U.S. patent application number 10/823945 was filed with the patent office on 2004-09-30 for method and apparatus for rapid screening of volatiles.
Invention is credited to Carnahan, James Claude, Lemmon, John Patrick, May, Ralph Joseph, Potyrailo, Radislav Alexandrovich.
Application Number | 20040191122 10/823945 |
Document ID | / |
Family ID | 24067840 |
Filed Date | 2004-09-30 |
United States Patent
Application |
20040191122 |
Kind Code |
A1 |
Potyrailo, Radislav Alexandrovich ;
et al. |
September 30, 2004 |
Method and apparatus for rapid screening of volatiles
Abstract
In one embodiment, the present method includes the steps of
introducing a volume of a sample into a vapor delivery line and
volatilizing at least a portion of the volume as it is carried
through the vapor delivery line. At least a portion of the
volatilized volume contacts a sensor element, which produces a
signal that is monitored to reveal information about the sample.
All components upstream of the sensor element are substantially
free of sorbent materials so that the sample volume does not
contact a substantially sorbent material before contacting the
sensor element.
Inventors: |
Potyrailo, Radislav
Alexandrovich; (Niskayuna, NY) ; Carnahan, James
Claude; (Niskayuna, NY) ; May, Ralph Joseph;
(Niskayuna, NY) ; Lemmon, John Patrick; (Delanson,
NY) |
Correspondence
Address: |
CANTOR COLBURN, LLP
55 GRIFFIN ROAD SOUTH
BLOOMFIELD
CT
06002
|
Family ID: |
24067840 |
Appl. No.: |
10/823945 |
Filed: |
April 13, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10823945 |
Apr 13, 2004 |
|
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09519330 |
Mar 6, 2000 |
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Current U.S.
Class: |
422/68.1 |
Current CPC
Class: |
G01N 33/0009 20130101;
G01N 33/0047 20130101 |
Class at
Publication: |
422/068.1 |
International
Class: |
G01N 033/00 |
Claims
What is claimed is:
1. An apparatus for rapidly screening volatile substances in a
sample, said apparatus comprising: a) an injector; b) a vapor
delivery line in fluid communication with said injector; c) a
sensor element in fluid communication with said vapor delivery line
and positioned downstream of said injector and said vapor delivery
line, wherein all components upstream of said sensor element are
substantially free of sorbent materials; and d) a monitor in
communication with said sensor element.
2. The apparatus of claim 1, wherein said sensor element is an
optical sensor element.
3. The apparatus of claim 1, wherein said sensor element is an
electrochemical sensor element.
4. The apparatus of claim 1, wherein said sensor element comprises
a semiconductor.
5. The apparatus of claim 1, wherein said sensor element is coated
with a chemically sensitive material to form a chemically sensitive
film proximate the surface of said sensor element.
6. The apparatus of claim 1, wherein said sensor element comprises
a quartz crystal.
7. The apparatus of claim 5, wherein said sensor element is coated
with a hard-soft block elastomer.
8. The apparatus of claim 7, wherein said sensor element is coated
with a silicone polyimide.
9. The apparatus of claim 7, wherein said sensor element is coated
with a block dimethylsiloxane-carbonate copolymer.
10. The apparatus of claim 5, wherein said sensor element is coated
with an amorphous fluoropolymer.
11. The apparatus of claim 10, wherein said sensor element is
coated with a random copolymer of tetrafluoroethylene and
perfluoro-2,2-dimethyl-1,3-- dioxole.
12. The apparatus of claim 1, comprising an array of sensor
elements in fluid communication with said vapor delivery line.
13. The apparatus of claim 5, wherein said monitor is adapted to
receive a signal from said sensor element representing a measured
property of said chemically sensitive film.
14. The apparatus of claim 13, wherein said monitor comprises a
frequency counter to produce data representing said signal as a
function of time.
15. The apparatus of claim 14, wherein said monitor further
comprises a computer adapted to store said data.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. application Ser.
No. 09/519,330, filed Mar. 6, 2000, the entire contents of which
are incorporated herein.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention is directed to a method and apparatus
for rapid screening of volatiles in reaction products and, more
specifically, to a method and apparatus for rapid screening of
volatiles in complex combinatorial libraries.
[0004] 2. Discussion of Related Art
[0005] Since its introduction in 1970, combinatorial chemistry has
become a popular research tool among scientists in many fields.
