Anal. Chern. 1986, 58,945-950
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Evaluation of Reference Methods for Measurement of Carbon Monoxide Emissions at Refineries Eva D. Estes* and David L. Hardison
Center for Environmental Measurements, Research Triangle Institute, Research Triangle Park, North Carolina 27709 Guy B. Oldaker 111'
Entropy Environmentalists, Inc., Research Triangle Park, North Carolina 27709 Frank E. Butler, Joseph E. Knoll, and M. Rodney Midgett
Environmental Monitoring Systems Laboratory, United States Environmental Protection Agency, Research Triangle Park, North Carolina 27711
Three colorlmetrlc methods for carbon monoxlde analysis have been evaluated as potentlal reference methods for determining the relatlve accuracy of nondlsperslve infrared (NDIR) carbon monoxide continuous emlsslons monltors. The methods are referred to as the ieuco crystal vlolet (LCV) method, the cacotheilne method, and the p-sulfamlnobenrolc acld (p-SABA) method. A laboratory lnvestlgatlonwas carrled out to determine method detectlon limits, ranges, and Interferences and to adapt the methods for use under field conditions. The methods were then tested at petroleum reflnery fluid catalytic cracking unlts, and the results were compared to those obtalned by NDIR and gas chromatographic (GC) instrumental methods. Results obtained by the LCV and cacothellne methods were blased high relatlve to results from the NDIR monltor and GC analysls. The p-SABA method was determlned to be the most effectlve of the three colorimetric methods for use In the field. By use of the NDIR method as the standard, the GC and p-SABA methods were biased -1.5 and +1.5%, respectively. The coefficients of variation for the NDIR, GC, and p-SABA methods were determined to be l,2, and 3%, respectlvely.
The U S . Environmental Protection Agency requires a reference method for analysis of carbon monoxide (CO) a t refineries equipped with fluid catalytic cracking units (FCCUs) to assess the accuracy of nondispersive infrared (NDIR) continuous emissions monitors ( I ) . The new reference method selected must include reliable techniques for both sample collection and analysis. The sample collection procedure should be simple and sufficiently rugged to meet the demands imposed by sampling outdoors under varying environmental conditions. In addition, an integrated technique is required to ensure that samples are representative and unaffected by CO concentration spikes, which are typical at combustion sources. The analytical technique must be applicable to emissions from different types of FCCUs, which vary from a few parts per million by volume to nearly 1000 ppmv CO. It must also rely on apparatus, reagents, and procedures that would be readily available at refineries. A literature survey indicated that Lambert and associates a t Kansas State University have recently developed two palladium-based methods for measurement of CO. These are the leuco crystal violet (LCV) method by Lambert and Wiens 'Current address: R. J. Reynolds Tobacco Co., Winston-Salem, NC 27102. 0003-2700/86/0358-0945SO - .1.50/0 .. .I
(2) and the cacotheline method by Lambert and Chiang (3, 4). A third promising method uses the silver salt of p-sulfaminobenzoic acid, which reacts with CO. This reagent, originally reported by Ciuhandu (5),was applied by Levaggi and Feldstein (6)to the analysis of CO at incinerators. They found close agreement among this method and other measurements made by a gas chromatographic (GC) technique and an NDIR monitor. A fourth colorimetric method, based on the formation of a carbonyl complex of ruthenium(I1) octaethylporphyrin, has been reported by Corsini et al. (7). Because preparation of the reagent is very tedious and the procedure requires strict time control, this method was not considered as a potential reference method. In an earlier study, Ferguson, Lester, and Mitchell (8) evaluated the LCV method and found a positive bias compared to NDIR measurements. In their work, they developed a method of sample collection and of introducing gas into reaction bulbs for analysis. They also confirmed the interference by NO, and SOzreported by Lambert and Wiens (2). Since these gases were present in refinery effluents at levels greater than 150 ppmv, the samples were scrubbed in alkaline permanganate. By use of their procedure, the SOz and NO, levels in a typical refinery sample were reduced to less than 5 ppmv. The absorbing solution also removes COz, which is present in the percentage range, and a gas volume correction must be made. These sample collection and introduction procedures, which are described in detail below, were used in evaluating the three colorimetric methods. EXPERIMENTAL SECTION Apparatus and Reagents. The reaction bulbs (100 and 175 mL) used for the colorimetric analyses were constructed of Pyrex glass with stopcocks made of Teflon and were leak-free at 40 mmHg. The bulbs were designed so that colorimetric reagent could be added and removed easily and accurately (see Figure 1). Prior to use, the exact volume of each bulb was determined by using distilled water. Commercially available gas sample bulbs such as Supelco 2-2161 and Alltech 7012 may also be used. Absorbance measurements were made on a Bausch and Lomb Model 100 spectrophotometer using 1.00-cm quartz cells. All reagents used were analytical grade or the highest quality commercially available. Aluminum cylinders containing standard CO concentrations in nitrogen were purchased from commercial vendors. The CO concentrations for these materials were traceable to National Bureau of Standards' Standard Reference Materials and had tolerances within 1%of nominal value. Calibration gases having concentrations established by U.S. Environmental Protection Agency Protocol 1 (9) (and, therefore, having tolerances within 1.0% of nominal value) were used as received. Reaction Bulb Filling Procedure. The sample filling system is shown in Figure 1. The LCV and p-SABA methods employed 0 1988 American Chemical Society
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ANALYTICAL CHEMISTRY, VOL. 58, NO. 4, APRIL 1986
-
MANOMETER
,
STACKWALL
'VALVE
SAMPLE BULBS
Figure 2. TEDLAR SAMPLE BAG
Figure 1.
