Optics: measuring and testing – For light transmission or absorption – Of fluent material
Reexamination Certificate
2002-02-14
2003-08-26
Pham, Hoa Q. (Department: 2877)
Optics: measuring and testing
For light transmission or absorption
Of fluent material
C356S440000, C356S246000, C385S025000, C385S031000
Reexamination Certificate
active
06611334
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to the analysis of samples by optical-based techniques. More particularly, the present invention relates to the coupling and routing of selected input and output lines or channels through which optical signals are directed, and to the routing of optical signals to and from such lines or channels. In particular, the present invention relates to the design and use of a device cooperating or integrated with a sample analysis system, which device enables selection and coupling through coordinated mechanical indexing movements and/or the use of optical fiber bundles whose ends are exposed to a detector. Such a device provides advantage in a wide variety of fields of application, particularly in applications involving the generation and transmission of analytical information. Specific fields of use include the preparation, sampling and analyzing of soluble materials as well as the testing of other fluids and solid materials exhibiting optical characteristics.
BACKGROUND OF THE INVENTION
Optical transport techniques are often utilized to direct a beam or pulse of light from a light source to a test site and, subsequently, to carry analytical information generated or measured at the test site to a suitable light receiving device. Analytical information transmitted by optical means can be chemical or biological in nature. For example, the analytical information can be used to identify a particular analyte, i.e., a component of interest, that is resident within the sample contained at the test site and to determine the concentration of the analyte. Examples of analytical signals include, among others, emission, absorption, scattering, refraction, and diffraction of electromagnetic radiation over differing ranges of spectra. Many of these analytical signals are measured through spectroscopic techniques. Spectroscopy generally involves irradiating a sample with some form of electromagnetic radiation (i.e., light), measuring an ensuing consequence of the irradiation (e.g., absorption, emission, or scattering), and interpreting of the measured parameters to provide the desired information. An example of an instrumental method of spectroscopy entails the operation of a spectrophotometer, in which a light source in combination with the irradiated sample serves as the analytical signal generator and the analytical signal is generated in the form of an attenuated light beam. The attenuated signal is received by a suitable input transducer such as a photocell. The transduced signal, such as electrical current, is then sent to a readout device.
As one example for implementing spectral analysis, a spectrophotometer uses ultraviolet (UV) and/or visible light, or in other cases infrared (IR) or near infrared (NIR) light, to scan the sample and calculate absorbance values. In one specific method involving the UV or UV-visible spectrophotometer, the UV sipper method, the sample is transferred to a sample cell contained within the spectrophotometer, is scanned while residing in the sample cell, and preferably is then returned to the test vessel.
The concentration of a given analyte in a sample through spectrochemical determination typically involves several steps. These steps can include (1) acquiring an initial sample; (2) performing sample preparation and/or treatment to produce the analytical sample; (3) using a sample introduction system to present the analytical sample to the sample holding portion of a selected analytical instrument (e.g., transferring the sample to the sample-holding portion of a UV spectrophotometer); (4) measuring an analytical signal (e.g., an optical signal) derived from the analytical sample; (5) establishing a calibration function through the use of standards and calculations; (6) interpreting the analytical signal based on sample and reference measurements; and (7) feeding the interpreted signal to a readout and/or recording system.
Conventional equipment employed in carrying out the above processes are generally known in various forms. Measurement of the analytical signal involves employing a suitable spectrochemical encoding system to encode the chemical information associated with the sample, such as concentration, in the form of an optical signal. In spectrochemical systems, the encoding process entails passing a beam of light through the sample under controlled conditions, in which case the desired chemical information is encoded as the magnitude of optical signals at particular wavelengths. Measurement and encoding can occur in or at sample cells, cuvettes, tanks, pipes, solid sample holders, or flow cells of various designs.
In addition, a suitable optical information selector is typically used to sort out or discriminate the desired optical signal from the several potentially interfering signals produced by the encoding process. For instance, a wavelength selector can be used to discriminate on the basis of wavelength, or optical frequency. A radiation transducer or photodetector is then activated to convert the optical signal into a corresponding electrical signal suitable for processing by the electronic circuitry normally integrated into the analytical equipment. A readout device provides human-readable numerical data, the values of which are proportional to the processed electrical signals.
For spectrophotometers operating according to UV-visible molecular absorption methods, the quantity measured from a sample is the magnitude of the radiant power or flux supplied from a radiation source that is absorbed by the analyte species of the sample. Ideally, a value for the absorbance A can be validly calculated from Beer's law:
A
=
-
log
T
=
-
log
P
P
0
=
abc
,
where T is the transmittance, P
0
is the magnitude of the radiant power incident on the sample, P is the magnitude of the diminished (or attenuated) radiant power transmitted from the sample, a is the absorptivity, b is the pathlength of absorption, and c is the concentration of the absorbing species.
It thus can be seen that under suitable conditions, absorbance is directly proportional to analyte concentration through Beer's law. The concentration of the analyte can be determined from the absorbance value, which in turn is calculated from the ratio of measured radiation transmitted and measured radiation incident. In addition, a true absorbance value can be obtained by measuring a reference or blank media sample and taking the ratio of the radiant power transmitted through the analyte sample to that transmitted through the blank sample.
Ordinarily, the sample is transferred to a sample cell that is contained within the analytical instrument (e.g., spectrophotometer) itself. An example of a conventional sample testing system is disclosed in U.S. Pat. No. 6,060,024. Samples are taken from test vessels and, using sampling pumps, carried over sampling lines and through sampling filters. The samples are then transported either to a UV analyzer containing six cells, to an HPLC system, or to a fraction collector.
Examples of UV-vis spectrophotometers are those available from Varian, Inc., Palo Alto, Calif., and designated as the CARY™ Series systems. In particular, the Varian CARY 50™ spectrophotometer includes a sample compartment that contains a sample cell through which a light beam or pulse passes. Several sizes of sample cells are available. In addition, the spectrophotometer can be equipped with a multi-cell holder that accommodates up to eighteen cells. A built-in movement mechanism moves the cells past the light beam.
In other recently developed systems, fiber-optics are being used in conjunction with UV scans to conduct in-situ absorption measurements—that is, measurements taken directly in the sample containers of either dissolution test equipment or sample analysis equipment. Fiber optic cables consist of, for example, glass fibers coaxially surrounded by protective sheathing or cladding, and are capable of carrying monochromatic light signals. A typical in-situ fiber-optic method associated wit
Fernando C. J. Anthony
Swon James E.
Pham Hoa Q.
Varian Inc.
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