Literature Cited American Conference of Governmental Industrial Hygienists, 31st Annual Meeting, Chicago, Ill., May 1969. Bear, F. E., Ed., “Chemistry of the Soil,’’ 2nd ed., Reinhold, New York, 1964, p. 134. Cerwenka, E. A., Cooper, C. W., Arch. Enciron. Health 3, 71-82 (1961). Clark, R. E. D., Analyst 82, 182 (1957). Dye, w. B.9 Bretthauer, E., S e h H. J.3 Blincoe, c.3 Anal. Chem. 35, 1687-93 (1963). Lott, P. F., Cukor, P., Moriber, G., Solga, J., Anal. Chem. 35,1159-63 (1963). McKee, J. E., Wolf, H. W., “Water Quality Criteria,” California State Water Quality Control Board, Pub. No. 3-A, 253 and 254, 1963.
Schwartz, K., Foltz, C. M., J. Amer. Chem. Soc. 79, 3292 and 3239 (1957) u.s. Department Health, Education, and Welfare, Public Health Service Pub. No. 1729, “The Surgeon General’s Conference on Solid Waste Management,” 1967. Watkinson, J. H., Anal. Chem. 32, 981-3 (1960). Watkinson, H., ibid. 38, 92-7 (1966). Chemical and Engineering News, 45 (23), 12 and 13, May 29, (1967) west, p. w:, ~ ~stateuniversity, ~ ~~t~~ i R ~ ~ L ~ .i~, private communication, 1968.
Af
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Received for reuiew January 5, 1970. Accepted May 18, 1970. Mention of commercial products does not constitute endorsement by the US.Public Health Service.
COM M UN I CAT1ON
Syringe Sampling Technique for Individual Colorimetric Analysis of Reactive Gases Marston C. Meador and Robert M. Bethea Chemical Engineering Department, Texas Tech University, Lubbock, Texas 79409
A flow apparatus for continuously producing small quantities (up to 280 liters per hour) of humidified air containing constant known amounts of atmospheric contaminants is described. Contaminant levels up to 400 p.p.m. NOz, SO?,CL are reproducibly maintained for periods in excess of eight days by use of Teflon permeation tubes filled with the desired material. A comparison of the standard bubbler technique, and glass and polypropylene syringe gas sampling showed the polypropylene syringe technique to be superior for the analysis of NO? by the Lyshkow-modified Saltzman method over the range 0.07 to 60 p.p.m. of NOr in air. The improved syringe technique was extended to the colorimetric analysis of SO2, Clz, HC1, and H F in dynamically polluted air. The Lyshkow method for SO?is applicable in the range of 0.17 to 50 p.p.m. The orthotolidine method for free chlorine is applicable in the range of 0.12 to 50 p.p.m. The modified method of Iwasaki, Utsumi, et al. (1956) for HCl is satisfactory in the range of 0.5 to 50 p.p.m. The bleaching reaction of Andrew and Nichols (1961) for H F is marginally acceptable in the 5 to 50 p.p.m. region.
I
n recent research to study the removal of trace amounts of reactive contaminants (NO2, SO?, Cln, HCl, and HF) from simulated spacecraft atmospheres, several methods were evaluated from a microkinetic viewpoint. Evaluation of the removal techniques required analytical capability for each reactive gas in the range of 1 to 50 p.p.m. This report is an account of the development of a combined, single-step syringe sampling technique for the individual analyses of NO>,SOr, C ~ ZHCl, , and H F in dynamically polluted air by colorimetric techniques. Experimental
The experimental system consisted of two distinct systems. The first system was an atmosphere preparation train capable of providing a reliable supply of synthetically prepared, polluted air of specified composition, humidity, and pressure.