Sample bulb filling system.
100-mL gas reaction bulbs and 10.0 mL of colorimetric solution, while the cacotheline method used 175-mL bulbs and 15.0 mL of solution. The manifold and bulbs were first evacuated and checked for leaks. Then the bulbs were closed off, the vacuum was recorded to the nearest mm Hg, and the manifold was flushed 3 times with sample gas. Following this, the bulbs were filled to atmospheric pressure and the pressure and temperature were recorded. The sample bulbs were then placed on a table shaker together with standards and blanks. An effort was made to maintain shaking conditions constant throughout the study. Leuco Crystal Violet Method. The LCV reagent contains iodate, leuco crystal violet, and tetrachloropalladate(I1). CO reduces Pd(I1) to Pd(O), which reduces iodate, producing hypoiodous acid. The acid oxidizes leuco crystal violet to crystal violet. In the present study, the leuco crystal violet concentration was increased to 5 times the value specified by Lambert and Wiens (2) in order to provide sufficient color reagent for high CO concentrations. Samples and standards were shaken for 30 min. At the end of the shaking period, the absorbances of the solutions were read at 589 nm. Cacotheline Method. The reagent contains tetrachloropalladate(I1) and cacotheline. CO reduces Pd(I1) to Pd(O), which reduces the yellow cacotheline to violet dihydrocacotheline. In the present study, the cacotheline concentration was increased to 1.5 times the value specified by Lambert and Chiang ( 3 , 4 )in order to provide sufficient color reagent for high CO concentrations. Samples and standards were shaken for 100 min, and absorbances were read at 520 nm. p -Sulfaminobenzoic Method. This method, developed by Levaggi and Feldstein (6),involves reduction by carbon monoxide of the silver salt of p-sulfaminobenzoic acid in an alkaline solution. A colloidal suspension of silver is produced and measured spectrophotometrically. The colorimetric solution was prepared according to the original method. Samples and standards were shaken for 120 min; absorbances were read at 420 nm for CO < 400 ppmv and at 600 nm for CO > 400 ppmv. Calculations. The sample absorbance per volume of gas (SA) was calculated according to eq 1,and an average SA for each bag sample and standard was calculated. A calibration curve conSA =
I
Ix
sample absorbance corrected for blank bulb volume - volume of reagent barometric pressure sample pressure in bulb
taining at least three points was constructed by using results of known concentrations of CO in nitrogen contained in Tedlar bags. Also, three bulbs, each containing an aliquot of colorimetric solution that had not been exposed to CO, were shaken to serve as a blank. The average blank value was subtracted from each sample absorbance. A graph of concentration vs. average absorbance per liter for each standard was plotted, and a linear regression analysis was used to determine the unknown CO concentration of the collected sample in each Tedlar bag using the average absorbance per liter for the sample. Sampling System. All field tests samples were acquired via a single, electrically heated, 5/s-in. borosilicate glass probe. The
Basic CO sample collecting system.
