mole, AS(PbCl+) = 12.6 cal/deg/mole, AS(PbBr+) = 9.4 cal/deg/mole, and AS(PbN03+) = 3.5 cal/deg/mole (6) indicate that the nature of the interaction between lead and oxalate is similar to the interaction d Pb2Twith other anions. The small AH values and positive AS possibly suggest that the interaction is mainly coulombic (6, IO). However, it must be pointed out that equilibrium measurements per se cannot (10) H. S. Harned and B. B. Owen, “The Physical Chemistry of
Electrolytic Solutions,” 3rd ed., Reinhold Publishing Corp., New York, 1958.
distinguish between coordination and simple ion association. Spectroscopic data, particularly Raman, would provide more conclusive evidence for either of these possibilities; however, the low solubility of lead oxalate has prevented success along these lines. RECEIVED for review July 8, 1970. Accepted September 14, 1970. Acknowledgment is made to the donors of the Petroleum Research Fund, administered by the American Chemical Society, for partial support of this research (PRFS:1396-G2,3).
Id lonizati J. B. Forehand’ and W. F. Kwhn2 Philip Morris, Inc.,P. 0. Box 3 0 , Richmond, Va. 23206 ~
FIELD IoNrzATIoN mass spectrometry has been shown to be a valuable tool for the analysis of complex mixtures (1, 2). The technique provides intense molecular ions for most organic compounds, with only slight fragment ion formation, Therefore, the spectra consist primarily of the molecular ions of the components of the mixture. The use of field ionization on a high resolution mass spectrometer allows the identification of the elemental compositions of the ions detected (3). In this paper, the technique of high resolution field ionization mass spectrometry has been applied to the condensable phase of cigarette smoke. Accurate mass measurements were made on 56 ions in the spectrum of this complex mixture, and their elemental compositions were determined.
~~
Table I. Typical Mass Spectrometer Operating Conditions Field ionization Electron impact (approximate) (approximate) Sample pressure 2 x 10-6rnmHg 6 X 10-6 mm Hg Focus potential 5.3 kV 7 kV 8 kV Accelerating potential 8 kV Field plate potential - 1 . 5 kV 8 kV Ion beam intensity 1 X 10-12 ampere 3 X ampere Ionizing voltage 70 eV
EXPERIMENTAL Apparatus. A CEC 21-110 High Resolution Mass Spectrometer was used for this study. The instrument was modXed to provide dual electron impact-field ionization capability using plans and drawings developed by Chait (4, 5). Stainless steel razor blades were used as field ionization anodes. Collection of Smoke Condensate. Two hundred unfiltered 85-mm cigarettes were smoked with an automatic smoking machine and the condensable phase of the smoke was collected by passing the smoke through a trap maintained at dry iceacetone temperature. The cigarettes were smoked to about a 10-mm butt.
FIELD I O N I ZAT I ON
1Present address, A. H. Robins Go., 1211 Sherwood Ave., Richmond, Va. 2 To whom inquiries should be addressed. (1) S. Evan, T. R. Kemp, and W. A. Wolstenholme, Abstracts.
17th Conference on Mass Spectrometry and Allied Topics Dallas, Texas, May 1969, pp 326-332. (2) H. D. Beckey, Angew. Chem. h t . Ed. Eng., 8, 623-639 (1969). (3) E. M. Chait, T. W. Shannon, W. D. Perry, G. E. Van Lear, and F. W. McLafferty, Abstracts, 16th Conference on Mass Spectrometry and Allied Topics, Pittsburgh, Pa., May 1968, pp 18-20. (4) E. M. Chait, T. W. Shannon, J. W. Amy, andF. W. McLafferty, ANAL.CHEM., 40,885 (1968). ( 5 ) E. M. Chait, E. I. DuPont de Nemours and Company, Wilmington, Del., personal communication, 1969.
