Method and apparatus for determining information concerning presence of constituents of a liquid sample with oxygen demand

Patent metadata

Field	Value
Publication number	US-9207204-B2
Application number	US-80113010-A
Country	US
Kind code	B2
Filing date	May 25, 2010
Priority date	May 25, 2009
Publication date	Dec 8, 2015
Grant date	Dec 8, 2015

Abstract

In a method and apparatus for determining information concerning the presence of ingredients with oxygen demand in a liquid sample, especially for determining the chemical oxygen demand of a liquid sample, especially a water, or wastewater, sample, by means of electrochemical oxidation of ingredients of the liquid sample, oxidation of ingredients of the liquid sample occurs on a boron doped, diamond electrode.

First claim

The invention claimed is:

1. A method for determining information concerning the presence of ingredients with an oxygen demand in a liquid sample by means of electrochemical oxidation of ingredients of the liquid sample, comprising the steps of:
providing a boron doped, diamond electrode;
placing the boron doped, diamond electrode in the sample;
providing a reference electrode;
placing the reference electrode in the sample;
permitting oxidation of the ingredients of the liquid sample on the boron doped, diamond electrode, at a controlled potential of the boron doped diamond electrode;
ascertaining from electrical current flowing via the boron doped, diamond electrode connected as a working electrode of a three electrode circuit, the quantity of material converted per unit time on the working electrode; and
ascertaining from the quantity of the material converted per unit time on the working electrode the chemical oxygen demand of the liquid sample, wherein:
the boron doped, diamond electrode is operated sequentially at least two different, predetermined potentials, and at each predetermined potential a measured value of the electrical current flowing through the liquid sample at the predetermined potential is measured;
the electrical current measured values are placed in a predetermined relationship to one another;
the quotient or difference or a measurement curve of the electrical current, measured values is formed, as a function of the predetermined potentials;
from the relationship placing, a chemical oxygen demand (COD) in the liquid sample is derived;
oxidation products formed on the boron doped, diamond electrode are quantitatively detected: and
the concentration of the oxidation products formed on the boron doped, diamond electrode is ascertained by determining redox potential by ascertaining a potential occurring at an additional metal electrode, which is immered into the liquid sample.

2. The method as claimed in claim 1 , wherein:
the boron doped, diamond electrode includes an electrically conductive base material, of niobium, silicon, silicon carbide, graphite, tungsten or tantalum, which has a coating of boron doped diamond, at a thickness between 1 to 50 μm.

3. The method as claimed in claim 2 , wherein:
boron is present in the coating at 1000 to 10000 ppm.

4. The method as claimed in claim 1 , wherein:
the boron doped, diamond electrode is operated as a working electrode of a three electrode circuit comprising said working electrode, a counterelectrode and said reference electrode.

5. The method as claimed in claim 1 , wherein:
the controlled potential is selected in such a manner that OH-radicals and/or ozone is formed in the liquid sample; and
the liquid sample is a water sample.

6. The method as claimed in claim 1 , wherein:
the boron doped, diamond electrode is operated at one of said predetermined potentials and the electrical current level of the electrical current flowing through the liquid sample is measured; and
from the measured electrical current level information concerning the presence of ingredients with a chemical oxygen demand in the liquid sample is derived.

7. The method as claimed in claim 1 , wherein:
a potential is moved linearly and a corresponding measurement curve of the electrical current level of the electrical current flowing through the boron doped, diamond electrode is recorded as a function of the linearly moved potential.

8. The method as claimed in claim 1 , wherein:
oxidation products are formed on the boron doped, diamond electrode; and
said oxidation products are ozone and/or OH-radicals and said products are quantitatively detected using a pH-sensor, an OH-radical sensor or an oxygen sensor.

9. A method for determining information concerning the presence of ingredients with an oxygen demand in a liquid sample by means of electrochemical oxidation of ingredients of the liquid sample, comprising the steps of:
providing a boron doped, diamond electrode;
placing the boron doped, diamond electrode in the sample; and
permitting oxidation of the ingredients of the liquid sample on the boron doped, diamond electrode,
wherein:
a predetermined electrical current level of an electrical current flowing through the liquid sample via the boron doped diamond electrode connected as a working electrode of a two, or three, electrode circuit is set;
the potential occurring at the predetermined electrical current level on the boron doped, diamond electrode is measured; and
from the measured potential, information concerning the presence of the ingredients of the liquid sample with an oxygen demand is derived, wherein:
sequentially, at least two different predetermined electrical current magnitude values of an electrical current flowing through the liquid sample are set;
at each predetermined electrical current level, a potential measured value of potential occurring on the boron doped, diamond electrode is measured;
the potential measured values are placed in a predetermined relationship to one another by forming the quotient or difference of the measured values or by forming a measurement curve of the measured values as a function of the predetermined electrical current level;
from the relationship placing a chemical oxygen demand(COD) in the liquid sample is derived;
oxidation products formed on the boron doped, diamond electrode are quantitatively detected; and
the concentration of the oxidation products formed on the boron doped, diamond electrode is ascertained by determining redox potential by ascertaining a potential occurring at an additional metal electrode, which is immersed into the liquid sample.

10. The method as claimed in claim 9 , wherein:
a value or a measurement curve obtained as a result of the relationship placing is compared with at least one stored reference value or at least one stored form of comparison curve; and
on the basis of this comparison, a quantitative evaluation of the chemical oxygen demand of the liquid sample is performed.

11. The method as claimed in claim 9 , wherein:
oxidation products formed on the boron doped, diamond electrode are quantitatively detected, said oxidation products are ozone and/or OH-radicals and the ozone and/or OH-radicals are quantitatively detected using a pH-sensor, an OH-radical sensor or an oxygen sensor.

Assignees

• Gahr Achim
• Bauer Rudolf
• Conducta Endress & Hauser

Inventors

• Gahr Achim
• Bauer Rudolf

Classifications

• G01N27/42 Primary

  Measuring deposition or liberation of materials from an electrolyte; Coulometry, i.e. measuring coulomb-equivalent of material in an electrolyte · CPC title

• G01N33/1806

  Biological oxygen demand [BOD] or chemical oxygen demand [COD] · CPC title

• G01N27/308

  at least partially made of carbon · CPC title