V O L U M E 27, NO. 5, M A Y 1 9 5 5 Table I.
Determination of Lranium in Synthetics b\ Xeutron 4ctikation 4nalysis
Drtrrinination
Uraniiim Taken,
Vranliim Found,
Y
1
0 34 0 34
34
34 34 34 34 0 34 0 34
s9 10
31
n
34
33 32 0.36
0 134 0 0 0 0 0
33
0 0 0 0
?dean Std. Der.
0 35 0 35 0 30 0 30 0.33 2.70C;
Table 11. Determination of L-ranium in Phosphate Ores Determination 1 2 3
Sample 1, r/Grain lil 161 171
161 138 168 138
163
Ib
11
12 Mean ;td. dev. % Std. dev. Reported fluorometric results
-1 fin
Sample 2 , y/Gram 288 261 262 275 249 256 271 240
($2 hours and processed by the procedure given in this repoit. Typical data obtained on this type of material are shown in Table I. Determination of Uranium in Phosphate Ores. A serieq of phosphate ore samples 13 as annlvzed bv irradiating portion. (approximate weight = 0.025 gram) of the material for 3.0 houi in the ORNL graphite reactor. hfter the irradiation, the 98111ples Kere dissolved and proceswd bv the procedure given in this report. The results obtained are shown in Table 11. Determination of Uranium in Soils. Several soil samples n el e analyzed by irradiating duplicate portions of the materials for 62 hours in the ORXI, graphite reactor. After irradiation, the samples were processed by the procedure described in this repoi t. The results are reported in Table 111.
Sample 3, y1Grain 172 164 1 ;18
Table 111. Determination of Uranium in Soils by h-eutron -4ctivation .4nalysis
149
I48 180
Sample
166 164
2
1
48.3,51,1 84.0,80.0
3
,_
174
166 169 165 5.5 3.3 160
Cranium Concentration, y/Gram 69.7,68.2
263 15.3 5.8
250
163 10 8 6.6 160
being the accuracg limit of the gamma counter, it is possible to (Letermine at least, 0.003 -i per gram. Increased sample .size and longer periods of irradiation in the reactor would greatl>-enhance this sensitivity. Considering all of the factors given above. it has been calculated that a t least 0.0001 y per gram of nranium cmi be tletected. RESULTS
Reproducibility. The prerision of analysis for ui,;iiiium is within = t ~ l O 7 ~ .The results report,ed in Tables I through I11 show the relative standard deviation for each set of tleterminations. Determination of Uranium in Synthetics. This investigation of the method of radioactivation analysis for uranium was first applied t80the determination of uranium in a series of eynthrt,ic aamples. The handling of t,he samples before irradiation has l,rrii d r ~ r ~ i b eabove. d The samples were irradiated for almut
.4CKNOWLEDGhIENT
The authors wish t,o arknodedge the work of T. C. Rains. J. H. Oliver, J. J. Manning. L. 11.Frakes, N. B. Tuck, S . F. Sharp. and W. L. Bruce in analyzing the irradiated materials. LITERATURE C I T E D
Borkowski. C. ,J., -1s.4~.CHEM.,21, 34s (1949). Boyd, G . E., Ibid.,21, 335-47 (1949). (3) Leddicotte, G. W., and Reynolds, S. .I Sitcleonics. ., 8 , S o . 3,
(1) (2)
62-5 (1951). (4) Leddicotte, G. W.,and Reynolds. S. A , , ORSL R e p t . , 1443 (Jan. 2, 1953); AECD-3489 (declassified Jan. 27, 1953). (5) Seaborg, G. T., and coworkers, Metallurgical Project R ~ p t . , CN-2689, 41 (Feb. 15, 1945) (classified). (6) Seyfang, il. P., and Smales, 1. _1., AERE Rept., C/R 980 (Oc>t. 3, 1952) (unclassified). (7) Smales, A. A., Ibid., C/R 930 (May 13, 1952) (unclassified). (8) Taylor, T. I., and Hayens, WT.T., Jr., Nucleonics, 6 , S e . 4 54-66 (1950). (9) Way, K., Fano. L., Scott. JI., and Thew, K., Natl. Bur. Standards U. s., Circ. 499 (1950).
RECEIVED for review Sol-ember 19, 1954.
Accepted January 17, 1953.
Analysis of Automobile Exhaust Gases by Mass Spectrometry J. K. WALKER and C. L. O'HARA, Consolidated Engineering Corp., Pasadena 15, Calif. IIass spectrometer techniques for the anal>-sisof automobile exhaust gases, and a sampling procedure for laboratory gas analysis are presented. These data are supplemented by results from continuous monitoring of exhaust gas composition at various engine speeds. The hydrocarbon content of automobile exhaust Yaries with engine speed, approaching steady state at high speed. The oxides of nitrogen produced, as indicated hi- continuous analysis, show an increase with engine speed.
A
U.4LPSIS of eshaust gases from automobiles has long presented a problem in the study of air pollution. The mass spwtrometer offers esceptional promise as a satisfactory means for complete analysis and monitoring of all combudon products from internal comliustion engines. \lass spectrometric tech-
niques for the determinntioii of c,shaust gases h a w Iwen reportrtl previously (1, .?, 9). The lubricating oil products of exhaust gases can be determined similarly ( 8 ) , but are not considered as nxtjor contributors to air pollution 111- virtue of their lolt-er vapor pressure. Khile reporting results of rwent mass spectrometric a n a I , ~ ~ s of engine rshauet, the problems encountered in analysis and t h e sampling techniques ava.ilahle should be reviewed. The greatest, single problem met in automolile exhaust gas analysis is that of obtaining represeiit'ative sampling. ;ilthough %yoof the conibustion products are gaseous at atmospheric pressure and anibient temperature, the other 15% are liquids condensed or ~ ( 1 sorbed below the operating tcmperatures. Previous reports have indicated the coiidensnhlr and soluble gaseous oomponentc other than u-ater to 1~ most significant in the problems of :iir pollution (4,10).
