The absorptivity a t 2550 A. was then measured using a Beckman ultraviolet spectrophotometcr. The value obtained was 16.8 mm.-l meter-' which agrces adcquntcly with the value of 16.7 mm.-l metcr-1 obtained by Inn and Tan:tka (S). In each of these ultrrtviolet determinntions, the ozone WRR introduced simultaneously into the infrarcd ccll and in each case the infrared absorptivity agreed with that listed in Table 11. COMPARISON WITH ULTRAVIOLET PHOTOMETER
The ozone calibration was also compared with the values indicated by an ultraviolet ozone photometer made by Harold Kruger Instruments Co., San Gabriel, Calif. For this comparison, air was continuously passed through the long-path cell a t several hundred liters per minute along with a flow of ozonized oxygen sufficient to maintain a steady concentration of ozone. The ultraviolet photometer was used to monitor the effluent, so that simul-
taneous readings could be obtained by the two methods on the same gaa mixture. The ultraviolet instrument had previously been calibrated by the builder, using an ozone stream whose concentration was measured with potassium iodide. The ozone concentrations indicated by the two instruments were in good agreement, as indicated by the data in Table 111. This implies that the particular potassium iodide method used to calibrate the ultraviolet photometer was valid. AIR ANALYSIS
The long-path method described here was used to measure the ozone concentrations found in so-called photochemical air pollution. Such concentrations are typically in the range of a few tenths of 1 p.p.m. (v./v.) and can be readily identified and measured with the long-path technique. These results are reported in detail elsewhere ( 4 ) . From the shape of the ozone band observed for the atmospheric samples it WLM~concluded that there were no important interferences from other compounds in
these samples. If methanol were present in appreciable concentration, for example, it would overlap the 9.6-micron ozone band but would be readily identifiable by the chracteristic Q branch of this band. ACKNOWLEDGMENT
The authors are grateful to the Smoke and Fumes Committee, Division of Refining, American Petroleum Institute, for its generous support and to the members of Project Advisory Committee VI for valuable advice and encouragement. LITERATURE CITED
(I) Birdsall, C. M., Jenkins, A. D.,
Spadinger, E., ANAL. CHEM.24, 662 (19.52'). \ - - - -
(2) Inn,'.E. C. Y.,Tanaka, Y., J. O p t . SOC.Am. 93,870(1953). (3) Renzetti, .N. A., Advances in Chem. Ser., No.21,230 (1959). (41 Scott. W.E..Steuhens. E. R.. He.nEt,. P. L., Doerr, k. Prbc. Am: Petrol: Znst. 37, Sect. 111, 171 (1957). \
,
e.,
RECEIVEDfor review Soptember 12, 1960. Accepted April 17, 1961.
Sodium Diphenylaminesulfonate as an Analytical Reagent for Ozone H. H. BOVEE' and REX J. ROBINSON Department o f Chemistry, University o f Washington, Seattle 5, Wash.
b Sodium diphenylaminesulfonate, selected as an analytical reagent for the determination of ozone, reacts with ozone to form a turquoise blue product with an absorption maximum at 593 mp. The reagent has been tested under various conditions to determine the effects of pH, temperature, concentration, type of sampling equipment, and rate of sample flow on its. reaction efficiency. The effects of nitrogen dioxide, chlorine, hydrogen peroxide, and other interferences have been investigated. An analytical procedure using 1% sodium diphenylaminesulfonate in 0.02% perchloric acid solution has been developed and tested for precision. It gave satisfactory results when. fleld tested with ozone formed by inert gas-shielded welding arcs and by an electrostatic &precipitator.
