Rapid Detection of Aniline Vapors in Air WILBUR A. RIEHL and KARL F. HAGER’ Ordnance Missile Laboratories, Redstone Arsenal, Huntsville, A l a .
Aniline vapor in concentrations above 5 p.p.m. (by volume) in air is known to be toxic. Current applications of aniline made it imperative that a fast and simple field method be developed. The concentration ’of aniline vapor in the air can be determined easily and rapidly by use of paper strips impregnated with the liquid or vapor of a furfural-acetic acid mixture (49& by volume, in glacial acetic acid). The test paper turns from white to pink or red in the presence of aniline vapor, having a range of determination from 5 to approximately I50 p.p.m. The speed and intensity of color development increases with the concentration of aniline vapors. The test is specific for aniline in the presence of many other organic vapors. The reagent mixture has a life of at least 1 month at room temperature.
0
RGANIC amines, such as aniline and its homologs, are known to be poisonouq in both the liquid and vapor phasese.g., concentrations higher than 5 p.p.m. (by volume) of aniline should be avoided in working areas ( 3 , 4,6-8). A rapid and extremely simple field method of analysis of aniline vapor in this concentration range is not available. The method probably in most common use is the official British method ( 1 ) . -4known volume of air has to be drawn through an acid solution and this solution subsequently analyzed using standard colorimetric techniques. Recommended spot test methods also require the presence of a liquid phase, and thus also require absorption of the vapors in a liquid. It has been found that the approximate concentration of aniline vapor in the atmosphere can be detected rapidly by use of paper strips impregnated with the liquid or vapor of a furfural-acetic acid mixture (4%, by volume, in glacial acetic acid). The test is based upon the rondensation to colored Schiff bases, as follon-s:
reagent mixture charge in the lower end and close tight with cork covered with aluminum foil. .411ow to stand for a t least 15 minutes before use. SENSITIVITY
The effect of aniline concentrations from 1 to I55 p,p.m. was determined by use of known samples. h 20-liter glass jug was used as a test chamber, into which known amounts of aniline were added and allowed to evaporate. Concentrations of aniline were calculated by use of JIg./liter
=
p,p.m, (by volume) (8, 6)
.If = molecular weight 7‘ = temperature in K. P = pressure in millimeters O
Assuming st.andard temperature and pressure, 20 liters of a 5 p.p.m. solution of aniline in air will then contain 0.38 mg. of aniline.
Table I. Effect of Aniline Vapors on Furfural-Acetic Acid Strips Concn. P.P,M.’ (Vol. ) 0 1
Exposure, I f i n . First Definitr formation COlOl
..
10 12
.. ..
10
5
t i
4
8 5
G
s.5
8
Relatir e Intensity S o observable change No observable change Pale pink
J
4 . .5
10
2 3
3 5
2.75
The prepared strips turn pink to red in the presence of aniline vapors, having a lower limit of detection a t about 5 p.p,m, The speed and intensity of color development increases. with the concentration of aniline vapors. REAGEXTS AND EQUIPMENT
15
60 G1
20
60 85
110
li
30
111
1.5
30 45
15.5
20 5
4;
5 10 60 110 155
PROCEDURE
60 30
35
Concn., P.P.M. 1
Pink
Sec.
55
Table 11.
Furfural, technical Glacial acetic acid Silica gel, 6 to 16 mesh Filter paper strips. 115 X 5 mm. Glass tube, approximately 178 X 25 mni. outside diameter. Perforated porcelain disk, approximately 20 mm.
Present address, Curtiss-Wright Plastics Division, Carlstadt. S . .J
10-3
where
Schiff base
Preparation of Reagent Mixture. Dilute 2 ml. of techniral grade furfural to 50 ml. in a volumetric flask with glacial acetic acid. Saturate approximately 13 grams of silica gel with this solution and drain off excess liquid for 3 to 5 minutes. Preparation of Tube and Strips. Constrict a glass tube (28 mm. outside diameter), approximately 178 mm. long, with four indentations 76 mm. from one end. Cut about two dozen stripe of filter paper (115 X 5 mm.) and fasten to cork by means of masking tape. Insert strips and cork into long end of tube Place perforated porceIain disk in position on short end. Place the
.lIP/i” X 1.61 X
15
Red
Deep red
D
Sensitivity of Furfural-Acetic Acid Strips Exposure, I’irit Formation t o Definite Color 10 min. 5 t o 8 min. 3 t o 5 inin. 30 t o 60 s e c . 15 t o 45 s e c . 5 to 45 sec.
