(3) Haldane, J. S., “Itespiration,” Yale University Press, S e w Haven, 1922. (4) Handbook of Physics and Chemistry, 42 ed., 1961. (5) Hawkins, J. X., Shilling, C. W., J . Biol. Chem. 113, 649 (1936). (6) Jay, B. E., Wilson, R. H., J . A p p l . Physiol. 15, 298 (1960). (7) Lange’s Handbook of Chemistry, 9th ed., p. 1709, 1956.
(8) Orcutt, F. S., Seevers, 11. H., J .
Biol. Chem. 116, 613 (1936). (9) Ibid., 117, 509 (19373. (10) Orcutt, F. S., Waters, R. ?*I., J .
Biol. Chem. 117, 501 (1‘337). (11) Seidell, A., “Solubilities of Inorganic
J . Biol. Chem. 61, 523 (1924). (14) Wilson, R. H., Jay, B. E., Clin Research 8, 92 (1960). (15) Wilson, R. H., Jay, B. E., J . A p p l . Physiol. 16, 374 (1961).
York, 1928. (12) Siebeck, R., Skand. i l r c h . Physiol. 21, 368 (1909). (13) Van Slyke, D. D., Seill, J. >I.,
RECEIVEDfor review August 21, 1961. Accepted January 2, 1962. Supported in part by Grant 5444, H-2153 from the Sational Institutes of Health.
and Organic Compounds,” Kew York Suppl. 2, p. 32, Van Kostrand, Xew
Vapor Phase Determination of Olefins by a Coulometric Method A. P. ALTSHULLER and S. F. SLEVA Roberf A. Toft Sanitary Engineering Center, Cincinnati, Ohio An instrument based on a bromocoulometric method has been evaluated for analysis of olefins a t concentrations between 2 0 and 1000 p.p.m. The instrument has been calibrated for its vapor phase response to a number of olefins, including ethylene, propylene, propadiene, 1butene, trans-2-butene, cis-2-butene, isobutylene, 1,3-butadiene, 1 -pentene, and 2-methyl-2-butene. The possible interference of a number of substances, including sulfur dioxide, nitric oxide, nitrogen dioxide, hydrogen sulfide, n-butyl sulfide, acrolein, phenol, ana m-cresol, has been investigated. Sulfur dioxide, hydrogen sulfide, nitrogen dioxide, and acrolein react appreciably with the brominating solution. Nitrogen dioxide lowers the response to olefins. Severe interference is experienced when the nitrogen dioxide concentration equals or exceeds that of olefins. Even when the olefins are present in excess, the interference b y nitrogen dioxide is sufficient to necessitate removal of most of the latter. In analyses of samples in containers, direct determination of these vapor phase interference effects may b e complicated further by gas phase reactions of olefin and nitrogen dioxide, and perhaps b y reactions within container walls. With this olefin instrument, diluted automobile exhaust and a variety of synthetic mixtures have been analyzed. Results have compared favorably with those obtained by the colorimetric dimethylaminobenzaldehyde method.