ANALYTICAL CHEMISTRY
826
Because the theoretical water content of exhaust gases (7) can be computed on the basis of the cornbustion products, the gasoline and soluble gas content of any one sample should be representative if the measured condensabie m-ater content is near theoretical. Providing complete vaporization of all condensable gases can be maintained, the limitations of the mass spectrometer and the problem of representative sampling can be somewhat overcome by continuous sampling directly from an operating engine into B mas8 spectrometer (11) (Figure 1). SAMPLE ANALYSES
In generd, the products of automobile exhaust may be separated into three classes: combustion products, hydrocarbons, and atmospheric gases. The combustion gases may he further classified as partial and complete oxidation products. It is also desirable to differentiate the cracked hydrocarbons from the gasoline. Table I lists three representative analyses taken from a 1954 a t a n d a d m a d e automobile, with the engine idling. The water content varies from 8.5 to 24.2 mole %without appreciable effect upon the hydrocarbon content. Previously reported analyses ( content, when the water content .61. are low in gasoline of the vapor is below 5%. From the analyses shown in.Teble I the water content of the combustion products can be computed to be 14.976, assuming an average fuel composition of CaH,,(7). Twelve actual samples showed an average water content of 16.7 mole %. Therefore,
.
the water and fuel products of the exhaust gases were sampled representatively and fully vaporized into the mass spectrometer. In addition to determining total hydroeazbon content of exhaust gases, it is important to know the compound types present-e.g., paraffins (C,N,.+,), olefins (C,,Hd, cyclo-olefins, diolefins and acetylenes, and aromatics (bemene homologs). Assuming that ail products containing three or more carbon atoms displayed in the mass spectrum of the mixture originate from unburned gasoline products, a modified gasoline-type analysis ( I ) can be performed. Similarly, this assumption can be made for d l products of five or mwe carbon atoms. The differonce between the C1+and C.+ hydrocarbons should be indicative of the cracked products in this molecular weight range. Table I1 lists the various hydrocarbon products. I n the second column, hydrocarbons with three or more carbon atoms (C,+), were determined by a summation of components of B complete analysis; in column three, gases were determined by type analysis.
Table 11. Hydrocarbons i n Automobile Exhaust (1000=.p.m. no load) Complete Analysis 0.07 + o . 0 2 * 0.04 &o.oz
TYPe
Analysis
0.07 *0.02
0.65
+ o.oe
0.23 + R O B 0 . 0 6 b +0.02 0.05 +0.02 0.09 + o m 0.07 +0.02
0.03
+o.oi
0.23
+o.m
0.05 rtO.03 0.46 *0.08
0.05 0.05 0.08
+ 0.01 + 0.02 0.02
0.10*0.04
0.03 +o.oi 0.03 jl 0.01 0.06 0.22
*+ 0.03
0.06 0.45i. 0.08
R hat the hydrocarbons in exhs sngine idling, under these particular conamons, are approximamay 50% gasoline and 50% cracked gasoline products. This does not take into consideration the products from the low vapor pressure lubricating oils. The C,+ m d CS+components of the analysis agree within the maximum order of uncertainty; therefore, the difference does not appear to be significant a t this concentration level. Figure 1. Mass spectrometer recording spectra of sample directly from operating ongine
Table I.
Cornpositioii of Automobile Exhaust Gases (1000r.".m. idle)
HYoFtOCAnBOS!
c,gasoline
IC
0.25
0.23
0.24 0.28
c.,
80.2 0.7.I
1 . 53"
80.1 0.68 2.23"
80.3
0.67
1.41"
CONTINUOUS ANALYSIS
ranresentative exhaust gas samples is difficult and the intermediutt3 prodycta may no longer be present an final analysk, i t Seemed advisable immediately to monitor the eases of interest a t vmious engine speeds. A portahle mass spectrometer was connlected directly to the automobile . . . .^ and the signihcant spectra peaks were recorded. Figure 2 presents a family of curves derived from the total recorded peak intensities on the monitor mass spectrometer us. engine revolutions per minute. Mass 2, indicative of the hydrogen content of the exhaust gas, reaches a maximum a t 1000 revolutions per minute. This is presumed to be the condition of engine performance most conducive to cracking of hydrocarbons and reaction of the combustion product.-i.e., the water gas reaction: CO H10 === Ha COI Sinm +ha *nllart.;nn nf
-
+
+
The air content of the exhaust, indicated by the m/e 32 curve, does not reach a maximum until 1600 revolutions per minute, a function of carburetion. The general trend of hydrocarbon content in the exhaust is represented by m/e 26, 27, 41, and 42. These gases appear to reach a maximum a t 2000 revolutions per minute. The products of the atmosphere, nitrogen and argon,
V O L U M E 27, NO. 5, M A Y 1 9 5 5
827
M/e GAS
0 (L, -I N
I
>
t v) z w t-
z -
0.07 -:=:=: o,owd-;+~~l/.T: C1.04%/
