Anal. Chem. 1984, 56, 2529-2534
2529
Flavin Mononucleotide Sensitized and Polyoxyethylene (20) Sorbitan Trioleate Micelle-Enhanced Gas/Solution Chemiluminescence for Direct Continuous Monitoring of Sulfur Dioxide in the Atmosphere Masayoshi Kato, Masaaki Yamads,* and Shigetaka Suzuki Department of Industrial Chemistry, Faculty of Technology, Tokyo Metropolitan University, Setagaya-ku, Tokyo 158, Japan
Gas/soiutlon chemllumlnescence, whlch Is realized by the nebullzatlon of reagent solutlon with a high veloclty stream of the sample alr gas, Is descrlbed for the direct contlnuous monitoring of sulfur dloxlde in the atmosphere. The weak emlsslon arlsing from the excited sulfur dloxide produced by the oxidetlon of sulfite by acidic permanganate soiutlon Is sensitized by flavin mononucleotlde; the sensitized emission is further enhanced by means of Tween surfactant micelles, Tween 85 (polyoxyethylene (20) sorbitan trideate) provldlng the largest micellar enhanced slgnai of 25 times. The slgnal Is proportlonai to the square of the sulfur dloxide concentratlon. Under conditions of 2 X I O 4 M permanganate (pH 2.5), 3.5 X IO-' M flavin mononucleotkle containlng 7 g L-l Tween 85 surfactant, and flow rates of each reagent (2.1 mL min-l) and alr stream (3.5 L min-'), the calibration graph provldes a detection limit of 3 ppb and a llnear range up to 30 ppb. 01 other substances Hkely to be present in the atmosphere, only hydrogen sulflde glves emlsslon, 1.6 ppm hydrogen sulflde provldlng a slgnal 0.2% that of sulfur dloxlde at the same concentration. Possible explanatlon of the sensltlzed and enhanced chemllumlnescence Is also presented.
Sulfur dioxide (SOz) is one of the most common and harmful air pollutants. Combustion of f w i l fuels is the main source in human activities. The maximum allowable exposure value as fixed by the Occupational Safety and Health Act (OSHA) is 5 ppm in 8 h weight average, but lower values have been reported to be toxic to plants and corrosive to metallic construction materials. Very recently SOz has been causing a serious environmental problem, i.e., acid rain which is widely believed to be responsible for acidifying soil and water (1,2). Therefore, its determination a t parts per million and lower concentrations has been the subject of much interest and the reduction in its emission is currently emphasized. There are many analytical methods available for the determination of SO2in the atmosphere (3-9);one of the most frequently employed methods is based on the Schiff reaction proposed by West and Gaeke (10). However, all of them suffer from shortcomings such as lack of sensitivity for ambient levels, lack of specificity, use of toxic mercury or its salt, instrumental and procedural complications, and long response times. On the other h d ,chemiluminescence (CL) techniques have received much attention for sensitive and selective detection of air pollutants (11,12). Gas phase CL based on the S2emission in a hydrogen-richflame (flame CL) or on the SO2 emission from the reaction with oxygen atoms permits the determination of SO2at parts-per-billion levels, although other sulfur compounds such as H3,CSz,COS, and CHBSHproduce essentially the same emission; at present, the flame CL method is being used routinely for continuous monitoring of atmospheric SOz,in which a heated silver scrubber is employed to 0003-2700/84/0356-2529$01.50/0
achieve selective removal of H2S. This paper describes a CL method for direct continuous monitoring of SOz free from the shortcomings stated above. The method is originally based on the principle that the oxidation of sulfite in acidic permanganate solution is accompanied by a weak CL in the spectral region of 450-600 nm, which arises from excited SOz (SO2*) (13-15). By the combined use of this CL technique and the accumulating method utilizing tetrachloromercurateas an absorber, Meixner and Jaeschke have determined atmospheric SO2 a t subpart-per-billion levels with the aid of a photon counter (14, 15). Quite recently we have applied this CL (solution/solution CL) technique to the flow injection analysis of sulfite at nanogram levels (correspondingto a 10-pL injection of an 80 ng mL-l sulfite solution), in which a photon counter is rendered unnecessary by virtue of the addition of a sensitizer to the CL system (16);the work was undertaken to establish a method for direct continuous monitoring of SO2 in the atmosphere without the use of absorbers. The fact that nitrite and sulfate are nonemissive in the CL system is an encouraging advantage to its establishment. On reaching a certain minimum concentration (called the critical micelle concentration, CMC), amphiphilic surfactant molecules dynamically associate in aqueous solution to form aggregates called micelles; many thermodynamic, transport, and spectroscopic properties show a distinct change in behavior with concentration around the CMC (17). Micellesolute interactions are also important phenomena in analytical chemistry, e.g., chromatography (18-20) and spectroscopic analysis (21,22). It is known that the local microenvironment in micellar media leads to significant increase in CL quantum yield (23-25). We already reported that the copper-catalyzed CL of 1,lO-phenanthroline was extremely enhanced in the presence of some cationic surfactant micelles (26). Thus, flavin mononucleotide (FMN) sensitized CL (gas/ solution CL) produced by nebulizing acidic permanganate solution, to which surfactapts have been added to increase the sensitivity, with SOz-containing air has been measured to accomplish the present purpose.
