VQ, and SC as O N . Line N P intersects the curve corresponding t o the 0 used; the ordinate of the point of intersection gives
or found on a nomograph corresponding to this expression.
m(-xm) = eqx,) +(-xm)= ST/^ is ob-x, > 0 is then found in
I am very grateful to Jean R. Proctor, of the Statistical Research Service, Department of Agriculture, for gracious assistance in checking my results.
ST =
from tained; tables and z,,,can be calculated (24) from .Y,
=
&x,
ACKNOWLEDGMENT
LITERATURE CITED
(1) Cacace, F., Inam-C1-Hay, 131, 732 (1960).
- K/8)
Science
( 2 ) Johnson, H. W., Stross, F. H., AKAI.. CHEM.31, 357 (1959). ( 3 ) “Tables for Statisticians and Bio-
metricians,” Karl Pearson, ed., Part I, Table 11, Cambridge University Press,
1948. ( 4 ) Vandenheuvel, F. A . , S~POS, J. ANAL.CHEM.33, 286 (1961).
c.,
( 5 ) Vandenheuvel, F. A., Sipos, J. C., J . Chromatog. 10, 131 (1963).
RECEIVEDfor review December 5, 1962. Accepted May 23, 1963. Contribution Yo. 115, Animal Research Institute.
Hydrocarbon Gas Analysis Using Differential Chemical Absorption and Flame Ionization Detectors W. B. INNES, W. E. BAMBRICK, and A. J. ANDREATCH American Cyanamid
Co., Stamford,
Conn.
b Parallel chemical absorbers combined with dual flame ionization detectors are used to determine the olefinic, paraffinic, and aromatic constituents in hydrocarbon gas mixtures. Design of the analyzer and a description of its various modes of operation are given. Applications illustrating its use include chromatographic analysis of gases in which the olefinic and paraffinic components are separately recorded, continuous analysis of auto exhaust for olefinic and paraffinic content during cyclic operation, studies of the effect of engine spark timing on the paraffinic and olefinic content of exhaust gases, and determination of olefinic, paraffinic, and aromatic content of gasolines.
T
determination of the olefin hydrocarbon content is important in assessing the smog potential of automotive exhaust gases. Numerous workers (7, 16, 22, 23) have shown that the paraffinic and C r C s aromatic hydrocarbons are relatively inactive and can almost be disregarded as photochemical smog precursors. Altshuller has indicated (1-2) that the Cs+ aromatics need to be considered. The hexane-sensitized, nondispersive infrared hydrocarbon analyzer has a high response to parafins and a low response to unsaturates (3, 6, 13). Its sensitivity for the analysis of treated exhaust gas samples is marginal. Spectral interferences are encountered from NOz, HzO, and COz. I t s use for measuring the mean smog potential of treated exhaust can therefore be questioned. The bromocoulometric (8) method for the determination of olefins in gaseous samples is based upon the measurement of the amount of bromine HE
1 198
ANALYTICAL CHEMISTRY
reacting with the double bonds in the olefin molecules. Although this method is applicable to auto exhaust gases, the speed of response is slow, the response varies for different olefins, and NOz interferes. Flame ionization detectors (3-5) have been used to determine the total hydrocarbon content of exhaust gases. They have sufficient sensitivity to measure the low concentrations found in treated exhaust, they are insensitive to inorganic gases, including CO, CO,, HzO, and oxides of nitrogen, and the response is linear up to high hydrocarbon concentrations. However, the olefins comprise only about 25% of the hydrocarbons emitted by automobiles. Therefore, this approach has limited value in asJessing smog potential. The methods described herein combine flame ionization detectors with selective chemical absorbers. Various hydrocarbon classes such as olefins plus acetylenes and paraffins plus aromatics are determined on a continuous, intermittent, or chromatographic basis.
