geneity of the standards, and (c) by increasing the counting statistics. Because of the features of activation analysis one may wish to reach highly sensitive and highly precise determinations in different material. The designed target holder-allowing the simultaneous irradiation of 40 samples-makes routine analysis readily performed by limiting the time consumption of a large cyclotron. The method allows analysis of homogeneous samples, as is the case for air filters, or of small inhomogeneous samples, e.g., samples that can be covered by the beam area. Furthermore, the method as suitable for thin samples can also be applied to determine concentrations in thick samples. ( B ) Charged particle activation allows lead determinations in aerosol samples from less than 0.1 m3 of air of remote areas. Typical sensitivities achieved during our routine analysis are 1 ng/cm2, allowing lead determination in air volumes as low as 0.1 m3/cm2. This is particularly interesting for air pollution monitoring. Large air samplers are no longer required for this analytical technique, and samplers having low flow rate and small collection area (1cm2) can be used instead ( 1 0 ) .The analysis is nondestructive, so that the samples can be reused for other purposes. Finally, other elements have been identified in the y-ray spectrum. They were, however, not analyzed quantitatively. There are As, Sn, Se, Cu, Zn, Mn, Fe, Ni, Sr, Cr, and Na. By changing the counting conditions, other elements could be seen, e.g., Ca, Sc, Ti, V, Co, Br, Ag, and Cd. Care, however, has to be taken on interfering reactions on lower 2 elements. The wide variety of elements seen makes this method very attractive for multielement analysis. Furthermore, lead isotopic analysis using prot.on activation could also be performed.
ACKNOWLEDGMENT We are indebted to the cyclotron staff and P. Macq for providing irradiation facilities. We also express appreciation to N. Jacob and J. Ligot for their valuable assistance in the laboratory analysis, and to J. Cara and P. Nemegeer for their very valuable technical aids. J. W. Winchester is acknowledged for his comments and review of the manuscript.
LITERATURE CITED (1) Georges Desaedeleer, Ph.D. Dissertation, Louvain University, October 1974. (2) M. Murozumi. T. J. Chovd, and C. Patterson, Geochim. Cosmochim. Acta. 33, 1247 (1969).
(3) T. J. Chow, K. W. Bruland, K. Bertine, A. Soutar, M. Koide, and E. D. Goldberg, Science, 181, 551 (1973). (4) "Airborne Lead in Perspective", National Academy of Sciences, Washington, D.C., 1972. (5) W. U. Auk, R . G. Senechal and W. E. Erlebach, Environ. Sci. Techno/., 4, 305 (1970). (6) M. B. Rabinowitz and G. W. Wetherill, Environ. Sci. Techno/., 6, 705 (1972). (7) Georges Desaedeieer and J. W. Winchester, Environ. Sci. Technol., 9, 971 (1975). (8) G. G. Desaedeleer, J. W. Winchester, R. Akselsson, K. A. Hardy, and J. W. Nelson, Trans. Am. Nucl. Soc., Suppl. 3, 21, 36 (1975). (9) G. G. Desaedeleer, J. W. Winchester and R. Akselsson, International Conference on Heavy Metals in the Environment, Toronto, 27-31 October. 