Process for simultaneous measurement of sulfur and non-sulfur containing compounds

A process and apparatus for the simultaneous measurement of sulfur-containing compounds and organic compounds with or without sulfur in their structures. A detector cell allows simultaneous measurement of compounds that can be ionized in a flame and thereby cause the electrical conductivity of the flame to increase, and the selective measurement of sulfur-containing compounds which simultaneously form sulfur monoxide. Sulfur monoxide, upon mixing with ozone, emits light from 240 to 450 nm. The intensity of the light can be measured and related to the concentration of sulfur in the sample, while changes in electrical conductivity of the flame measured by imposing a voltage across the cell quantifies the organic compounds irrespective of whether or not they contain sulfur. Ratios of the signals of light intensity and electrical conductivity are different for each compound and, when the detector is coupled with a chromatographic separation column and process, this ratio facilitates the identification of unknown constituents in a mixture.

FIELD OF THE INVENTION 
This invention relates to a process and apparatus for simultaneously 
detecting and quantifying trace amounts of sulfur and non-sulfur 
containing compounds. 
BACKGROUND OF THE INVENTION 
Various processes have been devised for the measurement of the chemical 
components of a complex mixture separated by gas, liquid or supercritical 
fluid carriers, and for the measurement of the composition of gas, liquid 
and supercritical fluid streams or the gases evolved upon heating a solid 
matrix. Representative of such processes are detection by changes in 
physical properties of the streams, including changes in the refractive 
index and thermal conductivity. Another detection scheme is based on the 
measurement of electrical currents induced by the formation of ionic 
species during combustion of a stream (flame ionization). Irradiation of a 
stream using electromagnetic radiation and radioactive sources or changes 
in the absorption of electromagnetic radiation by components of a stream 
are also employed. 
In general, these processes allow detectors that can be classified as 
either "general" or "universal" detectors. These detectors produce a 
response for all of the chemical constituents contained in a carrier 
stream (except for the eluent or carrier itself). Selective detectors, on 
the other hand, respond to specific chemical constituents based on one or 
more elements within each compound detected and/or unique physical or 
chemical properties of the components. Selective detection is often 
required when the chemical components of interest are present at low 
concentrations, together with much higher concentrations of other 
chemicals in the stream. 
Detection systems can be further classified as being non-destructive 
detectors, in which the chemical composition of the stream is not altered 
by the measurement process, or destructive detectors, in which the sample 
is destroyed or chemically altered as a result of the measurement process. 
Generally, to use a destructive detector, such as a flame ionization 
detector, in combination with a selective detector, it is necessary to 
split the sample stream prior to measurement of the chemical constituents 
by the respective detectors. Difficulties in controlling the amount of the 
sample stream which flows into the different detectors using stream 
splitting has severely limited the utility of this technique. 
In chromatographic analysis, the identity of a chemical compound is 
determined based on the "retention time" of the compound in a 
chromatographic system. The amount of the compound is determined based on 
the detector response. Typically, several analyses are performed using 
standard solutions of the test compound at different concentrations. Based 
on this information, a calibration curve is constructed by comparing the 
detector response (e.g. peak area) to the amount of injected compound. For 
both "universal" and "selective" detectors, retention time as well as 
response of a given chemical compound relative to a "standard" compound 
provide information regarding the identity of the chemical. 
Once response factors for a wide range of chemical compounds are known, it 
is possible to determine the concentrations of different compounds based 
solely on their retention times and detection response without the need 
for constructing calibration curves for each individual component. For 
example, relative response factors using a flame ionization detector are 
available for a large number of hydrocarbons and other chemical compounds 
found in petroleum and petrochemical samples, thus greatly simplifying 
quantifications of these complex samples. Comparison of the relative 
response factors for compounds on two or more different detectors provides 
even more information regarding the identity of a particular chemical 
compound, since fundamentally different measurement techniques are 
employed. 