By electrically subtracting the two signals, the resultant output can be used as a measure of olefin plus acetylene concentration. The 10-mv. outputs are electrically coupled (Figure 2) so that the output of each analyzer and the differential output can be recorded. ,4variable-gain potentiometer is placed in each output so that the electrical signals can be varied to give exact compensation. The outputs are recorded on a dual 10-mv. recorder, although individual recorders have also been employed Optimum performance of the analyzer for exhaust gas analysis requires: insensitivity to small change in flow of hydrogen or auxiliary air; stability of flame toward small changes in sample gas flow; linear response up to 5 mole yo hydrocarbon concentration; and insensitivity to small changes of the oxygen concentration in the sample gas. The following flow ranges to each analyzer appear to meet these requirements :
EXPERIMENTAL
Air and hydrogen flow (Figure 1) is controlled by pressure regulators a and b and capillary restrictors 2, 4, 5, and 6. Flow rates are measured with pressure gauges i and j . Sample gas flow is controlled by varying the forepressure (liquid bubbler level). Water is used in the bubbler, but high density saturated salt solutions-e.g., 5:OjO HgBrl 34% BaBrz with a specific gravity of 3.0-or mercury would be suitable for higher pressures. Sample flow is observed with a low-pressure gauge, k (0 to 30 inches of HzO), prior to restrictors 1 and 3, and may be controlled by needle valves A and B. Both time synchronization and equal instrument re3ponse for a given carbon concentration are required before vari-
Apparatus Design. Two flame ionization detectors (Carad Corp., Palo *klto, Calif.) are used because it is normally desired t o measure the concentrations of both olefins and total hydrocarbons. The analyzer is illustrated in Figure 1. (A detailed list of components is available from t h e authors.) For t h e analysis of olefinic hydrocarbons, the untreated gaseous sample is fed to one detector, while a gaseous sample which has been scrubbed through a HgS04-H2S04absorber is fed to a second detector. Thus the first detector has a signal proportional t o t,otal hydrocarbons, while the second corresponds to the saturate plus aromatic hydrocarbon content of the sample.
Hydrogen flow rate Sample flow rate Hydrogen-sample gas ratio Auxiliary air flow rate
+
30-70 cc./minute 20-50 cc./minute 1.0-1.5 500-1000 cc./minute
Air
Hydrog
Reservoir la,, feet of P4 tubing,
Duo1 Trace Recorder
olumn
Continuous or Chromotogrophic Injection Septum Aqueous Bubbler Pressure Regulator (Variable Hoight)
P l i a I
Figure 1.
able gas streams can he analyzed. To synchronize the signal3 to within 1 0 . 5 second requires that the effective dead volumes of the t a o systems be Rithin about 0.26 nil. when ;he flow rates are equal. Hoitever, a small difference in dead volumes can be offset by the use of slightly different flow rates. The copper tubing reservoir stoles .;lug samples ( 5 to 100 cc.) and presents R continuous flow of szmple gas to the analyzer. The water bubbler offers pressure relief as well as control, thereby avoiding pressure pulses and "flame-out" when thl: sample is injected. I n continuous analysis, the bubbler also serkes to bypass excess gas flow and reduce the reaponse time due to flushing of the sampling lines. Since almost all plastic tubing absorbs hydrocarbons, the system is completely metallic, except for fluorinated hydrocarbon tubing for the absorbers. Smalldiameter tubing and t,mall-bore manifolds are used to loner the response time, dead space, and surface area. Since flow through the capillaries and the adsorption of higher molecular weight hydrocarbons ori the tubing walls depend on temperature, it would appear desirable to operate a t a fixed elevated temperature. A value of 50" C. appears optimum for compounds with boiling points u p t o 5'00" C., if their concentrations do not exceed 1%. However, the analyzer described was iiyed under ambient ccnditions (25" to 35" C.), except for the high temperature chromatographic tkudies, when an oil bath was used for column immersion.
Hydrocarbon class analyzer
Chemical Absorbers. The effect of various chemical scrubbers on hydrocarbon gases has been reviewed b y Mullen (20). Francis and Lukasiewicz (11) reported on the determination of ethylene using HgSOd-HzSOl solutions and reviewed the limitations of other scrubbers with respect to removal of paraffins and revcrsibility. I n earlier
Table I.
work (6, IS), the authors demonstrated the general utility of HgSOrHzSOc in liquid or on a n inert support for subtractive olefin exhaust gas analysis. Chemical absorbers have been applied in chromatography (IO) to simplify chromatograms and make peak identification easier. Martin (17) has illustrated the use of concentrated sulfuric
Absorption of Hydrocarbon Classes by Chemical Absorbents
Absorbed, % 2OY0
Saturated soh.
0.f
470
HgS04, mercuric AgBO,, 20% H2S04 acetate 95% H&OI 0 0 0 0 0 0
Gas Methane Ethane Propane n-Butane n-Hexane n-Octane Cyclohexane Ethylene Propylene Isobutylene 2-Pentene 3-Heptene PMethylcyclohexene Benzene Toluene" p-Xylene" Acetylene a Accuracy is only ca.