Combinatorial screening for biological activity has been prevalent
in the pharmaceutical industry for nearly twenty years. Recently,
combinatorial screening of catalysts for the chemical and materials
industries has been developed and continues to be an attractive
research method.
[0006] One of the many challenges in the development of
combinatorial screening for production scale reactions is the
difficulty involved in emulating production scale behavior at the
micro-scale necessary for combinatorial work. Furthermore, rapid
analytical techniques capable of measuring both the
semi-quantitative and qualitative properties necessary for high
throughput screening of combinatorial libraries continue to elude
the industry. For example, high throughput screening of volatiles
in complex combinatorial libraries presents unique problems for
practitioners.
[0007] Traditional analysis methods for volatile species involve
gas chromatography (GC), mass spectrometry (MS), GC/MS, and various
spectroscopic techniques. The use of chemical sensors is an
appealing alternative for detection of volatiles. In particular,
chemical sensors potentially afford many attractive features for
screening of combinatorial libraries such as ruggedness, small
size, high sensitivity, and low cost. However, a single sensor
often suffers from a non-specific response, making the
identification and quantification of species problematic. To
address this issue, conventional chemical sensors have being
utilized in combination with one another to form an array of
sensors. The number of sensors in the array typically range from
less than ten to thousands depending on the type of sensor
response, complexity of analyzed mixture, concentration of each
vapor component, signal and noise levels produced by each sensor,
similarity of the vapor response patterns, and other factors.
[0008] Efforts to reduce the number of transducers in sensor arrays
have been directed to measuring multiple parameters from a single
sensing element. Although measurement of dual responses from a
single sensing device ostensibly provides twice as much information
as a single output sensor, this detection approach has
traditionally exhibited several limitations, including the
following:
[0009] 1. Data analysis from a dual-response sensor is complicated
because it may require multi-way calibration procedures.
[0010] 2. Further complications can arise from nonlinear sensor
response measured by one or both detection methods as a function of
concentration of multiple analytes.
[0011] 3. Information from a single sensor that operates in a
dual-response mode is obtained at the cost of complication of the
sensor design and reduction of its robustness.
[0012] 4. Further increase of information content of such a sensor
becomes problematic because it requires yet another measurement
technique.
[0013] 5. In a single sensor that operates in a dual-response mode,
it is difficult to implement adequate signal referencing strategies
for both detection methods.
[0014] As the demand for high performance materials continues to
grow, new and improved methods of providing products more
economically are needed to supply the market. In this context,
various reactant and catalyst combinations are constantly being
evaluated; however, methods for quickly and accurately determining
the identities of chemically or economically superior reactant
systems for industrial processes continue to challenge the
industry. New and improved methods and devices are needed for rapid
screening of potential reactant systems and catalysts.
SUMMARY OF THE INVENTION
[0015] Accordingly, the present invention is directed to a method
and apparatus that is capable of rapidly screening volatiles in
complex, multi-component samples. In one embodiment, the present
method includes the steps of introducing a volume of a sample into
a vapor delivery line and volatilizing at least a portion of the
volume as it is carried through the vapor delivery line. At least a
portion of the volatilized volume contacts a sensor element, which
produces a signal that is monitored to reveal information about the
sample. The method is adaptable to high throughput screening
because, inter alia, the sample volume does not contact a
substantially sorbent material before contacting the sensor
element.
[0016] Another aspect of the present invention is directed to an
apparatus which includes an injector; a vapor delivery line in
fluid communication with the injector; and a sensor element in
fluid communication with the vapor delivery line and positioned
downstream of both the injector and the vapor delivery line. All
components upstream of the sensor element are substantially free of
sorbent material. A monitor is placed in communication with the
sensor element to measure a property of the sample.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] Various features, aspects, and advantages of the present
invention will become more apparent with reference to the following
description, appended claims, and accompanying drawings, wherein
FIG. 1 is a schematic view of various aspects of an embodiment of
the present invention;
[0018] FIG. 2 is a graphical representation of data obtained from
an aspect of an embodiment of the present invention;
[0019] FIG. 3 is a graphical representation of data obtained from
an aspect of an embodiment of the present invention;
[0020] FIG. 4 is a graphical representation of data obtained from
an aspect of an embodiment of the present invention;
[0021] FIG. 5 is a calibration plot useful in carrying out an
aspect of an embodiment of the present invention;
[0022] FIG. 6 is a calibration plot useful in carrying out an
aspect of an embodiment of the present invention;
[0023] FIG. 7 is a graphical representation of data obtained from
an aspect of an embodiment of the present invention;
[0024] FIG. 8 is a correlation plot showing the effectiveness of an
embodiment of the present invention; and
[0025] FIG. 9 is a graphical representation of data obtained from
an embodiment of the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0026] Terms used herein are employed in their accepted sense or
are defined. In this context, the present invention is directed to
a method and apparatus for rapidly screening volatiles, especially
in complex, multi-component samples. The present method and
apparatus employs chemical sensors to obtain qualitative and
quantitative information about sample components. However, unlike
conventional sensor systems, the present system does not employ a
sorbing material upstream of the sensor element, thereby overcoming
a multitude of the aforementioned shortcomings presented by
conventional systems and allowing for both high throughput
screening and miniaturization.