The second system consisted of the sampling and analysis sections. Atmosphere Preparation Subsystem. Oil-free, breathablegrade air containing no measurable amounts of any reactive gas was supplied in commercial compressed air cylinders. The air passed through a standard pressure regulator, through a microfilter, and then through a flow regulating needle valve. A Hastings-Raydist mass flowmeter (model LF-20K) was used to measure the air flow. After flow measurement, the dry air was then split into two streams. One of these streams was then routed through a flow control valve to a water-filled, ceramic packed humidification tower. The humidifier was a 150-cm.-long section of 15.3-cm.4.d. steel pipe packed with 1.2-cm. ceramic Berl saddles. The cross-sectional area in the humidifier lowered the linear air velocity sufficiently so that water entrainment was not a problem. The fully saturated air was then combined with CO? and mixed with contaminated air. The CO? concentration was adjusted to the desired level by metering C 0 2 through a Brooks rotameter (model R-2-15AA, 15-cm. tube, spherical stainless steel float with integrally mounted Flo-Mite needle valve and differential pressure regulator) into the air stream after the humidifier. The other air stream was passed over a sealed Teflon tube which contained the pure liquid contaminant. The contaminant diffused through the walls of the tube into the flowing air stream. This stream of contaminated air was mixed with the humid air containing CO? to yield air at 50 relative humidity, 22” C., containing 0.5 % C 0 2 ,and the desired contaminant level. The combined air stream then passed into a manifold and split into constant composition streams for absorption and kinetic studies. The pressure control valve maintained a constant pressure in the system downstream of the flow control valve and vented any excess contaminated air. AS this system was designed to produce contaminated air in quantities suitable for small-scale studies, the volume available for analyses was small: approximately 5 of the system output of 280 standard liters per hr. Permeation Tube Technique. The Teflon (FEP) permeation tubes were used in two ways: to serve as direct calibration Volume 4, Number 10, October 1970 853
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standards for the various colorimetric determinations, and to prepare reproducibly low concentrations of polluted air for evaluation of the contaminant removal devices. Only minor modifications of the method of O'Keeffe and Ortman (1966, 1969) were found to be necessary for filling the permeation tubes. A dry ice-acetone bath was employed when filling SOs tubes because of its greater vapor pressure. The end of the tube for the sealing ball had to be very thoroughly stretched before filling the tube because of the increased rigidity of the Teflon at -78" C. A dry ice-acetone bath was used for filling tubes with Clz. As Cl? has a higher vapor pressure than SO?, cooling the lecture bottle to -15" C. before filling the tube greatly facilitated transferring the liquid ClZto the tube. Single steel balls of 0.8-cm. diameter were used exclusively to seal the 0.6-cm.-i.d. tubes. No problems with leaks or movement of the balls were encountered even with the high pressures produced by Clz. Determination of Permeation Rates. Permeation rates at constant temperatures for the tubes were determined gravimetrically after the tubes had reached equilibrium in a constant temperature bath (10.17" C. regulation). Based on the results reported in the literature (O'Keeffe and Ortman, 1966; Scaringelli, Frey, et al., 1967; Thomas and Amtower, 1966) the weight loss was assumed to be due entirely to permeation of the gas through the tube. The weight OS. time data for all permeation tubes prepared in this project were linear as long as the temperature was constant. Therefore, the permeation tubes were used for preparation of standard, dynamic samples of NOz, SO?, CIS,and H F at concentrations in the low p.p.m. range. No difficulty in reproducing permeation rates in terms of moles per hour per meter of tube was encountered as long as the temperature remained constant within ~k0.25"C. Because of anticipated difficulties at high pressures, we decided not to attempt to use permeation tubes for HC1. Colorimetric Analysis by the Syringe Technique
