Analysis of Barium Sulfate by Atomic Absorption Martha Magyar, John L. Bove,' Benjamin Nathanson, Stanley Siebenberg, and Edward F. Ferrand Department of Air Resources, New York, N.Y. 10003
A
A novel, simple method for analyzing total airborne barium collected in high-volume samples with use of atomic absorption spectrometry is described. The reducing potential of filter paper on barium sulfate is utilized to reduce quantitatively the insoluble barium compound to acid soluble barium sulfide.
B
arium-containing smoke suppressants have been suggested as a possible solution to the problem of smokeemitting, diesel-powered vehicles. The barium additive is blended in small quantities into the diesel fuel before its use. In addition to the need for evaluating the barium additive as a smoke suppressant, the toxicity of barium compounds in the exhaust (Sax, 1957) must also be considered. Concomitant with field testing of the barium-containing suppressant in a fleet of New York City buses, airborne particles were collected with use of a high-volume sampler and analyzed for total barium content (soluble barium compounds and insoluble barium sulfate). Analysis for total barium content has been performed by emission spectroscopy with a 1.5-m direct-reading spectrograph (Curry, 1969). This method produces satisfactory results, but requires expensive equipment and highly trained personnel. This communication describes a novel, simple method for analyzing total barium in high-volume samples by atomic absorption spectrometry. Chemical preparation of the samples is simple, quantitative, and the instrumentation is inexpensive and easy to operate. This analytical procedure utilizes the reducing potential of filter paper on barium sulfate, a phenomenon which has long been recognized (Pierce et al., 1959; Rieman et al., 1951). The manner in which small quantities of barium sulfate collected on a paper matrix can be quantitatively reduced to acid soluble barium sulfide is also described. Experimental
Instrumentation. Barium concentrations were determined with a Jarrell-Ash fully compensated atomic absorption spectrophotometer equipped with a Jarrell-Ash laminar-flow burner. This instrument incorporates all logic and command circuits necessary for automated sample presentation and concentration readout. It uses two monochromators which space-share the hollow cathode light that passes through the flame. The monochromators also time-share light that bypasses the flame, and subsequent electronic circuits correct light variations. The automatic instrument consists of a specimen handler (accommodates up to 200 samples), an aspiration probe, a preconcentrator system, a sequencer/programmer unit, a concentration computer/digitizer, and a teletype paper To whom correspondence should be addressed. Present address : Chemical Engineering- Deuartment, The Coouer Union . for the Advancement of Science and Art, Cooper Sqiare, New York, N . Y . 10003. 358 Environmental Science & Technology
tape punch. The analyses were performed by using the 4555 spectral line in conjunction with a fuel system of nitrous oxideacetylene. Although the instrumentation used in these analyses is highly automated because of the nature of some of the other work performed in these laboratories, any recognized model atomic absorption spectrophotometer can be used. Sample Collection. Airborne particles were collected on 8 x 10-in. Schleicher and Schuell 589 green ribbon paper mats with a high-volume sampler. One portion of this high-volume sample was used to analyze solution barium compounds while the other portion was used to analyze the total barium content (soluble barium compounds and insoluble barium sulfate). Analytical. Three types of barium samples were analyzed. In one case, a known volume of a solution of barium chloride was pipetted on 14 in.* of filter paper, followed by dilute sulfuric acid treatment to convert all of the barium to barium sulfate, In a second case, 1000 pg of solid barium was weighed, transferred to 14 i n 2 of filter paper, and then analyzed for barium. In the third, portions of high-volume samples collected a t a diesel bus fuel stop were analyzed for barium by the atomic absorption technique, and these findings were compared with the results obtained with a direct-reading spectrograph (Curry, 1969). CASE1. Solutions (1 ml) prepared from Baker and Adamson reagent-grade BaCh 2 H 2 0containing 250,500, and 1000 pg/ml of BaCh were pipetted onto a 14 in.2 (2-x7) strip of Schleicher and Schuell 589 green ribbon paper. The papers were then treated with 2 ml of dilute sulfuric acid solution (540-1). The samples were dried again at llO"C, and finally 0.5 g of ashless powdered filter paper (W. R. Balston Ltd.) was placed as a blanket over the samples. Platinum crucibles containing the samples were ashed in a muffle furnace for 0.5 hr at 350"C, followed by 1 hr at 600"C, and finally at 700°C for 1 hr. The ashed samples containing the residues of 250, 500, and 1000 pg/ml of barium were treated with 5, 5 , and 10 ml of Mallinckrodt Transist AR-grade nitric acid (1-to-3), applying heat as necessary to complete the dissolution. The resulting solutions were carefully heated on a hot plate to near dryness, transferred to volumetric flasks of appropriate capacity to keep the concentrations within the linear response of the instrument, and diluted to the mark, The 1000 pg/ml barium sample was diluted to 200 ml, the 500 pgjml barium sample was diluted to 100 ml, and the 250 pg/ml barium sample was diluted to 50 ml. The solutions at this point are ready to be analyzed with the atomic absorption spectrophotometer. CASE2. Reagent-grade barium sulfate (1000 pg) was washed onto a 14 in.