probe was fitted at the inlet with a borosilicate glass wool filter and protected with a stainless-steel sheath. The probe temperature was maintained above the moisture dew point. The probe outlet was connected to a moisture-removal system that consisted of an ice-cooled condenser and a borosilicate glass wool filter. All exposed surfaces of the condenser were either Teflon or borosilicate glass, connected where necessary with stainless-steel fittings. The outlet of the moisture-removal system was connected with unheated, 3/s-in. tubing made of Teflon to a stainless-steel manifold, located at ground level, which served two CO method sampling trains. The sampling train shown in Figure 2 was used for all the CO methods evaluated. The major components of the train were a sample conditioning system, a pump, a stainless-steel needle valve, a rotameter, and a Tedlar sample collection bag. The sample conditioning system has been described by Ferguson et al. (8)and includes three Smith-Greenburg impingers arranged in series. For each sample run, the first two impingers are each charged with 0.40 L of 0.25 M KMnO4/1.50 M NaOH (aq); the final impinger contains 0.25 L of the KMn04/NaOH solution. A stainless-steel three-way valve was positioned between the rotameter and the collection bag in order to enable operation of the train in either a sampling mode or a purge mode. The calibrations of the rotameters were checked against a bubble meter before use in the field. Bags were connected to the sampling train with stainless-steel quick-connects. For protection, the bags were enclosed within rigid plastic containers. The entire sampling system from the probe tip to the three-way valve was checked under vacuum for leaks before and after samples were acquired. Prior to use in the field, the bags were checked under both pressure and vacuum. In the field, the bags were checked while evacuated, immediately before sample acquisition. The CO method sampling trains were operated at a flow rate of 0.3 L/min. Each train was purged for approximately 5 min before acquisition of 30-min samples. Nondispersive Infrared and Gas Chromatographic Analyses. NDIR determinations of CO in the bag samples were made with either a Beckman Model 864 CO analyzer or a Fuji Model 3300 analyzer. Gas chromatographic analyses for carbon monoxide were performed by use of an EPA Method 25 (IO)analyzer, in which CO is reduced to methane and then measured in a flame ionization detector. The analysis system consisted of a Perkin-Elmer Model 3920-B gas chromatograph equipped with a flame ionization detector and fitted with a two-column series consisting of a 6-ft x l/s-in. stainless-steel column packed with 10% SP-2100 on 80/100mesh Supelcoport followed by a 6-ft X 1/8-in.stainless-steel column packed with 60/80 mesh Chromosorb 102. A column temperature of 50 OC was maintained with a carrier gas flow rate of 30 cm3/min of helium. The oxidation catalyst consisted of a 14-in. length of 3/s-in.-o.d. Inconel tubing packed with 2 in. of 19% chromium oxide on l/s-in. alumina pellets and was operated at 650 O C . The reduction catalyst consisted of a 2-in. length of 1/4-in.-o.d.Inconel tubing packed with 60/100 mesh Katalco 11-3 and operated at 540 "C. One-milliliter aliquots of sample or calibration gas were injected by using a 10-port stainless-steel rotary valve. Carbon monoxide was eluted from the column series and into the oxidation and reduction catalyst. Any organic compounds in the samples were backflushed from the columns by reversing column flow and heating to 120 OC. Chromatograms were recorded on a strip chart, and peak areas were measured
ANALYTICAL CHEMISTRY, VOL. 58, NO. 4, APRIL 1986 947 electronically. Analyses of samples and calibration standards were performed in triplicate. A
RESULTS AND DISCUSSION Methods Evaluation. The three colorimetric methods were evaluated in the laboratory to determine their suitability for use under field conditions. One of the major problems with the leuco crystal violet method is that the degree of color development is dependent upon the reaction time. For example, when 50 and 200 ppmv CO samples were shaken and measured periodically, the absorbances of the solutions were still increasing after 26 h. Further, when concentration VS. absorbance curves were made using reagent grade oxidized crystal violet, CO samples (50,100, and 200 ppmv) produced higher absorbances than would be predicted from the crystal violet absorbance curve and the reaction sequence. One possible explanation for this increase in crystal violet production is that the reaction with hypoiodous acid produces iodide ion that in turn reacts with iodate to produce more hypoiodous acid and thus continues the sequence. J. L. Lambert, coauthor of the original method, has confirmed this finding in private correspondence. However, attempts made to inhibit this postulated reaction by the addition of silver nitrate or nitrobenzene (electron-withdrawing material), and thus to complex the iodide, were not successful. Another major problem with the LCV method is the steadily increasing absorbance of the colorimetric solution. The absorbances of