An important class of selective detectors are devices for the selective 
measurement of sulfur-containing compounds. When present as impurities at 
low concentrations, sulfur-containing compounds are detrimental to a wide 
range of chemical processes. In consumer products, trace levels of 
sulfur-containing compounds can impart objectionable taste and odor to 
products. In petrochemical applications, trace sulfur contaminants can 
rapidly poison costly catalysts. For these reasons, numerous processes and 
apparatus have been developed for the measurement of low concentrations of 
sulfur-containing compounds in sample streams. 
Representative of such processes is that disclosed in West German Patent 
No. 1,133,918 to H. Dragerwerk and B. Drager for the flame photometric 
detector (FPD). Sulfur-containing compounds are oxidized in a hydrogen/air 
flame to form diatomic sulfur S.sub.2 in an electronically excited state. 
Emission of light from this species can be measured using a 
photomultiplier tube or similar light detection device equipped with an 
optical filter to eliminate the light emitted from other species in the 
flame. Through the use of different optical filters, the FPD can also be 
used for the measurement of phosphorus-containing compounds based on the 
emission of light from electronically excited phosphorus dioxide 
(PO.sub.2) formed in the hydrogen/air flame. Compounds that do not contain 
sulfur or phosphorus cannot be measured using the FPD. However, compounds 
that do not contain sulfur or phosphorus can result in a decrease or 
"quenching" of the detector response for sulfur-and phosphorus-containing 
compounds. S. O. Farwell and C. J. Barinaga, Sulfur-Selective Detection 
with the FPD: Current Enigmas, Practical Usage, and Future Directions, 24 
Journal of Chromatographic Science, 483 (1986). 
The reactive sulfur and phosphorus species generated in the FPD flame are 
short-lived and therefore require that the light measurement device be 
located in close proximity to the flame. This basic design requirement has 
precluded the simultaneous operation of the FPD with other "universal" 
detection systems, such as the flame ionization detector. Of course, there 
is no such thing as a truly universal detector. For example, the flame 
ionization detector responds sensitively to nearly all organic compounds 
(excluding formaldehyde and formic acid) but not to inorganic compounds 
(e.g., O.sub.2, N.sub.2, Ar, CO.sub.2, CO, SO.sub.2, H.sub.2 S, COS, 
etc.). 
Another example of selective detection of sulfur-containing compounds is 
that disclosed in U.S. Pat. Nos. 4,678,756 and 4,352,779 of R. E. Parks. 
According to this process, a sample is passed through a furnace containing 
a metal oxide catalyst to convert sulfur-containing compounds to sulfur 
dioxide. The sulfur dioxide is then passed through a second furnace, where 
the sample is mixed with hydrogen gas to facilitate the conversion of 
sulfur dioxide to hydrogen sulfide. The effluent of the second furnace is 
then directed into a reaction cell where the hydrogen sulfide is mixed 
with ozone and the resultant chemiluminescence is measured by means of a 
photomultiplier tube. In the system described by Parks, 
non-sulfur-containing compounds cannot be measured, since the expected 
products from the oxidation furnace (carbon dioxide and/or carbon 
monoxide) and from the reduction furnace (methane) either do not undergo 
an ozone-induced chemiluminescent reaction, or the light emitted from such 
reactions is eliminated through the use of optical filters. 
Numerous other patents and publications may be found which disclose other 
approaches to the selective detection of sulfur-containing compounds. 
Gaffney and co-workers have described a technique for the measurement of 
reduced sulfur compounds (e.g., hydrogen sulfide, methanethiol, dimethyl 
sulfide, etc.) based on reactions of the sulfur-containing compounds with 
ozone to form electronically excited sulfur dioxide (SO.sub.2 *) which 
then emits radiation in the 200 nm to 400 nm region of the spectrum. J. S. 
Gaffney, D. F. Spandau, T. J. Kelly, R. L. Tauner, Gas Chromatographic 
Detection of Reduced Sulfur Compounds Using Ozone Chemiluminescence, 347 
Journal of Chromatography 121 (1985). This detection system does not 
permit measurement of all sulfur-containing compounds (e.g., sulfur 
dioxide) and suffers from interferences from non-sulfur-containing 
compounds such as olefins. 
Birks and co-workers have described a sulfur selective detector based on 
fluorine-induced chemiluminescence. J. K. Nelson, R. H. Getty, J. W. 
