Infrared Determination of Chlorinated Hydrocarbon Vapors in Air P 4 L L F. URONE
AND
MARY L. DRUSCHEL'
Industrial Hygiene Dicision, Ohio D e p a r t m e n t of Health, Colicm bus, Ohio Because of the toxicity of chlorinated hydrocarbon vapors in air, their analysis is of importance. Infrared spectroscepy has a number of advantages in the analysis of compounds of this type, jet few publications have appeared. A method has been deieloped whereby the air is sampled with a cooled scrubbing soh ent, and qualitative and quantitatii e determinations of single or multiple-component vapor-air mixtures are made with an infrared spectrophotometer using a 1.0-mm. cell. -4 chart of the principal peaks of the spectra of fifteen chlorinated hydrocarbons is presented, and methods of measuring recorded spectra and preparing standard curves are described. Recoveries aieraged 9776, with an average deviation of 670. -4s little as 0.04 mg. of chlorinated hydrocarbon per milliliter of sampling solution can be analyzed. By using the proper solient, the method may be adapted for the determination of the vapors of other organic compounds.
C
spectra of various chlorinated hydrocarbons ( 7 , 8, 10, 12, 19, 36, 37, 50, 52, 58),but little of this viork has been directed tom-ard the determination of these substances in air ( 4 ) . For this reason, a method utilizing infrared spectrophotometric techniques was developed by this laboratory. IYSTRUMENTATION
A Beckinan infrared spectrophotometer, Model IR-2, equipped n-ith a wave-length drive mechanism and a Broa n recorder was used throughout this problem. For quantitative determinations, each peak was recorded between selected wave lengths, using a preselected, fixed slit width. The slowest speed available'on the wave-length drive mechanism (43 minutes for a complete scanning of the spectrum from 1 to 15 microns) was used. For qualitative determinations, the entire spectrum between 4.5 and 14.5 microns was recorded a t a rate of approximately 15 minutes per spectrum. I n order to obtain a relatively level backy n d , sprockets having the proper tooth ratios were placed on t e shafts of the wave-length drive and slit-width control and linked together with a chain (49). As the wave-length drive m as operated, the slit opening was accordingly increased or decreased. Thus, only one to three manual changes of slit width were required in the region between 4.5 and 14.5 microns, as compared to the seven to ten manual chan5es normally required for the Beckman IR-2 instrument. Recalibration, and possibly a change of sprockets, w ould be necessary on replacement of either the thermocouple or the Nernst glower. Sprockets having tooth ratios of 15 to 8, 15 to 9, and 15 to 10 have been used by this laboratory.
HLORIXATED hydrocarbons, widely used in industry, constitute a health hazard when present in air in comparatively small amounts (29, 44). For this reason, the quantitative determination of chlorinated hydrocarbon vapors in the air has been the subject of a large number of investigations. Usually these determinations are based upon one or more of the following proceDEVELOPMENT OF METHOD dures: (1) thermal or chemical decomposition folloiyed by chemiThe spectia of fifteen of the more commonly used chlorinated cal estimation of the total chlorides formed (14, 17, 18, 21, 23, 26, 38, 39, 43, 45, 51, 63, 5 6 ) ; (2) variations of the Beilstein test hydrocarbons \rere recorded for qualitative identification using a O.1-mm. cell. Inalytical quality reagents were used and no which depend upon the estimation of the intensity of the green attempt m ac made ton 3rd further purification. Figure 1 lists the flame developed when the chlorinated hydrocarbons are thermally decomposed in the presence of copper metal (16, 30,4 7 ) ; (3) modifications of the Fujiwara reaction H hich involve the estimation of the color developed CARBON TETRACHLORIDE from the reaction of the chlorinated hydrocarbons CHLOROBENZENE A A A . l%ithpyridine in alkaline solution ( 2 , 5, 15, 24, 46, CHLOROFORM 65); and (4) physicochemical techniques such as -A__ rn gi aviinetric methods after adsorption on charcoal or o-DICHLOROBENZENE p A Lsilica gel ( 9 , 22, 40), vapor pressure methods which @, @-DICHLOROETHYL ETHER A AA are based upon the pressures developed from the ETHYLENE CHLORIDE A - - A-A evaporation of the condensed vapors (11,31, 42,48), and light-absorption techniques (27). ETHYLIDENE CHLORIDE A A- L - - - As a rule, these quantitative estimations depend METHYL CHLOROFORM -A--upon the total amount of chloride present, ii respecMETHYLENE CHLORIDE A _______ tive of the source or sources. Mixtures of chlorinated hydrocarbons, which are frequently en~ 3 - m - A PENTACHLOROETHANE countered, are not usually separated into their PROPYLENE CHLORIDE A A . individual components, and the identity of the A AA A r-TETRACHLOROETHANE substances present, if desired, usually has to be A- - A A TElRACHLOROETHYLENE established by a separate qualitative analysis. Frequently this is not based upon the actual vapors A---1,l ,P-TRICHLOROETHANE present in the air. L A - - - A TRICHLOROETHYLENE Infrared spectroscopy, on the other hand, lends itself well not only to the qualitative identification 8.00 10.00 12.00 14.00 ( 1 , 34) but also to the quantitative estimation of compounds of this type (41, 57). A considerable amount of work has been published on the infrared
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1
Present address, Oak Rldge, Tenn.