blank solutions, measured 20,120, and 240 min after preparation, averaged 0.071, 0.113, and 0.156, respectively. To avoid an excessively high blank absorbance, the solution was used within 2-3 h of preparation. T o evaluate the stability of the cacotheline colorimetric solution, 1 L was prepared and used to run a blank and a 100 ppmv CO standard over a period of 8 days. The data show that the absorbance of the blank changes slowly with time, from 0.214 on day 1 to 0.230 on day 8. However, on the fourth day, the 100 ppmv CO sample absorbance began to decrease, and by the fifth day, there was a dramatic drop from 0.587 to 0.186. The data suggest that the colorimetric solution should be used within 3 days of its preparation. The major disadvantage of the cacotheline method is that 120 min of reaction time is needed for adequate color development. Attempts to increase the reaction rate by adding glass beads and by using ultrasonics were unsuccessful. The cacotheline method initially was proposed as the most suitable for use in the field for the following reasons: (1) the method has the advantage of using only one reagent solution, which is stable for at least 3 working days; (2) there are no interfering side reactions that prevent attaining a maximum absorbance; (3) the precision of the method is excellent; and (4) since the standard for CO emissions from an FCCU is 500 ppmv, the method has adequate sensitivity at the level of the standard. Therefore, prior to the field evaluation, a ruggedness test was performed to determine the sensitivity of the cacotheline method to slight changes in experimental parameters such as those that would be encountered when the method is used by several different laboratories. Following the procedure described in Youden ( I I ) , the effects of seven independent parameters were investigated by performing eight experiments. The tests revealed that the cacotheline method is not significantly sensitive to slight variations in the seven parameters evaluated: (1)tetrachloropalladate(I1) concentration, (2) shaking time, (3) shaking method, (4) percentage of acetic acid in the colorimetric solution, (5) age of the colorimetric reagent, (6) time elapsed after shaking prior to reading the absorbance, and (7) a system blank representing all other variables. To evaluate the stability of the p-SABA colorimetric solution, the absorbance of the unshaken, blank solution was
LCV CACOTHELINE pSABA.425 nm pSABA. 600 nm
CO CONCENTRATION, porn
Figure 3. Calibration data. Table I. Calibration Data for Colorimetric Methods for Carbon Monoxide Analysis
CO, ppmv 49 100 148 204 249 497 499 1007
slope intercept corr coeff
LCV
av A/L (SDP p-SABA at cacotheline 425 nm
1.93 (0.09) 4.73 (0.14)
0.17 (0.05) 0.62 (0.01)
9.28 (0.63)
1.33 (0.03)
p-SABA at 600 nm
2.24 (0.08) 4.87 (0.19) 7.36 (0.17) 0.36 (0.03) 12.35 (0.94) 2.30 (0.21)
21.33 (0.09) 41.01 (1.87)
0.040 0.618 0.9995
3.65 (0.02) 7.48 (0.08) 0.007 6 -0.1850 0.999 93
7.74 (0.34) 0.051 -0.208 0.999 90
0.009 -1.86 0.9937
SD, standard deviation determined from three measurements.
monitored over a period of 1 week. From the time of preparation to 3 h, the blank absorbance increased from 0.006 to 0.013. After 20 h, the blank absorbance had increased to 0.027, and after 45 h, the absorbance increased to 0.037. At the end of 1 week the absorbance was 0.057. This increase in absorbance is much slower than for the LCV method. To evaluate the stability of the p-SABA colorimetric solution with respect to color development, a 150 ppmv CO standard was run over a period of 1 week. After 2 days, there was a slight decrease in absorbance per liter of sample from 7.60 to 7.00, but then it leveled off, with readings of 7.06,7.02, and 7.14 on days 3,4, and 7, respectively. On the basis of these experiments, the colorimetric solution is judged to be acceptable for use for a period of at least 2 days. The major disadvantage of the p-SABA method is considered to be that a wavelength change for the spectrophotometer is required for samples below 400 ppmv CO in order to maintain reasonable sensitivity. Since the carbon monoxide emissions standard is 500 ppmv, bracketing of this value could require two calibration curves. TO ensure that the alkaline potassium permanganate cleanup procedure used for the LCV method was sufficient for the cacotheline and p-SABA methods, interference studies were carried out. Two bag samples were prepared, one containing 250 ppmv CO in nitrogen and the other containing 250 ppmv CO, 210 ppmv NO, and 375 ppmv SO2. Both bags were sampled through the cleanup solution and analyzed by the cacotheline method and the p-SABA method. For each method, both bags yielded the same result. Calibration data for the three methods are summarized in Table I and plotted in Figure 3. The sensitivities of the LCV and the p-SABA methods for samples e400 ppmv CO are
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ANALYTICAL CHEMISTRY, VOL. 58, NO. 4, APRIL 1986
Table 11. Detection Limits for Colorimetric Methods for Carbon Monoxide Analysis
method LCV
cacotheline p-SABA a
detection limit, ppmv 2-6" 25 3
Depends upon age of colorimetric solution.
