Measuring and testing – Gas analysis – Solid content of gas
Reexamination Certificate
2002-03-13
2003-05-27
Raevis, Robert R. (Department: 2856)
Measuring and testing
Gas analysis
Solid content of gas
C073S061710, C324S464000, C324S465000, C095S069000, C095S079000
Reexamination Certificate
active
06568245
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to devices and processes for determining concentrations of analytes in liquid solutions, and more particularly to the use of such apparatus and processes in combination with high performance liquid chromatography and other analytical separation methods.
A variety of separation methods are known for analyzing solutes in liquid media, including liquid chromatography, high performance liquid chromatography (HPLC), gel permeation chromatography capillary electrophoresis, centrifugation, and field flow fractionation. In all of these methods, it is essential to determine concentrations of analytes in the solution under study. Further, the ability to track changes in concentrations over time, corresponding to different regions or locations within a solvent eluting from a separation column, plays a key role in identifying the solutes involved. More particularly, these analytical systems typically employ detectors capable of generating a signal that varies with analyte concentration, yielding a chromatogram or plot of concentration verses time. Because different analytes (solutes) tend to travel through the separation column at different rates as the solution passes therethrough, different solutes exit the separation column at different times. Accordingly, regions of relatively high concentrations, temporally separated on the chromatogram, indicate the presence of several different solutes. In addition, each such region on the chromatogram corresponds to a region within the solution, in terms of differences in the time each such region exits the separation column. Such exit times are useful in identifying the solutes involved.
Generally, the detectors used in analytical separation systems are of two types: Selective detectors and universal detectors. Selective detectors respond only to a specific analyte or type of analyte. For instance, an ultraviolet absorbance detector responds only to molecules capable of absorbing ultraviolet light, e.g. proteins. An example of a universal detector is a refractive index detector, which responds to any analyte capable of changing the refractive index of the liquid that contains it.
One type of universal detector, introduced relatively recently but rapidly gaining acceptance for HPLC applications, is known as the evaporative light scattering detector (ELSD). This type of detector includes a nebulizer receiving a solution eluting from a separation column, then atomizing and spraying the solution as droplets, which dry to form residue aerosol particles. An air stream carries the residue particles past a beam of light, each particle scattering (reflecting or refracting) the light as it intersects the beam. One or more photodetectors sense the scattered light. The scattered light intensity increases with the size of the particle. Accordingly, the amplitude of the photodetector output signal is used to measure particle size.
Particle size is useful in determining concentration of the material forming the particle. If the nebulizer in the ELSD generates droplets at a constant size, the diameters of the resulting aerosol particles are proportional to the cube-root of the concentration. The intensity of scattered light is approximately proportional to the sixth power of the particle diameter for particles smaller than the wavelength of the coherent energy. Intensity is approximately proportional to the second power of the particle diameter for particles larger than that wavelength. The intensity/diameter relationship between these regions is complex. Thus, for small concentrations, the scattered light intensity is proportional to the square of the analyte concentration, while for high concentrations the scattered light intensity is proportional to concentration to the {fraction (2/3 )} power. With low concentrations being of primary interest in typical applications, the relationship of most concern is a variance of the output signal representing scattered light intensity as the square of the analyte concentration.
The ELSD is more sensitive than other universal detectors such as refractive-index detectors and viscosity detectors. Further, the ELSD responds to certain analyte molecules, such as polymers and carbohydrates, that do not provide a good ultraviolet or visible absorption signal. However, because of the square-law relationship just mentioned, the photomultiplier tube output signal rises rapidly with increasing concentration. As a result, the limited ranges over which photomultiplier tubes can operate impose severe limitations upon the dynamic range of the ELSD in terms of concentration measurements. ELSD systems can employ alternative detectors in lieu of photomultipliers. Nonetheless, the wide range of light intensities taxes the capabilities of these alternative detectors and the accompanying measuring circuitry. The practical dynamic range of an ELSD, in terms of a ratio of the highest measurable concentration to the lowest measurable concentration, is about 500.
A further problem associated with evaporative light scattering detectors is that the detector response is determined in part by the optical properties of the residue particles. In many cases these properties are largely unknown, requiring calibrations for each analyte under study.
In connection with analytical separation methods such as high performance liquid chromatography, but also more generally in the analysis of solutions as to the solutes they contain and their respective concentrations, it is an object of the present invention to provide a detector with a sensitivity at least comparable to the ELSD, which overcomes the aforementioned difficulties of the ELSD.
Another object is to provide a non-volatile analyte concentration detector with an enhanced dynamic range.
A further object is to provide a detector for determining analyte concentrations, with an output that varies with analyte concentrations according to a simpler relationship.
Another object is to provide a more compact instrument for measuring non-volatile analyte concentrations.
Yet another object is to provide a process for detecting concentrations of non-volatile analytes, for providing concentration measurements unaffected by the optical properties of the analyte particles involved.
SUMMARY OF THE INVENTION
To achieve these and other objects, there is provided a non-volatile analyte concentration detector. The detector includes an enclosure that defines a chamber. A first fluid passage is disposed to receive an aerosol stream composed of liquid droplets containing non-volatile material and suspended in a carrier gas. The first fluid passage is adapted to guide the aerosol stream toward the chamber as the liquid droplets substantially evaporate. As a result the aerosol stream as it enters the chamber is composed of reside particles of the non-volatile material. An ion generator is disposed near the chamber and adapted to generate multiple ions. A second fluid passage guides a gas flow toward the chamber and past the ion generator. The gas flow entrains at least a portion of the ions and carries the entrained ions into the chamber to merge with the aerosol stream, thus to apply a size-dependant electrical charge to each of the residue particles. The first and second fluid passages include respective first and second restrictions near the chamber to accelerate the aerosol stream and ion-carrying gas flow as they enter the chamber. A charge-responsive device is disposed downstream of an exit of the chamber to receive at least a portion of the charged residue particles. The device is adapted to generate an electrical signal having a level proportional to an aggregate charge of the received reside particles. Thus, the electrical signal indicates a concentration of the non-volatile material.
The charge-responsive device can include an electrically conductive filter adapted to entrap the reside particles, and a wire or other suitable electrical conductor electrically coupled with the filter. The level of electrical current through the conductor provides the indicati
Cygan Michael
Larkin Hoffman Daly & Lindgren Ltd.
Niebuhr, Esq. Frederick W.
Raevis Robert R.
TSI Incorporated
LandOfFree
Evaporative electrical detector does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Evaporative electrical detector, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Evaporative electrical detector will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3064073