T
importance of olefins in photochemical reactions in polluted atmospheres has stimulated t h e development of several methods for the determination of low concentrations of olefins (f-3,8, 9, 11, IS). Two of the proposed methods extend the well HE
418
ANALYTICAL CHEMISTRY
established bromination procedures to vapor phase olefin analysis (9, 11, 13). I n the method described by hkksic, bromine is maintained a t a predetermined excess concentration (11, I S ) . Any process that reduces this bromine level is determined by the length of time at constant current required to generate sufficient bromine to bring its concentration back to the predetermined level. The details of this coulometric method have been described (1l , 13). Commercial instruments based on this principle have been developed recently for continuous analysis of both the source and the The atmospheric level of olefins. present investigation is concerned with the evaluation of such an instrument for determining source concentrations of olefins, particularly in automobile exhausts. Relatively few data are available on the degree of bromination of various olefins with this type of instrument and with the brominating solution used. The amount of response obtained from the lower molecular weight olefins, ethylene, propylene, and propadiene, is of inherest, as is the range of response with variations in molecular structure in the higher molecular weight olefins. Many other substances, including various sulfur compounds, unsaturated compounds other than olefins, phenols, and some nitrogen compounds, are likely to react in brominating solutions. Consequently, sulfur dioxide, hydrogen sulfide, n-butyl sulfide, thiophene, acrolein, phenol, m-cresol, nitric oxide, and nitrogen dioxide were tested as possible interfering substances. The possibilities for removal of these substances were studied. Both automobile exhaust samples and a variety of olefin and nitrogen dioxide mixtures were analysed for olefin content. The olefin determinations obtained by this bromination technique
were compared with the determinations made by the colorimetric dimethylaminobenzaldehyde method (8). EXPERIMENTAL DETAILS
The instrument, Model 811-1, a product of Mast Development Co., Davenport, Iowa, was operated through the present study a t a conductivity level in the brominating solution corresponding to 10 pa. of sensing current and a sensing electrode voltage of 230 mv. Generating currents of 1 and 9 ma. were used. Only a single brominating solution was used in this work. This solution, designated EG-3, has the following formulation: acetic acid, 82 ml.; distilled water, 15 ml.; ethylene glycol, 3 ml.; and potassium bromide, 2 grams. Mercury catalysts were omitted because the manufacturer reported “noise” in the sensing electrode circuit in the presence of mercury salts (13). The calibration and interference checks were made by preparing vapor mixtures of the appropriate concentration in aluminized Scotchpak or Mylar bags (4). The gas mixtures were prepared by injecting the calculated volume of gas by use of a gas-tight syringe into a n air stream that carried the sample into the bag, which was then filled to the desired total volume. Vapor mixtures were prepared by injecting a liquid sample by use of a microsyringe into a small evacuated glass cylinder through a T containing a rubber septum. The contents of the cylinder were then flushed into the bag with an air volume several hundred times that of the cylinder The actual concentration in the bags in a number of the olefin calibration determinations was rechecked by determining the total carbon atom parts per million in the bags with a Carad Fiad flame ionization detector. In almost all runs the concentration of olefin in the bag was within 5y0 of the calculated concentration. The stability of olefins and other species in these I
90
-
ao c w 10
-
60
-
5
50
-
5 w
40-
t
B Z
P 4
w z
c
?
3c
-
20
-
10
I
'
C
0
100
200
300
500 600 , 7 0 0 OLEFIN CONCENTRATION.
400
BOO
900
IO00
iIO0
,200
PPM
HIGH RANGE
Figure 2.
plastic bags will be reported elsewhere
(4)
+
The values reported are the average of a t least six of the 5-minute integrated per cent generating times punched out on the Tally Printer (IS). Many of the values given were averaged over 1 to 2 hours of operation on an instrument measuring a given concentration of the various reactive species in a plastic bag. For calibrations, from 20 to 100 p.p.m. of olefin were used on the low generating range (1-ma. generating current) and from 100 to 1000 p.p.m. on the high generating range (9-ma. generating current). A number of analyses of bag samples were made on automobile exhaust and on this same exhaust after it was diluted about 35 to 1 with purified air in a dilution system (12). The instrument also was connected directly to the diluted exhaust sampling port. For a number of measurements, the instrument was preceded with U-tubes filled with Ascarite or with bubblers filled with water or other reagents. A flow of about 200 ml. per minute was used. A vent preceding the sample pump on the instrument permitted the escape of the excess over the instrument sampling rate of 65 ml. per minute. Some of the olefin and nitrogen dioxide mixtures and several samples of automobile exhaust were analyzed, both with the olefin instrument and by the colorimetric diniethylaminobenzaldehyde method ( 2 ) . A number of nitrogen dioxide analyses were made on the same or similar samples by the procedure described by Saltzman (141. RESULTS
Calibrations with Olefin in Air Mixtures. Calibrations for ethylene and propadiene in the high concentration range and for propylene, 1butene, trans-2-butene, cis-2-butene, isobutylene, 1,3-butadiene, 1-pentene, and 2-methyl-2-butene in both low and high concentration ranges are
given in Figures 1 and 2. These calibrations apply exactly only t o the instrument used during the period of this study. A number of instrumental characteristics, but especially the spacing and general condition of the platinum electrodes, may affect significantly the instrumental sensitivity. However, the electrode assembly was replaced with an improved version with no change in the response of trans2-butene. The results obtained on the range of sensitivities and the effects of variations in molecular weight and in structure, however, should be generally applicable to this type of instrument. The reproducibility in grnerating time for an olefin depends on concentration and on whether the high or low generating range is used. At 20 p.p.m. of olefin the variation amounts to 10 to 20%) iyhereas a t 40 p.p.m. of olefin the variations in generating time range from 4 t o 8%. At olefin concentrations above 40 p.p.m. the fluctuations in generating time usually ranged from 2 to 4%. At 200 p.p.m. of olefin, however, the variations in readings on the high scale can amount to 6%. Part of the fluctuations arise from solution noise and bromine losses from solution; however, several per cent fluctuation results from the Tally Print's reading only to the nearest per cent. At least three determinations were made for each olefin on each range. Percentage deviations of experimental points from the lines given averaged about 3% for the gaseous olefins. For the one liquid olefin, 1-pentene, the percentage deviation of experimental points from the line given was about 10%.