comparable and are significantly greater than the sensitivity of the cacotheline method. Above 400 ppmv CO, when a wavelength change is required for the p-SABA method, the sensitivity of the p-SABA method approaches that of the cacotheline method. Experiments were carried out to determine the detection limits of the three methods. The detection limit was defined as the change in concentration of CO that would result in a change in absorbance per liter equal to 3 times the standard deviation of the absorbance per liter of the blank solution. For each method, five blanks were analyzed and the standard deviation of the results was computed. Since the absorbance of the leuco crystal violet solution has been shown to increase with time, three sets of five blanks each were measured at times of 20, 120, and 240 min, respectively, after the solution was prepared. The data demonstrated that the standard deviation of the blank absorbance per liter increases with the age of the solution for the LCV method. The detection limits are summarized in Table 11. Field Testing. The field tests of the colorimetric methods were conducted on fluid catalytic cracking units (FCCUs) at two petroleum refineries that utilize the two major techniques for control of CO emissions. For the first and second field tests, samples were acquired from a stack serving a FCCU equipped with a CO furnace to control emissions. High-sulfur crude oil was processed at the refinery. For the third field test, samples were obtained from a FCCU employing a high-temperature combustion process that results in the production of minimal concentrations of CO when coke is burned off the catalyst during regeneration. The sampling location was downstream from an electrostatic precipitator that controls emissions of particulate matter. The petroleum refinery processed low-sulfur crude oil. The emissions from the two facilities were significantly different. Emissions from the unit controlled with the CO furnace, although typically below 100 ppmv CO, exhibited CO concentration spikes at levels to roughly 250 ppmv CO. In addition, relatively high concentrations of SOzexisted, because high-sulfur crude oil was processed. In contrast, the CO emissions from the unit that employed the high-temperature combustion process were low and steady. Sulfur dioxide concentrations were also low, consistent with the sulfur content of the crude oil being processed. The two effluents provided a rigorous challenge for the CO methods because a wide range of CO concentrations were presented and because different crude oils were processed using different techniques. The first field test was conducted to assess the performance of the colorimetric methods relative to the NDIR measurements. NDIR results were chosen as the reference because the method generally applied at FCCUs is EPA Method 10 (12),which uses NDIR analysis. NDIR analysis was performed continuously on a separate stream of sample gas during the 30-min periods that the samples were collected in Tedlar bags. The NDIR analysis was also performed on the three integrated bag samples collected simultaneously. Two of these samples were the duplicates passed through the alkaline permanganate solutions, which removed the C02, SOz, and NO,. The third bag was collected directly from the sampling system. The
Table 111. Results from Analysis for CO in Samples Obtained from Fluid Catalytic Cracking Unit, Field Test No. 2
CO concn, ppmva run
NDIR method
p-SABA method
GC method
1A IB 2A 2B 3A 3B 4A 4B 5A 5B 6A 6B 7A 7B 8A 8B 9A 9B 1OA 10B
66.9 66.6 49.3 49.4 61.0 61.4 37.1 36.0 36.0 36.0 37.5 37.6 38.4 38.8 175.5 176.3 307.9 308.5 403.2 407.5
71.4 71.4 55.7 53.0 62.3 64.8 41.5 43.0 39.0 40.9 40.0 42.7 43.0 42.1 178.4 176.9 316.2 299.9 401.0 412.4
66.1 65.7 47.2 47.3 58.2 59.1 35.0 33.6 34.1 33.4 34.4 34.6 36.9 39.5 174 173 303 306 401 410
Reported concentrations are on a moisture-free and carbon-dioxide-free basis.