[0027] In an exemplary embodiment, the method includes the steps of
introducing a volume of a sample into a vapor delivery line and
volatilizing at least a portion of the sample volume as it is
carried through the vapor delivery line. At least a portion of the
volatilized sample is brought into contact with a sensor element,
which produces a signal that is monitored to produce data relating
to the sample. It is noted that the sample volume does not contact
a substantially sorbent material before contacting the sensor
element.
[0028] As used herein, the term "substantially sorbent material"
includes materials that are typically used as either a stationary
phase in a gas chromatography column or as collector material in a
preconcentrator. Substantially sorbent materials retard or prevent
movement of one or more volatile species through adsorption,
absorption, ion exchange, ion exclusion, ion retardation,
chemisorption, dialysis, or the like such that sample components
either do not pass through an area (at a given temperature) or pass
through the area at differing rates. In particular, the vapor
delivery line of the present invention does not contain a material
that is substantially sorbent within the operating temperature
range of the present method, thereby allowing volatile sample
components to pass substantially freely through the vapor delivery
line to the sensor.
[0029] Preferred embodiments of the present method employ a
combination of (1) periodic introduction of a volatile containing
sample into an apparatus; (2) evaporation of volatile components in
the sample; and (3) measurement of a generated vapor pulse by a
sensing device. In these embodiments, the detection concept
involves temporal modulation of the concentration of analyte vapor
and measurement of both the temporal profile of the sensor response
and the magnitude of the signal change at a given time. This
approach allows for a reduction of the number of sensor elements
necessary for effective monitoring. Data handling is simplified
because both types of information (qualitative and quantitative)
about the analytes are provided in the temporally modulated sensor
output. Reduction of the number of sensor elements in a sensor
array leads to diminution of the physical size of the array. Upon
operation of multiple sensors in parallel, this feature allows for
effective analysis of dense combinatorial libraries of materials.
This flexibility also allows for miniaturization, with concomitant
cost savings and increased usefulness in space-limited
applications, such as high throughput screening of combinatorial
libraries.
[0030] An apparatus capable of performing various embodiments of
the present method is schematically shown in FIG. 1, wherein the
apparatus can include an auto-injector 20, an injection port 30, a
vapor delivery line 40, a sensor array 50, frequency counters 60, a
computer 70, flow controllers 80, a carrier stream line 90, a purge
stream line 100, and an exit port 110. In operation, auto-injector
20 is capable of introducing a volume of solution from one or more
of the samples from a combinatorial library 10 into the apparatus
through injection port 30. Various components of the sample are
volatilized as they travel through vapor delivery line 40. The
length of vapor delivery line 40 is chosen such that substantial
amounts of the volatile components evaporate before entering sensor
array 50; therefore optimal length of line 40 will vary depending
on the volatility of the sample. It is contemplated that
volatilization will take place at ambient conditions; however, if
desired, an external heating source (e.g., heating coil) can be
utilized to aid in sample evaporation in vapor delivery line
40.
[0031] The vapors are carried by an inert and/or non-explosive
carrier gas (e.g., nitrogen) into sensor array 50 where the
volatilized sample components contact the sensor elements.
Auto-injector 20, injection port 30, vapor delivery line 40 and
sensor array 50 are all in fluid communication with each other such
that volatilized sample volumes can freely flow through delivery
line 40 to the sensor elements of array 50, which may be, for
example, optical, semiconducting, or electrochemical in nature.