Birks, Flourine Induced Chemiluminescence Detector for Reduced Sulfur 
Compounds, 55 Analytical Chemistry 1767 (1983). Reduced organic 
sulfur-containing compounds (e.g., mercaptans, sulfides, disulfides, etc.) 
react with molecular fluorine to form vibrationally excited hydrogen 
fluoride and other electronically and vibrationally excited species which 
emit radiation in the red and near infrared region of the spectrum. 
Inorganic sulfur-containing compounds (e.g., H.sub.2 S, SO.sub.2, etc.) do 
not undergo fluorine-induced chemiluminescence, while many 
non-sulfur-containing compounds, such as olefins and aromatic 
hydrocarbons, do react and interfere in the measurement of sulfur 
compounds. 
Other workers have described a detection system based on the reaction of 
sulfur-containing compounds with chlorine dioxide. These reactions result 
in the formation of electronically excited diatomic sulfur, which emits 
radiation in the visible region of the spectrum (250 to 450 nm). 
None of these previously reported systems for the measurement of 
sulfur-containing compounds permit the simultaneous measurement of 
non-sulfur-containing compounds, without the need for splitting the sample 
to a second "universal" detector system. 
Halstead and Thrush have described the chemiluminescent reaction of sulfur 
monoxide with ozone. The Kinetics of Elementary Reactions Involving the 
Oxides of Sulphur III. The Chemiluminescent Reaction Between Sulphur 
Monoxide and Ozone, C. J. Halstead, B. A. Thrush, 295 Proceedings of the 
Royal Society, London, 380 (1966). Sulfur monoxide, produced from sulfur 
dioxide using a microwave discharge, was reacted with ozone. One of the 
reaction products was identified as electronically excited sulfur dioxide. 
The emission spectrum from this species was recorded and found to extend 
from 280 to 420 nm, with maximum emission at 350 nm. 
Previous studies have shown that sulfur monoxide is one of the species 
formed in the combustion of sulfur compounds in a flame. Sulfur Chemistry 
in Flames, C. H. Muller, et al., in 17th International Combustion 
Symposium, pp 867-879 (1989) and Experimental and Numerical Studies of 
Sulfur Chemistry in H.sub.2 /O.sub.2 /SO.sub.2 Flames, M. R. Zachariah, O. 
I. Smith 69, Combustion and Flame 125 (1987). Under the typical operating 
conditions of the FPD, sulfur monoxide is present at about 10 times the 
level of diatomic sulfur. 
On the basis of these observations, Benner and Stedman reported the 
development of a "Universal Sulfur Detector" (USD) based on the formation 
of sulfur monoxide in a hydrogen/air flame and subsequent detection of SO 
based on a chemiluminescent reaction with ozone. R. L. Benner, D. H. 
Stedman, Universal Sulfer Detection by Chemiluminescence, 60 Analytical 
Chemistry 1268 (1989). The original embodiment of the USD was a continuous 
monitor for the measurement of the total concentration of 
sulfur-containing compounds in ambient air. The USD is also described in 
the parent U.S. patent application Ser. No. 07/275,980. In this design, 
the air stream containing the sulfur compounds is mixed with an excess of 
hydrogen in a quartz burner assembly equipped with an external ignition 
source. A quartz sampling probe is used to collect sulfur monoxide and 
other products from the flame for transfer to a modified nitric 
oxide/ozone chemiluminescence detector. 
This detection system was found to provide greater sensitivity for the 
measurement of sulfur-containing compounds than existing sulfur-selective 
detectors and did not suffer interferences in the measurement of sulfur 
species due to the presence of higher concentrations of non-sulfur species 
such as water, carbon dioxide and heptene. 
The USD is designed so that the sulfur-containing compounds are contained 
in an air stream which is required to support combustion when mixed with a 
second stream containing hydrogen gas. The optimum gas flow rates were 
determined to be 400 to 500 mL/min of air and 300 mL/min of hydrogen. The 
optimum internal diameter for the quartz sampling probe was reported as 
about 0.1 mm. A key feature of the system reported by Benner and Stedman 
was the need to add a halogenated compound, such as CF.sub.2 Cl.sub.2, 
into the air stream in order to achieve stable instrument baseline and 
long term instrument stability. The fundamental design of the USD 
precludes the measurement of non-sulfur containing compounds by 
conventional means such as the detection of ionic species produced in the 
flame. 