Relative Intensity No observable change Pale pink Pink-red Red Deep red
A standard solution was prepared flesh daily by diluting 1.9 nil. (approximately 1.9 grams) of aniline to 500 ml. with acetone. Each milliliter of the latter solution when evaporated in the 20liter chamber then gave 5 p.p.m. of aniline. Upon addition of the standard solution the chamber was stoppered, inverted for 2 minutes, and shaken to miu the aniline vapor into the air. A test paper was then suspended from the stopper by use of masking tape so that it hung about one third from the bottom (to allow for the fact that aniline vapor is over three
1768
V O L U M E 27, N O . 11, N O V E M B E R 1 9 5 5 times heavier than air). Times were then noted a t which the color first formed and when it. became prominent. The relative intensity wax also estimated. Results are shown in Table I. Although the results are not so nearly reproducible as customarily expect.ed, or desired, for an ordinary quantitative method, they are quite satisfactory to serve &R a basis for a semiquantitative determination, or an ereeptiondy good estimation. Times and colors of normally expected results are listed in Table 11.
1769
It is necessary only to remove a strip of paper from the tube, and expose it to the air in question for 1 t o 10 minutes. The ooncentration may be estimated from the time necessary for development of a definite color. However, it would be preferable to compare the color obtained in a IO-minute exposure with those of standards.
SPECIFICITY
Na observable change of the test strips occurred in a 10-minute exposure to the vapors of the substances listed in the left-hand column of Table 111. All tests were made by suspending the strips from the cap of earh reagent bottle without direct contact with the reagent itself. Frehden and Goldschmidt reported results obtained with over 50 amines (8). In only a few cases was no coloration obtained. However, those authors' tests were made in solution rather than e ~was necessary to h a t to the vapor phase, and in most c a ~ it dryness.
Figure 1. Aniline test kit ready for use
STABILITY
Since acids catalyze the palycandens: S expected that t.he reagent, mixture shauia m e 1x8 enec~iiveness within a short time. Tests were made to determine the storage life of the furfural-acetic acid strips a t room and elevated (74" C.) temperatures. Using 10-minute exposures a t 5 p.p.m. it was found that after 30 to 34 days at. room temperature the strips failed to give an easily distinguishable color. The strips stored at 74" C. began to fail after only 12 to 13 days. Thus, storage in a cool location will lengthen the life of tho papers considerably.
7I O I $ 0
I
Figure 2.
Schematic diagram of prepared tube
Table 111. Specificity of Furfural-Acetic Acid Stripe (Io-minute expm"re to "spore
No Observable
Weak Color
Change Furiuryl alcohol
positive Color
Hydrsaine, Q5% Red fuming Whiteiuminp nitnoaoid Concentrated} ,' ' ' Hydrogen peroxide. 76% Ethyl alcohol Kerosine m-Nitroaniline
C"Nitroa"i1ine
PArninophenol nlminophenoi 2.4.6-Tribiomoaniiine Sulfaniiie acid
(
pNitrosniline (,".."..,
--:-",....".I..:"
Reagents required are inexpensive and readily available. The range of determination appears t o be 5 to 150 p.p,m, This is fortuitous, inasmuch as the maximum allowable concentration in air is 5 p.p.m. and above 100 to 150 p . p m the toxic symptoms are serious (S,8,7). Further, the test is specific for aniline in the presence of other vapors such a8 indicated in Table 111. In daily use at ambient temperature the reagent mixture has a life of a t least 1 month, and may be replaced by a fresh charge, if desired.
o-Aminophenol (purple) p-Bromoaniline (purple)
/__^_I
pAnisidine (mspenta) _ _ I ,
ACKNOWLEDGMENT
TIhe authors are indebted to the Ordnance Corps of the U. S. Arm y for permission to publish this study, and to John R. Nunne&:yand David Watson for their assistance in the experimental WOd
LITERATURE CITED
However, when the kit remained closed a t ambient temperture for 16 months, the limit of detection increased to only 25 p.p.m. At 100 p.p.m. a pink color then formed within 3 minutes. The pink to red color formed on the strips is not fast, and fades within several hours, even when sealed under nitrogen. CONCLUSIONS
This device offers an easily portable, pocket size method for the qualitative and semiquantitative determination of aniline vapors in the atmosphere. The procedure is extremely simple and rapid.
k p t . Sci. I d . Research @?it.), Leaflet No. 11 (1939). Srehden. O.,and Goldschmidt. L., Mikrochim. Acta. 1,388 (1937). 'weobs, M. B.,"Andytiod Chemistry of Poisons, Hazards. and So1vent.s."2nd ed., vol. 1, pp. 76,709, 760, Interscience, New York. 1949. hdnsnoe Corps, Dept. of the Army, "Ordnan,ce Safety Manual," ORD-M 7-224, 15-19 (1951). 'rentiss, A. M., "Chemicals in War." p. 701, McGraw-Hill, New York. 1937.
lumpel, W.. Mitt. C h m . Fmsch.-lnsts. I d . &err.,
4, 113-17 (1950). lax, N. I., "Handbook of Dangerous hhterials." p. 25. Reinhold. New York, 1951. layers. R. R., "International Critioal Tables," vol. 2, p. 318. MoGraw-Hill, New York, 1927. IYED
ior review February 21, 1955. Aooepted July 28, 1955
