ANALYTICAL CHEMISTRY
1480
Table
111. E x p e r i m e n t a l V a l u e s of P for Various H y d r o g e n - C o n t a i n i n g Solids
Solid Tritiated thallous hypophosphite, TlHTPOP Hydrated CuSOd Hydrated Mg(CIOa)zb NHiTCl Methyl-3-~-acetoxycholinate
Density, Grams/&.
P , Gram X 10‘
6.53
1,5/
2 9e 2.5e 1.54 0.7C
1.4 1.3 1.2f 1 59 1 . 4 It 0 12
Mean
Prepared by exchange between HTO and HsPOz, followed by neutralization with TlOH and evaporation in vacuo to recover solid salt ( 8 ) . b Prepared by adding a small amount of HTO to the anhydrous salt. See (8). d Density not known: estimated from similar compounds. 6 Approximate. I Calculated assuming no isotope effect on the exchange equilibrium. 0 Calculated from data in (3) and corrected for different planchet area used b y those authors. a
activity required to produce a given level of activity (as measured in the flow counter) in any hydrogen-containing compound (TR) can be calculated by applying the following principle: All solid materials having the same specific tritium activity (counts per unit time per unit weight of solid) will give the same observed activity in a given solid-phase counting apparatus, provided that the thickness of the solid is equivalent t o infinite thickness. This observed activity will be independent of the density of the solid and will depend only on its mass absorption coefficient. Since the mass absorption coefficient depends 011 thc ratio of atomic weight t o atomic number, it is a slowly varying function of atomic weight, and hence the ratio observed activity of solid T R specific activity of solid TR will be approximately constant for most hydrogen-containing aolids, even though they may vary widely in density. This principle can be verified both theoretically and eiperimentally. Table I11 gives the values of P obtained with the first
counter for five different hydrogen-containing solids in which some of the hydrogen has been replaced by tritium. It is seen that although the density varies over a tenfold range, the values of P are constant within about 7% and show no trend with increasing density. Thus from the known value of P, one can calculate the specificactivity of the tritiated hydrogen-containing compound necessary to give a convenient observed activity. Knowing the necessary specific activity, one can then easily calculate the tritiated water activity necessary to give this activity. SUMMARY
Exchange and tracer experiments with tritium can be set up and carried out using the windowless flow counter as an analytical tool, without having‘ to resort to gas-phase counting techniques for tritium assay. It is unfortunate that a more detailed and extensive investigation of the method could riot beundertaken. However, an investigator who uses the values of S and P given in Tables I1 and I11 and a counter similar to the first counter can, with reasonable confidence, estimate the activity of his tritiated water solutions with an accuracy of 15% and make up tritiated water solutions in the correct activity range for exchange or other tracer ekperiments. ACKNOWLEDGMENT
The author is indebted to Don A l . Yost for helpful discussione during the course of this work, t o David L. Douglas for performing the ionization chamber tritium assay, to Dan Campbell for the loan of another flow counter, and to the Research Corp. for a grant-in-aid in partial support of this research. LITERATURE CITED
(1) Douglas, D. L., thesis, California Institute of Technology, 1961. (2) Eidinoff, M. L., and Knoll, J. E., Science, 112, 260 (1950). (3) Jenkins, W. A., and Yost, D. hl., J . (‘hem. Phgs., 20, 538 (1952) “Radioactive ., Tracers in Biology,” p. 130, New (4) Kamen, &!I Tork, Academic Press, 1947. RECEIVED March 6, 1953. Accepted July 6 , 1953. Contribution No. 1777 from the Gates and Crellin Laboratories, California Institute of Technology, Pasadena 4, Calif.
Continuous Oxidant Recorder F. E. LITTMAIPr’ AND R . W. BENOLIEL’ Air Research Laboratory, Stanford Research Institute, Pasadena, Calif.
I
IU T H E course of investigations of smog in the Los Angeles
area, an unusually high concentration of an oxidant exhibiting the general properties of ozone was found in the atmosphere. As the concentration of this oxidant appeared to vary markedly with the intensity of smog, it was considered desirable to construct a continuous recording device to establish the relationship of the oxidant concentration with other manifestations of smog. Several types of continuous recording devices for such an oxidant (whichisgenerally considered to be ozone, though its identitjhas in some cases not been established) have been described in the literature. Dirnagl ( 8 ) described a modification of Schonbein’s ozonometer, using filter paper impregnated with buffered potassium iodide solution. Gliickauf ( 4 ) built an automatic device which was based on the titration of the system potassium iodideiodine-sodium thiosulfate using an electrometric end point. Regener (5) is using a similar device. All these instruments are based on the liberation of iodine from potassium iodide solutions, using certain safeguards such as 1
Present address, General Electric Co., Richland, Wash.
