Rapid Combustion Method for Determination of Sulfur in Lead Dioxide Candles Exposed to Atmospheric Pollution Prem N. Vijan Laboratory and Research Branch, Ontario Department of Mines, Toronto, Ontario, Canada
A high temperature combustion method is presented for rapid and accurate determination of sulfur in lead dioxide candles exposed to atmospheric pollution. The sulfur-bearing material is stripped from the candle, dry ashed, pulped, and weighed. A weighed portion is burned in oxygen atmosphere in an induction furnace and sulfur dioxide liberated is titrated iodometrically. Data are presented to show the close agreement of results obtained by the proposed method and the gravimetric method on duplicate field candles. The precision and accuracy of the method are tested on simulated lead dioxide candles. Seven man-hours are required for the analyses of 14 candles.
T
he emission of sulfur dioxide gas during smelting of sulfide ores can cause injury to vegetation which sometimes leads to claims for damages. The damage by Fumes Arbitrator Act provides the machinery for settling disputes arising from damage claims. The monitoring of atmospheric sulfur dioxide levels in the Sudbury district and other areas of known emission is carried out to assist in the administration of the Act. The lead dioxide candle is (Gt. Brit. Dep. Sci. Ind. Research, 1952; ASTM, 1966) widely used for measuring sulfurous contaminants in the atmosphere. It consists of a lead dioxide coated tapestry cloth wrapped around a cylindrical form. The coated surface has an area of 100 sq. cm. On exposure in the area to be monitored, it binds sulfurous gases in the atmosphere as lead sulfate. At the end of the sampling period, the coated cloth is stripped and analyzed for sulfur. The conventional gravimetric procedure (Gt. Brit. Dep. Sci. Ind. Research, 1952; ASTM, 1966) used up to this time is a reliable method but requires a close control of the conditions of precipitation to get the best results and is considered too time consuming for routine work. A simple and rapid, but accurate method was considered desirable for this determination. A few attempts have recently been made to simplify the determination of sulfur in lead dioxide candles. These involve the use of titrimetry, colorimetry, and acidimetry (Bowdon, 1964; Kanno, 1959;Rayner, 1966). All of them require the initial alkaline extraction of sulfate ion and involve various steps like filtration, ion exchange procedures, and pH control. They present difficulties in the analysis of control candles whose sulfur content is very low. The analysis time per candle is relatively very long and the methods are subject to various interferences. This paper describes a method that combines a simple procedure for sample preparation with the determination of
sulfur by high temperature combustion, (Gerhardt and Dyroff, 1956; Holler and Klinkenberg, 1951; ASTM, 1956) using potassium iodate as titrant for sulfur dioxide and starch iodide solution as indicator. Experimental
A Leco (Laboratory Equipment Corp.) induction furnace model 523-300equipped with model 518 Sulfur titrator and accessories for sulfur analysis, was used. Reagents used were a 1.1 11-gramsper liter potassium iodate solution, 1.5z hydrochloric acid, and a 1% solution of arrowroot starch containing 3.0grams of potassium iodide and a pellet of sodium hydroxide. All the chemicals used were reagent grade. Lead peroxide powder was obtained from British Drug Houses (Canada), Ltd. Gum Tragacanth No. 1 Ribbon Grade was used. Preparation of Standard Simulated Candles. Place 8.0 grams of lead dioxide and 0.050 gram of gum tragacanth on a 15 sq. cm. piece of household aluminum foil. Add calculated amount of lead sulfate (Table I). Mix the ingredients with a 10 sq. cm. piece of sulfur-free tapestry cloth (supplied by B. R. Dreisinger), rolled up to serve as a stirrer. Finally, cut the cloth into a few pieces and add to the mixture. Wrap the aluminum foil around the mixture.
Table I. Determination of Sulfur at Various Levels in Simulated Candles by Combustion Methods" Present
0.50 1 .OO
1 .OO 1 .oo 1.50 2.00 2.50 3.00 3.50 4.00 4.50 5.00 6.00 7.00 8.00 10.00
Found
Recovery
0.52 1.05 0.99 1.01 1.49 1.94 2.46 2.93 3.29 3.88 4.44 4.84 5.97 7.02 7.84 9.86
104.0 105.0 99.0 101 .o 99.3 97.0 98.4 97.7 94.0 97.0 98.7 96.8 99.5 100.3 98.0 98.6
z
Av. Recovery = 99.0 Std. dev. = 2.685z 0
Results expressed as mg. SO8 per 100 sq. cm. per day.
