Table 11.
Peak Currents in Air-Saturated Solutions
Peak Peak Currentb Currentb Concn., (Differenti- A v . ~Dev., (Nondifferen- .Iv.~ Dev., Ion mole/liter ally), pa. 70 tially), pa. 7% Cd 1.00 x 10-3 16 6 0.7 16.9 0 2 c 1.00 x 10-4 1.72 0.6 . . 1.00 x 10-5 0.17 6. c T1+ 1.00 x 10-3 9.85 0.4 9.84 0.1 c 1.00 x 10-4 1.01 2.0 ... a Indifferent electrolyte in each solution was 0.lM potassium chloride and acetic acidsodium acetate buffer, pH 5.4. * Average and average deviation of six determinations on same solution. c Oxygen reduction currents prevent measurement. Solutions
both the 0-xygen and thallium currents. When the air-saturated indifferent electrolyte is placed in the reference cell, however, curve B is obtained differentially. The thallium can be determined without interference from the oxygen, but the cadmium current is still masked. When the reference cell is made 10-4M in thallium as well, an accurate analysis of the cadmium may be obtained as shown in c u r x C.
Figure 4 illustrates a similar solution, but in this case the thallium is lO-3M and the cadmium is 2 X lO-5M. The cadmium wave is completely masked by the oxygen and thallium currents. Compensation of the preceding waves, as shown in curve C, permits a reasonably accurate (2.2% relative error) analysis of the cadmium, even though the cadmium is not detectable in curves A and B.
LITERATURE CITED
(1) Airey, L., Smales, A. A,, Analyst 75,
287 (1950). (2) Delahay, P., “New Instrumental Methods in Electrochemistry,” p. 372, Interscience, New York, 1954. (3) Ferrett, D. J., Phillips, C. S. G., Trans. Faraday SOC.51, 980 (1955). (4) Heyrovsky, J., Anal. Chim. Acta 2, 533 (1948). (5) Lingane, J. J., Kerlinger, H., ANAL. CHEM.12,750 (1940). (6) Jleites, L., Ibid., 27, 416 (1955). (7) Ross, J. W., DeXars, R. D., Shain, I., Ibzd., 28, 1768 (1956). (8) Semerano, G., Riccoboni, L., Gazz. chzm. ital. 72, 297 (1942). (9) Shain, I., Crittenden, A. L., ANAL. CHEM. 26,281 (1954). RECEIVEDfor revien- March 20, 1958. Accepted June 4, 1958. Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, March 1958. Work supported in part by the U. S. Atomic Energy Commission and in part by the Research Committee, Graduate School, Gniversity of Wisconsin, with funds made available by the Wisconsin Alumni Research Foundation.
Colorimetric Method for Continuous Recording Analysis of Atmospheric Sulfur Dioxide HAROLD
L. HELWIG and CHESTER L.
GORDON
Air Sanitation laboratory, California State Department of Public Health, Berkeley, Calif. )Sulfur dioxide in the atmosphere can be determined continuously with automatic sampling and recording apparatus. The reaction of sulfurous acid with pararosaniline hydrochloride and formaldehyde produces a red-violet color which is measured colorimetrically. At p H 1.5 this reagent is stable and exhibits good resistance to interferences at concentrations found in the atmosphere. Concentration limits for the instrument were established up to 5 p.p.m. but these can b e considerably extended or reduced.
