Patent Application
20180095027
Online wet chemistry analyzers are used in a variety of industries to provide a continuous indication of an analyte in a process sample. This continuous indication can be provided locally by the analyzer and/or remotely to one or more suitable devices in order to provide control and/or monitoring of a chemical process.
One particular example of an online wet chemistry analyzer is an online automatic colorimetric analyzer. Such devices are configured to generate a reaction in the process sample that creates a visual indication relative to the process sample. This visual indication is measured by an optical sensor or light detector in order to provide an indication relative to the reaction. Colorimetric analysis is used in a variety of settings ranging from medical laboratories to industrial wastewater treatment facilities. Such analysis may be used with or without an enzymatic stage and is applicable to detecting both inorganic and organic compounds. Colorimetric techniques are known for detecting calcium, copper, creatine, iron, phosphate, cholesterol, glucose, urea, trigylcerides, and silica.
One particular example of an automatic colorimetric analyzer is an online silica analyzer that employs a known reaction to render the silica in the process sample readily detectible. One example of such a reaction is known as the molybdenum blue method. In the molybdenum blue method, molybdate (usually in the form of potassium molybdate) is used to react with silica in the process sample in order to generate a compound suitable for colorimetric detection. In accordance with the molybdenum blue method, the silica content in water is measured based on the color of the silicomolybdic acid formed through the wet chemistry process. The molybdenum blue method can also be used for colorimetric qualitative analyses of phosphorous, arsenic, and germanium.
In online wet chemistry analyzers that utilize optical measurement techniques, it is important to facilitate an effective optical measurement. Aspects or properties of the sample or reagents that may interfere with the optical measurement that are not related to the presence or concentration of the analyte, generate measurement errors. Therefore, identifying and/or reducing such artifacts is beneficial in order to obtain higher precision and fidelity in optical colorimetric measurements.
A colorimetric analyzer includes a reaction chamber configured to receive a sample and at least one reagent. A measurement cell is operably coupled to the reaction chamber. The measurement cell has an illumination source and an illumination detector spaced from the illumination source such that illumination from the illumination source passes through the measurement cell to the illumination detector. A controller is coupled to the illumination source and the illumination detector. The controller is configured to determine an absorbance of a reducing reagent and store the determined reagent absorbance in the analyzer. The controller is configured to use the determined reagent absorbance to compensate at least one subsequent colorimetric sample measurement.
An analyzer, in accordance with embodiments of the present invention, can be used in any continuous process wherein reagents are mixed with a continuous stream of a liquid to be tested. For purposes of explanation only, embodiments of the invention are described as they would be used to test for the presence of soluble silicates (silica) for example in power plants where the presence of such silicates is undesirable because of their tendency to coat the turbine blades.
In a typical industrial use, it may be desirable to maintain the level of silica at 20 ppb. For purposes of explanation only, an embodiment of the present invention will be described as part of an automated continuous system for measuring the amount of silicate present in a continuous flow of water (e.g., from a power plant).
In colorimetric based chemical analysis, such as silica analysis, there is a potential interference caused by the light absorption of the reagent itself. This amount of interference can vary due to manufacturing, shelf life/drift, and delivery methods of the reagent. Embodiments of the present invention provide a system and methods to determine the interference from the reagent accurately and quickly using samples with a broad quality, enabling the use of process sample for on-line automated colorimetric analyzers.
During the silica measurement using a colorimetric method, a chelating reagent is typically added to the sample solution first, forming a complex. In one example, this chelating agent is an acid solution of MoVI, for example ammonium molybdate. Then, a reducing reagent is added to reduce the complex which turns the solution blue. Examples of reducing reagents include ascorbic acid and/or ferrous ion. An absorbance measurement of the blue solution at 810 nm, for example, is then carried out. According to Beer-Lambert law, the absorbance is proportional to the concentration of silica in the sample solution.
When ferrous ion (Fe2+) is used as the reducing reagent, the ferrous ion itself exhibits some absorbance at 810 nm. Thus, the absorbance at 810 nm from unreacted ferrous ion will potentially become an error for the measurement, especially when the silica concentration is low.
In accordance with an embodiment of the present invention, a reducing reagent absorbance is measured and used to provide a diagnostic output and/or compensate subsequent colorimetric measurements. For example, in an automated silica analyzer based on the colorimetric method, a reagent absorbance measurement process is added to measure the absorbance of the reducing reagent. In this process, the reducing reagent is added to the sample solution with the same reagent-to-sample ratio as used in the silica sample measurement process. Since no chelating reagent was added to the sample, the absorbance measured will be the absorbance from the reducing reagent. The reagent absorbance is saved in the colorimetric analyzer, and used to correct every silica measurement by subtracting the reagent absorbance from the measured absorbance during silica measurements.
Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. For example, embodiments of the present invention may be used to provide smart diagnostics for colorimetric analyzers. Such diagnostics can include providing a reagent quality feedback to a user. Such feedback may indicate that the reagent has passed its shelf life or is out of specifications if the interference can be correlated to the concentration of a given reagent. Moreover, while embodiments of the present invention have generally been described with respect to a silica analyzer, embodiments are practicable with any colorimetric analyzer where colorimetric reagents have inherent interference in colorimetric detection and are not affected by the chemistry.
The present application is based on and claims the benefit of U.S. Provisional Patent Application Ser. No. 62/402,069 filed Sep. 30, 2016, the content of which is hereby incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 62402069 | Sep 2016 | US |
