Abstract: A fiber optic laser-induced breakdown spectroscopy (LIBS) sensor, including a laser light source, a harmonic separator for directing the laser light, a dichroic mirror for reflecting the laser light, a coupling lens for coupling the laser light at an input of a multimode optical fiber, a connector for coupling the laser light from an output of the multimode optical fiber to an input of a high temperature holder, such as a holder made of stainless steel, and a detector portion for receiving emission signal and analyzing LIBS intensities. In one variation, the multimode optical fiber has silica core and silica cladding. The holder includes optical lenses for collimating and focusing the laser light in a molten alloy to produce a plasma, and for collecting and transmitting an emission signal to the multimode optical fiber.

Abstract: A portable Laser Plasma Spectroscopy (LPS) system and process is provided for performing in situ, near-real time, remote elemental analysis and identification of deposits or other foreign material found on surfaces of machine parts, such as turbine compressor blades or the like, wherein identification of the elemental constituents of a particular deposit is obtained without incurring significant ablative damage to the machine part substrate material underlying the deposit.

Abstract: The invention relates to a device for measuring the intensity of a luminescence radiation emitted by at least one chemical species probed, along a trajectory by an excitation radiation. The device comprises n measurement channels, where n is an integer greater than or equal to 2, each measurement channel being used to measure a fraction of the intensity of the luminescence radiation emitted along the trajectory.

Abstract: A DNA sample added with a plurality of fluorescent marks is irradiated with excitation lights having a plurality of wavelengths and when fluorescence intensities are detected separately, the excitation light and a position on the sample are relatively changed over a desired area once to thereby detect the plurality of fluorescent marks at high speed.

Abstract: A method for analyzing properties of a sample by measuring fluorescence parameters in multiple foci, comprises the steps of splitting a collimated primary laser beam with a splitting device into at least two collimated secondary laser beams and deflecting the secondary laser beams such that they propagate at different propagation angles with respect to an optical axis of a focussing optic, focussing the secondary laser beams with the focussing optic into at least two volume elements in the sample, detecting light emitted from the volume elements with a detecting device, and evaluating the detected light for obtaining the properties to be analyzed. Furthermore, a device for implementing this method is described. The invention is particularly suited for high-throughput screening applications.

Abstract: A Fluorescence Particle Spectrometer (FPS) performs real-time measurement of the fluorescence spectra of aerosol particles in the size range 1-10 &mgr;m diameter. The FPS has a sufficiently high sample rate (estimated to be a few liters/min) to measure aerosol within buildings (from 1 up to 600 particle fluorescence spectra per minute) at practical rates. A virtual impactor first concentrates aerosol particles, which are then drawn under negative pressure through an aerodynamic focusing nozzle in the inlet of the instrument, through the sample region, providing further concentration. The rate of particle spectra measured by the FPS increases significantly when the particle inlet is within a few meters of some common sources of indoor biological particles.

Abstract: To economically perform preparatory chromatography, a plurality of pumps each having a corresponding one of a plurality of pistons and a corresponding one of a plurality of cylinders are driven by one motor to draw and pump solvent simultaneously into corresponding columns. To form a gradient, the pumps are connected to two-way valves that are connected alternately to a first solvent and a second solvent, whereby the time said valve is in a first position controls the amount of solvent drawn from the first reservoir into said pumps and the amount of time in said second position controls the amount of said second solvent drawn from the second reservoir into said pumps and the solvent is mixed in the pumping systems. The detectors are photodiodes mounted to light guides in the flow cells that generate signals related to light absorbance and communicate with a controller, whereby the controller receives signals indicating solute between the light guides and causes collection of solute.

Abstract: A semiconductor forensic light is disclosed. The forensic light may use a variety of semiconductor light sources to produce light that contrasts forensic evidence against its background for viewing, photographing and collection. Example semiconductor light sources for the forensic light include light emitting diodes and laser chips. A heat sink, thermoelectric cooler and fan may be included to keep the forensic light cool. A removable light source head may be included on the forensic light to provide for head swapping to give the user access to different wavelengths of light.

Abstract: A system and method for online, essentially instantaneous analyses of ore compositions on a moving belt use laser-induced break-down spectroscopy (LIBS), wherein intensity ratios of emission lines characteristic of specific minerals or ions are calculated on areas of the moving belt, with elevated contents of identifying ions or species being detectable. The ratios are derived from ions present in the sample that differentiate a first substance from a second substance, thus allowing sorting of the samples. The substance may include an ion, an element, or a compound.