1975. D. B1. J. W.Nelson, E. Jensen, G. Desaedeleer, R . Akselsson, J. W. Winchester, Adv. X-ray Anal., 19, in press. J. L. Moyers, W. H. Zoller, R. A. Duce, and G. L. Hoffman, Environ. Sci. Technol., 6, 68 (1972). E. L. Jernigan, B. J. Ray, and R . A. Duce, Atmos. Environ., 5, 881, 1971. R . M. Daines, Environ. Sci. Technol., 4, 318 (1970). J. W. Winchester, W. H. Zoiier, R . A. Duce, and C. S. Benson, Atmos. Environ., 1 , 105 (1967). T. J. Chow, J. L. Earl, and C. F. Bennet, Environ. Sci. Techno/., 3, 737 (1969) ~ ~ , C. S. Martens, J. J. Wesolowski, R . Kaifer and W. John, Atmos. Environ., 7, 905 (1973). T. B. Johansson, R . E. Van Grieken, J. W. Nelson, and J. W. Winchester, Anal. Chem., 47, 855 (1975). T. A. Cahill, "Cyclotron Analysis of Atmospheric Contaminants", Report of Crocker Nuclear Laboratory, University of California, Davis, Calif., 1972. B. Parsa and S. S. Markowitz, Anal. Chem., 46, 186 (1974). P. Meyers, "Proceedings of the 2nd Conference on Practical Aspects of Activation Analysis with Charged Particles, Liege, 1967", Vol. 1, Euratom, Brussels, p 195. G. W. Reed, K. Kogoshi, and A. Turkevich, "Proceedings of the 2nd International Conference on the Peaceful Uses of Atomic Energy, Geneva, 1958", Vol. 28, paper 953, United Nations, N.Y.. p 486. E. A. Schweikert and Ph. Albert. "Radiochemical Methods of Analysis", Vol. 1, IAEA, Vienna, 1965, p 323. E. A. Schweikert, Trans. Am. Nucl. SOC., 13, 58 (1970). D. C. Riddle and E. A. Schweikert, Anal. Chem., 46, 395 (1974). J. C. Cobb, J. Geophys. Res., 69, 1895 (1964). J. R. Routti, "SAMPO. A Fortran IV program for computer analysis of gamma spectra from Ge(Li) detectors, and for other spectra with peaks", University of California, Rept. UCRL-19452, 1969. M. Barbier, "Induced Radioactivity", North Holland, 1969. R. E. Bell and H. M. Skarsgard, Can. J. Phys., 34, 745 (1956). Georges Desaedeleer, Claude Ronneau, and Desire Apers, Progress Report CNEPAC, Vol. 6, Brussels, 1975. Georges Desaedeleer, Environ. Sci. Techno/. (submitted). G. Desaedeleer and E. Schifflers, Atmos. Environ. (submitted). G. Desaedeleer and C. Ronneau, Trans. Am. Nucl. SOC.,Suppl. 3 , 2 1 19 (1975). I
RECEIVEDfor review October 29, 1974. Resubmitted July 10, 1975. Accepted November 12, 1975. The authors gratefully acknowledge the Centre National d'Etude de la Pollution Atmosphkrique par la Combustion for its financial assistance.
Rapid Photochemical Decomposition of Organic Mercury Compounds in Natural Water A. M. Kiemeneij and J. G. Kloosterboer" Philips Research Laboratories, Eindhoven, The Netherlands
A method has been developed for the determination of total mercury in water at concentrations in the ppb range. Decomposition of organo mercurials is carried out by means of ultraviolet radiation of a suitable wavelength from small, low-pressure lamps containing either Zn, Cd, Hg or a mixture of these metals in their cathodes. The formed inorganic mercury is determined in the usual way by cold vapor atomic absorption after reduction of Hg2+ to Hg'. Determinations with and without irradiation make possible separate deter-
mination of total and inorganic mercury, respectively. Irradiation times are approximately 20 min. The "photochemical" analysis of natural water samples is compared with the wet-chemical analysis. The results agree within 4 % at a level of 1 pg/l., even for unfiltrated samples. The photochemical method, which requires a minimum of reagents (only HCI and SnCI2), yields substantially lower blank values than the wet-chemical method.
ANALYTICAL CHEMISTRY, VOL. 48, NO. 3, MARCH 1976
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200
b -;y r
I1
._.
