(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
'
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.
ANALYTICAL CHEMISTRY, VOL. 47, NO. 2, FEBRUARY 1975
233
5c
/
-
40-
‘400
I v)
0
2500
2000
1800
I600
1200
1400
1000
FREQUENCY (cm-ll Figure 1. Infrared spectrum of petroleum-based charcoal
, - - L - - . LC j
MCB charcoal ground 18 5 hours; 0 30% in KBr; reference beam attenuation of Perkin-Elmer 521 4 50 r--~-
I _ -
zccc
800
1600
14CC
,200
W A V E N U M B E R (crn-7
Figure 3. Comparison of petroleum-based charcoal ground in air and in nitrogen ( A ) as in Figure 1; ( 8 )in nitrogen at atmospheric pressure after evacuation at Torr; grinding for 24 hours ( A ) and 40 hours (8);0.3% in KBr
2
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270
1
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-
-_____~,
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36 48 60 GRINDING T I M E , hours
__
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84
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Figure 2. Specific absorbance of the 1580 c m - ’ infrared band of petroleum-based charcoal as a function of grinding time Grinding in stainless steel vial with Spex Mixer/Mill; 0.1 % in KBt
The intensities of the absorption bands a t 1720, 1580, and 1240 cm-I depended upon the extent of grinding for all carbons examined. The dependence of absorption band intensity upon grinding time for the petroleum-based charcoal of Figure 1 is shown in Figure 2. The specific absorbance of the 1580 cm-’ band goes through a maximum at 14 hours of grinding, decreasing to an approximately constant value after 24 hours of grinding; longer grinding times develop a slight increase in the specific absorbance of this band. A grinding time of 24 hours was selected as the optimum value for all later work with this material. It should be noted that only a few milligrams of sample can be in the vial for thorough grinding; a maximum sample size of 50 milligrams for each 2-ml stainless steel vial was used in all experiments. The dependence of infrared absorption band intensity upon the extent of grinding raises questions concerning the origin(s) of these bands. Either physical or chemical factors, or both, could be responsible for the phenomena observed in Figures 1 and 2. All three principal frequencies could be assigned to known carbon-oxygen functional groups as proposed by Friedel and Hofer (6).On this basis, the band a t 1720 cm-I would likely be due to a ketone-like carbonyl, that at 1580 cm-l a chelated carbonyl group, and the one a t 1240 cm-l probably a simple carbon-oxygen or phenoxy linkage. The infrared (22) and Raman (26 spectra of graphite, however, show a strong absorption near 1580 cm-l which has been attributed to lattice vibration (26) or “aromaticity” of the graphite structure ( 2 2 ) . Be234
*
cause it is important to understand the phenomenological bases of any analytical method, a series of experiments was designed to determine the origin of the spectral features upon which the method is based. Palmer ( 2 7 ) ,and Harker, Horsley, and Robson (28) have shown that powdering in a ball-mill introduces structural defects into graphite which have a high reactivity toward oxygen. The possibility that surface oxidation of elemental carbons during the grinding process is responsible for the development of the bands in the infrared spectrum was examined. An evacuable grinding vial having a capacity the same as those used routinely for the grinding process and which could be attached directly to a vacuum system, was prepared from stainless steel using a Hoke valve. A 50-milligram sample of petroleum charcoal was placed in the vial together with the stainless steel balls ordinarily used and the vial evacuated a t 10-5 Torr for 6 hours. The vial was filled with pure nitrogen to atmospheric pressure and the sample ground for 40 hours. Another sample was ground for 24 hours in air under the same conditions for use as a reference. Figure 3 shows the result of this experiment. Curve A is the spectrum of petroleum charcoal ground 24 hours by the usual technique (in air) a t a concentration of 0.3% in KBr. The bands a t 1720, 1580, and 1240 cm-] are those observed in Figure 1. Curve B is the spectrum of petroleum charcoal ground 40 hours in a nitrogen atmosphere at approximately the same concentration. The absence of any absorption bands in the 2500-1000 cm-I region is definitive evidence that all three absorption frequencies in the infrared spectrum of petroleum charcoal, and presumably all other elemental carbon materials showing this set of bands, are due to carbon-oxygen functionalities and that all are produced by the grinding process. Experimental Variables. T h e development of any reliable spectrometric method requires the examination and control of the effect of a number of experimental variables. In this case, in addition to the effect of grinding time and technique, such factors as sample preparation, instrumental parameters, heating of the sample, and KBr pelleting technique were investigated. Several authors (reference 7 , p 316) have discussed the effect of moisture on infrared spectra of samples using the KBr technique. In this work infrared bands at 3440 and 1625 cm-’ appeared in the spectra after mixing the sample and KRr in a stainless steel vial using a Spex Mixer/Mill, drying a t 100 O C overnight and pelleting in an evacuated