buffered. solutions. To the authors’ knowledge, however, only the device described below produces a continuous direct reading record of the oxidant concentration in the air. PRINCIPLES OF OPERATION AND DESCRIPTION OF EQUIP.MENT
The reaction of ozone with potassium iodide in neutral (pH = 7 ) buffered solutions according to 03
+ 2KI + HzO
+0 9
+ + 2KOH I1
(1)
has long been used as a means for the quantitative determination of ozone. Treadwell (6) established that the amount of iodine produced is in stoichiometric proportion t o the amount of ozone, provided the p H of the potassium iodide solution is 7 or higher. In acid solutions, up t o 50% more iodine than expected from Equation 1 is produced. This reaction is not specific for ozone, as several other substances, notably nitrogen dioxide, nitric acid, and some organic hydroperoxides, are known or suspected of liberating iodine from bufferedneutral potassium iodide solutions. Tests with synthetic
1481
V O L U M E 25, NO. 10, O C T O B E R 1 9 5 3 The unusually high concentration of an oxidant, which appears to be ozone, in smoggy Los Angeles air is one of the few distinguishing characteristics of the local atmosphere. In order to study the relationship between the occurrence of smog and the fluctuation of the oxidant concentration, a continuous recorder was built which produces a direct reading record of oxidant concentration in terms of ozone equivalents. The instrument consists essentially of a continuous air-liquid contacting device and a recording colorimeter. It is based on the liberation of iodine from a buffered, neutral potassium iodide solution by the oxidant. The light transniittance of the resulting yellow- solution is measured by a double-cell colorimeter and continuously recorded on a strip chart. The contacting solution is regenerated by passing it through a bed of activated carbon, and is re-used. By maintaining constant air and liquid flows, i t is possible to calibrate the instrument directly in terms of ozone equivalents in parts per hundred million by volume. Thus, a continuous, pen-drawn record of the fluctuation of the oxidant level can be obtained. Satisfactory performance for 18 months was achieved and an excellent positive correlation was established between the oxidant and smog, as manifested by reduced visibility, eye irritation, and crop damage.
function in this region, provided a narrow-band filter is used (Figure 2). The use of 10-mm. thickness of corning S o . 5860 filter was found t o be satisfactory. Thus, we have a basis for converting the absorbance of such a solution into equivalents of iodine and, consequently, equivalents of ozone. If the flow rates of the air stream and the potassium iodide solution in contact with it are known and kept constant, the above relationship peimits direct calibration of a continuous instrument in terms of equivalent ozone concentrations. Thp oxidant recorder consisted of two functional parts: a iecording colorimeter and a continuous gas-liquid contacting device. Several types of gas-liquid contactors were tried. Bubblers are not well suited for continuous operation because of their large holdup. 4 glass column containing a wire helix in the aniiular space between the walls of the tube and a solid glass rod was tried, but the absorption efficiency was low. A similar tube, the surface area of which was enlarged by covering it with fritted glass, eshibited an interesting behavior, as shown in Figure 3. I t s effic,iency was a function of the solution flow rate, falling off on both sides of the optimum rate. .4 20-inch column packed with l / 4 inch borosilicate glass single-turn helices was found t o be the most satisfactory contact device, as it exhibited complete removal of the ozone from the air stream a t all flow rates tested. The complete scrubbing unit is shown i n Figure 4. 971
I
I
BPILANCED
mixtures of nitrogen dioxide in air indicated that the instrument responds t o this gas in the range of 0 t o 100 parts per 100,000,000 by volume but shows only one third of the amount present. As the highest nitrogen dioxide concentration encountered a t Pasadena was about 10 parts per 100,000,000 by volume (as determined by the Griess-Ilosvay method), the maximum error due to this substance should be less than 3 parts per 100,000,000; in localities where higher concentrations occur, appropriate corrections would have to be made. Recent tests performed in this laboratory indicated an excellent agreement of the results obtained by this method with ozone concentrations determined by the p r e s w a b l y specific method based on the cracking of stretched rubber bands, as described by Bradley and Haagen-Smit (1). Thus, it appears that the results obtained in Los Angeles can be interpreted as true ozone concentrations. A solution of iodine in 20% potassium iodide exhibits a yellow color owing to its characteristic absorption spectrum (Figure 1). The absorption curve shows an intense maximum a t about 3550A., which appeared suitable for colorimetric determinations of iodine in concentrations of 0 to 100 peq. The relationship between the absorbance and the iodine concentration appears to be a linear
a cn 0
o'21 0.1
lODl N E CONCENTRATION O ',+',";N :2 ; 0 % K I SOLUTION
m
a
O' 2kO 3b0 3;O
3&
3&
3 k O 4b0 4;O
4jO
WAVELENGTH, mp
Figure 1.
