(2) Baker, H. A., Doerr, It. C., Intern. J . Air Pollrtlion 2, 142 (1!)59).
(3) Circle, S. J., Stone, L., Boruff, C. S., IND.ENG. CHEM.,ANAL. ED. 17, 259 (1945). ( 4 ) Gerber, M. I., Dobrinskaya, A. A., Neiman, M. B., Trudy Vsesoyuz. Konj. Anal. Khim. 2 , 585 (1943). (5) Hughes, K. J., Hurn, R. W., 53rd
Annual Meeting, Air Pollution Control Assoc., Cincinnati, Ohio, May 22-26,
1960. ( 6 ) Kyryacos, G., Mens ace, H. R., Boord, C. E., ANAL.&EM. 31. 222 ( 1959). (7) Malmberg, E. W., Smith, M. L., Bigler, J. E., Bobbitt, J. A., “A Study of Cool Flames and Associated Reactions in an Engine,” pp. 389-91, Reinhold, New York, 1955. (8) Moshier, R. W., IND.ENQ. CHEM.,
ANAL.ED. 15, 107 (1943). (9) Ncligan, R. E. Mader, P. P., Chambers, L. A,, 53rd Annual Meeting, Air
Pollution Control Assoc.. Cincinnati. Ohio May 22-26, 1960. ‘ (10) Piotnikova, M. M., Gigienu i Sanil.
2 2 , 10 (1957). (11) Powick, W. C., Znd. Eng. Chem. 15, 66 (1923). (12) Rose, A. H., Jr., Brandt, C. S., J . Air Pollution Control Assoc. 10, 331. ( 1960). (13) Rosenthaler, L., Vegezzi, G., 2. Lebensm.-Unlersuch u. Forsch. 99. 352 (1954). (14) Schuck, E. A., Doyle, G. J., Re t.
No. 29, Air Pollution Foundation, &n Marino, Calif., October 1959. (15) Senderikhma, D. P., “Determination of Acrolein in the Air!” in “Limits of Allowable Concentrations of Atmos-
phcric Pollutants,” Book 3, 1957, V. A. Ryazanov, ed., transl. by B. S. Levine; distr. b U. s. Dept. of Commerce, Office of Jech. Service, Washington, 0..C., 1959, pp. 137-40.’ (16) Uzdina, I. L., Hag. Tmah 15, 63
(1937). (17) Van Sandt, W. A., G a u l , R. J., Roberts, W. J., A m . Znd. Hyg. Assoc. Quart. 16,221 (1955). (18) West, P. W., Sen, B., Z . anal. Chem. . 153, 177 (i956j. . . RECEIVED for review October 3, *1960. AcceDted Januarv 19. 1961. Division of Wat& and Wiste ’ Chemistry, 138th
Meeting, ACS, New York, N. Y., September 1960. Work performed at the Laboratory of Engineering and Physical Sciences, Division of Air Pollution, Public Health Service, U. S. Department of Health, Education, and Welfare.
Determination of Nonaromatic Unsaturates in Automobile Exhaust by Spectrophotometric Titration PAUL P. MADER, KARL SCHOENEMANN, and MARCEL EYE Air Pollution District, County o f 10s Angeles, Los Angeles 13, Calif.
b A procedure has been devised for the determination of Cd and higher molecular weight olefins in automobile exhausts and other gas mixtures. It takes advantage of the high molar absorptivity of the free tribromide ion in ultraviolet. It is sensitive for concentrations ranging :between 25 and 1000 p.p.m. The results obtained by this procedure are consistent and reproducible.