A N A L Y T I C A L CHEMISTRY, VOL. 47, NO. 2, FEBRUARY 1575
die. The band a t 1625 cm-', due to molecular HlO, is particularly troublesome because of its partial overlap with the 1580 cm-I carbon band and the resultant uncertainty as to its contribution to the integrated absorbance of that band. Exhaustive drying, even in a vacuum oven, of sample, KBr and sample-KBr mixtures diminished but did not eliminate the band a t 1625 cm-'. I t was determined that the mixing-grinding step is chiefly responsible for the water band a t 1625 cm-l and that temperature, time, and pressure of drying are secondary variables. Figure 4 demonstrates the effects of mixing and drying upon the incorporation of water into the KBr matrix and its appearance in the spectrum. Spectrum 4A shows a substantial H20 band a t 1625 cm-' after 15 minutes of mixing-grinding even though the sample-KBr mixture was dried for 2 hours in a vacuum oven a t 50 "C. Spectra 4B and 4C demonstrate the decreased band size with decreased mixing-grinding time, although the sample for Spectrum 4H was heated a t a higher temperature and for a longer time in the vacuum oven. (The 1725 cm-l band in Spectra 4.4 and 4H represents organic material distilled from the gaskets of the vacuum oven and has no bearing on this discussion.) Spectrum 4 0 is that of KBr heated in an analytical drying oven a t 110 "C and pelleted without the mixing-grinding step. The procedure adopted for the determination of all spectra in this work was essentially that for Spectrum 4C. Samples were prepared using thoroughly dried spectrometric grade KBr, mixed by grinding for 30 seconds in a stainless steel vial, and dried a t 120 "C overnight prior to pelleting. No subsequent evidence of significant interference hy water in the spectrometric measurement of carbon was detected, although it is responsible for a hlank observed in quantitative studies. During the study of the effect of moisture on the infrared spectrum of carbon in the KBr matrix, the effect of heating on the absorbance of the 1580 cm-1 carbon band was quantitatively examined. A t 120 "C, no measurable effect of heating the sample-KBr mixture beyond 16 hours was found and it is likely that shorter times would be as effective. The effect of heating of the pellet by the spectrophotometer wurce was also examined. No measurable effect on the spectrum was found with the sample remaining in the sampling area over a period of two additional hours. Bevond a minimum requirement, heating of the sample does not appear to be a critical variable. The only instrumental parameters which are critical are the gain and optical attenuation which remained a t fixed values for all quantitative spectral measurements. Both scan speed and slit program were also held a t constant values for all quantitative work.
EXPERIMENTAL P r o c e d u r e I. Materials w i t h o u t O r g a n i c Content. Approximately 10 grams of sample, containing from about 0.10 to 1.0 weight percent elemental carbon, are digested with hot 6F HC1 for two hours and subsequently washed with distilled water by centrifugation to remove soluble salts. The residue is digested with a 28% H F solution for about 10 days to break down any siliceous materials and to remove silicon as SiF4. The residue is thoroughly washed with distilled water hy Centrifugation to remove soluble salts. It is then digested with hot 6 F HC1 to remove any insoluble fluorides formed in the last step. The residue is washed by centrifugation with distilled water. The resulting sample is dried for infrared analysis. Fifty milligrams or less of the dried separate is ground in a stainless steel \rial with stainless steel balls for 24 hours using a Spex Model 8000 Mixer/.MIl. A mixture of about 5% of the ground material in spectrometric grade KBr is accurately prepared and is homogenized for 30 seconds with the Spex Mixer/Mill. The homogenized mixture is heated for 16 hours at 120 "C. The sample for infrared analysis is prepared by diluting this mixture one to ten
70
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-
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80
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1
