2370
Anal. C h e m .
1980,52, 2370-2375
und Wehrtechnick: Erding. West Germany, 4-6 July 1978; p 95a.09.02. (7) Fair, P . S.; Brown, J. R.; Rhine, W. E.; Eisentraut, K. J. presented at the 1979 Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy: Cleveland, OH, March 1979; Abstract No. 357. (8) Rhine, W. E.; Fair, P. S.;Saba, C. S.; Brown, J. R.; Eisentraut, K. J. presented at the 1979 Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy: Cleveland, OH, March 1979; Abstract No. 439. (9) Saba, C. S.; Rhine, W. E.; Brown, J. R.; Fair, P. S.; Eisentraut, K . J. presented at the Sixth Annual Meeting of the Federation of Analytical Chemistry and Spectroscopy Societies: Philadelphia, PA, Sept 1979; Abstract No. 161. (IO) Kahn, H. L.; Peterson, G. E.; Manning, D. C. At. Absorpt. Newsl. 1970, 9 (3), 79. (11) Kriss, R. H.;Barteis, T. T. A t . Absorpt. News/. 1970, 9(3), 78. (12) Bartels. T. T.; Slater. M. P . At. Absorpt. News/. 1970, 9(3), 75. (13) Taylor, J. H.;Bartels, T. T.; Crump, N. L. Anal. Chem. 1971, 43, 1780.
Saba, C . S.; Eisentraut. K. J. Anal. Chem. 1977, 49(3), 454. Saba, C . S.; Eisentraut, K. J. Anal. Chem. 1979, 51(12), 1927. "Trace Metals in Oils by Wet Ash-Spectrographic Method"; U.O.P. Method 389-71, Universal Oil Co.: Des Plaines, IL, 1971. . . Hofstader. P.A.; Milner, 0. I.; Runnels, J. H. "Analysis of Petroleum for Trace Metals"; American Chemical Society: Washington, DC, 1976. (18) Morrison, G. H. "Trace Analysis Physical Method": Interscience: New York, 1965; p 121. (19) "Analytical Methods for Atomic Absorption Spectrophotometry"; PC-1: Perkin-Elmer Corp.: Florwalk, CT, March 1973.
RECEIVED for review June 26,1980. Accepted September 25, 1980. This work was initially presented in part a t the 1979 Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, Abstract No. 607.
Determination of Total Biogenic Sulfur Gases by Filter/Flash Vaporization/Flame Photometry S. 0.
Farwell,"
D. P. L i e b o w i t z , ' R. A. K a g e l , and D. F. Adams
D e p a r t m e n t of Chemistry, University of Idaho, Moscow, I d a h o 83843
Complete conversion of H2S,COS, CH,SH, CH3SCH3,CS2, and CH,SSCH, to SO2 has been shown to occur in a quartz tube held at a furnace temperature of 1050 OC for sample alr flows from 30 mL/min to 2.8 L/min. The resultant SO2-containing air flow is passed through an Inline, precleaned Gelman Spectrograde filter which collects an average of 1.5 f 0.3 kg of S/47 mm filter prior to SO2 breakthrough. The sulfur collected on the filters Is extracted with a recovery of 100 f 3 %. Final quantitative determlnatlons of the sulfur in the filter extracts are performed vla the flash vaporlzatlon/flame photometric (FV/FPD) technique uslng platinum boats. Equivalent FV/FPD linear responses were observed for H2SO4, Na2S04, K2S04, and (",),SO4 standards in the range of 0.4-12 ng of S. Repeated analyses of sulfate standards showed a relative standard deviation (RSD) = f7.0 %. Experimental results obtained for NaHCO,, Na2C03,NaOH, NaCI, KHCO,, K2CO3, KOH, NH4HC03, (NH4)2C03,NH,(aq), FeCI,, MnCI2, and Na2HgCI4as chemical impregnants In glass fiber filters for SO, collection and their compatibility with the FV/FPD system are also described.
T h e determination of biogenic sulfur emissions poses the challenging task of collecting and measuring sulfur-containing gases a t low and sub-parts-per-billion concentrations in air. The majority of the analytical techniques available for atmospheric sulfur compounds were developed primarily for the measurement of the higher concentrations found near localized anthropogenic emissions and, therefore, lack the required detectability for assessing biogenic sulfur fluxes into the atmosphere. Recently, Farwell e t al. ( 1 ) reported the development of a deactivated cryogenic preconcentration glass capillary chromatographic system with sufficient selectivity and detectability for the determination of volatile sulfur compounds a t ultratrace levels. This methodology has been successfully applied to field analyses of sulfur compound emissions from a variety of soils and water bodies in the 'Present address: American C y a n a m i d Co., 1937 West M a i n St., Stamford, C T 06904.
