V O L U M E 23, NO. 10, O C T O B E R 1 9 5 1
1431
Table 111. Dissolved Oxygen Determinations in Mixtures of Aerated and Deaerated Natural" and Synthetic Brines Deviation Dissolved Oxygen, from Mg./L. A Dissolved Linearity, Exptl. Calcd. b Oxygen % 0.25 .... .... 1.20 1:24 +0.04 +3.2 -0.02 -1.1 1.76 1.74 2.02 2.00 -0.02 -1.0 2.25 .. .... .... 0.18 .... 0.51 0157 +0:06 +10.5 1.00 0.94 -0.06 -6.4 50 75 1.35 1.33 -0.02 -1.3 87.5 1.54 1.50 -0.04 -2.7 100 1.90 ... .... .... Natural, contg. 20% S a c 1 0 0.13 ... .... .... hlg 12.5 0.46 0.45 +0.01 2.2 25 0.82 0.77 -0.05 - 6.5 50 1.40 1.43 10.03 2.1 75 2.05 2.10 +0.05 2.4 87.5 2.36 2.43 +0.07 2.9 100 2.75 .. .... a Natural brine from Arbuckle limestone, near Delaware, Okla. b Calculated assuming linearity of dissolved oxygen content between 0% and 100% aerated brine.
Aerated Composition Brine, Aerated Brine Deaerated Brine % Natural. contg. Natural, contg. 0 Mg++ hfg** 50 75 87.5 100 20% NaCl Natural, contg. 0 Mg 25 +
+
+ ++ +
+ +
....
pumps and flanges. The significance of such checks is that dissolved oxygen present in brine to be injected into disposal wells can cause troublesome plugging of filters and low injection rates.
Other uses for the dissolved oxygen meter include checking produced brine a t the well head for possible air entrainment, and determining rate of oxygen reduction by chemicals under various conditions, for water treating and corrosion control. As a corrosion research tool, this apparatus may save considerable time in estimating the corrosiveness of brines, where under some conditions the corrosion rate of immersed steel is roughly proportional to the concentration of dissolved oxygen. LITERATURE CITED
(1) Am. Pub. Health Assoc., New York, "Standard
Methods for the Examination of Water and Sewaee." 9th ed.., 1946. ~L'' Can' Resmrch' (2) Gigui.re' '' A" and I
.
~
J'
23B,76 (1945).
(3) Laitinen, H. A., and Kolthoff, I. JI., J . Phys. Chem., 45, 1079 (1941). (4) Lingane, J. J., and Laitinen, H. A., IND.E m . C R E M . , A N 4 L . ED., 11, 504 (1939). (5) Winkler, H., Be?., 21,2843(1888). RECEIVED November
3, 19.50.
Isolation, ldentification, and Estimation of Gaseous Pollutants of Air Examination of Los Angeles County, Cali$, Smog MARTIN SHEPHERD, AND S. 31. ROCK, ROYCE HOWARD, AND JOHN STORMES National Bureau of Standards, Washington, D . C., Consolidated Engineering Gorp., Pasadena, Calif.
P
REVIOUS attempts to concentrate air pollutants in a cold trap and to analyze the concentrates by mass spectrometer have been disappointing, as the mass spectrograms obtained showed little of interest. There are a t least two reasons for the disappointment: failure to arrange to capture the pollutants completely in the trap, and to prevent reactions between the vaporized pollutants before spectrometric examinations. It has long been known that water can be passed through an ordinary in-seal trap a t the temperature of liquid air, even though its vapor pressure is about 10-28 mm. of mercury a t such temperatures ( 5 , 7 ) . Extremely small frozen particles are formed a t these low temperatures, and these fine crystals are carried in the gas stream through the trap to the warm exit, where they vaporize. A suitable filter a t the cold spot will prevent such losses ( 7 ) . Furthermore, if the concentrate is allowed to evaporate before an analysis, some of the substances present may react among themselves or with the water always present, and the original composition of the sample may thus be altered. Thus, the concentrate must be maintained a t the condensing temperature until its actual separation is begun, to prevent or minimize reactions. Happ, Stewart, and Brockmyre have reported the mass spectrometric analysis of low concentrations of vapors in air ( 2 ) ; but the amounts of these vapors exceeded the amounts dealt with in the present work by several orders of magnitude, and no especial concentration of the vapors was obtained.
METHOD
The method was first proposed by the senior author (7), and has since been slightly modified in detail. It consists of three essential steps: Isolation of the gaseous and vaporous pollutants from the air on a filter a t the temperature of liquid oxygen. Without prior evaporation, separation of the isolated concentrate by isothermal distillation or sublimation a t low temperatures and pressures. Immediate analysis of the distillates delivered directly to the mass spectrometer. Sampling and Isolation of Pollutants. The concentrating sampler is shown in Figures 1 to 3. A tightly wound glass-wool filter is held in place between glam spokes sealed to the inner tube. (The glass wool must be purified by heatin in air t o 550' to 600" C. in an annealing furnam.) The inlet is enyarged t o permit collection of a considerable amount of ice before plugging. The ground joint permits introduction and withdrawal of reagents if chemical analysis is desired. Stopcocks 1 and 2 a t inlet and outlet are ground for high vacuum use. Interchangeable spherical joints provide for connection to other apparatus. (-4 number of such samplers may be used in series, but a single one was found sufficient in this work.) I n use, the sampler is immersed in liquid oxygen contained in a Dewar tube placed within a box, whose two high sides support the inlet and outlet arms of the sampler. The outlet of the sampler is connected to the inlet of a 0.Obcubic foot wet-test meter (with liter dial), and the outlet of this meter is connected throueh a needle valve t o a suitable mechanical pump capable of movlng several liters of air per minute through the system.