S
is an intermediate in the manufacture of sulfuric acid. It is also used in the manufacture of sodium sulfite, and in refrigeration, bleaching, fumigating, and preserving. Released, too, as a by-product in the burning of sulfur-containing coals and oils and in the smelting of many ores, it is undoubtedly one of the most important of the air pollutants. As available conductometric methods for measuring sulfur dioxide concentrations on a continuous basis were not considered specific, work was initiated to ‘C‘LFUR DIOXIDE
1 8 10
ANALYTICAL CHEMISTRY
determine the feasibility of using colorimetric methods. The basic fuchsin-formaldehyde reagent developed by Steigmann (8, 9) has been dealt with in detail in a number of papers on the determination of atmospheric sulfur dioxide (6, 7 , 10). Atkins (1) found that the color response obtained by combining sulfur dioxide with fuchsin-formaldehyde reagent in a n acid medium follows Beer’s law up to a concentration of 1 mg. of sulfur dioxide in 500 ml. of solution at 25” t o 30” C. West and Gaeke (11) found that their colorimetric system obeys Beer’s law up to approximately 25 y of sulfur dioxide per 10 ml. of reagent. Moore, Cole, and Kata ( 6 ) did concurrent studies of sulfur dioxide and nitrogen dioxide in Kindsor, Ontario. using the conductometric and fuchsinaldehyde method for sulfur dioxide and the Saltzman method for nitrogen dioxide, and sampling with automatic impingers. They found that conductometric measurements of sulfur dioxide gave higher values than the chromogenic reactions of fuchsin-aldehyde and sulfite, and attributed this to nitrogen dioxide interference a t threshold levels.
They applied a factor based on nitrogen dioxide levels to the colorimetric values and found that these agreed with conductometric values. The present authors believe that correction for the effect of nitrogen dioxide at levels found in the atmosphere would not be significant for the colorimetric reagent used in the studies described. As a point of departure, the method proposed by K e s t and Gaeke (11) utilizing sodium tetrachloromercurate with pararosaniline hydrochloride and formaldehyde was chosen for primary investigation. It is acidic in nature and the oxidizability of sulfite solutions in the alkaline ranges, it was believed, might be avoided by working in the acid range. illso, the methods described previoudy (1, 6-10) with modifications were felt not to be as easily adaptable to continuous recording instruments a6 the K e s t method. The criteria felt necessary for colorimetric measurements in continuous recording machines were determined to be the follon.ing: Specificity of reagent for substance Time for color response
St’ability of reagent Stability of the resultant’ color Because pararosaniline Iiydrochloride is rhroniophoric with the addition of sulfurous wid in the presencc of fornialdehj-dr, t,he specificity of this reacation \vas vheckcd along with the stability of tlic rcagcnt. An ahsorption c.ur\-e \ m e ~iiackwith a Cary RIotlrl 11 recording spcctropliotometcr bct\vrtln 400 and 600 nip (Figure. 1) \\-it11 mnsiinuni absorption ocrurring a,t 560 nip. T(3sts to deterniiiitl shdf-lifc for prcmisrtf reagents as would be required for taontinuous recording dwiccs n-ere matlc using a Bauscli &- Lonib Sprctronic 20 colorimeter and standard sodium pyrosulfitc solution t o determin(> caolor rrspoiiv. Daily comparisons over a 2-n-eek Ii(,riod w r ( >made using freshly p r q m w l rcagc’nts and aliquots of reagelit? stored in stopptwd bottles at room tenipcratwc. Thvse stored solutions had t’lie. composition with the indicated additions niatlt, a t thP time of the daily t ( d as &on-n in Table I. Stability antl color rcsponsc. o w r B 2-\vc~>k pc,riod w r e good for the rragmt n.ith :ind \ ~ i t h o u t.sodivni trtrachloronicrcurate. Ho\vever. aquc’ous solutions of tiye and altlcliytle gar(’ slightly fastcr (lolor responer than thr solutions c~~iitniningsodium t~.trachlorcmervurstc. contiiiuous recording tli4c.w w r r of intt.rest and fast reeponec n-as desir: h l ( ~ , it \vas felt that comparisons b e t w c n tiisbilled n-atcr antl sodiuni tetrscliloromercur~~tesolutions as colIcrting nitdia should bc madctlinto R 20-liter glass c.ont:iint,r antl miscd to give a conrc>ntration of 1.9 y of sulfur diosidr per nil. Aliquots \vwe xvithdrawn by syringo and bubblrd into test tubes. Roadings in prr (wit transniittance \ v t w t a k m at 5 , 20, and 30 minutes, ant1 tlit, results a w tabulated in Table
Table I.