Abstract: The invention relates to a device and a method for optically measuring the concentrations of a substance contained in a fluid medium. With the solution according to the invention the accuracy of measurement is to be increased in accordance with the object over a greater period without any additional calibration measurements, and ageing of a fluorescent substance within a layer is to be taken into consideration, in particular, and the long-time drift of such a measurement system is to be reduced. To achieve this, a layer containing such a known fluorescent substance or layer system are employed in which fluorescence is excited. The fluorescence changes depending on a substance concentration or a pH-value, and the intensity varying correspondingly in time or phase shift of the fluorescent light is allowed to be measured with at least one optical detector with the known intensity or phase of the fluorescence exciting light.

Abstract: A sensor platform for use in sample analysis comprises a substrate (30) of refractive index (n1) and a thin, optically transparent layer (32) of refractive index (n2) on the substrate, (n2) is greater than (n1). The platform incorporates one or multiple corrugated structures in the form of periodic grooves (31), (33), which defines one or more sensing areas each for one or more capture elements. The grooves are so profiled, dimensioned and oriented that when coherent light is incident on the platform it is diffracted into individual beams or diffraction order resulting in reduction of the transmitted beam and an abnormal high reflection of the incident light thereby creates an enhanced evanescent field at the surface of the or each sensing area. The amplitude of this field at the resonant condition is greater by an order of approximately 100 than the field of prior art platforms so that the luminescence intensity created from samples on the platform is also increased by a factor of 100.

Abstract: A sensor platform for use in sample analysis comprises a substrate (30) of refractive index (n1) and a thin, optically transparent layer (32) of refractive index (n2) on the substrate, (n2) is greater than (n1). The platform incorporates one or multiple corrugated structures in the form of periodic grooves (31), (33), which defines one or more sensing areas each for one or more capture elements. The grooves are so profiled, dimensioned and oriented that when coherent light is incident on the platform it is diffracted into individual beams or diffraction order resulting in reduction of the transmitted beam and an abnormal high reflection of the incident light thereby creates an enhanced evanescent field at the surface of the or each sensing area. The amplitude of this field at the resonant condition is greater by an order of approximately 100 than the field of prior art platforms so that the luminescence intensity created from samples on the platform is also increased by a factor of 100.

Abstract: In a method for multi photon excitation of a sample a laser beam is split into at least two coherent partial beams each having a beam axis and a same intensity distribution about its beam axis. The partial beams are directed from different directions towards a common measuring plane running transversely to the beam axes at an inclination angle <1 between the beam axes of the partial beams; and the partial beams are projected onto the measuring plane by means of a common lens system. Thus, an interference pattern formed by the coherent partial beams within the measuring plane provides areas of maximum light intensity adjacent to areas of minimum light intensity.

Abstract: Apparatus and methods are disclosed for imaging surfaces that comprise a sample. One embodiment of the present invention is an imaging apparatus comprising a holder for a surface, a light source adapted to illuminate the surface, a diffractive element between the holder and the light source and an imaging detector adapted to receive light from the surface. In a method for imaging a surface comprising a plurality of discrete features, light is selectively diffracted on to one or more predetermined features of the surface at a predetermined point in time. This step is repeated until substantially all of the features on the surface are illuminated. Light is detected from the surface to thereby image the surface.

Abstract: The invention is directed to an arrangement for the optical detection of a moving target flow for pulsed energy beam pumped radiation generation based on a plasma. It is the object of the invention to find a novel possibility for detection of a moving target flow for energy beam pumped radiation generation based on a plasma which allows reliable orientation of the excitation beam on the target without the detector being subjected to influence and damage due to radiation emitted by the plasma. According to the invention, this object is met in that a target generator provides a target flow with relatively constant target states in an interaction point, a sensor unit is directed to a detection point which lies close to the interaction point in the direction of the path.

