AMI. Chem. 1993, 65, 724-729
724
Use of Packed Column Supercritical Fluid Chromatography with Ozone-Based Sulfur Chemiluminescence Detection A. L. Howard and L. T. Taylor* Department of Chemistry, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061
The use of the ozone-bawdsulfur chemilumlnercc~lco detector (SCD) coupled with packed cdumn supercritical fluld chromatography (SFC) was evaluated. Optimization studies performed include the quenchlng effect of the C02 mobile phase and organic species on the chmiiumineocent specks (SO2*) and the necessary air and hydrogenflow rates to gain maximum SCD senrltlvity. Dotectivitiesof 2 pg S h and 1 pg S/s (S/N = 3) were obtaimd when capillary SFC (60nL injection) and packed column conditions (5OOnL Injection) were employed, respectlvely. The resuits obtalned when 60 nL was InJectedwere In agrment with thoro obtained with open tubular and packed caplliary cdumn SFCISCD by other Investigators,indkating that the increased flow of COz does not further quench the chemih#nlneocent species from that occurring in capiltary SFC. Detector linearity was 3-4 orders of magnitude. MetharmknodlfkdC02was also demonstrated to be compatible with the SCD even with the high moblie phase flow rate. The analyses of polycyclic aromatic sulfurcontalninghydrocarbons(PASH), dieselfuel, and sulfonylurea herbicides were explored as posslMe appilcatlons.
INTRODUCTION The use of packed columns rather than open tubular columns for chromatographicanalysis is of interest for several reasons. The columns are typically more rugged and offer faster analysis times than capillary columns due to their larger inner diameters (i.d.) and shorter length. They also have higher sample capacities and higher efficiencies (per unit length) than open tubular columns because of their higher surface area. This higher capacity is especially important when trace analysis is necessary. Another means of further enhancing trace analysis is by the use of an element-selective detector for the desired analyte. Such specificdetection often eliminates the need for extensive sample clean-up prior to analysis that could result in analyte losses. Therefore, coupling a packed column chromatographic system to an element-selective detector yields a powerful means of trace analyte quantitation. Of all the possible chromatographic techniques commonly used today, supercritical fluid chromatography (SFC) is more compatible with gas chromatographic detectors than is high-performance liquid chromatography (HPLC). The investigation of sulfur-containing compounds as components of complex matrices is a very important aspect of trace analytical determination. The quantitation of these compounds is important industrially,l-g biologically,lo and e n ~ i r o n m e n t a l l y . ~ JIndustrial ~-~~ applications include the analyses of foods,1s2beverages,3 flavors: paper: petrochem(1)Long, A. R.;Short, R.; Baker, S. A. J. Chromatogr. 1990,502,87. (2)Long, A. R.;Hseih, L. C.; Marlborough, M. S.; Short, C. R.; Barker, J. Agric. Food Chem. 1990,38,423. (3)Mishalanie, E. A.;Birks, J. W. Anal. Chem. 1986,58,918. (4)Saito, K.; Horie, M.; Hoshino, N.; Nose, N.; Mochizuki, E.; Nakazawa, H.; Fujita, J. Assoc. Off. Anal. Chem. 1989,72,917. S. A.