Composition o f Premixed Reagents
10 10
1
1 1
10
10
1 1
10 10 a
1 1
1 1 1 1 1
1
1
1
1
1
1
0.1.11 Ya2HgCl.i. solution of pararosaniline hydrochloride. 0.02% aqueous formaldehyde. 4.37 m g . of ?ia?S205per 100 ml. of distilled HA).
* 0.04‘;;
c
d
0.3
Figure 1. Absorption curve for sulfite pararosaniline h y drochloride in distilled water
y
0.2
2
-
4
L YI 0
: 0.1
bo0 0
75
25
50
WAVE
Table II.
500 0
75
50
400 0
25
L E N G T H , M$L
increnimts of 5 and 15 niinutcs wit11 ra.rying concentrations of pararosnnilinr hydrochloride (Figure 2 ) . From these determinations it was apparent that 0.5 ml. of 0.04% solutioii of pararosaniline hydrochloride, or 200 y per 1.0 ml. of rragent, approximately half of the concentration of dye. suggested by K e s t and Gackt (fl), n-ould give the more sensitive rragent, and further work n-as done t o olitain t h r most sensitive concentration of para,rosaniline hydrochloride based on this
standardized sulfur dioxide solutions to 10-nil. aliquots of various concentrations of sodium tetrachloromercurate. The grmter magnitude of t h r color reapoiisr was noted in the absence of sodium tet~racliloromercurntc. It appeared t,hat,thc reagmt I\-ithout sodium tetrachloromercurate gm-e better response arid \\-odd be the most feasible for use in continuous recording analyzers. Comparisons were then made with solutions containing 0.54 y of sulfur dioxidr per nil. of reagent a t time
Color Response o f Dye-Aldehyde Reagent to Gaseous Sulfur Dioxide
SO?
Added, y/10 111. 1 9 :3 ti
5 0 it5 11 0
(Per cent transmittance) Collwting 1Iedia 0 13/ SalHgC11, 10 111. Ihstilled IYater, 10 111 ___ Time Intervals for Colorkvelopmrnt, 1Iin . 30 5 20 30 5 20 88 87 86 71 65 65 8:3 80 7 $1 68 67 ti7 84 io 76 5 46 44 41 5 -81 I I 31 74 32 31 67 65 63 5 21 5 21 22
;.
Table 111.
11.
Color Response o f Reagent a t Given Time Intervals (Per rent transmittance) SO,
TIicv (lata indicate that thc. rate and niagnitutl(. of color rwponsr of the reagc,nt arc greater in the nhsence of sodiuni Furtlicr tests tt.trachloroinercuratr. t’rt’ mad(>to comparcl the dye-aldehyde rwgrnt with and n ithout the addition of sodium trtrachloromercurate for time of optimum response anti magnitude of c d o r rlevclopment. Table I11 s h o w twinparati\ e caolor response a t various timc intervals aftrr the addition of
Reagents Added for Daily Test, 111. Sulfited Dyeb Aldehydrc
Composition of Stored Reagents, 111. X&yHgCl,a HZO Dye* Aldrhydec
Reagent
Time Intervals for Color Ilevelopment, 1 I i n .
Added.
-,(’I0 0.1JI S:i?HgC‘I< 1 1 7 0.05JI Sa,HgCI, 1 4 i Distilled water 1 4
111. 2
3 97
8
90
2
84
5
-i
Si
93
84 76
80 70
2
$13
92
n0
8 2 2 8
86
78
67 83
59
76 55 78 37
7 2
30
50
80 42 30
25
10
12
92 76 ti5 89 72 49
91 74 62
87 72
15 90 -, I
3
59 86
76
r-
31 22
33
TI 45 75 33
21
21
48 id
VOL. 30, NO. 1 1 , NOVEMBER 1958
181 1
Table IV. Range of Sensitivity of Pararosaniline Hydrochloride Reagent to Sulfur Dioxide -(
so2
per Ml. Reagent 0.01 0.02 0.05 0.08 0.10
0.50 0 TO 1 00 1.26 2.00
Transmittance 5 min. 10 min. 15 min.