T
HE determination of trace concentrations of ozone in air in the presence of the oxidizing gases has long been recognized as difficult. The ozone analytical methods in general use today are nonspecific and
often of insufficient sensitivity for work in the industrial hygiene and air pollution fields. Potassium iodide reagents, although widely used for ozone determination, have been especially vulnerable to the effects of interferences. Neutral, buffered, and alkaline potassium iodide are the preferred absorption reagents, but when the released iodine is measured by a titrimetric procedure, the sensitivity is relatively low. With measurement of the released iodine by colorimetric procedures, sensitivity is increased to a satisfactory level. The use of traps to remove potential interferences has not been very successful. None of the traps tested was 100% efficient in removing the interference and all absorbed a t least a part of the ozone. Since the amount of ozone available for measurement is normally very small, even partial absorbance in a trap could critically affect the result. For this reason traps should be avoided whenever possible. Many other chemical and physical methods for ozone measurement have been proposed but have not gained wide acceptance. Thorp (IO), in his ozone
bibliography, gives an excellent summary of ozone methods prior to 1954. Since 1954 several papers have proposed new approaches to the ozone determination problem. Among these is the phenolphthalin oxidation reaction described by HaagenSmit and Brunelle (6), the long-path ultraviolet absorption equipment of Renzetti (6), and the nitrogen dioxide equivalent method of Saltzman and Gilbert (7). I n the research reported here sodium diphenylaminesulfonate (NaDS) was chosen for investigation as an analytical reagent for ozone, after a number of organic compounds were screened for optimum analytical properties. Because its oxidation potential (- 0.85 volt) is appreciably more negative than iodide's (-0.69 volt), i t is less susceptible to oxidative interference than iodide. Further, when interfering reactions do take place, specific colors are formed which differ from the color obtained with ozone. This not only enables the analyst to recogI Present address, Boeing Airplane Co., Seattle 24, Wash.
VOL. 33, NO. 8, JULY 1961
1 115
1.2s
-
-
-
-
1.00
0,7s0
I
9m 0.104
-
0.25-
0.00-
I
1
I
-
WAVE. LEHQTH, rn#
Figure 1. Absorption curves for NODS reagent and ozone oxidation product 1 0.2y0 NaDS In 0.02% HClOl Ii.
NaDS reagent plus ozone
nize the occurrence of other reactions and possibly to identify them, but also permits spectrophotometric measurement of the blue color due to ozone a t wave length 593 mp with reduced interference from other gases. EXPERIMENTAL
Procedure. Place 10 ml. of reagent (1% NaDS in 0.02% HClO, solution) in a midget im inger (Ace Catalog No. 7531) a n 8 pass the sample through a t the rate of 2.83 liters per minute (0.1 cubic foot per minute) for 10 minutes or until satisfactory color has developed. Replace any evaporation loss by diluting to 10 ml. with distilled water and measure the color density a t 593 m r with a Beckman DU spectrophotometer. Determine the quantity of ozone by comparison with a calibration curve. Reagent Characteristics. NaDS dissolves readily in water t o give a colorless solution which is stable for several weeks. Ozone reacts with NaDS to give a turquoise blue color with maximum absorption at 593 mp.
U u
5
0.09
m
-
a 0
m
0.03-
&"
Figure 2. Effect of pH on development of ozone absorption peak at 593 mp
11 16
ANALYTICAL CHEMISTRY
The spectral curves of the reaction product and reagent are compared in Figure 1. The reagent does not develop its characteristic blue color with ozone when in neutral or basic solution. Optimum results are obtained a t a pH of about 3, as indicated in Figure 2. The stability of the colored product is somewhat temperaturedependent. At temperatures approaching 0' C. i t is stable for days, but a t room temperature there is a slow decrease in density with lapse of time. Samples should be read within 2 or 3 hours or refrigerated until measurement can be made. Calibration Curves. The calibration curves shown in Figure 3 were constructed from data obtained by reacting varying amounts of ozone with NaDS reagent and are typical. An ozone generator was constructed from a small ultraviolet lamp, GE OZ4S11, mounted in a flask with a paraffin seal. About 10 mg. per minute of ozone was formed in air p w e d over the lamp, when the current through the lamp was at the recommended maximum of 350 ma. The rate of ozone formation could be reduced by decreasing the current or increased by using a pure oxygen gtream. In Figure 4 is diagrammed the ozone generation and sampling equipment used in this study. The ozone generator was standardized by measuring the output with a neutral potaasium iodide method according to the procedure of Goldman and Jacobs (4). Since ozone quantity is directly proportional to time, the amount in the samples can be adjusted to any desired level. If i t is impractical to set up an ozone generator with calibration in the above manner, calibration curves as shown in Figure 3 may be used. These curves exhibit some nonlinearity, indicating that Beer's law is not followed exactly. The variance appears to be caused by the slight inst,ability of the colorimetric product during the sampling and postsampling period. The slope of the curve for the 75-mm. cell is 227 gg. of ozone per absorbance unit in the important range between 0.0 and 0.1 p.p.m. Similarly, for the 10mm. cell the slope is 30 pg. of ozone per absorbance unit. The molar absorptivity is 2100 for both cells. The validity of the calibration curves and efficacy of the reagent can be confirmed by running duplicate analyses by both the iodide and NaDS methods. Increasing Sensitivity. For measurement of ozone concentrations in air of less than 0.1 p.p.m. i t was found desirable to increase the sensitivity of the method. This was accomplished by employing a long-path light cell in the spectrophotometer. A cell 8 mm. wide, 15
PP.M. OF OZONE
0.0 10 ao M I C R O Q R A M S OF OZONC
0
Figure 3. Calibration curves for ozone absorbed by mtdget impinger Top scale. P.p.m. ozone for 10-minute acale (28.3Ilters)
mm. deep and 75 mm. long with optical Ius windows waa found to work aatis!actonly with 10-ml. a m p l e volumes and incressed the sensitivlty approximately 7.5-fold as compared to the atandard 10-mm. Corex cell. Special adaptors to accommodate long cells can be obtained commercially or can be fsbricated locally to modify the Beckman DU. Interferences. I n the presence of nitrogen dioxide NaDS develops a yellow-green color. With chlorine, a violet solution is obtained. Hydrogen peroxide gives a similar violet coloration, which is slow to develop. Sulfur dioxide in excess gives a bright
F
/7
IUI
K
L
M
N
A
Figure 4. Ozone sampling equipment A.