0003-2700/80/0352-2370$01 .OO/O
eastern and southern United States during the past 3 years (2-5). The filter/flash vaporization/flame photometric detection system discussed in the present paper was developed as a second independent technique for quantitative determination of the total gaseous sulfur flux. In the past, liquid chemical devices were most commonly employed for the collection of gaseous sulfur compounds (6-8). However, various chemically impregnated filters have also been reported for the collection of SOz in air samples ( S 1 4 ) . After collection of the SO2 on impregnated filters, there are numerous methods available for the quantitative measurement of the trapped sulfur (6, 8). One such method for sulfur detection and quantification that requires minimal sample preparation has been developed by Roberts et al. (15). Their flash vaporization/flame photometric detection (FV/FPD) technique involves rapid thermal vaporization of a sulfur sample extract placed on a stainless steel strip, followed by flame photometric detection of the resultant SO2. FV/FPD determinations of (NH4)2S0,,NH4HS04,H2S04,and CaS04 standards resulted in equivalent sulfur responses with a detection limit of l ng of s. Husar et al. (16) substituted tungsten boats for the stainless steel strips and thereby increased the number of determinations possible with one sample boat. Whereas equivalent FV/FPD responses were obtained for (NH4)-+304, NH4HS04, H2S04, and ZnSO4, equivalent responses were not observed for the alkali metal sulfates with the tungsten boat FV/FPD system. Tanner et al. ( 17) demonstrated that platinum FV/FPD sample boats have even longer lifetimes than tungsten boats but also reported problems with the volatization of alkali metal sulfates which resulted in nonequivalent sulfur responses. A further variation to the FV/FPD method has been introduced by Huntzicker et al. (18) who placed several microliters of the solution to be analyzed on a 0.025 cm diameter platinum wire rather than a strip or boat. Differences in the response of the latter FV/FPD method were consistently observed for HzSO4 and (NH,),SO,; however, equivalent responses were noted when ammonia solution was added to the sample extracts to neutralize any acid sulfates. For evaluation and optimization of a method for biogenic sulfur emissions using the general filter collection and FV/ FPD techniques, some means of converting the major biogenic 0 1980 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 52, NO. 14, DECEMBER 1980
sulfur gases (H2S, COS, CH3SH, CH3SCH3, CS2, and CH3SSCH3)t o SO2prior to collection was required. de Souza e t al. (19) showed that H2S, CH,SH, CH3SCH3,and CH3SSCH3 are quantitatively converted t o SO2 in an 800 "C Vycor tube. However, no data were reported for the conversion of COS and CSz or the effect on conversion efficiencies if the air flow through the hot Vycor tube was t o exceed 150 mL/min. This paper describes the development and characterization of a n analytical system for measuring total biogenic sulfur gases that combines (a) thermal conversions of the reduced sulfur gases to SO2, (b) subsequent collection of the resultant SO2on Spectrograde glass fiber filters, (c) liquid extraction, and (d) final analysis of the filter extract by flash vaporization and flame photometric detection. The experimental results obtained with various chemically impregnated filters, filter cleaning procedures, and sample recovery techniques are also discussed.
EXPERIMENTAL SECTION F i l t e r s and Chemical Impregnants. Type E, A, AE, Spectrograde glass fiber filters, and Micro-Quartz 47-mm filters were obtained from the Gelman Instrument Co. Nucleopore Model 420400 47-mm polycarbonate filter holders were used. The (NH4)2C03,NaHCO,, Na2C03,NaOH, NaC1, KHC03, KzC03, KOH, KC1, FeCl,, MnCl,, and glycerol were obtained from J. T. Baker Chemical Co. The NH4HC03and ",(as) were from Fisher Scientific Co. All the previous reagents were Reagent Grade and were used without further purification. Photo-Flo and Triton X-100, used as surface active agents, were obtained from Eastman Kodak and Rohm and Hass, respectively. The sodium tetrachloromercurate (TCM) was prepared according to procedures described by West et al. (20). Calibration System and Standards. The following sulfur gases with the corresponding minimum purities were obtained from Matheson Gas Products: HzS,99.5%; COS, 97.5%; CH,SH, 99.570; SOz, 99.9%. The CSzwas Baker Analyzed Reagent Grade with a minimum purity of 99%. The CH3SCH3and CH3SSCH3 were Eastman Reagent Grade with minimum purities of 98% and 97%, respectively. These sulfur compounds were used to prepare Teflon permeation tubes according to recognized procedures (21, 22). The permeation tubes were maintained at 30 A 0.01 "C in a constant-temperature water bath and were calibrated gravimetrically. Standard sulfur gas concentrations were prepared by procedures previously described ( I ) . Purified sulfur-free air was obtained by passing compressed laboratory air through a multibed adsorbent filter in a Drierite 6.7 cm X 29.9 cm gas drying cartridge (1).