Light Absorbance of Iodine in 20qo Potassium Iodide
I
I
CIRCUIT
l
I
I
I
,
/;I
a
w
0
a
80-
Ya
70-
0
f
s":
40-
eo: 20 40 60 80 100 I20 I40 XIOF* OZONE EQUIVALENT XLV2 N IODINE
Figure 2. Calibration of Iodine Solutions in 20q' Potassium Iodide
A btorage bottle contained about 2 liters of a potassium iodide rolution made up of 200 grams of potassium iodide, 36 grams of disodium phosphate dodecahydrate, and 14 grams of potassium dihydrogen phosphate per liter of solution. The solution was fed by gravity to a Sigmamotor ump (made by E & M Enterprises, Middleport, Tu'. Y . ) , whicc elevated it into an overflowtype constant-head reservoir, with the excess returning by gravit into the storage bottle. The solution flowed by gravity througl an activated carbon filter a flowmeter, and a regulating stopcock and entered the top of the contacting column. This type of a constantrhead gravity flow is far more fiatisfactory in eaqe of adjustment and flow stability than that produced by the various "constant feed" pumps. The activated carbon filter served to remove any free iodine from the potassium iodide solution, thus making it possible to re-use the solution almost indefinitely. After coming in contact with the air stream, the potassiumiodide solution flowed through a 10-mm. optical cell and returned to the storage bottle. The air stream was drawn through a flow meter and entered the contacting column a t the bottom, thus getting scrubbed countercurrently as it passed through the column. I t s volume was regulated by means of an adjustable leak. It then passed through a pump and was discharged. The recording colorimeter consisted of a modified Lumetron 402-E colorimeter and a Brown strip chart recorder wired as a mechanical slide-wire, as indicated in Figure 5. The balancing photocell and the Brown amplifier were hooked up acrosR the slide-wire of the Brown recorder after the slide-wire calibrating shunt was removed. The measuring photocell, which was in series opposition with the balancing cell, was connected to the
ANALYTICAL CHEMISTRY
1482
moving contact of the recorder and to one aide of the slide-wire. This arrangement was essentially identical with that used in the original Lumetron colorimeter, exce t that the Brown was substituted for the manually operated 3ide-wire; the reading indicates per cent absorption. The potentiometric components of the Brown recorder (standard cell calibrating resistors, and so on) were disconnected. The use o f a high-gain amplifier in the Brown recorder is depirable.
L U M E T RON
100I
I
c
I
I
I
I
Figure 5.
AIR FLOW 1 4000 CC/MIN
60 v)
m
4
5000 CC/MIN
!4 20
OZONE CONCENTRATION ABOUT 70 PPHM AS MEASURED BY SPRAY CONTACTOR
A. B. C.
I'
I
1
1
' JI
BROWN RECORDER
Wiring Diagram of Continuous Recorder
u.
Balancing photocell Measuring photocell Amplifier
E.
Motor Slide-wire
by the filters (3200 to 3800 A.) resulted in a unbalanced condition which the amplifier recognized and corrected, but did not measure. Thus, this system is independent of the very considerable fluctuation of the output of the ultraviolet lamp, as it indicates only the relative amounts of light reaching the photocells, provided that the light is very nearly monochromatic and of sufficient intensity to activate the Brown amplifier. The assembled recorder is shown in Figure 8
ML 20% KVMIN
Figure 3.
Absorption Efficiency of SinteredGlass-Lined Column
Considerable difficulty was experienced in the choice of the light source. The short rated life of the projection bulbs used in the original equipment made them unsuitable for the purpose. Mercury vapor lights were thought to be unsuitable because of the inherent instability of their light output, shown in Figure 6 , A . However, this can be entirely compensated for by the hookup described above, and the stability of the resulting system is satisfactory (Figure 6 3 ) . CONSTANT
Figure 6.
Light Stability Tests
HEAD
Table I.
Transmittance and Brown Recorder Readings for 0 to 50 X 10-6 N Iodine Solutions %
Tramniittance
Solution Distilled water 20% KI 50 X 10-6 S 1 2 in 25 X 10-6 N 11 in 12 X 10-6 ?u' IP in 6 X 10-8 N In in 3 X 10-6 S IP in
Figure 4.