V O L U M E 2 4 , NO. 4, A P R I L 1 9 5 2
627
fifteen compounds and pictorially indicates the relative intensity of the principal peaks of each as determined a t a concentration of %Yoin carbon disulfide, X study a t lower concentrations of the more intense peaks of each compound was then initiated. Table I gives the data obtained from 10, 5 , and 1% solutions in carbon disulfide. From this t'able it was evident that in order to measure the small amounts of chlorinated hydrocarbons to be found in air, the sensitivity of the met,hod had to be increased. This was acconiplished by suhstituting a 1.0-nim. cell for the 0.1-mm. cell being used. In addition, although it was recognized that carbon disulfide \\-as t o be prclferred for qualitative determinations, it v a s felt that a less tosic and less volatile solvent than carbon disulfide would prove to be of greater practical value for field n-ork. Cyclohexane, l,bdiosane, acetonitrile, mineral oil, and isooctane (2,2,4-triniethj-lpentane) were investigated for solvent, properties and for transparency in the infrared region between 8.0 and 14.5 microns (54). Iso-octane Kas selected because of it,s relatively low volatility, nontoxicity, solvent properties, and relative transparency in the infrared. The five chlorinated hydrocarbons most frequently encountered by this laboratory-carbon tetrachloride (.S, SS, 8.5. .TO, 58)
Tahle I. .ibsorption Data for Various Chlorinated Hpdrocarhons in Carbon Disulfide Solution Using 0.1-11m. Cell Ih/I
Ware
Coinpound Ca1hon tetrachloride Chlorobenzene
Lrngth. g
1%
5%
10%
12.70 9.23 9.78 13.55 14.25 8.26 13.21 8.88 9.67 13.39
Cliloroforin o-Dichlorobenzene @, 8-Dichloroethyl ether
8.87
Ethylene chloridr
Ethylidene chloride
CHaCHCIz
I I c t h y l chloroform
CHsCCla
Methylene chloride
CHSClz
Pentachloroethane
CHC12CClr
Propylene chloride
CHzCICHClCHs
s-Tetrachloroethane
CIzHCCHCI2
Tetrachloroetiij Iene
Ci?C:CC12
1,l.P-Trichloroethane
CIH?CCHCI,
Trichloroethylene
CIHC:CCI,
9.59 13.34 8.17 10,63 11.30 13.90 8.15 9.49 10.23 9.23 14.06 7.93 13.61 11.01 12.21 12.99 13.85 9.80 13.53 8.33 12.56 13.26
13.56 11.01 12.46 12.90 10.74 12.90 13.68
10.78
chloroform ( 3 , 4,19, 33, 35), ethylene chloride ( 7 , 22, 50, 52, .is), tetrachloroethylene (4,58), and trichloroethylene (4,2 - w e r e then chosen for a more intensive study with iso-octane as the solvent and the 1.0-mm. absorption cell for increased sensitivity. One milliliter of the compound to be studied was quantitatively pipetted below the surface of iso-octane in a 100-nil. volumetric flask and brought up to volume with iso-octane. This gave a concentration of 10 to 30 mg. per ml. of solution, depending upon the density of the chlorinated hydrocarbon under study. By means of suitable dilutions with iso-octane, concentrations rauging from 0.04 to 8.0 nig. per ml. were obtained, and the infrared curves of the more appropriate peaks were then recorded for thP various concentrations. Measurement of Recorded Spectra. Most of the al,coi~ption peaks were measured by the "base-line" method of Heigl, Bell, and White (28). From these data, standard curves using log I b / I versus concentration were drawn in order to determine t h e best peaks for analytical work. Z is the perpendicular distance on the recorded spectra from the zero line to the absorption peak. Ib, measured a t t'he same wave length, is the perpendicular distance from the zero line to the hase line. A straight line dran-n between tx-o selected spectral points on either side of the absorption peak serves as t,he base line. These base-line points are selected to give a line as nearly parallel as possible to the radiant energy background and yet be a t ahsorpt,ion minima. T h e absorption minima iiiust be practically free of any variation i n absorption caused by changing peak shapes and wave-length shifts