Determination of Trace Quantities of Hydrocarbons in the Atmosphere E. R. QUIRAM and W. F. BILLER Products Reseorch Division, Esso Research and Engineering Co., linden,
b A freeze-out mass spectrometer method for determining hydrocarbons in the atmosphere i s based on a concentration technique in which the fixed gases in the sample, such as oxygen, nitrogen, and hydrogen, are pumped off a t the temperature of liquid nitrogen, whereas the hydrocarbons are not. Methane cannot b e determined, because it cannot b e retained a t the temperature of liquid nitrogen. W a t e r and carbon dioxide are reduced to a significantly low level under high vacuum with the aid of appropriate absorbents. Studies on synthetic mixtures of hydrocarbons in simulated air samples indicate essentially complete recovery of the hydrocarbons. This method i s novel in that water vapor, carbon dioxide, and residual air no longer interfere in the analysis and the hydrocarbon concentrate can be expanded into the mass spectrometer reservoir in its entirety for spectrographic analysis without fractional distillation.
N. J.
hydrocarbons by a freeze-out technique prior to analysis with a n infrared spectrophotometer, using a specially built 100-cm. gas cell. Silica gel has been used in lieu of the cold trap technique for determination of small quantities of gaseous hydrocarbons. Quiram, Metro, and Lewis ( 2 ) collected the hydrocarbons on silica gel at -100" F., desorbed the gases into an evacuated sampling container, and finally analyzed the material by mass spectrometer. The present investigation uses a freeze-out technique for removing the hydrocarbons from the atmosphere and a mass spectrometer for identifying and determining the amount of hydrocarbons. Water and carbon dioxide are removed under high vacuum with the aid of appropriate absorbents. The mass spectrometer is a suitable
instrument for this analysis, as it requires only an exceedingly small sample and yet is capable of identifying and estimating a great many molecular species. Hon-ever, the mass spectrometer has its limitations. The pattern which it provides for each compound often covers up the presence of other compounds and consequently introduces errors in the determination. For this reason a n alternative method of calculation is proposed for complex mixtures, although it gives only a close approximation of the total hydrocarbon content. APPARATUS AND CHEMICALS
Gas-collecting bottle (Figure l), volume at least 2 liters. Freeze-out trap (Figure 1).
F
it is desirable to know the total concentration of hydrocarbons in the atmosphere in a refinery area. The need for such information most frequently arises from safety considerations, although it may also be desired for detection and control of losses, or control of air pollution, a subject in which there is constantly increasing interest. The determination of hydrocarbons in air has aln-ays been difficult, particularly in the concentration range of only a few parts per million. Arailable methods have not been entirely satisfactory, and it was felt that further work was needed. The method described represents an improvement over previous procedures, in both convenience and accuracy. There are many analytical methods for collecting, identifying, and quantitatively measuring contaminants in the air. Shepherd, Rock, Howard, and Stormes (3) have described a freeze-out technique whereby the frozen concentrate is separated by isothermal distillation or sublimination a t low temperatures and pressures. Mader, Heddon, Lofberg, and Koehler ( I ) collected the REQUENTLY
1166
ANALYTICAL CHEMISTRY
\IACUUV STOPCOCK 4mm -
f FREEZE OUT TRAP
GAS SAMPLING B O T T L E
Figure 1.
Freeze-out trap and gas-sampling bottle
Hydrocarbon concentration thimble (Figure a),volume 10 to 12 rnl. Ascarite-Dehj-drite absorber (Figure 2). Place approximately 10 grams of Ascarite in the short a r m of the absorber and 3 to 4 grams of Dehydrite in the long arm of thc container. Phosphorus pentoxide absorber (Figure 2 ) . Add 0.5 to 1.0 gram of the reagcnt and then tilt and rotate the vessel so that some of the reagent will cling to the side walls. This gives a greater surface area for the adsorption of water. The vacuurxi manifold system (Figure 3) must be capable of maintaining a good 1-acuum. Any type of diffusion pump and mechanical pump may be used, if i t can maintain a vacuum of 15 microns of mercury or better in the manifold system. Thermocouple pressure gage, capable of measuring pressures from 1 t o 1000 niicrons of mercury. A Hastings gage, Model G-V-3, was used in this WO?k.
