure 2 was obtained. To improve the reading accuracy of the tobaccos very low in arsenic, a 100-ml aliquot of diluted digest solution was used in the arsine generator in place of the normal 50 ml.
RESULTS AND DISCUSSION Effective Digestion Procedure. Initial tobacco digestions were carried out using mixtures of only nitric and sulfuric acids. Low and inconsistent results were obtained which only served to confirm the difficulties experienced by others (11, 1 3 ) using this method of wet ashing. The suggestion of Gross ( 1 4 ) that nitrogen compounds surviving initial digestion can interfere during hydride generation prompted the adoption of perchloric acid treatment subsequent to initial nitric/sulfuric digestion, which Cassil (13) has found adequate to remove this interference. This yrncedure still gave low and somewhat variable results, even with standard samples. On the cue that high tempera tures prior to complete oxidation might be the cause of AS,?-+loss (15, 1 6 ) , the use of sulfuric acid and the high temperatures associated with the SO3 fuming stage were abandoned. The use of only nitric and perchloric acids (7-9), arranged with a partial reflux assembly ( 3 ) , not only avoided the high temperatures but also avoided carbonization, which could result in reduction of As5+ to As3+ (151, the risk of anhydrous perchloric formation (7, 1 7 ) , which was possible under the former conditions, and completed. the initial stage of digestion in one half instead of three hours. The apparatus devised for these digestions adopted some of the features of the Bethge apparatus ( 3 ) arranged for complete retention of acid vapors and allowed the occasional perchloric acid digestion to be safely carried out over an enameled steel tray in a regular fume hood. However, the Teflon-covered silicone rubber O-ring used with the polished glass spherical joint of this apparatus ( 3 ) is safe only while the Teflon skin remains intact ( 1 8 ) .Hence, this critical component should be carefully inspected prior to each use. With polished conical glass ,joints, Teflon sleeves are recommended, though Halocarbon grease, (a polychlorotrifluoroethylene oil thickened with silica gel, marketed by Halocarbon Products Corporation, 82 Burlews Court, Hackensack, N.J. 07601) or concentrated sulfuric acid are also serviceable in this application. A specially designed perchloric acid hood with built in flush-down is mandatory for long term use. Perchloric acid use removed concern for interfering organic nitrogen compounds (14 ), hence only residual N oxide removal to avoid oxidizing conditions for the arsenate reduction step (19) was required prior to arsine generation. Gross ( 1 4 ) has removed the arsenic from the N-oxide solution by precipitation. and then carried out the analysis
A N A L Y T I C A L CHEMISTRY, V O L . 47, N O . 2, FEBRUARY 1975
Table 111. Arsenic Retention during Digestion
Table 11. Effect of Zinc Dose on Blank Readings Am.ount of zinc, 9
.Absorbance reading
T o t a l arsenic, ug
tsperirnent S o .