0003-2700/93/0365-0724$04.00/0
icals,6J and pharma~euticals.~~2~8~9 Biological applications include the analysis of blood and urine samples for pesticide metabolites.10 The investigation of water and soil samples for trace levels of harmful, thermally labile pesticides3JlJ3 are some examples of environmental analyses. The most commonly used sulfur-selectivedetectors with SFC include the flame photometric detector (FPD),14J5 fluorine-induced sulfur chemiluminescence detector (FSCD),7J6redox chemiluminescence detector (RCD),17J*and ozone-based sulfur chemiluminescence detector (03-SCD).lgJO All of the above detectors are based on the generation of a reactive moiety by first oxidizing the compound of interest. This oxidation process (catalyticor combustive)either creates the chemiluminescent species directly or yields an oxidation product that is then reacted with another molecule to yield the chemiluminescent species. In the case of the FPD, the chemiluminescent species SZ*is generated in a combustion source under reducing flame conditions. For the FSCD and the 03-SCD, it is created by reacting the oxidation product with fluorine gas and ozone, respectively, to produce HF* in the former and SOz* in the latter. The RCD is the only detector listed that responds directly to any oxidizable material. Here, the responsive sulfur compound is oxidized by NO2 on a catalytic metal surface. The resulting NO produced is then transferred to a reaction cell where it is reacted with ozone to form NOz*. Most of these detectors have several inherent drawbacks in the SFC mode. The chemiluminescent species produced with FPD is highly susceptible to quenching from COZ or other organicspeciessince the chemiluminescenceis produced and detected above the flame at an elevated temperature and atmospheric pressure. In addition, there is a marked baseline rise that occurs during pressure/density programming which must be removed by either electronic subtraction or by the use of a very slow flow rate restrictor. Moreover, FPD does not produce a linear response due to the diatomic nature of ~
~
~~~~~~~
(5)Andrawes, F.; Chang, T.; Scharrer, R. J. Chromatogr. 1989,458, 145. (6)Patterson, P. L. Anal. Chem. 1978,50,345. (7)Bornhop, D.J.; Murphy, B. J.; Krieger-Jones,L. Anal. Chem. 1989, 61,797. (8) Ahmed, A.-E. H. N.; El-Gizawy, S. M. Analyst 1989,114,571. (9)Cross, R.F. J. Chromatogr. 1989,478,422. (10)Van Welie, R. T. H.; Van Duyn, P.; Vermeulen, N. P. E. J. Chromatogr. 1989,496, 463. (11)Markides, K. E.; Lee, E. D.; Bolick, R.; Lee, M. L. Anal. Chem. 1986,58,740. (12)Mangazii, F.; Bruner, F.; Penna, N. Anal. Chem. 1983,55,2193. (13)Leck, C.;Bigander, L. E. Anal. Chem. 1988,60,1680. (14)Olesik, S. V.; Pekay, L. A.; Paliwoda, E. A. Anal. Chem. 1989,61, 58.
(15)Pekay, L. A.; Olesik, S. V. Anal. Chem. 1989,61,2616. (16)Foreman, W. T.; Shellum, C. L.; Birks, J. W.; Sievers, R. E. J. Chromatogr. 1989,465,23. (17)Foreman, W. T.;Sievers, R. E.; Wenclawiak, B. W. Fresnius' 2. Anal. Chem. 1988,330, 231. (18)Wenclawiak, B. W.; Sievers, R. E.; Foreman, W. T. Proceedings of the International Symposium On Supercritical Fluids; Perrut, M., Ed.; Nice, France, 1988;Vol. 1. (19)Chang, H.-C. K.;Taylor, L. T. J. Chromatogr. 1990,517,491. (20) Pekay, L.A.; Olesik, S. V. J.Microcol. Sep. 1990,2,270. 0 1993 American Chemical Soclety
ANALYTICAL CHEMISTRY, VOL. 65, NO. 6, MARCH 15, 1993
the chemiluminescent species. The single largest disadvantage of this detector, however, is ita compound-dependent response. The FSCD also suffers from this variable response as well as requiring the use of toxic fluorine gas. The RCDs worst disadvantage is that the catalytic oxidation must occur at an elevated temperature (250-400 "C) which might not be suitable for thermally unstable analytes. Selectivity and sensitivity are also dependent on the type of metal surface as well as temperature. Lastly, the RCD is the least selective of these detectors since its response does not depend upon the presence of a specific atom