[0032] The output frequency of each sensor element is monitored by
corresponding frequency counters 60 and stored in computer 70. In
alternative embodiments, computer 60 can control the flow of the
carrier gas through flow controllers 80, which regulate gas flow
through both carrier stream line 90 and purge stream line 100. To
allow for adequate evaporation upstream of sensor 50, carrier
stream flow is preferably between about 1 mL/min and about 1000
mL/min and more preferably between about 150 mL/min and about 500
mL/min. Vapors exit the apparatus through exit port 110.
[0033] The sensor elements are typically formed of an oscillating
crystal structure (e.g., transducer) which produces measurable
frequency variations responsive to certain stimuli. An acceptable
crystal structure in certain applications is an AT-cut quartz
crystal oscillating in a thickness-shear mode (TSM) and having a
fundamental frequency of between about 1 MHz and about 50 MHz.
[0034] The sensor elements are preferably coated with a chemically
sensitive material to form a chemically sensitive film proximate
(i.e., on or near) the surface of the sensor element. A variety of
art-recognized materials can be applied to the surfaces of the
sensor elements and analyte-coating interactions can be detected
using a variety of art-recognized sensing techniques. For example,
a large number of vapor-sorbing materials are often used in
piezoelectric, optical, and other sensors. Operation of these
sensors is based on the interactions of a chemically sensitive film
with a vapor while monitoring variations in certain film properties
as a function of analyte concentration or concentrations of
multiple analytes in a mixture. The measured film property can be a
change in mass, viscoelasticity, or other mechanical property, as
well as dielectric or optical properties. The optical properties
can be altered with an analyte partitioned into the film and can be
monitored as the change in the absorbance, scattering, refractive
index, luminescence, or the like. A chemically sensitive dye can be
incorporated into the bulk of the film or a dye molecule can be
directly attached to a molecule of the film. Changes in optical
properties of the dye can be indicative of variations in the
chemical environment proximate the sensor.
[0035] In addition to art-recognized sensor coatings, the sensor
elements of the present apparatus can be coated with polymeric
films that include hardblock and softblock polymer base structures
(referred to herein as "hard-soft block elastomers"). Such films
can be formed of, e.g., thermoplastic elastomers, polyether block
polyamides, silicone polyimides, and combinations thereof.
Acceptable silicone polyimides (sometimes referred to as "silicone
polyetherimides") include Siltem.RTM. 2000 elastomers (available
from the General Electric Company, Pittsfield, Mass.) Acceptable
elastomers also include XD-7.TM. BPA-PC-Silicone 50%
dimethylsiloxane (available from the General Electric Company,
Pittsfield, Mass.). Additionally, one or more sensor elements of
the present apparatus can be coated with an amorphous
fluoropolymer, such as random copolymers of tetrafluoroethylene and
perfluoro-2,2-dimethyl-1,3-d- ioxole sold under the trademark
Teflon AF (available from Du Pont Corporation, Wilmington,
Del.).
[0036] These films can be formed in accordance with any
art-recognized method for disposing polymer films on sensor
substrates, including dip coating, spin coating, spray coating,
vapor deposition, laser-assisted deposition, and the like. When an
array of sensor elements is used, it can be advantageous to coat
various elements with different chemically sensitive materials,
each containing different functional groups to provide unique
sensor response to the presence of volatile compounds in the sample
stream.
[0037] The monitor, which can include a frequency counter, is
adapted to receive a signal from the sensor elements representing a
measured property of the chemically sensitive films. Upon exposure
to the analyte stream, the oscillation frequency of each sensor
element varies as a function of both the composition of the sample
stream and the concentration of the chemical species of interest. A
temporally modulated combination of responses from each of the
transducers provides a unique signature indicating the presence of
certain chemicals. The data produced can be displayed with and/or
stored in a computer for analysis.
EXAMPLES
[0038] The following examples are provided in order that those
skilled in the art will be better able to understand and practice
the present invention. These examples are intended to serve as
illustrations and not as limitations of the present invention as
defined in the claims herein. Unless otherwise noted, all of the
following examples employ the apparatus shown generally in FIG. 1
and described supra.