ANALYTICAL CHEMISTRY
1432 .-The:sampler is prepared :for use a8 follows: Carefully clean 1ubricant.from the inlet stopcock, Using a minimum Of carbon tetrachloride and preventing any of this reagent from entering cock and the ground the carefully lubricate the joint .at the top. Insert the dry key of the inlet cock in the closed position, warm the sampler with an'elcctric pad, and evacuate (backing pump) overnight.
removed chemically without otherwise altering the composition the or if it can be separated by distillation, the ratio ai ooncentration can he increased greatly. Water also interferes badly in the higher hailing range. Its separation by distillation is not alwi~yseffective, and chemical removal without altering composition is not always possible. In spite of these handicaps, some compounds present in the original air on the order of a 0.000001 p.p.m. can be isolated from the air, identified, and estimated. Separation of Pollutant Concentrate by Isothermal Distillation or Sublimation. The malytiml separation of gases hy fractional isothermal distillation a t low temperaturea and pressures has been described in considerable det,ilil (6, 6). A very brief explanation of the simple modification of the methods previously described, as they were used in this work, i R given here. The concentrating sampler itself was used as the distilling tube. Distilling temperatures \!-ere adjusted and controlled as previously reported (5,in particular pages 1154 t o 1157 and Figure 7). The sampler fitted snugly into an aluminum cylinder which hung from the mouth of a Dewar tube. The cylinder provided sufficient heat capacit,y to maintain an established temperature sufficiently well for an isothermal distillation. A thermocouple well accommodated a copper-constantan couple. The distilling tube was connected to a tube, A (Figure 3), containing enough Asoarite to remove 300 ml. of carbon dioxide (which may he collected from 1000 liters of air). A was connected through a manifold and stopoaeks 3, 4, and 5 so that it could lie by-passed.
Figure 1. Concentrating Sampler
The air sample is taken as follows: With the dry key of the inlet cock in the open position, the outlet cock open, and the sampler immersed in liquid oxygen t o within 1 inch (2.5 cm.) of the ring seal, turn on the pump and adjust the needle valve a t the inlet of the test. met,er until the sampling rate equals 1 to 1.1 1,itqrs per..minute. Read meter temperature and t,he harometer every half hour. Check meter mater levo1 ewry 3 to 4 hours. Maintain' level of liquid oxygen. If inlet tends to plug with ice, lift sampler slightly (1 inch) from Dewar flask unt,il plug disappears. At termination of sampling, close bath stopcocks, lifting the dry key before inserting in the closed posit,ion. Msinhiin level of liquid oxygen. . ' Transfer the sampler t o the snxlytieal laboratory, and. then lubricate, the inlet, cock.* I+cu?te, rhile?Jill immersed in liquid ler :er
Figure 2.
Sampler in h w a r T u b e and Hor Support
SV
then be separated hy d i d a t i o n ior mass spectrometric a'nalyr or stored overnight in liquid nitrogen before t,he separation made.. . .
T h e amounts of sample to be taken will depend somewh,at
On the,oondition of the air sampled. If the pollutants amount to 0.3 p.p.'m., 200 liters of air will probably he sufficient. Howevt%, smaller samples may yield the desired information, and larpW i n ~ far i a tha ~ rniI.m+ I..anrl m 9 . r ha n m a e t r r l tn rk ".."_. ...;Id more information, especially concerning substances that are preseht in really minute amounts. .If;the concentrate were allow6.d to vaporize, the pollutant 1 l ~nl_...ll atmnonhora fraotion would he present in essent 1....~.,1 ~_. r..l._ nf I.oarhnn _. -."_.. diolide, ab this gas forms ahout 0.03% by volume of t.he ordinary will nothe removed during evacuation at liquidnitrogen temperature. In this case the ratio of concentration is limited ta ahout 3000 t o 1. But if carbon dioxide can he ~ r r i l lhn ~ V..II..I.II nnn~
yl
.--
_lll-.
atmo;phereana
the inlet system of the mass speetrometer,'whose calibrated volume included the spaco in C and connections hack t o cocks 4 and 5. The volumes of the distillates could thus be determined manometrically. I n the system actually employed in this work, the constant volume beyond cocks 4 and 5 was of the order of 6 ml., and 5 closed-end mercury-in-glass manometer was used to measure pressures. (A better system is now availahle.) Some difficulty wm experienoed in completely absorbing carbon dioxide. If the Ascarite was slightly moistened a t the inlet of tube A , the absorption was obligingly rapid; hut too much water caused further difficultyby condensing in C, and providing an annoying diluent t o the pollutant fraction of the distillate. (Ascarite will, of course, remove acid gases and, to some extent, unsaturated hydrocarbons.) The experimental oompromises attempted not &hVayshappily concluded, and standardization of the procedure a t this point is desirable. Air initially preeent
...-, ~ . . ~ ~ ~ " - -
V O L U M E 2 3 , NO. 10, O C T O B E R 1 9 5 1
1433
Previous attempts to concentrate air pollutants in a cold trap and analyze the concentrates by mass spectrometer have had disappointing results. -4 new method by which the air of Los Angeles County has been examined combines the isolation of gaseous pollutants on a filter a t liquid oxjgen temperatures, separation of the isolated froAen concentrate by isothermal distillation or sublimation a t low temperatures and pressures, and identification and estimation of distillates hy the mass spectrometer. The method is capable of determining as little as 10W4 p.p.m. of some pollutants from a 100-liter sample of air; with larger samples, 0.000001 p.p.ni. of some substances can be determined. The gaseous phase of the Los Angeles smog was found to be of the order of 0.5 p.p.m. of t h e air. \bout sixty chemical compounds or families of compounds were identified or tentatively identified, and the amounts of some of these were determined. I t was shown t h a t the gaseous phase of the smog was priniaril: a mixture of h:dro-
or contributed from desorption or frwd from occlusion was rcmoved by evacuating C Lvhile st'ill a t the temperatures of liquid nitrogen, prior t o vaporizing rach distillate into the spect'rometer. The temperature steps selected for the isothermal distillation in the present experiments, 2' to 10" C., were not optimum, as the gasometric unit of the spectrometer demanded more distillate for a single analysis than was always yielded by such temperature differences. Particularly in the higher boiling range, where a leisurely approach was niost required, limiting the stepwise distillation to small increments of temperature would not deliver enough distillate for analysis. Thus all substances present could not have been completely identified, even if all the calibrating patterns had been available, since the spectrograms of the distillates of the heavier compounds were too complex for complete analysis. h complete analysis may not be possible without the further complication of molecular distillation, fractional rather than straight-run distillation, or even steps of chemical separat'ion prior to the mass spectrometric analysis. A modification of the inlet system of the spectrometer is clearly needed. But the simple isothermal distillation emploj-ed did make a reasonable spectrometric analysis possiblc.