The reagents used as FV/FPD standards and their corresponding sources were: NH,HS04 from Fisher Scientific Co.; ("4)804, NaZSO4,ZnS04,and H,S04 from J. T. Baker Chemical Co.; (NH.J2S03 from Matheson Co.; KzS04from Mallinckrodt Inc. Deionized, distilled water was used to prepare the standard solution and was used for all filter extractions. Flash Vaporizer/Flame Photometric Detector. The flash vaporizer employed in this work was based on the initial concept of Roberts and Friedlander ( 1 5 ) . However, a novel solid-state controller for the flash vaporization apparatus was designed specifically for this application and differs from previous units in its programmable range of charging voltages, its accurate feedback voltage control circuitry, and its safety features. The operation of the flash vaporizer circuitry can be described by dividing the schematic diagram shown in Figure 1 into two sections. The first section, located respectively in the upper left-hand and lower right-hand portions of Figure 1,is the charging and charge control circuit. The charging circuit operates from a 25-V regulated power supply constructed from T1, D1, C1, IC1, D2, R1, R2, and C2. Voltage regulation is provided by IC1, a LM309K regulator, that is floated to provide 25 V by adjusting R2, a 10-turn potentiometer. Diode D2 is included to protect the regulator during power shutdown because of the large capacitance on the output side of IC1. Light-emitting diode D6 serves as an indication of power on/off. A constant-charging current of 1 A is provided by Q2, D4, D13, R5, and R6. This charging current
2371
02
&
PD3 Figure 1. Flash vaporizer schematic. Circuit components: D1, MDA-804, M7620 (Motorola); 0 2 , D8, D11, D13, 1N4004; D3, 1N4751 (30 V, 1 W); D4, 1N4735; D5, D6, D7, D10, LED; D9, 1N34A (germanium, 0.3 V); D12, 1N4721; IC1, LM309K (heat sink) (National Semiconductor);Q1, 2N3906; Q2, TIP-34C (heat sink); A l , A2, LH2111D (National Semiconductor); SCR1, GE380A; SCR2, GE-ClO6; C1, 4100 pF, 50 V; C2, l O p F , 25 V; C3, C7, 0.1 pF, 5 0 V ; C4, C5, C6, 110000 pF, 25 V; T1, 24 V; CT, 1 A; SOL, ST-81, solenoid, 12 V (Echlin); R1, y30 Q,' I 2W; R2, R13, 10-turn, 1 kR; R3, 22 kQ, 1/4 W; R4, 5.6 kQ, l 2 W; R5, 250 Q,5 W; R6, 5 Q , 5 W ; R7, 220 Q,' I 2 W; R8, R9, R16, R29, R26, 1 kQ, ' I 4W; R10, 10-turn, 1 k 0 (Bourns); R11, 220 9, ' I 4 W; R12, R14, 10-turn, 500 0; R15, 680 R, '1, W; R17, 10 k 0 , ' I 4W; R18, 1 k 0 , ' I 2W; R19, R21, 0.14 0 ; R20, R22, 0.10; R23, 40 a, 1 W; R25, 5.6 kQ, ' I 4W; RL, flash vaporizer strip; S1, S2, SPST; S3, S5, SPST, momentary contact; 5 4 , solenoid switch: F1, 1 A, 250 V.
is controlled by transistor Q1 which is in turn controlled by either front panel switch S2 or comparator A t . A ground signal from either 5 2 or the output of A1 turns the charging current off. When S2 is open, the output of A1 remains high as long as the charge on capacitors C4-C7 is not as great as the desired flash vaporization voltage which is preset by operator adjustment of the 10-turn R13 potentiometer on the front control panel. The readout dial on R13 is calibrated to correspond directly to the charge on capacitors C4-C7 by potentiometers R10 and R14. Light-emitting diode D5 is on when the charging circuit is on and LED D7 indicates when the capacitors C4-C7 have reached the preselected charging voltage. Comparator A2 functions to detect when the charge on C4-C7 is below the 0.3 V provided by the germanium reference diode D9. If the charge on C4-C7 is less than 0.3 V, then LED D10 attached to the output of A2 is on. Thus, the on/off status of D10 indicates whether it is safe for the operator to open the flash vaporization cell for access to the sample strip RL. The second section of the schematic diagram, located in the lower left-hand portion of Figure 1, is the flash and discharge circuit. The flash circuit is activated by switch S5 which triggers the silicon-controlled reactifier SCR2, which in turn triggers SCR1. This sequence allows the current stored in C 4 4 7 to pass through the flash vaporizer strip RL. Series resistors R19-R22 limit the peak current to less than 1000 A, thereby keeping SCRB within its maximum ratings. Diode D11 prevents any ringing effect due to the current surge. Since the silicon-controlled rectifiers SCRl and SCRB require that the current go to essentially zero before they will turn off, it is necessary to disable the charging circuit by closing S2 before actuation of S5. Safe access to the flash chamber and its contents is possible by pressing switch S3 which activates the selenoid SOL and shorts capacitors C4-C7. The circuits in Figure 1 were constructed on Vectorbord and mounted in an enclosed 30 cm X 34 cm X 20 cm instrument cabinet. A flash vaporization cell identical with the one described by Roberts and Friedlander (15) is mounted on top of this cabinet. The detector used with the flash vaporizer was a Meloy Labs Model SA-285 continuous sulfur analyzer. This Meloy Labs FPD was calibrated periodically with two sulfur dioxide permeation tubes of different loss rates. Peak height responses of the FV/FPD samples were registered on a Varian Aerograph Model 20 strip chart recorder. Additional Instrumentation. A Hewlett-Packard Model 5840 gas chromatograph with a flame photometric detector was used to monitor the thermal conversion of reduced sulfur gases to SOz (1). The thermal conversion-mass balance study was conducted
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ANALYTICAL CHEMISTRY, VOL. 52, NO. 14, DECEMBER 1980