Thc adapt'er is used for attaching the hydrocarbon concentration thimble t o the mass spectrometer (Figure 5 ) . 31ass spectrometer, consolidat,ed hlodrl 21-103, or an instrument equivalent in perfori1i:tnce. JVet test gas meter, calibrated in liters uf air, may be purchased from a n y laboratory supply house. Blower and vacuum unit, may be purchased froiii any laboratory supply house. Direct-reading mcuurn gage, range 0 to 760 nim. R'allace and Tiernan vacuum gage, Model FA 129, was used, but a mercury manometer can be cmployed if necessary. The principal part of the apparatus is :i rnanifoid connected through a cold t r a p to niechanical and oil diffusion vaciium pui~ips. I t is fitted with a mercurj- imriuirieter and a tlierinocouple gage. Tlie manifold (Figure 3) contaiiis :L iiun!L)cr of outlets for connecting the sample fri,rze-oi.it trap, the hydrocarbon rcceiwr, and the absorbers for wat'er and carbon dioxide. The vacuum manifold system is constructed from borosilicat,e glass tubing. 1':icuum st,opcocks are used throughout the system to prevent air leakage.
The mercury manometer serves as a safety-indicating device, vvhich enables the analyst to read a t a glance the pressure within the manifold system. A knowledge of this pressure permits better control of the gaseous components during their evpansioii from the freeze-out trap.
A thermocouple gage capable of measuring pressures from 1 to 1000 microns of mercury is fitted betnceii the manifold and mercury inrnometer. Any type of diffusion pump and mechanical pump may be used, if it can maintain a vacuum of 15 microns of mercury or better in the manifoid system. The glassware can easily be fabricated by any glass-blower. Glass wool is packed inside the freeze-out trap to increase the surface area. This permits greater efficiency in retaining the more volatile components in the trap. The Ascarite-Dehydrite absorber is fabricated with two side arms. The long a r m of the absorber contains Dehydrite and can be immersed in liquid nitrogen, t o facilitate more rapid removal of the gaseous components from the freeze-out trap. Chemicals. Stopcock grease, spectro_vacuum lon. vapor pressure. Ascaritc, 8 t o 20 mesh. Dehydrite, aiihydious magnesium perchlorate. Pliosl,horus pentoxide, phosphoric anhydride. Liquid nitrogen. SAMPLING PROCEDURES
K h e n the hydrocarbon concentration in the atmosphere is above 10 p.p.m. the grab-sample technique is recommended (Method ii). K h e n the hydrocarbon concentration is less than 10 p.p.m., a larger volume of air must be sampled (IIethod B). Method A. Sampling of Hydrocarbons above 10 P.P.M. Evacuate a clean d r y gas-collecting bottle t o a prcssuie of 1 nim. or less. T a k e tlie container t o t h e aiea of sampling and slonly open tlie stopcock. K h e n atmospheric picssure is reached, close
c.=;LI
n
-2
HYDROCAR6ON CONCENTRATiON THtMBLE
Figure 2.