NDIR results for CO were the same for all four samples, after a correction was applied for the COz content of the untreated sample. In all subsequent tests, the NDIR results quoted were those from the integrated samples collected in the Tedlar bags. Eleven duplicate samples were acquired for the field test, with concentrations of CO ranging from 28 to 129 ppmv as measured by NDIR. Samples from three runs were returned to the laboratory and analyzed by GC, and the results were in close agreement with those obtained from NDIR analyses. The cacotheline method gave results that were biased roughly 20% high relative to NDIR measurement results. In addition, for some samples, a precipitate was observed to form in the colorimetric solution after the shaking operation. The precipitate interfered with the spectrophotometric measurement. The poor performance of the method was unexpected in view of results from the laboratory study, which was conducted under essentially the same conditions as those for the environmental samples. Analysis for possible interfering substances uncovered only argon, which does not interfere. Triplicate analyses by EPA Method 7 (13)showed NO, to be absent. Further, a similar bias was found for the LCV method in this and a previous study (8). Although the nature of this bias remains undetermined, it is significant that the two biased methods share a chemistry based on palladium. Only a limited number of samples were analyzed by use of the p-SABA method because insufficient gas remained after the cacotheline and LCV measurements. Nevertheless, the results obtained exhibited good precision and compared favorably to results from NDIR measurements. Four methods were used in the second test: (1)the NDIR method, (2) the p-SABA method, (3) the cacotheline method, and (4) the GC method. Ten duplicate samples were acquired and individually analyzed. Six pairs of samples once again showed high positive bias by the cacotheline method. At this point, the method was dropped from further consideration. The results of the other three methods are shown in Table 111. The concentrations for runs 1-7 are representative of normal operation for the fluid catalytic cracking unit. The concentrations observed for runs 8-10 are unusually high and reflect upset conditions. This unplanned upset affected the field test only insofar that it provided a desirable, wide concentration range over which to evaluate the methods. Pre-
ANALYTICAL CHEMISTRY, VOL. 58, NO. 4, APRIL 1986
Table IV. Summary Statistics and Precision Estimates for Analyzing CO in Samples Collected at Fluid Catalytic Cracking Unit
949
Table V. Results from Analyses of CO in Samples Obtained from Fluid Catalytic Cracking Unit, Field Test No. 3
CO concn, ppmv'
p-SABA
parameter
NDIq method
method
GC method
run/sample
mean, ppmv CO range, ppmv CO precision, ppmP coeff of variation, % repeatability, % no. of runs
121.55 36.0-407.5 1.01 1 h3.2 10
124.75 39.0-412.4 1.03 3 h9.7 10
119.61 . 33.0-410.0 1.02 2 16.5 10
1A 1B 2A 2B 3A 3B 4A 4B 5A 5B 6A 6B 7A 7B 8A 8B 9A 9B 10A
'Values represent geometric standard deviations. *Limits define 95% confidence intervals.
cision estimates for the three methods were derived from the variation between duplicate samples for each run. For these estimations, differences originating from the bags containing the samples were assumed to be negligible. The analytical results were transformed to logarithms in order to stabilize the within-run variation and to obtain an overall precision estimate. Precision estimates, expressed as geometric standard deviations, and coefficient of variations and repeatability estimates for the three methods are presented in Table IV. An analysis of variance involving a general linear model procedure was used in order to test the hypothesis that all three methods gave the same results. This analysis indicated that the methods exhibited significant differences among themselves. A Duncan's multiple range test was used to separate the mean results and thereby to distinguish differences between individual methods. This test indicated that each method gave results that differed significantly relative to the other two methods. From a practical standpoint, the differences observed among the methods' results are small. Relative to the NDIR method, the p-SABA method provides results that are biased 2.6% high, while the GC method is biased 1.5% low. Biases of these magnitudes are typically overwhelmed by imprecision originating primarily from other methods that supply necessary, complementary results. For example, in order to obtain the concentration of CO in the exhaust from the fluid catalytic cracking unit, the CO analytical results obtained by using the methods described here must be adjusted for the volume of COz absorbed in the conditioning system containing the alkaline permanganate solution; therefore, COz must be quantified concurrently with
co.