by using a packed Teflon 1.8 m X 0.31 cm Chromosil310 column and a Varian Model 1400 GC with a flame photometric detector. The reduced sulfur gases were converted to SOz via thermal oxidation in a Model F-21115 Thermolyne tube furnace. Filter Procedures. All rotometers and needle flow controllers were calibrated with a wet test meter. Initial blank filter breakthrough studies were at flow rate of 20 mL/min and a sulfur dioxide concentration of 112 ppb. Air passing over the SOz permeation tube was drawn through the filter holder and passed on to the Meloy FPD. Breakthrough was determined when the FPD response increased from base line. Following the preliminary breakthrough studies at low flow rates and high SOz concentrations, breakthrough studies were performed at SOzconcentrations of 10-20 ppb and at a flow of 2.8 L/min. All impregnating solutions were prepared on a weight/volume basis in deionized distilled water and are reported according to percent concentration of the specific chemical impregnant. Some solutions contained 10% glycerol as a humifactant. When Spectrograde filters were impregnated, diluted PhoteFlo solution was added to the impregnating solution as a wetting agent. Gelman AE filters were precleaned by a procedure outlined by Roberts and Friedlander (15). Gelman Spectrograde filters were precleaned by two methods. The first procedure used was outlined by Dasgupta et al. (23). The second precleaning procedure follows. Filters were placed on Pyrex watch glasses in a 500 "C muffle furnace for 12 h. The filters were then removed from the furnace, allowed to cool to room temperature, and soaked in deionized distilled water with ultrasonic vibration for 10 min, followed by several rinses with deionized water. The clean filters were placed on a glass plate, air-dried, and stored in plastic filter holders. The precleaned filters were extracted by cutting the filters into quarters and soaking for 15 min in 6 mL of deionized distilled water with ultrasonic vibration. After the extract solutions were filtered through a fritted glass funnel, the filtrates were concentrated for FV/FPD analysis by either of two following procedures: (a) water-washed Dowex 50W-X8 cation-exchange resin in the hydrogen form was added to the extract solution and was allowed to stand for 10 min with occasional stirring prior to filtering. The final filtrate was then transferred to a 10-mL beaker and slowly evaporated to dryness. The dry residue was then taken up in 1 mL of deionized distilled water. (b) Small ion-exchange columns were used rather than adding the exchange resin directly to the filter extract. These columns were 14.4 cm X 0.7 mm 0.d. glass disposable pipets which were packed to half their capacity with the water-washed Dowex 50W-X8 resin. Before introducing the filtrates onto these columns, each column was flushed several times with 1 N HC1, followed by several water rinses. The filter extract solutions were added to the resin columns via a Pasteur pipet, followed by 1mL of deionized distilled water to rinse the extract solution through the column. The columns can be reused following regeneration with several 1 N HC1 and deionized distilled water rinses to ensure low sulfur carry-over from previous samples. The final solutions for FV/FPD analysis were made up to exactly 1 mL in water. Flash Vaporizer Procedures. All stainless steel strips and tungsten and platinum boats were precleaned to reduce the background sulfur response. The cleaning procedure involved rinsing the strips or boats in 3.0% H3P04 for 10 min with ultrasonic vibration, followed by several rinses with deionized distilled water and drying in an oven at 110 "C. Even after this cleaning procedure, several blank conditioning flashes were necessary to produce a constant low background FV/FPD response for the strips and boats. Aliquots of 1.5 pL, or less, of standard or filter extract solution may be placed on the FV strip or boat. The aliquot size was limited by the spreading of the solution to areas which are not sufficiently heated. Aliquots were placed on the strip by discharging the syringe to produce a small drop of solution on the end of the needle and transfer was made by contacting the solution droplet with the strip or boat. When flashing larger aliquots, e.g., 1.5 pL, it was necessary to add the solution in several stages by the method described above and to allow sufficient time for the solution to evaporate before flashing. Thermal Conversion Study Procedures. Air from the permeation tube system containing the six reduced sulfur gases
was passed through a 30 cm X 0.64 cm quartz tube, which was positioned inside a Thermolyne tube furnace. Samples of the exhaust gas from the thermal conversion tube were trapped in a 3.0-mL Teflon loop. The subsequent glass capillary GC/FPD analysis procedure has been described previously ( I ) . Initial conversion studies were performed at 400 and 700 mL/min flow rates through the tube furnace, which was held at temperatures of 30,500,600,700,800,900,1000,and 1050 "C. Since the thermal conversion system must be compatible with the higher air sample flow rates from the isolation chambers used in the field studies ( 2 , 3 ) , conversion efficiencies had to be evaluated at higher flow rates. At a sample flow rate of 2.8 L/min the residence time for the gases in the thermal conversion tube is reduced by a factor of about 5 when compared to the 40G700 mL/min flows. This problem was circumvented by replacing the straight quartz heater tube with a coiled quartz tube that has an equivalent length of 139 cm. The 2.8 L/min air flow rate could not be obtained in a direct manner with the regular permeation tube calibration system, hence a double dilution flask was employed. In the double dilution flask, 100 mL/min of air flow from the permeation tube system was mixed with 2.7 L/min of sulfur-free air to yield the 2.8 L/min flow to the thermal conversion tube and the corresponding 3.0 mL Teflon sample loop. Analyses of the products from the thermal conversion system were performed by removing the Teflon loop from the conversion system and connecting the loop to the glass capillary GC/FPD injection system via cleaned Swagelok Quick-Connects ( I ) . The mass balance experiments of reduced sulfur gas conversion to sulfur dioxide were performed with the Varian GC/FPD using a Chromosil310 column. This packed column GC was used due to the relatively poor efficiency that the present SP-2100 borosilicate glass WCOT columns have for sulfur dioxide ( I ) .