Volume 3, Number 10, October 1969 931
Field Candles were made as described in Method D2010-65 (ASTM, 1966). Procedure. Cut the lead dioxide-coated cloth with a sharp razor blade and strip it open with two pairs of tweezers. Carry out this operation on a glazed paper surface under the fume hood. Transfer the fabric to a 225 sq. cm. piece of aluminum foil, keeping the coated surface upwards. Deposit a thin layer of zinc oxide powder on top of the lead dioxide coating. This is accomplished by dispensing zinc oxide from a flat-topped glass bottle fitted with an 80-mesh nylon net. Wipe the ceramic former as well as the glazed paper surface with a piece of filter paper and place it on top of the zinc oxide coating. Ignite the filter paper and let the glow spread quietly until the whole fabric and the lead dioxide have burned down to a greyish mass. Gather the ashed material in the center of the aluminum foil and turn it over a few times playing a quiescent propane torch flame over it to burn any remaining fibres. Transfer the material quantitatively to a weighed Snap Cap plastic vial (5 cm. high x 2.5 cm. diameter). Reweigh the vial and record the weight of the ash. Add a plastic ball (0.5 cm. diameter) to each vial and shake for 5 minutes in a mixer-mill to pulverize the ash. Treat the simulated candles in the same manner as the stripped field candle. Weigh accurately about 1 gram of each sample into the zircon crucibles. Add one scoop each of the tin metal accelerator, the iron chip accelerator, and a ring of copper metal to each crucible. Cover the crucibles with the porous silica covers. Also weigh accurately about 38 mg. of lead sulfate in duplicate and add the accelerators likewise. Get the sulfur titrator ready for operation and assemble the induction furnace using clean vycor combustion tube. Adjust the oxygen flow to 1 liter per minute and complete the titration (Laboratory Equipment Corp., 1956). Interpose the lead sulfate standards in the middle and at the end of the series of samples. Record the burette readings and express the results as milligrams of sulfur trioxide per 100 sq. cm. per day of exposure period.
Table I1 shows the results obtained on a field candle. The pulp from the ashed candle was titrated 10 times on different occasions. The results show a standard deviation of 0.0162. The degree of precision confirms the homogeneity of the Pulp. Table I11 shows the results of experiments designed to compare the precision of the combustion method with that of the conventional gravimetric method. The results refer to two dissimilar sets of candles, a i is evident from their exposure dates, and have no bearing on the accuracy of the combustion method. Table IV shows the results obtained on duplicate field candles analyzed by the gravimetric and the combustion methods. The College Street candles were supplied by the Air Pollution Control Laboratory, Toronto, and the rest were
Table 11. Repeat Analysis of an Ashed Candle. Mg. SO8 per 100 Sq. Cm. per Day Mean Dev. Date Analyzed 0.98 -0.008 22-2-67 0.98 -0.008 0.97 -0.018 22-3-67 0.98 -0.008 17-4-67 " 0.99 +0.002 " 0.98 -0.008 0.99 +0.002 0.99 +0.002 ' +o. 042 1.03 ' 0.99 +o. 002 6'
6'
Std. dev. 5
Mg. SO3
Method Gravimetrica
Mean Table I shows the results obtained on simulated candles containing known amounts of sulfur. An over-all average recovery of 99% is obtained with a satisfactory degree of accuracy. The results also indicate that the sulfur losses occurring as a results of the ashing process are negligible. Majority of the field candles contain less than 120 mg. of sulfur trioxide although considerably higher values have been recorded once in a while. None of the field candles analyzed in the author's laboratory even exceeded 300 mg. sulfur trioxide content. The results in this table are expressed as milligrams of SOsper 100 sq. cm. per day, based on a 30-day exposure period, for the sake of uniformity. 932 Environmental Science & Technology
010 0.0162
Burwash Candle exposed from Jan. 4 to Feb. 1, 1967.