and, as a result, may be more likely to respond to interferents. The 03-SCD does not suffer from many of these disadvantages. It is less susceptible to quenching from COZor other organic species since the chemiluminescence is created and detected at ambient temperature and reduced pressure (- 10 Torr). Because the detector response is more "quench resistant" it has also been shown to be compatible with methanol-modified COzlgand reversed-phase packed capillary HPLC mobile phases.21-22 One of the greatest advantages of this detector is its equimolar response to sulfur regardless of what or how it is bonded in the molecule. This has been proven repeatedly with GC,29-25SFC,l9vmand packed capillary HPLC.21922 To date only SFC open tubular (50-100-pm i.d.) and packed capillary (250-pm i.d.) columns have been employed. These columns typically generate 1-2 orders of magnitude less decompressed COZper unit time than a packed column (1-mm i.d.). Since many of the detectors discussed have severe quenching problems under these conditions, their use with larger i.d. columns is precluded. This is not the case with the OsSCD, however, as will be described herein. The main focus of this study was to determine what factors are important in sensitivity optimization for packed column SFC/SCD. Both the effects of COZflow rate and coeluting organic species on detector response were evaluated. Detector performance was also evaluated under various flame compositions. The analysis of polycyclic aromatic sulfur-containing hydrocarbons (PASH), diesel fuel, and sulfonylurea herbicides are given as applications. EXPERIMENTAL SECTION Instrumentation. A Model 350 SCD (SieversResearch, Inc., Boulder, CO) was interfaced to the chromatographic system via a ceramicprobe which waa placed in the flame ionization detector (FID). The FID block temperature was held at 375 "C. The flow rates of the hydrogen and air used in the FID were measured by Top-Trak mass flow meters (Sierra Instruments, Carmel Valley, CA) in standard cubic centimeters per minute (SCCM). Ozone was generated in the detector by a 5-kV spark discharge in Grade 4.3 oxygen (Airco Specialty Gases, Research Triangle Park, NC). A Model 1.5vacuum pump (Edwards High Vacuum, Wilmington, MA) was used to achieve the 10-12-Torr chemiluminescence reaction cell pressure. The pumping capaicity of this pump was -450-500 mL/min. Other aspects of the detector's operation have been discussed in detail elsewhere.21~22 The design of the two SFC systems employed here differed significantly. The Model501SFC system (Dionex,Lee Scientific Division, Salt Lake City, UT) employed a computer-controlled syringe pump to deliver the COz mobile phase with an integral restrictor being employed to maintain overall system pressure. SFC grade carbon dioxidewas obtained from both Scott Specialty Gases (Plumsteadville, PA) and Air Products and Chemicals, Inc. (Allentown, PA). A He-actuated valve with either a 60-,
725
loo-, or 500-nL loop with timed split injection capabilities was used to manually introduce sample onto a 10-cm X 1-mm4.d. Deltabond Cyano (CN)packed column with d, of 5 pm (Keystone Scientific, Bellefonte, PA). A standard HP FID from a Model 5890 GC (Hewlett-Packard,Avondale,PA) was used to combust the chromatographic eluent. The SCD signal was recorded with a Model SP4290 (Spectra Physics, San Jose, CA) or a Model 3394A (HP) integrator. The HP SFC system used a peltier-cooled reciprocating pump to deliver the COz mobile phase. An auxiliary pump was also connected into the system which allowedfor any organicmodifier to be added on-line. All injections were made via a Model 7673 auto injector with an air-actuated Rheodyne valve employing a 5-pL sample loop. A 20-cm X 4.6-mm4.d. Hypersil silica (Si) (HP) column was used to achieve the chromatographicseparation with a split being made postcolumn to the FID and, therefore, the SCD. An84 mL/min (at60 "C and 200 atm) integral restrictor (HP)to the FID was used to achievethe split flow. Theremainder