RESULTS AND DISCUSSIONS Flash Vaporization/Flame Photometric Detection System. Initially, stainless steel strips were used on t h e F V / F P D system t o evaluate the response of various sulfate salts. The results of this experiment showed that HzS04and the sulfate salts of sodium, potassium, and ammonia all gave approximately the same linear FV/FPD response over a range of 1.6-12.0 ng of S. Stainless steel strip lifetimes were approximately 50 flashes per strip when flashed a t 10.8 V. Due to the limited lifetimes of the stainless steel strips, an attempt was made to substitute tungsten boats for the FV strips. However, the repeatability found with t h e stainless steel strips could not be obtained by using tungsten boats and the F V / F P D response was also nonlinear. Nevertheless, equivalent responses were obtained for (NH4)2S04,H2S04, and Na2S04,which disagrees with the F V / F P D results reported by Husar e t al. for tungsten boats (16). The use of platinum boats was also investigated due to their reported long lifetimes (24). Equivalent linear responses were obtained for Na2S04,H2S04,and (NH4)&304standards by use of a platinum boat. T h e lifetimes of the platinum boats were in fact extremely long compared to the lifetimes obtained by using stainless steel strips, e.g., several platinum boats were flashed several hundred times without a decrease in response. Tanner et al. (24) reported an increase in FV/FPD sensitivity when platinum boats were used instead of stainless steel strips. Similarly, a F V / F P D sensitivity enhancement of approximately 10-fold was observed for platinum in our comparative study of these two metals. However, the detection limit obtained with the platinum boats was almost identical with the 0.14 ng of S detectability observed for the stainless steel strips because of equivalent FV/FPD sulfur blank values for the two different metals. A FV/FPD repeatability of *6.5% RSD was obtained with the platinum boats, which closely compares to the f7.0% RSD for the stainless steel strips. An example of the typical F V / F P D response repeatability for a sulfate standard on a platinum boat is shown in Figure 2. I t was imperative to place the solution aliquot on the same portion of the FV boat or strip and to employ a constant FV discharge
ANALYTICAL CHEMISTRY, VOL. 52, NO. 14, DECEMBER 1980
2373
Table I. Effect of 2.8 L/min Flow Rates and Various SO, Concentrations on the SO, Collection Capacity of Spectrograde 47-mm Filters amt SO, as ng S/min
SO, 112 PPB,, 0
5.7
200 ML/MIN
total S collected before breakthrough, fig
37.2
5.5 4.1
70.0
85.0
02
3.1
100 7
IO
20 30 40 5 0 60 70 BO 90 lo0 110
TIME (MIN)
Figure
2. SO,
breakthrough for various glass fiber filters.
i
125 140 212 350
3.6 2.6 2.3 3.5 5.3
x = 3.8
i
1.2
Table 11. Sulfur Dioxide Collection o n Various Chemically Impregnated Gelman AE Filtersa results impregnant 10% glycerol-20% KOH
n o breakthrough @ 10 h b
10%glycerol-10% KHCO,
n o breakthrough @ 10 h b no breakthrough @ 10 h b breakthrough @ 35 minb no breakthrough @ 10 h b no breakthrough @ 10 h b n o breakthrough @ 10 h b breakthrough @ 4 5 minb immediate breakthrough immediate breakthrough immediate breakthrough immediate breakthrough immediate breakthrough break t hrou h @ 4 0 min% n o breakthrough
10% glycerol-10% K,CO,
h d’w Figure 3. FV/FPD response repeatability for six determinations of an 8 ng sulfur standard.
10%glycerol-10% KCI
voltage to achieve maximum repeatability. U n t r e a t e d Filters. The first phase in the development of the collection system was the study of blank filter interactions with SOz. Figure 3 shows the results of this initial study for the glass fiber filters. A blank holder without a filter in place was run as a means of comparison. Gelman types A and AE filters gave an immediate but somewhat slower breakthrough than the blank. However, Spectrograde filters exhibited no breakthrough for approximately 40 min, indicating considerable sulfur dioxide interaction. These Spectrograde filters are manufactured with an organic silicone resin a t high temperatures and Gelman Co. claims the manufacturing procedure produces a filter with negligible SOz interaction (25). However, in the original publication on the development of the Spectrograde filters, Gelman reported a collection of 100.8 pg of SOz for a 47-mm filter (26). In addition, Coutant reported a maximum collection of 18.2 pg of SO2for a 47-mm Spectrograde filter (27). The maximum SOz capacity observed in this work for the Gelman Spectrograde filters was 13.2 pg of SOZ/47-mmfilter, with an average range of 3.1-6.6 pg of S/47-mm filter. Consequently, air researchers are warned of artifact sulfate formed by interaction of SOz with the Gelman Spectrograde glass fiber filters even though the commercial literature states that these filters “are a unique breakthrough for air pollution sampling because of their negligible SOz pickup” (25). Breakthrough experiments a t air flow rates higher than 200 mL/min were also performed on the Spectrograde filters to evaluate the filters under sampling flow rate conditions of 2.8 L/min. Types A and AE filters exhibited immediate breakthroughs a t SO2 concentrations of 10-20 ppb and a flow rate of 2.8 L/min. The corresponding Spectrograde filter results are shown in Table I. As seen in Table I, the range of sulfur collected by different Spectrograde filters varied from 3.1 to 5.5 pug of S/47-mm filters. Thus, the range of sulfur collected per 47-mm Spectrograde filter at the higher flow rate and a t the lower parts-per-billion concentrations used in Table I correlate with the range of sulfur collected on Spectrograde filters a t the lower 200 mL/min flow rate. Therefore, the amount of SOp collected is apparently governed by a capacity factor for each filter and is not dependent on SO2 concen-