-
98 95 92 88
81
48 35 23 16 9
(
98 93.5 90 85 82
38 24 14 10 4
97 93 90 84.5 81
35 22 13 9
2
derivation. Higher concentrations of sulfur dioxide were later checked against the reagents indicated in Figure 2 at 0.5 and 1.0 ml. of 0.04% pararosaniline hydrochloride per 10 ml. of reagent and the same relative response was noted. Using concentrations of 80, 100, 160, and 200 y of pararosaniline hydrochloride per 10 nil. of reagent, response \vas checked with concentrations of sulfur dioxide from 0.01 to 6.0 y of sulfur dioxide per ml. of reagent. The response of the higher concentrations of dye to high concentrations of sulfur dioxide is n-ithin +4% of the readings obtained using 80 y of dye per 10 ml. of reagent after 5 minutes' reaction time. After 10 minutes, the readings were within +2% of the suggested reagent. At the lower concentrations of sulfur dioxide, readings were within =k 1.0% which is about the reliability of the colorimeter being used. The reconimended reagent is based on 80 y of pararosaniline hydrochloride per 10 ml. of reagent. The range of sensitivity of this reagent is shown in Table IV. T o check interferences from oxidants, 10-ml. portions of collecting media were placed in each of five test tubes and approximately 60 ml. of nitrogen dioxide were bubbled through them. Color was then developed by the addition of 1 ml. of solution containing 26 y of sulfur dioxide per ml. This high concentration of nitrogen dioxide did not appreciably affect the color response of the reagent. After color was developed in the foregoing tubes, a gas stream containing 20 p.p.m. of ozone, generated by passing a stream of oxygen through an ozonator, \vas passed through tubes 3, 4, and 5, and decolorization occurred. I n tube 3, about 140 ml. of ozone completed decolorization. I n tubes 4 and 5 , about 180 ml. of ozone were required. After bleaching with ozone, 1 ml. of aldehyde, 1 ml. of dye, and 1 ml. of sulfur dioxide solution were added t o tube 3 and color was produced. 18 12
ANALYTICAL CHEMISTRY
I n tube 4, 1 nil. of aldehyde and 1 ml. of sulfur dioxide solution were added. No color was produced until 1 ml. of dye was added, a t which time intense color resulted. I n tube 5 , 1 nil. of dye and 1 ml. of aldehyde were added. A light shade of pink was produced, characteristic of the aldehydedye mixture. Upon the acldition of sulfur dioxide the strong color reaction occurred. Further tests ivere made to find the threshold level of ozone interference. A stock of stable ozone solution ( 2 ) containing 4.92 y of ozone per ml. was prepared and a series of varying ozone concentrations was prepared by dilution. One milliliter of ozone solution of knoivn concentration was added to a mixture of 9 ml. of the reagent formulation as developed for use in the analyzer and 1 ml. of solution containing a known concentration of sulfur dioxide. A final concentration of 0.011 y of ozone per ml. was the smallest amount of ozone which gave a detectable interference with the measurement of a final concentration of sulfur dioxide of 0.027 y per ml. At a final concentration of 1.0 y of sulfur dioxide per nil., the threshold level of interference by ozone was 0.11 y of ozone per ml. Assuming 100% collection efficiency of the reagent for sulfur dioxide and ozone, this experiment would indicate that, in air dreams, concentrations of ozone of 0.04 and 0.4 p.p.m. would show possible threshold interference with the measurement of concentrations of sulfur dioxide of 0.1 and 5.0 p.p.m., respectively, a t flow rates set u p for the machine used. T o test the effect of the reverse order of addition of ozone and sulfur dioxide, a stock of reagent was prepared by using a hydrochloric acid solution of p H 1-55, containing 2.56 y of ozone per ml., in place of distilled water. The