Schematic Flow Diagram of Continuous Oxidant Recorder
W
100 20Yc KI
IC1
100 10 25
KI KI KI
79 Si
20% 20% 20% 20%
Scale Reading 2 2 91
76 48 21
53
60 -
0
-
c
-
e
20-
5 5 L
---_
2 MM FILTER
5
5 MM
l
FILTER
I O MM FILTER\\
C O R N I N G 158M) FILTER
\'
a \
6 5
0
\
80
100 120 140 IODINE CONCENTRATIONS (XIO-6N12)
20
40
60
0 50 25 12 6
3
14
40-
A mercury vapor light of the type designated AH-3 (85 IT)or A H 4 (100 W) was ueed in conjunction with the two No. 5860 ultraviolet filters (Corning Glass Works) in series. The use of a 10-mm. thickness of this filter resulted in a much straighter calibration curve than could be obtained with only one filter. This w a ~probably due to the suppression of the slight red transparency characteristic of these filters. Other Corning filters were used, but found to be inferior for this purpose. The effect of filter thickness on the calibration curve for iodine in 20% potassium iodide is shown in Figure 7. With the balancing photocell of the Lumetron colorimeter adjusted so that a reading of zero (corresponding t o 100% transmittance) was obtained with unaerated potassium iodide solution, the introduction of a solution absorbing in the region transmitted
Eouivctlent Oa Concn.. P. P. H.M. 0
Figure 7 . Effect of Thickness of Corning Filter on Colorimetric Behavior of Iodine Solutions in 20940 Potassium Iodide
In order to calibrate the recorder in terms of ozone e q u i v a l e n t , s , the air and liquid streams were 6xed at 5 liters and 5 ml. per minute, respectively. This rate is sufficient t o produce the desired iodine concentrations and is satisfactory with regard to the operation of the contacting column. Under these conditions, au equiva, lent ozone Concentration of 120 parts per 100,000,000 (corresponding t o 100 peq. of iodine)produced a 90% scale deflection, and an ozone concentration of 30 parts per 100,000,000 ( f r e q u e n t l y found at Los Angeles) resulted in a 42% scale deflection. The calibration was performed by diluting solutions of known amounts of iodine in 20% ,potassium iodide with colorless potassium iodide solutions (produced by filtration through a bed of activated carhon) and checking their transmittance.. A typical calibration run is showo in Table I and Figure 9. T h e i n s t r u m e n t was checked by running it in parallel with a spray contactor ( 8 ) both on synthetic mixtures of ozone and air, and on the Los Angeles atmosphere. The results agreed within 5%.
indicsted by a daily shift of the zero position and could be a8certained by checking the color of the unaerated potassiumiodide solution against distilled water. It should show less than 5% absorption. The rubber tubing in the Sigmamotor pump should be protected against abrasion by a Tygou sleeve. This combin* tion lasts much longer than &her one alone. 7SMOG OBSERVATIONS UAY24.1951IN PASADENA
c H E 4 V I SMOG
Figure 8.
Oxidant Con-
centration Recorder
APPLICATIONS, MAINTENANCE, AYD RESULTS
Several models of this instrument have been used extensively in studies of LOBAngeles smog over about 18 months. The instrument appeared t o be reliable, requiring only a minimum of maintenance. I t h a s been foundnecessary tozero theinstrument about twice a week by running fresh potassium iodide solution into the optical cell, and t o wash aut any accumulations of crystalline solids (mostly phosphates) from the contacting column. The column had t o be cleaned (with hot trisodium phosphate solution) about once a month, and the activated carbon filter replaced at about the same interval. Exhaustiou of the filter waa 0
z
w
w
10 94 95
0
Figure 9.
10
20
30
ACKNOWLEDGMENT
LITFRATURE CITED (1) Rradiey, C . E., and €lasgen-Smit, A. J.. Rubber Chem. and Technol., 24, 750-5 (1951). (2) Crahtree. J., and K e m ~ .A. R.. I d . Rng. C h a . . 38, 278-98
20
4
Typical daily curves (Figure 10) show an excellent positive correlation with smog as indicated by eye irritation, crop damage, and reduction of visibility, thus indicating a close relationship of the two phenomena The set of curves shown in Figure 11 demonstrates the variation of oddaut concentrations on June 12, 1952, throughout the Los Angeles Basin, from Cstalina Island t o Mount Wilson. The authors are indebted to P. L. Magill for his active interest and to the Western Oil and Gas Association, which supported this work.
60
c
Figure 11. Oxidant Concentration at Various heations
50 60 IODINE CONCENTRATION (10-6N12SOL 1 40
Iodine Concentration vs. Transmittance and Brown Recorder Readings
(1946). (3) Dirnapl. V.,Bull. Am. Meteorol. Soe.. 30, 21P17 (1949). (4) Glnckauf, E., et al.. J . Chem. Soc., 1944, 1. ( 5 ) Regoner, V. H., "Investigation in the Physics of Atmospheric Oaone," University of New Mexico, Interim Rept. 12 (Nov. RO l a m _",
(6) Treadwell, W.,Anal. C h m . , 48, 86 (1906). RECEIYFID ior review May 8, 1953. Accepted July 20, 1953. Presented before the Division of Analytical Chemistry, Symposium on Air Polhtion, at the 123rd Meeting of the A ~ ~ n r c CBEWICAL m SOCIETY,Lon Angelea. Calif.