10%glycerol-10% NaHCO,
10% glycerol-10% NaOH
10% glycerol-10% Na,CO, 10%glycerol-10% NaCl 10% glycerol-20% “,OH
10% glycerol-10% NH,HCO, 10% glycerol-10% (NH,),CO,
10% glycerol-10% FeC1, 10% glycerol-10% MnC1,
0.5% glycerol-25% ethanol-0.1 p\I Na,I-IgCI, 5% glycerol-2.5% NaHCO,
@ 4 hd
2.5% NaHCO, 1.0% NaHCO, 0.25% NaHCO, 0.15% NaHCO, 0.1% NaHCO,
no breakthrough @4hd no breakthrough @ 4 hd n o breakthrough @4hd no breakthrough @ 4 hd breakthrough @ 3 h 15 mind
Flow rate = 200 mL/min. SO, concentration = 1 1 2 ppb ( v / v ) . SO, concentration = 1 9 ppb (v/v). SO, concentration = 97 ppb ( v / v ) . tration or air flow rate through the filter. I m p r e g n a t e d Filters. Fourteen inorganic compounds listed in the Experimental Section were investigated for their ability to collect SOz when used as an impregnant of Gelman AE glass fiber filters. The results of the impregnated filter experiments are summarized in Table 11. Several publications have concluded that retention of sulfur dioxide on filters is due to oxidation of sulfite to sulfate by the existence of basic substances or sites on the filter material (27-30). Hence, the collection process should stop and breakthrough should occur after a saturation level is reached. It. can be seen from Table
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ANALYTICAL CHEMISTRY, VOL. 52,NO. 14, DECEMBER 1980
I1 t h a t the generalization stated above holds true for some cases but not in others. The more basic sodium and potassium hydroxide, bicarbonate, and carbonate salts consistently collected sulfur dioxide at levels far exceeding those expected in sampling for biogenic sulfur emissions. The less basic aqueous ammonia, and somewhat less basic ammonium bicarbonate and carbonate salts, exhibited immediate breakthrough at both high and low sulfur dioxide levels. However, the chloride salts of potassium and sodium collected more sulfur than the basic ammonium salts. In an earlier publication, Adams et al. (11) suggested that sulfur dioxide is retained by salts containing anions which form acids weaker than H2S03. This generalization holds true when potassium or sodium hydroxide, bicarbonate, and carbonate are used for chemical impregnants but not with the similar ammonium salts or with the sodium and potassium chloride salts. The anions of these ammonium salts do form acids weaker than H2S03,but they did not collect SOz. The anions of the sodium and potassium chloride salts form acids stronger than H2SO3; however, they collected more sulfur dioxide than the ammonium salts listed in Table 11. Consequently, neither of the proposed mechanisms can account in all cases for the collection of SO2 on impregnated filters. T h e results of the ferric and manganese chloride salts are also shown in Table 11. Since iron and manganese are reported to be catalysts for SO2oxidation to sulfate, it was hypothesized that this catalytic activity might promote collection of SOZ. However, filters impregnated with these salts exhibited faster breakthroughs than untreated filters. This observation may be due to their acidic nature, a conclusion also drawn by Coutant who reported similar results with ferric and manganese salts (27). As shown in Table 11, tetrachloromercurate (TCM) impregnated filters were not as efective for SO2 collection as the other sodium- and potassium-based impregnants. Glycerol was added as a filter humifactant since it has been reported that collection efficiencies decrease a t relative humidities below 30% (10,13, 1 4 ) . However, Lewin et al. (14) reported that the use of glycerol, which stabilizes SO2as SO?-, is unnecessary when the sulfur is determined as SO4'-. There was no noticeable decrease in SO2 collection efficiency when glycerol was eliminated from the impregnated filters during our investigations. Spectrograde filters were not suitable for impregnation since their silicone surface causes them to be highly hydrophobic. An attempt was made to use Photo-Flo, a wetting agent, to allow the impregnating solution to soak into the filter surface. However, this procedure produced filters which displayed immediate SO2 breakthrough. Since the system initially proposed required a filter which collects SOz,but allows the passage of the reduced sulfur gases, experiments were performed to compare the response of the reduced gases through a blank filter holder and a holder with an AE filter impregnated with NaHC03. The results showed that all the reduced gases except H2S had no retention. de Souza et al. (19) and Braman et al. (31)reported conditioning solid N a H C 0 3 and Na2C03 filters with HzS to prevent its retention. Thus, a NaHC03 impregnated AE filter was conditioned with 90 ppb H2Sfor 3 h. Although this conditioning slightly reduced the amount of H,S retained on the NaHC03 filter, a significant amount of H2S was still retained and the preconditioning treatment would obviously increase the sulfur blank of the filter. These two factors demonstrated that sulfur gas pretreated filters had minimum utility in our particular methodology. FV/FPD Interferences. The investigation of sulfur blank values from impregnated glass fiber filters resulted in a disappointing discovery. The FV/FPD response obtained from the sulfur-containing extract of a NaHC03 impregnated glass