EXPERIMENTAL SECTION Detector Design. The use of a nebulizer to apply the solution/solution CL to the gas/solution CL is an idea from the work by Birk and Kuge (27), in which the liquid chromatographic effluent is nebulized by the reagent gas (O,/O,) for ita CL detection. A schematic diagram of the detector is illustrated in Figure 1. The detector consists of a reaction cell (A) and a nebulizer (B). A fine spray of the reagent solutiob is produced by a high velocity stream of the sample air gas and directed toward the top of the reaction cell. The aerosol strikes the surface where a liquid film is formed. Light emission may arise from either the liquid phase or the gas/solution interface owing to the chemical reaction and energy transfer processes. Unlike the work by Birks and Kuge (27),no special device is made for the efficient detection of the light emitted, e.g., the use of a mirror. 0 1984 American Chemical Society
2530
ANALYTICAL CHEMISTRY, VOL. 56, NO. 13, NOVEMBER 1984 6cm
,
1 J
Drain
1FT Sample gas
F E
t Reagent solutlon
Figure 1. Detector construction for gas/solutlon CL (for key, see text).
The bottom of a 30 mm o.d., 27 mm i.d. Pyrex test tube is used for the reaction cell A, the end of which is narrowed by means of glass blowing and stuck to a l/z-in. stainless steel tube (C) with a silicon adhesive and Araldite. The reaction cell is externally shielded from room light with black tape and installed in a photomultiplier tube (PMT) cooler housing (D). The nebulizer B consists of a short piece of a Pyrex tube (6.0 mm o.d., 1.0 mm i.d.) with a slightly thinned tip into which is placed a loosely fitting stainless steel tube (E) of 0.9 mm 0.d. and 0.5 mm i.d. via a black silicon septum (F). With a silicon adhesive, the short piece of the tube is attached to a 6.0 mm o.d., 4.0 mm i.d. stainless steel tube (G)which is passing through tube C, a 1/2-in. Swagelok union tee (H) with an unused port, a 6-mm union (I) using Teflon ferrules welded to the union tee H, and a 6-mm union (J). The nebulizer and tube E are held in place and adjusted vertically for maximum sensitivity by the union I and the septum F, respectively. The reagent solution and the sample air gas enter the tube E and the side port of the union tee J, respectively. Apparatus. A schematic diagram of the entire experimental setup is provided as shown Figure 2. A potassium permanganate solution acidified with sulfuric acid and FMN solution are delivered at the same flow rates by a two-channelperistaltic pump (A, ATTO SJ-1215). Surfactants are added to the FMN solution as required. The two solutions join before reaching at the detector((=);the distance between the junction and the nebulizer is ca.30 cm. Low concentration SOzused to examine the detector characteristicsis provided by passing 103ppm SOzfrom a cylinder and air from a compressor (Hitachi Super Bebicon) through a standard gas generator (B, Standard Technology SGGU-72).The generator can prepare diluted SOz as low as 3 ppb (if SOz free air is used) at a maximum flow rate of 3.5 L m i d . Teflon tubing of 1mm and 5 mm i.d. is used for flow lines for the reagent solution and the SO2 gas, respectively, except pump tubes. The light produced was detected directly by a PMT (Hamamatsu Photonics R268) with no wavelength discrimination. The PMT was cooled to ca. -20 OC in an electronic cooler (D, Hamamatsu Photonics C659B) and operated at -700 V from a high voltage dc stabilizer (E, Hamamatsu Photonics C446A). The signal from the PMT was fed to an electrometer (F, TOA Electronics PM-18C) and then recorded via a laboratory-builtlow-pass active filter (G,frequency cutoff ca. 0.1 Hz) between the electrometer and the recorder (H, Rikadenki B-281s). UV spectra of FMN were measured by a spectrophotometer (Hitachi 220A) and its fluorescence spectra by a fluorescence spectrophotometer (Hitachi MPF-4).