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with spectrometric grade KBr through accurate weighing and the sample is again homogenized in a stainless steel vial for 30 seconds using the Spex Mixer/Mill. T h e entire sample is transferred to a KBr die and pressed in uacuo a t 10,000 pounds. The spectrum is obtained with a Perkin-Elmer Model 521 Infrared Spectrophotometer purged with dry compressed air. After the sample is in place, the optical attenuator is set to yield 40% transmittance a t 1800 cm-'. The spectrum is recorded from 4000 to 600 cm-I in boththe transmittance and absorbance modes; minimum scan speed is used from 1800 to 1200 cm-'. The infrared band centered a t 1580 cm-' is used for analytical calculations. The baseline technique is employed and values of S A (u)dv are obtained with a planimeter. Procedwre 11. Materials w i t h O r g a n i c Content. A solution of equal parf,s of 30% hydrogen peroxide and 2F KOH is slowly added to 20-60 grams of oven dried sediment (110 "C) until no further reaction is evidenced through bubble formation, a period usually of one to three days in length. This oxidation and dissolution step removes a substantial amount of the organic matter present. T h e residue is centrifuged in 2F KOH and then in distilled water. The remaining solids are then digested with hot 6 F HC1 for two hours and subsequently washed with distilled water by centrifugation to remove soluble salts. The residue is digested with a 28% H F solution a t room temperature for about 10 days to break down any siliceous minerals and to remove silicon as SiF4. The residue is washed with distilled water by centrifugation to remove soluble salts. I t is then digested with hot 6F HCI t o remove any insoluble f1,uorides formed in the last step and the residue is washed by centrifugation with distilled water. Another basic peroxide treatment similar to the first step is used to remove any remaining organic matter. The final washings are with weakly acidic HC1 to prevent dispersal of the solids. The resultant dried sample is used for the infrared analysis which is carried out precisely as described in Procedure I.
RESULTS AND DISCUSSION Basic Relationships. A linear relationship between the absorbance a t 1580 cm-l, Alsso, and mass of carbon (m,) for the petroleum-based charcoal of Figure 1 was established. (Mass of carbon (m,) is actually the mass of ground,
ANALYTICAL CHEMISTRY, VOL. 4 7 , NO. 2, FEBRUARY 1975
235
I60
j A (v ldw
A I40
Table I . Analysis of Fly Ash Samples Using Procedure Ia
D
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020
040
060
080
cR = 0.932%C - 0.174.
120
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160
I80
% CARBON A D D E D
Figure 5. Recovery of carbon from synthetic sediments ( A ) S A ( u ) d u vs. % carbon added: (5)Alsso vs.
"/A
carbon added
and therefore oxidized, petroleum charcoal employed as a standard. Calibration curves used in analysis were based upon this material and the carbon content,s of all materials reported herein are relative to it rather th.an pure elemental carbon.) A least-squares treatment of replicate data yields the linear equation AISRO= 0.273 mc
+
0.009
with a correlation coefficient of 0.9986. The plot of integrated absorbance over the region 1670-1400 cm-1, SA (v)dv, us. the mass of carbon also shows excellent linearity. The equation of the least squares line from the replicate data is
J A ( v ) d v = 28.33 wiC
-t
1.04
with a correlation coefficient of 0.9996. The linearity between both A1580 and JA(v)du and the mass of carbon in the KBr pellet, m,, demonstrate that a valid working curve can be based upon either A1580 or J-A(v)du.The intercepts of both plots were shown, in separate experiments, to equal the pure KBr absorbance which is caused by H20 in the region measured. Synthetic Sediments. The validity of the application of this spectrometric method to the determination of elemental carbon in sediment materials was established through the preparation and analysis of synthetic samples. Carboncontaining sediments were simulated by mixing accurately weighed amounts of the petroleum charcoal standards with ignited samples of sediments taken from the Santa Barbara Basin off Southern California. Procedure I, outlined above, involves an acid treatment for the dissolution of mineral followed by grinding of the dried residue and infrared analysis. 236
*
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Figure 5 shows the results of the carbon recovery studies with the synthetic sediment samples. Calibration curves, based upon the linear relationships between both SA (u)dv and A 1 5 ~ 0 ,and mass of carbon, were used in determining the mass of carbon in each sample. Figure 5.4 reports %C recovered on the basis of the measurement of S A (u)du and Figure 5B is on the basis of the A1580 measurement. A least-squares treatment of the data in Figure 5A yields the linear equation
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9.9 10.0 a Calculations based upon JA(u)dv. 30 hours of grinding. Duplicates based upon separate samples of the same isolate. * 60 hours grinding.