of the peaks due to the varying concentrations of the chlorinated hydrocarbons. All measurements of t,he recorded spectra are made in millimeters and should be accurate to 0.5 nim. I n some cases the method of Kright (57) was more convenient because of solvent background characteristics. In these cases, log I,/Z is plotted in preference to log I b / z , I , differing from Zb i n that I , is the perpendicular distance from the zero line to a preselected spectral point. This point is so chosen as to be TI-ithin 0.5 micron of the absorption peak and nearly independent of the change in the concentration of the solute in the dilute solutions. Because of instrumental variations, it is more convenient to subtract the logarithm of ZJZ of the solvent blank-i.e., log I:/Iofrom the logarithm, of IJZ of the known concent,rations hrfore plotting the standard curves. This necessitates the running of a solvent. blank and application of the same correction whenever a series of analyses is run. Whenever a misture of two or more chlorinated hydrocarboii.3 is encountered, it may be possible t,o select absorption peaks that are but little affected by the presence of the others. The fact that t'he solutions being analyzed are very dilute is a contributing factor in this respect. However, when it is not possible to find peaks that are not affected by t'he presence of the other substances, the solutions must be analyzed in the manner usually used for mixtures (6, I S , 28, 52). Figure 2 shon-s the standard curve for the ethylene chloride peak a t 14.00 microns plott'ed in terms of log I b / I , and the standard curve for the carbon tetrachloride peak a t 12.75 microns plotted in terms of log I , / I - log If/Io. In this case, the 14.00
11.90 12.84
Table Saiii~le so.
1
2 3
4 J
Components Ethylene chloride Carbon tetrachloride Ethylene chloride Carbon tetrachloride Tetrachloroethylene Tetrachloroethylene Ethylene chloride Carbon tetrachloride Tetrachloroethylene Ethylene chloride Carbon tetrachloride Tetrachloroethylene Ethylene chloride Carbon tetrachloride
dmount Taken Mg./ml. 1.26 0.32 0.25 1.60 1.63 1.63 0.25 0.32 0.32 1.26 0.32 0.33 0.26 1.60
IT. .4nalyses of Synthetic \fixtures
Peak Measured 14.00 12.75 14 00 12.75 12.88 11 01 14.00 12.75 11.01 14 00 12.75 11.01 14.00 12,75
I
IP
Log
Io
le
Mm.
Mm.
Xm.
IO .TI m.
Ih/I
Mm.
197 203 211 09 166
... ... ...
117 160 187 31 133 39 187 154
...
. .
0.22>31 0.10380 0 05308 0.50379 0,09691
20s
...
.
.
I
194
...
...
210
...
i 46 i 67 140
83 116
iii
160
142
85
166
188 30
...
... ...
...
... ... ,..
i34
101
171 134
248 101
174 134
248 101
...
...
iii
. .
0 04b3.'
...
0 , 22272
...
0 . oi922
248
-
Log IC/I Log I y P
... ...
.. .. ..
0 , 4iia.r
idios
... ...
0.
...
0 . is304 0.09887
0.10404
0 . Sois5
Amount Found .l.lg./ml. 1.23 0.33 0.26 1.67 1.55 1.50 0.23 0.32 0.33 1.23 0.32 0.33 0.24 1.62
Kerorrry 1'1
$97,7 103 104 104 95.0 92.0 92.0 100 100 97.7 100 100 !I6 0 101
ANALYTICAL CHEMISTRY
628 micron peak of ethylene chloride is not influenced by small concentrations of the four other chlorinated h y d r o c a r b o n s which received the more int e n s i v e study. The 12.75micron peak of carbon tetrachloride, however, is slightly affected by the 13.21-micron peak of chloroform and the 12.84-micron peak of trichloroethylene. For most practical purposes this influence is small and may be disregarded. Similar aurves using the base-line method of Heigl, Bell, and White (28) or the reference point method of Wright ( 5 7 ) were prepared for the other chlorinated hydrocarbons. Table I1 tabulates the data used in analyzing five synthetic mixtures. I n each caje the choice of measuring by the base-line method or the rcference point method depended upon which of the methods iyas more applicable in light of the recorded spectrum background.
0
I:
MILLIGRAMS PER MILLILITER
Figure 2.
