small volumes of titrant. When the hydrogenation of P-4000 was attempted in the Hydro-Analyzer, no uptake of hydrogen was measured, indicating much less unsaturation than in P-2000. Because of the non-availability of polyoxypropylene glycols which contain “known” amounts of unsaturation, two polyoxyalkylene allyl ethers of average molecular weights 580 and 2340 were synthesized by NaOH catalyzed addition of either ethylene oxide (EtO) of mixture of ethylene oxide and propylene oxide ( P r o ) t o allyl alcohol. Two-milliliter ali-
quots of these reaction mixtures, which were not purified by water washing, vacuum stripping, etc., were hydrogenated with the results presented in Table IV. The fairly good agreement between the calculated and measured amounts of unsaturation in these four oxyalkylate samples is evidence for the validity of the CH3COOH-modified hydrogenation procedure even in the presence of NaOH catalyst and reaction by-products. RECEIVED for review May 18,1971. Accepted July 19,1971
Effect of Inlet Residence Time on Analysis of Atmospheric Nitrogen Oxides and Ozone Samuel S. Butcher’ Department of Chemistry, Bowdoin College, Brunswick, Me. 04011
Ronald E. Ruff Department of Cicil Engineering, Unicersity of Washington, Seattle, Wash. 98105 OZONE,NITRIC OXIDE, AND NITROGEN DIOXIDE have been recognized as components of photochemical smog. The concentrations of these substances are monitored by many control agencies using a variety of instrument systems. The reaction between ozone and nitric oxide is sufficiently rapid that a change of light intensity in the instrument inlet prior t o chemical analysis can give rise to a systematic error. The magnitude of the error depends o n the residence time in the inlet; significant errors can occur for a residence time of 10 seconds.
Table I. Rate Constants for 25 “C,One Atmosphere Reference ki k? k .i k; ks
ki; ks ki
0-25 hr-1 8.9 X ppm-2 hr-‘ 1320 ppm-lhr-l 4 . 5 x 10-8 ppm-? hr-l 0.19 ppm-’hr-l (ethylene) 38 ppm-’hr-1 (trn/rs-butene-2) 1 . 3 x 10-7 ppm-1hr-I (methane) 6.25 ppm-’1ir-l
(1)
(2) (3) (2)
(4) (4) (5) (6.)
CALCULATIONS AND DISCUSSION
The importance of the light intensity is determining the relationship between the concentrations of NO, NO2, and 0 3 in the atmosphere has been discussed by Leighton ( I ) and more recently by Schuck and Stephens ( 2 ) . The fastest reactions for this system in the presence of sunlight are listed below.
+0
ki
(1)
O+02+M+03+M
kz
(2)
ka
(3)
NO2
0 3
+
/IV + N O
+ NO
+
NO2
+
0 2
If the concentration of oxygen atoms reaches a steady state, the rate expression for N O is given by d(NO)/dt = kl(NO9) k3(NO)(Os). Since, in the presence of sunlight, the two terms o n the right hand side of this equation are much larger than d(NO)/dt, we have, to a fair degree of approximation, (NO)(03)/(NOz) = k l / k 3 . If the light intensity decreases suddenly, as when the sample enters the analytical system inlet, reaction 1 is no longer important and the N O and 0 3
concentrations decrease because of reaction 3. The actual rate of change will depend on a large number of factors including the magnitude of the light intensity change in the action spectrum of NO, and the concentrations of other atmospheric constituents. Some of the other reactions which should be considered are listed below.