5 10 15 20
0.04,0.035 0.085 0.120 0.130
0.15
1 2
1.3 1.3
3 4 5
1.3 1.3 Digest
0.57
1.oo 1.05
on redissolved arsenic. The bulk of the N-oxides were removed by water addition and boiling off ( 1 0 ) and the final traces removed and destroyed by a further water addition plus a small amount of ammonium oxalate solution and boiling off again (11, 12). Neither repeated water additions and boiling off alone, nor ammonium oxalate additions and boiling alone were effective for complete N-oxide removal. The cause of some reading variability of some early standard samples in the initial stages, it was suspected, arose from residual ammonium oxalate interference during arsine generation, but test additions of ammonium oxalate. ammonium chloride, or oxalic acid to the Gutzeit generator independently, established that there was no effect from a series of constant readings. Arsine Generation a n d Collection. The first step of arsine generation, reduction of arsenate to arsenite, was a time-dependent process. By using standard samples containing 3 pg of each of arsenic (V) and arsenic (III), a series of runs established that a minimum of about 15 minutes was required for this reduction step to be complete (’Table I). Vogel (19) recommends standing a t room temperature 20-30 minutes, and more recently Chu et al ( 1 2 ) recommend heating a t 85 “ C for 5 minutes to ensure completion of the reduction. The practice of addition of a further small portion of KI and of stannous chloride solutions just prior to zinc addition, was adopted directly from standard procedures (14, 20) for ensuring reducing conditions and zinc sensitization during arsine generation. Raising the amoi int of zinc used raised the blank reading significantly, as expected (Table 11),but unexpectedly showed that the zinc selected on the basis of its low (2 ppb) arsenic analysis, actually contained about 80 ppb. Thus, the suggestion of Schmidt and Royer (21 ) that sodium borohydride gives improved results partly through lower blanks, becomes appropriate. The packed tube moistened with lead acetate solution for HrS removal normally recommended for Gutzeit determinations (20) was unnecessary for AA analysis of non-proteinaceous materials, but employment of a drying agent was essential, not so much to avoid flame interference but to prevent blockage of the U-tube with ice. Silica gel or magnesium perchlorate were avoided since Braman e t al ( 2 2 ) have reported interference by partial adsorption from these agents, but anhydrous calcium chloride or Drierite was found effective and non-interfering. For absorption readings, arsine has been swept directly into the AA flame ( 2 3 ) , has been collected over a period of time in a balloon ( 22, 21 ) prior to discharge, and has been collected by freezing out in a U-tube cooled in liquid nitrogen (4-6). The short arsine generation times provided, together with the lower sensitivity burner available, precluded application of the first method in this study, and doubts about the risks of leakage, possible arsine memory effects, and the rapid ageing o f the rubber and consequent risks of variable discharge rates either in use or when renewed, gave some lack of confidence with the second. Hence, the U-tube procedure advocated by Holak and others (4-6 ) was adopted with the modifications of all glass construction and connections. and spring-loaded stopcock closures (Figure 1). In addition, aspiration of arsine gas directly sublimed from the frozen state into the burner from the U-tube greatly improved the reproducibility, and was a
Tobacco 4s,
ug
Spike As, ug
5, As” 2.5, As” -2.5, As3+ 1.25, A s 5 +
5 , As3+ None
A s found, ug
6.2 6.4
2.6 6.4 0.0
condensate 6 1.3 5 , As’‘ Typical result from HN03/H2S04 digestion.
3.7“
procedural modification which still gave a sharp easily measured signal. A further minor advantage of the freezing out technique is the visible indication of inadequate N oxide removal by the appearance of blue and pale yellow bands in the U-tube just beyond the arsine band. The possibility of interfering memory effects caused by silicone grease was checked by running a high arsine standard sample followed by a series of blanks. The first blank gave the same reading as the last. Atomic Absorption Optical Options. Three lamp options were open for determination of arsenic by atomic absorption argon-filled hollow cathode, neon-filled hollow cathode, and electrodeless discharge. Because the last of these has been found less stable than the others by Menis and Rains (241, the first two types were tested in this