0.59 0.62b
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The positive intercept and slope less than unity reveal the presence of a blank and proportionate error, respectively, in the analysis. In separate experiments, utilizing the same procedure for samples containing only the ignited mineral residue, the blank was determined as 0.041 f 0.005. While the origin of the difference between the experimentally determined blank and the intercept of the least squares line as well as the small negative proportionate error in the analysis are unknown, their presence does not affect the applicability of the method. Separate experiments have demonstrated that neither the chemical treatment of the petroleum charcoal, nor variations in the grinding time beyond 24 hours, significantly affect the infrared analysis. These recovery studies demonstrate that, employing Procedure I, the analysis of elemental carbon in the presence of inorganic materials by infrared spectrometry is feasible. Fly Ash. Preliminary application of the method to fly ash samples from several power plants was attempted. Duplicate results of some of these analyses are listed in Table I for materiais having a range of carbon content from 0.6 to 10% by weight. The duplicate analyses were based upon different samples of the same isolate, thus indicating only the reproducibility of the method. Because of the refractory nature of these samples, a somewhat longer grinding time was employed and for several samples, as indicated by Table I, the effect of grinding time upon the analysis was examined. The results of this study indicate a satisfactory reproducibility of the method in application to such materials. No independent carbon analyses of the fly ash samples were available. M a r i n e Sediments. Extension of the method to marine sediment samples containing significant quantities of organic matter represents a separate problem. Infrared spectra of marine sediment residues prepared according to Procedure I reveal several additional absorptions, including strong bands in the 3000-2800 cm-l, 1700 cm-I, and 1400 cm-l regions due to hydrocarbon-containing organic residues. These organic residues do contain humic a,cids ( 2 9 ) , as well as other degradation products ($01, and have the characteristic infrared spectrum of alkyl carboxylic acids. Becauw the spectra of typical humic acid residueb (31) have absorptions partially overlapping the 1580 crn--l band produced by elemental carbon, the functional groups responsible being similar, these materials must be removed prior to analysis. A variety of chemical treatments including basic extractions and oxidations, separately and in Combination, led to a procedure effective in removing humic acid residues while not significantly affecting the el-
ANALYTICAL CHEMISTRY, VOL. 47, NO. 2, FEBRUARY 1975
0400
: :I
30
I 20
-
% R = O 81% C
+ 0 024
.
0 IO0
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0
0 200
0 I00
3 300
0500
3400
PERCENT CARBON I N SYNTHETIC S E O I M E N T ( % C )
Figure 7. Recovery of carbon f r o m synthetic sediments utilizing cedure II
Pro-
Table 11. Analysis of Synthetic Sediments for Percent Elemental Carbon Using Procedure I1 Sediment
+
peholeum charcoal
%C added %C found
Sediment
Sediment
FPL fly ash (oil) CE fly ash (coal)
0.28
0.29
0.29
0.25
0.25
0.31
Table 111. Analysis of Marine Sediments for Percent Elemental Carbon Csing Procedure IIa Scan 78P
zcc0
le00
1600
LFGS19G
7-Tow K1-SFF
ZTs 111 512
A h 111C:
0.0055 0.099 0.051 0.048 0.027 0.0056 0.090 0.049 0.051 0.029 The coordinates and depth at which sediment cores were taken are found in Reference ( 1 ) . Duplicate values were obtained through analyses of separate samples of the same isolate; i . e . , are indicative of the precision of the method.
1400
WAVENUMBER ( e r n - ' )
Figure 6. Effect of chemical treatments on infrared spectrum of sediments ( A ) Santa Barbara Basin sediment (Procedure I);( B )single KOH treatment of sediment in A; (C) precipitant from extract of B; (D)single H202 treatment of sediment in A; (E) residue from typical deep-sea sediment (Procedure II)