b
0
I W
Ln Z 0 W LT
1
,/
Figure 4. Impregnant interferences on FV/FPD responses: (a) normal FV/FPD responses for the first and second flashes of an initial sulfate standard; (b) typical FV/FPD responses for a sulfate extract from a NaHC0,-impregnated filter; (c) decreased FV/FPD response for the same sulfate standard in (a) due to the prior analysis of the (b) filter extract solution. fiber filter was not identical with the response from a standard sulfur solution. For instance, the FV/FPD analysis of an extract from an impregnated filter results in two peaks, an initial sharp spike followed by the small peak normally associated with the background response from a strip or boat. Furthermore, after FV/FPD analysis of this impregnated filter extract, the subsequent FPD responses to a standard sulfur solution were reduced by factors between 80 and 95%. An example of this impregnant interference can be seen in Figure 4. Additional investigation of the impregnant interference effect showed the presence of two separate interferences, one from the high concentration of alkali metal cations and another due to the bicarbonate or carbonate anions. The initial sharp interference FV/FPD response illustrated in Figure 4 was apparently caused by either a flash-induced pressure surge or flame emission from the relatively high concentration of alkali metal cations, while the reduction in the normal FPD sulfur response was due to carbon dioxide produced from the decomposition of bicarbonate and carbonate (32,33). Consequently, filters impregnated with sodium or potassium hydroxide were investigated in place of the corresponding bicarbonate and carbonate salts to avoid C 0 2 quenching interference, and the Dowex 50W-X8 procedures were employed to minimize the alkali FPD interference. However, there was still a significant amount of alkali interference when these solutions were analyzed. Therefore, the decision was made to investigate Gelman Spectrograde filters as an alternative to impregnated filters. Spectrograde Filters. A problem encountered with the use of Spectrograde filters was due to their relatively high sulfur blank. When these Spectrograde filters were cleaned by a previously published procedure (23),the hydrophobic character of the filters was eliminated and the filters exhibited immediate SO2 breakthrough. Thus, the filter cleanup procedure described in the Experimental Section was developed to eliminate the hydrophobic character of the Spectrograde filters without modifying their ability to collect SO2. An average sulfur blank value of 0.46 f 0.10 pg of S was obtained for 47-mm Spectrograde filters cleaned by the procedure developed in this laboratory. Table I11 shows typical results obtained for the SO2 collection capacity (expressed as micrograms of S)of the precleaned Spectrograde filters. The average collection capacity of these filters was 1.5 i 0.3 pg of S/47-mm filter. T h e results of experiments investigating the overall collection and recovery efficiencies using Spectrograde filters are presented in Table IV. These experiments were performed by using an SO2 permeation tube as the source of sulfur. As
ANALYTICAL CHEMISTRY, VOL. 52, NO. 14, DECEMBER 1980
S/47 mm upper limit of sulfur collection for these filters. For those areas with relatively high sulfur fluxes, e.g., 1.0 g of S/(m2 year), the capacity of the Spectrograde filter would be exceeded in a matter of minutes. If impregnated collection filters could be used, collection capacity would not be such a problem; however, the chemically impregnated filters examined were not compatible with the FV/FPD analysis system. Thus, a t the present stage of development, it is necessary t o obtain an initial estimate of the sulfur flux rate with the primary measurement system. These initial measurement data can then be used to determine a sampling period for the filter technique which is compatible with the sulfur collection capacity of the Spectrograde filters.
Table 111. Sulfur Dioxide Collection Capacity of Cleaned Spectrograde Filters
filter no.
amt SO, collected, reported as u g of S
2
1.6 1.9
3 4
1.2
5 6
1.7 1.7
7
1.8 1.3 1.2
1
tube furnace temp, " C 1050 1050 1050 20 20 20 20 20 20
1.1
8 9
2375
LITERATURE CITED Table IV. Collection and Extraction Efficiences of Cleaned Spectrograde Filters amt S amt S filter added found % overall in rg efficiency no. in Clg 1.06 1.43 1.39 1.00 1.26 1.42 1.13
1.08 1.04
1.37 1.06 1.24 1.40 1.11
1.16 1.42
98 137" 101 94 102 101 102 98 93
1.13
1.32
High value probably due to contamination during extraction. a
,CARLE PERMEATION TUBES
TUBE FURNACE 30ML T E F L O N LOOP
SAMPLING VALVE
&GC/WCOT/
FPD~
I CAP TRAP
Flgure 5. Schematic of system for thermal conversion studies.
shown in Table IV, the overall sulfur recovery efficiency is approximately 100%. Thermal Conversion of Reduced Sulfur Gases to SOz. A tube furnace temperature of 1050 "C was required to convert all the reduced sulfur gases to SO2 a t the air flow rate of 2.8 L/min. T h e order of reduced sulfur gas conversion t o SOz, from the easiest to the most difficult in terms of temperature requirements, was as follows: CH3SSCH3 < CH3SH < CH3SCH3< H2S = CSz < COS. The results of the thermal conversion-mass balance study showed that a total average conversion of 100 f 3% was obtained a t the furnace temperature of 1050 "C. Figure 5 illustrates the experimental system used in the thermal conversion studies. The SOz collection efficiency of Spectrograde filters was not affected by passing the air sample through the conversion furnace.