application. A referee has commented that the electrodeless discharge lamps now available are as stable as hollow cathode lamps, and provide many times the output intensity. While there was some sample-to-sample variability, the neon-filled lamps generally had a higher initial output than the argon-filled, and maintained this output well. Although the cool, argon-hydrogen-entrained air flame is generally the preferred configuration for arsine determinations (24, 25), this type of burner was not available a t the time. Of the two types available, air-acetylene and nitrous oxide-acetylene (entrained air), the latter was selected because it gave the lower background noise and provided adequate sensitivity for the samples being examined. It was operated to be slightly oxidizing, since the neutral flame recommended by Smith and Frank (26) tended to carbon-up rapidly. The slits were set a t 300 pm, the widest available and the grating monochromator was adjusted for the 193.7-nm As line which was used throughout. While the 197.2-nm As line provided the highest absorbance for a 1000 ppm A$+ solution, the 193.7-nm line gave 95% of this absorbance and has also generally been adopted for arsenic determination by others (24, 25). The 189.0-nm line gave only 20-25% of the absorbance of the 197.2-nm line and was also highly sensitive to interference by water vapor (25). Absorbance readings were initially made on the standard meter fitted on this instrument, but the built-in damping severely depressed the readings obtained for high arsenic values (above 6-7 pg As) taken either from the meter, or from a recorder wired to the recorder outlet. By wiring a fast response recorder directly to the galvanometer outlet of the instrument, effectively by-passing the damping, a sharp, very near linear response could be obtained over a much wider range a t the expense of only a small increase in background noise. The best least-squares fit of points in standard curves was obtained by simply using peak height, in agreement with Holak ( 4 ) .Peak area, either by planimeter, the base X height, or height X width a t half height; or peak weights, from cut-outs of the chart itself, or from Xeroxed copies of the chart (since Xerox copy paper was more uniform in weight), all gave greater scatter in stan-
A N A L Y T I C A L C H E M I S T R Y , V O L . 4 7 , NO. 2, F E B R U A R Y 1975
231
Table IV. Arsenic Concentrations Determined for Some Exotic and Domestic Tobaccos Arsenic concentrations found, PPma T a h i c c o type
Basnia Burley Dark-fired J aff na Jaggery L.40, powdered P 3 L , powdered X30, powdered Vadakan Cigarettet, blend Cigarette* Cigar, blend Pipe, mild
SOW'e
Greece Malawi Malawi S.India S . India S. Rhodesia S. Rhodesia S. Rhodesia S.India
R e p l i c a t e results
1.80, 1.95, 1.75 0.43,0.39,0.46 0.55,0.58 0.23,0.28,0.33 0.73,0.63, 0.75 0.59,0.55 0.67,0.72 0.63 0.45,0.45,0.40
Tu'. America 0.83, 0.92
Mean
Tobacco type
Re1 std de", i4
1.83 5.6 0.43 8.4 0.56 12.6 0.28 17.9 0.71 9.1 0.57 4.9 0.70 5.1 0.63 . 0.43 7.0
..
0.88
7.3
Virginia 0.82,0.77 0.80 4.5 N.Anierica 0.55, 0.40, 0.50 0.48 16.0 Virginia 1.30>1.27, 1.40 1.34 5.2 Calculated on basis of tobacco moisture content as packed. Exotic tobaccos tended to be drier. Moisture content of fresh pipe tobacco was 20-22% dried at 120 "C, and 15-16.570 dried a t room temperature. Papers removed. dard plots. The detection limit found for a response just greater than the blank reading was 0.2 pg As, and for twice the blank reading, 0.6 pg As. Reports of detection limits for arsenic achieved by this configuration or variations range from 0.02 to 0.2 p g ( 4 , 23-25). A key advantage of the arsine freezing collection technique is the concentration feature. Larger generator sample sizes can thus be used to compensate for lower sample arsenic concentrations. Arsenic Retention Tests. T o ensure that arsenic was not being lost during the digestions, additions of known amounts of pentavalent and trivalent arsenic were made prior to digestion with no significant losses found (Table 111).Also, as a further check, the contents of the receiver of the distillative digestion apparatus was checked for arsenic and none found. The result for Experiment 6 in Table I11 is included as an example of the noncorrespondence of the results from most of the nitric acid/sulfuric acid-based digestions. Arsenic Concentrations of Exotic a n d Domestic Tobaccos. For all tobacco samples, triplicate analyses were run except when there was very close agreement between the first two results, or when there was