responses of the reagent containing ozone and the regular formulation )yere compared by adding 1 ml. of standard sodium pyrosulfite solution to 10-ml. aliquots of the reagents. Addition of 0.6 and 1.0 y of sulfur dioxide resulted in color development equivalent to 0.5 and 0.9 y of sulfur dioxide in the ozonized reagent at 5 minutes with no further increase in color a t 10 minutes. The same additions t o the recommended formulation gave color response equivalent to 0.6 and 1.0 y of sulfur dioxide a t 5 minutes mith further increase of color on 10 minutes' reaction time as previously observed (Table IV). Bddition of ozone solution after sulfur dioxide had been in contact with the recommended reagent for 15 minutes did not decrease the developed color. These experiments indicated that the reactions of sulfur dioxide lvith czone and the chromogenic reagent were competitive, but that sulfur dioxide xhich reacted with the reagent to produce maximum
I-
9
1.5
1
q L
3
1.0
I Y
z
2
z+a
.5-
U W
E l -
* -I
0
20
30
40
PER CENT
50
60
70
80
TRANSMITTANCE
Figure 2. Comparisons of varying concentrations of dye for color development 0.54 y of sulfur dioxide per ml. of reagent
color was not available for reaction with ozone under the conditions dcwibed. A machine for continuous ccnductometric recording of sulfur dioxide ivas modified by adding a colorimeter having a 2-cm. path and a mercury lamp as the light source. It was necessary to add a synchroverter to the amplifier to utilize the recorder. T o establish the effect of ozone in the gaseous phase, streams of sulfur dioxide and ozone of k n o m concentration mere passed through the niodifietl analyzer using diffuser bulbs ( 5 ) to produce sulfur dioxide and ozone. A stream of air containing sulfur dioxide n as passed through the analyzer. ilfter the system had equilibrated and the recorder trace was stable, a second diffuper bulb, using stable ozone solution as a source for the production of a dilute stream of ozone, m s placed in series with the sulfur dioxide diffuser bulb (Table V). Over the range of sulfur dioxide concentrations of 0.11 to 2.5 p.1i.m. in air, selected ozone concentrations between 0.08 and 2.0 p.p.ni. in the air stream caused negligible interferencp with sulfur dioxide measurement. The residence time of the mixture of sulfur dioxide and ozone in the flon system appeared to be insufficient for appreciable reaction to take place. I n this experiment n ith sulfur dioxide and ozone in the gas phase, the failure to observe the indicated threshold of interference of ozone with sulfur dioxide measurement, as found in the previous experinipnt n ith ozone and wlfur dioxide in solution, is attributed to the relative insolubility of ozone in the reagent a t atmospheric pressure. TTest and Gaeke ( 1 1 ) indicated that high concentrations of nitrogen dioxide interfered seriously \I ith the determination of sulfur dioxide by the TT'est method. The present authors found that a solution of sodium nitrite, equivalent to 2 p.p.m. of nitrogen dioxide, when added to 10-nil. portioiis of a solu-
tioii of 0.15 y of sulfur dioxide per ml. c a u s d a n increase in t,ransniittance from '76 to 827,, a variance of By,' equivalent to about 0.01 p.p.m. of sulfur dioxide. The B 6: L colorimeter was used in conjunction lrith a glass counter flow contact column to set' up a flow system for measuring interferences from nitrogen diosiclc, gas (Figurc 3). With diffuscr l ~ u l la s~ constant sources of sulfur tliosidc>and nitrogen dioxide, the flow of sulfur dioxide was adjusted to give 0.4 11.p.111, of sulfur dioxide, which was quivalcnt to transmittance nt esta1)lislirrl liquid floiv-. K i t h a cwmirrcut f l o ~of riit,rogen dioxide at, tlicl follon-ing concentrations, the corresponding pi'r cent twismittanccs were: 1.0 p.p.ni., S4: 1 ~ 4p.p.ni., 86; 1.8 p.p.ni., 6 7 ; 2.0 p.p.ni., 88; and 2.6 p.p.ni., 89. Xt a sulfur dioside concentration of 4 ppiii., a concciit,ration of iiiorc than 6 p.p.m. of nitrogen dioxidc n-w ncwssary to decolorize the solution. d t nitrogrn diositlc concent'rations less t,liaii 1 .O p.i),1ii., no interference was notcd. REAGENTS