*(2-x7) strip of Schleicher and Schuell589 green ribbon paper and was placed in a platinum crucible. Fourteen runs were performed. The samples were dried at 110"C in an oven, ashed in a muffle furnace, and prepared for atomic absorption analysis in the same manner described in Case 1. CASE3. Airborne particles were collected at a bus fuel stop on an 8-XlO inch Schleicher and Schuell 589 green ribbon paper matrix, using a high-volume sampler (HEW,1962) capable of handling 30 to 50 cfm of air sample. Of the 8 0 - i ~ ~ paper matrix used, 7-X9 in. (63 in.*) were exposed to air
sample. On each sample, a strip (10.1 in.*) was cut from the exposed mat with use of a plastic cutting guide. The strips were folded into platinum crucibles, ashed, and chemically treated prior to atomic absorption analysis in the same manner as in Case 1. A corresponding segment (4-X7 in.) of the same highvolume sample was wet-ashed with nitric acid-perchloric acid, followed by hydrogen peroxide, dissolved in nitric acid, and diluted with water f$r analysis. The analysis was performed utilizing the 4555 A line of a Jarrell-Ash 1.5-m directreading spectrograph (Curry, 1969). Results
CASE1. When barium chloride solutions were converted to barium sulfate and then reduced to barium sulfide through the ashing technique, the recovery of barium was excellent. Several runs performed on samples containing 1000, 500, and 250 pg/ml of barium gave an average recovery of 100,99, and 96 %,
Table 111. Comparison of Analytical Results of 11 Samples Collected a t Bus Fuel Stops Barium found on 63-in.2 matrix, pg Total barium,a Atomic Direct-reading Run pg/m3 absorption* spectrograph; 1.27 153 158 1 90 0.83 104 2 3 4 5 6 7 8 9 10 11
1.43 1.27 1.18 5.1 8.6 6.1 13.0 20.1 8.2
199 134 156 946 1330 841 1417 2146 1271
160 138 132 706 1040 851 1531 2337 1254
0 An average barium concentration of 0.03 mg/m3 was reported from New York City’s Aerometric network from June to December 1969. * Reading represents the average of five runs of the original solution. c Analysis performed utilizing the 4555 A line of a Jarrell-Ash no. 66-000 Compact Atom Counter (1.5-m direct-reading spectrograph).
Table I. Results of Recovery Experimenta Run 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
Barium concn, pg
Recov. barium, %
1000 1000 1000 1000 1000 1000 1000 1000 500 500 500 500 500 250 250 250 250 250
110 100 100 96 98 100 110 89 100 101 98 100 96 100 96 94 100 92
Av,
z
barium recov.
Standard deviation
100
7
99
2
96
4
0 Aqucous BaClz converted to BaSO4. Filter-paper ashing technique. Analysis by atomic absorption.
respectively. The results are summarized in Table 1. CASE 2. The recovery of 14 runs containing 1000 pg of solid barium sulfate was excellent. The average recovery for the 14 runs was 9 4 z , Table I1 summarizes these results. CASE 3. Total airborne barium collected with a high-volume sampler on 80- x 10 in. Schleicher and Schuellj89 green ribbon paper was analyzed by both atomic absorption and emission spectrography. The results agree well. There seems to be no high or low trend for either method. The results are summarized in Table 111. The Wilcoxan matched-pair signed rank test was used to determine whether the atomic absorption and the directreading spectrograph readings were the same. This test gives 23 for the sum of values of differences in which the direct-reading spectrograph was higher and 43 for differences in which the atomic absorption was higher. Since the critical value for a two-tail test at 5 risk is 11, it is evident that for this sample observations, the Wilcoxan test does not distinguish between the two methods. The two methods can therefore be considered comparable. Discussion
Table 11. Results of Recovery Experimenta Av. % Recov. barium Standard Run barium, recov. deviation 1 2 3 4 5 6 7 8 9 10 11 12 13 14
96 100 99 88 94 99 88 100 80 98 100 93 95 88
94
6
4 1000, g solid Bas04 added. Filter-paper ashing technique. Analyzed by atomic absorption.
The results obtained in all three cases demonstrate that insoluble barium sulfate can be determined by atomic absorption spectrometry when it is present in small quantities. Work is currently in progress to determine the upper limit for the determination of barium sulfate and, further, to explore the use of this reduction technique to other insoluble compounds. Literature Cited Curry, R. H., Jarrell-Ash, Fisher Scientific, Waltham, Mass., private communication, 1969. Pierce, W. C., Haenisch, E. L., Sawyer, D. T., “Quantitative Analysis,” John Wiley and Sons, Inc., N.Y.,1959, p 368. Rieman, W., Neuss, J. D., Naiman, B., “Quantitative Analysis,” McGraw-Hill Book Co., Inc., N.Y., 1951, p 277. Sax, N. I., “Dangerous Properties of Industrial Materials,” Reinhold Publishing Corp., N.Y., 1957, p 332. U.S. Department of Health, Education and Welfare, Public Health Service, Washington, D.C., “Air Pollution Measurements of the National Air Sampling Network 1957-1961,” publication 987, 1962. Received for reciew October 8, 1969. Accepted December 14, 1970. Volume 5, Number 4, April 1971 359