SUMMARY OF INVENTION 
The present invention describes a process and apparatus for the 
simultaneous measurement of sulfur-containing compounds and 
non-sulfur-containing compounds based on the combustion of species in the 
hydrogen/air flame of a flame ionization detector, measurement of the 
ionic species produced in the flame, and concurrent withdrawal of sulfur 
monoxide produced in the flame and measurement of the sulfur monoxide by 
ozone-induced chemiluminescence. 
The integrated detection system simultaneously measures organic compounds 
capable of producing ionic species upon combustion in the hydrogen/air 
flame and selectively measures all sulfur-containing compounds based on 
conversion of these sulfur-containing compounds in the same hydrogen/air 
flame to form sulfur monoxide, which is withdrawn from the flame and 
detected by means of ozone-induced chemiluminescence. 
An important advantage of the present integrated detector device is that it 
is not necessary to split the sample stream before it enters the detector 
cell. The selective detection system simultaneously forms both sulfur 
monoxide, from which sulfur-containing species are measured, and ions 
containing carbon, from which organic compound concentrations can be 
deduced. This device provides a means for direct operation of a 
"universal" detector (such as the flame ionization detector) and selective 
detection, without the need for splitting the sample stream. 
In addition, in the present invention the response of two different 
detectors for the same compound is simultaneously measured, which greatly 
simplifies use of relative response factors in the identification of 
chemical compounds.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
There is shown in FIG. 1 a preferred embodiment of the apparatus for the 
simultaneous detection of sulfur-containing compounds and 
non-sulfur-containing compounds after elution from a chromatographic 
column. The column 10 is contained in an oven 12, has an injection port 14 
for injection of the sample and a supply 16 of the chromatographic mobile 
phase consisting of either a gas, liquid or supercritical fluid source. 
The effluent of the chromatographic column 10 is directed into the inlet 
18 of an apparatus 19 for the combustion of the chemical constituents of 
the carrier stream in a hydrogen/air flame 20. A commonly available flame 
ionization detector may be used, if adapted as described below. A hydrogen 
gas source 17 and a compressed air or oxygen source 15 is in fluid 
communication with the interior of combustion apparatus 19. Standard means 
for adjusting the flow of these gases to create an appropriate flame may 
also be included and are well known in the art. As seen in FIG. 2, an 
external electrical potential 22 is applied between the base of the flame 
20 and a metal tube 26, which serves as a collector for ionic species 
formed in the flame. The existence and quantity of ionic species formed in 
the flame 20, are derived from the current generated between the base of 
the flame and the metal tube 26. The current data is transferred to a 
microprocessor unit 31, which is capable of displaying the current 
detected as a function of time on a recorder 33. 
In conjunction with the measurement of ionic species formed in the flame, a 
flame sampling probe 28 is positioned above the flame to withdraw 90-95% 
of the flame gases from the flame assembly via a transfer line 30 into a 
chemical reaction cell 36. In the chemical reaction cell 36, the flame 
gases are mixed with a stream containing ozone produced by means of an 
electrical discharge of air or oxygen. Sulfur monoxide and other reactive 
species formed in the flame 20 will be carried to the chemical reaction 
cell 36 via the transfer line 30, and will undergo chemical reactions with 
ozone to produce species such as sulfur dioxide in an excited electronic 
state, which will emit radiation. 
The radiation emitted by the transient excited species is measured by means 
of a photomultiplier tube 38 after passage through a quartz window 40 and 
an optical filter 42. A vacuum pump 44 is used to withdraw the gases from 
the flame via the sampling probe 28, the transfer line 30 into the 
chemical reaction cell 36, and withdraw the gaseous products after 
completion of the chemiluminescent reaction from the reaction cell 36. A 
chemical trap 46 is used prior to the vacuum pump 44 to remove reactive 
chemical compounds, such as ozone and oxides of nitrogen, to prevent 
degradation of the vacuum pump and pump oil. A gas ballast and an oil 
return filter 48 is connected to the exhaust of the vacuum pump to 
facilitate the removal of water vapor and other gases from the vacuum pump 
44 and the recycling of oil vapor from the pump exhaust. The pump 44 is 
exhausted out vent 50. 