A spread of only 10 to 2001, was found in the responses of the various fourand five-carbon olefins tested. Within
Calibration for olefins, high range
this range the loa response of 1-butene and the high response for 2-methyl-2butene are in agreement with the order of reactivities usually found for these types of olefins in various gas and solution reactions (6). The total range of responses is small enough that the differences should nearly balance out in combustion mixtures containing a aide variety of olefins. Consequently, the total olefin concentration can be expressed in terms of any olefin in the middle of this range. Since calibration data are available only for truns2-butene on both sourcr- and atmospheric-type instruments over a TI ide variety of generating currents and gas flow ratcs ( I S ) , this olcfin n a s chosen for the purposc The loner responqe to propylene comparcd to the higher olefins causes a minor problem in the calculation of the olefin concentration. In samples from some types of sources (6, 10) the propylene is present a t considerably higher conecatrations than any of the individual olefins of higher molecular weight. As a result of the 80 to 90% response of propylene compared to the response of higher molecular weight olefins, a calculation of olefin concentra tion based on trans-2-butene tends to underestimate the contribution of propylene. The expression of olefin concentration in terms of propylene is an even poorer choice, however, since the olefin concentration computed would be significantly higher than that actually present. Response of Nonolefinic Species. The behavior of sulfur dioxide, hydrogen sulfide, and n-butyl sulfide and thiophene with the instrument has been investigated (Table I). Sulfur dioxide gives about the same response on the instrument as a n equal concentration of trans-2-butene. HyVO1. 34, NO. 3, MARCH 1962
419
~
Table I.
Substance trans-2-Butene Sulfur dioxide Hydrogen sulfide Acrolein trans-2-Butene Sulfur dioxide Hydrogen sulfide n-Butyl sulfide Thiophene ricrolein .icrolein Phenol rli-Cresol
Response of Instrument to Nonolefins hverage Response
P.P.11. by Volume
Relative to trans-2-Butene,
40 40 20 10 400 400 400 100 100
100 80
200 400
200 200
330
60 100 100
310
6" 26-98
5-35 5-3T la
1"
5
Calculated Average P.P.M. as trans-2-Butene 40
32
66 6 400 400 1240 6 26-98b 1O-7Ob 1O-15Ob 2 2
Background readings on lo^ scale were about 2% of full scale. t o increase for almost 2 hours but remained constant for about the last half hour. a
* Response continued
drogen sulfide gives about three times t h e response of a n equal amount of trans-2-butene, Fyhereas the n-butyl sulfide gives no more than 6% response. Thiophene a t 100 p.p.m. brominated slowly but did reach a final value about equal to that of an equivalent amount of trans-2-butene. Xeither phenol nor vz-cresol showed any indication of brominating significantly (Table I). This result was unexpected, since phenols usually brominate readily. Acrolein was tested as representative of aliphatic compounds, other than olefins, with double bonds in their structures. Acrolein a t 200 and 350 p.p.m. brominates slo~vly; however, acrolein a t 10 p.p.m. brominates rapidly, giving about 60% of the response of trans-2-butene. Midget bubblers containing water remove about SOY0 of the hydrogen sulfide from a 20-p.p.m. hydrogen sulfide in air mixture during the first half hour of operation. During the next half hour of running time only about 60% of the hydrogen sulfide is removed, since the water becomes saturated Lvith the gas. Similarly, bubblers containing water remove about 7 5 7 , of the sulfur dioxide from a mixture of 40 p.p.m. of sulfur dioxide in air during the first half hour and about 507, of the sulfur dioxide during the second half hour of use. Acrolein at 180 p.p.m. is not removed effectively by passage through the water bubblers, even during the first half hour of use; however, a t lower concentrations their effectiveness should be extended. An Ascarite tube proved to be more effective in removing interfering substances. When mixtures containing 40 p.p.m of sulfur dioxide, 40 p.p.m. of acrolein, or 20 p.p.m. of hydrogen sulfide were passed through Ascarite, approximately 90% of these materials 420