ut] 103
wm
SOg
FMN + Surfactant
Flgure 2. Schematic diagram of apparatus (for key, see text).
Reagents. Chemicals of analytical grade were used as received. The water used was prepared by distillation of Millipore (Milli-R) water in an all-Pyrex glass apparatus, with a Teflon membrane inserted to block mist evolved. A ca. 2 x M potassium permanganate solution was prepared and stored in the dark after being titrated with an oxalate solution. A diluted permanganate solution was daily prepared from the stock solution and acidified with 5 X M sulfuric acid to desired pH values. A FMN (monosodiumsalt) solution and ita surfactant solution were daily prepared. Cylinders of 103 ppm SOz,93 ppm NO, 86 ppm NOz, and 223 ppm H2Sbalanced with nitrogen gas were purchased from Takachiho Chemical Industry Co. Ozone was generated by irradiating an oxygen stream (70 mL m i d ) in a quartz tube with a low pressure mercury lamp (6 W)and introduced into the flow line between the standard gas generator and the detector. The concentration of ozone generated was controlled by variable shielding of the lamp and determined by the ASTM method (28). The air in the laboratory was used for dilution without refinement, The concentration of diluted SOz was checked by the West and Gaeke method (IO)as needed.
RESULTS AND DISCUSSION Flow Rates of Reagent and Air Streams. It is obvious that the finer the aerosol produced, the more effective the gas/solution CL reaction, resulting in stronger light emitted. The production of fine aerosol depends strongly on the total flow rate of reagent stream and drastically on the position of the tip of tube E in the nebulizer. Thus, the effect of the flow rate of the air stream was first studied at given total flow rates of the reagent stream by adjusting the tube E vertically so that maximum sensitivity was obtained. The CL signal giving the maximum sensitivity increased with an increase in the air flow rate; a flow rate of 3.5 L min-' (the maximum flow rate achieved) was chosen for further experiments. The total flow rate of reagent stream was subsequently explored by adjusting the nebulizer vertically while producing of fine spray. A total flow rate of 4.2 mL min-l provided the highest signal when the flow rates of each stream were the same and when the distance between the top of reaction cell and the nebulizer was ca. 1.5 cm. This total flow rate gave the 2-5 traveling time, the time from confluence of two reagent streams until nebulization. It was visually confirmed that under the conditions determined a fine spray was produced and directed toward the top of the reaction cell. Reagent Concentrations. Three reaction variables, the concentrations of permanganate and FMN and the pH of permanganate solution, were optimized under the conditions determined above. The permanganate and FMN concentrations which give a maximum signal can be deduced from Figure 3. The optimized concentrations of permanganate (8 x lo4 M) and FMN (3.5 X M) are slightly higher than those for the solution/solution CL in the previous work (16). The differences may come from the type of CL reaction,
ANALYTICAL CHEMISTRY, VOL. 58, NO. 13,NOVEMBER 1984 2531
solution exists mainly as HS03- and SO2in the low pH ranges; the concentration of hydrosulfite decreases with a decrease in the pH value whereas that of SO2 increases. In addition, the overall CL reaction 2HS03- 2Mn042Mn042- 2H+ SO2- + SO2*
+
-
0
IO
5
1
Concentration o f
FMN, 10-3 M
Flgure 3. Effect of FMN concentration on CL signal in the presence of different concentrationsof permanganate: [SO,] 0.53ppm, pH of KMnO, solution 2.5; [KMnO,] 2 X IO" M (U),4 X lo-' M (A),8 X lo-' M (0)10 , X lo-' M (0).