ASCARITE -DEHYDRITE ABSORBER
P H O S P H O R U S PENTOXIDE ABSORBER
Equipment for concentrating hydrocarbons
t h e stopcock and bring t h e bottle back t o t h e laboratory for analysis. Assemble the vacuum manifold system shown in Figure 3. Test for leaks by evacuating the system to a pressure of 10 to 20 microns, then remove pump from system by closing stopcock 6 . If the indicator of t h e Hastings gage shons no apparent rise in pressure after 5 minutcis, one can be reasonably sure that the vacuum system is tight and is functioning properly. Connect one end of a short length of neoprcnc tubing to stopcock 1 of the manifold system and the other end to the gas-collwting bottle. Remove entrapped air in the neoprene tubing by opening stopcocks 6 arid 1. Record the height of the mercury in the mercury manometer after pumping for 5 minutes. Close stopcock G and keep it closed throughout the opcration. Attach a clean dry frwze-out trap, previously degassed by gentle flaming while under vacuum, to tlie other end of the gas-collecting b(Jttk, iiTirig lowvapor-pressure stopcock greasc. Vsing a small glass adapter, coiiiiect another short length of neoprciLe tubing t o stopcock B of the fiewe-out trap. Conncct the other end of this tubing to another vacuum pump. With stopcocks -1 and B of the freeireout trap closed, inimerqe the trap in liquid nitrogen and start vacuuin pump 2 . Open both stopcoclis of the gsscollectiiip bottle :md stopcock B of the freeze-out trap. dftcr npproxim:ltcl:i. 1 minute c l u ~sto1)cocli B and opcn stopcock -1. This permits some of tlie sninple in tlie sanilile container to enter the freeze-out t13p. After a few seconds, close atopcocl~: A and after 1 minute open stopcock B again to reniolc tlie fixed Repeat this sequence of operations until the pressure in the mercury manometer has nearly reached thc initial recordsd pressure. At no time during this transferring step are both stopcocks A and B open at tlie same time. When tlie pressure in the mercury manometer has come u-ithiii 40 nim. of the initial recorded prcssure, open both stopcocks A and B and coiitinue pumping until the initial recorded pressure is reachcd. Open stopcoch B very slo~,lj-,so that the remaining material in the m ~ i p l cbottle doe? not surge through the freeze-out trap too rapidly. Close stopcock 1 of the manifold system and stopcocks A and B Shut off vacuum pump 2. Remove tlie neoprene tubing attached to the nianifold system and disconnect the gassampling bottle from the freeze-out trap. Method B. Sampling of Hydrocarbons Less Than 10 P.P.M. Assemble t h e sample-collecting apparatus as shown in Figure 4. T h e amount of air sampled will depend upon t h e concentration of hpdrocarbons in t h e atmosphere. From t h e table below, select t h e proper size of air sample nhich will produce a sufficient amount of hydrocarbons to give a satisfactory measurement on the mass spectrometer. VOL. 30, NO. 7,JULY 1958
1167
Hydrocarbon Concn. in Air,
Vol. of Air to Be Sampled,
2 -0.2 0 5-0.1
20.0 100,o 200.0
P.P.AI. 10 -2
FOR
Liters
The flon- rate of air through the freezcout trap should be approximately 1
liter per minute. This can readily be accomplished by selecting a capillary tube haring a bore size that will give a pressure in the trap of 60 to 70 mni. of mercury. A tubing 8 inches long, haring a capillary bore of 0.5 to 0.6 mni., operates satisfactorily. The Kallace and Tiernan pressure gage is satisfactory, but any other pressuremeasuring device can be used. This method of sampling prevents condensation of liquid oxygen from the air in t,he freeze-out trap, by maintaining the pressure below the vapor pressure of oxygen a t the temperature of the trap. After the proper volume of air has been sampled, close stopcocks -4and B, disassemble t,he apparatus, and return the freeze-out trap to the laboratory while still immersed in liquid nitrogen. Concentration of Hydrocarbons. While still immersed in liquid nitrogen, attach t h e freeze-out trap used in Method A or B t o the manifold system a t stopcock 2 . Connect a clean, dry hydrocarbon concentration t,himble to stopcock 3. Prepare t h e bscarite-Dehydrite absorber and phosphorus pentoside absorber as described under “Apparatus.” Attach the Ascarite-Dehydrite absorber to stopcock 4 and phosphorus pentoxide absorber t’ostopcock 5 . K i t h stopcocks 4 and 5 in the closed position, open stopcocks 2, 3, and 6 of the manifold system and stopcock B of the freeze-out trap. Continue pumping until the Hastings thermocouple gage indicates a pressure of approximately 20 microns. Close off the manifold system from the vacuum pump by closing stopcock 6. Remove the liquid nitrogen container from around the freeze-out trap and place it under the concentration thimble. Permit at least 30 to 45 minutes for transferring the contents of the freezeout trap t o the concentration t’himble.
$TUBING
T~
TO DIFFUSION PUMP AND VACCUM PUMP
I 1
1168
e
ANALYTICAL CHEMISTRY
,
I‘ I
Khen large volumes of air (more than 50 liters are sampled), the amount of irater in the freeze-out trap may he wceedingly large, and to ensure coinplete removal of all materials from the trap, it may be necessary to extend the time required for transference t o at least 60 to 90 minutes. Applying heat t o the trap Jyill facilitate a mor? rapitl transference. Close stopcock 2. Close the stopcock on the thimble, open stopcocks 6 and 4 of the manifold system, and evacuate the Ascarite-Dehydrite absorber. As the absorents have an appreciable vapor pressure, the Hastings gage will indicate R pressure of approximately 100 microns. Flame the Ascarite absorber gently and continue pumping for approximately 15 minutes; then close stopcock 6, open the thimble stopcock, and remore
ll
I
Figure 3.