Hydrochloric Acid Solution (1 0%). Dilute 10 nil. of concentrated hydrocbhloric' acid t o 100 nil. n-ith distilled water as solrent for pararosaniline hydrochlwitlc~.. Pararosaniline Hydrochloride Solu4 of pararosanition. Dissolve 0 ~ gram line hycirochloritir in 100 ml. of 10% h y d I'o (411 1 ori c n c i d , Formaldehyde Solution (Reagcnt grad(, 40% fornialclchyde). T o 20 litcrs of tliatillrd witw add sufficient c~onceiiti,:itcdhydrochloric acid (about 80 nil.) to bring t h e pH to 1.5. Add 10 nil. of formaldehyde solution and mix wt>ll, Then add 40 nil. of p,zr:irosaniline Iiydrochloride solution, mix. and check the pH. Kruger ( 4 ) states that the niiscci reagent should h a w a light transmittance of not less than 85% in a 2 . 5 - m ~cell at 560 mp; if' transmittance is less than 8570, pH i q a b o w 1.5 :ind more hydrochloric acid i3 indicatrrl. INSTRUMENTS AND APPARATUS
Line-operated pH meter. Bausch & Lonib Spwtronic 20 colorimeter. using 1-inch cells. Cary rccordiiig quart z spectrophotometer. Modal 11. using 1-cm. cells. Ilodificd Kruger conductometric automatic recording sulfur dioxide niachine. The contiucti\ ity cells were replaced b\ a colorimeter cell having it 2-cni. path and a mercury lamp light sourw. A syncrovertw n as added and necessary circuit changes mere made to use the Rristol recorder. CALIBRATION
Static calibration of the automatic recording instrument was undertaken to provide a usable range from 0 to 5
1
R E A G E H T STORAGE AND
:MP
FLOW CONTROL AND METERING
I
1
VACUUM SOURCE
1 1
Table V. Effect of Ozone on Sulfur Dioxide Analysis in Gaseous Phase Input Gas Stream, P.P.11.
SO*
SAMPLE
FLOW
CONTACT COLUMN
1
1
CONTROL
0 0 0 0 0 2
!
11 48 48 48
80 5
03 0 28
0 08
YO? Found, P.1'. 11,
0 11
0 28 3 0 0 16
0 0 0 0
48
20.
2 -18
45
48 80
1
Column efficiency was checked n it11 the diffuser bulbs a t various flow rates. The efficiency a t an air flow rate of 250 nil. per minute ivas found to be 95 to S P E N T REAGENT I 96.5%. At air flow rate of 1 liter per SAMPLE INLET STORAGE minute, efficiency dropped to T3 to 75% I I indicating the need for a more cfficimt Figure 3. Flow diagram utilizing connieans of scrubbing the sulfur diovidc tact column and Bausch & Lomb colorfrom the air. imeter Output of the sulfur dioxide diffuser bulb lvas checked b y collecting in a smog bubbler and titrating n ith 0.01S p.p.ni. of sulfur dioxide for full-scale iodine. Output was found t o be condeflection of the recorder. K i t h a stant for a given set of conditions of solution of sodium pyrosulfite t o test flow and temperature. The nitrogen inachine response, it was found that dioxide diffuser bulb output n a s checkctl 1.35 y of sulfur dioxide per inl. gave with Saltzman reagent in smog bubblers. 99% deflection. T o establish a lower and output was constant for B gircn set limit, the authors found that 0.015 y of conditions. of sulfur dioxide pcx nil. g a w a deflection of Zy6. The machine n a s calibrated DISCUSSION on the basis of pas and liquid flon rates of 250 nil. per minute of air, t o 3.3 nil. This method is considerd flexiblc per minute of reagent, because these and useful for air pollution nork. flon- rates gave good sensitivity and BJ- varying reagent and sample flonresponse for the proposed range of rates, concentrations in the order of detection. parts per hundred million can be ohtained in areas of lo^ concentrations, 3.885 -,of XanSsOj = 2.62 */ of SO? and higher concentrations can also 