Abstract: An apparatus for monitoring vapor phase polycyclic aromatic hydrocarbons in a high-temperature environment has an excitation source producing electromagnetic radiation, an optical path having an optical probe optically communicating the electromagnetic radiation received at a proximal end to a distal end, a spectrometer or polychromator, a detector, and a positioner coupled to the first optical path. The positioner can slidably move the distal end of the optical probe to maintain the distal end position with respect to an area of a material undergoing combustion. The emitted wavelength can be directed to a detector in a single optical probe 180° backscattered configuration, in a dual optical probe 180° backscattered configuration or in a dual optical probe 90° side scattered configuration. The apparatus can be used to monitor an emitted wavelength of energy from a polycyclic aromatic hydrocarbon as it fluoresces in a high temperature environment.

Abstract: Fluorescently marked targets bind to a substrate 230 synthesized with polymer sequences at known locations. The targets are detected by exposing selected regions of the substrate 230 to light from a light source 100 and detecting the photons from the light fluoresced therefrom, and repeating the steps of exposure and detection until the substrate 230 is completely examined. The resulting data can be used to determine binding affinity of the targets to specific polymer sequences.

Abstract: Process for detecting the phenomenon of fluorescence in a microscope, wherein the sample is irradiated by a modulated and/or pulsed laser light source, and the fluorescence is detected at least in two different phase positions of the detector.

Abstract: An apparatus for flash photolysis has a light source and an optical fiber for directing light from the light source and through a sample. A laser or other such device is provided for initiating a chemical change within the sample. Additionally, a device is provided for determining the change in absorption of light by the sample during the chemical change.

Abstract: A method and apparatus for spectrochemical analysis of liquids, including molten metals, using laser-induced plasma spectroscopy. The apparatus preferably comprises a high power pulsed laser focused on the surface of a liquid stream flowing in a measurement cell, and an optical spectrometer-detector assembly, which receives, detects and analyzes the radiation emitted by the high temperature plasma thereby excited. The measurement cell, and optional pump, establish laminar flow of the liquid flow, thereby permitting the laser to repeatedly sample a fresh un-perturbed surface, while also ensuring that bubbles formed in the liquid are removed from the focal volume Preferably, a blower prevents aerosols and matter ejected from the sample responsive to the incident energy from interacting with subsequent laser pulses, and from accumulating on the optic.

Abstract: The present invention relates to a method and apparatus for detecting transitions between different gas or liquid products in a flow path and, more particularly, it relates to an apparatus and method utilizing Raman spectroscopy for detecting transitions between petroleum products. A Raman spectrometer is preferably to produce a monochromatic excitation beam at a wavelength of approximately 670 nm. The spectrometer consists of an entrance slit, a combined diffraction grating/focussing element, and an exit slit. The Raman signal, which exits the spectrometer exit slit is detected by a highly sensitive photomultiplier tube, and sent to a computer device for data acquisition and analysis. The proposed invention detects liquid or gas products in a flow path by detecting the changes in the composition of various petroleum products flowing through a gasoline pipeline, by means of exposing samples of various petroleum products to the Raman spectrometer system.

Abstract: A mass spectrometer system comprising a laser and a mass spectrometer. The mass spectrometer has a vacuum interface that provides entrance of a gaseous sample into an extraction region of the mass spectrometer. The laser is positioned to provide laser light incident on a sample non-gaseous substance positioned adjacent the vacuum interface. The laser light provides vaporization of the sample, which provides a high concentration of gaseous molecules from the sample substance at the vacuum interface.

Abstract: To measure property-specific distributions like surface area and mass concentrations, in a particle field that attenuates light passing therethrough, such as a spray or aerosol, a probe beam having a suitably selected wavelength is directed into and thereby caused to interact with the particle field. Light produced by this interaction is detected by sensors separated a distance from the beam. Extinction of the probe as it propagates through the particle field is quantified by determining the amount of light exiting the field in comparison with the amount of light entering the field. The property specific concentrations are determined from the light detected by the sensors after correcting for the extinction of the beam as well as attenuation of the light traveling the distance from the beam to the sensors. The light produced by the interaction of the probe with the particle field may include scattering, fluorescence, or both.

Abstract: The invention concerns an apparatus and a method for measuring at least one optical characteristic, which can include in particular turbidity (T), absorbance (A) and fluorescence (F), of a medium (1), and a micro-bioreactor, a connector and associated male and female parts. The apparatus comprises a light source (3) provided with means for controlling (6) the intensity of the beam transmitted (11) by the source, a photodetector (4) for measuring the intensity of the beam reflected (12) by the medium, a feedback regulating system (7) operating on the control means such that the measured intensity of the reflected beam is equal to a predetermined nominal intensity, and means for reading the transmitted beam intensity, said intensity representing the medium optical characteristic(s). The apparatus also comprises means for adjusting the nominal intensity, such that the transmitted beam stabilised intensity is within a predetermined range. The invention is applicable to micro-bioreactors.