+ Reactants Products 2 N 0 + 02 2NOz O3 + Hydrocarbons Products O 3 + NOz NO;, + O2 0
(4 1
+
+
+
+
ks
(5)
ke
(6)
kq
(7)
Values for the rate constants (1-6) are collected in Table I for 25 “C, 1 atmosphere pressure. Under most conditions, reactions 4, 5, 6, and 7 are too slow to be of importance for the expected residence times; these reactions will be neglected in the present analysis. We shall also assume that the light intensity drops to zero for a period of time (equal to the
Visiting Scholar, University of Washington, 1970-71 (3) M. A. A. Clvne. B. A. Thrush. and R. P. Wayne, Trcms. Frrrnd~iy Soc., 60, 359 i1964). (4) J. J. Bufalin! and A. P. Altshuller, C N I I J. . Clicrn., 43, 2243 (1965). (5) F. J. Dillemuth. D. R. Skidmore, and C. C. Schubert. J . Phys. C h m . , 64, 1496 (1960). (6) H. S. Johnston and D. M. Yoct, J . Chem. Pliys., 17, 386 (1949). \
(1) P. A. Leighton, “The Photochemistry of Air Pollution,” Academic Press, New York, N.Y., 1961. (2) E. A. Schuck aad E. R. Stephens in “Advances in Environmental Sciences and Technology, Vol. I,” J. N. Pitts and R . L. Metcalf, Ed., Wiley-Interscience, New York, N.Y., 1969. 1890
,
ANALYTICAL CHEMISTRY, VOL. 43, NO. 13, NOVEMBER 1971
am
No, w m
NO, w m
Figure 1.
~ 1 0 7 ~ , time ~ 0 ,
required for a 10% error in (NO)
Figure 3. A(N02), amount of NO2 formed in 10 seconds Y azo-
TIME OF DAY
Figure 4. Effect of a 10-second residence time on observed concentrations Heavy lines, measured concentrations; light lines, calculated atmospheric concentrations NO,
Figure 2.
710%,,oa,time
wm
required for a 10% error in (03)
residence time of the inlet system) before the concentrations of NO, NO,, and 0 3 are actually measured. With these approximations the concentration changes in the inlet will depend only upon k3, the residence time, and the initial concentrations of NO and 03. There are a number of ways of representing the errors which will arise due to the reaction in the dark inlet tube. For NO and 0 3 , it is convenient to consider the length of time required for a 10% change in the sample concentration to occur. The expressions for these times are given below for the case in which (NO) # (03).
(O$ and (NO) are now the actual atmospheric concentrations. TlO%,NO and 710%,oaare also represented in Figures 1 and 2. If the residence time is 10 seconds, the error in (NO) will be greater than 10% in that area above the 10-second isopleth in Figure 1 and less than 10% for the area below the 10second isopleth. The error in ( 0 8 ) will be greater than 10% for the area to the right of the 10-second isopleth in Figure 2. Since the time required for a given relative error to occur for NOz depends o n three variables, we have chosen to consider the time required for a given absolute error, which depends only o n (NO) and ( 0 3 ) . The results are shown in Figure 3 for a 10-second residence time. The 10-second figure for the residence time was chosen arbitrarily for purposes of illustration. However, Yamada and Charlson (7) in a survey of a large number of sampling stations report modal inlet dimensions of 7 m in length and 1.2 cm in diameter and a modal flow of 5 liter/min. These (7) V. M. Yamada and R. J. Charlson, Enriron. Sci. Technol,, 3, 483 (1969).
ANALYTICAL CHEMISTRY, VOL. 43, NO. 13, NOVEMBER 1971
1891
values correspond to a residence time of 9.5 sec. The expected effect of the dark reaction is calculated for atmospheric data (8) using a 10-second residence time. The measured concentrations and calculated atmospheric concentrations are shown in Figure 4. I n obtaining this figure, the ozone concentration was taken to be that for oxidant. It should be noted that since (NO,) [= ( N O z ) (NO)] is conserved in the dark reaction, no error is expected in this quantity due to these considerations. O n the other hand, measured values of ( N O ) and (0,) will be systematically low, (NO2) will be high. The quantity ( N O ) ( 0 3 ) / ( N 0 2 )which , has been used as a measure of the photochemical equilibrium and the amount of sunlight, will be systematically low. The effect considered here is based entirely o n the gas phase dark reaction. Reactions with the wall of the inlet system have been neglected as have reactions which may occur within the analytical instrument being used. Additional experimental data are required t o determine the magnitudes of these errors. It may be seen from Figure 4
+
(8) P. A. Leighton, “The Photochemistry of Air Pollution,” Academic Press, New York, N. Y . , 1961, p 273.
that large relative errors for a given species will occur only when the concentrations are low-near the detection limit for many of the wet chemical instruments now in use. However, with the advent of more specific and sensitive methods for measuring nitrogen oxides and ozone (9-11), consideration should be given to reducing the errors due t o the residence time. Decisions concerning the design of sampling lines must consider losses due to residence time, in addition to those resulting from the impaction of aerosols and chemical losses o n the surfaces.