Vacuum manifold
-
e -
A19 IN
TRA? R E T TEST METER
Figure 4.
VACUUM P d M P AND B L O W E R
IYALLACE-TIERNAN PRE S S U Q E G A G E
Hydrocarbon-collecting assembly for atmosphere
the liquid nitrogen. Permit a t least 30 t o 45 minutes for the carbon dioxide and the bulk of the u ater to be absorbed in the Ascarite-Dehydrite absorber. There should now be no visible signs of moisture in the thimble. Place the liquid nitrogen around the concentration thimble and let stand for 5 minutes. This will return the hydrocarbons to the thimble. Close the thimble stopcock and stopcock 4 of the manifold system. Open stopcocks 6 and 5 and evacuate the phosphorus pentoside absorber and manifold to a pressure of approximately 20 microns. Now close stopcock 6, open the thimble stopcock, and r e m o w the liquid nitrogen. Allow a t least 20 minutes for the remaining water in the sample to be absorbed in the phosphorus pentoxide. Return the hydrocarbons to the concentration thimble by placing the liquid nitrogen bath around the thimble for 5 minutes. Close stopcock 5, open stopcock 6, and evacuate the system for approximately 1 minute to remove any air that might have leaked into the system. Close stopcock 3 and the stopcock on the concentration thimble, remove the liquid nitrogen, and disconnect the thimble from the manifold. Analysis of Hydrocarbons. .4ttach t h e hydrocarbon concentration thimble t o t h e inlet system of t h e mass spectrometer. h f t e r pumping out t h e mass spectrometer induction system, a d m i t t h e entire contents of t h e concentration thimble t o t h e mass spectrometer reservoir. By means of t h e micromanometer, measure t h e total pressure of t h e sample admitted. Record the mass spectrum of the sample. CALCULATIONS
Two methods of calculation are offered. The choice of method \Till depend upon the complexity of the mass spectrum. If the air sample being analyzed contains only a relatively few hydrocarbons, the mass spectrum will not be too complex and an analysis based on the summation of the partial pressures of all components is recommended. This type of analysis gives a breakdown of the individual components. T h e n the sample of air contains a mixture of many hydrocarbons, the mass spectrum may be too complex for accurate determination of the individual components, and a method for total hydrocarbon content may be used instead. This type of analysis is based on experimental data which indicate that nitrogen and other fixed, nonhydrocarbon gases are essentially completely removed in the concentration technique. Itrater and carbon dioxide are present in Eignificantly low concentrations. The proposed method of calculation involves determining the partial pressure of water and carbon dioxide in the concentrated sample. The difference between the sum of the partial pressures of these components and the total
LIolc volume per cent Cz and higher I’ hydrocarbons = sample size (ml.) x 100 -
p
3
~
-
RESULTS AND DISCUSSION
FROVT V t k
High Concentration Blend. To evaluate t h e method, synthetic gas blends n ere prepared bl- a dilution technique t o cover several desired concentration ranges Blend 1 contained 83.3 p p m of hydrocarbons in air. The composition of t h e hydiocarbons \ \ a s :32y0 ethylene and 68y0 n-butane Table I slioirs t h a t recolcly of hydrocarbons mas good. Result. obtained by the t n o method. of calculation described are remarhahl! close. The alternate method of anal! sic. based on the difference between total pressure and sum of partial presfurcq of non-
Figure 5. Adapter for attaching thimble to mass spectrometer
pressure admitted to the mass spectrometer is due predominantly to hydrocarbons. Sitrous oxide is not retained in the dscarite absorber. Therefore, if the peak heights at m/e 30 and 44 are significantly large, the presence of this material is suspected. Results will be in error to the extent that this component is present in the sample. B y means of Boyle’s lam, the mole volume per cent hydrocarhon is calculated as folloms :
where
PI= pressure in hydrocarbon VI
=
Pz
=
ST2 =
concentration thimble due to hydrocarbons, mm. volume of hydrocarbon concentration thimblr, nil. total pressure in nim. due t o hydrocarbons admitted to mass spwtrometer reserroir volume of mass spcctrometer reservoir in nil. plus volume of hydrocarbon eoncentration thimble
The volumr of gas, 1-3, a t atmospheric pressure in the hydrocarbon concentration thimble is calculated in the f o l l o ~ ~ i nmanner: g
Pa x ’c’z atmospheric pressure
The mole volume per cent of Cz and higher hydrocarbons in the sample is calculatd as follows:
Table
I.