20
40
60
80
100
120
160
140
MASS
CHARGE
Figure 1. Electron impact and field ionization mass spectra of the condensable phase of cigarette smoke
ANALYTlCAL CHEMISTRY, VOL. 42, NO. 14, DECEMBER 1970
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Table 11. Accurate Mass Measurement Measured mass
Calculated mas3
30.0134 30.0309 31.0014 32.0089 37,0049 39.9862 41.0069 41,9993
30.Ol06 30.0344 31.0184 31.9898 37.0290 39.9624 41.0027 41.9980 42,0106 43.0058 43.0184 43.9898 45.0340 46.0055
43.0035 43. 0161 43.8859 45.0380 46.0010 54.0161 55.0360 56.0369 57.0613 58.0389 59,0450 60.0200 60,0562 61.0220 62.0252 72.0547 73.0558
74.0338 75.0482 76,0423 77.0456 82.0293 84.0793 85.0759
54.0106
54.0218 55.0422 55,0548 55.0296 56.0374 56.0262 57.0704 57.0578 58.0419 58.0293 59.0497 59.0371 60.0211 60.0575 61.0290 62.0368 72.0575 73.0653 73.0528 94.0368 74.0242 75.0446 75.0320 76.0524 76.0398 77.0391 37.0477 82.0419 82.0293 84.0813 85,0891
Difference, millimass units
Measured mass
Calculated
2.8
85.0759
85.0653 85.0756 86.0004 86.0116 86.0242 88,0524 88.0636 92.0626 92.0586 92.0500 92.0473 93.0552 93.0578 93.0704 98.0368 110,0368 110.0480 110.0732 112.0524 112,0398 114.0681 114,0555 116.0473 116.0374 116.0500 117,0552 117,0578 117.0426 117.0453 124,0524 124.0636 126.0317 126.0191 126,0218 126.0681 126.0555 144.0575 144.0324 144.0449 144.0422 150.1045 150.1157 151,1123 151,0997 162.1157 163.1235
3.5 17.0 19.1 24.1 23.8 4.2 1.3 11.3 2.3 2.3 3.9 4.0 4.5 5.5 5.7 6.2 18.8 6.4
e
88.0619 92.0587
93.0619 93.0862 98.0380 110.0403 110.0733 112.0476
0.5
10.7 9.1 3.5 3.0 9.6 4.7 7.9
114.0602 116.0467 117.0464
1.1
1.3 7.0 11.6 2.8 9.5 3.0 3.0 9.6 4.4 8.2 10. I 2.5 6.5 2.1 12.6 0 2.0
13.2
The liquid smoke condensate was injected directly into the heated reservoir of the modified CEC 21-110 High Resolution Mass Spectrometer and both electron impact and field ionization mass spectra were obtained. Typical instrument conditions under which the spectra were obtained are given in Table I. Bar graphs of the field ionization and electron impact mass spectra of the condensable phase of cigarette smoke are shown in Figure I . Only those peaks with a relative intensity of 1% or more of the base peak intensity are shown. The exact mass of each Peak above i n k 30 of sufficient intensity in the field ionization spectrum was measured. No peaks were observed above mje 163 probably because of the low concentration of er Components in the smoke condensate. cause of the low intensity of most of the ions, the peak matching unit of the mass spectrometer could not be used. Therefore, the mass spectra were recorded on photographic 46
86.0142
I24 0542 I
126,0270 126,0624 144.0414
150. 1083 151.1058 162.1123 163.1209
m S S
Difference, millimass units 10.6 0.7 13.8 2.6 10.0 9.5 1.7
3.9 0.1
8.7 11.4 6.7 4.1 15.8 1.2 3.5 7.7 0.1 4.8
7.8 7.9 4.7
0.6 9.3 3.3 8.8 11.4
3.8 1.1 1.8
9.4 4.7 7.9 5.2 5.7 6.9 16.1 9.0 3.5 0.8 3.8 7.4
6.5 6.1 3.4 2.6
plates and the distances between the lines were measured manually using a Sarrell-Ash Recording Microphotometer. With this instrument, the line positions can be read to the nearest o,ool Mm. Therefore, fie average error in the measured is about twice as great as the expected using an automated reader or a peak unit, The relatively larger the low end of the spectrum might be due to the lack of low mass reference ions. The reference ions which were used for mass measurement were the molecular ions of water, acetone, toluene, and the n-hydrocarbons from C8 to CI6. The hydrocarbon mixture was injected into the instrument along with the sample, while the other reference compounds were components of the sample mixture. Since most of the ions measured were relatively low mass ions, the accuracy was sufficient to distinguish in most cases between the possible elemental compositions. The results of the mass measurements are presented in Table IC1 along with the probable elemental compositions for each ion. ]In those cases where it was impossible to distinguish between
ANALYTICAL CHEMISTRY, VOL, 42, NO. 14, DECEMBER 1970
two or more ions, using mass measurement data alone, all of the possibilities are listed. Wherever possible, when two or more elemental compositions are given for a particular ion, the ones which, in the authors’ opinions, are most reasonable are denoted by an asterisk. These judgments were based on the mass measurement data and the history of the sample. Many
of the ions appear to be protonated species formed by ionmolecule reactions due to the high sample pressure in the source.