Where: x = number of burette divisions of potassium iodate used for sample. y = number of burette divisions of potassium iodate used for standard. W = total weight of ash in grams. w = weight of ash, taken for analysis, in grams. S = milligrams SO8 present in lead sulfate taken for standardization. D = number of days the candle was exposed. Results and Discussion
=
Table 111. Comparison of Precision of Gravimetric and Combustion Methods
Calculations: x w s Milligrams SO3 per 100 sq. cm. per day = - X - X Y W D
*o.
Mean = 0.988
Combustionb
per Sq. Cm. per Day 1.49 1.45 1.50 1.42 1.45 1.46 1.52 1.46 1.45 1.45 1.46 1.32 1.30 1.27 1.32 1.29 1.32 1.28 1.29 1.30
__.
Mean
Mean Dev. +0.03 -0.01
Std. Dev.
+0.04
-0.04 -0.01 0.00 +0.06 0.00 -0.01 -0.01 AO.021
0.030
+o
.02 0.00 -0.03 +0.02 -0.01 +0.02 -0.02 -0.01 rt0.016
0.020
Candles analyzed by gravimetric method were exposed from 5-5-67 to 31-5-67. Candles analyzed by combustion method were exposed from 2-6-67 to 22-6-67. a
*
5.0 I
33r4mw w
m
~
???1? ? ? ? ?
t/
w
0 0 0 0 0 0 0 0 0
I + l
I I + I
I
0.2
I I
1
I
0,s
1
I
l
l
1
I
1.0
2.0
I
I
A
5.0,
mg. SO3 per 100 $9. em. per day ( Combustion Method ) t - N Q \ N r tm
???"?
3 3 w w o
w m m m???
Figure 1. Plot of Table IV data (gravimetric method us. combustion method)
A O O N
~ ) m ~ w m wmw r t W???? Y-??? 0 3 - 3 0 3 0 0 N
? 0
I
furnished by the Sulfur Fumes Arbitrator of the Department of Mines, Sudbury. The curve in Figure 1 shows the plot of data in Table IV in the form of milligrams SO8 per 100 sq. cm. per day by gravimetric method versus those by the combustion method. For all the duplicate determinations, the differences expressed as percentage of the gravimetric results give an average of 7.3 %. A mean deviation of f 0.092 and a standard deviation of 0.131 from the gravimetric results is shown up to 4.17 mg. of SO3 per 100 sq. cm. per day level. The total amount of sulfur trioxide, in terms of milligrams of so3 per 100 sq. cm. per day, for all samples analyzed by the combustion method is 96.2% of the amount determined by the gravimetric method. The agreement between the two methods shown by the results in Table IV is good, considering that the deviation shown from the true results are composite of sampling, handling, and analytical errors. The combustion results, on the whole, appear to be slightly lower than the gravimetric results. The gravimetric results, on the other hand, tend to be slightly higher than the true values. A few ashed simulated candles represented in Table I1 were also analyzed by the gravimetric method and the results were higher by an average of 2.5 %. Several barium sulfate precipitates obtained from routine gravimetric analyses of sulfur dioxide candles were examined spectrographically and all of them showed more than trace amounts of lead. This could be due to the coprecipitation unless a very strict control of precipitation conditions is exercised. The combustion method is subject to interference by nitrogen and chlorine if present in appreciable amounts. The two elements are present as trace impurities in lead dioxide and have negligible effect on the iodometric titration. If the exposure conditions are such that large amounts of chlorine and nitrogen are present in the candle material, modified titration procedures are available to prevent interference (Conrad, Evans, et a/., 1959; Nagel, 1960). Interference due to nitroVolume 3, Number 10, October 1969 933
gen and chlorine becomes evident from the intensification of blue color of starch solution in the titration vessel (left-ward swing of galvanometer needle of the titrator from its initial setting), before the normal fading due to sulfur dioxide begins. The tolerance to chlorine is much greater than to nitrogen because at low concentration chlorine is liberated as hydrochloric acid under the conditions of combustion used. No interference due to chlorine and nitrogen was encountered in this work. The combustion method measures total sulfur in the candle irrespective of its source. The depositing of the zinc oxide layer on the stripped candle material slows down the vigorous reaction and prevents the formation of fine beads of metallic lead. The attractive feature of the method is dry ashing, which destroys the active ingredient, lead dioxide, and eliminates any possibility of sulfur contamination from the laboratory atmosphere. It also eliminates the time consuming procedures like extractions, filtrations, ion exchange, evaporations, and pH adjustments. Burning the sample in a high frequency induction furnace offers the obvious advantage of speed. One candle requires 30 minutes to analyze. The average yield of ash per candle is about 7.5 grams. One gram is normally used for analysis, leaving behind enough for storage and rechecking. If desired, the exposure period of the candles can be considerably shortened because the method is particularly