RECEIVED for review May 20, 1971. Accepted July 21, 1971. Partial support for this work was obtained from these grants from the Air Quality Office of the Environmental Protection Agency : 2-TO1 AP00029-07, Air Pollution Training; and A P 00336, Influence of Aerosol Characteristics of Visibility. (9) J. A. Hodgeson, K. J. Krost, A. E. O’Keeffe, and R. K. Stevens, ANAL.CHEM., 42, 1795 (1970). (10) A. Fontijn, A. J. Sabadell, and R. J. Ronco, ibid.,p 575. (11) G. W. Nederbragt, A. van der Horst, and J. van Duijn, Nature, 206, 87 (1965).
~~
Liquid Anion Membranes Dependence of Selectivity Factor on Organic Salt Concentration Pier Roberto Danesi, Giancarlo Scibona, and Bernard0 Scuppa Industrial Chemistry Laboratory, Commitato Nazionale per L’Energia Nucleare, Centro di Studi Nucleari della Casaccia, Rome, Italy
PREVIOUS WORK ( I , 2 ) o n the behavior of liquid anion membrane electrodes has shown that the potential of these electrodes can be described by means of the equation (at 25 “C) P
P
Ji
J2
with ai, Ki, and ui, respectively, activity, distribution constant, and mobility in the organic phase of the ith ion. The two integrals
and
are given in Reference (2) and
can be neglected when the mobility of the organic cation is much smaller than that of the anions. By considering a twoanion system with anion mobility larger than that of the organic cation, Equation 1 becomes V = 59 log [(al‘
+ Pz.la2’)/(al’’+ PZ.IUZ”)I
(2)
The selectivity factor of the liquid anion electrode, Pz.1 is given by P2.i = K Z U Z / ~ U ~ (3) By using the equilibrium constant of the biphasic ion exchange 2 e 25 1, K2.1,and the ion pair formation reaction, . (where square brackets represent constant Kij = activities or concentrations), Equation 3 becomes
+
+ [u]/[i] [a
(1) P. R. Danesi, F. Salvemini, G. Scibona, and B. Scuppa, J . Phys. Chew., 75, 554 (1971). (2) J. Sandblom, G. Eisenman, and J. L. Walker, ibid., 71, 3862
(1967). 1892
P2.i
=
( u z / u ~ .> ( K ~ J / K .~ Kz.1 J)
= UZ/UI
. K*z,i
(4)
Although K I J , K ~ Jand , K2.1 are thermodynamic quantities, a concentration variation of the liquid ion exchanger can affect the macroscopic dielectric properties of the organic phase and, consequently, their values. Of course, the (u&1) ratio can also be concentration dependent. A dependence of P2.*o n the liquid exchanger concentration is therefore with the expected. I n the present work the variation of P2.1 concentration of the liquid exchanger for membranes consisting of benzene solutions of tetraheptylammonium nitrate interposed between aqueous solutions containing the nitrate and chloride anions has been experimentally studied. The implications of the P2.1variations on the analytical determination of the ion concentrations by means of liquid ion exchanger membrane electrodes are also evaluated. EXPERIMENTAL
Reagents. HC1, H N 0 3 , LiC1, and LiN03 of analytical grade purity, supplied by Carlo Erba, have been used in the experiments. Benzene of the same type of purity, Carlo Erba, has been used. Tetraheptylammonium iodide (THAI), Eastman Kodak, has been used t o prepare the other alkylammonium salts. The preparation of THACl and THAN03 has been already reported (3). In order to take into account (3) P. R. Danesi, M. Magini, and G . Scibona, “Solvent Extraction Research,” A. S. Kertes and Y. Marcus, Ed., John Wilev & Sons, New York, N.Y., 1969, p 185.
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