of the chromatographic eluent was then diverted to a multiwavelength detector (MWD). A computer-controlled variable restrictor was used to maintain overall system pressure. It was placed after the MWD. Such a back-pressure control device allowed the pressure and flow rate to be decoupled. Up to 2 GC detector signals and 3 MWD wavelengths could be stored at one time with the Vectra QS/20ChemStation ued for data collection. The interface of the SCD to the HP SFC's FID was somewhat complicated by a new FID design. The major design change which confounded this interface was the fact that the flame jet has been changed to a fixed tube. Reportedly the height of this tube is the same as the removable one previously used (Dionex), but our investigation did not support this notion. The probe had to be significantly lengthened in order to be within the recommended 2-mm distance from the tip of the jet. This new type of jet also changed the flame geometry since a significantly higher hydrogen flow rate (300SCCM or greater) was necessary to achieve maximal response. The hydrogen flow rate also affected the SCDsensitivity more than that of the Dionex system. Another design change was the route of hydrogen introduction into the FID. It was introduced at the base of the FID and allowed to flow concentrically around the restrictor and then into the jet. For the COz quenching study, all GC data were obtained with a Model 5890 Series I1 GC (HP) equipped with a Model 7673 autoinjector (HP) and a Vectra QS/20 ChemStation (HP). Chromatographic conditions were as follows: 25-m X 200-pmi.d. 5 % phenyl column (HP),grade 5.0 helium carrier gas (Airco), and 1-pL injection volume (methylene chloride). All capillary SFC data were obtained using the Dionex system under the followingconditions: 5-m X 50-pm-i.d. SB-biphenyl-30column, timed split injection (0.01 min). Chemicals. All solvents were HPLC grade and were used as received. The sulfonylureaherbicides (Dupontde Nemours,Inc., Wilmington, DE), PASH (Aldrich, Milwaukee, WI), and diesel fuel were also used as received. Stock solutions (1mg/mL) of the sulfonylureas and the PASH were prepared in acetonitrile and methylene chloride (Fisher, Pittsburgh, PA), respectively. The diesel samples were injected neat.
RESULTS A N D DISCUSSION
Detector Sensitivity Optimization. There are several key operating variables of the SCD that must be examined if the detector is to be operated at its maximum sensitivity and slectivity in the SFC mode. These parameters include (1)probe position (height and concentricity), (2) air/hydrogen flame composition, and (3) decompressed COz flow. The first step to optimal SCD sensitivity is proper installation of the probe interface to the FID since this is the crux of the SFC/SCD system. For ideal installation to be achieved proper probe height (into the FID) as well as probe (21) Chang, H . 4 . K.; Taylor, L. T. Anal. Chem. 1991,63,486. (22) Howard,A. L.; Taylor, L. T. HRC 1991, 14, 785. concentricitymust be assured. In most cases, the probe height (23) Shearer,R.L.;O'Neal,D.L.;Rios,R.;Baker,M.D.J.Chromatogr. was adjusted so that it was approximately 2 mm above the Sci. 1990,28, 24. tip of the flamejet of each SFC instrument. Once the correct (24) Gaines, K. K.; Chatham,W. H.; Farwell, S. 0.HRC 1990,13,489. (25) Johansen, N. G.; Birks, J. W. Am. Lab. 1991,112. probe height was obtained, a probe-centering tool, developed
726
ANALYTICAL CHEMISTRY, VOL. 65, 16
NO. 6, MARCH 15, 1003 SCD Background Signal (mV)
Peak Area ( x 10')
*
3 01 ~
+ ,
I
25120
I
'
-
I
I
I
k
i
10.
01
8' 195
215
235
255
120
275
140
160
180
200
220
1 240
Air Flow Rate (SCCM)
Hydrogen Flow Rate (SCCM)
Fburo 1. Effectofairflowrateon SCDresponee. Conditions: Dionex SFC system; 100% COn, 250 atm, and 100 'C; H2 flow rate, 227 SCCM; 100 ng of DBT in methylene chlorick was inJocted. Other conditions given in the Experimental Section.
Flguro 5. Effect of varying hyckogem flow rate upon SCD background signal. CondMons same as Figure 2.