0
0 0 0 0 100 100 100 100 100 100 5
0 0 0 0
0 9.4 ~~
100 100 67 60 70 46
0 22 0 0 100 100 &lOyo because of
0
0 0 0 8 100
io0
95% 0 0
0 0 11 0 31
80 % 0 0 0 0
60% 0 0
7 0
0 0 0 0
0
0
11 _-
6
n -
100 100 100 100 100 94 100 100 16
Gi
0 100 88 0 85 0 70 0 32 13 33 0 0 0 11 0 hangup; otherwise, estimated to he =k5(%.
100 100 100 100 100 100 100 100
100
VOL. 35, NO. 9, AUGUST 1963
1199
,-
1
I
’-I* I
I
I
Although glycerol in diatomaceoca earth is employed as the nonabsorbent, water or salt solutions on diatomaceous earth are other alternatives which afford low hydrocarbon solubility.
aromatics but did not completely absorb ethylene and acetylene. As the Ag&O4HzS04 became exhausted, ethylene was found to be eluted several minutes after its absorption. By placing H&Or H2S04 in series with the-Ag2S64-H~SO1, complete absorption Of was obtained. BY Proper selection of chemical absorbers, analysis of the following- hydrocarbon classes appears feasible.
After adjusting flow rates to specified values, checking for gas leaks, making sure the recorders give equal response per millivolt i n m t signal. and zeroing. a sample *of me‘ihane standard i s ‘ in-
~~
TOTAL HC’S
I
VARIAN RECORDER
Figure 2.
Electrical control system
acid on silica gel to remove the olefins and so obtain a chromatogram of the paraffins. Rowan (21) has demonstrated the use of Molecular Sieves combined with sulfuric acid and mercuric perchlorate in the identification of aromatics, naphthalenes, n-paraffins, isoparaffins, n-olefins, and iso-olefins. The authors have reported (IS) on subtractive methods using HgSOd-HzSOd solutions. I n subtractive techniques, a chromatogram of the original mixture is obtained and several chromatograms are obtained for the treated gas. The “olefin” concentration is then determined by comparing the chromatograms. Liquid phase absorbers gave incomplete absorption. To obtain more efficient contacting and complete absorption, the chemical solutions were impregnated on 80- to 100-mesh diatomaceous earth. The absorbers were prepared by mixing 1 ml. of the solution per gram of diatomaceous earth. The absorber section was 4 inches in length and 0.25 inch in diameter and had a pressure drop of 1 inch of water a t a flow rate of 30 ml. per minute. Various chemical mixtures were tested for selectivity and completeness of absorption. Table I illustrates the results obtained using HgS04-HzSO4, AgzSOdHzS04, &SO4, and mercuric acetate. Gas standards were prepared by injecting the hydrocarbon into 2-liter glass flasks to give a concentration equivalent to 5000 p.p.m. of carbon. A 5-ml. sample of the gas mixture was then injected into the analyzer and the concentration measured by the peak height. The values reported are relative to diatomaceous earth saturated with water. The response for methane was checked before each analysis. Concentrated HCI, concentrated HNO!, and bromine water were ineffective absorbers. Mercuric acetate did not show a distinct separation of hydrocarbon classes, although it removed most of the unsaturates. Ag2SO4-H2SO4(SSSA) removed olefins, acetylenes, and aromatics, while HgS04-HzSOl (MSSA) removed only olefins and acetylenes. Concentrated &SO4 removed the C,+ olefins and
1200
ANALYTICAL CHEMISTRY
Hydrocarbon class indicated bv Type of absorber First First Second absorber Second absorber Differential absorber absorber system system signal MSSA P p -I- $ 9 SSSA” P P d A 0 Q + A + O Glycerol SSSA* MSSAb A + O P 0 P+4+A+O Glycerol P = paraffins; + = aromatics; A i. acetylenes; 0 = olefins. SSSA. 4’34 silver sulfate, 05% sulfuric acid. * MSSA. 20% mercuric sulfate, 20% sulfuric acid.
-+- + +
+
“Olefins” (0 + A) are defined as the hydrocarbons removkd by 20% HgS0420% H ~ S O ~and , include olefins and
jected to check for time synchronization. If the initial response Of the two units does not coincide, the flow rates are adjusted until the response time is equal. When flow synchronization is realized, a slug sample (>30 cc.) of methane standard is iniected. The responses are then equaliz&j by potentiometer adjustment. As a final check,
--
“Paraffins” (’ $1 are defined ” the hydrocarbons not rem x d by 20% Hgso4-20% HzS04, and include paraffinic and aromatic hydrocarbons.
c~ DlFF ABS
1
7
1 5ft3 Mylar 8 ~ inside ftberpak
PUMP
Bleed
- -
I
~
”1I r-’
1
VEHICLE
I
/I
I
Clayfon C-l Dynamometer
j dI Inertia Wheel
Absorption Ulit
%fer f i / / e d Trench
Figure 3.