Synthetic Hydrocarbon-Air Bland
Mole yc of hydrocarbons theoretirally present! 0.00833 (83.3 p.p.m., 1’) Composition of hydrocarbons in blend, 32% ethylene, 6870 n-butan? Sample of air tested, 2.00 liters Pressure of concentrated material in mass spectrometer, 42.0 microns Mass Spectruni DataPeak Peak m/e height m/e height
Precise Method of Calculation (Summation of Partial Pressures) r
Xcrons Compn. Pressure Contributed bv nbutane 25 10 Contributed by ethylene 12 48 Total due to hydrocarbons 37 58
66 8
33 2
H\&mxdmns in concentrated material, ml. 0.161 Hydrocarbons in sample, mole 7 . 0.00805 (80.5 p.p,m., 1’) Recovery 06.670 Alternate
( - % proximate) ~ alculation
?\lethod of Microns
Pressure
Contributed by water 2.63 Contributed by carbon dioxide _. Total of nonhydrocarbons 2 63
Pressure due t o , hydrocarbons. 42.0 2.63 = 30.3T microns Hrdrocarbons in concentrated material, ml. 0.168 Hydrocarbons in sample, mole ‘ C 0.0084 (84.0 p.p.m., 1’) Recovery lOO.SC,
VOL. 30, NO. 7, JULY 1958
1169
hydrocarbons, probably gives slightly high results. This may be due to the fact that nonhydrocarbon gases, such as air, may be present in trace amounts and are not taken into consideration in the calculations. Only 2 liters of sample was required for this analysis. This saniple contained approximately 0.16 ml. of gaseous hydrocarbons, yet it was large enough t o contribute approximately 40 microns of mercury pressure in the mass spectrometer reservoir. The mass spectrum peak heights were exceedingly high, nhich indicates that at least a forty fold decrease in sample size could be tolerated in analyzing a sample of air containing this concentration of hydrocarbons. Table II.
Analysis of Synthetic Hydrocarbon Blend
Hydrocarbon Content, P.P. M. Sample Sample Component Theoretical 1 2 Ethane 0.01 0.11 2.28 2.34 Propane Isobutane 14.07 15.17 Isobutylene 1.80 1-Butene 9.37)12.99 13.10 %Butene 1.82 n-Butane 1.77 2.12 Isopentane 1.67 2.86 n-Pentane 1.71 1.59 .,. 0.30 Ethylene 0.11 Propylene - ~ Total 34.50 36,3Oe 37.70* By difference between total pressure and sum of partial pressures of nonhydrocarbons. * By summation of partial pressures. ~~
Table Ill. Mass Spectrometer Data of COAR-API Synthetic Sample m/e Sample 1 Sample 2 12 8.5 8.7 14 40.5 41 .O 15 162.0 160.0
16 18
5.7 17.5
120 0
26 27
560.0 274 0 290.0
28 29 30
8.0
i .5
32
38
39 41 42 43 44 49 50 51 52 55 56 57 58 72 Volume of sample, ml Pressure in mass spectrometer, microns
1 170
5 .3
4 0 124 5 586 0 277 .O 305.0 8.~ .2 1.2
84.0 485.0 1000.0 376.0 1095 0 61 0 17 0 53 0 43 0 12 5 114 0 220 5 85 0 30 5 9.2
86.0 500.0 1056.0 390.0 1125 0
2040
2040
17.7
62 0 17 0
53 43 12 110 234 96 31 10
5
0
5
0 0 0 0 1
18 1
ANALYTICAL CHEMISTRY
Low Concentration Blend. Blend 2 was composed of the following materials : Total hydrocarbons Carbon dioxide Nitrogen
Mole yo 0.00345 0 043 99.96
The hydrocarbons used in the preparation of this synthetic gas blend were obtained from Phillips 14 mixture, which had the following composition: Component Ethane Propane Isobutane Isobutylene 1-Butene n-Butane 2-Butene Isopentane n-Pentane
Mole 70 0 04 6 62 40 75 5.23 27.17 5.12 5 28 4 84 4 95 100 00
This blend was analyzed twice. The result for sample 1 was calculated by difference between total pressure and sum of partial pressures of nonhydrocarbons. The result for sample 2 was calculated on the basis of the individual components by summation of the partial pressures. Table I1 indicates that with this size of sample the maximum deviation for each individual component should be no greater than 1 p.p.m. Increasing the sample size a t least 100-fold should improve the accuracy significantly. 30 appreciable difference was noted between results by the two methods of calculation. The pertinent mass spectrographic data obtained from these two runs are shon n in Table 111. Peak heights a t m / e 18 and 44 are exceedingly low, which indicates that water and carbon dioxide have been completely removed in the concentration technique. This same sample has been cooperatively tested by the COAR-API Subcommittee on Analytical Methods for Atmosphere. The data in Table IV Table IV. API Cooperative Results on Synthetic Gas Sample
