indicated that the membranes had not suffered physical damage as in the previous permeation method (5). Comparative West-Gaeke vs. Turbidimetric Evaluation. Using disodium tetrachloromercurate(I1) as the absorber solution, the colorimetric West-Gaeke method for sulfur dioxide determination was used to determine the permeation monitor calibration constants. A set of duplicate calibration experiments was conducted to substantiate the previously determined sulfur dioxide permeation rates and illustrate the quantitative nature of the newly developed technique. The calibrations were made after an exposure of 3 h of 660 pglm3 of sulfur dioxide a t 24 “C. The mean percentage deviation between the two methods of calibration was less than 2%. These results indicated essentially 100%of the sulfur dioxide that permeated into the manganese solution was converted t o sulfuric acid a t a rate rapid enough to avoid affecting the sulfur dioxide permeation constants. A cursory feasibility study of the newly developed method was conducted in the field for a period of 1month in parallel with a West-Gaeke bubbler assembly. The results obtained from both methods indicated that only rural background levels of sulfur dioxide were present (below 10 pg/m3 of sulfur dioxide). Conclusions
This research, which involved the development of the manganese(I1) chloride procedure, was successful in producing a viable alternative to the 40-year old lead peroxide candle method. This work has demonstrated the high degree of quantitation achieved by the manganese method as opposed to the nonquantitative lead candle method. The maximum possible exposure period, based upon the average evaporation loss of absorber solution under field conditions, was determined to be 3 months. The detection limit was established to be 10 pg/m3 of sulfur dioxide for a 7-day exposure period. The blank absorbance value a t 25 “C was 0.01 provided the PDA reagent was of acceptable quality. The absorbance vs. sulfate concentration calibration curve
was linear over a range of 0.1-10 ppm. The absorber solution was nontoxic and therefore was handled with care to avoid contamination by biologically active organisms. The high stability of sulfuric acid in aqueous solutions enabled collected samples to be stored for extended periods of time in glass or polyethylene vials without decomposition or adsorption. The method was found to be specific for sulfur dioxide and independent of humidity effects over a range of a t least 0-80% relative humidity. The effect of temperature on the rate of permeation of sulfur dioxide through the polymer membrane resulted in a 6% decrease in permeation for every 10 “C increase in temperature. Literature Cited (1) “Evaluation of Total Sulfation in Atmosphere by the Lead Peroxide Candle”, American Society for Testing Materials, 1965, D 2010-65. (2) Huey, N. A., Air Pollut. Control. Assoc. J., 18,610 (1968). (3) McCabe, L. C., in “Proceedings of the US.Technical Conference on Air Pollution”, McGraw-Hill, New York, 1952, pp 538-41. (4) Hickey, H. R., Hendrickson, E. R., Air Pollut. Control Assoc. J., 15,409 (1965). (5) Reiszner, K. D., West, P. W., Enuiron. Sci. Technol., 7,526-32 (1973). (6) Stephen, W. I., Anal. Chim. Acta, 50,413-22 (1970). (7) Dasgupta, P. K., Lundquist, G. L., Reiszner, K. D., West, P. W., Anal. Chim. Acta, 94,205-7 (1977). (8) O’Keeffe, A. E., Ortman, G. C., Anal. Chem., 38,760-3 (1966). (9) Vasilev, S. S., Kostanov, L. I., Lostorakaja, T . L., Acta Physicochirn., U S S R , 3, 413 (1935); “Gmelins Handbuch der Anorganischen Chemie”, 8th Auflage, Schwefel, Teil B, Lieferung 3, Verlag Chemie, GMBH, Weinheim/Bergstr., 1963. (10) Grodzovski, M. K., Z. Fiz. Chim. USSR, 6,478 (1935);Gmelins Handbuch der Anorganischen Chemie, “8th Auflage, Schwefel”, Teil B, Lieferung 3, Verlag Chemie, GMBH, Weinheim/Bergstr., 1963. (11) Bassett, H., Parker, W. G., J . Chern. Soc., 1540 (1951). (12) Matteson, M. J., Stober, W., Luther, H.. Ind. Eng. Chem. Fundarn., 8,577 (1969). (13) Dasgupta, P. K., Louisiana State University, 1975, unpublished studies.