Auto exhaust sampling system
-
Change of elution time of unsaturate peaks with moisture content of the silica gel and concentration of the olefin. Incomplete resolution of olefins from parafins when the column is used at elevated temperature. Unsymmetrical olefin peaks.
-
EXTRAPOLATED TO
-
TO HANGUP
kI
~
MIN
0 f-
Figure 4.
1
TIES
Slug analysis of auto exhaust
a slug sample of a paraffin-olefin standard is injected and analyzed for total, olefinic, and paraffinic hydrocarbons. At the conclusion of any testing or after about 10 cc. 0 : pure “olefinic” hydrocarbon have been passed through the absorber, the standard should be rerun to check absorber efficiency. Where total unsaturate analysis is desired rather than “olefins,” an S S S h column is used instead of an MSSA column. If aromatic analysis is desired, the glycerol “nonabsorber” is replaced with SSSA. The d fferential signal between the two syrtems under the latter condition is a measure of aromatic hydrocarbons. MODES OF OPERATION
Continuous Analysis. For continuous analysis, the sampling system shown in Figure 3 appears satisfactory on catalytically trea1;ed exhaust gas and for a more limited period on untreated exhaust gas. To repeat the California 7-mode cycle ( l a ) , the driving instructions were put on a tape recorder to guide the orerator. Calcium sulfate (SI) (50 cc.) was used as a secondary liquid water trap to protect the oil-free graphite pump. I t should be changed after about 30 minutes’ usage a t 25’ C The condensed mater automatically d-ains out of the primary trap (Figure 3 ) . Chromatographic Analysis. For chromatographic analysis, a therniostated silica gel column is used (Figure 1). The bubbler backpressure is increased until the same flows
are realized as for continuous measurement. The system should then be in balance and a multiple component gas standard should be analyzed. The first detector indicates “paraffins,” while the second recorder responds to “olefins.” However, the steep slope of the methane peak makes it dificuit to avoid some methane response on the olefin analyzer, since adequate synchronization is difficult to achieve when the peak is eluted very rapidly. Various types of chromatographic columns were investigated in prior work (9) for determination of individual hydrocarbons in exhaust gas, but none of these satisfactorily resolved the unsaturates over the C1 to Ca range in less than 5 minutes. High background signals because of volatility of the substrate were objectionable with hexamethylphosphoramide (9). Silica gel presented the following problems :
Table
II.
Differential chemical absorption largely overcomes these difficulties. Identification and resolution problems are decreased by separation of olefins from paraffins. The splitting of the gas stream after the chromatographic column so that it flows through two flame ionization units permit twice normal column flow rates. Various silica gel column temperatures have been used, and the effect of temperature has been reported (6, 14). I n the routine analysis of catalytically treated exhaust gas, a column temperature of 157’ C. appears optimum because of short elution time required, although complete resolution of C1 to C, compounds is not achieved. Silica pel does not separate hydrocarbon isomers, but other column materials in conjunction with absorbers should be applicable where this is wanted. Slug Sample Testing. This is very conveniently done by hypo-injecting 10 to 200 cc. of sample so as t o give a plateau response. Glycerol, which does not absorb paraffins or olefins, can be used in minimum amount as a lubricant for the hypo plunger. This method, which seems preferable for most work, permits very quick testing without the transfer line problems encountered in continuous analysis. Retention in the flow system (hangup) is apparent from the nature of the response, as illustrated by Figure 4. A large sample or extrapolation to longer times may be used to estimate a true value. Other alternatives involve determining thc area under the response curve or operating a t higher temperatures. RESULTS
Slug Sample Analysis. Some rrsults obtained by the slug method on proportional and bag samples of exhaust gas are given in Table 11. The analysis shows t h a t the olefin
Slug Analyses of Proportional and Total Bag Samples of Treated Auto Exhaust“
0
P+$J
O+A
Time after run, hr. 21 P+$ O + A Mole yo HC
48
P+$
O>A
Large bag sample o.ii00.154j o.io7-oToo4nProportional sample 0:io0 o: O ~ O P = paraffins; 0 = olefins; = aromatics; A = acetylenes. All results as well as continuous HC recordings in Figure 7 refer to same run. Samples collected from cold start over 19-minute interval using California 7-mode cycle. 0
VOL 35, NO. 9 , AUGUST 1963
1201
Jackson, Wiese, and Wentworth (16) found that retarding the spark on an automobile from normal setting to 0" before top dead center lowered hydrocarbon emissions as measured with infrared. The ratio between flame ionization and infrared was also affected. Data obtained by the slug method on a test car confirmed this indication, and showed that retarding the spark would not be expected to reduce smog, since it did not lower olefin concentrations.