emental carbon in the sample. Procedure 11, outlined above, involves a double oxidation with hydrogen peroxide in base. Figure 6 indicates the nature of the effect of base and hydrogen peroxide on a sample of marine sediment with an unusually high content of organic residues. The spectra of Figure 6 are of Santa Barbara Basin sediments deposited between 1858 and 1886. These samples are used for purposes of illustration only, as the organic content was so high for these anoxic sediments that analysis for elemental carbon was not attempted a t this time. All analyses reported ( 1 ) are for deep-sea sediments. Figure 6A is the infrared spectrum in the region 20001200 cm-l for an 0.7% sample of 1886-1888 Santa Barbara Basin sediment residue (Procedure I) in KBr. Strong broad bands a t 1720, 1600, and 1400 cm-1 are due t o organic phases. The spectrum of the same material after a single treatment with the KOH solution is shown in Figure 6B. Although some organic residue has been dissolved, a large quantity remains. Figure 6C is the spectrum of material precipitated from that extract with HC1; it is the spectrum in the 2000-1200 cm-l region of a typical organic residue. Figure 6D is the spectrum, under the same conditions, of a similar Santa Barbara Basin sediment (1858-1860, same core) residue after a single treatment with hydrogen peroxide. While some HrO was present in this sample, absorbing between 1600-1700 cm-l, a t 3400 cm-I and 1400 cm-', most of the organic matter has been removed from this sample by the hydrogen peroxide treatment. A typical
spectrum of a deep-sea sediment after chemical treatment is shown as Figure 6E. Any effect on the spectrum of carbon of the chemical treatment employed in the analytical procedures for eiemental carbon was explored. Although the formation of carbon-oxygen functional groups on the surface of carbon has been shown due to the grinding process, the possibility of surface oxidation by hydrogen peroxide or blocking of oxidizable sites by other reagents was considered. Two approaches to this question were used, both employing synthetic sediment samples. In one series of experiments, accurately weighed quantities of the previously analyzed fly ash samples or petroleum charcoal were mixed with ignited sediment residues and the samples carried through the entire Procedure 11. Results of these analyses are shown in Table I1 and indicate that the double H202 oxidation does not significantly oxidize the carbon surface or remove quantities of carbon. A more definitive study of the effect of chemical treatment on the analysis of elemental carbon was desired, however. Another series of synthetic sediments was prepared in the same manner using the petroleum charcoal standard. The results of these experiments are shown in Figure 7. A linear relationship is evident, t h e least squares treatment of which yields %R = O.Sl%C
- 0.024
The intercept of 0.024% is consistent with blank values and the negative proportionate error does indicate a small proportional loss of carbon which dictates the use of a calibration curve such as Figure 7 . Since the relationship is linear, such an application will not affect the accuracy of the method.
A N A L Y T I C A L CHEMISTRY, VOL. 4 7 , NO. 2, FEBRUARY 1975
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SUMMARY OF APPLICATIONS The application of this spectrometric method for the quantitative determination of elemental carbon was in the previously cited ( l a ) analysis of marine sediments. The reproducibility of the method in this application is indicated by the duplicate analyses listed in Table 111. Some analyses of fly ash and atmospheric dust samples have shown that the method is applicable to a wide variety of natural materials. Further, separate experiments have shown that the sensitivity of the method can be significantly improved by employing the ordinate expansion mode of the infrared spectrophotometer.
LITERATURE CITED (1) (a) D. M. Smith, J. J. Griffin, and E. D. Goldberg, Nature (London). 241, 268 (1973); (b) A. M. Swain, Quart. Research, 3, 383 (1973). (2) F. T. Lindgren, G. R . Stevens. and L. C. Jensen, J. Amer. Oil Chem. Soc., 49, 208 (1972). (3) A. Steyermark, "Quantitative Organic Microanalysis," second ed., Academic Press, New York, N.Y.. 1961, p 151. (4) F. Saker, Microchem. J., 16, 145 (1971). (5) C. E. Childs and E. B. Henner, Microchem. J., 15, 590 (1970). (6)R . A. Friedel and L. J. E. Hofer, J. Phys. Chem., 74, 2921 (1970). (7) R . A. Friedel. "Applied Infrared Spectroscopy," D. N. Kendall. Ed., Reinhold, New York, N.Y., 1966, Chap. IO. (8) R. A. Friedel and H. L. Retcofsky, "proceedings of the 5th Carbon Conference," S. Mrozowski, Ed., Pergamon Press, New York. N.Y., 1963, pp 149-165. (9) R. A. Friedel and G. L. Carlson, Fuel, 51, 194 (1972). (10) R. A. Friedel and J. A. Queiser, Bu. Mines Bull., 632, 1966. (1 1) M. G. Pelipetz and R . A. Friedel. Fuel, 38, 8 (1959).