Syringes have been suggested for analysis of higher concentrations (above 1 p.p.m.) of NO? (Averell, Hart, et al., 1947; Patty and Petty, 1943; Saltzman, 1954). Since the concentrations of interest in this project were in the range of 1 to 50 p.p.m., it was decided to evaluate the syringe technique as a substitute for the more common bubbler method. The plastic syringes gave more reproducible results than glass syringes made by the same manufacturer. Glass syringes consistently indicated a concentration lower than the actual concentration as calculated from the air mass flow rate and the contaminant permeation rate. They were also tried for the analysis of SO2. The same phenomenon occurred regardless of the amount of pretreatment or how many samples had been taken with the glass syringes. Because of these variations, disposable 50-ml. polypropylene syringes (Becton, Dickinson, and Co., no. 85OL/S)were selected instead of the glass syringes for routine gas analysis by colorimetry. Disposable 22-gal. stainless steel needles with polypropylene hubs (Becton, Dickinson, and Co., no. 1000) were used. Each syringe required preconditioning prior to use. Most of the oil used by the manufacturer for lubricating the plunger was removed by rinsing once with acetone. Then, a high concentration (several thousand p.p.m.) of the gas was left in the syringe overnight. A noticeable effect occurred when the syringes were unused for periods greater than 1 hr. The initial results obtained after such a period indicated a lower concentration than was 854 Environmental Science & Technology
actually present. If the period between samples was close to an hour, usually only the first sample gave low results. After an overnight period, it was not uncommon for the first three samples to be in error. This seems to indicate a surface adsorption phenomenon. The only disadvantage of the syringe technique is the lower detection limit achievable. This results from the low gas volume to reagent volume ratio obtainable. Three milliliters was the minimum amount of liquid that could be used with the Bausch and Lomb Spectronic 20 colorimeter when using nominal 1-cm.4.d. cuvettes. This provided a ratio of 47 to 3. Ratios of 3000 and higher are commonly used in bubblers and continuous analyzers. This ratio could be increased by taking multiple gas samples. The precision of this method, however, was very poor. Nitrogen Dioxide. In the evaluation, 5 ml. of the Lyshkow (1965) modified Saltzman NOz reagent were drawn into the 50-ml. syringes. All air was then expelled from the syringe. The syringe was filled to the 50-ml. mark with sample gas from the gas preparation system at the rate of 2-ml. gas (or less) per sec. NO, absorption and color development were complete after 1 min. of gentle hand shaking. The liquid in the syringe was then expelled into a cuvette and read in a colorimeter at 550 m@ using unexposed reagent as the 100ZT reference. The NOn concentration was then changed oker the range of interest, 0.5 to 50 p.p.m. to evaluate the sensitivity of the method and adherence to Beer's law. When it became obvious that the method would definitely be applicable, the above procedure was repeated and a calibration curve was obtained. Pentuplicate determinations here made at each point. The relative error for analysis of NOs by syringe was 0.43% at 41.3p.p.m., 1 . 0 3 ~ a t 2 6 . 3 p . p . m . , 2 , 8 3 ~ a t 9 . 8 p . p . m . , 1 . 7 7 % at 5.7 p.p.m., and 2.29% at 2.6 p.p.m. The lower detection limit for NOr by the syringe technique was determined experimentally as 0.07 p . p m Beer's law was followed to 60 p . p m NO,. The syringe technique has several important advantages. Analyses can be made rapidly and conveniently. Even with the 1-min. color development period for NOz samples could be taken every 3 min. with the same syringe. This allowed a large number of analyses to be made over a short period of time. Equally important is the small air sample size required, 45 ml. In our system, this was so small as to have no appreciable effect on system equilibrium. Also important are the nominal cost of the syringes and the decreased reagent requirements. Sulfur Dioxide. As a result of Lyshkow's (1967) demonstration that SOz could be reproducibly absorbed in water rather than in sodium tetrachloromercurate(I1) solution prior to addition of the p-rosaniline color developing reagent, it seemed reasonable to suppose that SOs could be absorbed directly into the p-rosaniline solution (West and Gaeke, 1956), thereby giving a one-step procedure with direct color formation in the syringe, A calibration curve was prepared using this method. The data were linear on a semilogarithmic plot. The relative error for SOawas 1.73% at 33.5 p.p.m., 3.12z at 25.3 p,p.m., 1.95% at 15.3 p.p.m., 1.84z at 10.9 p.p.m., 2 . 