CONCLUSIONS
A second analytical system for determining biogenic sulfur gases has been developed and has been shown to meet the requirements for biogenic sulfur field sampling. However, the field analyst must be aware of the SOz collection capacity for the Spectrograde filters. From our most recent biogenic field studies, an average sulfur flux of 0.03 pg of S / ( m 2 year) has been determined (34). For this sulfur flux rate, 4-h sampling periods a t 2.8 L/min with our field enclosure system ( 2 , 3) will collect about 0.6-0.7 pg of S and be within the 1.5 pg of
Farwell, S. 0.;Gluck, S. J.; Bamesberger, W. L.; Schutte, T. M.; Adams, D. F. Anal. Cbem. 1979, 57, 609. Pack, M. R.; Bamesberger, W. L. J. Air Adams, D. F.; Farwell, S. 0.; Pollut. Control Assoc. 1979, 29, 380. Robinson, E.; Pack, M. R. "Assessment Adams, D. F.; Farwell, S. 0.; of Biogenic Sulfur Emissions in the SURE Area", Final Report on Project 856-1, submitted to Electric Power Research Institute: Palo Alto, CA, 1979. Hakkarinen, C.; Adams, D. F.; Farwell, S. 0. "Measurement of Gaseous Sulfur Emissions from Soils in the Eastern United States", paper presented at the Fourth International Conference on the Commission on Atmospheric Chemistry and Global Pollution, Boulder, CO, Aug 1979. Adams, D. F.; Farwell, S. 0.; Pack, M. R.; Robinson, E. "Estimates of Natural Sulfur Source Strengths", paper presented at Second Life Sciences Symposium on Potential Environmental and Health Consequences of Atmospheric Sulfur Deposition", Gatlingburg, TN, Oct 1979. Adams, D. F. I n "Air Pollution", 3rd ed.; Stern, A. C., Ed., Academic Press: New York, 1976; Vol. 111, Chapter 6. Drushel, H. V. I n "The Analytical Chemistry of Sulfur and its Compounds"; Karchmer, J. H., Ed.; Wiley-Interscience: New York, 1972; Part 11, Chapter 7. Tanner, R. L.; Forest, J.; Newman, L. I n "Sulfur in the Environment"; Nriagu, J. O., Ed.; Wiley: New York, 1978; Part I, Chapter IO. Pate, J. B.; Lodge, J. P.; Neary, M. P. Anal. Cbim. Acta 1883, 28, 341. Huygen, C. Anal. Cbim. Acta 1983, 2 8 , 349. Adams, D. F.; Bamesberger, W. L.; Robertson, T. J. J. Air Pollut. Control Assoc. 1988, 18, 145. Johnson, D. A.; Atkins, D. H. F. Atmos. Environ. 1975, 9 , 825. Axelrod, H. D.; Hansen, S. G. Anal. Chem. 1975, 4 7 , 2460. Lewin, E.; Zachin-Christiansen, B. Atmos. Environ. 1977, 7 7 , 861. Roberts, P. T.; Friedlander, S. K. Atmos. Environ. 1878, IO, 403. Husar. J. D.; Husar, R. 8.; Stubits, P. K. Anal. Cbem. 1975, 4 7 , 2062. Tanner, R. L.; Cedewall. R.; Garber, R.; Leahy, D.; Marlow, W.; Myers, R.; Phillips, M.; Newman. L. Atmos. Environ. 1977, 77, 955. Huntzicker, J. J.; Hoffman, R. S.; Ling, C. S. Atmos. Environ. 1978. 12, 83. de Souza, T. L. C.; Bhatia, S. P. Anal. Cbem. 1878, 48, 2234. West, P. W.; Gaeke, G. C. Anal. Chem. 1958, 28, 1816. O'Keeffe, A. E.; Ortman, G. C. Anal. Cbem. 1968, 38, 760. Lucero, D. P. Anal. Cbem. 1971, 4 3 , 1744. Dasgupta, P. K.; Hanley, L. G.; West, P. W. Anal. Cbem. 1978, 50, 1973. Tanner, R. L.; Newman, L. J. Air Pollut. Control Assoc. 1978, 26, 737. Gelman Products Catalog No. PB338. Ann Arbor, MI. Gelman, C.; Marshall, J. C. Am. Ind. Hyg. Assoc. J . 1975, 36, 512. Coutant, R. W. Environ. Sci. Technol. 1977, 7 7 , 873. Lee, R. E.; Wagman, J. A m . Ind. Hyg. Assoc. J . 1986, 2 7 , 266. Pierson, W. R.; Hammerle, R. H.; Brachzck, W. W. Anal. Cbem. 1876, 4 8 , 1808. Seinfeld, J. H. "Air Pollution: Physical and Chemical Fundamentals"; McGraw-Hill: New York, 1975; pp 188-193. Braman, R. S.; Ammons, J. M.; Bricker, J. L. Anal. Cbem. 1978, 50, 992. Rupprecht, W. E.; Phillips, T. R. Anal. Cbim. Acta 1889, 4 7 , 439. Von Lehmden, D. J. Jt. Conf. Sens. Environ. Pollut. [ Conf. Proc.], 4th, 1977, 360-5. Adams, D. F.; Farwell, S. 0.; Pack, M. R.; and Robinson, E. "Biogenic Sulfur Gas Emissions from Soils in Eastern and Southeastern United States", paper no. 80-40.5 presented at the annual meeting of the Air Pollution Control Association, Montreal, Canada, June 1980.
RECEIVED for review May 5, 1980. Accepted September 12, 1980. This work was supported in part by the Electric Power Research Institute under Contract No. 856-2. Reference t o commercial products is for identification purposes only and does not constitute an endorsement of these products by EPRI or the University of Idaho.
