among many possible choices. The process takes 1.5 hr a t the most and could easily be performed by a technician.
LITERATURE CITED (1) P.F. Lynch and C. W. Brown, Environ. Sci. Techno/., 7 , 1128 (1973). (2) . , C. W. Brown. P. F. Lvnch. and M. Ahmadiian. Anal. Chem., 46, 189 ( 1974). (3) C. W. Brown, P. F. Lynch, and M. Ahmadjian, Eflviron. Sci. Techno/.. 8, 669 (1974). (4) C. W. Brown, P. F Lynch, and M. Ahmadjian, ~ p p l Spectrosc, . Rev,, g, 223 (1975)
(5) P. F. Lynch, S.-Y. Tang, and C. W. Brown, Anal. Chem., 47, 1696 (1975). (6) M. Ahmadjian, C. D. Baer, and C. W. Brown, manuscript in preparation. (7) M. Ahmadjian, C. D. Baer, P. F. Lynch, and C. W. Brown, Envlron. Sci. Techno/., submitted for publication. ( 8 ) R . D. Cole, J. lnst. Petrol., 54, 282 (1968). (9) J. S . Mattson, Anal. Chem., 43, 1872 (1971). (10) R . E. Baier, Proc. 13th Conf. Great Lakes Res., 114-127 (1970). (1 1 ) F. K. Kawahara, J. Chromatogr. Scb, 10, 629 (1972).
RECEIVEDfor review July 21, 1975. Accepted October 13, 1975. This research was supported by a U.S. Coast Guard Contract (DOT-CG-81-74-1099),
Ultraviolet Spectrophotometric Method for Inorganic Mercury in Presence of Methylmercury Reginald 0. Arah' and Bruce McDuffie" Laboratory for Trace Methods and Environmental Analysis, Department of Chemistry, State University of New York a t Binghamton, Binghamton, N. Y. 1390 1
Mercuric saits in aqueous 6 M HCI form complex chloro anions, principally HgC1d2-, which absorb strongly in the UV; 3 X l o 4 abs. M - I cm-I. Methylmerat A,,, of 230 nm, E cury salts, by contrast, absorb much less In the UV (€230 g 1.5 X l o 3 abs. M-' cm-', having less tendency to form anionic complexes such as CH3HgCI2-. Thus UV absorbance in HCI can be used to determine inorganic mercury(Hg") in !he presence of methylmercury If other absorbers are either known or absent, as in an illustrative experiment demonstrating the photochemical conversion of CH3HgCI to Hg" in HCI medla.
Ultraviolet absorption spectra of organomercury compounds (halides) were first studied in 1913 ( I ) . There is a decreased absorptive power by comparison with the inorganic mercury halides and this has been attributed to the hypsochromic action of the C-Hg bond. The effect of the electronegativity of the anion of both inorganic and organic mercury compounds has also been demonstrated, in the decreased absorbance of Hg(CN)Z compared to HgC12, and in the decrease in absorbance on going from CH3HgI through CH3HgBr to CH3HgCl ( I , 2 ) . In high chloride media, HgClz forms the anionic complexes HgC13- and HgC14*- which absorb strongly in the UV at A, of 230 nm, with t values of -1.0 X lo4 and -3.0 X lo4 abs. M-' cm-l, respectively ( 3 ) . On the other hand, methylmercury chloride (MMC), which forms when C1- is added to CH3Hg+ solutions [KfCH3HgCI = 1.8 X M-' ( 4 ) ] ,has little tendency to form anionic chloro complexes, and absorbs weakly in the UV a t 230 nm. In distilled water, MMC has a peak absorbance at 189 nm ( t = 1.0 X I O 4 abs. M-' cm-'1, but the peak decreases and shifts to 206 nm ( e = 5.4 X lo3 abs. M-' cm-l) in 6 M HCl ( 5 ) .At 230 nm in 6 M HCl, MMC and any chloro anionic complexes that may form absorb much less than HgC1dZ-. Thus, UV absorbance in this region can be used with fair accuracy to determine inorganic mercury (Hg") in the presence of methylmercury, if other absorbers are either known or absent. Present address, Chemistry Department, Howard University, Washington, D.C. 20001.
The method is illustrated by the photochemical conversion of MMC to Hg" in HC1 media, the products after irradiation being analyzed for %Hgl' by UV absorbance.
EXPERIMENTAL UV spectra of HgC12 and MMC solutions in 6 M HC1 were obtained using an Applied Physics Carp. Cary 14 Recording Spectrophotometer or a Perkin-Elmer Model 202 UV-VIS Spectrophotometer, with matched 1-cm silica cells with ground glass stoppers. To prevent inhalation of toxic MMC vapors, the cells were filled carefully in a hood. In the photochemical experiment, two different MMC solutions (0.5 m M MMC in 6 M HC1 and 1.0 m M MMC in 12 M HC1) were irradiated with a 254-nm source for 72 hr, under conditions yielding partial conversion to Hg". After irradiation, each solution was quantitatively diluted to a total mercury concentration of 0.05 mM, in 6 M HC1, and the UV spectra were run vs. a 6 M HC1 reference solution. Calibration spectra were obtained on reagent grade 0.05 m M MMC and 0.05 m M HgC12 in the 6 M HC1 medium.