1 3 z at 6.1 p.p,m., 2.07% at 2.9 p.p.m., and 4 . 5 9 z at 1.2 p.p.m. Using 3 ml. of reagent and 47 ml. of gas, the method had an experimental lower detection limit of 0.17 p.p.m. The method was better in the range of 1 to 33 p.p.m. Because of these results, the one-step method was accepted and used for all subsequent SOzanalysis. All analyses were made at 560 mp. The shelf life of Lyshkow's (1967) concentrated prosaniline solution was verified as six months. The working solution pre-
pared from this concentrated reagent has a shelf life limited to about a week. Free Chlorine. The o-tolidine method was selected for primary evaluation for two reasons. It offered direct, rapid color development which made it readily adaptable for use in the syringes. The method had also been used successfully by Andrew and Nichols (1961, 1962) for the analysis of free chlorine in air. The optimum concentration of o-tolidine was found to be 0.005 g. per liter for the air sample volumes used in this work. Reagent prepared using this o-tolidine concentration gave stable, reproducible colors when 100 ml. of concentrated HC1 per liter were used in the reagent. The absorption maximum occurred at 450 mp. To achieve maximum sensitivity, the minimum amount of liquid, 3 ml., was used in the syringes to absorb free chlorine from a 47-ml. gas sample (23" C., 685 mm. Hg abs.). Under these conditions, the lowest detectable amount was 0.12 p.p.m. Clnin air. The manner of drawing the gas sample into the syringe affected the reproducibility of the method. The consistency was improved when the syringe was held above and nearly perpendicular to the gas sample line. In this way the Cln bubbled through the o-tolidine reagent in the syringe and was immediately absorbed. Contact of the free chlorine with the syringe walls was thus minimized. This was necessary as free C12 is apparently preferentially absorbed on the walls of the plastic syringe. Reproducibility was also enhanced by thoroughly rinsing the syringes with fresh reagent between each sample. The relative error using the above technique was 1.43% at 38.4 p.p.m.. 3.44% at 27.9 p.p.m., 2.92% at 17.4 p.p.m., 2.21 at 10.9 p.p.m., 2.61 % at 6.5 p.p.m., and 3.41 % at 4.0 p.p.m. Reproducibility was poorer when glass syringes were used. Hydrogen Chloride. For the evaluation of the various colorimetric methods for HC1 analysis, standard samples were prepared gravimetrically from reagent grade NaCl and a constantly boiling HCI-water solution. These samples were prepared to correspond to the amount of HC1 which would be absorbed in 3 nil. of reagent from a 47-ml. gas sample at concentrations of 0.5 to 50 p.p.m. of HC1 in air. The revised method of Iwasaki, Utsumi, et a[. (1956) was found to be marginally acceptable with respect to sensitivity. The unexposed reagent had a yellow color which deepened to a reddish-brown on exposure to HC1. The absorption maximum occurred at 460 mp. The use of distilled water containing less than 0.7 p.p.m. total solids significantly reduced the color of the unexposed reagent. The increased solubility of Hg(SCN)e in the mixed solvent (2 volumes 1,4dioxane plus 1 volume ethanol) used in this method increased the sensitivity to HC1 over that of the Andrew and Nichols (1961, 1962) method. Sensitivity was also increased by using spectrograde, rather than technical grade, 1,4-dioxane. Increasing the Fe+,, concentration by one third of the recommended amount resulted in a further sensitivity increase of 25 %. After these improvements had been incorporated into the procedure, a calibration curve was prepared with 2 ml. of mixed reagent plus 1 ml. of standard solution in each cuvette. The standard solutions were volumetrically diluted from a primary standard so that only 1 ml. of solution had to be added to the mixed reagent to achieve a given air equivalence. The deviation from Beer's law in the range of 0 to 5 p.p.m. was quite severe. In the region of 5 to 50 p.p.m. HC1 in air, however, Beer's law is followed reasonably well. This was not a handicap for utilization of the method because a full-range calibration curve had been prepared.
