Methods for photometric analysis

• US 5,478,750 A
• Filed: 08/18/1994
• Issued: 12/26/1995
• Est. Priority Date: 03/31/1993
• Status: Expired due to Term

• Current Assignee: Abaxis Incorporated (Zoetis Incorporated)
• Original Assignee: Abaxis Incorporated (Zoetis Incorporated)
• Inventors: Bernstein, Daniel M., Lingane, Paul J., Ostoich, Vladimir E., Nagle, Robert
• Primary Examiner(s): Housel, James C.
• Assistant Examiner(s): Pyon, Harold Y.
• Application Number:
  US08/292,558
• Time in Patent Office: 495 Days
• Field of Search: 422/55, 422/64, 422/65, 422/67, 422/101, 436/8, 436/164, 436/165
• US Class Current: 436/164
• CPC Class Codes: G01N 21/07 Centrifugal type cuvettes G01N21/09 takes precedence
• CPC Class Codes: G01N 21/255 Details, e.g. use of specially adapted sources, lighting or optical systems
• CPC Class Codes: G01N 2201/0415 Carrusel, sequential
• CPC Class Codes: Y10T 436/10 Composition for standardization, calibration, simulation, stabilization, preparation or preservation; processes of use in preparation for chemical testing

Abstract

The present invention provides a compact, highly automated photometric analyzer for measuring the concentration of substances found in a fluid, typically a blood sample or other body fluid sample taken from a patient. The operator places a small quantity of the sample into a special rotor and then loads the rotor into the analyzer. The analyzer accepts the rotor, centrifuges and dilutes the sample, and distributes the sample into a plurality of cuvettes near the outer edge of the rotor. Some of these cuvettes hold reagents which react with the sample. The analyzer then measures light absorption within the sample at a number of preselected frequencies. According to the present invention, a pair of specially designed apertures direct light from the sample through a plurality of beam splitters, interference filters, and associated photodetectors. The system also includes means for performing automatic calibration and error checking functions. These means include a through hole through the rotor, and an opaque body carried by the rotor. Additionally, measurements may be repeated through a given cuvette and the results averaged to minimize the effect of random variations between measurements.

Claims

1. A method for monitoring the light intensity of a light source in a photometric fluid analyzer which lessens over time, wherein the analyzer further includes a sample rotor having a plurality of cuvettes for holding a quantity of the fluid to be analyzed and a through hole in the place of one of the cuvettes, and a light detector disposed to detect light directed through the cuvettes, the method comprising:

moving the rotor to a position wherein light from the light source is directed through the through hole;

measuring a signal from the light detector while the light is directed through the through hole and strikes the light detector at full intensity;

comparing the measured signal to a value selected to correspond to an acceptable light intensity level generated from the light source;

indicating the need to replace the light source when the measured signal differs by more than a predetermined amount from the selected value; and

replacing the light source when the indicated signal differs by more than a predetermined amount from the selected value.

2. A method for compensating for the effects of scattered light in a photometric fluid analyzer having a light source, a sample rotor having a plurality of cuvettes for holding a quantity of the fluid to be analyzed and an opaque body disposed at the position of one of the cuvettes, and a light detector disposed to detect light directed through the cuvettes, the method comprising:

moving the rotor to a position wherein the opaque body disposed at the position of one of the cuvettes is aligned with the light source and the light detector so that light from the light source will be prevented from directly impinging on the light detector by the opaque body while allowing scattered light to strike the detector;

flashing the light source while the rotor is positioned to prevent the light from directly impinging on the light detector while allowing scattered light to strike the detector;

measuring a signal from the light detector while the light is prevented from directly impinging on the light detector by the rotor and while scattered light strikes the detector;

moving the rotor to a position wherein one of the cuvettes holding the fluid is aligned with the light source and the light detector so that light from the light source can be directed through the fluid and onto the light detector;

flashing the light source while the rotor is positioned to pass light through fluid in a cuvette;

measuring a signal from the light detector while the light is directed through the fluid; and

modifying the signal measured when the light was directed through the fluid based on the signal measured when the scattered light struck the detector.

3. A method for determining the concentration of a substance in a fluid sample in a photometric fluid analyzer having a light source, a sample rotor having a plurality of cuvettes for holding a quantity of the fluid to be analyzed, and a light detector disposed to detect light directed through the cuvettes, the method comprising:

mixing a first quantity of the sample in an assay cuvette with a reagent selected to produce a chemical reaction between the reagent and the substance whose concentration is to be measured, the reaction producing a known reaction product;

moving the rotor to a position in which light is directed from the light source through the sample in the assay cuvette;

simultaneously measuring light transmitted through the sample in the assay cuvette at a first wavelength which is selectively absorbed by the reaction product and at a second wavelength which is not absorbed by the reaction product;

storing a first value corresponding to the amount of light transmitted through the assay cuvette at the first wavelength;

storing a second value corresponding to the amount of light transmitted through the assay cuvette at the second wavelength;

moving the rotor to a position in which light is directed through a reference cuvette not containing the reaction product;

simultaneously measuring light transmitted through the reference cuvette at the first wavelength and at the second wavelength;

storing a third value corresponding to the amount of light transmitted through the reference cuvette at the first wavelength;

storing a fourth value corresponding to the amount of light transmitted through the reference cuvette at the second wavelength;

comparing the first and second values to produce a sample value;

comparing the third and fourth values to produce a reference value; and

comparing the sample and reference values to determine the concentration of the substance in the fluid sample.