B. C. D. E.
F. G. H. 1.
J.
K. 1.
M. N.
generation and
Ozone cyHnder Pressure regulator Alr Inlet Flowmeter Drying cdumn Ozonelamp Three-way stopcock Sampling flask Bypass trap Suction pump Milliammeter 300-ohm realatonce Varlable redstance Voltage regulator
yellow solution. The characteristic blue color formed by ozone is easily recognized after some experience with the method. Sinre nitrogcn dioxide is frequently found in conjunction with ozone, its intrrferpncc effect was measured on thrcc reiigcnts: neutral potassium iodide, alkaline potassium iodide, and NaDS. The relative drgree of interferenrc is shown in Figure 5. Interference with the NaDS reagcnt is less than one half the effect on alkaline potassium iodide and only one fourth that obtained with the neutral potassium iodide reagent. PRECISION AND ACCURACY
Despite the large number of articles on ozone measurement, there is a paucity of precision data in the literature. Boelter, Putnam, and Lash (2) invcstigated the effect of p H on the measurement of ozone concentrations from 91 to 270 mg. per liter, and considered variations of +5 to -4% in the results within experimental error. Birdsall, Jenkins, and Spadinger (1) measured from 3 to 25 volume % of ozone with a standard deviation of error equal to 1.4Oj,. Wadelin (If) gives data for amperometric titration of several samples of about 0.2 p.p.m. of ozone with a standard deviation equal to 0.0146 p.p.m. or approximately 0.7%. The precision of the NaDS method was determined by bringing the ozone generator to an equilibrium state of output and making a series of duplicate runs. Data for the midget impinger are shown in Table I. At the present time the absolute accuracy of this or any method for ozone determination cannot be determined, since there is no way to obtain an accurately known amount of ozone a t a suitable concentration. Most analytical methods for ozone determination are based directly or indirectly on the reaction with potassium iodide to form free iodine. Similarly, the NaDS method depends on the calibration of an ozone generator with potassium iodide. The accuracy of the NaDS method is, therefore, directly related to the accuracy of the potassium iodide method, the generally accepted standard. FIELD TESTS
I t was desirable to compare the NaDS method with the commonly used neutral KI ( 4 ) and alkaline KI (3) methods as applied to field tests. A Gast suction pump was connected with three midget impingers in parallel (one for each method). The test sample was introduced through a common manifold. A series of tests was run on ozone
Table
I. Precision Data Obtained with Midget lmpinger
10-Mm. Cell Absorbance 6eviation 0.119 0 0011 0 120 0 OOO1 0,119 0.0011 0.120 0,0001
75-Mm. Cell
Absorbance Deviation
0 883 0 893 0.873 0.873
0 12cI 0.0001 0 888
o.iii O.ooO9 O.SS3 0.121 0.120 0.120 0.121
PER
IO ML. SAMPLINQ REAQENT
Figure 5. interference by nitrogen dioxide in terms of ozone 1. Neutral KI II. Alkaline KI 111. NaDS
formed by an electrostatic precipitator. Ozone WM formed by silent electrical discharge and forced out the back of the instrument by a small fan. The results of these tests are shown in Table 11. The quantity of ozone waa varied by increasing the sampling t i e while the concentration remained constant, The somewhat lower results obtained with the alkaline K I method were expected, in view of other findings (3, 8, 9). The NaDS results and the neutral KI results are in good agreement. One of the major ozone hazards encountered in industrial hygiene practice is found in the vicinity of inert gaashielded welding arcs. An opportunity arose to take samples near an automatic Heliarc welding machine, employed to weld stainless steel tanks using helium to shield the molten metal from air oxidation. A series of 10minute tests was taken a t different distances from the arc to obtain a wide range of ozone concentration (Table 11). Again, the agreement between the NaDS results and the neutral K I results is very good. Although the field testing has been somewhat limited in scope, i t appears that the NaDS method is a satisfactorily accurate and consistent procedure for the measurement of ozone. DISCUSSION
The average deviations obtained in this work using the NaDS method varied from 0.45 to 0.77% for different measurement cells. This degree of precision compares favorably with the available data of other workers and is ample for the purposes for which the method was designed.