Continuous Hydrocarbon Class Analysis. For transient processes
emissions were very low 011 both a relative and absolute basis using thc California, cold-start, 7-mOde cycle, although the catalytic muffler had been in service for 14,000 miles. Slug techniques can be used for gasoline class analysis. Total unsaturates are determined by using SSSA, and paraffins plus aromatics by use of MSSA. If total hydrocarbons, satr urates, and saturates plus aromatics are known, the amount of olefins, aromatics, and paraffins can be calculated on a carbon basis. Results of such application are given in Table 111. The sampling procedure found to give the highest response relative to theoretical (over 75%) involves injecting 2 111. of sample into a 2-liter flask containing glass beads. After shaking for about 4 minutes, a 100-ml. sample is withdraffn and injected into the analyzer, and peak respoiisci are mcas-
such as normal automobile operation, it) is important t o follow very rapid clianges in emissions continuously. I n evaluating devices (12, 18, 19) for exhaust treatment, California has adopted standard cycles on a dynamometer corresponding to typical car operation. Various weighting factors (18) corresponding to exhaust flow rates are applied to the various modes to arrive a t an over-all evaluation over a 20-minute period from a cold start. Results of analysis of "olefinic" hydrocarbons and total hydrocarbons in untreated exhaust using MSS-4 us. glycerol, both supported on diatomaceous earth, are shown in Figure 5. A continuous determination of "olefins" and "paraffins" in catalytically treated exhaust gas from the same car is given in Figure 6. Because of solubility of oxyorganics in water and the high boiling point of some hydrocarbons, particularly higher aromatics,
u r d \\ itli glyccrol, SSS+1, and AlSSA absorbers. The responses show absorption characteristics as illustrated by Figure 4, but the use of a large sample decreased the effect on peak height. Measurement of areas under the response curves or use of higher operating temperature n-ould have largely eliminated this source of error. Class Analysis of Gasolines
Table 111.
GasoGasoline line A B
(regu- Gasoline std." lar) Found Theory yo on carbon basis Olefins 29 23 17 19 Aromatics 45 37 28 25 Paraffins 26 40 55 56 ;\fade up from 60% n-octane, 2'05c 3-hexene, 20% toluene by volume.
(pre-
mum)
HILLMAN EXHAUST
9
w2-
eo& O*A
70 -
Q
60
CaHs
-
50-
1
I
2
1C"Cll
1
40r
I
1
0 eC
I
3020-
5:
0-
X
i. I
I
HILLMAN EXHNJST
+ CzH;
70
0.S
1 5
I
4
1 I
c 0.0
Figure 6.
1202
0
Continuous analysis of treated exhaust gas
ANALYTICAL CHEMISTRY
Figure 7. Simultaneous chromatographic analysis of auto exhaust with class separation using silica gel column a t 150" C.
1
I
i
c
I1 iwt
30 MPH :ruisa Sampla Before Converter
Largo Bog Sample From Same Colifornio Test AI To I n Tobla
Raferrsd
30-
FcI
20
-
LITERATURE CITED
MIN 4
Figure 8. Simultcneous silica separation
gel ( 1 60” C.) chromatographs with class
tllVX CUlllll(J11elltS ar: IlOt CUllll)l(’t’(’ly measured when a water phase is condensed out a t room temperature. The responses a,ppc:ar to correspond Kith changes in mode, and the peak widths measured a t half peak height appear equal to thorje obtained from nondispersive infrared analysis. Retention effects appear less iniportant for treated than for untreated exhaust gas. -In attempt was made to assess retention in {,he total system quantitatively by ohserving the departure from plug flow d i e n methane and liquid gasoline were rapidly injected into the exhaust mar ifold. Retention was observed by an increase in the width of the eluted peak as measured at half peak height. The width observed for the injection of 50 cc. of methane was 3 seconds. With the injection of 5 cc. of gasolinr A (Table 11), t,he n-idt,h obscr\-ed as 5 wconds, indicat,ing that little ahorption had occurred. The exhaust gas was stnipled
iriiiiietliatcly bcfurc tlie coil\ ertcr \+itli tlie car a t 30 m.p.11. and 9-hp. load, through 10 feet of 1/4-inch copper tubing, a water trap, calcium sulfate trap, and pump. The cyclic studies in Figure 6 clearly show that the catalytic treatment eliminated “olefinic” hydrocarbons more rapidly and completely than “paraffinic” hydrocarbons. -1fter warmup, olefinic concentrations are extremely Ion.. Chromatographic Analysis Using Absorbers. An example of this application on auto exhaust is shown in Figure 7 . The various saturates and unsaturates u p t o hevane are separated and fairly well resolved in less t h a n 4 minutea. Resolution of the numerous components without chernical absorption would have been poor. The prime photochemical smog formers, including ethylene, prop-lene, and butene (7, l e ) , are clearly < h0\\11. Figure 8 shows the analysi, of cxliaust gases before and after catalytic
Diluted Gas Sample From Catalytic Crackinq Of Gas Oil With Frrrh Silica Alumina Catalyst.