Receic’ed for reoieu: June 26, 1978. Accepted April 30, 1979.
A Personal Chlorine Monitor Utilizing Permeation Sampling James K. Hardy, Purnendu K. Dasgupta, Kenneth D. Reiszner, and Philip W. West* Environmental Sciences Institute, Chemistry Department, Louisiana State University, Baton Rouge, La. 70803
A method for the determination of personal exposure to chlorine is described. Samples are collected by permeation through a silicone membrane into 10 mL of a fluoresceinbromide absorbing solution. The resulting eosin is measured spectrophotometrically and the C12 exposure (timeweighted-average) is calculated. The detection limit of the method is 0.013 ppm (0.038 pg/m3 a t 20 “C) for an 8-h exposure with a working range of 0.1-2.0 ppm. The device responds in less than 1 min and is unaffected by variations of temperature and humidity. Response of the device is dependent on pH and is optimized by buffering the absorbing solution at pH 7.0. No significant interferences are encountered, but the solution fades if exposed to intense sunlight for extended periods. A device can be constructed that is small in weight and size and can serve as either an area or personal monitor. Federal regulations have set the present personal exposure limit for chlorine a t 1 ppm (8-h time-weighted-average) ( I ) , 1090
Environmental Science & Technology
emphasizing the need for monitoring methods that reflect actual individual exposures. Current procedures used to determine personal exposures to Cl2 are active sampling methods in which the air sample is drawn through a liquid absorber. These involve the use of a pump, battery pack, and glass impinger. Two of the present approaches used for determining the collected Cle involve the use of o-tolidine (2) or methyl orange ( 3 ) .In the first, the sample is collected in NaOH and, a t the end of the collection period, o-tolidine is added. A yellow color is produced and measured spectrophotometrically. The latter technique relies on a quantitative bleaching of a methyl orange solution, which is also determined spectrophotometrically. The color developed in the o-tolidine method is unstable, and the reaction itself is acutely dependent on pH ( 4 ) . The methyl orange method, like all other bleaching methods, lacks precision and accuracy a t low chlorine concentrations. The relatively bulky, inconvenient, and expensive collection devices now available are a deterrent to personal monitoring.
0013-936X/79/0913-1090$01 .OO/O @ 1979 American Chemical Society
P-"
VI 0
2 0 5 b
I
c 0
2
)
0 1-
l
1
0
5
10
15
ppm.h
Figure 1. Calibration curve
The problems of the mechanical and chemical processes involved add further to the need for a better approach for personal monitoring for chlorine. A new method is proposed which is low in cost and simple to use. I t may be employed for sampling periods as short as 30 min or as long as 12 h. The new method utilizes a permeable membrane for sample collection, where the permeation rate is proportional to the external Clz concentration ( 5 ) .Samples are collected directly into a color developing solution, which has proven to be stable over long periods of time. At the end of exposure, the solution is transferred to a cuvette and measured spectrophotometrically. The absorbing solution consists of a fluorescein-bromide mixture in which C12 oxidizes bromide to bromine, which in turn brominates fluorescein (6, 7) to form eosin, which is then measured a t its absorption maximum, 519 nm. The detection limit for this method is 0.013 ppm of C12 for an 8-h exposure, with a working range of 0.1-2.0 ppm. For shorter periods of time, concentrations as high as 5 ppm can be accurately measured.