Abstract: The present invention provides a biochip reader for reading with a detector the fluorescence image information from genes to which fluorescent substances are stuck and which are poured into biochip cells, by emitting coherent light beams such as laser light onto the cells as excitation light. The present invention aims to achieve a biochip reader that is small, cheap, and highly durable.

Abstract: An arrangement for determining the position of a light source includes a light-sensitive detector device and an arrangement for casting a shadow onto part of the light of the light source shining onto the detector device. The shadowing arrangement is formed by at least one rotationally symmetrical body.

Abstract: An instrument for measuring reliably and instantaneously the chemical quality of cooking oil, and for distinguishing between color changes due to chemical changes and color changes due to the presence of minute size food particles in various oils.

Abstract: A prism-based cytometry excitation optics system redirects, shapes and combines plural beams provided by light sources, so they can be focused by an objective into closely spaced spots within the channel of a cytometry flow cell. The mounted set of dispersive prisms redirect beams of different wavelengths so that beams with separated inputs emerge from the final prism, substantially overlapping in position and nearly parallel to one another. Preferred embodiments having a mounted set of four distinct isosceles triangular prisms are described with particular orientations and positions, but the specific design parameters may vary depending on the choice of beam wavelengths, spot separations in the flow cell, and choice of prism material. The prism system has inherently better thermal and long-term stability compared to mirror-based optics.

Abstract: A fluorescing molecule is bound to an microscopic slide (24). The microscopic slide (24) is coupled to a first end face of an optical waveguide (1) by means of an immersion oil. The optical waveguide also possesses a shell surface (3) having the shape of a paraboloid of revolution, and a second end face (4). The molecule is located at the focal point of the paraboloid of revolution. Essentially the entire light of the molecule radiated into the half-space facing the optical waveguide (1) enters the optical waveguide (1). In particular, evanescent radiation (7) also enters the optical waveguide (1). This is totally internally reflected at the shell surface (3) having the shape of a paraboloid of revolution, emerges collimated from the second end face (4), and reaches a detector (30). In this way, essentially the entire evanescent radiation of the molecule can be registered.

Abstract: A flow cytometer includes a flow cell for flowing a sample liquid in a flowing direction, to form a sample flow the sample liquid containing particles to be analyzed, a laser diode radiating a laser beam having an elliptic cross section, a beam collimating section for collimating the laser beam radiated from the laser diode, a beam spot forming section for focusing the collimated beam at the sample flow in the flow cell to form a beam spot, and a light receiving section for receiving light generated from the particles at the beam spot to detect optical information of the particles, wherein the laser diode is arranged such that a minor diameter of the elliptic section of the laser beam is parallel to the sample flow.

Abstract: The present invention provides a method for identifying a test compound that binds to a target species. The method includes: incubating at least one test mixture under isothermal denaturing conditions, each test mixture comprising at least one test compound, and at least one target species, wherein the isothermal denaturing conditions are effective to cause at least a portion of the target species to denature to a measurable extent; detecting a denaturation signal of each target species in the presence of the at least one test compound by a change in the diffusion properties of the target molecule using fluorescence correlation spectroscopy; and comparing the denaturation signal of each target species in the presence of at least one test compound with a denaturation signal of the same target species in the absence of the at least one test compound under the same isothermal denaturing conditions.

Abstract: Particle analyzing systems with fluorescence detection are disclosed, primarily in connection with particle sizing based on scattered light intensity or time-of-flight measurement. In one system, emission of fluorescence is used as a threshold for selecting particles for further analysis, e.g. mass spectrometry. In another embodiment, laser beams arranged sequentially along an aerosol path are selectively switched on and off, to increase the useful life of components, and diminish the potential for interference among several signals. Other embodiments advantageously employ color discrimination in aerodynamic particle sizing, single detectors positioned to sense both scattered and emitted fluorescent radiation, and laser beam amplitude or gain control to enhance the range of fluorescence detection.