carbons, and of hydrocarbons combined with o x > gen, nitrogen, and chlorine. AIost important, these hydrocarbons, principally the unsaturated ones, when oxidized with ozone and nitrogen dioxide (both hnown to he in Los Angeles air) in the presence of ultraviolet light, produce substances which constitute a large proportion of the smog concentrates. These oxidation products cause eye and respiratory irritation such as are produced b y the real smog, and smell 1il.e the smog and its concentrates. HaagenSmit has experimentally shown t h a t these products cause the specific types of plant damage obser\ ed during actual smogs, and the present work offers suhstanti,tl proof of his hydrocarbon theor! of the origin o f the more interesting portion of the Los ingeles smog. Cnexplained residues in the mass spectra o f the smog concentrates ma! eventually indicatc. the presence of other irritants. The new method nia? be applied to special prohlems in air pollution o\er large areas or inside industrial plants.
Mass Spectrometric Examination of Distillates of Pollutant Concentrate. The mass spectrometer offers the greatest possibilities i i i rxariiinirig distillates from the isothermal separation. It is capable of identifying and estimating more of the molecular species lilccly t o be present than is any other instrument. However, the infrared and ultraviolet spectrometers may well assist in such annlysc.;, if sufficient sample can eventually be niade availablej :mci mirrochemical niethods should be employed w2irrevc.i. powiblt>. The mass spectrometer will 'erve to indicate possihlcx 1-hcniical methods. Thr Consolidated Engincwing Corp. general analytical mass sl)ectronietrr, llodel 21-102, was used in this investigation. It has h r i i :&quately described by Washburn, Wiley, Rock, and Berry (8, 9 ) ) and general niethotls applicable to the t,ype of analysis involved in this problem have bren reported by Rock (3). The distillates of rach saniplc \\-ere esaniined under stantiaid operating conditions, except that a few were run above the usual pressure. ,111 r u m were kept within the limits assuring linear superposition and linearity with prpssure. I n many CBRCB, distillates \vere analyzed before arid after the removal of cwhon dioxitltx by .lisc:tritr. COVl'OSITIOK OF SlIOG CONCENTRATE
IN LET
l
l
ii Figure 3. Assembly of Concentrating Sampler and Ascarite Tube and Condenser for Isothermal Distillation
Identification. .4 study of all the mass spectra obtained from all the smog concentrates secured permitted identification of some materials, and indicated the probability or possibility of the presence of n i a i i ~ -others. It was also posrihle to rule out many compounds on the basis of absent peaks. The residual spectra in Tahle 11- ni:iy rnahle the reader to t.hrc,k for other compound8 not, included iii the listing below. Tl'ith improved fractionation niethods and niorr: rct'erencc calibrations more compounds may be identified with certaintl- in future investigations. Even with the limitations inevitable when a new nicxthod is first briefly employed, considerable information was obtaiiirtl rcgarding :t iiunihcr of compounrli.. First, the coinpourids iioi.nially present i n air 'ivere (1: Tvatrr ~ a p o r ,iiiti,ogcn, o\;ygt311,a r g o n , rtrrd carbon dioxide. T h r spectra of thcsc compounds \yere su1)tracted i n cacli fraction, leaving residual peaks of t h e compouiids which may be classed as pollutants. Of tlicse. the t'ollou.ing could t w identified : A.icetylrnr Butanrs (43 '58 mtio in priniaril). Ca fractions ran
alioiit
10 t o
ANALYTICAL CHEMISTRY
1434 Table I. 1
Vol. of Line 1 . 2 3
4 5 6 7 8 9
Distillate 61
82 83 84 55 86 Total
Distillate Ml.’ 0.783 0.132 0.013 0.097 0.123 0.132
...
2 Smog in Distillate MI.’ 0.0047 0.0218 0.0046 0.0263 0.0129 0.0008
...
3
(Experiment VII) 9 6 6 7 8 Added Hydrocarbon Found, Mole % 13BdtaGH4 C I H ~ ChHa diene C& CsHs . . . 0.6 1.1 1.2 . . . . . . 0.7 1.7 5.4 0.6 3.0 1.7 ... 5.7 5.6 3.7 2.3 4.2 . . . 2.0 3.5 ... 1.7 6.7 . . . . . . . . . . . . 0.3 0.8 . . . . . . . . . . . . . . . 0.08
. . . . . . . . . . . .
. . . . . .
Total hydrocarbons added Total hydrocarbons reacted and/or escaped
1. Thus the presence of butanes is indicated, but acetone remains a possibility.) Pentanes Benzene Toluene Xylenes and/or ethylbenzene (pattern fits xylene better than ethyl benzene) Carbon tetrachloride Trichloroethylene Nitrous oxide Sulfur dioxide (found as a gas in one sample only, and that from a relatively clear day) I n addition, various classes of compounds are probably present. Because of the large number of possible compounds and the complexity of the fraction spectra they cannot be identified with absolute certai,nty. However, the preponderance of peaks usual in hydrocarbon spectra provides highly suggestive evidence of the presence of that class of compounds. Types of materials in the “probable” category are: Ethylene Ethane Propylene Propane C6Hshydrocarbons C6HI0hydrocarbons C6H10 hydrocarbons
10
4
Smog Air, P.P.M. 0.031 0.144 0.030 0.173 0.085 0.005 0.468
“Witches’ Brew” 132 Liters of Air Sampled
C6Hl2 hydrocarbons CeH14hydrocarbons C7Hlahydrocarbons C& hydrocarbons c& hydrocarbons CJ&a hydrocarbons Mass 120 aromatics
As would be expected, peaks become small at the higher masses. With the sensitivity available in the Consolidated Model 21-102 used, only a few fractions of scattered samples showed peaks of 0.5 division or more above 120. However, trace peaks indicate the presence of C,Hz, and C,H2,+9 hydrocarbons to (21%. There is also a possibility that hydrocarbons less saturated than C,Hz, were present. In some fractions, ethylene, ethane, propylene, and propane may have been present. Because the peaks prominent in the spectra of these compounds were usually masked by heavier paraffins (or nitrous oxide on mass 30, in the case of ethane) these must also remain in the possible rather than the probable category. Ketones and aldehydes have parent peaks a t the same masses &s paraffins. They could be present, but in the fractions run could not be explicitly identified. There w8s positive evidence of the presence of nonhydrocarbon organics, in the peaks a t such masses aa 31, 45, and 59. These again will require closer fractionation for identification. The spectra of many of the light fractions which contained little above Cswere completely analyzed. It was in these that the presence of acetylene, for example, was established. Very little 46 peak was observed, so that little nitrogen dioxide was present. It may have been present, however, as a radical in organic compounds. This gas reacts fairly rapidly with mercury in the presence of water vapor, and with other components of the samples, and this may have accounted for some loss
11 12 13 14 Volume of Hydrocarbons, P.P.M. 13-
CsHe 0.031 0,’006 0.015 0.003 0.002 . . . 0.013
...