"
B
Figure 1. View of two silica irradiation cells with the light source Dimensions: Height 50 mm, internal diameter 33 mm, and external diameter 70 mm
Inorganic mercury in water may be easily determined by reduction with stannous chloride to Hgo, followed by the detection of mercury vapor by means of cold vapor atomic absorption (1). This method is insufficient for the determination of the total concentration of mercury in water since organic mercury compounds are not reduced by SnC12. Owing to the conversion of Hg2+ to CHSHg+ in natural water and owing to the presence of mercury in a large number of organic pollutants, it is often observed that a high percentage of the mercury is present in the form of organic compounds. Some organic mercurials like CHBHgC1 and ( C H ~ )Hg P may be reduced by a combination of CdC12 and SnC12, but this method requires large quantities of reductants and the use of strong acid and strong alkali (2). Organic mercury compounds can be decomposed by heating with strong oxidizing agents such as KnCr20.i or HN03/HC104, followed by reduction of the formed Hg2+ to Hgo (3, 4 ) . Both methods are rather time-consuming and not very suitable for automation. Goulden and Afghan ( 5 ) have used ultraviolet irradiation as a means of decomposition, following the original proposal of Armstrong, Williams, and Strickland (6). After the photochemical oxidation, the formed inorganic mercury is reduced to Hgo in the usual way by SnC12. This method reduces the consumption of oxidizing agents and thus diminishes considerably the risk of contamination; it also leads to shorter analysis times. Determinations with and without irradiation enable the separate determination of total and inorganic mercury, respectively. In the following, an improvement of the method of Goulden and Afghan is reported which simplifies their procedure. Considerably shorter times of irradiation (10-20 min as compared with 2 h) and a much lower consumption of reagents are required, thus facilitating "unattended" automated operation.
EXPERIMENTAL Chemicals. Hydrochloric acid, which was used for the acidification of the samples, was specially prepared by dissolving purified gaseous hydrogen chloride in deionized, quartz-distilled water. Methylmercurychloride and diphenylmercury were of synthetic grade (Merck-Schuchardt, 297%). All other chemicals were re576
ANALYTICAL CHEMISTRY, VOL. 48, NO. 3, MARCH 1976
225
250
-
275 hlnml
Figure 2. Absorption spectra of CH3HgCI ( A ) , CHSHgBr ( B ) , CGHSH~C (c), I and (CsHd2Hg ( D )
Solvent: ethanol. The arrows indicate the principal wavelengths emitted by the light sources agent grade. Stock solutions of methylmercurychloride and of diphenylmercury, considered as representative for the more stable arylmercurials, contained 200 mg Hg/l. and were diluted to 2 mg/l; no acid was added. If kept in the dark, even the dilute solutions proved to be quite stable over a period of several weeks. Stock solutions of Hg(N03)2 contained l mg Hg/l. and l M "03. Test solutions were prepared by suitable dilution of the stock solutions with 0.25 M HC1. Apparatus. Photolysis of organomercurials was carried out with small low-pressure spectral lamps (12-15 W) emitting either the Hg, Cd, or Zn spectrum which have their strongest lines at 254, 229, and 214 nm, respectively (Philips spectral lamps No. 93109, 93107, and 93106). Alternatively, a 75-W combined Zn-Cd-Hg lamp may also be used (Philips spectral lamp 93146). In our setup, the latter caused considerable heating of the sample solution, but this was not prohibitive for short times of irradiation. For prolonged irradiations, it was necessary to use a water-cooling jacket around the irradiated sample. We used toroidal silica irradiation cells which can be placed around the lamp (Figure 1.4).The use of the cell shown in Figure 1B obviates the transfer of the sample solution to the aeration bottle of the AAS detection