For the analysis of an air stream containing HCl, 2 ml. of reagent plus 1 ml. of water were used to correspond to the volume of liquid used in the calibration. Because of the flat slope of the calibration curve in the region of 5 to 50 p.p.m. HC1, the relative errors for analysis of samples in this concentration region were quite high. At 30 p.p.m. HC1 in air, the relative error was 24.7%. It was 16.8% at 22.0 p . p m and 10% at 12 p.p.m. In the low p . p m range, 0 to 5 p . p m HC1 by volume, corresponding to the adsorber and reactor effluent concentrations, the relative error was consistent and only 8 %. This was determined using 10 determinations at the 2 p.p.m. of HC1 in the air level. It was thus felt that this method is acceptable for use with low concentrations of HC1 in air even though the precision of the method leaves something to be desired at the higher HC1 levels. The lower detection limit of this method was found experimentally to be 0.5 p.p.m. of HC1 in air. Hydrogen Fluoride. The ferric sulfosalicylate method reported by Andrew and Nichols (1961, 1962) was found marginally usable in the range of 5 to 50 p.p.m. H F in air when using 47-1111. gas samples. The bleaching was evaluated spectrophotometrically at 520 mp. The precision of this method was a uniform i1 . 5 z T which corresponded to a relative analysis error of 16 to 19% depending on the concentration. It was necessary to prepare all reagents with commercial fluoridefree distilled water containing less than 0.7 p.p.m. total solids. It was also necessary to rinse all pipets, syringes, and cuvettes five times with fluoride-free distilled water prior to preparing any calibration standard or taking gas samples for H F analy-
sis Calibrations were performed using 2 ml. of the Andrew and Nichols reagent plus 1 mi. of distilled water. Calibration standards were prepared using 2 ml. of reagent plus 1 ml. of standard NaF solution. Even when the unexposed reagent used as a blank was set at 80 Z T for 0 p.p.m. HF, the usable colorimetric range was only 14.1 ZT. Thus, 47 p.p.m. H F in air corresponded to 94.1 Z T . Acknowledgment The authors are grateful to NASA for the support of this research under Contract NAS1-7584 and for permission to publish these results. The authors are grateful to R. R. Graham for assistance in designing and testing of the systems described above. Literature Cited Andrew, T. R., Nichols, P. N. R., Material Research Laboratory Rept. No. MR 907, Mullard Radio Valve Co., Ltd., Mitcham, Surrey, England, (1961, appended 1962). Averell, R. P., Hart, W. F., Woodbury, N. T., Bradley, W. R., Anal. Chem. 19,1040 (1947). Iwasaki, I., Utsumi, S., Hagino, K., Ozawa, T., Bull. Chem. SOC.Japan 29,860 (1956). Lyshkow. N. A., J . Air Pollut. Control ASS.15. 481 (1965). Lyshkow; N. A.,'ibid. 17,687 (1967). O'Keeffe, A. E., Ortman, G. C., Anal. Chem. 38, 761 (1966); ibid. 41,1580 (1969). Patty, F. A., Petty, 6. M., J. Ind. H y g . Toxic. 25, 361 (1943). Saltzman, B. F., Anal. Chem. 26, 1949 (1954). Scaringelli, F. P., Frey, S. A., Saltzman, B. E., Amer. Ind. H y g . Ass. J. 28, 260 (1967). Thomas, M. D., Amtower, R. E., J. Air Pollut. Control Ass. 16,618 (1966). West, P . W., Gaeke, G. C., Anal. Chem. 28, 1916 (1956). ~I
Receioedfor reoiew September 29,1969. Accepted April 3, 1970. This work was presented at the 1969 Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, Pittsburgh, Pa, March 6 , 1969. Volume 4, Number 10, October 1970 855
