# US 5,708,275 A · PH measurement utilizing a light source

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- Number: US 5,708,275 A
- Document ID: US5708275A
- Status: Granted
- Kind: A
- Application number: 08/660,140
- Filed: 1996-06-07
- Granted: 1998-01-13
- Earliest claimed: 1996-06-07
- Assignees: Honeywell Inc.
- Inventors: Michael L. Rhodes
- Web page: https://patentgrep.com/patent/US5708275A

## CPC

- G01N 21/274: {Calibration, base line adjustment, drift correction}
- G01N 21/64: Fluorescence; Phosphorescence
- G01N 21/80: Indicating pH value
- G01N 2021/6417: {Spectrofluorimetric devices}
- G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q)

## Abstract

The pH of a material containing lignin is determined by directing an ultraviolet light at the material. One of the characteristics of lignin is giving off a fluorescence in response to an ultraviolet light. A monochrometer is used to observe the fluorescence and produces a signal of the intensity of the fluorescent light at varying wavelengths. This signal is displayed on a display means such as a computer screen. Calibration occurs before the pH measurement of the material occurs. The calibration data along with information from the signal is used to calculate the pH of the material. No contact with the material is required in determining the pH of the material.

## Claims

### Claim 1

A method for determining the pH of a lignin containing substance comprising:
a) directing an ultraviolet light at the substance;
b) measuring the intensity of the fluorescence of the substance at particular wavelengths; and
c) determining the pH of the substance with information from a graph.

### Claim 2 (depends on 1)

The method of claim 1 further including a step of calibrating a known value of pH prior to step a).

### Claim 3 (depends on 2)

The step of calibrating of claim 2 wherein the step comprises:
a) taking a sample of the substance;
b) placing the sample in a solution of a known pH;
c) directing ultraviolet light at the sample in the solution of a known pH;
d) measuring the intensity of the fluorescence of the sample in the solution of a known pH at particular wavelengths;
e) recording information obtained from the intensity measurement;
f) repeating the steps from step b) for different pH values; and
g) using information from the intensity measurement for different pH values to create a graph.

### Claim 4 (depends on 3)

The process for calibration of claim 3 wherein steps b) through d) are performed a plurality of times.

### Claim 5

A method for determining the pH of a lignin containing material comprising:
a) directing an ultraviolet beam at the material;
b) measuring the intensity at particular wavelengths of a fluorescent light beam emitted from the material alter the ultraviolet light beam has hit the material; and
c) determining pH based on the measured intensity at said particular wavelengths.