A
of research on the mechanism of smog formation, i t is generally agreed that olefins discharged into the atmosphere from automobiles constitute a major source of smog (2, 4 ) . These olefins undergo photochemical reactions in sunlight t o form compounds which irritate eyes, damage crops, and reduce visibility. Since recent evidence strongly suggests that olefins in the size range of four to six carbon atoms are dominant in the development of smog manifestations (I, b ) , we have developed a method for the rapid estimation of these olefins in exhaust samples, a t the same time minimizing the interference from the relatively large quantities of ethylene and propylene present in exhaust gasp‘ The procedure, described below, has proved valuable in this connection, particularly in research on the relation of automobi:e exhaust composition t o fuel romposition. It involves the absorption of the hydrocarbons from the gas phase with carbon tetrachloride and the subsequent determination of olefins by s
A
RESULT
standard bromometric methods, with slight modifications. The method is applicable for olefin concentrations ranging between 25 and IO00 p.p.m. by volume. The olefm recovery ranged between 80 and 105% for compounds having five or more carbon atoms in the molecule; approximately 50% of the Cd olefins are recovered, and the presence of ethylene does not affect the results. PROCEDURE
Apparatus and Reagents. Beckman Model D U spectrophotometer, with hydrogen discharge lamp and 1-cm. silica cells. CARBONTETRACHLORIDE. The solvent used was Mallinckrodt analytical reagent or Baker analyzed reagent. These reagents did not show absorption at 290 microns. TITRATJNQ REAGENT.Standard bromate-bromide solution (0.1N) was prepared by dissolving 5.58 grams of potassium bromate and 19.80 grams of potassium bromide in distilled water and diluting t o 2 liters. The normality of the solution was checked against 0.1N sodium thiosulfate. The 0.01N bromate-bromide solution w~ prepared by diluting the 0.1N solution 1 to 10. STANDARD REAGENT SOLVENT. This solvent, was prepared by mixing the following reagents:
Glacial acetic acid Methanol Concd. hydrochloric acid 40T0 potassium bromide 20oj, aqueous zinc sulfate
50 ml. 20 In! 1 . 2 ml 2 ml. 4 mi.
DILUTEREAGENT SOLVENT. For use when the olefin concentration in the gas stream was lower than 100 p.p.m. by volume, a more dilute solution of standard reagent was prepared as follows: Standard reagent Glacial acetic acid Methanol
100 175 ml. 75 ml.
Collection and Analysis of Samples.
In t h e study of t h e olefin content in t h e exhaust vapors of automobiles, representative portions of t h e exhaust stream were diverted into a n accumulator tank installed in the trunk of a testing vehicle. Sampling procedure and time interval between sample collection and analysis were kept constant, since these factors have a marked influence on olefin recoveries. Exhaust samples were withdrawn from the storage facility through Ascarite traps into evacuated 2-liter flasks with double stems and ground, leakproof glass stopcocks. One of the stems was used for collection of the gas samplc; the other was covered with a serological stopper for the introduction of the absorbing solution. The flasks were wrapped completely with black masking tape, which prevented light exposure and thereby retarded oxidation processes during subsequent handling. Twenty milliliters of carbon tetrachloride were then added t o the flask by inserting a hypodermic needle through a serological stopper and injecting the liquid with a syringe. After the bulbs had been shaken on a mechanical shaker for 30 minutes, the absorbing solution was transferred into a 50-mi. volumetric flask. The 2-liter flask was washed with two 14-d. VOL. 33, NO. 6, M A Y 196‘
733
Table 1.
/
Sample and Reagent Sizes
(General guide) Solvent, MI. MI. Fullsample 70 of dilute re agent 51-100 20 70 of dilute reagent 5 55 of standard 101-500 55 of standard 501-1OOO 3 2 ml. CCI, 1001 and 1 4 rnl. 55 of standard more cc4 Olefins, P.P.M. 0-50
+ +
portions of carbon tetrachloride and the rinsings were combined and diluted to 50 ml. with carbon tetrachloride. Aliquots were then withdrawn from the volumetric flasks and transferred into a 125-ml. Erlenmeyer titration flask with side arm. The Rample size required for analysis depended on the expected olefin concentrations (see Table I). When high olefin values were indicated (from former runs or previous experience), a 1-ml. aliquot was used. Four milliliters of carbon tetrachloride were added to bring the total sample volume to 5 ml. If the sample volume was 5 ml., no additional carbon tetrachloride was required. To these samples 55 ml. of the standard reagent were added. When the olefin content was below 100 p.p.m., 20-ml. aliquots or the full sample had to be used. In that case 70 ml. of the dilute reagent were used. The flask containing the sample and reagent was placed on a magnetic stirrer, and a Teflon-coated stirring bar was added. With a transfer pipet, attached to a syringe, enough of the solution was withdrawn through the side arm of the flask to fill a 1-cm. silica cell. The absorbance of this solution was determined with a Beckman DU spectrophotometer, after a 15-minute warm-up period. The optimum wavelength setting was 290 mp; the absorbance of free air served as reference. The solution was withdrawn from the silica cell and returned to the flask. The titration was accomplished by adding small amounts of the diluted titrating reagent from a 5-ml. microburet. During the titration care was taken to keep the tip of the buret below the surface of the solution. The first additions of the titrating solution were carried out with 0.2- to 0.3-ml. portions, until an absorbance of about 0.2 was reached; after that the amounts added were limited to 0.1 ml. After each addition the solution was stirred for exactly 2‘ minutes, before the next absorbance reading was taken. The titration was continued until an absorbance of about 0.7 was reached. The end point of the titration waa determined by plotting the absorbance us. milliliters of titrating solution and recording the indicated titer a t the intersection of the tangents (see Figure 1)i.e., the break point. From the volume of titrating reagent and its normality,
734 *
ANALYTICAL CHEMISTRY
.ma
.