system, since a glass frit is mounted near the bottom of the cell, giving the possibility of aeration through the side-tube. The outer walls of the cells were coated with aluminum which in turn was protected by a varnish layer. The analytical determination was carried out as described by Hatch and Ott ( I ) , Le., the mercury vapor, formed upon the reduction of Hg2+ is transferred from the sample solution to an optical cell of the atomic absorption spectrophotometer by bubbling air through the sample solution. T o prevent condensation of moisture in the optical cell, the latter was heated to 60 'C with an infrared lamp; further drying of the vapor proved to be unnecessary. Glass tubing was used to prevent loss of mercury vapor by diffusion through the tubing. The optical cell had a path length of 19 cm. Atomic absorption measurements were performed on a Pye-Unicam SP 1900 AA spectrophotometer using a deuterium background corrector. Separate measurements showed that the background corrections were negligible for all our samples. Procedure. Sampling. Samples of natural waters were acidified to 0.25 M HC1 immediately after being taken in order to prevent adsorption of Hg2+ on the wall of the vessel; the samples were not filtered. Photolysis. One hundred ml of the samples were transferred to an irradiation cell (Figure 1 A ) and irradiated for 10 min with either the Cd or the Zn-Cd-Hg lamp. After irradiation, the solution was transferred to the aeration bottle of the mercury detection system and 0.5 ml of a solution of 10% SnC12 in 1 M HCl was added. (This quantity proved to be sufficient for samples containing up to 10 fig Hg/l.). Together with the sample solutions a number of test solutions were irradiated and analyzed. When the cell of Figure 1B was used, the SnC12 was added directly to the contents of the irradiation cell. W e t Chemical Decomposition. For the purpose of comparison, a number of samples were analyzed after wet chemical decomposition. According to Omang ( 7 ) ,organomercurials dissolved in natural water samples are completely decomposed after standing for 20
1;'\ l2I\ A
I
16
08
Figure 3. Percentage recovery of mercury from CH3HgCI added to deionized water as a function of the time of irradiation for various light sources Concentration: 4.1 pg Hg/l. Reference: Hg(NO&. The small recovery observed for t = 0 is probably caused by the thermal or daylight decomposition; it was not observed with diphenylmercury h with 2 or 4% KMn04, depending on the concentration of the organomercurials. In order to be sure of the complete destruction of mercury compounds, adhering to suspended particles, the treatment with KMn04 was followed by partial evaporation and subsequent digestion in a Teflon bomb as described by Omang and Paus (8) for the analysis of geological materials. To an acidified sample of 1 1.20 g of KMn04 was added. After standing for 20 h, the solution was concentrated by evaporation t o 60-70 ml, care being taken that no precipitation occurred. This solution was transferred to a 100-ml volumetric flask and made up to volume with deionized water. From this solution, 10 ml were pipetted into a Teflon digestion bomb and further evaporated to approximately 2 ml. Then 2 ml of hydrofluoric acid (3840%), 2 ml of concentrated hydrochloric acid, and 1 ml of concentrated nitric acid were added. After it had been tightly sealed, the bomb was heated t o 120 O C for 20 min. After cooling to room temperature, the bomb was opened and the hydrofluoric acid was complexed with 20 ml of a saturated solution of boric acid. Finally the solution was diluted to 100 ml. Owing to the presence of the oxidizing agents, these solutions required a larger amount of SnC12 (5 g in 5 ml concentrated HC1) for the complete reduction of the Hg2+. The use of NH20H.HC1 for the reduction of the excess oxidant was avoided since high blank values originating from this compound have been reported ( 4 ) .