CdHe 0.057 0.047 0.003 0.022
...
...
o:Oog 1.2 1.19
o.’O$i 1.2 1.14
o:iig 1.2 1.07
CnHd
Bdta-
diene 0.062
0.005
...
15
C ~ H I ~CeHl
0:026
0:014
...
0.005
0.005
0.012 0.003
0:0&
0:046 1.2 1.15
0.043 0.007 0.001 0.070 1.2 1.13
... 1.2 1.13
Table 11. Amounts of Smog Found in Los Angeles Air Diatillate
XI-C4
X-l-C4
IX-C2
s1
0.007
0.001
...
0:002
0.004 0.276 0.127 0.021 0.011
s2
93 54 55 S6 57 S8
o:001
0:oio 0.034 0,032 0.024 0,024 0.023 0.002
59 510 511 512 513 ... S14 515 ... ... 516 517 Total 0.169
0,004
... ... ... ...
... ... ...
...... ... ...
0,444
:
0 008 0,044 0.021 0.036 0.064 0.060 0.016 0.031 0.018 0.049 0.032
0.008 0.001 0.003 0,001 0,392
Smog, P.P.M. VIII-C1 X-2-09 X-9-07 ... 0.400 0.216
:
0 006 0.017 0,010 0:005 0.008
0:001 0,005 0.001 0.001 0:026 0.056
... ~ 0.136
... ... ...
...
... ... ... ... ... ... ... ... ... ... ...
...
... ... t . .
... ... ...
... ...
... ... ... ...
X-10-05 0.149
...
... ...
... ... ... ... ... ...
... ...
...
...
... ... ... ... . . . . . .... 0.400 0.216
0.149
in the inlet system of the spectrometer. Also, its sensitivity is evceptional in that it is not a linear function of pressure, aa measured by the closed-end manometer of the inlet system; nor is its pattern stable. Thus its mass spectrometric detection and determination are doubtful. Nitrous oxide was identified from peaks 30 and 44. Sulfur dioxide was found in only one sample, and in very small amount there. Hydrogen sulfide vas not observed; if present, the amount w u very small, possibly obscured by the oxygen isotopes on mass 34. I t may also have disappeared by reaction in the inlet system. In the more complex fractions containing c6 and heavier, which could not be completely analyzed, certain materials stood out because of their distinctive spectra. For example, the metastable-transitior, group a t mass 90, together with half-mass peaks around mass 45, served immediately t o identify toluene. Next, the 117, 119, and 121 peaks, with the distinctive ratio common to ions containing three chlorine atoms (1.000:0.979:0.262) suggested carbon tetrachloride. The half-mass peaks around 58 as well as the pattern coefficients at 47 and 49 and 35 and 37 clinched the identification. Similarly, benzene, trichloroethylene, and a combination of mass 106 aromatice were identified in most fractions. The mass 106 aromatics contain the xylenes, and possibly ethylbenzene. The spectra of the heavier fractions included a t least mass 112probably C8Hla. The fact that succesfiive fractions brought in first peaks 69 to 72, then 83 to 86, 97 to 100, and 111 to 112 strongly suggested that hydrocarbons through CS and, in some cases, heavier are present. These were C,Hz,+*, C,Hz,, and possibly C,H2,-z, or even less saturated compounds. In general, the fractions were not sufficiently narrow to permit identification above Cs. The presence of n- and isobutane and isopentane was established with reasonable certainty, however. It was also apparent from the mass spectra that materials other than hydrocarbons were present. The peaks a t m / e 31, 45,46, 60, and other masses not appreciably in hydrocarbon
V O L U M E 23, NO. 10, O C T O B E R 1951
.., ... ..
.
.
,
,
,
,
. N.m.I C. C - m .
.
,
.
1435 spectra indicated that some oxygenated materials and possibly some nitrogenated compounds were present. An attempt was made to simplify the heavier fractions and emphasize distinctive groups differing from fraction to fraction. First, the contributions of all identified compounds were removed from the spectra. Then, each spectrum was considered as a calibration, and its contribution, based on heavier peaks, was removed from the spectrum of the immediately lighter fraction. In several cases, the residual spectrum after this subtraction yielded useful information, such as strong indication of C, and Cbhydrocarbons in some of the lighter fractions. In one sample (IX-C2) peaks 60, 45, and 31 increased simultaneously in fraction S9 (31 was 0.8 division in S8 and 1.5 divisions in S9). Approximately the same ratios held among these thrm peaks in samples S10 and S11 as well. The pertinent peak ratios were in the range shown below for fractions S9 to S l l .
Residual smogPattern 31 60-90 45 60-100 60 100
m/e
3
n
.C.,.F.
..
. . .. . .. . . . . . .