.ea
.
.)(D.
8
a.
.xD
.
TITRATION SOLUTION, ML
Figure 1. Titration of 2,4,4-trimethyl-l -pentene with 0.01N bromate-bromide solution
the results can be calculated aa parts per million by volume, according to the following equation : ( P.p.m. = ( v ) ( w / w . 4 )108) V. where V = volume of titrating solution, ml. N = normality of titrating solution V c = volume of gaa sample (corrected to 760-mm. pressure and 2’73.2’ K.)
Calibration of Procedure for Pure Compounds. Weighed amounts of liquid olefins were transferred from a weighing tube into an evacuated 50liter round-bottomed borosilicate flask b flushing the liquid sample with dry firtered air to atmospheric pressure. Gaseous olefins were introduced into the flask by a calibrated syringe and needle, through a serological stopper. A manifold system was fabricated whereby duplicate Zliter samples could be taken from the olefin-air mixture and analyzed in the manner described. The recoveries of individual hydrocarbons, aa determined by this procedure, are listed in Table 11. Two experiments were carried out to determine recoveries of olefins when blends of several compounds were involved. Each blend consists of eight olefins, four of which had shown high recoveries, and four had low recoveries. The exact percentage of recoverable material could be calculated from Table 11. Samples were prepared and analyzed aa. previously described for individual olefins (Table 111). RESULTS AND DISCUSSION
Analyses of Automobile Exhausts.
Results of olefin analyses on automo-
bile exhausts are presented in Table IV. These data were obtained on gas samples collected on successive days of road testing. This ensured a greater degree of uniformity between different exhaust batches. The results demonstrate the excellent reproducibility that can be attained by this procedure. The mean deviation of replicate samples from the same exhaust never exceeded 3.6%. Recoveries of Pure Compounds. The recoveries of individual hydrocarbons determined by this titration procedure are included in Table 11. The low recoveries of olefins in the CI to Cs molecular weight range are presumably due to their high vapor pressures and low solubilities at ambient temperatures. Separate infrared and/or gas chromatographic determinations can be used with this procedure, wherever it is essential to determine the low molecular weight olefins quantitatively. Since only small amounts of these compounds are transformed into air contaminants, their exclusion in the determination of “total olefins” appears to be more of an advantage than a disadvantage in alr pollution work. With cis 2 butene, the recovery measured was approximately 56%. Starting with C6’ olefins the recoveries obtained ranged between 90 and 100%. Only 2,6-dimethyl-3-heptene showed a somewhat lower recovery possibly due to the rapid formation of hydroperoxides and organic peroxides with air oxygen in the gas phase leading to a premature end point. Other phenomena, such as wall absorption or vapor preasure, could also have contributed to lower re-
- -
Table II.
No.of Detm. 2 2 2 2 2 2
Recoveries of Oleflns from Olefin-Air Mixtures
Added, P.P.M.
Compounds Acetylene Ethylene Propadiene Propylene 1-Bubne
1293 1300 466 1267
466
466 1230
cM-2-Butene
2
466 466 1812 86 1 103 1172 98 1332 105 868 104 506 512 381
3
ZPentene
2
1-Hexene
2
2-Hekeoe
2
Cyclohexene
4
%Methyl-1-pentene
4
4Methyl-l+yclohexene
319 405 412
2
1-Heptene
4
1-Octene
388 388 292 365
4
2-Octene
367 336
4
2,4,4Trimethyl-l-pentane
316 384
4
204 315
2 2 2 2
Rennene Toluene 2-Methylpentane 2,3-Dimethylbutane Table Ill.