Experimental Reagents. High-quality distilled, deionized water was used throughout. All reagents were reagent grade where possible. Fluorescein (no. P780, 96% assay, Eastman Kodak Co.) was obtained in acid form, and eosin (no. E-511,87% assay, Fisher Scientific Co.) was obtained as the disodium salt. A fluorescein stock solution was prepared by dissolving the following in deionized water and diluting to 2 L: 0.011 g of fluorescein, 6.19 g of NaBr, 2.24 g of NaOH, 13.6 g of KHzP04. The fluorescein and NaOH were added first with a few milliliters of water, and the mixture was then agitated vigorously to convert the fluorescein to its sodium salt (uranin), thus increasing its solubility. The resulting solution was 16 pM fluorescein-0.03 M NaBr with a pH buffered a t 7.0. The reagent is slightly light sensitive but may be stored in the dark for a t least 1 month without significant alteration. Naturally, it must be protected from direct exposure to sunlight when used in a personal monitor. Decomposition does not change the linearity of the method but the range decreases with decomposition of fluorescein. High blanks are an indication of Clz in the water or decomposed reagents. Low blanks are an indication of impure fluorescein or decomposition of the reagent due to exposure to sunlight. The blank absorbance vs. water, typical of our studies, was 0.029. Apparatus. The calibration chamber, permeation devices, gas filtration and dilution system, and other auxiliary equipment have been described by Reiszner and West ( 5 ) .The permeation devices used in this study employed General Electric single-backed dimethylsilicone membranes of 0.025 mm thickness. Calibration of Permeation Devices. Standard Clp-air mixtures were prepared by passing dry filtered air over a
0
IO
30
20
Temp
40
50
60
CC)
Figure 2. Effect of temperature on permeation
standard permeation tube ( 8 , 9 ) ,which emitted Clz a t a constant rate. A 10-mL aliquot of the fluorescein solution was pipetted into the permeation device, which in turn was placed in the calibration chamber. The solution was transferred into a cuvette a t the end of the exposure period, and the absorbance measured a t 519 nm with the original fluorescein solution taken as blank. The calibration constant ( K )of each device was calculated by exposing the monitor to a known concentration of Clz for a measured period of time, This constant is defined as:
K
=
A/(Ct)
(1)
where K = constant, absorbance units/(ppm-h), t = exposure time, h, C = Clz concentration, ppm, and A = measured absorbance a t 519 nm with a 1-cm cell. The constant, K , is the reciprocal of the constant k , as defined in the original theory on permeation sampling ( 5 ) . A linear response to cumulative dosage was verified by determining the absorbance after exposure to various Cls concentrations and exposure periods. The results are shown in Figure 1. The devices used in this study had K values of about 0.05 absorbance unit/(ppm.h) or, in absolute units, 0.56 pg of Cls/(ppm.h). Although membrane thickness and exposed surface area can be varied to alter sensitivity, changes should be made only with caution. Analysis. I t is imperative that the analysis procedure be the same as that used for calibration. Then, by exposing the device for a known length of time, the following equation can be used to find the average time-weighted Clz exposure: C(ppm of Clp) = A / ( K t ) where K is the constant as defined in Equation 1.
Results and Discussion
Effect of Temperature. Because calibration of the devices was done a t 24 "C, it was necessary to determine if changes in temperature would cause any deviation in response. The effects of temperature were studied over a range of 0-55 "C. As illustrated in Figure 2, no significant deviations in response were observed. Effect of Humidity. A dry air stream was used for Calibration, and it was felt that some deviations in permeation may occur a t higher relative humidities (RH).Humidity was varied by mixing a humid air stream with the dry Clp-air stream coming from the permeation chamber. The humid stream was produced by directing air flow through two impingers, the first containing water and the second left empty to serve as a condensation trap. By varying the water level and temperature of the first impinger, it was possible to vary the humidity without changing the flow-meter settings. All RH measurements were made in the exposure chamber with a solid state probe. Over a range of 0-97% RH, response remained unaffected. Volume 13, Number 9, September 1979
1091
Table 1. Response Time llme, mina
absorbance, 519 nm
0
0
3
0.013 0.013 0.013 0.012
6 9 12
a This represents elapsed time: the solution in the monitor was changed at 3-min intervals.