, ,
.=. , . .O;
m
API 301,
Acetic Acid 8 98 100
API 384, Methyl Formate
100 28I'/=
Mean Pattern
83 77 100
This material is not a hydrocarbon, nor is it any one compound in the API Mass Spectral Data Catalog. The closest approxima tion from known patterns is a combination of acetic acid and methyl formate, as shown by the mean pattern above. Unfortunately, this identification cannot be considered conclusive because of the fact that spectra not yet available might fit these peaks equally well. Hence, these materials can be reported merely as a possibility. By the time fraction 515 was reached, the ratio had changed appreciably. In another sample (X-C4), two fractions (55 and S7) were compared by taking the ratios of the residual patterns (Table IV) a t the same masses. The ratios covered a range of 0.1to 4 + , and could roughly be divided into groups around 0.1 to 0.3 designated ( l ) , 0.6 to 1.0 designated (2), and higher designated (3). The masses falling in each group are: (1) 31,45, 59, 81, 95, 96, 105, 111, 113, and 126; (2) 32, 43, 53, 57, 58, 61, 63, 66 to 69, 71 to 72, 79, 82 to 86; 97, 99, 100, 112, and 114; (3) 37,49 to 52, 60. Reference to summarized mass spectral data (S) shows that most of the peaks (1) are largely associated with nonhydrocarbons. These peaks therefore probably indicate the presence of oxygenated, nitrogenated, or other organics. \Vith the exception of peak 32, on the other hand, the peaks with ratio (2), particularly those that are the largest in the residual spectrum, do appear in hydrocarbon spectra. The peaks in the Ce, C,, and Cs range ( m / e 82 to 114) in particular, suggest that these peaks are due to hydrocarbons. This group includes many of the major residuals. The masses nThose peaks show the highest ratios (3) suggest nearly stripped carbon skeletons, or highly unsaturated materials. They may, of course, be due rather t o nonhydrocarbons whose spectra were not available to the author s. While positive identification cannot be made from these data, they clearly indicate the presence of compounds of different types in the fractions compared. Thus, such devices as comparison of peak ratios and removal of adjacent fractions gave qualitative information, useful as indication of what may be present. In most cases, however, it was apparent that the spectrum still was not sufficiently simplified for straightforward and complete identification, compound by compound. All told, it is possible to suggest about 60 varieties of compounds which are possible contributors to the gas phase of the smog, and there is no doubt of the existence of many unidentified chemical compounds in these smog concentrates. But it is apparent that a major part of the smog-gas concentrates con-
ANALYTICAL CHEMISTRY
1436 Table IV. IX-C2-S8a
-S9
Patterns of Residual Spectra after Removal of Identified Conipounds -S11
-Sl5
-S17
X-C4-S4b
~___
_.____~__ -
26.2
247.4
470 7
0.7
1.1
18.0
10.3 17 2 3.4 36.0 14.5
3.0 2.7 31.4 9.4 10.9
0.8 1 5 7.0 15.7 8.4
51.5 -~
37.6
172.7
1.0
0.2
5,l
4.1 5.3
7.2 11.2
2.5 4.6 5.3 t .3
Sample S o . -S5 -SG-
XII-Cj-s?c -53
-Si
43 peak__^ 365.5 89.4 57.9 ~
hIole % d 16.7 2.2
~~
1.6
~
~
-S4
~____~~-___ -S6
-S3
~ - . ~ ~ _ _ - _ _ _ _
-
23.3
103.0
0.7
4.4
301.0
64.1
7.5
..
...
...
2.3 5.3 16.3 44.4 1.7
4.7 5.8 18.7 37.0 4.1
0.3
...
,
mfe
12 13 14 15 16 17 18 19 19'/, 20 22
. I .
...
,..
...
...
,.. ... 0.7 ...
24 23 26 27 28 29 30 31 32 33 34 35
12.2 42.8 197 111 off 182 103.3 3.2
1.1 3.7 20.6 50.5 off 43.5 29.0 1.3 33.5
36 37 38 39 40 41 42 43 44
1 9 13 7 19.5 62.1 12.6 70.3 46 2 100
45
1.9
...
...
... ...
...
0.4
...
56
57 58 59 GO 61 62 63 64
65 66 67 68 69
70
0.3
... 0 1 3 50 49 63 19 2 5
4 7 3
2
,
6 6 0 8
. .
0 2
0 6 0 4 2 7 2 3 4 7 433 25 2 25 8 7 2 5 5 49 5 57 5 39 0 39 6 100 100 8 6 1 2 3 4 2 0 17 4
3.3 6 5 3 8 2 7 3 8 0 8 8 4
0.1 0.7 1.8 1.6 0.7 2.0 0.9 7.8
21.0 19.5
15.7 17.7 5.8
,..
1.5 5,O 1.5 0.8 0.8
...
...
...
1.7 0.5 0.2 0.1
. .
0.2
.1. ..9
76 77 78 79 80 81 82 83 84 85
...
86 87 88 89 90 91 92 93 94 95
...
... ... ... ...
.. ,., , 1.9 2.7 1.5 1.9
0.3 0.1
...
... ...
... ... ... ... ...
... ... 1 4 28 143 119 161 19 21 12
4 8 8
4 6 4
1 2
0.23 0.23
...
0.17
...
"'19 0.13
...
0.1
... ... 1.9 6.9 33.2 125 85.9 186 18.3 132 29.1 2.1
4.3 14.2 64.6 31.2 41.9 57.9 0.8 0.9 0.2
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1 1
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1 5 9 23
0 3 0 0 10 0 60 6 73.6 100 3 4 0.2
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... 0.2 ... 0.87 3.2 16.01 47.74 47.58 69.22 12.61 3.39 8.37
...
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0.19
0.30 3.97 3.67 27.2 6.07 61.23 43.09 100 Off
1.86
0.8 1.9 9.7 40.3 33.4 61.3 27.7 8.2 8. I
0 ,n 2 1 10.6 41.1 33.7 53.9 8.5 33.3 12.4 0.5
... ... ...
0.4 1.7 2.7 19.4 4.0 43.8 26.5 100 17.2 6.0
1.7 0.3
63.2 64.3 40.4 7.7 1.1 1.3 1.3 1.6
24.5 35.8
1.3
0 2
0.2
0.2 0.6 0.5 4.1 3.8 5.4
0.3 2.9 2.5 15 0 18.0 9.6 4.7 0.2 0.5
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0 8 7 7 6 4
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22 9 12 8
:; 1 6
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0.32 1.97 2.52 0.40 0.55
5.5 30.1 16.1 4.3 3.7
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0.79 0.6 1.65 10.4 5.69 3.23 1.4
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0.3
1.4 2.5 10.5 5.8 4.3 1.1
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1.7 2.9 19.7 4.7 43.4 23.8 100 15.5 28.8 5 0
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6.2 1.7 2.6 50.3 52.7 107,5 2;,; 11.7
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17 1 2 10 13 14 8 12 10 79
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27 27 75 41 493
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1.9
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Off
0.41 0.19 1.15 3.06 3.67 2.68 3.89 2.35 31.52
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129.5 114 21.2 3.3 1.8 1.0 1.4 2.1 0.6 1.9
2:3 7.0
0.1 0.3 0.5
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0 1 0 2 0 3 2 1 5 3 3 7 2 2 3 4 1.6 10 0
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0.23 0.21
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1.9 2.8 9.2 26.4
20.2 7.1 0.8 1.6 3,2 4,5 1.9 9.8 5,F 96.5
...