Total Hpdrocarbons Found, Laboratory P.P.M. 37.0 .I B 38.5 49.5 C 51.0 D 38.0 E 77.0 Fa 38 0 G 33.5 H 35.4 I 38.0 J 39.0 K AV. 39.8 Std. dev. 5.75 a Xot included in averages. Laboratory F reports 17.3% toluene in blend, whereas no toluene wa8 added to sample.
indicate that the standard deviation for 10 of the 11 participating laboratories is 5.7 p.p.m. Laboratory F data are apparently in error and were not included in making this estimate of precision. -4 breakdown of the individual hydrocarbons is shown in Table V. Traces of impurities reported in these data may be due to an incorrect interpretation of the mass spectra or to the fact that the sample containers or mass spectrometer block and reservoir were dirty. This suggests the desirability of running a background on the mass spectrometer prior to running the sample, to be sure that the system is clean. I n general, hoTvever, the agreement between laboratories was very good; and the impurities are in such low concentrations that they make no significant difference in the total hydrocarbon content of the original blend. Analysis of Air Sample. I n analyzing atmosphere containing trace quantities of hydiocarbons, it is necessary t o sample a much larger volume t h a n in ttsting the procedure on standard blends. This is acconiplished by immersing t h e freeze-out t r a p in liquid nitrogen and passing air through the t r a p a t a s l o ~ r , predetermined rate. T o prevent condensation of liquid oxygen, a relatively low pressure is maintained in the trap. Two hundred liters of air, collected on a slightly hazy day in an industrial area, v a s sampled b y this samplecollecting technique. The relevant mass spectrographic data, shown in Table VI, indicate the hydrocarbon content to be approximately 0.11 p.p.m. !Then the sample-collecting technique described is used. The mass spectrum of the sample is extremely comples and positive identification of all coniponents would be very difficult. I n view of the complexity of the pattern, calculations were made by difference between total pressure and sum of partial pressures of nonhydrocarbons. Even with the limitations inevitable in the interpretation of mass spectra data, considerable information can be obtained on a number of compounds. Peak heights at m,'e 44, 30, 16, and 14 are nornially associated with carbon dioxide, osygen, nitrogen, nitric oxide, nitrogen dioxide, and nitrous oxide. As it has been established that carbon dioxide, oxygen, and nitrogen are removed during concentration, it was felt desirable to determine whether the large peaks a t m/e 44,30, 16, and 14 in the spectrum of the air sample xere contributed by oxides of nitrogen. A synthetic mixture was prepared containing the following components: Kitrous oxide 0.078470 iiitric oxide 0.072670 Nitrogen dioxide 0.0640% Carbon dioxide 13.3% Nitrogen 86.5'30
Table
V.
API Hydrocarbon Breakdown on Synthetic Gas Sample Laboratory
Component Ethane Propane Isobutane Isobutylene 1-Butene 2-Butene n-Butane Isopentane n-Pentane Ethylene Propylene Pentylenes Benzene Hexanes Hexenes n c6 Methane Toluene c6 olefins Aromatics
+
+
Theoretical 0.04 6.62 40.75 2; ??\37.68 5.28 5: 12 4.84 4.95
... ...