I
2
3
4
5
6
7
8
9
IO
I1
12
PH
Figure 4. Effect of pH on response
20
IO
Solution
Concentratton
(pM fluorescein)
Figure 3. Clz saturation point for absorber solutions
Response Time. Permeation through a membrane is not an instantaneous process. With some membranes, the response may take several hours (5).In an industrial environment, the device may be subjected to brief periods of high C12 concentrations and it is important that it responds quickly. By exchanging the solution a t 3-min intervals in a device being exposed to a C12 stream, response was found to be 100%within the first 3 min (Table I). This places the response time a t less than 3 min, and the actual value probably is less than 0.5 min. Effect of Absorber Concentration. While fluorescein does not absorb very strongly a t 519 nm, the variation of the blank a t this wavelength could be significant when low concentrations of Cl2 are to be determined and high fluorescein concentrations are used. For this reason it was desirable to keep the fluorescein concentration as low as possible, bearing in mind the amount of eosin formed is independent of the fluorescein concentration, unless the latter becomes the limiting reagent. On the other hand, the use of too dilute an absorber solution would result in rapid saturation leading to the bleaching of the product. The lower limit of the absorber concentration was dictated by the upper limit of the cumulative exposure to be measured. After a study of various absorber concentrations (Figure 3), it was found that a 16 pM solution of fluorescein was the optimum choice for measuring 0.8-16 ppm-h of C12 exposures in the devices being studied. If higher C12 levels are anticipated, the fluorescein concentration can be increased. Experience has shown that the permeability of different batches of membrane varies widely. The concentration of fluorescein must be increased in proportion to any increase in permeability if the range of the method is to be maintained. Calibrations must be carried out with the same reagent that is used in the field exposure. Dilution of the reagent after exposure may be necessary to obtain on scale readings. Anticipating the use of a personal chlorine monitor under a wide variety of lighting conditions, an evaluation of the effect of light on the absorbing reagent was undertaken. The fact 1092
Environmental Science & Technology
5 50
500
450
400
X(nm) Figure 5. Effect of pH on fluorescein absorbance that bromide ion is light sensitive would lead one to expect a positive response to sunlight. Fortunately, no positive response was noted even after exposure for about 4 h to intense direct sunlight. The fluorescein color (absorbance at 490 nm) did fade almost completely during this exposure and the absorbance of the solution was slightly below that of the blank. This intense fading was reduced to about 50% in a prototype personal monitor, with all areas except the membrane face protected during a 4-h exposure. Eosin, which is formed from exposure to chlorine, also fades but at a reduced rate, which means that the primary concern must be with the fluorescein itself. Effects of pH. The effects of pH of the absorber solution were studied to determine the region of optimum response. Buffered adsorber solutions a t p H 5 , 6, 7, 8, 9, and 10 were studied. It was found that solutions with pH in the range 5-8 resulted in the greatest conversion of fluorescein to eosin (Figure 4). Solutions with pH values less than 5 resulted in the formation of a precipitate where solutions with pH >8 resulted in reduced eosin production. Buffering of the absorber solution to pH 7 was chosen to assure optimum eosin formation without the risk of precipitation. I t was also noted that while for fluorescein was pH dependent, the A,, for eosin the A,, remained constant over the entire pH range studied (Figures 5 and 6). Evaporation Study. To compensate for possible evaporation losses, the initial studies were conducted by diluting both the sample and blank to 25 mL with deionized water. Later studies indicated that less than 3.5% evaporation loss occurred when one of the devices that contained 10 mL of the absorber solution was exposed for 8 h to completely dry air a t
Table II. Field Evaluation
W
0
z
dale p H : 5 . 6 . 7 , s .9.10
co
impinger, pm ip Of ci2
12/1/78
0.47 1.10 0.28 0.80 0.90 0.04 0.03
z Q
Lz
c
12/4/78 12/5/78 12/6/78
0.09 0.09 0.20 0.20
12/6/78 600
550
500
X Figure 6.
450
i21717a
0.93 0.93
inrr!