1
:i. l’,, Hellar, T. A , S. l’., “Hydrocarbons and .\ldehytles in tlie I m Angeles iitnrosphere,” Air Pollution Control h s o c . Preprin 29, (1962). ( 2 ) hltshtller, A . P . , Clrrnons, C. A , , ( 1 I .iltdiider, 11cPherson,
c-
(--- TIWE
80
oxidation. Although the samples arc not strictly comparabie, since the untreated sample is exhaust gas from 30-m.p.h. cruise and the treated sample is from the California cycle, cold-start, 19-minute run described above, the difference in relative amounts of paraffins and smog-forming olefins is large. Figure 9 illustrates the analnis of thc gas from the catalj-t’ic cracking of gas oil (,ver a itmir1ai.d silica-alumina catalyst.
Figure 9. Simultaneoussilica gel ( 1 58’ C.) chromatographs with class separation
.\SAI. c H E \ I . 34, 1622 (1!lez), ( 3 ) Andreatel), A . J.,Arch. E n c i r o u l i e n i ( h 4, 101 ( 962) (4) Andreitch, ii. J , E’einlmd, It , L \ s . 4 ~ , , CHEM.22, 1021 (1960).
( 5 ) Andreit.h, A. J , Innes, I\‘. 13
, 1;. S. Patent 3,027,241 (1962). (6) Andreitch, A . J , Innes, \V. B., “Instrument Society of America,” Xew Tork, N Y .,Preprint 46-hY60 (September 1960). ( 7 ) Faith, W. L., Itenzetti, K . .4.,A i r Pollutio z Found ( L o s An,geles), Hept.
30,1-21(1960).
( 8 ) f b i d . , 33, 67 (1961).
( 9 ) Feinland, It., Andreatch, A. J . , Cotrupe, L). P., ANAL.CHEW 33, 991
(1961).
(10) Ferrii, C. R . , Chase, J. O., Hum, R. I\’.) ‘Analysis c ~ fConiplex Mixtures Using tin Lrnsaturate Lliscrirninatiny Chroma tograph,” ‘lhird Symposium on
Gas Cb romatography, East Lansing, Mich., June 1961. (11) Franl:is, A. IY., Lukasiewicz, S. J., I X D . b;YG. CHEM., -4X.4L. Ell. 17, 703 (1945). (12) Hass,
G., Brubacher, R I . , “Test Procedure for Motor I*ehicle Exhaust k;miss~ons,”Air Pollution Control .4ssoc. Preprint 44 (1962). (13) InneE, 11.. B., .4ndreatch, i\. J., I n d . Wa!er Tl’antes 5 , 185 (1960). (14; InneE, TV. B., Duffs, R., Air Poliutzon Control Assoc. Kept. 11, 369 (1961). (15) Jackron, M. IT’., Wiese, W. M., Wentwcrth, J. T., S A E Preprint 486A (March 1962). (16) Leigk ton, P. A, “Photocliemistr, of Air Pollution,” Academic Press, New York, 1961. ( l i ) Martin, R.L., ANAL.CHEM.34, S96 (1962). (18) Midaleton, J. T., “Criteria for Certification of Exhaust Devices,” Air Pollution Control Assoc. Preprint, 1962. (19) Middleton, J. T., Middleton, D. C., ‘.Air Pollution and California‘s State Control Program,” API Preprint, May 1962. (20),MyIlin, P. Il.., “3Iodern (+:is Analysis, Ir terscience, Sew Tork, 1