...
... ...
... ...
...
...
A 0.3 6.2 40.2
*D
R-
0.6 7.1 42.7
0.4 7.4 41.5
0.1 7.4 39.3
0.2 7.4 42.1
0.1 5.0 30.7
0.2 7.6 39.5
0.4 8.1 39.7
... 3.0 36.4
34.7
34.7
34.7
29.0
30.8
24.6
30.4
33.9
31.5
5,6 7.6 4.2
5.6 4.8 4.5
4.6 5.1 4.4
4.7
...
... ...
7.5 4.6 4.2 4.0
1.4 .,. 1.2
...
...
... ... ... ...
26.7 3.6 3.4 3.1
4.7 4.5 4.6
0.8
5.6 6.0 4.8 1.2
i.2
5.2 4.3
0.2
...
0 3 0.3
0.1 0.4
0.2 1.2
...
...
...
...
...
...
Trace
0.5 0
... ...
...
...
0.3
...
... ...
... ...
This blend was concentrated and analyzed by the concentration technique employed for the air sample. Table VI1 shows that the pattern of the residual peak heights of the nitrogen oxides blend is remarkably similar to the pattern of pure nitrous oxide. This suggests that nitrous oxide is unaffected during concentration, whereas nitric oxide and nitrogen dioxide are removed in the absorbents or in the mass spectrometer. A quantitative measurement based on the pattern of pure nitrous oxide indicates the concentration of nitrous oxide in this synthetic concentrated blend t o be approximately 0.0807%, representing a recovery of 103% based on the original sample. Table VI1 also shows the similarity between the pattern of pure nitrous oxide and the pattern obtained from the residual peaks of the concentrated air sample. These data indicate that the peak heights a t m/e 44,30, 16, and 14 in the air sample are probably contributed by nitrous oxide. A quantitameasurement shows the nitrous oxide content of the air sample to be 0.166 p.p.m. Although aldehydes have not been investigated, it is reasonable t o expect that they also will be removed, as they are known to react chemically with sodium hydroxide (Ascarite).
B
... ...
.
.
E
H
I
...
Table
...
0.2 1.5 0.1 0.1
...
...
...
0.8 8.3 0.4 0.5
... ...
... ...
*..
...
... 1.7
... ... ...
...
VI. Analysis of Air Sample
Volume of sample concentrated, 200 liters. Presgure in mass spectrometer, 17.1 microns Peak Peak m/e Height m/e Height 12 14 15 16 18 25 26 27 28 29 30 32 38 39 41
5.0 75.2 49.0 33.0 172.5 13.3 72.5 157.5 145.5 137.1 160.5 2.0 17.0 88.5 172.5
43 44 56 ..
56 57 58 69 70 71 78 83 84 91 92
270.0 385.0 32 _- 5 48.2 64.5 12.2 10 0 1.5 0
I
...
... I
.
...
.
1.4 0.8
... ...
1.o
... ... ...
...
...
1.8
6.2 1.3
2.3
...
...
2.8
...
...
2.3 0.5
Table VII. Mass Spectrum Pattern of Nitrous Oxide, Synthetic Gas Sample, and Atmospheric Sample
% Base Peak Pure Synthetic nitrous gas Atmospheric oxide sample" sample
m/e
7 6.6 44.5 100.0 18 ~-
14 16 30 44 a
77 9 -6.5 42.6 100.0
19
6_.
8.6 41.7 100.0
After removal of YO, NOZ, CO,, and
N*.
ii.0
13.3 8.0 5.0 7.0 4.0
the Committee on Analytical Research, API, in the cooperative evaluation of this method is also gratefully acknowledged.
Hydrocarbon concentration 0.112 p.p.m. Nitrous oxide concentration 0.166 p,p.m.
LITERATURE CITED
bere; R ACKNOWLEDGMENT
The results discussed represent the efforts of a number of other workers a t the Esso Laboratories in addition to the authors. The authors take this opportunity to express their appreciation of these contributions. The assistance of
RECEIVEDfor review June 10, 1955. Accepted March 18, 1958. American Petroleum Institute, New York, h'. Y., May 1957.
VOL. 30, NO. 7, JULY 1958
1171