1 ) ~ 2 62 -{ of SO, per liter of air = recorded by reversing the ratios of 1 p p.m. at 25" C. sample and reagent flow rates. I n tlw Assuming that all sulfite is available system set up to utilize this method, as sulfur dioxide, a t flow rates of 250 the range of concentrations expected ml. per minute for air, and 3.3 nil. per was from 0 t o 5 p.p.111. of sulfur dioxidv. minute for reagent, the following relaSensitivity of the reagent was checked tions are present to give the concenin the range from 0.01 to 5 y of sulfur tration of standard solution desired: dioxide per ml. of reagent. It was found to be sensitive to x-ariations of 0.002 y 250 ml. X 3.885 y of Sa?S205= of sulfur dioxide per nil. of reagent a t low concentrations. although in the. 0.97 y of ?;a?S20j = higher concentrations, using a 1-inch 1 p.p.m. of SO, in a 250-ml. air sample cell, the sensitivity to variation tended For 3.3 nil. of reagent: to decrease as the liniits of the instrument were approached. The findings of K e s t and Gaeke (11) regarding conformance to Beer's law in the range reagent, which is equivalent to 1 p.p.m. of of 0 to 2.5 y of sulfur dioxide per nil. of SO2 in air at these flow rates reagent m r e confirmed. A stock solution was made to contain The pH of the reagent is critical for 29.4 mg. of sodium pyrosulfite per liter. optimum response. This is believed This was standardized using 0.0LY to be due to the formation of the triiodine. Standard dilutions equivalent hydrochloride of pararosaniline, which to 0.5, 1.0, 2.0, 3.0, 4.0, and 5.0 p.p.m. is more susceptible to substitution than of sulfur dioxide in air were prepared, the mono- or dihydrochlorides. and points on the recorder were checked When sulfur dioxide is dissolved in against previous determinations. ReIvater it produces two forms (tautomers producibility was excellent a t calculated (3) of sulfurous acid-I, a weaker acid flon- ratrs. than 11. SAMPLE METERING
VOL. 30, NO. 1 1 , NOVEMBER 1958
1813
OH
SO, + H20
-+
I S I
=
OH I Weaker arid, reducible
OH 0
+ H+ +
I S- = II
0
0 I1
Stronger acid, oxidizable
As the p H is increased, this reaction shifts to the right. At p H 1, I > 11; a t p H 3. I1 > I : and above p H 7 , there is very litfle, if any, of I present. It is believed that a t pH 1.5 there is more of I present, which is not as readily oxidizable as I1 a t that pH. Thus, interferences resulting from the oxidation of sulfur dioxide by oxidizing substances in the atmosphere are inhibited. There was some deposition of dye on the walls of the contact column due to evaporation. This was not found deleterious and the glassware was easily cleaned by flushing nith 95% ethyl alcohol.
The reagent described has been continuously circulated in the modified Kruger machine for 6 weeks and, with rezeroing of the machine cach time the supply and waste bottles were exchanged, there was no appreciable loss in sensitivity. ACKNOWLEDGMENT
The authors are indebted t o Harold Kruger of Harold Kruger Iiistruments, San Gabriel, Calif., for invaluable assistance in furnishing instrument components and advice in the niodifications of the instrument and for coniparative work in checking sensitivity, specificity, and stability of t h r rcagent described. LITERATURE CITED
(1) Atkins, S., ASAL. CHEJI.22, 947-8 (1950).
(2) Ingole, Robert S., Georgia Institute of Technology, Engineering Experiment Station, Atlanta, Ga., private communication. (3) Kolthoff, I. M.,Miller, G. S., J . A m . Chem. SOC.6 3 , 2818-21 (1941). (4) Kruger, H., Harold Krriger Instruments, San Gabriel, Calif., private .. ....... . ~.. ~ .......
(5) llrKelvey, J. H., Hoelscher, H. E., A S A L . CHEJI. 29, 123 (1957). 16) Moore, G. E.. Cole. -1.F. W., Kate. ( 7 ) 'Paulus, H. J., Floyd, E. P., BJ ers, D. H., i l n i . I n d . Hjjg. .-lssoc. Quart.