A detailed view of an embodiment of the flame source and flame sampling 
probe 28 is shown in FIG. 2. The flame sampling probe 28 consists of a 
high purity (&gt;99.99%) aluminum oxide tube with an internal diameter of 
0.020 in. and a length of 3.2 to 4.2 in., with minimal contamination of 
the probe material by silicon dioxide. In a preferred embodiment, the 
probe material may be either a high purity ceramic or high purity 
crystalline sapphire or ruby tube. 
In the ionic detector apparatus 19, the sample stream to be analyzed is 
mixed with hydrogen gas and enters the flame jet 24. The flame source is 
comprised of a flame jet 24 that extends into the body of the ionic 
detector 19. The flame jet 24 is comprised of an outer chamber 25 and an 
inner tube chamber 27. The outer chamber 25 is in fluid communication with 
the source of hydrogen gas 17, and the inner tube chamber is in fluid 
communication with column 10 via inlet 18. The base of the ionic detector 
19 is in fluid communication with the source of compressed air or oxygen 
15. A stream of air is passed around the exterior of the tube and mixed 
with the stream containing the hydrogen and sample at the outlet of the 
tube 23. 
An external ignition source is used to initiate combustion of these gas 
streams. In the preferred embodiment, the flow rate of the sample stream 
is 0.5 to 30 mL/min, the flow rate of the hydrogen gas stream is 170 to 
190 mL/min and the flow rate of the air or oxygen stream is 275 to 350 
mL/min. 
The high purity aluminum oxide sampling probe 28 is positioned 4 to 8 mm 
from the top of the flame jet 24, and the height can be adjusted by means 
of a positional set-screw (not shown). 
Exhaust gases from the flame 20 are withdrawn by means of a vacuum pump 44 
through a transfer line 30 which is constructed of a chemically inert 
material to facilitate complete transfer of sulfur monoxide and other 
flame exhaust gases into the chemiluminescent reaction chamber 36. 
In the preferred embodiment, the transfer line 30 is comprised of a 5 ft. 
length of 1.7 mm ID by 1/8 in. OD tubing composed of PFA, which has been 
treated with carbon black or other opaque materials in order to prohibit 
the passage of light through the walls of the transfer line tubing and 
into the chemiluminescent cell. 
The present invention is distinctly different from the USD system of Benner 
and Stedman discussed above. As previously noted, the design of the USD 
precluded the measurement of non-sulfur-containing compounds based on the 
formation of ionic species in the flame. In contrast with USD, in the 
present invention the sample is mixed with a hydrogen stream and then is 
mixed with air and the temperature of the hydrogen/air flame 20 is much 
higher (&gt;150.degree. C.) due to the higher gas flow rate employed and the 
use of a smaller size flame than the diffuse flame employed in the USD. 
The higher flame temperatures are important in the formation of ionic 
species from organic compounds during combustion. The optimum materials to 
be used for sampling the flame exhaust gases in the of the present 
invention are high purity aluminum oxides, with minimal contamination by 
silicon dioxide, in contrast to the pure silicon dioxide (quartz) sampling 
probe employed in the USD. Use of a sampling probe 28 composed of silicon 
dioxide (quartz) in the present invention resulted in lower overall 
sensitivity of the detector for sulfur-containing compounds versus a high 
purity aluminum oxide sampling probe. Finally, the present invention does 
not require the addition of a halogen-containing compound to the air 
stream for baseline stability. 
Detailed views of the chemiluminescent reaction cell 36 are shown in FIG. 
