Single source, single detector chip, multiple-longitudinal...

Details Single source, single detector chip, multiple-longitudinal... Single source, single detector chip, multiple-longitudinal...

2001-03-02

2003-06-17

Stafira, Michael P. (Department: 2877)

Optics: measuring and testing

For light transmission or absorption

Of fluent material

C356S440000

Reexamination Certificate

active

06580507

ABSTRACT:

TECHNICAL FIELD
The present invention relates to absorbance and fluorescence electromagnetic radiation monitoring systems, and more specifically to photometry, spectrometry and spectrophotometry systems which comprise a sequential combination of a single source of electromagnetic radiation, a multiple longitudinal flow cell channel containing system and a single low cost, low drift electromagnetic radiation detector chip.
BACKGROUND
Electromagnetic radiation absorbance and fluorescence monitoring systems which comprise a source of electromagnetic radiation and at least one detector system, wherein electromagnetic radiation of known incident radiant power (P
0
) is caused to interact with a sample, (often situated in a longitudinal flow cell channel), and wherein the results of said interaction are detected by said detector system, are well known. Samples which can be monitored thereby include:
at least partially transparent solids;
liquids;
suspensions;
gases;
vapors; and
analyte dissolved or dispersed in carrier gas or liquid.
For instance, in use, partially transparent solid or fluid, (eg. gas, vapor, liquid, fluid suspension etc. typically flowed into or through a containing cell), samples can be placed in the path of an electromagnetic beam, and incident Radiant Power (P
0
) of electromagnetic radiation passed therethrough is attenuated, relative to (P
0
), thereby via absorption, which is dependent on atomic and/or molecular structure of analytes contained within the sample and present carrier gas etc. Said attenuation is related to the concentration of analytes in the sample present by Beer's Law, and is evidenced by exiting electromagnetic radiation of reduced radiant power (P).
Continuing, electromagnetic radiation absorption monitoring systems may be of either “Single Beam” or “Double Beam” configuration. “Single Beam” systems utilize only one flow channel, (per analyte), and incident radiant power is measured by first introducing blank carrier “reference” medium and measuring radiant power out (P
0
) During an analysis procedure this is followed by entry of “reference” medium which further contains sample analyte, and the measurement of transmitted radiant power (P). “Single Beam” photometry or spectrophotometry systems then require that the same flow cell channel be utilized in determining both (P
0
) and (P). With (P
0
) and (P) so determined analyte absorbance (A) is calculated as a negative Logarithmic ratio:
A
=−Log ((
P
)/(
P
0
));
where the ratio (P)/(P
0
) is termed the Transmittance (T). The magnitude of (A) is further related to analyte structural properties through its wavelength dependent molar absorptivity (a or &egr;), to the flow cell channel length (b), and to analyte concentration (C) by Beer's Law:
A=abC;
or
A=&egr;bC.
Thus in order to calculate concentration (C):
C=A/ab=A/&egr;b
(a) or (e) and (b) must be known at an isolated wavelength at which (A) is calculated from:
A
=−Log(
T
)=−Log((
P
)/(
P
0
)).
(It is noted that (a) and/or (b) can be determined by standard calibration procedures).
Note that any procedure which involves a ratio (P)/(P
0
) inherently provides for canceling out long term temporal variations of source intensity and detector response. However short term source drift and fluctuation within the time frame between flow exchange of blank carrier and analyte containing carrier, hence if (P
0
) and (P) are measured with a significant intervening time, (eg. typically minutes), therebetween, and system drift and/or fluctuation occurs in that time period, the effects will not be canceled and error will be introduced into results achieved by the use of a single beam system.
As a result of problems inherent in use of “Single Beam” applications, “Double Beam” absorbance measurement is commonly employed wherein (P
0
) and (P) are measured simultaneously or with a very short time period, (eg. milliseconds), therebetween. Additionally, “Double Beam” systems do not require physical medium exchange within a given flow cell channel.
Two basic versions of “Double Beam” electromagnetic radiation absorption monitoring systems exist and are termed “double beam in time” and “double beam in space” systems respectively.
In the first version, (ie. a double-beam-in-time system), a single detector is typically used, and a beam of electromagnetic radiation provided by said source thereof is caused to exit said source of electromagnetic radiation, and is sequentially in either order:
caused to pass through a sample in a flow cell channel which sample is typically dispersed or dissolved in a carrier gas or liquid and enter said detector system where (P) is measured; and alternatively,
caused to pass directly from said source of electromagnetic radiation and enter said detector system without passing through said sample, (optionally through a second reference flow channel which contains a blank carrier medium), and enter said detector where (P
0
) is measured.
Note that the single Detector is caused to switch between monitoring (P) and (P
0
) in a synchronized alternating manner so as to keep the measurements separate, and such is typically accomplished at high speed. Forming a ratio of (P) and (P
0
) signals sequentially developed by the detector then provides indication of the absorbance (A) of the sample, and except for the effects of very short temporal fluctuations, (shorter than the switching speed between the detector monitoring (P) and (P
0
) signals), all system parameters are normalized by said ratioing, leaving final dependency of (A) solely on a, b and C. Note that where (P
0
) is determined where a blank carrier medium is placed in the reference electromagnetic beam pathway, said ratioing approach also serves to cancel the absorption effect of the carrier medium.
In the second version, (ie. a double-beam-in-space system), two detectors are typically utilized, and a beam of electromagnetic radiation provided by the source thereof is permanently divided into two fixed paths, (eg. by a beam splitter), and:
one portion is caused to pass directly from the source of electromagnetic radiation through a non-sample containing reference flow cell and into one detector, such that attenuation is dependent only on ambient, (eg. blank carrier gas);
while the other portion is simultaneously caused to pass through the a sample containing flow cell and into the other detector.
(Note that two optical beams and two flow cell channel means are typically present, in one of which sample is caused to be present, (thereby facilitating measurement of (P)), while the other has no sample present and serves as reference, (thereby facilitating measurement of (P
0
)).
Forming a ratio of the signals ((P)/(P
0
)) from the two detectors provides indication of the Transmittance (T) and absorbance (A) of the sample, and normalizes essentially all temporally variant system parameters, as well as canceling the absorbance of the reference medium. Differences, however, in the inherent electronic gain and chromatic response etc. of the two separate detector systems to similar input signals can enter errors into results achieved by this approach.
The first version of the electromagnetic radiation absorption monitoring systems, (ie. “double beam in time”), is then subject to errors which develop because of very short term fluctuations in the source of electromagnetic radiation which vary with time more quickly than optical beam switching, and the second version, (ie. “double beam in space”), is subject to errors which result from the fact that two different detector systems are utilized, and that said detectors can have different operational response, (eg. gain, chromaticity, etc.), to the same input thereto.
At this point, with an eye to the present invention, it should be appreciated that a Double-Beam-In-Space system which comprised a single source of electromagnetic radiation, a multiplicity of flow cell channels, and a single detector would provide utility.
Continuing, in both Double-Beam-In-Space and Doubl

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