...
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...
1.8 3.0 9.7 28 8
25.6 0.8 0 8 21.4 5.3 7.4 3.5 16.7 10.1 134.7
1.4 0.17 0.04
. .
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3 7 2 9 5 8 5 8 111 9 0 10 9 52 9 177 112 196 110 107 61 9 100 100 4 4 5 0 0 16 7 182
0.9 0.1
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1.9 0.6 8.2 12.5 48 0 27.2 20.0
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0'60 1.04 6.3 4.6 2.4
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?
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32.7 26.0 6.1 0.4 1.9 0.5 0.4 0.2 0.1
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0 3 1.7 1.8 9.6 13.3 7.8 1.9 0.13 0.33 O,l5
1.5 5.3 6.1 8.0
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101 102
...
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71 72 73 74 75
96 97 98 99 100
0 1
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46
47 48 49 50 51 52 53 54 55
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1.31 2.87 10.97 22.5; 0.2
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5
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V O L U M E 23, NO. 10, O C T O B E R 1 9 5 1 Table I\’.
Patterns of Residual Spectra after Removal of Identified Compounds (Concluded)
IX-C2-S8“-SQ 26.2 0.7
: 1437
247.4 1.1
-S11 470.7
-815
-S17
51 5
37.6
X-C4-S4b
Sample No. -85 -S6
-S7
172.7
43 Peak 365.5 89.4
57.9
25.3
2.2
1.6
0.7
...
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18.0
1.0
0.2
5.1
... ...
0.8 0.6 8.4
...
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Mole 16.7
-S4
-S5
-S6
103.0
301.0
64.1
7.5
4.4
...
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XII-CI-S~C -S3
%d
m/e
103 104 105 106 107 108 109 110
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140
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163 or 164 165 or 166 167 or 168
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111 112 113 1Id 115 116 117 118 119 120 121 122 123 124 125 126
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1.4 1.2
16.7 10.1 2.1 1.9
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1.0
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0.G
0.07
1.9 3.1
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0.4
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0.3 1.2 0.6
Residuals for distjilates IX-C2-S1, - S3, - S5, - S6. and b Residuals for distillates X-C4-S2 and - S3 were small. C Residuals for distillate XII-C5-S1 were small. d Estimated on 43 peak. a
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- S7 \rere small.
sisted of hydrocarbons as such and in combination with o\ygen, oxygen and nitrogen, and chlorine. Identification of Irritant and Plant-Damaging Fraction of Smog Concentrates. When the mass patterns of all identified substances had been removed from the spectra of the distillates of the smog concentrates, there always remained in the higher mass range an unidentified residual spectrum that was obviously a mixture. T o explain these residual spectra, a rather modest version of the Los Angelep type of smog was produced synthetically in the gas chamber of the Earhart Plant Laboratory a t the California Institute of Technology. Haagen-Smit made the necessary facilities available and supervised the production of the “smog.” Six hydrocarbons, previously found in the concentrates of actual smog, were introduced into the air, together with ozone and nitrogen dioxide in the presence of ultraviolet light. The hydrocarbons were ethylene, propylene, isobutylene, 1,3-butadiene, 72-hexene, and benzene, each present t o the approximate extent of 1.2 p.p.m. About 0.5 p.p.m. of ozone was present, and about 0.3 p.p.m. of nitrogen dioxide. Thus the hydrocarbons were in excess. All the gases were introduced into the air through adjacent nozzles, and interaction probably occurred mainly within the few cubic yards of space surrounding the nozzles. The sampler %-asplaced about 8 feet from this area. The ultraviolet lamp used was the Keese Engineering Co. Model 9OSTP. The air in the chamber was taken in through activated charcoal filters, and was circulated a t a rate sufficient t o mix the reaction products thoroughly and continuously carry them away as faPt as they were formed. The reaction products formed a haze, and smelled like the real smog and also like the smog concentrates. They irritated th: eyes and respiratory tract of the four men preparing this “witches brew,” and caused characteristic damage to the leaves of certain plants, all in the manner of the real smogs. The contaminated air in the gas chamber was sampled exactly as air had been sampled t o isolate smog from the Los Angeles air, The concentrate so obtained was distilled isothermally, and mass spectra of
the six distillatc.s n r r e ptudied. First, the substances known t o be present were removed from the spectra of the synthetic smog. Next, the substances identified in the spectra of the actual smog concentrates were removed from their spectra. Finally, the residual spectra of the synthetic smog were compared with the residual spectra of the actual smogs. Marhed similarities between the synthetic pattern and the actual pattern were a t once apparent. For example, the C,H,, peaks continued to mass 112 (C,) instead of stopping a t 84, the mass of the heaviest compound added. Although no compounds with appreciable peaks a t mass 31 and 45 were included in the synthesis, these peaks were well above isotope value, as they are in the smog sample. In addition to the benzene, Borne toluene was observed. (This was taken from the spectrum aa an identified material before the residual pattern was computed.) Furthermore, the total gaseous smog content of the sample was of the same orderas that found in sample XI-Cd, taken during one of the worst Rmogs in the fall of 1950. These considerations prompted a computation of the amount of the actual smog residuals that could be accounted for by the synthetic smog residuals. This was done as described below. The residual spectrum of one of the distillates (Sa) of the synthetic smog was used as a calibration pattern. The concentration of it which could have been in the residual spectra of many of the distillates of the actual smog Concentrates was computed as follows: The spectrum of Sa, which could be contained in the residual spectrum without introducing appreciable negative residuals was computed; these computed peaks were summed a t all masses; all peaks in the residual spectrum were summed; and the ratio of the sum of the peaks of the computed contribution of Sd t o the sum of the residuals was considered an indication of the proportion of the residual which could be accounted for by the synthesized material. (The synthetic brew contained a material ion-
1438
ANALYTICAL CHEMISTRY