1
2,o
pH
of
3,O
permanganate solution
Figure 4. Effect of pH on CL signal: [SO,] 0.53 ppm; [KMnO,] 8 X 10" M; [FMN] 3.5 X loa3M.
heterogeneous or homogeneous. An increase in both solution concentrations above the optimal concentrations causes a decrease in the signal (A- 1537 nm, a maximum wavelength for FMN fluorescence, because the light emitted is also considered to be its phosphorescence as described later) which is mainly due to the intense colors of reagent solutions, showing absorption maxima at 450 nm for FMN and 527 and 546 nm for permanganate. The dependence of the signal on the pH of permanganate solution is shown in Figure 4, indicating that an optimum pH value is ca. 2.5. Lower pH values lead to a decrease in the signal. This can be explained on the basis of the CL reaction scheme proposed by Meixner and Jaeschke (15)
-
HS03- + Mn042HS03
-
S20e2-
HS03
+ Mn042-
+ 2H+ S042- + SO2* S206"
where hydrosulfite is liberated from the disulfitomercurate complex by acid. In the present work it is formed by direct absorption of SOz into the reagent solution and takes part in the following three equilibria (29): S02.H20
H+ + HS03- (Kl = 0.0139)
H++ S032- ( K 2 = 6.24 x 2HS03- F! S2Ob2- + H2O (Ka= 0.076).
HS03-
K I ,K2, and K3 are equilibrium constants. Sulfur dioxide in
-
+
+
indicates that very acidic conditions are not desirable for the CL reaction. These are the reasons for the decrease in the signal at lower pH values. FMN-Sensitized CL. As described in a previous paper (16),the FMN-sensitized CL was 330 times stronger in intensity than the unsensitized emission arising from S02*. However, it was not so strong that its spectrum could be measured by use of a monochromator; this was also the case for the CL enhanced further by surfactant micelles as stated later. The SO2* seems to be in the triplet state (3SOz*) from its emission spectrum (450-600 nm) which Stauff and Jaeschke have measured by means of interference filters (30). This is supported by the idea that there is an emission only from the triplet state in the visible range (31) and from the fact (the internal heavy atom effect) that the CL from SO2* is sensitized by 9,lO-dibromoanthracene(a triplet counter) solubilized with a nonionic surfactant but not by $10-diphenylanthracene (a singlet counter). The 3B1state, the emission from which is in the 390-450 nm range under reduced pressure (31,32),may be assigned for the 3S02*although there must be a large shift in emission wavelength in solution. Accordingly, the FMN* formed by the energy transfer from the 3SOz* is considered to be in the triplet state (3FMN*), indicating that the light observed is phosphorescence from 3FMN*, or delayed fluorescence from the singlet FMN* (lFMN*) or delayed excimer fluorescence from the excimer (lFMN2*) produced by triplet-triplet annihilation (3FMN* + 3FMN* lFMN2* F? lFMN* + 'FMN). It is reported that for l-chloronaphthalene these emissions are simultaneously observable in micelles under certain conditions (33). At any rate, it is obvious that the 3FMN* plays a key role in the sensitive determination of SO2. This is supported by the fact that the addition of lead or silver salt to the CL system results in an increase in the signal due to the external heavy atom effect, although permanganate ion in the CL system has already exerted the external heavy atom effect. Micelle-Enhanced CL. In order to investigate whether micellar media function effectively for the present CL system, cetyltrimethylammoniumbromide (CTAB, CMC = 9.2 X lo4 M) as cationic surfactant, sodium lauryl sulfate (SLS, CMC = 8.1 X lov3M) as anionic surfactant, and polyoxyethylene (20) sorbitan monolaurate (Tween 20, CMC = 0.060 g L-l) as nonionic surfactant were added to the FMN solution. The results are shown as a function of the SO2 concentration in Figure 5, along with that in the absence of surfactant. Tween 20 enhanced the signal several times, despite of the turbidity due to the emulsion formation; on the contrary, ionic surfactants suppressed the signal. Other nonionic surfactants such as sorbitan monolaurate (Span 20, CMC = 2 x lo4 M), polyoxyethylene (9.5) octylphenol (Triton X-100, CMC = 3 X lo4 M), and polyoxyethylene (23) dodecanol (Brij-35,CMC = (6-9) X M) were also tested. Span 20 (1.4 X M) and Brij-36 (1.0 X M) suppressed the signal slightly; 6 X M Triton X-100 gave a little enhanced signal. With the ionic surfactant micelles, the electrostatic repulsion of the reactants (H' for cationic, HS03-, MnO;, and FMN- for anionic micelle) from the micelle owing to their charges seems to be responsible for the inhibition of the CL reaction. The heavier inhibition for CTAB is explained as considerable consuming of Mn04- and/or HS03- due to the redox reaction with Br- at the high concentration as a counterion of the surfactant. On the other hand, the reactants can
-
ANALYTICAL CHEMISTRY, VOL. 56, NO. 13, NOVEMBER 1984
2532
100
10 a
N
2 o m
‘Z
1
u -I 1
0‘
0,l
0,Ol
1
0,l Concentrotion o f SO2,
uum
Flgure 5. Effect of surfactant micelles on CL signal: [KMnO,] 8 X M, pH 2.5, [FMN] 3.5 X M; CTAB (1.8 X M) (W), SLS (1.5 X lo-, M) (A);Tween 20 (5 mL L-’) (0); none (0).