Example 1
[0039] For determination of volatile arene oxidation products in
combinatorial samples, model mixtures containing varying amounts of
toluene, acetonitrile, phenol, benzoquinone, and hydroquinone were
prepared as illustrated below in Table 1:
1TABLE 1 Hydro- Toluene, Acetonitrile, Benzoquinone, quinone Sample
mL mL Cresol, g g g 0 5 5 0 0 0 1 5 5 0.015 0 0 2 5 5 0.044 0 0 3 5
5 0.0739 0 0 4 5 5 0.153 0 0 5 5 5 0.1993 0 0 6 5 5 0 0.0154 0 7 5
5 0 0.0387 0 8 5 5 0 0.0768 0 9 5 5 0 0.1232 0 10 5 5 0 0.223 0 11
5 5 0.0473 0.0735 0 12 5 5 0.0811 0.106 0 13 5 5 0.0966 0.1008 0 14
5 5 0.1296 0.0339 0 15 5 5 0.0603 0.1748 0 16 3 7 0.247 0.049 0 17
8 2 0.098 0.1202 0 18 5 5 0 0 0.1137 19 5 5 0 0 0.235 20 1 9 0.0885
0 0 21 8 2 0.0993 0 0 22 2 8 0.1228 0 0 23 9 1 0.1159 0 0 24 5 5 0
0 0.0835 25 5 5 0 0 0.175
[0040] The sensor array included four AT-cut quartz crystals with
gold elecrodes. These crystals oscillate in TSM with a fundamental
frequency of 10 MHz. Three of the crystals were coated with
different chemically sensitive materials, and all four were
arranged in a low-dead volume flow-through gas cell. The resonant
oscillation frequency of each crystal was monitored as a function
of time. The identification and thickness of the films are detailed
below:
2 Sensor Elements in the Film Thickness Array Coating Material kHz*
Sensor 1 None 0 Sensor 2 Hard-soft block elastomer 5 Siltem 2000
Sensor 3 Amorphous fluoropolymer 13 Teflon AF 1600 Sensor 4
Hard-soft block elastomer 7 BPA-PC-Silicone 50% DMS "XD-7"
*measured as the change in oscillation frequency of a 10-MHz
crystal upon film deposition.
[0041] The flow rate of the nitrogen carrier gas was 500 mL/min.
The flow rate of the purge line was 4.5 L/min. The auto-injector
sequentially introduced a 2 .mu.L aliquot of each sample mixture
into the vapor delivery line. The purge line was operated for 250 s
with a 380 s delay after injection of a sample volume into the
system.
[0042] The time dependent frequency changes of each sensor in the
sensor array upon introduction of samples with different amounts of
cresol are illustrated in FIG. 2. The data demonstrate that each
sensor can be useful for detecting certain analytes. Specifically,
sensor 1 can be useful for analysis of analytes with high boiling
temperatures approximately 50 s after sample injection. Sensor 2
can be useful for analysis of analytes having both low and high
boiling temperatures approximately 20 and 50 s after sample
injection, respectively. Sensor 3 can be useful for analysis of
analytes with low boiling temperatures approximately 20 s after
sample injection. Sensor 4 can be useful for analysis of analytes
having both low and high boiling temperatures approximately 20 and
50 s after sample injection, respectively. With the conditions
used, the highest sensitivity for analysis of low boiling
temperature analytes was provided by sensor 4, where the maximum
signal change for these types of analytes was about 140 Hz. The
highest sensitivity for analysis of high boiling temperature
analytes was provided by sensor 2, where the maximum signal change
for these types of analytes was about 110 Hz.
[0043] Because it showed high sensitivity to arene oxidation
products, sensor 2 was utilized to evaluate the discrimination
ability of time-modulated detection for identification and
quantification of cresol and benzoquinone. FIG. 3 depicts the
temporal response of sensor 2 to increasing amounts of cresol in
injected samples. Numbers 1-6 indicate cresol amounts of 0, 3, 8.8,
14,8, 30.6, and 40.0 .mu.g respectively. FIG. 4 depicts the
temporal response of sensor 2 to increasing amounts of benzoquinone
in injected samples. Numbers 1-6 indicate benzoquinone amounts of
0, 3.1, 7.7, 15.4, 24.6, and 44.6 .mu.g respectively. Each
acquisition channel in FIG. 3 and FIG. 4 corresponds to 7.25 s.
[0044] Calibration plots for determination of cresol and
benzoquinone with a single sensor are presented in FIGS. 5 and 6,
respectively. They were constructed by plotting the frequency shift
of sensor 2 measured 72 s after injection as a function of analyte
concentration for each of the samples.