Total Ethylene Propylene Acetylene
ci8-2-Butane
Total Total olefine Recoverable olefins Olefins found Recovery
0 0
0 265 224 224 682 702 230 298 1578 770 93 1144 91 1356 99 861 103 479 506 347 360 320 386 373 373 378 389 293 293 327 340 387
380 300
313 320 327 387 308 173 173 253 253 0
680 903 489 357
0 0
0
%
Recovery 0 0 0 20.9 48.1 48.1 55.4 57.1 50.0 53.2 87.1 89.3 90.3 97.6 95.3 101.9 93.8 99.2 99.0 94.8 98.8 91 .o 94.5 100.3 94.4 90.6 90.6 97.3 100. 1 102.2 102.2 90.0 93.1 105.2 103.3 90.0 93.5 101.1 103.3 100.8 98.9 84.6 84.6 80.4 80.4 0 0 0
Added, p.p.m. 342 105 259 332
1038 1320 1141 1110 1193
recover able,^ p.p.m. 320 107 234 314
Run I1 Added, Recoverablela p.p.m. p.p.m. 383 359 368 242 213
374 220 200
-
-
-
975
1206 1143 1122 1122 1207
1153 0 242
0
246 0 670
-
-
4764 5803 p.p.m. 1891 p.p.m. 1714 .p.m.
916
90.68 (of e matanal bx:? P.p.m. added timw % recovery (from Table 11).
-
Table IV. Determination of Olefln Content in Exhaust Vapors, Using Three Fuels to Operate Automobile Engine
Date
Fuel
10/7/58
A-1
10/8/58
A-1
10/9/58
A-1
10/27/58 5 1 2 . 4 10/28/58 5 1 2 . 4 10/29/58
8.12.4
10/21/58
H-30.9
10/22/58 H-30.9 10/24/58
H-30.9
5/13/60
5
4/14/60
5
6/2/60
5
5/3/60
3
5/23/60
3
0
Analysis of Known Olefin-Air Mixtures
Run I Olefin ZPentene I-Hexene ZHexene Cyclohexene
Found, P.P.M.
covenes. Position of double bond, number of branched chains, and concentrations used did not significantly affect the analyses of compounds used in the experimenta. Two aromatic and two pareffinio compounds were tested; they did not consume bromine, and therefore, are not expected to interfere in the olefin determination. Recoveries of Ole5n Mixtures. T h e results of analyses of known mixtures of eight clcfins (Table 111) indicated t h a t 90.6 and 98.3oJoof all olefins could be accounted for by this procedure. The olefins which were expected to be recovered were calculated from Table 11, from parte per million of olefin
0
677 -
4591 919 5800 p.p.m. 2072 p.p.m. 2037 .p.m. 9 8 . 3 8 (of e matenal b 3 z k t
5/26/60
3
4/18/60
2
6/9/60
2
6/6/60
2
4/22/60
1
6/1/60
1
6/8/60
1
Ole- % Deviation fine fromMean P.P.h. of Duplicates 87 87 85
0.00 1.2
83
82 82 213
200 217 213 169 149 324 328 374 376 377 351 307 307 319 313 318 313 236 242 224
236 207 212 124 130 118 124 148 16.3 133 140 133 135 132 133
VOL 33, NO. 6, MAY 1961
0.00 3.1 0.9 3.2 0.6
0.3 3.6
0.0 0.9 0.9 1.3 2.6 1.4 2.3 2.5 2.0 2.5 0.1 0.1
735
added timrs per ccnt recovery, measured for this olefin. Spectrophotometric End Point De-
The spectrophotometric end point detection employed in this procedure, first described by Sweetser and Bricker (6),takes advantage of the high molar absorptivity of the tribromide ion a t 290 mp. ‘l’liis ion is formed at the end point of the bromate-bromide titration when the first amount of unconsumed bromine combines with excess bromide in solution to form tribromide ion. Ita immediate effect on the absorbance of the solution is indicative of the titration end point. Use of Catalyst. Zinc sulfate a8 catalyst in this photometric titration procedure was preferable to mercuric chloride or mercuric oxide ordinarily recommended for olefin analyses. This catalyst did not exhibit any appreciable absorption at 290 mp, did not lower the molar absorptivity of the tribromide ion (J), and did enhance the bromine addition rate of slowly reacting olefins. tection.
