Photoelectric endpoint detection

Claim 1

In a device for automatic titration of a liquid containing an indicator substance adapted to change between different forms having different light absorption characteristics over a color change interval indicative of a predetermined endpoint, said device comprising means for introducing titrant ions into a liquid to be titrated, means for detecting the endpoint, means for measuring the amount of titrant ions required to achieve the endpoint, the improvement wherein the means for detecting the endpoint comprises: means for directing light through the liquid; means for providing first and second light beams, the intensity of each light beam being colorimetrically responsive to one form of the indicator; light detecting means for generating first and second signals corresponding to the intensities of the first and second light beams; means for generating a third signal corresponding to the ratio of the logarithms of the first and second signals; means responsive to the third signal generating means for detecting when the third signal reaches a predetermined value corresponding to the endpoint; and means responsive to said third signal detecting means for signalling to the measuring means that the endpoint has been reached.

Claim 5

A method useful for colorimetric titration of a liquid having different light absorption characteristics on different sides of a color change interval indicative of a predetermined endpoint, comprising: introducing a titrant into the liquid; passing light through the liquid during the introduction of titrant; generating a first electrical signal corresponding to the intensity of light passed through the liquid at a first wave length corresponding to the light absorption characteristics of the liquid at one side of the color change interval; generating a second electrical signal corresponding to the intensity of the light passed through the liquid at a second wavelength corresponding to the light absorption characteristics of the liquid at the other side of the color change interval; generating a third electrical signal corresponding to the ratio of the logarithms of the first and second signals; continuing the introduction of titrant until the third signal reaches a predetermined value corresponding to said endpoint; and measuring the quantity of titrant introduced into said liquid prior to the time said third signal reaches said predetermined value.

Claim 7

A method useful for colorimetric titration of a liquid acidic solution of an acid-base indicator having different light absorption characteristics on different sides of a color change interval indicative of predetermined acid-base endpoint, comprising: passing an electrolysis current through said liquid to generate hydroxyl ions therein to titrate the acidity; passing light through the liquid during the titration thereof; measuring the intensity of light passed through the liquid at a first wavelength corresponding to the light absorption characteristics of the liquid at one side of the color change interval; measuring the intensity of the light passed through the liquid at a second wavelength corresponding to the light absorption characteristics of the liquid at the other side of the color change interval; continuing the titration until the ratio of the logarithms of the intensities of said light at the first and second wavelengths reaches a predetermined value corresponding to said endpoint; and measuring the amount of electricity passed through the liquid in said electrolysis current until the ratio of said logarithms reaches the predetermined value corresponding to the endpoint.