migrate easily on the surface of the nonionic micelle, regardless of their charges and be subject to a micellar effect. That Tween 20 enhances the signal but Span 20 does not implies that the poly(oxyethy1ene)chain (hydrophilicgroup) appears to take part in the micellar effect because Tween 20 is synthesized by the addition of ethylene oxide to Span 20. However, it is conceivable that the long alkyl chain (hydrophobic group) also plays an important role in the micellar effect because Brij-35 and Triton X-100 have a poly(oxyethylene) chain. These may be closely related to the finding that Tween 85, one of Tween surfactants described later, suppressesthe signal in the absence of FMN; that is, the HSOs radicals as precursor of the SO2* molecules seem to be scavenged by the ethylene oxides of surfactant through hydrogen atom abstraction reaction. Other Tween surfactants containing an average of 20 units of ethylene oxide per molecule as well as Tween 20 were further evaluated for micellar enhanced CL. The results are provided as a function of the surfactant concentration in Figure 6. Tween 85, polyoxyethylene (20) sorbitan trioleate, exhibits the micellar effect with 15 times signal enhancement a t 21 g L-l. Such a feature is rationalized in terms of the structure of micelle formed. Tween 85 has three long alkyl chains and one polyoxyethylene (20) chain in its molecule whereas other Tween surfactants have one long alkyl chain and three short oxyethylene chains (20 units in three chains). This difference in molecular structure should influence significantly the micelle structure. That is to say, Tween 85 is likely to form micelles with an unique structure, e.g., bilayer aggregates (lamella or vesicle structure) as dialkyl type surfactants form (34-36), Le., in structures which exhibit higher organization, stability, and rigidity than those of normal micelle (23). It is known that in such bilayer aggregates the CL reaction proceeds more efficiently than in normal micelles (23). It is generally accepted that in solution excited triplet states are liable to be deactivated by molecular oxygen and impurities. For this reason solution phosphorescence in analytical chemistry has been observed in micellar solution (micelle-stabilized room temperature phosphorescence) (21) or in sensitizer-containing solution (sensitized room temper-
10
I
20
1
30
Concentration of Tween surfactants, g L-’ Figure 8. Effect of Tween surfactant micelles on CL signal: [SO,], 30 ppb; Tween (polyoxyethylene (20) sorbitan fatty acid ester) 20 (monoiaurate, CMC 0.060 g L-‘) (a),Tween 40 (monopalmitate,CMC 0.029 g L-’) (O),Tween 60 (monostearate, CMC 0.027 g L-’) (A), Tween 80 (monooleate, CMC 0.013 g L-’1 (O),Tween 85 (trioleate, CMC (unknown) (A). Other condltlons are given in Figure 5.
