ect METROMEX (11, 12). METROMEX operations are based in metropolitan St. Louis, Mo., and vicinity being aimed, in part, a t studying the effect of atmospheric pollution as it relates to inadvertent weather modification. The wide range of metal concentrations in rainwater from such an area and the capricious nature of rainfall volume proved these techniques to be well suited to such conditions.
( 1 1 ) S.S.Miller, Enwron. Sci. Techno/., 6,508 (1972). (12) S. A . Changnon, Jr., F . A . Huff. and R. G . Sernonin, Buli. Amer. Meteor. Soc.. 52,958 (1971).
ACKNOWLEDGMENT This research has been under the general direction of Richard G. Semonin and Donald Gatz. Received for review August 20, 1973. Accepted December 7, 1973. The work has been supported under contract AEC-1199 of the US. Atomic Energy Commission and contract 14-06-D-7197 with the Division of Atmospheric Water Resources Management, Bureau of Reclamation, U S . Department of the Interior. Part of this paper was presented as Paper No. 205 a t the Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, Cleveland, Ohio, March 1973.
Analysis of 1,2,3,4,10,1O-Hexachloro1,4,4a,5,8,8a-hexahydro-1,4-endo-exo-5,8dimethanonaphthalene by Nuclear Quadrupole Resonance Spectrometry Dina Gegiou Experimental Research Department, General State's Laboratories, 16 A. Tsocha St., Athens, Greece
Nuclear quadrupole resonance (NQR) spectrometry has been used for elucidating the structure of several organochlorine compounds commonly used as pesticides and of a number of cyclodiene chlorinated insecticides including the title compound. commercially known as aldrin (1, 2 ) . In all the examined compounds, assignment of signals to specific chlorine atoms was made utilizing spectra-structure correlation charts and other data, except in the case of aldrin in which one resonance frequency only was observed (2). The absence of other resonances in the spectrum of aldrin was considered as due to lack of instrument sensitivity or to a considerable disorder in the crystal lattice. In order to check the latter possibility, the aging technique was used in which a sample of aldrin was maintained for several days at a temperature just below the melting point. Aging did not produce any detectable effect on the NQR spectrum. In addition, samples of aldrin were crystallized from hexane, acetone, and benzene with no apparent change in the NQR spectrum (2). In the present note, we report the complete NQR spectrum of aldrin a t various temperatures, since sometimes more than one temperature is needed in order to avoid missing one or more resonances, because of accidental superposition in frequency a t a single temperature (3). The observed signals were tentatively assigned to the specific chlorine atoms following the reasoning outlined by Roll and Biros (2).
EXPERIMENTAL The sample of aldrin used in this work was analytical grade of 99% purity, purchased from Shell Chemical Co., New York, N.Y., without further purification. (1) E. G. Brame, Jr.,Ana/.Chern., 39,918 (1967) (2) D.B. Roll and F. J . Biros, Anal. Chern., 41,407 (1969). (3) P. J. Bray, R. G. Barnes, and R . Bersohn, J. Chern. Phys., 25, 813 (1956). 742
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The spectra, shown in Figure 1, were obtained at four different temperatures, namely at 77 "K (liquid nitrogen), 193 "K (dry iceacetone), 273 "K (ice-water), and 300 "K (room temperature), because of the stability and ready accessibility of these baths, using the Decca-Radar nuclear quadrupole resonance spectrometer. A half-gram sample of aldrin was placed in a glass tube of 1-cm diameter and positioned in the spectrometer coil. Frequency measurements were accurate to fO.001 MHz and temperature measurements to f l "C.