Use of Nonpolar Solvent. Methanol, frequently employed as solvent for hydrocarbons, could be applied only for liquid olefins already in solution. When gaseous olefins were involved, .the recoveries were incomplete and variable. After investigating a large number of compounds, i t was found that the use of a nonpolar solvent, such as carbon tetrachloride, resulted in a higher collection efficiency for olefins in the gas phase. SUMMARY
A procedure for the determination of olefins in the gas phase at concentrations ranging between 25 and loo0 p.p.m. is based on the absorption of the gas in the nonpolar liquid and the spectrophotometric titration of suitable aliquots with small increments of bromine, released from a bromate-bromide solution. Fkcoveries for Cr+ olefins were excellent; the recoveries for C, olefins were approximately 500Jo; recoveries
for low molccular w i g h t olcfins were low. This method has bcen usrd for the determination of olefins in the exhaust of automobiles, and has yielded consistent and reproducible results. LITERATURE CITED
(1) Air Pollution Control District, Los
Angeles, unpublished reports.
(2) Haagen-Smit, A. J., Ind. Eng. Chem. 44 1342-8 (1952). (3) Ikwh, J. B. Bredstreet, R. B., INO. ENQ.CHEW,ANAL. ED.12, 387 (1940). (4) Mader, P. P., Heddon, M. W., Eye, M., Hamming, W. J.,, Ind. Eng. Chem. 48, 1508-11 (1956). (5),Schuck, E. A. Ford, H. W., Ste hem, E. R., “Air Poilution Effects of frradiated Automobile Exhausts aa Related to
Fuel Composition(” Air Pollution Foundation, h Angeles, Calif., Rept. 26 (October 1958). (6) Sweetser, P. B., Bricker, C. E., ANAL. CHEM.24, 1107 (1952).
RECEIVED for review February 15, 1960. Resubmitted September 19, 1960. Accepted January 9, 1961.
Filter Photometry Using Cadmium Sulfide Detectors G. A.
ROW
Quality Control and Analyfical laboratories, The Dow Chemical Co., Rocky Flats Plant, Denver, Colo.
b The need for an inexpensive, small, and rugged fllter photometer for use in in-line applications has prompted a study of the cadmium sulfide cell for use as a light detector. Data are presented which show the advantages and disadvantages of the cell. Designs and schemutic diagrams of filter photometers using cadmium sulflde detectors are shown. Of primary interest were photometers in which the separation of the sensing unit and the readout meter was possible so that maximum utility was obtained for glove box operations and remote monitoring.
I
where radioactive materials are handled, there is considerable interest in in-line andysis and remote monitoring to avoid handling and consequent personnel exposure. A common means of analyzing these streams is by color, so that a simple filter photometer has many applications. Several Atomic Energy Commission installations (1-5) have designed and constructed simple, small, and inexpensive filter photometers. ‘Fhese normally utilize a phototube N INSTALLATIONS
1 Present address, Beckman Instrument Co., Inc., Fullerton, Calif.
736
ANALYTICAL CHEMISTRY
and then use a small current amplifier and meter at a remote or separate location to indicate the solution concentration level. To avoid the difficulties of small signal transmission and the cost of amplifiers, the cadmium sulfide cell was investigated for use as a light detector. THEORY
In the design of filter photometers, a phototube or barrier layer cell is usually used. For a stable output which is a necessity in process photometers, the phototube is normally chosen since the selenium barrier layer cells have a considerable amount of fatigue and drift although their high current output is advantageous. The phototube, however, is a high impedance device which yields only relatively small currents. This requires an electrometer amplifier for meter presentaTable 1. Characteristics of Cell Spectral response 330 to 740 mp (SW Sensitive area 0.65 X 0 . 5 4 in. Maximum ~olarizina 250 v. d.c. voltage Maximum photocurrent 50 ma.
tion. For remote monitoring i t also requires the transmission or preamplification of small signals. Commercially available cadmium sulfide photoconductive cells are satisfactory for many filter photometer applications. Advantages of RCA Type 7163 and 6957 cadmium sulfide photoconductive cells are as follows: Adequate spectral response over the entire visible spectrum, high light sensitivity so that small lamps and interference filters can be used without need for a n amplifier, low dark current, output which is linear to incident radiation, and a large sensitive surface so that glass cells of convenient size can be used. The disadvantages are: Change of sensitivity with temperature, and rise and decay times for steady value photocurrent which can be appreciable. Some characteristics of the RCA 7163 cadmium sulfide photoconductive cell are shown in Table I. The light sensitivity of these cells is very high and interference filters can be used with small pilot lamps to provide adequate output for 250-fita. meters. With small lamps the response time is slow (98% of final value in 3 seconds) b u t for in-line applications this is not significant. Higher illumination intensities yield faster response times. The