0.0009 0.0001 O.OOO1 O.OOO9
0.883 0.873 0.868 0.883
0 0030 0 0130 0.0090 0.0070 0.0080 0.0030 0.0030 0.0070 0.0120 0.0030
Av. 0.1201 0.00054 0.8800 0.0068 Av. dev., % 0.45 0.77 Wave length. 593 mp Reagent. 10 ml. of 1.0% NaDS 0.02% HClO, solutiqn. Oeone sample. 2.83.1iters per minute of air for 3 minutes a t 350-ma. current. Table II. Comparison of Analytical Methods Using Ozone Formed by Two Different Sources
Electrostatic Inert Gas-Shielded Precipitator Welding Arc 08, Os, Os, 011 pg. p.p.m. fig. p.p.m. NaDS R - . -8 20.8
32.0 42.0
NaDS _1 . _8
1.9 1.9 1.9
Neutral KI 10.1 22.1 31.7
42.2
1.8
2.0
1.9 1.9
0.8
4.3
10.4 17.6 33.2
0.01
0.08 0.17
0.36
0.60
Neutral KI 1.2 4.2 10.4 17.9 36.2
0.02 0.08 0.17 0.37 0.65
Alkaline KI 8.6 19.0 29.0 40.4
1.5 1.7 1.7 1.8
The oxidieing agents which interfere with the ozone determination have their maximum absorptions at wave lengths other than 593 mp. For example, the absorption peaks for nitrogen dioxide, chlorine, and hydrogen peroxide are at 410,555, and 575 mp, respectively. Interference from these sources can be minimized by the use of a narrowband spectrophotometer. The colors developed by interfering gases range from yellow to violet and are visually distinguishable from the turquoise blue formed by ozone. This color cue indicates both the presence of an interference and the specific cause. Development of the typical ozone color shows the absence of significant interference, and also serves as a visual guide to proper sampling time. VOL. 33, NO. 8, JULY 1961
1 117
ACKNOWLEDGMENT
The authors express appreciation to the Environmental Research Laboratory, University of Washington, and its former director, Ross N. Kusian, for the loan of special equipment. LITERATURE CITED
(1) Birdsall, C. M., Jenkins, A. C. Spadinger, E., ANAL. CHEM.24, 662-4 (1962). ,- - -- ,. (2) Boelter, E. D., Putnam, G. L., Lash, E. I., Zbid., 22,1533-5 (1950).
(3) Byers, D. H., Saltzman, B. E., Am. Znd. H y g. Assoc. J . 19,251-7 (1958). (4) Goldman, F. H., Jacobs, M. B.
“Chemical Methods in Industrial Hygiene,” pp. 104-5, Interscience, New York, 1953. (5) Haagen-Smit, A. J., Brunelle, M. J.,
J. Air Pollution 1,51-9 (1958). (6) Renzetti, N. A,, ANAL. CHEM.29, 869-74 (1957). (7) Saltzman, B. E., Gilbert, N., Am. Znd. Hug. ASSOC. J . 20,379-86 (1959). (8) Smith, R. G., Diamond, P., Am. Znd. Hy g. Assoc. Quart. 13,235-8 (1952). (9) Storlazzi, M., Bovee, H. H., “Design
of Referee Method for the Determina-
tion of Trace Concentration of Ozone in Air,” p . 8-11, Environmental Research Laporatory, Dept. of Publie Health and Preventive Medicine, University of Washington, Senttle, Wash.,
1955. (10) Thorp, C. E., “Bibliogrnphy of Ozone Technology,”‘Vol. I, Armour Research Foundation, Chicago 16, Ill., 1954. (11) Wadelin, C. W., ANAL. CHEM.29, 441-2 (1957).
