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Anal. Chem. 1982, 54, 2113-2114
to come from improved ionization efficiency, increased collection of secondary ions by the mass spectrometer, and improved detectors. The technique of computerized signal integration however has t3hown its ability to improve the sensitivity of the solid-state standard addition method to more realistic concentration levels. An analysis time of several minutes instead of seveiral seconds does not seem unreasonably long to provide an order of magnitude higher sensitivity. One caution, however, is that the sample to be analyzed by this technique must be homogeneous enough in depth to sputter through several hundrled nanometers of material while integrating a reliable signal intensity.
ACKNOWLEDGMENT The authors wish to acknowledge the assistance of Susan Palmateer for measuring the resistivity of the silicon wafer, and William Harris, Jr., for manuscript preparation. The use of the ion implantation facilities of the National Research and Resource for Submicron Structures a t Cornell University is acknowledged. LITEXATURE CITED (1) Andersen, C. A,; Hinthome, J. R. Anal. Chern. 1976, 45, 1421-1438. (2) Rudat, M. A,; Morrison, G. H. Anal. Chem. 1979, 51, 1179-1187.
Simon, D. S.;Baker, J. E.; Evans, C. A., Jr. Anal. Chem. 1976, 4 8 , 1341-1348. Ganjel, J. D.; Leta, D. P.; Morrison, G. H. Anal. Chem. 1978, 5 0 , 285-290. Havette, A.; Siodzian, G. J. f h y s . Lett. (Orsay, F r . ) 1980, 4 7 , 555-558. Gries, W. H. I n t . J. Mass Spectrom. Ion Phys. 1979, 3 0 , 97-112, 113-125. Leta. D. P.; Morrison, G. H. Anal. Chem. 1980, 52, 514-519. Leta, D. P.; Morrlson, G. H. Anal. Chem. 1980, 52, 277-280. Busch, K. W.; Howeii, N. G.; Morrison, G. H. Anal. Chem. 1974, 4 6 , 575-581. Zhu, D.; Harris, W. C., Jr.; Morrison, G. H. Anal. Chem. 1982, 5 4 , 419-422. Leta, D. P. Ph.D. Thesis, Corneli University, Ithaca, NY 1980. Ruberol, J. M.; Lepareur, M.; Autier, B.; Gourgout, J. M. V I I I t h International Congress on X-Ray Optics and Microanalysis and 12th Annual Conference of the Microbeam Analysis Society, Boston, MA, 1977, pp 133A-133D.
Paul K. Chu George H. Morrison* Department of Chemistry Cornell University Ithaca, New York 14853 RECEIVED for review February 19, 1982. Accepted July 19, 1982. Funding of this project was provided by the National Science Foundation and the Office of Naval Research.
Determination of Ethylenediamine in Aqueous Solutions by Ion Chromatography Sir: In a recent publication, Wimberley suggests an alternative eluent for the determination of divalent cations by ion chromatography (I). As an extension of this work, we have investigated the determination of ethylenediamine in aqueous solutions. Using ZnC12 and HC1 in the eluent, we were able to successfully chromatograph ethylenediamine and demonstrate a linear response with conductomietric detection. Our experiments substituted ZnC1, and HC1 for ZII(NO~)~ and HNOBbecause the chloride causes less suppressor column degradation (2). EXPERIMENTAL SECTION Apparatus. A Dionerr Model 16 ion chromatograph with a 0.1-mL sample loop was used for all experiments. A 4 X 50 mm cation precolumn (Dionex part no. 030830) and a 7 X 60 mm cation suppressor column (Dionex part no. 030834) were used for the separation. A Shimadzu C-R1A integrating recorder was used to record and integrate the signal. A Hewlett-Packard 5995A gas chromatograph/mass spectrometer was used to confirm that the eluting species was ethylenediamine. Chemicals. All chemicals were reagent grade and dissolved in grade 3 (18 MQ/cm) deionized water. RESULTS AND DISCUSSION Attempts to separate ethylenediamine by using the conditions established by Small et al. were unsatisfactory because ethylenediamine is stronglly retained to cation exchange resins (3). Retention times were too long to be practical and peak shapes were unsuitable for quantitation. The chromatographic system, as described by ,Jaworski, is also unsuitable because a 2 N HC1 mobile phase would expend the suppressor during the course of one deternnination (4). In a solution containing 0.004 N HC1 and 0.0025 M Zn2+ the ethylenediamine in complexed to form the Zn(NH2CHzCHzNH2)2+ chelate (5,6).This complex changes the
free energy of solvation for the ethylenediamine and changes the partition coefficient between the complex in solution and that bound to the resin. This change allows the ethylenediamine to be chromatographed with acceptable peak shapes. After separation, the complex enters the suppressor column where Zn2+ is precipitated and HC1 is stripped by the hydroxide form resin; hence, the ethylenediamine enters the conductivity detector as the free base in a background of deionized water. We determined that suppressor column regeneration as described by Wimberley proved generally adequate (1). However a more thorough regeneration was achieved by first washing the exhausted suppressor for onehalf hour with a solution containing 0.0025 M HC1 and 0.0025 M rn-phenylenediamine dihydrochloride, followed by a regeneration cycle with 1N NaOH. Several experiments were run in an attempt to optimize the chromatogram. Initially both a precolumn and an analytical column were used for the separation. This produced acceptable results with retention times of approximately 25 min. Methanol and 2-propanol were separately added to the eluent in 5 % and 20% concentrations (v/v) to reduce adsorption. The addition of organic solvents to the eluent produced tailing of the peak and reduced the detector response. Finally, the analytical column was removed and the separation performed on the precolumn only. This decreased the retention time of ethylenediamine to approximately 7 min. Using only a precolumn, all alkaline earth cations were eluted before 4 rnin and were only slightly resolved from one another. All monovalent cations and amines tested (Li+,Na+, NH,', K+, Rb+, Cs+, methylamine, trimethylamine, ethylamine, diethylamine, triethylamine, ethanolamine, diethanolamine, and triethanolamine) were found to elute near the dead volume. Nine standard solutions of ethylenediamine (0, 1.0,5.0,10,15, 20,50, 75, and 100 ppm) were prepared from
This article not subJect to US. Copyright. Published 1982 by the American Chemical Society
Anal. Chem. 1982, 5 4 , 2114-2115
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Table I. Elution Data for Ethylenediamine ppm
retention time, min
concn, ppm
retention time, min
100 15 50 25
6.53 6.81 1.20 7.80
20 15 10 5
8.01 8.24 8.27 8.60
concn,
0
IO
30
20
40
Flgure 1.