RESULTS AND DISCUSSION Figure 1 shows that the NQR spectrum of aldrin exhibits at room temperature three resonance signals. while at the lower temperatures. the expected six signals. Previously ( 2 ) ,only one signal was observed a t room temperature, probably because of instrument insensitivity. The 35Cl pure quadrupole resonance frequencies as a function of temperature are given in Figure 2. No evidence of a phase transition or discontinuity in the plot is observed; the resonance frequency decreases at higher temperatures in qualitative agreement with Bayer's theory ( 4 ) . Therefore, the changes in the spectral pattern of Figure 1 are attributed to lattice or torsional oscillations of the molecule. The high frequency signals ( e . g . , at 77 "K) at 38.485 and 38.382 MHz may be assigned to the two vinylic chlorine atoms, since they are known to occur at higher frequencies than aliphatic chlorine atoms (2). Among the four remaining signals, the two higher lying signals a t 37.225 and 37.140 MHz are assigned to the two chlorine atoms of the dichloromethylene group. since spectra-structure correlations seem to indicate (1) that the resonances of dichlorosubstituted carbon atoms occur at higher frequencies than monochloro-substituted carbon atoms; thus, the signals of (41 H
Bayer. Z Physik. 130,227 (1951)
I
300 c
38 140
r l
9 2 150
J
Figure 1. 35CI pure quadrupole resonance of 1,2,3,4,10,10-hexach Ioro- 1,4,4a,5,8,8a-hexahydro-l,4-endo-exo-5,8-dimethanonaphthalene at a ) 300", b ) 273", c ) 193", and d) 77' K (resonance frequencies in MHz)
360
365
375
370
380
385
FREQUENCY (MHZ)
Figure 2. The nuclear quadrupole resonance frequency of 35CI as a function of temperature in 1,2,3,4,10,10-hexachloro1,4,4a,5,8,8a-hexahydro-1,4-endo-exo-5,8-dimethanonaphth al ene
the chlorine atoms on the bridgehead carbon atoms are, probably, those centered a t the two lower remaining frequencies of the quartet, 36.920 and 36.865 MHz. However, the above assignments are only tentative, since in some cases, as with the spectra-structure correlation charts for vinylic 35Cl atoms, insufficient data have been collected for meaningful correlations. Thus, in hexachlorocyclopentadiene ( 5 ) , the assignments for the vinylic chlorine atoms and the dichloromethylene group atoms are reversed.
The present results complete the set of cyclodiene chlorinated pesticides previously published ( 2 ) and show that further development in instrumentation will extend the applicability and usefulness of the NQR technique in analytical problems (6).
ACKNOWLEDGMENT The skillful assistance of M. Voudouris is appreciated. Received for review August 7 , 1973. Accepted November 27, 1973.
(5) "Radio Frequency Spectroscopy," Decca Radar Ltd., Instrument Division, Walton-on-Thames. Surrey, England, p 44.
(6) R.
S.Drago, Anal. Chem., 38 ( 4 ) , 31A (1966).
Use of a New Variable Wavelength Detector in High Performance Liquid Chromatography C. David Carr Varian Instrument Division, Separation Sciences Application Laboratories, 61 1 Hansen W a y , Palo Alto, Calif. 94303
The combination of high performance liquid chromatography (HPLC) with sensitive low dead volume ultraviolet (UV) absorption detectors has permitted the analysis of many compounds difficult to analyze by previously available methods. Most of these detectors make use of the strong 254-nm emission line from low vapor pressure mercury lamps. There are, however, many compounds suitable for separation on modern HPLC columns which do not have sufficient absorbance a t 254 nm to be satisfactorily detected. In most cases, detection of those compounds must rest on less sensitive detectors such as the differential refractive index detector. Another approach to detection of non-absorbing compounds is the formation of UVabsorbing derivatives such as 2,4-dinitrophenylhydrazines and anisate or benzoate esters. This approach has been successfully used in the analysis of steroids ( I , 2 ) , aliphatic carbonyls and polyols ( 3 ) ,and hexachlorophene ( 4 ) . (1) F. A . Fitzpatrick and S. Siggia, Anal. Chem., 44, 2211 (1972).
Some compounds that have required use of low-sensitivity detectors or derivatization do have reasonable extinction coefficients at some wavelength other than 254 nm. Aldehydes have an absorption maximum at 210 nm, bromides at 208 nm, nitrates at 210 nm, and many conjugated systems have absorption maxima ranging from 210 nm to over 300 nm. Even such UV-absorping compounds as benzene and naphthalene which have absorption maxima a t 255 nm and 275 nm, respectively, have absorption coefficients 40 and 20 times greater a t 202 nm and 220 nm (5).Thus, by proper selection of the detecting wavelength, it becomes possible to analyze many compounds with no (2) R. A. Henry, J. A . Schmit, and J. F. Dieckman, J . Chromatogr. Sci., 9,513 (1971). (3) M. A. Carey and H. E. Persinger, J. Chromatogr. Sci., 10, 537 (1972). (4) P. J. Porcaro and P. Shubiak, Anal. Chem., 44, 1865 (1972) (5) H. H . Willard, L. L. Merritt. Jr., and J. A . Dean, "Instrumental Methods of Analysis," 4th ed., D. Van Nostrand Co., Princeton. N.J., 1965, p 8 5 .
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