ature phosphorescence) (37). A protective, rigid, and structured environment of micelle reduces the quenching and the intramolecular processes competing with light emission; the use of a sensitizer with a high phosphorescence quantum efficiency causes strong phosphorescence. Thus, the unique micelles which Tween 85 produces likewise stabilize and protect the 3FMN*, the extent of which depends on the solubilization site of FMN in the micelle. From UV spectra of FMN showing that the ,A, at 265 nm in water is shifted to 275 nm in 10 g L-l Tween 85 solution, in contrast to 266 nm in Tween 80 (polyoxyethylene(20) sorbitan monooleate) solution at the same concentration,it is reasonable to consider that the environment in which FMN molecules are solubilized is more hydrophobic in Tween 85 than in Tween 80. The hydrophobicity in the solubilization site appears to be stronger than that in isopropyl alcohol (A, 269 nm). Sulfur dioxide and flavin (isoalloxazine of FMN) are easier to be dissolved in such hydrophobic medium than in water, resulting in an occurrence of more efficient energy transfer from ?SO2* to FMN. On the other hand, it can be said that the micellar effect does not work on the emission efficiency from the ‘FMN* even if the light observed is fluorescence, because fluorescence measurements of FMN reveal no change in its spectrum and intensity in the presence of Tween 85 surfactant. Spectroscopic and electron microscopic studies are necessitated for more detailed elucidation of the micellar effect and the micelle structure. Calibration Graphs. Figure 7 shows calibration graphs in the presence and in the absence of Tween 85, in which the square root of the signal is plotted as ordinate. The proportionality of the root of signal to the SO2 concentration is based on the CL reaction scheme stated early, that is, the formation of one SO2* molecule from two SO2molecules. The poor linearity is mainly ascribable to the permanganate concentration being too low compared with the SOzconcentration. The turbidity of surfactant solution due to the emulsion formation is a minor reason because the linearity remains poor in the absence of the surfactant. The calibration graph at the surfactant concentration of 21 g L-l provided a linear range of 6-90 ppb. As can be seen from the figure, the SO2 concentration giving the upper limit of linear range decreases with an increase in the surfactant concentrationalthough the lower detection limit is lowered. This indicates that no addition of the surfactant is desirable for the determination of SO2 at
ANALYTICAL CHEMISTRY, VOL. 56, NO. 13, NOVEMBER 1984 2533
15
N
L4 40 2 10 c 0
.*mm
L
-I LJ
1 min
IC U
0
0.4
0,2
0
Concentration o f
SO2,
0,6
PPm
Flgure 7. Calibration graphs in the presence of different concentratbns of Tween 85 surfactant: [Tween 851 0 (0);7 (A);14 (0); 21 (A):28 g L-' (0). Other conditions are given in Figure 5.
Air
Figure 9, CL signal profiles: [KMnO,] 2 are given in Figure 8. 15
N
3;
4
7
10
I
0
m
.3
Lo
0 J
vw
0
e
5
a, D U v)
0
200
400
600
Concentrotion o f SO2, ppb
Figure 8. Reoptimization of permanganate concentration in the presence of 7 g L-' Tween 85: pH 2.5 [FMN] 3.5 X 10" M; [KMnO,] 2 X lo-' M (0); 4 X lo-' M (0); 8 X lo-' M (A).
sub-part-per-million levels. Reoptimization of the permanganate concentration in the presence of 7 g L-l Tween 85 provided a detection limit of 3 ppb (the lowest concentration prepared) and the linear range up to 30 ppb at 2 X lo4 M permanganate (Figure 8),the micellar effect leading to ca. 25 times signal enhancement. The use of the surfactant solution at concentrations higher than 7 g L-I caused a severe deterioration of the linearity. The figure also shows that the permanganate solution at lower concentrations decreases the upper limit of linear range, although it increases the sensitivity. In the calibration graph (Figure 81, the 3 ppb standard is
Air(S02 o f f )
Air+S02