6
Peak Area ( x lo6 )
Table I. Effect of COa Quenching Study on SCD Rerponw decompressed peak area/lpmol S peak aredpmol S flow rate (mL/min)
0.8
38906 40647 44304 44049 47821
0.8 0.9 1.1 1.3
Capillary SFC/SCDb 1588 1537 1520 1496
2653 2599 2537 2495
Packed Column SFC/SCDc 1483 1362 1267 1263 1314
2282 2001 2050 2153 2026
0.5 0.6 0.7
55 120
140
160
180
200
220
68 76 91 120
240
Hydrogen Flow Rate (SCCM) FIgm 2. Effect of hydrogen flow rate on SCD response. Conditions: air flow rate, 235 SCCM; 36 ng of DBT was injected. Other cohdttions as In Figure 1.
by Sievers Research, was used to tighten the probe to the probe holder while simultaneously ensuringita concentricity. The use of this tool drastically improved one's ability to recenter the probe after length adjustment versus estimating ita concentricity visually. After the proper interface was obtained, the SCD sensitivity was then optimized by maintaining a constant hydrogen flow rate (227SCCM) and varying the air (2W400SCCM) in 25 SCCM incrementa. After each air flow rate change the flame was allowed to stabilize for 2 min, An injection of DBT was then made, and the SCD response (peak area) was obtained. This process was continuedover the entire air flow rate range. As can be seen in Figure 1,the optimum SCD response was found at an air flow of 235 SCCM under these conditions. When sensitivity over the full range (200400SCCM) of air flows was examined, there were several local maxima obtained as was found by Olesik et al.20 for capillary SFC. Only the absolute maximum is shown in Figure 1. This maximum sensitivity was found under drastically different flame conditions from those prescribed for GC or SFC (- 200/400 air/H2) by other users. A 20% decrease in sensitivity from that seen at 2351227was obtained under these conditions. As can be seen in Figure 2,changes in hydrogen flow rate do not appear to affect the sensitivity to the same extant as changes in air flow rate. This has also been demostrated in packed capillary HPLC/SCD.21.22 However, below a hydrogen flow rate of -180 SCCM, there was a significant drop in detector
- (thianthrene)
GC/SCDo 15788 16698 18412 17976 19945
0.4
U
-(thianaphthene)
a Optimal GC/SCD flame conditions: 385 SCCM air flow rate/ 204 SCCM hydrogen flow rata, injection reproducibility (n = 3) 5 1% Optimal capillary SFC/SCD flame conditions: 330 SCCM air flow rate/207 SCCM hydrogen flow rata, injection reproducibility (n = 3) 5 2%. Optimal packed column SFC/SCD flame conditions: 235 SCCM air flow rat4227 SCCM hydrogen flow rata, injection reproducibility (n = 3) 5 1%
.
.
response. One possible reason for this behavior isthat optimal reducing flame conditions were not maintained below this hydrogen flow rate; thus less SO was produced from the combustion process. A second reason is that the flow rate capacity of the vacuum pump (450mL/min) was not being met or exceeded at this flow rate, thereby drawing sulfurcontaining room air into the system via the vacuum pump. Evidence supportingthe latter can be found in Figure 3where the SCD background signal was shown to increase when the hydrogen flow rate was leea than 180 SCCM. A significant increase in background signal, however, was not observed when the H2 flow was maintained at 227 SCCM and the air was decreased, thereby indicating that flame composition is also partially responsible for the drop in SCD sensitivity (Figure 2). It should be noted, however, that the flow rate of decompreeaed C02 entering the flame in packed column SFC becomes significant in meeting this total flow requirement. The effect of COz quenching (Table I) was also thought to be important in assessing SCD sensitivity since the amount of C02 entering the detector was increased by almost 2orders
ANALYTICAL CHEMISTRY, VOL. 65, NO. 6, MARCH 15, 1803