Effect of pH on eosin absorbance
24 “C.Therefore, all further studies were conducted without efforts to compensate for the evaporation loss. I t should be pointed out that the evaporation loss will increase with elevated temperature, and quantitative transfer and dilution may be necessary if high degrees of accuracy are desired. Interferences. Only gaseous pollutants can conceivably interfere with the permeation process. Furthermore, in order to cause an interference, the interferent would logically be an oxidant that would convert bromide to bromine or react with fluorescein or eosin directly. Ozone and nitrogen dioxide were therefore expected to have some effect. Nitrogen dioxide, with an exposure limit of 5 ppm ( I ) , could conceivably present a serious problem. By exposing the devices to 5 ppm of NO2 for 6 h, it was found that the response was only +0.01% of an equivalent Clp exposure. While the exposure limit to ozone, 0.08 ppm ( I ) , is well below that of Clp, even low 0 3 levels might cause significant errors a t low Clp concentrations. Devices exposed to 5 ppm of 0 3 for 4 h produced no measurable response. Therefore, neither NO2 nor 0 3 represent significant interferences. During field tests of the monitor, an inadvertent loss of hydrogen chloride occurred. The monitor seemed unaffected, but laboratory studies were undertaken which confirmed that exposure to 1500 ppm-h of HCl was without effect. Field Tests. Independent field testing was conducted a t a local chlorine production facility. Five calibrated Clp monitors and a supply of the reagent were furnished for testing. At the discretion of the plant personnel, replicate samples were taken with the monitors and with battery-operated pump with impinger samplers placed in areas of the plant considered to represent typical exposures. Monitoring was conducted for 2-h periods with the subsequent analysis being done by the plant personnel. Data so observed are shown in Table 11.
a
permeation device, ppm of C12
0.52 1.10 0.44 0.80 0.70 0.25 0.16
0.40 0.20 0.20 0.20 0.97 0.95
0.67 1.20 0.49 0.90 0.60 0.28 0.22 0.20 0.20 0.20 0.20 1.10 0.97
0.56 0.52 0.90 0.26 0.30 0.10 1.10
Determination made by modification of methyl orange method (10).
Conclusion The results reported here show that ‘the measurement of C1, can be accomplished in a simple yet efficient manner by using a technique that allows direct conversion of chlorine to a measurable product. Of special importance are the small size and convenience of the monitoring device employed, The complete personal monitor for chlorine is a passive device the size and weight of a radiation dosimeter that serves the dual function of quantitatively sampling and determining Cls. The device can serve for personal or area monitoring or for ambient air studies. Acknowledgment
The authors acknowledge the cooperation of Dow Chemical
Co. and the special assistance of Charles E. Halphen, Louisiana Division, Dow Chemical Co., Plaquemine, La., in conducting field tests. L i t e r a t u r e Cited (1) Fed. Regist., 36 (No. 105) (1970). ( 2 ) Stern, A. C., “Air Pollution”, 2nd ed., Vol. 11, Academic Press, New York, 1968, pp 99-101.
(3) HEW Publication No. (NIOSH) 76-170. (4) Johnson, J. D., Overby, R., Anal. Chem., 41,1744-9 (1969). (5) Reiszner, K. D., West, P. W., Enuiron. Sci. Technol., 7, 526-32 (1973). (6) Fenton, P. F., J . Chem. Educ., 21,488 (1944). ( 7 ) HEW Publication No. (APTD) 69-33. (8) Scaringelli, F. P., O’Keeffe, A. E., Rosenberg, E., Bell, J. P., Anal. Chem., 42,871-6 (1970). (9) O’Keeffe, A. E., Ortman, G. C., Anal. Chem., 38,760-3 (1966). (10) Dharmarajan, V., Rando, R.,Am. Ind. Hyg. Assoc. J., 40,161-4 (1979).
Received for reuieu! J u n e 26, 1978. Accepted April 30, 1979.
Volume
13, Number 9, September 1979
1093