200 220
2LO
260 280
300
hinml-
Figure 4. Absorption spectrum of a natural water sample from the river Waal
The sample contains 0.25 M HCI for preservation. Optical path length: 1 cm I ZnCdHg
-
n
time of irradiation 1 minl--+
Figure 5. Percentage recovery of mercury from CH3HgCI added to natural water from the river Waal as a function of the time of irradiation for various light sources Concentration: 4.1 @gHg/i. Reference: Hg(N0& A 0.5 -
RESULTS AND DISCUSSION The low-pressure lamps produce far-uv light much more efficiently than the large medium-pressure mercury light sources (550 W) which were used by Goulden and by Armstrong ( 5 , 6) and generate much less heat. Since the molar extinction coefficients of a large number of organic mercury compounds increase strongly with decreasing wavelength in the region between 200 and 250 nm, the light from Zn or Cd lamps is much better absorbed than the Hg light. See Figure 2 and Ref. 9 for more examples. The use of toroidal cells further increased the efficiency of the irradiation. The recovery of mercury from aqueous solutions of methylmercurychloride as a function of the time of irradiation for a number of light sources is shown in Figure 3. Clearly, the efficiency of destruction increases in the order Hg < Cd < Zn although the relative intensities of the lamps were in the opposite order, namely, Hg:Cd:Zn = 6:2: 1. In going from Cd to Zn, the initial slope of the curves increases more than is accounted for by the increase in extinction coefficient as gauged from Figure 1. The same order Hg < Cd < Zn was observed in the case of diphenylmercury. This compound even has a slightly lower extinction coefficient a t 214 nm (Zn) than a t 229 nm (Cd). This shows that for both methylmercurychloride and diphenylmercury, the quantum efficiency for photodecomposition increases with decreasing wavelength, in accord with what might be expected. Both absorbance and quantum yield, therefore, favor the use of short wavelength light
0
1
2
3 4 5 Hg added ( pg/l I-+
Figure 6. Calibration curves for the standard addition of CH3HgCI ( 0 )and (C6H5)2Hg (0)to deionized water (lower curve) and natural water (upper curve)
Light source: combined Zn-Cd-Hg lamp. Irradiation time: 10 min. For comparison some results obtained with Hg(NO& are also given (x)
sources. In natural waters, on the other hand, the background absorption of dissolved organic compounds which increases towards the uv (Figure 4) favors the use of the more intense long wavelength sources. For our samples, the cadmium lamp offers a good compromise (Figure 5 ) . If the heating of the sample is not considered as disadvantageous, the more powerful combined Zn-Cd-Hg lamp offers the best results. In Figure 6, calibration curves are given for the standard addition of organomercurials to deionized and natural water, respectively. The natural water samples were taken from the main arm of the river Rhine, the Waal. They contained approximately 0.8 pg Hg/l. The calibration curve for the natural water sample has a slightly smaller slope than ANALYTiCAL CHEMISTRY, VOL. 48, NO. 3, MARCH 1976
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ods require that the mercury to be determined is present in a rather high concentration in a small sample volume and hence cannot be applied to natural water samples. The risk of losing mercury on preconcentration by evaporation has Sample treatment Hg f o u n d , pgl1.a been stressed ( 4 ) . Therefore, the method proposed by .-_____ Omang (7) for the destruction of dissolved mercury comUnirradiated 0.31 pounds by treatment with potassium permanganate was Irradiated 1 0 min 1.01 1.00 combined with the method reported by Omang and Paus (ZnCdHg lamp) 30 min 1.15 1.11 (8) for the destruction of geological materials by digestion 30 min 1.05 1.12 Stored with KMnO, 2% KMnO, 0.98 (0.06) 1.02 (0.03) with hydrofluoric, hydrochloric, and nitric acid in a Teflon 4% KMnO, 1.04 (0.08) 0.97 bomb. The results are shown in Table I. 4%KMnO, 1.07 1.01 It is seen that the irradiation time of 10 min, judged as Stored with KMnO,, 2% KMnO, 1.00 (0.24) 1.06 (0.23) partly evaporated 4% KMnO, 1.07 (0.27) 1.06 (0.31) sufficient from Figure 5, is too short for the complete destruction of all mercury compounds in the sample. Howand redi1ute.d Stored with KMnO,, 2% KMnO, 1 . 