ANALYTICAL CHEMISTRY
was removed. This efficiency is retained for a t least 2 hours. Analysis of Nitrogen Dioxide and Olefin Mixtures. Sitrogen dioxide interferes markedly with the determination of the olefins cvith t h e present instrument. If nitrogen dioxide gas a t several hundred parts per million is passed through t h e reaction chamber, no positive response occurs; ho\vel-er, the conductivity a t the sensor electrodes appears to be affected. The response of the instrument to olefin samples introduced subsequently will be negligible until most of the nitrogen dioxide has been swept out of the brominating solution or removed by reaction. Reaction of the nitrous acid formed from the nitrogen dioxide a t the electrodes may interfere with the proper generation of bromine (7). Alternatively, the nitrous acid may react directly with the bromide to generate bromine. Kitric oxide does not interfere significantly. Not much nitrogen dioxide is found in the effluents from most combustion sources, since the nitrogen oxides are present initially mostly as nitric oxide. If a sample containing 100p.p.m. or more of nitric oxide is collected into a container for later analysis, however, significant quantities of nitrogen dioxide are formed during the holding period before analysis. The interference of nitrogen dioxide a t various concentrations therefore must be known, and in analyses in which nitrogen dioxide interferes significantly, it must be removed. For these analyses a pretreatment or clean-up procedure was developed for removal of nitrogen dioxide before it enters the olefin analyzer. Synthetic mixtures containing 500 p.p.m. of olefins and 170, 500, 850, and 1700 p.p.m. of nitrogen dioxide were prepared. An olefin concentration was chosen similar to those found
in automobile exhaust samples already analyzed. A Phillips mixture containing the butanes, butenes, and 1,3butadiene was used. The nitrogen dioxide concentrations used are believed to be as high as or higher than those in analyzed samples of automobile exhaust, incinerator effluents, etc. TS'hen the nitrogen dioxide concentration exceeds the olefin concentration and the nitrogen dioxide is not removed, the readings on the analyzer rapidly drop to zero. When fresh brominating solution is used, the readings increase but are still lower than the true values even before they start to drop to zero. The olefin concentrations also are well below the correct values when the nitrogen dioxide concentrations are equal to or somewhat lower thaii that of the olefin. Only when the olefin concentration is much greater thari that of the iiitrogen dioxide can the olefin concentrations be determined accurately without prior removal of nitrogen dioxide. These conclusions apply specifically to the concentration range studied. If the concentrations of both nitrogen dioxide and olefin are in a lower range, the interference of the nitrogen dioxide with the brominating solution occurs later. Under most experimental conditions, however, pretreatment to remove nitrogen dioxide appeared desirabIe. The three alternative methods of removing nitrogen dioxide investigated ryere the use of Ascarite tubes, bubblers containing the colorimetric reagent for nitrogen dioxide (14, and bubblers containing water. The results are given (Table 11) in terms of the olefin concentration found in the bag samples. B e h e e n each pair of runs with nitrogen dioxide and olefin mixtures, a test run was made on 500 p.p.m. of oIefin alone. These checks were made to ensure that the brominating solution had not been contaminated with nitrogen dioxide. The effectiveness of the nitrogen dioxide removal methods