3. The cell 36 is composed of aluminum and machined to an internal volume 
of about 10 cubic centimeters. There are four ports in the reaction cell 
36. Port A 52 is the sulfur monoxide inlet, port B 54 is the ozone inlet 
from the ozone generator, port C 58 is the pressure transducer used to 
monitor the internal cell pressure and port D 60 is the vacuum outlet. A 
sulfur monoxide inlet tube 53, in fluid communication with transfer line 
30, enters through Port A 52 and into the interior of reaction cell 36. An 
ozone inlet tube 55 enters through Port B 54 and into the interior of 
reaction cell 36. In a preferred embodiment, the ends of sulfur monoxide 
inlet tube 53 and the ozone inlet tube 55 are within 5 millimeters. 
Ozone inlet tube 55 is in fluid communication with ozone generator 56. A 
source of compressed air or gas 60 is fed through conduit 62, via 
regulator 64 and filter 66, into ozone generator 56. Ozone generator 56 
consists of an electrical discharge device that produces consistent and 
quantifiable amounts of ozone. 
On the face of the chemical reaction cell 36 opposite the vacuum outlet 60, 
the quartz window 40 is held in a sealing relationship. All gases exit the 
reaction cell 36 via vacuum Port D 60. Light emitted by transient excited 
species within the interior of the reaction cell 36 passes through the 
quartz window 40, through the optical filter 42, and is measured at the 
photomultiplier tube 38. Data concerning the quantity of light generated 
is transferred to controller 39 for display on recorder 41. 
EXAMPLE 1 
In this Example, the apparatus shown in FIGS. 1, 2 and 3 consists, in part, 
of a Hewlett Packard Model 5890 gas chromatograph equipped with a 30 
m.times.0.32 mm ID fused silica capillary column 10, coated with a 4 
micrometer film of methyl silicone (Supelco, Inc.). A helium carrier gas 
operated at a flow rate of about 2 mL/min is used to transfer organic 
compounds and sulfur-containing compounds from a heated injection port 14, 
through the chromatographic column 10 and into the integrated 
organic/sulfur detection system. The flame sampling probe 28 consists of a 
3.2 cm.times.0.5 mm ID ceramic probe positioned 6 mm from the tip of the 
flame jet 24. The instrument for the measurement of ozone-induced 
chemiluminescence of the flame exhaust gases is a Sievers Research, Inc. 
Model 350 Sulfur Chemiluminescence Detector equipped with an Edwards Model 
E2M-1 vacuum pump. 
As shown in FIG. 4, when a mixture containing parts-per-million levels of 
nine different sulfur-containing compounds in gaseous propylene is 
injected into this system, two different detector signals are obtained, 
simultaneously, from a single sample injection. The lower chromatogram A 
is obtained by the measurement of ionic species produced in the 
hydrogen/air flame from the combustion of organic compounds. The upper 
chromatogram B is obtained by collection of sulfur monoxide formed in the 
flame and measurement of the radiation emitted from the flame exhaust 
gases after they are mixed with ozone. 
In chromatogram A, the sulfur-containing compounds are present at much 
lower concentrations are not detected. Only propylene and two other 
non-sulfur-containing compounds, ethanol and hexane which are present in 
the sample, are under these operating conditions. In contrast, only the 
sulfur-containing compounds are detected by the second component of the 
integrated detection system (chromatogram B), even though the 
non-sulfur-containing compounds are present at more than a million times 
greater concentrations. In addition, this example illustrates another key 
feature of the present invention. Under the conditions employed, carbonyl 
sulfide and propylene are not chromatographically resolved, with both 
compounds exiting the chromatographic column and entering the detection 
system simultaneously. In contrast with other sulfur-selective detection 
systems, the presence of a much higher level of a non-sulfur-containing 
compound (propylene) does not reduce or in any way interfere with the 
measurement of the much lower level of carbonyl sulfide in the sample. 
EXAMPLE 2 
Utilizing the same apparatus as previously described in Example 1, but with 
a 30 m.times.0.32 mm ID fused silica capillary with a 2 micrometer coating 
of methyl silicon, and under similar conditions as detailed in Example 1, 
a sample of a naphtha feed stock was injected into the gas chromatograph 
and the organic components and the sulfur-containing compounds measured 
using the integrated detection system. As illustrated in FIG. 5, the lower 
chromatogram C demonstrates that the naphtha sample is primarily composed 
of a large number of aliphatic, aromatic and olefinic hydrocarbons. The 
upper chromatogram D shows the input from the chemiluminescent detector 
portion of the detection system. The complex nature of this sample does 
not permit complete resolution of all of the components and, in 
particular, trace levels of the sulfur-containing compounds and higher 
levels of the non-sulfur-containing hydrocarbon compounds cannot be 
measured with other detection systems. In the present invention, the trace 
levels of the sulfur-containing compounds can be sensitively measured by 
the ozone-induced chemiluminescence component, while the higher levels of 
hydrocarbons are simultaneously measured by the flame ionization component 
of the detection system. 