suitable for the determination of low sulfur values. The method has been in satisfactory use for more than a year. Acknowledgment
The author thanks D. A. Moddle and W. 0. Taylor for their valuable suggestions and comments, and B. R. Dreisinger and A. C. Rayner for providing the material for this work and permission to publish the results. Literature Cited Am. SOC. Testing Materials; ASTM Standards Industrial Water; Atmospheric Analysis, 813, 1966. Am. SOC.Testing Materials; ASTM Standards on Petroleum Products and Lubricants, 949,1956. Bowdon, S. R., Znt. J . Air Water Poll., 8, 101 (1964). Conrad, A. L., Evans, J. K., Gaylor, U. F., Anal. Chem. 31, 422 (1959). Gerhardt, P. B., Dyroff, G. V., Anal. Chem. 28,1725 (1956). Gt. Brit. Dep. Sci. Ind. Research, Fuel Research, 10, 22 (1952). Holler, A. C., Klinkenberg, R., Anal. Chem. 23, 1696 (1951). Kanno, S., Znt. J . Air Poll., 1, 231 (1959). Laboratory Equipment Corp., St. Joseph, Mich., “Leco Method for Sulfur Determination,” (1956). Nagel, B. E., General Motors Corp., Detroit, Mich., private communication, 1960. J 16,418 (1966). Rayner, A. C., Air Pollution Control ASSOC., Received for review September 20, 1968. Accepted April 24, 1969.
Effects of Air Pollutants on Growth, Leaf Drop, Fruit Drop, and Yield of Citrus Trees C. Ray Thompson and 0. C. Taylor Statewide Air Pollution Research Center, University of California, Riverside, Calif. 92502
Commercially producing lemon and navel orange trees were studied to determine the effects of the air pollutant complex, especially photochemical oxidants and fluorides, in the Los Angeles Basin on the following responses: growth; weight of prunings; leaf drop; fruit drop; and yield of mature fruit. The results showed that overall growth was not affected significantly. Leaf drop was significantly less in lemons where carbon filtered air was supplied to the trees. A similar trend was present in oranges but was not significant statistically. Fruit drop in navel oranges was significantly less in carbon filtered air than in ambient. Yield of fruit is also reduced significantly by photochemical oxidants, sometimes by as much as 50%.
T
he deleterious effects of photochemical smog on economic plants are becoming well recognized wherever the emissions from automobiles and other fossil fueled combustions are high and weather patterns are stable (Middleton, 1961; Middleton, Emik, et al., 1965). Fluorides emitted from phosphate fertilizer manufacture, aluminum reduction, steelmaking, ceramic firing, and some chemical processing can cause plant damage if levels are not controlled (Thomas, 1961). Air pollutants were suspected as the cause of reduced productivity of citrus in the Los Angeles Basin in the early 934 Environmental Science & Technology
1950’s but because these trees fail to show outward, easilyrecognized pathological symptoms from either photochemical smog or fluoride except under severe conditions of exposure, proof of actual injury was unavailable. Also, if damage occurred, an accurate determination of the actual economic losses being suffered by agriculture forced the devising of a field scale study under a unique cooperative venture (Richards and Taylor, 1960) which was supported by agriculture, industry, local and national governments, various private organizations, and the University of California. The details on greenhouse design (Thompson and Taylor, 1966) and the systems for air treatment with NO and H F have been published elsewhere (Thompson and Ivie, 1965). The effects of the treatments on apparent photosynthesis and water use of citrus trees were published previously (Thompson, Taylor, et a[., 1967) and showed that both responses were significantly reduced by the photochemical smog complex. Ambient fluoride levels had no demonstrable effect. The present manuscript gives final data on the growth, leaf drop, fruit drop, and yield of two species of citrus as they were affected by the air pollutant complex in the Los Angeles Basin.
Methods The experimental arrangement of the three citrus groves, two lemon and one orange, used in this study is detailed in a previous report (Thompson, Taylor, et al., 1967). The studies were begun on lemons in June 1961 and February