Abstract: The present invention provides a biochip reader for reading with a detector the fluorescence image information from genes to which fluorescent substances are stuck and which are poured into biochip cells, by emitting coherent light beams such as laser light onto the cells as excitation light. The present invention aims to achieve a biochip reader that is small, cheap, and highly durable.

Abstract: A method and apparatus for detecting a fluorescent substance tagged to a microparticle are described. The device comprises a single capillary flow carrier system for transporting the microparticle past a selected location, a source of electromagnetic radiation for irradiating the substance tagged to the microparticle, and a detection system for measuring fluorescent light emitted from the substance at the selected location. The method comprises transporting the microparticle to a selected location, irradiating a fluorescent substance tagged to the microparticle, and measuring the fluorescent light emitted from the fluorescent substance at the selected location.

Abstract: A system for detecting controlled substances on an object including at least one laser for illuminating at least part of an object with laser energy and either a second harmonic detector or a luminescence controlled substance detector, or both. Additionally, a system also including a Raman scattering controlled substance detector is disclosed.

Abstract: The present invention relates to an array reader having a light source configured to emit an excitation light, a substrate comprising a plurality of sites spatially configured as a two-dimensional array having a plurality of rows and a plurality of columns, where each site is configured to support a sample. The array reader includes a changing device configured to determine which of said plurality of sites is illuminated at any given instant and a detector comprising a two-dimensional array of light sensitive elements, transmission grating beam splitter (TGBS) disposed along an optical path between the substrate and the detector, and a single light focusing element disposed along an optical path between the substrate and the detector. The TGBS is configured to receive non-collimated light emitted by at least one sample illuminated by said excitation light.

Abstract: A fluorescent optical imaging system (10) produces two separate spots (S1 and S2) on a sample (12) by a pair of excitation laser beams (B1 and B2) that are generated by first and second lasers (L1 and L2). Excitation laser beams (B1 and B2) pass at slightly different angles, first through an aperture (15) of a 45° fold mirror (13), and then through an objective element (14). As a result, emission light beams (16, 18) are generated from each illuminated spot (S1 and S2) and are reflected and redirected by mirror (13) through a secondary lens (19) before reaching one of two detectors (PMT 1 and PMT 2). Emission beam (16) reflects off a second 45° mirror (22) prior to reaching detector (PMT 1), while emission beam (18) travels directly to (PMT 2). If desired, optical separation elements (24), such as dichroic filters, prisms, or gratings, can be positioned in front of each detector (PMT 1 and PMT 2).

Abstract: A method and apparatus for spectrochemical analysis of liquids, including molten materials, using laser-induced plasma spectroscopy. The apparatus preferably comprises a high power pulsed laser focused on the surface of a liquid stream flowing in a measurement cell, and an optical spectrometer-detector assembly, which receives, detects and analyzes the radiation emitted by the high temperature plasma thereby excited. The measurement cell, and optional pump, establish a steady flow of liquid, thereby permitting the laser to repeatedly sample a fresh unperturbed surface, representative of the liquid volume, while also ensuring that bubbles and waves formed in the liquid are removed from the focal volume. Gas (usually air) blown above the liquid prevents aerosols and matter ejected from the sample responsive to the incident energy from interacting with subsequent laser pulses, and from accumulating on the optics.

Abstract: The invention relates to a method of detecting the presence of a liquid introduced into a mix of constituents.

Abstract: A method and apparatus for detecting a fluorescent substance tagged to a microparticle are described. The device comprises a single capillary flow carrier system for transporting the microparticle past a selected location, a source of electromagnetic radiation for irradiating the substance tagged to the microparticle, and a detection system for measuring fluorescent light emitted from the substance at the selected location. The method comprises transporting the microparticle to a selected location, irradiating a fluorescent substance tagged to the microparticle, and measuring the fluorescent light emitted from the fluorescent substance at the selected location.

Abstract: The invention relates to a fluorescence-measuring system as can be employed for high-throughput screening in drug development. The arrangement for fluorescence excitation contains a two-dimensionally extended sample-receiving device and at least two illumination sources for exciting the fluorescence of the samples. The illumination sources are extended linearly and arranged in such a way that the illuminated area of the sample-receiving device is homogeneously illuminated directly or via deflecting mirrors at an opening angle of ≦30°.

