# US 4,397,957 A · Specific-ion gas-sensing carbonate analyzer

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- Number: US 4,397,957 A
- Document ID: US4397957A
- Status: Granted
- Kind: A
- Application number: 06/351,813
- Filed: 1982-02-24
- Granted: 1983-08-09
- Earliest claimed: 1982-02-24
- Assignees: The Dow Chemical Company
- Inventors: Joseph L. Allison
- Web page: https://patentgrep.com/patent/US4397957A

## CPC

- G01N 33/182: {Specific anions in water}
- G01N 27/4162: {investigating the composition of gases, by the influence exerted on ionic conductivity in a liquid (conductometry in general G01N27/06; amperometric gas sensors G01N27/404)}
- G01N 31/00: Investigating or analysing non-biological materials by the use of the chemical methods specified in the subgroup; Apparatus specially adapted for such methods
- Y10T 436/204998: Inorganic carbon compounds
- Y10T 436/235: In an aqueous solution [e.g., TOC, etc.]
- Y10T 436/25125: Digestion or removing interfering materials
- Y10T 436/25875: Gaseous sample or with change of physical state
- 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)
- Y10T: TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION

## Abstract

A method for determining the concentration of carbonate salts in solutions containing other inorganic salts. The method includes converting the carbonate salts to carbon dioxide by acidifying the sample, sweeping the acidified solution with an inert gas to strip the carbon dioxide from the solution and contacting an ion-selective gas-sensing electrode with the gas stream. The electrode includes a buffered solution which changes in pH depending on the concentration of carbon dioxide in the gas stream thereby providing a measure of the carbonate salt concentration in the sample.

## Claims

### Claim 1

A method for determining the concentration of a carbonate salt in a solution sample, comprising the steps of:
(a) acidifying the sample to convert the carbonate salt to carbon dioxide;
(b) sweeping the acidified solution with an inert gas, thereby stripping the carbon dioxide from the solution and forming a gas stream containing the carbon dioxide; and
(c) contacting an ion-selective gas-sensing electrode with the gas stream, the electrode including a second solution which is subject to changes in pH when contacted by the gas stream containing different carbon dioxide concentrations, the electrode having an electrical output responsive to the changes in pH of the second solution, whereby the electrical output of the electrode provides a measure of the concentration of the carbon dioxide in the gas stream and the concentration of the carbonate salt in the sample.

### Claim 2 (depends on 1)

The method of claim 1, wherein a reducing agent, in sufficient quantity, is added to the sample before sweeping the acidified sample with an inert gas, thereby preventing substances in the sample which will release halogen gases upon acidification from releasing the same.

### Claim 3 (depends on 2)

The method of claim 2, wherein the reducing agent is hydroxylamine or hydroxylamine hydrochloride.

### Claim 4 (depends on 3)

The method of claim 3, wherein the sample is a solution of sodium chloride brine and the carbonate salt is sodium carbonate.