was in the following order: Ascarite tube, t\To nitrogen dioxide reagent bubblers, two water bubblers, Neither of the liquid absorbers was completely satisfactory even at the lowest nitrogen dioxide concentrations. The Ascarite tube removed nitrogen dioxide satisfactorily at both concentration levels. It is unlikely that the drop in olefin concentration during the second half hour, when the Ascarite tube with 500 p.p.m. of olefin and nitrogen dioxide are used, results from ineffectiveness of the Ascarite. The decrease in olefin concentration in these determinations actually results from the loss of olefin through gas phase and wall reactions in the bag. These results indicate that an Ascarite tube provides adequate removal of nitrogen dioxide. Further investiga-
tion is needed to determine the losses that will occur from chemical reactions if samples must be held for several hours before analysis. Raw Automobile Exhaust Analyses. Several samples of automobile exhaust \yere collected in Scotchpak or Mylar bags. When the bag samples were drawn through the olefin analyzer, the readings approached the proper olefin levels b u t then dropped rapidly to zero. This behavior is the result of nitrogen dioxide interference. The nitrogen dioxide concentrations in the bag samples were determined and proved to be in the 100- to 200-p.p.m. range. Removal of the nitrogen dioxide is essential. Test's of various methods for nitrogen dioxide removal (Table 111) confirmed the results obtained with olefin and nitrogen dioxide mixtures (Table 11). Passage of the effluent through an Ascarite tube probably is the simplest and most effective way of removing most of the nitrogen dioxide (and other acid gases and polar materials) from the effluent before it enters the olefin analyzer. If samples are held, gas phase olefin and nitrogen dioxide reactions can reduce the olefin content of t,he samples. The olefin concentrat'ion in source effluents, particulnrly in automobile exhaust, therefore, should be measured within 1 hour, preferably within hour, after collecticln of the sample. Diluted Auto Exhaust Analyses. A more extensive study was made of automobile exhaust from the primary stage of a two-stage dilution system. This stage provided a convenient, continuous, and controlled source of automobile exhaust diluted about 35 to 1 n.ith purified air ( 1 2 ) . The resulting complex hydrocarbon mixture permitted the evaluation of the instrumcmt near its lower limit of dependable operation. Samples were taken both in plastic bags and by direct connection of the instrument to an outlet from this stage of dilution (Table IV). The composition of the exhaust varies as the engine is programmed through a 10-minute set of operating conditions. Owing to the integrating effect of the minute measuring period, most of the large difference in concentrations between cruise and deceleration conditions are smoothed out. Although various methods for removing nitrogen dioxide and other polar interferences were used, the olefin concentrations appear essentially independent of the pretreatment method. This result holds for analyses with the olefin analyzer and by the colorimetric method. Analyses for nitrogen dioxide in the primary dilution line gave average concentrations between 0.7 and 1 p.p.m.; however, analyses for nitrogen dioxide in samples held in plastic bags for several hours gave about 12
Table
II.
Rlisture Coniposition i n P.P.M. Xitrogen Olefin diositle
Analysis of Olefin and Nitrogen Dioxide Mixtures
Pretreatment
Iiurinirig Time, N i n
P .I-'.11.
500
170
Ascarite tube
0-30 30-60 GO-90
4115-510" 495-500 475-490
500
170
Tn o h-01reagent bubblers
0-30 30-60
475-480 450-470
500
170
Txo n ater bubblers
0-30 30-60
455 450
500
500
;\scarite tube
0-30 30-60
480
500
500
TKO 1-02reagent bubblers
500
500
TMo wnter bubblers
450
30-60
440-465 405-135 445
0-30 30-60
405-465
0-30
GO-90
a
Olefin,
385-430
Range of concentrations based on three sets of analysis.