V O L U M E 23, NO. 10, O C T O B E R 1 9 5 1 izing to masses 49 and 60 which was not apparent in the true smogs. Therefore negative residuals were permitted a t these masses in fitting 54 t o the residuals.) When this was done it was a t once apparent that the residual pattern of the synthetic smog would account for a significant part of the residual patterns of the actual smogs. Indeed, as much as 50% of some of the actual smog distillates could be accounted for by the distillate of the synthetic smog. Only one of the six distillates of the concentrate of the synthetic smog was used in this computation; and the calculation was not extended to all the distillates of all the smog concentrates, even in any one concentrate. Thus, the mass spectrometric data indicate that a considerable fraction of the complex residual mixtures caould be explained by the reaction products of the witches’ brew. The evidence furnished by this experiment can now be added to that given by Haagen-Smit’s carefully controlled experiments showing characteristic plant damage and his analyses indicating the presenre of peroxides in particulate matter separated from the I m .ingeles air (1). The results of these three independent investigations mutually verify Haagen-Smit’s theory that a very significant part of the gaseous phase of the Los Angeles smog consists of hydrocarbons and their oxidation products. Estimation of Smog Concentrates and Some Components. In the following section, gaseous smog is defined as the gases and vapors found in the air after all components normal to air itself have been removed. The term as used in this last section of the paper is not to be confused with the ordinary conception involving par ticulate matter. (Oxygen, nitrogen, carbon dioxide, argon, :ind water vapor are the gases normal to air ) The amount of gaseous smog was determined by measuring the amount of each distillate manometrically as previously described. The amount of each distillate was calculated in milliliters, the total amount of the components of air as determined niass spectrometrically was subtracted from the total volume of the distillate, and the residual amount of gaseous smog was thus computed in milliliters. These amounts were in turn related to the volume of the air sampled, and the amount of gaseous smog in the air was expressed i n parts per million by volume. This procedure is illustrated in Table I, wherein the amounts of material involved in the witches’ brew experiment are set forth. The data for each of the six distillates of the air concentrate are given in lines 1 to 6. Column 1 gives the total volume of each distillate. Column 2 gives the volume of the gaseous smog concentrate in each distillate; and column 3 gives the parts per million of the gaseous smog concentrate found in the original air sample. The mole per cent of each of the six hydrocarbons added to the air, as found by the mass spectrometer (A&- the oxidation reactions had occurred), are noted in columns 4 t o 9; and the parts per million of these hydrocarbons in the original air sample are given in columns 10 to 15. The total amount of gaseous smog in the air sample was 0.468 p.p.m. There were, of course, traces of substances not deliberately added. The mass spectrometer is enthusiastic about finding such things when they are present, even though their existence was not suspected. Chlorine may have come from the water used to confine the four gaseous hydrocarbons which were added. Toluene and xylene may have been impurities in the benzene. Bcetone may have been a reaction product, or otherwise about the place. Ozone would not be expected to show on the mass spectra, nor would chlorine as such in the concentrations occurring here. Both react too rapidly with the stopcock lubricant of the inlet system. Table I1 gives data for the amounts of gaseous smog concentrate found in some of the air samples examined, including the two typical smogs listed in Table 111. The total smog concen-
1439 trate varied from 0.131 to 0.449 p.p.m. (by volume). These amounts are minimum, as the existence of hydrocarbons of high boiling points and correspondingly low saturation pressures precluded the transfer of all of each of the gaseous smog concentrates to the manometric “buret” of the inlet system of the mass spectrometer. However, not much change in the amounts expressed would be expected. They are of the correct order of magnitude. The amounts of some of the air pollutants which have been detected by this method are worth a moment’s reflection on the part of the microanalyst. The mass spectrometer is capable of detecting 2.9 X 10-6 ml. of a number of the pollutants. This corresponds to about 3 X lo-*’%, or 3 X 1 0 - ~p.p.m. if a 100liter sample of air is taken; or 3 X 10-5 if concentrated from a 1000-liter sample. Carbon tetrachloride, trichloroethylene, xylene, toluene, etc., were determined in these sniall amounts in some of the dietillates of smog concentrates. I t would have been possible to increase the air sample tenfold, although this would have been inconvenient a t times unless ten samplers had been operating in parallel. Also, the more sensitive mass spectrometer now available, with a smaller inlet reservoir, will yield yet another order of magnitude in this direction. So it is that 0.000001 p.p.m. may be realized in determining pollutants by this method. Table I11 gives the approximate concentration of compounds identified i n some of the distillates of two typical gaseous smog concentrates, and of one distillate from the concentrate of the exhaust gas from an idling truck. These selected distillates were among the most important of the present survey. The composition is reported on the air- and water-free basis. Estimation of all the compounds previously listed was not possible. The degree to which the synthetic smog pattern fits the actual smog patterns is given in line 16 labeled “proportion of residuals accounted for by XII-S4.” From 5 to 60% of the composition of the distillates of the smog concentrations can be accounted for in this way. This matching of the actual m-ith the synthetic pattern is observed in both samples; and this was true of all other smog samples examined. The other important feature of the tabulated data is the great abundance of hydrocarbons found. Together with their reaction products, they essentially constitute the gaseous phase of the smog. Lines 17 and 18 of the table give the highest mass found and the corresponding hydrocarbons in each distillate. Hydrocarbons up to Clo were found in some of the spectra, and up to C,, were indicated. One of the most interesting distillates was the first one of about fifteen from the concentrate of exhaust gas from the idling truck. This contained a remarkably large amount of acetylene-70.5 mole yo. If it can be shown that there is no other large source of acetylene in the Los Angeles air, the determination of acetylene in the air itself might serve to establish the proportion of automobile exhaust in the air, although a calculation would be difficult, as the average acetylene contribution for autos would have to be statistically determined. In studying Table 111, it should be remembered that the amounts appearing in the columns refer to portions of the sample, not the total sample. Thus the high amount of acetylene found in the first distillate from the auto exhaust reduced to only 0.5% referred to the whole gas exhaust sample. (Total sample is designated by the Roman numeral; distillates of the samples are designated S1, 52, S3, etc.) Carbon monoxide does not appear in the table, but it was determined occasionally by the Sational Bureau of Standards colorimetric carbon monoxide indicator ( 4 ) . The amount generally found a t 808 Spring St. and elsewhere in Los Angeles was 0.0003 to 0.0004% by volume. As much as 10 times this amount was observed during heavy smogs. Table IV gives the residual spectra of distillates of the synthetic smog. Such residual spectra formed the basis for identifying the