Example 2
[0045] To show the present method and apparatus's effectiveness in
identifying and quantifying volatile components in complex
mixtures, the general process of Example 1 was repeated with a
single sensor coated with a Siltem.RTM. 2000 polymer film. The
disclosed apparatus and method of temporal modulation of analyte
concentrations permits selective determination of arene oxidation
products in complex mixtures. For example, injection of pure
solvents such as benzene, toluene, acetonitrile, water, and their
mixtures do not produce any interference with the measurements of
arene oxidation products. Exemplary data showing the excellent
selectivity of the sensor coated with a Siltem.RTM. 2000 polymer
film are presented in FIG. 7, where lines 1-6 represent injected
samples of water, acetonitrile, benzene, toluene: acetonitrile
solution--1:1, toluene alone, and sample #3 from Table 1,
respectively. Furthermore, addition of hydroquinone to solutions
(see Table 1) did not alter sensor response, thereby demonstrating
that the sensor is substantially immune to this interference.
[0046] Selective determination of cresol and benzoquinone in
complex mixtures was achieved with a single sensor coated with a
Siltem.RTM. 2000 polymer film. Referring again to Table 1, samples
0-10 were used to construct the sensor calibration model, and
samples 11-17 were used as the validation set. The model was
constructed using a method of locally weighted regression (LWR)
available, for example, in PLS_Toolbox.TM. software (Version 2.0,
available from Eigenvector Research, Inc., Manson, Wash.) operated
with Matlab.TM. software (Version 5.3, available from The Mathworks
Inc., Natick, Mass.). In the LWR method, local regression models
were produced using points that were near the sample to be
predicted in independent variable space. Furthermore, each
calibration sample was weighted in the regression according to how
close it was to the sample to be predicted. This method is
especially useful for modeling of non-linear systems. The coated
sensor is one such system because of its non-linear response as a
function of analyte concentration (see FIG. 5).
[0047] For selective determination and quantification of cresol and
benzoquinone in complex mixtures, data collected with the sensor
were preprocessed before constructing the calibration model and its
validation. The preprocessing involved taking the first derivative
of the temporal profiles to improve the reproducibility. For
analysis, a time window between 50 and 150 s. after sample
injection was utilized.
[0048] The validation plot between actual and predicted
concentrations of cresol and benzoquinone in complex mixtures
(samples 11-17 of Table 1) is presented in FIG. 8.
Example 3
[0049] To assess the speed of analysis using the disclosed method
and apparatus, several samples containing phenol as an arene
oxidation product were prepared as described in Table 2 below:
3 TABLE 2 Acetonitrile, Sample # Benzene, mL mL Phenol, g 1 5 5 0 2
5 5 0.0209 3 5 5 0.0956 4 5 5 0.1624 5 5 5 0.2041 6 5 5 0.3397 7 5
5 0.7132
[0050] Measurements were performed with a sensor coated with a
Siltem.RTM. 2000 polymer film. The flow rate of the carrier gas was
500 mL/min. The flow of the purging line was 5 L/min. The purge
line was operated for 90 s with a 150 s delay after injection of
the sample into the system. It is noted that the duration of purge
line operation can be easily decreased by using a higher purging
flow. The minimum time delay period was limited by the requirements
to rinse the injector and to purge the sensor.
[0051] Data presented in FIG. 9 demonstrate that, at the conditions
used, maximum sensor response from the phenol component was
observed 10 s after sample injection. Measurements of volatile
arene oxidation products in complex samples were accomplished
within 30 s after injection of the sample into the sensor. The
inset of FIG. 9 shows rapid sensor response from 860 to 920 s.
[0052] It will be understood that each of the elements described
above, or two or more together, may also find utility in
applications differing from the types described herein. While the
invention has been illustrated and described as embodied in a
method and apparatus for rapid screening of volatiles, it is not
intended to be limited to the details shown, since various
modifications and substitutions can be made without departing in
any way from the spirit of the present invention. For example,
additional analytical techniques can be used in concert with the
present system when needed. As such, further modifications and
equivalents of the invention herein disclosed may occur to persons
skilled in the art using no more than routine experimentation, and
all such modifications and equivalents are believed to be within
the spirit and scope of the invention as defined by the following
claims.
* * * * *