X
lo-'
M. Other conditions
plotted slightly upward on the straight line due to the memory effect in the standard gas generator. This indicates that the standard gas at concentrations less than 3 ppb cannot be prepared by the present generator unit even if a cylinder of SO2 gas at lower concentrations is used. The signal profiles are depicted in Figure 9, a short response time and low memory effect being realized. The signal observed in the absence of SO2 is based on the background emission but not on SO2 in the laboratory air used. This was confirmed by the use of pure N2 gas instead of the laboratory air. Effect of Other Substances. In the previous solution/ solution CL experiments (14),it was revealed that substances likely to be present in the atmosphere gave no emission, except sulfide ion. Thus CL generation by H2Sin the present system was investigated together with NO, NOz, and 03. Compared to the signal for SO2at the same concentration, 1.6 ppm H2S provided a 0.2% signal; 0.6 ppm NO and NOz gave no emission. Although 0.3 ppm O3gave no emission per se, it suppressed the signal for 30 ppb SOz by 1.7%; 0.1 ppm O3 did not affect the signal. Interferences by H2S and O3can be negligible in practice because in the atmosphere H2S is generally present in concentrations less than ca. 10% that of SO2and because O3is present in concentrations less than 0.1 PPm. In conclusion, we have developed a sensitive, specific, simple, and rapid technique for the determination of SOz. The method is unique in being capable of detecting SOz at parts-per-billion levels with no use of absorbents and with no interference, in contrast with the West and Gaeke method and the flame CL method. The poor linear dynamic range does not cause serious problems in practice because there is no large change in concentration of ambient atmospheric SO2 and because the linear dynamic range can be shifted to higher SO2. concentration regions by varying the permanganate and/or surfactant concentrations if needed. Therefore, it can be used for direct and precise measurements of SO2in the atmosphere, especially in connection with acidic deposition. On the other
Anal. Chem. 1s84, 56, 2534-2537
2534
hand, CL in oriented systems like micelles and vesicles is very attractive in the viewpoint of analytical chemistry because there is much possibility of enhancing quantum efficiency or energy transfer efficiency and because they permit the use of CL reagents and sensitizers insoluble in water. Registry NO. SOz, 7446-09-5; HzS, 7783-06-4;flavin mononucleotide, 146-17-8;Tween 85,9005-70-3; Tween 20,9005-64-5; Tween 40,9005-66-7; Tween 60,9005-67-8; Tween 80,9005-65-6.
LITERATURE CITED (1) Krug, E. C.; Frlnk, C. R. Sclence 1983, 221,520-525. (2) Streets, D. 0.; Knudson, D. A.; Shannon, J. D. Envlron. S d . Techno/. 1983, 17. 474A-485A. (3) Dasgupta, P. K. Anal. Chem. 1981, 53,2084-2087. (4) Rlgo, A.; CherMo, M.; Argese, E.;Vlglino, P.; Dejak, C. Analyst (London) 1091, 106,474-478. (5) Lambert, J. L.; Chejlava, M. J.; Beyad, M. H.; Paukstells, J. V. Talanta 1982, 2 9 , 37-40. (6) Ramasamy, S. M.; Mottola, H. A. Anal. Chem. 1982, 54,283-286. (7) Blzluk, M.; Kozlowskl, E.; Balulescu, G. E. Anal. Lett. 1981, 14, 1377- 1389. (8) Marshall, G.; MMgley, D. Anal. Chem. 1982, 54, 1490-1494. (9) Bhatt, M. A.; Gupta, V. K. Analyst (London) 1983, 108, 374-379. (10) West, P. W.; Gaeke, 0. C. Anal. Chem. 1056, 28, 1816-1819. (11) Stevens, R. K.; Hodgeson, J. A. Anal. Chem. 1973, 45,443A-449A. (12) Fontijn, A. I n “Modern Fluorescence Spectroscopy”; Wehry, E. L., Ed.; Plenum Press: New York, 1976; Vol. 1, pp 159-192. (13) Stauff, J.; Jaeschke, W. Afmos. Envlron. 1975, 9 , 1038-1039. (14) Jaeschke, W.; Stauff, J. Ber. Bunsenges. Phys. Chem. 1978, 8 2 , 1180- 1184. (15) Melxner, F. X.; Jaeschke, W. A. Int. J. Envlron. Anal. Chem. 1981, 10,51-67. (16) Yamada, M.; Nakada, T.; Suzukl, S. Anal. Chlm. Acta 1983, 147, 401-404.