MILLIGRAMS PER MILLILITER
Representative Standard Curves
SAiMPLING
.kiter the determination of the practicability and the sensitivity of the method, the prolileni of finding a suitable airFigure 3. sampling method remained. Figure 3 schematically s h o m the apparatus used to chech sanipling procedures and to prrpare air samples containing hnon n amounts of the chlorinated hydrocarbons. The vapor-air mixing chamber was an adaptation of that of Gisclard (26). The air passing through the jet blows down into the open end of the stopcock, evaporating some of the chlorinated hydrocarbon. The vapor-air mixture then passes out of the mixing chamber through a U-tube filled with anhydrous magnesium perchlorate and into an all-glass midget impinger (20) partially filled with glass beads and containing 5 ml. of iso-octane. Magnesium perchlorate was chosen as the desiccant because its greater drying efficiency prevented clogging of the impinger tube with frozen water vapor. There exists an explosion possibility in places where there may be very high organic vapor concentrations or some back-diffusion of the iso-octane into the drying tube. 111 these cases, an efficient drying tube using a desiccant such a. anhydrous calcium sulfate should be used. Under ordinar) operating conditions, horn-ever, the amounts of organic vapors to be encountered are a t most in milligram quantities, and these do not easily react with magnesium perchlorate a t temperatures bvlow 100" c. The glass beads, from 3 to 4 mm. in diameter, serve to break up the air stream and to reduce the amount of iso-octane needed. The dry ice-acetone bath is used t o increase sampling efficiency and to prevent evaporation of the solvent during the sampling period, Methyl Cellosolve has proved to work satisfactorily in the place of acetone and may be preferred because of its higher boiling point. Before each determination, the stopcock containing the chlorinated hydrocarbon was removed and weighed. A measured amount of air was drawn through the apparatus a t a known rate,
MICRO
STOPCOCK
Apparatus for Testing Sampling Techniques
and the stopcock was weighed again. The amount of evaporation of the chlorinated hydrocarbon vias controlled by the amount of time the stopcock was left open. To obtain higher concent,rat,ions in a reasonable length of time, a small electric hot plate was used t o warm the small bulb. The entire apparatus was thoroughly flushed with air after the stopcock was closed and during the time that the stopcock was being weighed. For the low boiling compounds, a semimicro stopcock weighing less than 11 grams \vas used; thus the stopcock plus the chlorinated hydrocarbon could be weighed on the microbalance. For the high boiling compounds (above 100" C.) a stopcock with a 6-mm. bore \vas used. Ho.il-ever, in place of the bulb as used by Gisclard, a 10/30 standard-taper ground-glass joint was attached. A standard-taper, 5-ml. volumetric flask fits this joint and can be removed for weighing on the microbalance after a stopper is inserted. Table I11 shows the amounts of the various chlorinated hydrocarbons introduced into the syst,em and the amounts recovered. The average recovery was 97%; and the average deviation was approximately 6%. Obviously, the sensitivity of the method depends upon the intensity of the absorption of the peak being measured-i.e., the molecular extinction. For most of the conipounds studied a 1,O-liter sample of air would suffice to determine concentrations in the vicinity of 10 p.p.m. and upward. A 30liter sample of air would be sufficient for concentrations in the vicinity of 1 p.p.m. T h e n the concentrations of the chlorinated hydrocarbons in the air are high, shorter sempling periods may be used or aliquot parts may be taken by using proper dilutions. Five milliliters of iso-octane were used in the impinger for each determination and no final adjustment of the volume was found necessary prior t o running the sample on the infrared inst'rument. A4sis shoan by Table IT,less than 0.7% of the iso-octane evaporates during a 20-minute sanlpling period of 0.5 liter of air per minute and only l,7yc during an hour sampling period. Conse-
629
V O L U M E 24, NO. 4, A P R I L 1 9 5 2
minute. .ifter sampling, the impinger tulw is removed and the flask is stoppered u i t h an unluhricated S o . 24 standard-taper stopper arid returned to the laboratory for analysis. The samples are stahle for a t least a month R-hen stored in the dark. I n the lulioratory, a portion of the sampling solution is transferred to a rock-salt cell of 1.0-mm. thickness. For qualitative identification, the entire spectrum hetneen 4 . 5 arid 14.5 microris is scanned at, a rate of approximately 15 minutes per spectrum and the principal peaks of the halogenat,ed hl-drocarbons are subsequently identified. For quantitative estimations, the preselected peaks are rerun at a lower Apeed, and the measurements are made as described above, either by the base-line method 01'by the procedure outlined by Wright. Comparison n-ith standard curves gives the aniount of chlorinated kijdrocarbons present. 1 04" 1 . 9:3'1
'f r t ! ,/
1 00 1 !I0
96 98
1 32 1 Ill
lv :mounts of ~ I i I ~ i I i n ~ hytli~oc:ii~lmri> ~ted c a n be found in the s r c ~ i n c limpinger. .-In:iir flon- rate of 0.3 1itc.i. 1)er minute \vas found to give oiltiniuiii effiriency. Rate> g i w t e r than thiy ciusecl too grrat a 1093 of solvent through spr;iyinp : i i i i i t~vaporation. Slon-er rates unduly i r i c i w w thcl length of w i i l i l i i i g time.