1 2 (0.38) 0.99 (0.39) ever, the results of prolonged irradiation compare nicely partly evaporated, 4% KMnO, 1.08 (0.42) 1.09 (0.43) with the results obtained after complete wet-chemical dedigested in bomb struction. The latter method is considerably more compliand rediluted cated and yields substantially higher blank values than the a Blank values were obtained from deionized water. When photolytic method. they exceeded the detection limit (0.03 pg/l.) they were Since the photochemical method requires only the use of subtracted from the results. Subtracted blanks are given in HC1, SnC12, and uv light, it can easily be adapted for unatparentheses. tended automated operation. Table I. Comparison of Photochemical and Wet Chemical Decomposition of Mercury Compounds in an Acidified Natural Water Sample (River Waal)
LITERATURE CITED that for deionized water or for inorganic mercury in natural water (not drawn) pointing to a slight incompleteness of the decomposition of the added organomercurials. However, even if the added compounds are completely decomposed, this may not be the case for the compounds originally present in the sample, especially if the latter has not been filtered. The organomercurials may be strongly adsorbed on or even absorbed in solid particles in the sample. Therefore, we compared the photochemical destruction method with a wet chemical method. Many wet-chemical digestion meth-
(1) (2) (3) (4) (5) (6)
(7) (8) (9)
W. R. Hatch and W. L. Ott, Anal. Cbem., 40, 2085 (1968). L. Magos, Analyst (London),96, 847 (1971). Y. Kimura and V. L. Miller, Anal. Cbim. Acta, 27, 325 (1962). T. C. Rains and 0. Menis, J. Assoc. Off. Anal. Cbem., 5 5 , 1339 (1972). P. 13.Goulden and B. K. Afghan, Tech. Bull. 27 (1970), Inland Waters Branch, Dept. of Energy, Mines, and Resources, Ottawa, Canada. F. A. J. Armstrong, P. M. Williams, and J. D. Strickland, Nature (London), 211, 481 (1966). S. H. Omang, Anal. Chim. Acta, 5 3 , 415 (1970). S. H. Omang and P. E. Paus, Anal. Cbim. Acta, 5 6 , 393 (1971). B. G. Gowenlock and J. Trotman, J. Cbem. Soc., 1454 (1955).
RECEIVEDfor review July 7, 1975. Accepted October 23, 1975.
Determination of Aliphatic and Aromatic Hydrocarbons in Marine Organisms J. S. Warner Battelle Columbus Laboratories, 505 King Avenue, Columbus, Ohio 4320 1
A simple and sensitive procedure is described that is suitable for determining aliphatic and aromatic hydrocarbons in large numbers of samples of marine organisms. The procedure involves aqueous caustic digestion, ether extraction, silica gel chromatography, and gas chromatography. Recoveries greater than 70% were obtained from organisms that contained petroleum components at levels of 0.1 to 10 bg/g. Many of the aromatic hydrocarbons were Identifled by chemical ionization mass spectrometry. The method is applicable to a wide variety of organisms.
Assessment of the extent and effects of contamination of the marine environment by petroleum fractions or crude oils requires a knowledge of the petroleum hydrocarbon uptake of marine organisms. Because of factors such as seasonal variations, discontinuous feeding habits, differences in life stage, specimen variability, and varying environmental stresses, numerous samples need to be analyzed in order 578
ANALYTICAL CHEMISTRY, VOL. 48, NO. 3, MARCH 1976
to obtain reliable and meaningful results. The analytical methodology involved needs to be diagnostic and reliable, but also needs to be as simple as possible to permit the analysis of relatively large numbers of samples. Previously reported methods have been used primarily to obtain a gas chromatographic fingerprint and a quantitative determination of saturated hydrocarbons, especially pristane, phytane, and normal paraffins. In much of our work, we were more interested in aromatic hydrocarbons which are generally more toxic, more water soluble, and more readily concentrated by many marine organisms than saturated hydrocarbons (1, 2 ) . We also studied the olefinic hydrocarbons associated with the aromatic fraction. The procedures used by Clark and Blumer (3-5) involve a prolonged Soxhlet extraction of moist tissues using methanol or benzene-methanol followed by a series of separatory funnel extractions using pentane. Blaylock et al. (6) used an alcoholic KOH digestion procedure which facilitated the complete release of hydrocarbons from cellular particles; however, six or more separatory funnel extractions