RECEIVED for review June 29, 1970. Accepted September 4, 1970.
Carbowax as Dispersant in Counting and Sizing of Small Alumina Particles Using a Coulter Counter Elmer C. Lupton, Jr., and Patricia A. Shelby Air Force Rocket Propulsion Laboratory, Edwards, Calif. 93523 ACCURATE SIZING of small particles with a Coulter Counter requires the use of a dispersing agent t o ensure that each particle is wetted by the solution (1-5). In addition to the general considerations which concern users of the Coulter Counter, we faced two special problems which affected our choice of dispersant. These problems were the fact that the total sample available weighed 1-10 mg and the fact that the quantity of interest to us was the weight average diameter (6) ( 2 n d 4 / 2nd3)of the sample. The former problem meant that only one dispersion could be made, and the latter required that we obtain extremely accurate counts and sizings on larger particles but permitted considerable inaccuracy in the sizing of the smaller particles. Flinchbaugh (5) has noted that there is a considerable drop in the number of small particles counted when large particles are present in the suspension. Therefore, we reasoned that a suspension which allows larger particles to fall much faster than smaller particles when stirring rate is reduced would produce very accurate sizings of large particles at high stir rates and moderately accurate sizings of small particles at slow stir rates. By making measurements on small monosized particles at slow and fast stir rates, we planned to correct for the small amount of their sedimentation which does occur. In order to determine the best dispersing agent for our purposes, we made a series of comparison tests. The following dispersants were used : ethanol, “Leak Tec,” 2 4 2 methoxyethoxy)ethanol) bis(2-methoxyethy1)ether (diglyme), bis(2-ethoxyethyl)ether, glycerine, Triton X-100, and Carbowax-1500. Triton X-100 is reported in the literature ( 2 , 5 ) to be the dispersant of choice.
Table I. Effect of Stirring Rate Change on Counts (Model A Coulter Counter, 70-p aperature, 1 NaCl solution/raw counts listed) Fast stirring Slow stirring No stirring 3.5-p 3595 3484 3433 3476 R = 3497 5.0-p 1179 1112 1115 1138 8 = 1136 7.0-/J 421 429 408 410 8 = 417 10.0-p 123 117 126 134 = 125 14.0-p
R=
41 37 38 42 40
2
3148 3248 3139 3149 = 3171
8
1011 1026 993 969 = 1000
8
307 328 351 43 5 = 355
8=
72 56 62 68 65
8=
18 13 11 11 13
8
2927 2861 2875 2830 2871 = 2873
8
869 847 958 860 = 859
8
279 263 230 275 = 262
8=
59 41 55 48 51
x=
10 14 12 10 12
EXPERIMENTAL
A Model A Coulter Counter was used for all measurements. The sample of alumina was prepared by shaking Baymal colloidal alumina, average particle size 200 I*, for one minute with a Wig-L-Bug apparatus. The Carbowax dispersant used (1) Coulter Counter User’s Manual, Coulter Electronics Industrial Division, 2501 N. Mannliein Rd., Franklin Park, Ill. 60131. (2) Bibliography available from Coulter Electronics Industrial Division, above address. (3) E. P. Chaffin,“Size Analysis of Metal Powders,” Murex Limited,
Rainham, Essex, England. (4) W. M. Wojcik, R.M .Raybeck, and E. J. Paliwoda, J. Metals, 19 (12), 38 (1967). ( 5 ) D. A. Flinchbaugh, ANAL.CHEU.,41,2017 (1969). (6) G. Herdan, “Small Particle Statistics,” 2nd ed., Butterworth, London, 1960.
was a 50150 (w/w) solution of Carbowax-1500 in water. Before use, the dispersant was filtered through a 0.8-p M F Millipore filter. The sample which produced the results listed in the table above was prepared as follows: Alumina (0.990 mg) was weighed using a Cahn electrobalance. The alumina, still in its aluminum weighing boat, is placed in a 250-ml volumetric flask. Added are 1 ml of Carbowax dispersing solution and 4 ml of water. The water was previously filtered to remove all particles larger than 0.8 micron. The flask is then placed in an ultrasonic cleaner for 30 seconds. The aluminum boat is then removed and any particles remaining on the boat or on the neck of the flask are washed back into the flask with 5 ml of filtered water. The flask is then placed in the ultra-
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