ANALYTICAL CHEMISTRY
1440 nature of the irritant portion of the Los Angeles smog. ( I t is realized, of course, that irritants other than the products of reaction of unsaturated hydrocarbons with ozone and nitrogen dioxide may exist; but there is no longer doubt that these products constitute the important part of the Los Angeles difficulty. j All identified compounds have been removed from these spectra; but even in this reduced form they will still illustrate the complexity of this analytical problem. It is hoped that mas8 spectronietrists, on reading these mixture spectra, may recognize patterns not familiar t o the authors, and, so doing, will report their findings. A further illustration of the complexity of the mixtures t o be analyzed is shown by the three lower mass spectrograms of Figure 4. The bottom spectrogram is that of distillate 54 of the synthetic smog, which was the key calibrating spectrogram used in the witches' brew experiment. Next upward are the two spectrograms of distillates from samples I X and X, noted in Table 111. Finally, the top spectrogram is that of a concentrate from 150 liters of air sampled a t El Rancho del Lago Lindo, located on the desert near Palmdale, about 60 miles from Los Angeles and across the Sierra Madre range. This spectrogram reflects the calm of the desert itself, with none of the peaks so abundantly characteristic of the air of Los ilngeles. It gives assurance that the method here reported is capable of yielding a suitable blank under proper (and acceptable) atmospheric conditions.
ACKHOW LEDGMENT
The authors gratefully acknowledge the cooperation of Gordon Larson, director of the Los Angeles Air Pollution Control District, and his associates, and of -4.J. Haagen-Smit of the California Institute of Technology. LITERATURE CITED
Haagen-Smit, 4. J., Air and Stream Pollution Symposium, Section on Air and Stream Pollution, XIIth International Congress of Pure and Applied Chemistry, New York, N. y . ,September 10 to 13, 1951. Happ, G. P., Stewart, D. W.,and Brockmyre, H. F., ASIL. CHEM.,22, 1224 (1950).
Rock, S. M., Ibid., 23,261 (1951). Shepherd, hlartin, Ib-id., 19,77 (1947). Shepherd, Martin, J . Research A'atl. Bur. Standards, 2, 1145 (1929); Research Paper 75, p. 1154.
Shepherd, Martin, J . Research N a t l . Bill.. Slnndards, 26, 227 (1941); Research Paper 1372.
Shepherd, Martin, Proo. First U . S. Technical ;lir Pollution ('onference, Washington, D. C.. May 1960. Washburn, W. H., Wiley, H. F., and Rock, 9 . >I., IND.EXG. C H E M . , .ih'.41,.
ED.,15, 64 (1943).
1%-ashburn,W.H., Tl-iley, H. F.. Rock, S,SI..and Berry, C. E., Ibid., 17, 74 (1946). R E C E I V E JDu l y 2 , 1953
Autoradiographic Technique with Carbon 14 in Rubber A. D. KIRSHENBAUiM, C. W. HOFFJIAN, AND A. V. GROSSE Research Institute, Temple Unicersity, Philadelphia, P a .
The uniformity of dispersion of carbon black in rubber is at present determined from the tensile strength, elongation, and modulus values; but low modulus, elongation, or tensile strength values are also caused by polymer breakdown. The autoradiographic technique making use of carbon 14 was used to study the distribution of carbon black in rubber. Good and bad carbon black-rubber mixes containing carbon 14 were prepared, having tensile strengths varying from 300 to 3300 pounds per square
I
T H E manufacture of rubber products such as tire treads, additives such as carbon black and zinc oxide are incorporated into the rubber to give special desirable characteristics. These additives are dispersed by mixing or milling, and it is important that they be well dispersed throughout the rubber. The uniformity of dispersion of carbon black in rubber is generally reflected by the stress-strain properties of the loaded rubber stocks. But low modulus, elongation, or tensile strength values are also caused by polymer breakdon-n. The method used by the authors to study the distribution of carbon black in rubber was a visual observation of the carbon black dispersed in the rubber, made possible by the autoradiographic technique with carbon 14. Carbon 14 is an isotope of carbon and is chemically the same as the carbon atoms in the carbon black; the only difference is that it has a higher atomic weight and is radioactive, emitting soft beta particles having an upper energy limit of only 150 to 170 kv. ilutoradiography is a technique by which radioactivity present
inch. Autoradiographs of these mixes showed visible variations in the carbon distribution which agreed closely with the tensile strength data; photomicrographs of the same mixes showed no differences among the various mixes. The autoradiographic technique was also used to track down the agglomeration of carbon black in the rubber. This method makes it possible actually to see how well the carbon black is dispersed and determine what causes carhon black agglomeration in rubber.
in a material may be precisely located. This technique utilizes Bacquerel's discovery that radioactivity affects the photographic emulsions, producing a blackening of the film. The first autoradiographs using carbon 14 were obtained by Grosse and Snyder ( 4 ) . ;\raking use of this technique, a trace of radioactive carbon (carbon 14j was incorporated into the carbon black to be used, and the radioactive carbon black was then dispersed into the rubber. Samples of cured and uncured rubber containing the radioactive carbon black were put into direct contact with x-ray film, and after a suitable exposure time the films were developed. The radiations given off by the radioactive carbon blackened the films, producing patterns which are pictures of the carbon black as distributed in the rubber. In order to make an autoradiograph, sufficient radioactivity must be present in the material being studied; otherwise long exposure times are required. -4total fluu of S 1 0 5 beta particles per square centimeter of film is necessary to produce a detectable blackening, and a t least 10 to 100 times this activitv is npeded t o produce a satisfactory image ( I , 3 ) .