The third field test, which involved the NDIR method, the p-SABA method, and the GC method, was conducted at a fluid catalytic cracking unit employing a process different from the process associated with the unit sampled in the earlier two field tests. For the third field test, 10 duplicate samples were acquired and analyzed by use of the three methods; the results are shown in Table V. The concentrations encountered were near the detection limits of the p-SABA method and the NDIR instrument and ranged from 3.4 to 12.4 ppmv CO as measured by the NDIR method. These concentrations are typical of emissions from FCCUs that employ the high-temperature combustion process. Statistical analyses were performed on the results using the same methods as were used on the results from the second field test. These analyses indicated that the methods were equivalent. Additional statistical analyses were conducted on the pooled results from field tests no. 2 and 3. The results of these analyses indicated that the methods differed significantly both among and between themselves. However, the differences between the individual arithmetic means for the p-SABA and the GC methods are small relative to the mean for the NDIR method results. Accordingly, the p-SABA method differs by +1.5% and the GC method by about -4.9%. The bias indicated for
10B
NDIR method p-SABA method 12.3 12.4 6.6 6.6 6.9 6.8 9.7 9.7
11.0 11.1 7.1 7.0 8.4 8.1 3.7 3.6 3.4 b 4.0 3.7
11.2 9.9 4.6 5.1 6.0 4.9 9.2 9.1 10.7 10.1 4.9 4.9 6.3 6.7 1.8 1.6 2.9 2.1 3.4 3.6
GC method 10.9 10.2 6.05 5.79 6.02 6.69 7.76 8.17 10.0
8.81 5.44 5.37 6.69 6.64 2.93 2.68 3.01 b 2.82 3.48
'Reported concentrations are on a moisture-free and carbon-dioxide-free basis. Insufficient sample for analysis. the p-SABA method is insignificant from a practical standpoint, It is unlikely that this small difference would have a noticeable effect on results obtained from ordinary testing situations such as those conducted either to assess the conformance of a stationary source with CO emission standards or to assess the accuracy of CO continuous monitors installed on stationary sources. The bias value indicated for the GC method is probably an overestimate because of the contribution of the field test no. 3 results, which were lower (but not significantly different) than the NDIR method results. For this reason, it is concluded that the bias estimate derived from the results of field test no. 2, namely -1.5%, is the better indicator of how well the GC method performs relative to the NDIR method. This bias value is considered inconsequential in view of how the method would be ordinarily applied and the results interpreted.
CONCLUSIONS Three source tests were conducted at two types of CO removal FCCUs at refineries. Two tests were conducted at a CO furnace facility that was found to yield 28-129 ppmv CO in the first test and 36-408 ppmv CO in the second test. The test at the high-temperature combustion process unit yielded 3-12 ppmv CO. From the laboratory and field tests, it is concluded that both the p-SABA and GC methods are capable of giving results that are essentially equivalent to results provided by the NDIR method, and either method could serve as a reference method for determining the relative accuracy of NDIR CEMs. The p-SABA method is recommended because it is less expensive and simpler to operate. If the GC method were readily available, it would also be an acceptable reference method. Both the p-SABA and GC methods are sufficiently sensitive to yield positive results for the lowest CO refinery sample tested. Although the LCV and cacotheline methods were biased high compared to the NDIR CEM when used to analyze oil refinery samples, they performed well in the laboratory and should not be eliminated from consideration for use at other sources, such as hazardous waste incinerators. ACKNOWLEDGMENT We wish to express our appreciation for the guidance in this project of W. F. Gutknecht of RTI. We also appreciate the
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Anal. Chem. 1986, 58, 950-956
efforta of K. R. Loder and K. R. Hazel of Entropy in collecting field data and G. B. Howe of RTI for the GC analyses. We thank J. C. Suggs of USEPA for the statistical evaluation of field data. Registry NO.LCV, 603-48-5;p-SABA, 138-41-0;CO,630-08-0; cacotheline, 561-20-6.
LITERATURE CITED (1) Fed. Reglst. 1984. 4g (no. 29), 5326-5327. (2) Lambert, Jack L.; Wiens, Robert E. Anal. Chem. 1974,46,929-930. (3) Lambert, Jack L.; Chiang, Yuan C. Anal. Chem. 1983, 5 5 , 1828-1830. (4) Lambert, Jack L.; Chiang, Yuan C. Anal. Chem. 1984, 56, 808. (5) Ciuhandu, Gheorghe 2.Anal. Chem. 1957, 155, 321-327. (6) Levaggi, D. A.; Feidstein, M. Am. Ind. Hyg. Assoc. J . 1984, 25, 64-66. (7) Corsini, A,; Chan, A.; Mehdi, H. Talsnta 1984, 34, 33-38.
(6) Ferguson, Bruce €3.; Lester, Rlchard E.; Mitchell, W. J. ”A Study to Evaluate Carbon Monoxide and Hydrogen Sulfide Continuous Emission Monitors at an Oil Refinery”, EPA-600/4-82-054. Aug 1982. (9) “Traceabllky Protocol for Establishing True Concentrations of Q s e s Used for Calibration and Audits of Continuous Source Emission Monitors (Protocol No. )”I, June 1978, included wlthln “Quality Assurance Handbook for Air Pollution Measurement Systems. Volume 111. Stetionary Source Specific Methods”, EPA 6R0/4-77-027b, Aug 1977. (IO) Code of Federal Regulations, Title 40, Part 60, Appendix A, 1983 pp 593-61 2. (11) Youden, W. J. In “Statistical Manual of the Association of Officlal Analytical Chemists”; Washington, DC, 1975; pp 33-36. (12) Margeson, John H.;Knoll, Joseph E.; Midgett, M. Rodney; Oidaker, Guy E. 111; Reynolds, Wayne E. Anal. Chem. 1985. 57, 1586-1590. (13) Code of Federal Regulations, Title 40. Part 60, Appendix A, 1983; pp 467-474.