of magnitude from that seen with open tubular SFC/SCD. In this experiment the SCD response/pmol S under capillary GC, capillary SFC, and packed column SFC were compared. The GC/SCD case was used as the “ideal” SCD response situation since the mobile phase (He) is composed of much lighter, monatomic species as compared with COZin SFC. Two PASH (thianaphthene and thianthrene) were used for probe molecules. As is shown in Table I, there was a decrease in SCD sensitivity from the GC/SCD case to the capillary SFC case. This difference in sensitivity was obtained under similar decompressed flow rate conditions indicating that it was the presence of COZand not the mobile phase flow rate that w8p causing the decrease in detector response. The nondependence on flow rate was further supported by the packed column versus the capillarycolumn SFC results. Here, the amount of COz introduced into the detector does not appear to greatly affect the detector sensitivity. This type of relationship indicated that the quenching effect that the C02 has on the chemiluminescent species is maximal with the amount of COz entering the detector in the capillary case. Detector Performance. Upon optimization of the SCD sensitivity, the detector’s performance was evaluated under packed column SFC conditions. This assessment entailed determining the detector’s linear dynamic range, selectivity ratio, detection limit, and response factor (under various conditions). The detector’s linear dynamic range was found to be 3-4 orders of magnitude with a correlation coefficient of 0.9991. Selectivity of sulfur over hydrocarbon was found to be 107 (mol of S/mol of hydrocarbon) when the dibenzothiophene (DBT) peak coeluted with the solvent (toluene). In an attempt to substantiate nondependence of C02 flow rate on sensitivity, sulfur detectivities as well as detection limits were determined under both capillary SFC (60 nL) and packed column (500 nL) injection conditions. Identical pressure (250 atm) and temperature (100 “C) were employed. The detectivities resulting from the injection of DBT under these conditions were slightly higher in the capillary case (1.7 pg S/s) versus those for the packed column (1.3 pg S/s).Such asmalldifference ( 1 . 3 ~1,7pgS/s,reapedively) s indetectivity, however,was not statistically significant. These detectivities translated into mass detection limits of 36 and 81pg S injected, respectively. The real difference in the detection limit can be demonstrated best when the concentration of the injection solution is examined. The solution injected under capillary conditions (60 nL) was 7.83 ppm DBT, whereas the solution injected under the packed column conditions (500 nL) was 978 ppb DBT. In a previous investigation19 employing capillary SFC, it was shown that the response of the detector is equimolar with respect to sulfur by the injection of only sulfur-containing species both for 100% C02 and 2 % methanol-modified COZ mobile phases. In most “real worJd” samples, the sulfur compounds being examined are usually not the only components present in the mixture being injected. As a result, the examination of response factors under conditions of organic species coelutionwas of interest. In order to determine if coeluting specieschanged the detector’sequimolar response to sulfur, calibration curves (Figure4) were constructed (peak area vs pmol of sulfur) for DBT under two different seta of chromatographic conditions: (1)separation from the solvent peak (solid lines) and (2) coelution with the solvent peak (dashed lines). The following organic species were used as potential coelutanta: an aliphatic alcohol, an aliphatic hydrocarbon, an aromatic hydrocarbon, and a chlorinated hydrocarbon. Response factors (Table 11)were then calculated by dividing the slopes of these curves obtained with each potential coelutant by the slope obtained for hexane under each elution condition. As was expected, under
727
Peak area ( x l o 6 ) 25
7 I
/
/
I
20
15
10
5
0
200
0
600
400
800
1000
Coelu t ion Solvent
*
Hexane
-
Methanol
M e t h y l e n e Chloride
a
Toluene
Flgure 4. Effect of coelutlon of organic specks on equlmoler SCD response. CondAions: coelutlon occurred at 400 am, seeparatton at 250 atm;ak fbw rate, 235; hydrogen flow rate, 227 SCCM; temperature lOO”Cpobe,DBT;(-)probe/sdventpeakseparatkn,(---)codutkn.
Table 11. Response Factor Comparison injection solvent
SD equation of the linea slope Coelution
hexane y = 7 2 2 4 x + 155146 methanol y = 10833~+ 313034 methylene y = 5 7 9 5 ~ 97535 chloride toluene y = 10887~ - 276176
+
SD intercept
response factorb
99 262 682
41764 110999 375873
0.666 1.215
529
241854
0.655
1
Separation hexane methanol methylene chloride toluene
y = 18102x+49767 y = 2 4 5 2 1 ~ 254664 y = 19613~- 64040
+
176 416 197
74636 175868 88565
1 0.739 0.924
+
1055
474586
1.031
y = 17328~ 502725
a At least four different concentration levels injected a minimum of three times each were used to construct the calibration curves. b With respect to the slope for the hexane injections.