insufficient sample (Table IV). On the basis of these results, that is a range of 0.3-1.8 ppm for exotic samples, and 0.5-0.9 ppm for domestic, it was concluded that there is now no significant difference in the arsenic concentrations of these two groups. Perusal of earlier arsenic values in tobacco does appear to bear out the initial premise that the arsenic concentrations of North American tobaccos generally was higher than the product of developing countries (Table V) (27-35). But the recent neutron activation-based results of Chun ( 2 ) , and Nadkarni e t al. ( I ) (1970, 1971, Table V) agree substantially with the atomic absorption results of this paper and thus support the conclusion that there has been a marked improving trend. This trend can probably be jointly ascribed to Government regulatory action of the use of arsenicals on materials for human consumption (36) together with the advent of the far more cost-effective chlorinated pesticides which appeared just after the end of the Second World War (36). In the light of the favorable trend shown for current arsenic levels in tobacco, there still remains one disquieting facet of the presence of arsenic a t any level. This is the knowledge that a significant fraction of the arsenic present 232
Table V. Trends of Arsenic Concentrations in Tobacco with Place and Timea Result or r a n g e , ) SOlrriC
dS .AS
ppn~
Cigar Italy (0.8-10.2) (1.6-4 .O) Snuff Italy Pipe USA 6.0-28.9 Unspecified Brazil, Java 0.33-4.6 Pipe USA 18.8-20.7 Cigar and pipe USA 1-40 Cigarette USA 2.5-20 3.7-49 Snuff USA 11.8-12.5 Unspecified USA Cigarette USA 4.5-10.6 Leaf A4r g e nt i na 18-3 5 Cigarette Argentina 5.8-1 5 .O 0.0-13.7 Cigarette Europe USA 24. 0-106 Cigarette Cigarette Turkey (4.8-6.2) (32.2-39.3) Cigarette USA Cigarette USA 3.9 Cigarette Korean 0.5-0.8 USA Cigarette 1.&1.7 a Ref. 27-35. b Parenthesized if on a dry basis. Recalculated t o an As basis when analyses quoted as A s 2 0 3 in reference. is volatile in the smoke (1, 10, 33-35, 37) and that arsenic itself has been, a t least statistically, implicated as a carcinogen (33, 38-41) although with some dissent ( 4 2 ) .The real hazard from this vector will not be known until more information is collected on the form in which arsenic is present in tobacco, and more definitive data are available on the particular forms of arsenic which are the sigificant carcinogenic factors. ACKNOWLEDGMENT The authors thank the Tobacco Export Promotion Council of Rhodesia, the Institute Experimental du Tabac, Greece, the Cancer Registry and Research Project, India, and the Tobacco Research Office, Malawi for samples. LITERATURE CITED (1) R. A. Nadkarni, W. D. Ehmann, and D. Burdick, Tobacco Sci., 14, 37 (1970). (2) S. Y. Chun, Korean J. FoodSci. Tech., 3, 144 (1971). (3) H. G. Griffin and M. B. Hocking, J. Chem. fduc., 51, A289 (1974). (4) W. Holak, Anal. Chem., 41, 1712 (1969). (5) E. J. Knudsen and G. D. Christian, Anal. Lett., 6, 1039 (1973). (6) R. M. Orheim and H. H. Bovee, Anal. Chem., 46, 921 (1974). (7) G. F. Smith, Analyst, (London), 80, 25 (1955). (8) M. K. John, Anal. Chem., 44, 429 (1972). (9) G. K. Pagenkopf, D. R. Neuman. and R. Woodriff. Anal. Chem., 44, 2249 (1972). (10) R. E. Remington, J. Amer. Chem. Soc., 49, 1410 (1927). (11) "Official Methods of Analysis of the Association of Official Agricultural Chemists," 10th ed., W. Horwitz, Ed., Association of Official Agricultural Chemists, Washington, D.C., 1965, pp 354-358. (12) R. C. Chu, G. P. Barron, and P. A. W. Baumgarner, Anal. Chem., 44, 1476 (1972). (13) C. C. Cassil, J. Ass. Offic. Anal. Chem., 20, 171 (1937). (14) C. R. Gross, lnd. Eng. Chem., 5, 58 (1933). (15) R. E. Remington. E. J. Coulson, and H. von Kolnitz, lnd. Eng. Chem., Anal. Ed., 6, 280 (1934). (16) H. S. Satterlee and G. Blodgett, lnd. Eng. Chem., Anal. Ed. 16, 400 (1944). (17) L. A. Muse, J. Chem. Educ.. 49, A463 (1972). (18) L. McBride, G. F. Smith Chemical Company, Columbus, Ohio, Personal Communication. (19) A. I. Vogel, "A Texbook of Quantitative Inorganic Analysis," 3rd ed.. Wiley and Sons, New York, N.Y., 1961, pp 796-798. (20) L. K. SharD, "lnorqanic Chemistry," Bailliere Tindall and Cox Ltd., London, 1962; p 158. (21) F. J. Schmidt and J. L. Royer, Anal. Lett., 6, 17 (1973). (22) I?. S. Braman, L. L. Justen, and C. C. Foreback, Anal. Chem., 44, 2195 (1972). (23) High Sensitivity Arsenic Determination by Atomic Absorption: pamphlet No. As-3A, Jarrell Ash Co. Applications Laboratory (Division of Fisher Scientific), January 1971 (24) 0. Menis and T. C. Rains, Anal. Chem., 41, 952 (1969).