RECEIVEDfor review July 8, 1985. Accepted November 27,
1985.
Development and Analytical Performance of Tubular Polymer Membrane Electrode Based Carbon Dioxide Catheters Walter N. Opdyckel and M. E. Meyerhoff*
Department of Chemistry, The University of Michigan, Ann Arbor, Michigan 48109
The development and analytical performance of a new potentlometric pC0, (partlai pressure of CO,) senslng catheter Is described. A unlque sensor geometry Is achleved by utlilzlng an Inner tubular polymer pH electrode In conjunction wlth an outer gas-permeabie silicone rubber tube. Once assembled, thls flexible catheter has an outer diameter of 1.1 mm. When filled wlth an approprlate reference soiutlon and Internal electrolyte, the resulting devlce responds rapldly (180 s for t,,,) and reproduclbly to pC0, changes In the normal and abnormal physiological concentration range (15-150 torr) with nearly Nemstlan behavlor (54-61 mV/decade change In pC0,). Long-term stability of the Inner pH electrode and consequently the gas sensor Is dependent on the Internal reference solutlon composilion. Favorable stabliHy (f2 mV over 45 h) is achleved wlth a phosphate buffered Internal reference solution. Contlnuous pC0, values obtalned with the new sensor during 6-h in vitro blood pump studles correlate well with conventional bioodgas Instruments. Preilminary results for sensors Implanted Intravascularly In a dog demonstrate their suitability for continuous In vivo monltorlng of PCOP.
The clinical significance of blood gas measurements has long been recognized (1-3). Abnormal partial pressures of oxygen (PO,) and carbon dioxide (pC02) in blood can be indicative of respiratory or metabolic disorders. As a result, frequent blood gas analysis is crucial to the management of surgical and intensive care patients. Typically, these measurements are performed on discrete arterial blood samples using commercially available blood-gas analyzers (4-6).However, since serious changes in blood gas levels may occur in a matter of minutes or less, the lag time associated with discrete sample in vitro methods poses a danger to the patient’s welfare. For this reason, it would be desirable to develop a reliable and ’Present address: Diversey Wyandotte Corp., Wyandotte, MI. 0003-2700/86/0358-0950$01.50/0
relatively inexpensive device capable of continuously monitoring gas levels in vivo. In this report, we describe an essentially disposable electrochemical pCOz sensor that appears suitable for such purposes. Many methods already have been proposed for continuous monitoring of blood gases, and these techniques have been reviewed by several authors (7-11). While no method has yet received universal acceptance, considerable emphasis has been placed on inexpensive electrochemicaldevices that utilize outer gas-permeable membranes to achieve high selectivity. The Clark-type voltammetric PO, electrode has been successfully miniaturized for in vivo measurements (12, 13). However, miniaturization of the classical Severinghaus-type potentiometric pCO2 sensor (14,15)has met with less success, since this sensor relies on a fragile glass pH electrode as the internal sensing element. Miniature metal/metal oxide pH electrodes have been suggested as alternatives to glass for the fabrication of pCOz catheters (16-18);however, the sensitivity of such internal electrodes to redox species along with the delicate nature of the sensing tip region may explain why such devices have not found wide use despite some promising preliminary in vivo results (19-21). Recently (221, we reported on the development and analytical applications of new potentiometric gas sensors based on polymeric pH electrodes of the type described by Schulthess et al. (23). By use of this neutral carrier-type internal pH membrane electrode, small, inexpensive, and durable ammonia and carbon dioxide gas sensors may be fabricated whose response properties compare favorably with commercial glass membrane based sensors. The purpose of this paper is to extend this concept by describing the design and performance of a new pC02 gassensing catheter that is based on an internal tubular polymeric pH electrode. A schematic diagram of this sensor is shown in Figure 1. The unique feature of this device in comparison to other miniature pCOz sensors is the geometry of the sensing region. The polymeric pH-sensitive membrane is situated safely within the wall of the internal tubing rather than at the vulnerable tip. This protects the sensing region from Q I986 American Chemical Society