conditions where the DBT peak was separated from the solvent peak, the response factors were approximately 1for all of the solvents evaluated except for methanol. However, when the DBT was coeluted with the solvent peak, the response factors were lower than those obtained in the “separated” case and were no longer equimolar with respect to sulfur. There appears to be no particular trend based on solventtype. Therefore,when one is interested in the analysis of total sulfur in an unknown, it might be helpful to use a more universal detector (i.e., FID, UV) under identical chromatographic conditions prior to SCD analysis. This will allow one to gauge the environment in which the sulfurcontainingcompounds are eluting since this ultimately affecta the total sulfur response obtained. The effect that the flame composition has on the response factor of a series of compounds was also examined. The impetus for this experiment was time savings. If sensitivity were not the issue in an SFC/SCD analysis, would the flame composition affect the sulfur response factor? It it did not, a full-scale optimization of the SCD response would not be necessary every time; for example, the probe was moved or replaced. In order to determine if flame composition did
728
ANALYTICAL CHEMISTRY, VOL. 65, NO. 6, MARCH 15, 1993
Table 111. Effect of Flame Composition on Response Factors hydrogen response factors flow rate benzodiphenylene (SCCM) thianthrene dibenzothiophene sulfide Air Flow Rate = 256 SCCM
A
11
""
I
176 194 206 222 241 256 293 326
1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00
1.12 1.09 0.95 1.09 1.05 1.03 1.01 1.23 1.08 9.35
av RF RSD
1.07 1.06 1.03 1.01 0.96 0.89 1.02 1.83 1.11 26.8
response factors air flow benzodiphenylene rate (SCCM) thianthrene dibenzothiophene sulfide Hz Flow Rate = 207 SCCM 217 1.00 1.05 1.00 233 1.00 1.04 0.98 243 1.00 1.07 1.04 256 1.00 1.09 1.01 274 1.00 1.06 1.05 305 1.00 1.08 1.08 343 1.00 1.13 1.14 average RF 1.07 1.04 RSD 2.8 5.3
n = 3 for each response factor. Injection reproducibility (peak area) < 1 %.
Figure 6. SFC/UV/SCD analysls of total sulfur content In three diesel fuel samples (A) NBS standard, (B) commerclal fuel, and (C) reduced sulfur fuel. Conditions: HP SFC system; COP;150 atm, 30 OC; column, 200 X 4.&mm 1.d. H y p e d SI;flow rate, 2 mL/mln (liquid); hydrogen flow rate, 300 SCCM; air flow rate, 266 SCCM. Peak klentfflcatbnas In Figure 6. 0 C-0-CH,
0-CH,
1. THIFENSULFURON METHYL H
HARMONY
H CH,
0
LL I
0
J1
@-)
2. METSULFURON METHYL
I . THIANAPHTHENE H
ALLY
H 0-CH,
0 C-0-CH,
CH
2. DlsWZOTHlOPENE
I
15mh.
Flgure 5. Packed column SFC/SCD PASH separatlon. Peaks are as follows: (1) thlanaphthene, (2) thlanthrene, (3) dlbenrothlophene, and (4) 1,2-benrodlphenylene sulfide. Conditions: Dionex SFC system; COP; 100 O C ; pressure programmed, held at 125 for 3 mln, ramped at 10 atm/mln to 280 atm, rampedat 125 atm/mln to 400 atm; column, 100 X 1-mm 1.d. Deltabond CN; InJectbn volume, 1 0 M L (methylene chloride) Injected; hydrogen flow rate, 208 SCCM; alr flow rate, 343 SCCM.
&o:&T 0-CH,
4. CHLORSULFURON GLGIN
0
C-0-CH,
0-CH,
5. TRIBENURON METHYL H
0 C-0-CH,
0-CH,
6. BENZSULFURON METHYL &CHFSO-T-!-T