RECEIVED for review November 14 1960. Accepted April 5, 1961. Research s u p orted in part by a grant, AT 57-20?, &om the U. S. Public Health Service.
Spot Tests Based on Redox Reactions with Devarda’s Alloy and Raney Alloy FRITZ FEIGL laboraforio da Product30 Mineral, MinistGrio da Agriculfura, Rio de Janeiro, Brazil Translated by RALPH E. OESPER, University of Cincinnati Reductive cleavages of various organic compounds can be accomplished by a wet method using Devarda’s alloy or nickel-aluminum a l k y (Raney alloy). These reactions are due to the action of nascent hydrogen or nickel hydride. Raney nickel, formed by the activation of Raney alloy, is shown to be the more powerful reductant. Analytical applications of the redox reactions with Devarda’s alloy or Raney alloy can be achieved if products are formed which may be detected directly or indirectly in the gas phase. In this way it was possible to develop new tests for: benzonitrile, tribromoaniline, arylsulfinic, arylsulfonic, aminophenylarsonic, and stibinic acids, sulfanilic acid and its derivatives, phenylhydrazine (hydrazones, osazones), pyridine, aromatic sulfones, and Raney alloy. All of these tests can be carried out successfully by spot test analysis and they have microanalytical limits of identification. REPORT (a) announced that certain organic compounds undergo hitherto unreported reductive cleavages if their aqueous alkaline solutions were treated with nickel aluminum alloy (Rrtney alloy, Murex, Ltd., London). The resulting Raney nickel acts, through its content of nickel hydride, as a powerful hydrogen donor. Application of these findings, together with comparison studies of the action of Devarda’s alloy in alkaline or acid surroundings, led to the new and selective tests described here.
A
DETECTION METHODS
Benzonitrile, by Reductlon to Benzylamine. The action ,of, metallic
sodium on alcohol solutions t o yield the corresponding primary amines from nitriles has already been used for preparation purposes (18). Accordingly, benzylamine can be prepared by this procedure from bemonitrile (phenyl cyanide) : CsHrCN
+ 4H
O .-L
C‘HICH~NHS (1)
The benzylamine condenses with sodium l ,%naphthoquinone4sulfonate to give a quinoidal brown-violet product
(9,11): 0
&OsNa 0
PRELIMINARY
11 18
0
ANALYTICAL CHEMISTRY
The sulfurous acid resulting from this and analogous reactions of the sulfonate with compounds bearing active CHs- and “2groups cannot be detected, as it reduces the reagent to 1,2-naphthol-4sulfonic acid (14). The hydrogenation (Equation 1) proceeds rapidly if the solution of benzonitrile is warmed along with Devarda’s alloy or Raney alloy; the resulting benzylamine is carried along with the water vapors and can be detected in the
gas phase by the color reaction, Equation 2. Consequently, a far-reaching sensitive test for benzonitrile could be developed on this basis, assuming the absence or the formation of bases that are volatile with water vapor and that enter into condensation reactions analogous to Equation 2 with sodium 1,s naphthoquinone-4-sulfonate. Such interfering compounds include: aniline, tolidine, naphthylamine, nitro-, chloro-, and bromoaniline, and piperidine ( 4 ) . If the possible presence of such materials must be taken into account, a preliminary separation from the benzonitrile is essential. The test solution should be acidified with dilute sulfuric acid and shaken with ether. The interfering bases remain in the water layer as sulfates, and the ether extract can then be tested for benzonitrile. Procedure. A micro test tube ia used. One drop of the alcohol or ether solution is mixed with 1 drop of 5% caustic alkali solution, and several milligrams of Devarda’s alloy are added. The suspension is warmed cautiously until the vigorous evolution of hydrogen has subsided. The mouth of the test tube is then covered with a piece of filter paper moistened with a freshly prepared 0.5% water solution of sodium 1,2-naphthoquinone4sulfonate. The test tube is then placed in a boiling water bath. A positive response is indicated by the development of a brown-violet stain on the reagent paper within a few minutes. Limit of identification: 3 pg. of benzonitrile. Tribromoaniline, by Conversioninto Aniline. Tribromoaniline, which is readily obtained by bromination of aniline or acidic aniline salt solutions,