EXAMPLE 3 
The apparatus detailed in Example 1 was modified by removal of the flame 
sampling probe 28 from the system and adjustment of the hydrogen flow rate 
to about 30 mL/min and the air flow rate to about 250 mL/min. These flame 
conditions are the same as those employed in the standard operation of a 
flame ionization detector. Under these modified conditions, a sample 
containing a mixture of hydrocarbons was injected into the chromatographic 
system and the flame ionization response for each compound was measured 
relative to normal hexane. The flame sampling probe 28 was then 
reinstalled, flow rate adjusted to the conditions detailed in Example 1 
and the sample re-injected. The response relative to hexane (Relative 
Response Factor, or RRF) for representative hydrocarbons determined under 
these two different operating conditions are shown in Table 1. These data 
show that the operating conditions of the integrated detector system do 
not significantly change the RRF compared with those obtained using 
standard FID operating conditions. This is remarkable considering the 
large differences in the gas flow rates between standard FID and the 
conditions employed in the present invention. This means that it will be 
possible to directly apply the extensive compilation of relative response 
factors published for a standard FID to data obtained with the new 
simultaneous detection system. 
Also shown in Table 1 are the response factors for selected sulfur 
compounds relative to diethylsulfide. Response factors are calculated 
relative to diethylsulfide since hexane produces no response in the 
sulfur-selective portion of the simultaneous detection system. As can be 
seen from this data, significant differences exist in the relative 
responses of different sulfur compounds when measured by the different 
detectors of the simultaneous detection system, which in principle, can be 
used as a means of compound identification. 
TABLE 1 
______________________________________ 
RRF 
SULFUR RRF RRF 
MODE STANDARD SULFUR 
COMPOUND FID FID DETECTOR 
______________________________________ 
c-2-hexane 0.19 0.19 0 
Benzene 1.72 1.72 0 
Toluene 2.85 3.15 0 
n-octane 3.41 3.69 0 
o-xylene 1.28 1.45 0 
Napthalene 0.32 0.39 0 
Dimethyldisulfide 
0.63 2.09 
Diethyldisulfide 
0.86 1.67 
______________________________________ 
EXAMPLE 4 
The apparatus detailed in Example 1 was modified for use as a supercritical 
fluid chromatograph. A CCS model 7000 SFC fluid controller was used to 
deliver supercritical carbon dioxide. A 150 mm.times.1 mm stainless steel 
column packed with 3 micrometer particles of octadecyl silyl treated 
silica was housed in an HP 5890 oven for temperature control. A short 
length (about 5 cm) of 0.025 m ID fused silica tubing was connected 
between the exit of the column and the inlet of the flame source to act as 
a restrictor. Combustion gases from the hydrogen air flame were collected 
using a 3.2 cm.times.0.020 in. ID sapphire tube 28. 
FIG. 6 shows the simultaneous analysis of organic compounds (chromatogram 
E) and sulfur-containing compounds (chromatogram F) present in a sample of 
crude oil using the present invention coupled with supercritical fluid 
chromatography. Previous attempts to employ existing sulfur-selective 
detectors for supercritical fluid chromatography, even without 
simultaneous measurement of non-sulfur-containing organic compounds, have 
not been successful due to low sensitivity and large changes in the 
detector baseline during pressure programming. In the present invention, 
no increase in the baseline is observed during pressure programming for 
either the non-sulfur-containing flame ionization detector response E or 
the sulfur-selective chemiluminescence detector response F. 
The description and examples above are given as a means of illustrating the 
present invention. They are not, however, intended to limit or narrow the 
invention as set forth in the claims below.