Abstract: A surface plasmon resonance apparatus for detecting a soluble analyte (e.g. a protein) or a particulate analyte (e.g. a cell), the apparatus comprising: (a) a sensor block adapted to receive a sensor, said sensor, for example a sensor slide, having a metallized sensor surface capable of binding the analyte; (b) a light source capable of generating an evanescent wave at the sensor surface of a sensor slide on the sensor block; (c) a first detector capable of detecting light from the light source which is internally reflected from the sensor surface; and (d) a second detector (e.g. a video camera) capable of detecting light scattered or emitted from an analyte bound thereto. Optionally the apparatus further comprises a second light source for increasing the intensity of the light scattered or emitted from an analyte bound to the sensor surface, preferably, this is sited to such as to minimize the amount of light transmitted therefrom which is detected by the first detector.

Abstract: The present invention relates to a photometric device for measuring optical parameters. The invention functions in the ultraviolet light range through use of a monochromator and splits the test light in multiple channels by a rotor assembly, including a mirror.

Abstract: Laser pulses from laser head 12 pass through objective lens 16 to a focal spot in sample spot 17. If a pulse hits a fluorophore molecule in the focal spot a fluorescence photon is emitted which is collected by lens 16, reflected by dichroic mirror 15 through filter 20, which blocks photons of other wavelengths, to single photon counting photomultiplier unit 21. On detecting a photon, photomultiplier unit 21 generates an output pulse which is coupled, with a short delay, by pulse controller 30 to driver circuit 24 which causes laser head 12 to generate another laser pulse. Thus the interval between the laser pulses is substantially equal to the time between excitation of, and fluorescence emission by, the fluorophore molecule. Computer 23 coupled to photomultiplier unit 21 and driver circuit 24 determines the decay time by measurement of a number of fluorescence events.

Abstract: A particle detector has a chamber defining a pathway that a target particle follows between an entry and an exit point, a solid-state energy source such as an LED, and a re-emission sensor. The energy source imparts energy to the particle between the two points, and the sensor includes an arcuate or multi-planar lens to focus energy re-emitted by the particle. The particle is identifiable by its re-emitted energy spectrum. A scanner re-directs the beam from a single energy source to track the particle between the entry and exit points. Alternatively, the energy source is a plurality of source elements that each scan the particle at a single position. Another embodiment is a chipscale detector system wherein energy source elements are disposed on a source layer, sensor elements are disposed on a sensor layer, and one or more target particles to be detected are retained on a capture layer disposed therebetween.

Abstract: An installation is provided for multi-dimensional non-linear imaging of a material comprising intrinsic chromophores, using laser scanning.

Abstract: The invention relates to a method and system for focusing a laser scanning cytometer. In the illustrative embodiment, during one cytometric measurement process, a single laser is used for focusing the cytometer and for taking cytometric measurements. Laser light is transmitted though an objective lens and directed at a substrate in order to cause markers in a sample on the substrate 122 to fluoresce. A byproduct the of cytometric measurement is that a portion of the laser light incident on the substrate 122 with or without a sample is backscattered. The objective of the illustrative system collects the backscattered light along with the fluorescing light. Optical elements separate this backscattered laser light from the fluorescing light. The illustrative system uses the backscattered light to focus the objective.

Abstract: Light from an object such as a cell moving through an imaging system is collected and dispersed so that it can be imaged onto a time delay and integration (TDI) detector. The light can be emitted from a luminous object or can be light from a light source that has been scattered or not absorbed by the object or can include a light emission by one or more probes within or on the object. Multiple objects passing through the imaging system can be imaged, producing both scatter images and dispersed images at different locations on one or more TDI detectors.

Abstract: An apparatus and a method are disclosed for use with Laser Induced Breakdown Spectroscopy (LIBS) systems that can be applied to the real time analysis of molten materials or liquid. Since it is difficult to prepare a surface representative of the bulk when dealing with high temperature molten material, the invention, in one aspect, uses a forced gas flow through a tube insertable inside the molten material to generate a bubble. The inner surface of the bubble is a representative of the composition of the material. LIBS performed on such a surface produces an accurate real time analysis of material, even when other processing of material, e.g., copper smelting, etc., is being conducted.

Abstract: The present invention approximates and automatically subtracts continuum backgrounds in laser-induced breakdown (LIBS) and Raman spectra measured by non-gated detectors. Significantly, reference spectra are not used to determine background positioning in the present invention.