A N A L Y T I C A L CHEMISTRY, VOL. 47, NO. 2 , FEBRUARY 1975
(25) A. Ando, M. Suzuki. K. Fuwa, and B. L. Vallee, Anal. Chem., 41, 1974 (1969). (26) K. E. Smith and C. W. Frank, Appl. Spectrosc., 22, 765 (1968). (27) R. Spallino, Gazz. Chim. /tal., 43, 481 (1913). (28) H. Popp, 2. Angew. Chem., 41 838 (1928). (29) F. P. Carey, G. Blodgett, and H. S. Satterlee, lnd. Eng. Chem., 6, 327 (1934). (30) C. C. Cassil and C. M. Smith. Amer. J. Pub. Health, 26, 901 (1936); Chem. Abstr., 30, 7781 (1936). (31) E. E. Barksdale, Virginia MedicalMonfhly, 67, 393 (1940). (32) E. F. Paulsen and E. S. Lio, An. Asoc. Ouim. Argent., 31, 68 (1943); Chem. Abstr., 38, 456 (1944). (33) R. H. Holland, R. H. Wilson, A. R. Acevedo, M. S. McCall, D. A. Clark, and H. C. Lanz, Cancer, 11, 1115 (1958). (34) D. C. Vucetich and R. Carratala. Rev. Asoc. Med. Argent., 56, 397 (1942): Chem. Abstr., 40, 2929 (1946). (35) M. E. Daff and E. L. Kennaway, Brit. J. Cancer, 4, 173 (1950). (36) B. A. Porter and J. E. Fahey, Residues on Fruits and Vegetables, in: "lnsects, The Yearbook of Agriculture," U S . Gov. Printing Office, Washington, D.C., 1952, p 300.
(37) M. D. Thomas and T. R. Collier, J. hd. Hyg. Toxicol., 27, 201 (1945). (38) H. S. Satterlee, New EnglandJ. Med., 254, 1149 (1956). (39) F. A. Patty, in "Industrial Hygiene and To~icology,'~2nd ed., Vol. 11, F. A. Patty, Ed. lnterscience Publishers, New York N.Y., 1967, p 877. (40) W. P. Tseng, H. M . Chu, S.W. How, J. M. Fong, C. S. Lin. and S.Yeh, J. Nat. Cancer lnst., 40, 453 (1968). (41) M. E. Daff, R. Doll. and E. L. Kennaway, Brit. J. Cancer, 4, 173 (1950). (42) D. V. Frost, Fed. Proc., 26, 194 (1967).
RECEIVEDfor review July 2, 1974. Accepted October 21, 1974. Presented a t the 57th Canadian Chemical Conference, Regina, Saskatchewan, June 2-5, 1974, and a t the Symposium: Trace Analysis in Biological Materials, Halifax, Nova Scotia, August 21-23, 1974. The authors are grateful to the National Research Council of Canada for partial financial support.
