Method and apparatus for identifying causes of repeatability problems in near infrared analytical instruments

• US 4,969,115 A
• Filed: 11/23/1988
• Issued: 11/06/1990
• Est. Priority Date: 11/23/1988
• Status: Expired due to Term

• Current Assignee: Futrex, Inc.
• Original Assignee: Futrex, Inc.
• Inventors: Rosenthal, Robert D.
• Primary Examiner(s): Lall, Parshotam S.
• Assistant Examiner(s): Melnick, S. A.
• Application Number:
  US07/274,836
• Time in Patent Office: 713 Days
• Field of Search: 364/571.05, 364/571.03, 364/557, 364/556, 364/498, 250/339, 250/341, 250/252.1 A
• US Class Current: 702/28
• CPC Class Codes: G01N 21/359 using near infrared light

Abstract

A method and apparatus for determining whether a subsequent sample is substantially identical to an initial sample in a near infrared quantitative analysis instrument. An initial sample is measured for a plurality of characteristics which include the ambient temperature of the analysis instrument at the time of reading, the temperature of the sample itself, the optical energy level of the sample, the moisture content of the sample, and the percent protein of the sample. These characteristics are stored in a computer to provide a series of comparison criteria. A subsequent sample is then measured for the same characteristics as the initial sample and these characteristics are compared to the comparison criteria to determine if the subsequent sample is substantially identical to the previous sample. The subsequent sample is determined to be substantially identical to the initial sample for a given criterion if the subsequent sample'"'"'s measurement for the corresponding characteristic is within a tolerance for that criterion. If the subsequent sample is judged to be substantially identical to the initial sample for all criteria, it is determined to be substantially identical to the initial sample.

Claims

1. A method for determining whether a subsequent sample is substantially identical to an initial sample in a near infrared radiation analysis comprising the steps of irradiating the initial and subsequent samples with near infrared radiation in a near infrared analysis instrument and measuring optical densities of said samples, the method further comprising the steps of:

(a) obtaining a plurality of comparison criteria values for the initial sample by measuring a plurality of characteristic values from the following;

ambient temperature of said instrument at time of measuring the initial sample'"'"'s characteristics, the temperature of the initial sample, the optical energy level of the initial sample, the moisture content of the initial sample, and the percent protein of the initial sample;

(b) storing the comparison criteria values of the initial sample;

(c) measuring a plurality of characteristic values of a subsequent sample which correspond to characteristics measured by the initial sample, said plurality of characteristics of the subsequent sample being obtained from the following;

ambient temperature of said instrument at time of measuring the subsequent sample'"'"'s characteristics, the temperature of the subsequent sample, the optical energy level of the subsequent sample, the moisture content of the subsequent sample, and the percent protein of the subsequent sample; and

(d) comparing the characteristic values measured for the subsequent sample to the corresponding characteristic values measured for the initial sample in order to determine whether or not the subsequent sample is substantially identical to the initial sample.

2. The method of claim 1 wherein one of the characteristic values that is measured on the initial sample and the subsequent sample is percent protein, the method further including the steps of averaging the measured percent protein values for the initial sample and the subsequent sample and providing a readout of said average.

3. The method of claim 1, wherein one of the characteristic values that is measured of the initial sample and the subsequent sample is ambient temperature of the instrument, wherein an ambient instrument temperature for the subsequent sample within about ±

0.5°

F. of the ambient instrument temperature of the initial sample indicates that the ambient instrument temperatures for both the initial sample and the subsequent sample are substantially identical.

4. The method of claim 1, wherein one of the characteristic values that is measured of the initial sample and the subsequent sample is sample temperature of the initial sample and the subsequent sample, wherein a measured sample temperature for the subsequent sample within about ±

2°

F. of the measured sample temperature of the initial sample indicates that the sample temperatures for both the initial sample and the subsequent sample are substantially identical.

5. The method of claim 1, wherein one of the characteristic values that is measured of the initial sample and the subsequent sample is optical energy level, wherein an optical energy level for the subsequent sample within about ±

0.5% of the optical energy level of the initial sample indicates that the optical energy levels of both the initial sample and the subsequent sample are substantially identical.

6. The method of claim 1, wherein one of the characteristic values that is measured of the initial sample and the subsequent sample is moisture content, wherein percent moisture of the subsequent sample within about 0.5% by weight of the moisture content of the initial sample indicates that the moisture contents of both the initial sample and the subsequent sample are substantially identical.

7. The method of claim 1 wherein one of the characteristic values that is measured of the initial sample and the subsequent sample is percent protein, wherein a percent protein of the subsequent sample within about 0.6% by weight of the percent protein of the initial sample indicates that the percent protein of both the initial and the subsequent sample is substantially identical.

8. An apparatus for determining whether a subsequent sample is substantially identical to an initial sample comprising a near infrared analysis instrument having means for irradiating a sample with near infrared radiation and means for measuring the optical density of said sample, the apparatus further including:

(a) means for obtaining a plurality of comparison criteria values for a sample by measuring a plurality of characteristics from the following;

ambient temperature of said instrument at time of measuring the initial sample'"'"'s characteristics, the temperature of the initial sample, the optical energy level of the initial sample, the moisture content of the initial sample, and the percent protein of the initial sample;

(b) means for storing measurements of a plurality of said characteristics made by the measuring means for an initial sample;

(c) means for comparing measurements made for a subsequent sample with said measurements of a corresponding plurality of said characteristics made for the initial sample; and

(d) means for indicating whether the subsequent sample is substantially identical to the initial sample based on the comparison of measurements made for the initial and subsequent samples.