'I'nlile \-.
Compariwn of inal? ses of a Trichloroethylene Exposure
'lut so.
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IIalirie Inrliwror I n t r ~ g r a t t ~Avcr;igi,-l d
P.P..lf. 1 J0 1
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Infrnred N e t b o d P. P.41. 176 160
A,
2: , .>
'10
I'KOCEDUR E
+
Five inilliliters of pi,:ic.tic.:il grade iso-ortme, 99.5 %, are p u t iiito :i borosilicate glass, stmdard-taper. urilubricated, midget inipiiiger (20) which is approsiniately half filled with glass bead?, 3 to 4 nini. in diameter. The impinger is carefully p u t into a dry ice-;icetone bath, a wide-niouthed Thermos bottle or Dewar flask serving a,? the container ~ O I the , txith. A small G-shaped drying tulx containing anh>-tfrousmagnrrium perchlorate (note explosion hazard mentionwi :ti)ove) is attached to the inlet tube of the inipinger, and a measuring drvire and a suction pump arc' att:ccalied to the outlet. .I11 connections must be made with h\.tiriJcarbon-resiRtant tuliing such as Tygon or be glass t o glass. A i i stoppers ~ ~ used must br (,overed with metal foil. Glass tubing with hemispherical joints or Tygon tubing may be used to facilitatcs a:iinpling. For qualitiitive purposes, carbon disulfide niay be uwd as the sampling r;olvcrit. Ikpending upon the miicetitration of the halide present in the :ttiiiosphere, a known volunie of 1 t o 30 liters of air is dratvn through the impingrr at :I rate of :ipprosiiii:itel;\- 0.5 liter per
(1) Bariies, R. B.. Gore, R. C',, Stafford, R . I\-,, and l\.illianis, 1.. Z . , A S A L . CHEM.,20, 402 (1945). ( 2 ) Rarrett, H. AI., J . I n d . H Y Q . Toxicol.. 18, 841 (1936). (3) Bennett, JT. H., and Ileyer. C. F., Ph!/a. Rev., 32, 888 (1928). (4) Berton, d.,Bull. soc. c h i m , F m u c e . 16, S5S (1949) (j)Brain. F.H., A n a l y s t , 74, 555 (1949). (6) Hrattain, R. R., Rasniussen, R. ,5,, :ind C'ravath, A. 11.. J . A p p l i e d Phys.. 14, 418 (1943). ( 7 ) Cheng. H.-C., and Lecomte, J., J . p j ! ~ .rudticni. ~. 6, 477 (1936). ( 8 ) Conrad-Billroth, H., 2. l i h ~ s i k .L ' h m . , B25, 139 (1934). (9) Cook. W..1., and Coleman, .1.L., J . I d . Hyg. Tozicoi., 18, 194 (1936). (10) Coiin, C'., and Sutherland, G . H. B. >I,,Proc. Roil. Soc. ( L o n d o n ) ,
A165, 43 (1938). (11) Couchrnan, C. E.. and Ychulze, I\-.€I., J . I d Hug. I'ocicol., 21, 256 (1939). (12) Cross, P. C., and Daniels, F., J . C'horz. Phiis., 1, 48 (1933). (13) Daasch, L. I\-.,.kx.4~.C H E ~ I 19, . . 779 (1947). (14) Danner, C. E., and Goldenson, ,J,, J . I d . H u ~ TozicoZ., . 29, 218 (1947). (15) Dwoga, 11. P., and Pollard, =1. G., J . Soc. Chem. I d . ( L o n d o n ) , 60, 218 (1941). (16) Davis Emergency Equipnient Co., IIIC., Sewark, S . J., bulletins. (17) Dudley, H. C y . , U. 9.Puhlic Health Service, Pub. Health Repts., 56, 1021 (1941). (IS) Elkins, H. B., Hobby, h. I