p.p.m. of nitrogcn dioxide. Other analyses indicate sulfur dioxide concentrations of 0.3 to 0.5 p . p m in the primary dilution stage gases. About 0.2 to 0.4 p.p.m. of acrolein is present a t this stage of dilution. Aromatic hydrocarbons are present in the same range of concentration as olefins. Olefin concentrations determined coulometrically with the olefin analyzer are 25 to 50y0 higher than those determined colorimetrically. Part of this difference results from the difference in response of the two methods to olefins. The olefin analyzer responds to propylene, whereas the colorimetric response to propylene is not significant. Since the propylene concentration in the primary stage of dilution is about 3 p.p.ni., this concentration of propylene should be added to the colorimetric olefin concentration. With this correction, the olefin concentrations determined by the two methods will differ by from 5 to 25% with an average difference of 157& Part of the remaining difference may result from the differing methods of calculating olefin concentration in parts per million by volume. I n the instrumental method, the olefin is calculated as trans-2-butene, and therefore, if the actual average olefin concentration is greater than that indicated by the trans-2-butene response, the calculated olefin concentration will be low. Similarly, in the colorimetric determination, the absorptivity selected, 0.10 pg.-l ml. cm.-l corresponds to that of 1-butene and, therefore, if the actual average absorptivity is somewhat lower than 0.10 pg.-1 ml. cm.-l, the calculated olefin concentration will be low.
Table Ill.
Analyses of Raw Automobile Exhaust
Olefin as trans-2-
Run
Butene, P.P.M .
G1
600 i 25.
Clean-up Method Two NOz reagent bubblers Two water bubblers 77 One KO2 reagent bubbler Two S O 2 reagent bubblers hscarite tube T8 Two water bubblers hscarite tube 79 Two NO2 reagent bub blers Two water bubblers ;Iscarite tube 0
580 i 25 530 i 12
540 i 30 615 =t25
420 3= 25 + 12
480
300
=I= 13
310 =k 12 380 i 20
One standard deviation.
It is necessary to assume an average vapor density for the olefins, if micrograms per liter are to be converted to parts per million by volume in the colorimetric data. At the awrage vapor density selected, 3.0 grams per liter, the average carbon number of olefins to which the method responds (butenes and higher olefins) is assumed to be slightly more than five. Gas chromatographic analyses indicate the reasonableness of such an average carbon number; however, the value may be erroneous by 10% (IO). On the low generating scale the generating time of the olefin analyzer fluctuates a few per cent because of solution noise and bromine loss. It VOL. 34, NO. 3, MARCH 1962
421
Table IV.
Analyses of Diluted Automobile Exhaust
Type of Sample
Olefin, P.P.M. by Volume Pretreatment Coulometric” Colorimetric6 62 Bag Xone 21 f 1 ... Two water bubblers 20 f 2 14 Two reagent bubblersc ... 14 70 Bag None 25 =k 3 One reagent bubbler 26% 2 Direct None 282 3 ... 51 Direct None 16 i 1 One water bubbler 2523 One reagent bubbler ... 17% 1 75 Direct One reagent bubbler 20 It 3 16 i 2 76 Direct None 23 i 3 18 i 1 One water bubbler 24 f 3 16 f 1 One reagent bubbler 23 f 3 15 f 1 80 Bag Sone 26 f. 1 ... One water bubbler 26 i 2 ... -1scarite tube 28 i 1 ... Calculated as trans-2-butene from averaged readings on olefin analyzer. * Calculated as 1-butene, using absorptivity of 0.10 pg.-1 nil. em.-’ and vapor density of 3.0 grams per liter. Bubblers contain colorimetric reagent for nitrogen dioxide determination. Run No.