(12) R . A. Friedel. J. A. Queiser, and H. L. Retcofsky, J. Phys. Chem., 74, 908 (1970). (13) F. S. Karn, R. A. Friedel, and A. G. Sharkey, Jr., Fuel, 51, 113(1972). l i d ) R. A. Friedel and M. G. Pelipetz, J. Opt. SOC.Amer., 43, 1051 (1953). ' R . A. Friedei. "Proceedings of the 4th Carbon Conference," S. Mrozowski. Ed.. Peraamon Press. New York. N.Y.. 1960. DD 321-336. R. A. Friedel, R. A. Durie.'and Y. Shewchyk. Carbon, 5, 559 (1968). J. K. Brown, J. Chem. Soc., 744 (1955). R. A. Friedel, Appl. Opt., 2, 1109 (1963). R . A. Friedel and H. L. Retcofsky, "Spectrometry of Fuels,'' Plenum Press, New York, N.Y., 1970, Chap. 5. V. A. Garten and D. E. Weiss. Aust. J. Chem., 10, 295 (1957). V. A. Garten and D. E. Weiss, "Proceedings of the 3rd Carbon Conference," S. Mrozowski, Ed., Pergamon Press, New York, N.Y.. 1959, p 295. R. A. Friedel and G. L. Carlson, J. Phys. Chem., 75, 1149 (1971). J. S. Mattson and H. B. Mark, Jr., J. Colloid lnterface Sci.. 31, 131 (1969). J. S. Mattson, H. B. Mark, Jr.. M. D. Malbin. W. J. Weber, Jr., and J. C. Crittenden. J. Colloid lnterface Sci., 31, 116 (1969). J. S. Mattson, H. B. Mark, Jr , and W. J. Weber, Jr., Anal. Chern., 41, 355 (1969). F. Tuinstra and J. L. Koenig, J. Chem. Phys., 53, 1126 (1970). D. J. Palmer, J. Colloidlnterface Sci., 37, 132 (1971). H. Harker, J. B. Horsiey, and D. Robson, Carbon, 9, 1 (1971). V. I. Kasatochkin, 0. K. Bordovskiy, N. K. Larina, and K . T. Cherkinskaya, Dokl. Akad. Nauk SSR, 179,690 (1967). R. A. Friedel and A. J. Nawalk, Nature (London), 217, 345 (1968). F. J. Stevenson and K. M. Goh, Geochirn. Cosmochim. Acta, 35, 471 (1971).
RECEIVEDfor review June 7, 1974. Accepted October 7 , 1974. One of the authors (D.M.S.) acknowledges a leave granted by Hope College and the support of National Science Foundation in the form of a Science Faculty Fellowship. This research was supported by a grant from the Environmental Protection Agency.
Inductively Coupled Plasma-Optical Emission Analytical Spectrometry. A Study of Some lnterelement Effects George
F. Larson, Velmer
A. Fassel,' Robert H. Scott,* and Richard N. Kniseley
Ames Laboratory ERDA and Department of Chemistry, Iowa State University, Ames. Iowa 500 10
Investigations of the extent to which certain interelement or interference effects occur in an inductively-coupled plasma are reported. Under conditions normally employed for analytical purposes, it is shown that: a) two solute vaporization interferences often observed in flames are eliminated or reduced to negligible proportions in the plasma; b) increasing concentrations of an easily ionizable element (Na) up to concentrations of 6900 pg/ml exerted an unusually low influence on the observed emission intensities of three selected elements (Ca, Cr, and Cd) of widely differing degrees of ionization. The high degree of freedom from interelement effects of this analytical technique is further documented by the observation that a variety of matrices did not affect the emission intensity of Mo to a significant extent.
During the past decade, inductively-coupled plasmas have emerged as very promising excitation sources for the optical emission determination of trace elements in solution. The ultimate scope of application of this analytical T o w h o m requests for r e p r i n t s should h e directed. Present address, N a t i o n a l Physical Research Laboratory, C o u n c i l for Scientific a n d I n d u s t r i a l Research, Pretoria, S o u t h Africa. 2
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approach will depend to a great extent on its degree of freedom from interelement interactions or interferences. Spectral interferences are not included in the present study, because these interferences are usually strongly dependent on the spectral bandwidth of the spectrometer and the spectral characteristics of the elements. These interferences, therefore, do not necessarily characterize the source alone. The remaining group of interferences may be classified according to several viewpoints ( I ): transport, solute vaporization, vapor-phase, and plasma geometry interferences; specific and nonspecific interferences; and physical and chemical interferences. These various types of interferences are not mutually exclusive in their actions or mechanisms. In this paper we show that: a) two solute vaporization interferences often observed in flames are eliminated or reduced to negligible proportions in the plasma; b) increasing concentrations of an easily ionizable element (Na) up to concentrations of 6900 pg/ml exerted an unusually low influence on the observed emission intensities of three selected elements (Ca, Cr, and Cd) of widely differing degrees of ionization. The high degree of freedom from interelement effects of this analytical technique is further documented by the observation that a variety of matrices did not affect the emission intensity of Mo to a significant extent. 1975