RESULTS AND DISCUSSION Solutions of HgC12 and of MMC in 6 M HC1 each followed Beer's law, at concentrations up to 0.05 mM and 10 mM, respectively, using 1-cm cells. Also, the absorbance of a 1:l mixture of HgC12 and MMC in 6 M HC1 was found to be strictly additive. The absorbances at 230 nm of the 0.05 mM MMC and HgC12 solutions (Figure 1, curves a and c ) were 0.08 and 1.79, respectively, or a ratio of about 1:22. There is a definite peak at 230 nm from the irradiation in 6 M HC1, and a large peak from irradiation in 12 M HC1 (Figure 1, curves b and d ) , the peak absorbances being 0.18 and 1.31, respectively. Assuming Beer's law for the binary mixtures, these peak absorbances yield Hg" concentrations of 0.0029 m M and 0.036 mM, respectively, corresponding to 5.8% conversion of MMC to Hg" from irradiation in the 6 M HC1 case, and 72% conversion from irradiation in the 1 2 M HC1 experiment. From these results, and comparing curves a and b of Figure 1, it is evident that as little as 1%Hg" could be detected easily in methylmercury salts. Of course, in using this method to assay the purity of unknown methylmercury compounds, the absorbance data would give the maximum % Hg" impurity, since other UV absorbers might be ANALYTICAL CHEMISTRY, VOL. 48, NO. 1, JANUARY 1 9 7 6
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absorbance in low C1- as in high C1- medium. Thus, if one were to base the calibration data and analysis on the change in absorbance upon adding a high C1- concentration, many potential interferences could be eliminated. Metals that form UV-absorbing chloro anions (e.g., FelI1) still could interfere. Although other methods exist for determining Hg" in MMC [e.g., spontaneous Hg" polarographic wave ( 5 ) ;differential reduction to HgO followed by flameless AA] or vice versa [extraction of MMC into benzene, followed by gas chromatography with electron-capture detector ( 6 ) ] , the UV spectrophotometric method may recommend itself for its simplicity, especially for following changes in the HgI1 concentration as in acid cleavage or photochemical experiments.
LITERATURE CITED
WAVELENGTH, n m
Figure 1. UV method for Hg" in the presence of methylmercury, using 6 M HCI medium (a) Pure MMC, ( b ) MMC irradiated in 6 M HCi at 254 nm for 72 hr, (c) pure HgCI2, (4 MMC irradiated in 12 M HCI at 254 nm for 72 hr. All at 0.05 m M total Hg
present. However, many of these absorbers (e.g., organic compounds, NOS- ion) would have approximately the same
(1) F. Ley and R . Fisher, Z.Anorg. Chem., 82, 329 (1913). (2) C. R. Crymble, J. Cbem. Soc., 105, 658 (1914). (3) Ya-Chi Yuan, "Development of an Ultraviolet Spectrophotometric Method for Determining Atmospheric Sulfur Dioxide", M.A. Thesis, State University of New York at Binghamton, Binghamton, N.Y., 1972. (4) G. Schwarzenbach and M. Schellenberg, Helv. Chim. Acta, 48, 28 (1965). (5) R. 0.Arah, "Voltammetric and Other Properties of Methylmercury Solutions and Distribution of Methylmercury in Environmental Samples". Ph.D. Dissertation, State University of New York at Binghamton. Binghamton, N.Y., 1975. (6) G. Westoo, Acta Cbem. Scand., 20, 2131 (1966).
RECEIVED for review April 7, 1975. Accepted September 24, 1975. The authors gratefully acknowledge support from The Rockefeller Foundation and from the Research Foundation of State University of New York under Grant 407287A.
Analysis of Saturated Hydrocarbons by Field Ionization Mass Spectrometry Medislav Kuras Laboratory of Synthetic Fuels, institute of Chemical Technology, 166 28 Prague 6, Czechoslovakia
Miroslav Ryska Institute of Macromolecular Chemistry, Czechoslovak Academy of Sciences, 162 06 Prague 6, Czechoslovakia
Ji;i Mostecky' Department of Petroleum Technology and Petrochemistry, institute of Chemical Technology, 166 28 Prague 6, Czechoslovakia
The dependence of sensitivity coefficients of Cs to C12 paraffins and Cs to CI4 cycloparaffins on molecular weight and structure, and the influence of these coefficients by possible adsorption on the emitter, have been Investigated. By adding aromatic hydrocarbons of differing types, It is possible to equalize the sensitivity coefficients so that their values within the various hydrocarbon groups lie in the experimental error range regardless of their molecular weight and structure.
Field ionization extends the scope of mass spectrometry for analyzing petroleum fractions. Field ionization gives rise virtually to molecular ions only, even if paraffins and cycloparaffins are used as starting compounds; for saturat196
ANALYTICAL CHEMISTRY, VOL. 48, NO. 1, JANUARY 1976
ed hydrocarbon mixtures, it provides information similar to that obtained by low voltage methods for aromatics and olefins. Mead (i ) applied field ionization in the analysis of petroleum waxes. Assuming the sensitivity coefficients to be independent of the molecular weight of the C ~ O - C hydro~O carbons, he obtained good agreement with results provided by the cooperative matrix method. On the other hand, Hippe and Beckey ( 2 ) ascertained for low molecular weight hydrocarbons a considerable dependence of the sensitivity coefficients on molecular weight, structure, and mixture composition. This accounts for their proposal of the iterative procedure for analyzing gasolines; however, this procedure is too involved and time-consuming to make it suitable for serial analyses.