50
Ethylenediamine
Concentration
bo
80
70
90
100
I Q Q ~ ~
Callbration curve for ethylenediamine.
I ""I
0
5
""I
10
" " i " " 1 15
20
TIME lMlNl
Determinatlon of ethylenediamine In llvestock iodine supplement: Dionex 4 X 50 mm catlon exchange column; eluent, 0.004 N HCI-0.0025 M ZnCI,; flow rate, 1.53 mL/mln; full scale = 3 pmho/cm; sample, 1.31 g/L iodine supplement. The resultlng concentration of ethylenediamine was determlned to be 12 ppm. Flgure 2.
ethylenediamine dihydrochloride to study linearity. A minimum of three points at each concentration was tested and a deviation from linearity above concentrations of 25 ppm was observed (see Figure 1). The data corresponding to integrated peak area vs. concentration (for concentrations of 0-25 ppm) were analyzed by linear regression and found to have a linear correlation of 0.99 with a relative standard deviation of 2.8% for eight measurements at 15 ppm. The minimum detectable limit was estimated to be less than 1 ppm by measuring signal to noise ( S I N ) at 1ppm. The signal was measured as max-
imum peak height of ethylenediamine at 1 ppm, and noise was determined as the maximum peak to peak voltage variation in the base line for 1min before and 1 min after the peak. The resulting SIN ratio was calculated to be 105. It should be noted that using only a precolumn for separations greatly diminishes the capacity of the system. We observed that as concentration of sample increases, the retention times decrease slightly (see Table I). Small et al. have characterized a similar peak shift for many monovalent amines (3). For confirmation of the identity of the peak, the effluent was capturedafter the peak passed through the conductivity cell. This fraction was adjusted to a pH of approximately 9 using NaOH and extracted into chloroform. The organic solvent was evaporated down using a nitrogen stream at ambient temperature and placed into a solid probe cup for mass spectral analysis. The resulting electron impact mass spectra matched that of ethylenediamine. As a final experiment, a veterinary iodine supplement containing ethylenediamine dihydroiodide and sucrose was dissolved in deionized water and analyzed. Ethylenediamine was determined in amounts proportional to the therapeutic levels of iodine indicated (see Figure 2). Again the ethylenediamine was confirmed by mass spectral analysis. This determination is suited for a variety of applications for both solutions and salts containing ethylenediamine. ACKNOWLEDGMENT We wish to thank James Molnar, FBI Laboratory, for operating the mass spectrometer and interpreting the spectra. LITERATURE CITED (1) Wimberiey, J. W. Anal. Chern. 1981, 5 3 , 2137. (2) "Dionex Technical Note 4"; Dionex Corp.: Sunnyvale, CA, Aug 1980. (3) Small, H.; Stevens, T. S.;Bauman, W. C. Anal. Chern. 1975, 4 7 , 1801-1809. (4) Jaworski, M. Chromafographia 1980, 13, 2. (5) Douglas, B. E.; McDaniel, D. H. "Concepts and Models of Inorganic Chemistry"; Blaisdeli Publishing Co.: London, 1965; pp 391-397. (6) Gouid, E. S. "Inorganic Reactions and Structure"; Hoit, Rinehart and Winston: New York, 1961; p 335.
Richard C. Buechele* Dennis J. Reutter Forensic Science Research and Training Center FBI Academy Quantico, Virginia 22135
RECEIVED for review April 19,1982. Accepted June 7, 1982.
Exploding-Film Sample Introduction for Mass Spectrometry of Involatile or Thermally Labile Substances Sir: During the past decade, the search for techniques to obtain electron-impact mass spectra of thermally labile and/or involatile materials has become increasingly important. The usefulness of placing the sample near (I)and within ( 2 , 3 )the 0003-2700/82/0354-2114$01.25/0
electron beam in the mass spectrometer ion source has been demonstrated. Both of these techniques, however, require evaporation of the sample as a prerequisite to obtaining a mass spectrum. The technique described here does not depend 0 1982 American Chemical Society