(17) MukerJee,P.; Mysels, K. J. “Critical Micelle Concentrations of Aqueous Surfactant Systems”; NSRDS-NBS-36, Washington, DC, 1971. (18) Yarmchuk, P.; Welnberger, R.; Hlrsch, R. F.; Cline Love, L. J. Anal. Chem. 1982, 54,2233-2238. (19) Armstrong, D. W.; Stine, G. Y. J. Am. Chem. SOC. 1983, 105, 2962-2964. (20) Dorsey, J. G.; DeEchegaray, M. T.; Landy, J. S. Anal. Chem. 1989, 55,924-928. (21) Cline Love, L. J.; Skrllec, M. Int. Lab. 1981, 50-55. (22) Slngh, H.; Hinze, W. L. Anal. Lett. 1982, 15,221-243. (23) Nlkokavouras, J.; Vassilopoulos, G.; Paleos, C. M. J . Chem. Soc., Chem. Common. 1981, 1082-1083. (24) Shinkal, S.; Ishlkawa. Y.;Manabe, 0.; Kunitake, T. Chem. Lett. 1981, 1523-1526. (25) Paleos, C. M.; Vassllopoulos, G.; Nlkokavouras, J. J. fhofochem. 1082. ... -, 18. ., 327-334. - -. - - .. (26) Yamada, M.; Suzukl, S. Anal. Lett. 1984, 17, 251-263. (27) Blrks, J. W.; Kuge, M. C. Anal. Chem. 1080, 52,897-901. (28) ASTM D 1609-80. (29j Huss, A., Jr.; Lim, P. K.; Eckert, C. A. J. Phys. Chem. 1982, 86, 4224-4228, (30) Stauff, J.; Jaeschke, W. 2.Naturforsch., 8 1978, 338,293-299. (31) Pearse, R. W. B.; Gaydon, A. G. “The Identification of Molecular Spectra”, 4th ed.; Chapman and Hall: London, 1976; pp 297-298. (32) Su, F.; Bottenhelm, J. W.; Thorseil, D. L.; Calvert, J. G.; Damon, E. K. Chem. Phys. Lett. 1977, 49, 305-311. (33) Turro, N. J.; Alkawa, M. J. Am. Chem. SOC. 1980, 102,4866-4870. (34) Deguchl, K.; Mino. J. J. Colloid Interface Scl. 1978, 65, 155-161. (35) Nakashima, N.; Asakuma, S.; Kunltake, T.; Hotani, H. Chem. Lett. 1984, 227-230. (36) Fendler, J. H. “Membrane Mimetic Chemistry”; Wlley-Intersclence: New York, 1982; pp 158-183. (37) Donkerbroek, J. J.; Gooljer, C.; Velthorst, N. H.; Frei, R. W. Anal. Chem. 1982, 54,891-895.
RECEIVED for review March 16,1984.Accepted June 4,1984.
Fly Ash Analysis by Complementary Atomic Absorption Spectrometry and Energy Dispersive X-ray Spectrometry Thomas E. Murphy* and Phyllis A. Christensen Ash Grove Cement Company, Research Lab, 640 Southwest Blvd., Kansas City, Kansas 66103
Roger J. Behrns and Douglas R. Jaquier Ash Grove Cement Company, Louisville, Nebraska 68037
Gross errors may be encountered In the flame atomlc absorption determlnatlons of the major oxldes In fly ash If matrlx and background differences are not resolved. Sets of fly ash reference materlals are not available. Sample-standard dlfferences have been obvlated by means of llthlum metaborate fuslon of fly ash and selected NBS reference materlals and the subsequent volumetrlc comblnatlon of the dllute nltrlc acld solutions of the reference materlals. Fly ash data thus generated have been verlfled by energy dlsperslve X-ray analysls, and a llmlted use set of fly ash reference materlals for rapld X-ray analysls of fly ash has resulted.
During recent years, fly ash has gained much attention from the construction industry as a useful and increasingly important raw material (1, 2 ) . Estimated power plant ash production for 1982 was 65.41 million tons, and utilization was 13.55 million tons. This makes it the fourth most abundant solid mineral, ahead of Portland cement and iron ore (3). Once considered a nuisance waste product as well as a disposal 0003-2700/84/0356-2534$01.50/0
problem, fly ash is now recognized as a valuable substance which confers certain desirable characteristics in its many applications (4, 5). Useful qualities of a fly ash may be dictated by its chemical analysis, and this may vary widely throughout the country, depending on the coal type (6, 7). ASTM has attempted to classify fly ash by type, according to the sum of SiOz,A1203, and Fez03 (elements expressed as oxides for convenience). Under this scheme, a fly ash with a total of these three oxides 170% may be termed either a “class F” or a “class C” fly ash. Those below 70% and above 50% are class C fly ashes (8). Other important considerationsare the content of NazO, KzO, and SOB. The amounts of CaO and MgO present are generally of secondary importance except as possible indicators of carbonation and hydration potential (9). CaO and MgO are also utilizable for analytical purposes, since the basicity of the ashes may be measured by titration and various chemical relationships may be derived (10). Extensive claims regarding the performance and utility of a fly ash have been made (11,12),and often this is correlated with chemical compositions (13). The physical enhancements 0 1984 American Chemlcal Society