is possible to determine this background only by making clean air measurements before and after the actual determination. This source of error, if corrt’cted for, could reduce the coulometric olefin values about 10% under some operating conditions. Interferences differ in their effects on these two methods of olefin analysis; however, both the concentrations determined and the lack of effect of pretreatment indicate a rather small interference by nitrogen dioxide, sulfur dioxide, acrolein, and other sulfurcontaining or unsaturated species in the exhaust. Aromatic hydrocarbons interfere in colorimetric determinations. The composition of aromatics reflects fuel composition, and since the fuel contains 40% aromatics, some aromatic interference in exhaust analysis is very likely. This source of error may account for a part of the remaining difference between coulometrically and colorimetrically determined olefin concentrations. This discussion is intended to indicate the difficulties in obtaining close agreement between two independent methods in class-type analyses of highly complex gas mixtures at trace levels. In view of the problems involved, the agreement obtained probably should be considered satisfactory. DISCUSSION
The instrument discussed is capable of measuring the concentration of propylene and higher olefins in the range between 20 and 1200 p.p.m. Since the readout on the instrument prints the per cent generating time only once every 5 minutes, the device
422
0
ANALYTICAL CHEMISTRY
cannot indicate rapid changes in concentration. The generating rate could be measured over a shorter time interval; however, any drastic reduction in this time interval would affect adversely the accuracy of the readings, Under the operating conditions discussed, at k a s t four of the 5-minute readings should be averaged before conversion t o olefin concentration. Since the first and sometimes the second reading aftcr a sample is introduced into the instrument must be discarded because the instrument is not yet in equilibrium with the sample, a minimum of one half hour of operating time or six readings are believed to be essential in obtaining a reliable average reading for conversion. The above considerations apparently do not prevent use of the instrument for determining an integrated olefin concentration for a stream that varies in concentration. The olefin concentration obtained by direct measurement of diluted automobile exhaust of varying concentration did not differ markedly from the concentration obtained on a bag sample. The bag sample was collected during the entire 10minute repetitive cycling period programmed into the automobile. The response and accuracy of the instrument for raw and diluted automobile exhaust are believed to be satisfactory; however, the analysis of other sources may present greater difficulties. Since nitrogen dioxide interferes negatively and since many sulfur-containing compounds and unsaturated oxygenates interfere positively, these materials must be eliminated. If the
olefins are present in excess and the loading of these other materials is not great, these interferences can be reduced or eliminated by the methods discussed in this paper. If the olefins exist a t lower concentrations than the interfering species, however, accurate measurements of olefin concentration may be difficult. At the present time, the coulometric method after adequate cleanup of interferences where needed appears satisfactory for many source or process stream applications. At lower concentrations, the dimethylaminobenzaldehyde colorimetric procedure probably is the method of choice for tots1 olefin analysis ( 2 ) . Gas chromatography is necessary to determine ethylene and propylene. Gas chromatographic determination of individual olefins combined with either the coulometric or colorimetric method provides an excellent combination for adequate determination of the total olefin concentration and for detailed analysis of the olefin composition of a source or atmosphere.
LITERATURE CITED
(1) .4ltshuller, A. P., Cohen, I. R., ANAL. CHEM.32, 1843-8 (1960).
(2) Altshuller, A. P.,Sleva, S. F.. Zbid., 33, 1412 (1961). ’ (3) Altshuller. A . P.. Sleva. S. F.. Wartburg, A. F ,’ Zbid., 3 2 , 946-54 (1960). (4)Altshuller, A. P., Wartburg, A. F., Cohen, I. R., Sleva, S. F., Intern. J . Air Pollution, to be published. (5) Cvetanovi6, R. J., J . Chena. Phys. 30, 19-26 (1959). (6) Eggertsen, F. T., Kelsen, F. M., AKAL.CHEM.30, 1040-3 (1958). ( 7 ) Lingane, J. J., “Electroanalytical Chemistry,” 2nd ed., pp. 546-51, Interscience, New York, 1958. ( 8 ) MacPhee, R. D., ANAL.CHEY. 26, 221-5 (1954). (9) Mader, P. P., Schoenemann, K., Eye, M., Ibid., 26, 733-6 (1961). (10) Neligan, R. E., Mader, P. P., Chambers, L. A., J . Air Pollution Control Assoc. 11, 178 (1961). (11) Kicksic, S. W., Rostenbach, R. E., J . Air Pollution Control Assoc. 11, 417 (1961). (12) Rose, A. H., Jr., Brandt, C. S., J . Air Pollution Control Assoc. 10, 331
(1960). (13) Rostenbach, R. E., Kling, R. G., “Technical Reports 4 and 5 on Olefin Study to Air Pollution Foundation,” Nov. and Dec., 1960 and “Operation and Maintenance Manual. Olefin Analyzer MCD Model 810-1 and 811-1,” Dec. 27, 1960. (14) Saltzman, B. E., ANAL.CHEW 26, 1949-55 (1954).
RECEIVEDfor review September 12, 1961. Accepted December 6, 1961. Division of Water and Waste Chemistry, 140th Meeting, ACS, Chicago, Ill., September 1961. Work performed at the Laboratory of Engineering and Physical Sciences, Division of Air Pollution, u. S. Department of Health, Education, and Welfare, Public Health Service, Cincinnati 26, Ohio.