15,277-82(1954). (8) Steigniann, .\., .Is.%L. CHETI. 22, 492-3 (1950). ((3) Striemann. -4.. J . Sor. C h ~ n / .I n d . I - -
~
\
-~
(10, Urone, P. F., Boggs, W. E,, SAL. CMEM. 23, 1517-19 (1951). (11) 1Yrs.t. P. IT-.. Gaeke, C;. C., Ihid., 28, 3816-10 ( l W h ) .
RECEIVED for rwien Sovember 2, 1957. Arcepted June 3. 1958. IXvision of Water, Sewage, and Sanitation, Sym~)osiunion Air Pollution, 134th AIeeting, riCS, Chirxgo, Ill., September 1958.
Aromatic Hydrocarbons in the 170" to 180" C. Fraction of Petroleurn BEVERIDGE J. MAIR, SHIRLEY P. DAVIDSON, NED C. KROUSKOP, and FREDERICK D. ROSSlNl Chemical and Petroleum Research laboratory, Carnegie Institute of Technology, Pittsburgh 1 3, Pa.
b Seven hydrocarbons were found to constitute substantially all of the aromatic portion normally boiling between 170" and 180" C. of the representative petroleum which has been under investigation by the American Petroleum Institute Research Project 6. These compounds were individually concentrated by extended use of the fractionating processes of distillation (both regular and azeotropic) and adsorption. Identification of the compounds was made from measurements of the simple physical properiies coupled with infrared spectral examination. The estimated relative amounts of these seven aromatic hydrocarbons are as follows: lI2,3-tri1 -methyl-3methylbenzene, 54.5%; isopropylbenzene, 22.6y0; 1 -methyl44sopropylbenzene, 12.1 %; sec-butylbenzene, 5.0%; 1 -methyl-2-isopropylbenzene, 2.5%; isobutylbenzene, 2.4%; and indan, 0.9%. These seven compounds together constitute 0.35% of the original petroleum.
analysis of the hydrocarbons in the aromatic portion of this petroleum normally boiling in the range from 170" t o 180" C. has been completed. M E T H O D OF ANALYSIS
Two lots of aromatic material, 170" to 180' C., w r e available. Lot I came from previous work in which a relatively small sample (about 6 liters) of thr naphtha fraction of this p~troleum was separated by adsorption with silica gel to give two portions: an aromatic and a paraffin-ryclo portion. The aromatic portion \vas distilled and the niaterial boiling in the rangc from 170" to 180" C. was combined t o constitute Lot I. From these data. tht. aromatic portion from 170" to 180' C. was found to constitute 0.357, of the entire petroleum. Drtails of the foregoing operations have becn given ( I ) ; and Lot I is identical with Lot V of the Ponca petroleum describpd previously. The relative amounts of the individual constituents n-ere detrrmined from infrared measurements on a part of the s PART of the continuing work of entire lot. the American Petroleum Institute Lct I1 was produced by combining Research Project 6 on the composition into one portion all of the aromatic of its representative petroleum (4, material, exccpt for a small sample of
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ANALYTICAL CHEMISTRY
1.2,3-trimethylbenzene, remaining in t,he desired range from previous work on a large samplc of petroleuni ( 8 ) . Small amount's of nonaromatic constituents were rcniovcd from this material by adsorption n-ith silica gel. Tlic purr aromatic portion was distilled to obtain in one lot all of the aromatic hydrocarbons normally boiling in the rang(' from 170" to 180' C . The data of this distillat,ion arc givc,n in FigurP 1, which shows the location with rpspect t o boiling point aurl refractive index of the compounds found in this material. The first pcrt'ion of the distillatc consisted largely of 1,2,4trimethylbenzene, which boiled below 170" C., and thrx portion near the tail end consisted largely of 1,3-dieth!.lbenzene and I-mcthyl-3-propylbenzene (m-cynirne). both of which boil a b o w 180" C. T h t ~prment analysis does not include thme thwe compounds; 1,2,4triinetIiylb(.iizcne is covered in an analysis of the atljacrnt, loncr boiling portion ( 3 ) . Further processing of this material by distillation '(regular or azeotropic) or by adsorption was designed t o concentrate the individual hydrocarbons for positive identification. The relative amounts of the individual compounds