Spectrometric Method for the Quantitative Determination of Elemental Carbon Dwight M. Smith,' John J. Griffin, and Edward D. Goldberg Scripps Institution of Oceanography, La Jolla, Calif. 92037
A characteristic transmission spectrum for a variety of elemental carbons is produced through surface oxidation accompanying an extensive grinding process in air. A linear relationship between the absorbance of a band at 1580 cm-' and the mass of carbon exists. An acid treatment with HCI and HF is used to remove mineral constituents of materials to be analyzed and, for samples containing organic material, basic peroxide treatments are also used. The preparation and analysis of synthetic sediment materials has demonstrated quantitative recovery of added elemental carbon. The method has been applied to fly ash samples and marine Sediments with excellent reproducibility and should be applicable to a wide variety of natural materials containing elemental carbon.
A record of historic and prehistoric burning of carbonaceous materials may be found in the elemental carbon contents of marine and lacustrine sediments ( I ) . However, practicable methods for the determination of this elemental carbon in such materials, ranging between 0.OOX and 0.X percent by weight in pelagic sediments. are not to be found in the literature. Methods currently employed to determine carbon in materials of similar composition (2-5) involve the combustion of carbon with subsequent determination of the resulting carbon dioxide. Analyses of this kind may include carbon from organic and carbonate sources, as well as any in the elementary state, and when employed a t or below the ppm level, are complicated by reagent and equipment blanks. An analytical method which would allow discrimination with regard to the type of carbon present, and which could be made specific for elemental carbon, was necessary for the study of carbon in marine sediments (I ). Friedel and Hofer ( 6 ) published the first transmission infrared spectrum of activated carbon by utilizing special sample preparation and instrumental techniques. Although
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Present address, Department of Chemistry, University of Denver, Denver, Colo. 80210.
infrared spectra of a number of carbon contaiiiing materials such as coals (7-11), coal pyrolysis products (12, 1 3 ) , chars (14-19), carbon black ( 2 0 , 2 1 ) and graphite ( 2 2 ) ,and ATR spectra of sorbates on activated carbon (23-25) have been reported, the transmission spectra of carbons have not been obtained because of the intractability of, and high scattering by, these materials. A reduction of the sample to a finely divided form, effected by several hours of grinding in a ball mill, was necessary to produce an absorption spectrum. The spectrum was obtained utilizing the standard KBR pellet technique, and employing either reference beam attenuation or scale expansion modes of the infrared spectrophotometer. Absorption bands a t 1735, 1590. and 1215 cm-l, were attributed to the existence of carhon-oxygen functional groups by analogy with similar bands in spectra of coals and carbon blacks (7-11, 20, 21 ). The development of the analytical method discussed in this paper was based upon the infrared absorption spectra of ground separates of elemental carbons.
BASIS AND DEVELOPMENT OF THE METHOD Spectra. Figure 1 shows the infrared transmission spectrum of a petroleum-based charcoal (MCB) in the range 2500-1000 cm-', showing absorption hands at 1720, 1580, and 1240 cm-l. This material was ground for 18.5 hours in a stainless steel vial and the spectrum obtained from a 0.30 weight percent mixture in a KBr pellet. The spectrum was taken with a Perkin-Elmer 621 Infrared Spectrophotometer utilizing reference beam attenuation. A number of other carbons, including decolorizing carbon (Norit A ) , fly ash, lampblack, forest fire charcoals, and graphite, yielded the same set of absorption bands after an appropriate period of intensive grinding. Petroleum-based charcoal was chosen as a reference standard for this work because of its low ash content, about 1%,relative to other elemental carbon materials examined. The 1580 cm-' absorption band was selected for analytical study because it is both the most characteristic and most intense in the spectrum.
A N A L Y T I C A L C H E M I S T R Y , VOL. 47, N O . 2, FEBRUARY 1975
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