Stabilised Formazin Composition for Turbidity Standards
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Solution Overview
Problem
Formazin turbidity standards degrade quickly when diluted to low turbidity values, leading to instability and inaccuracies in turbidity measurements, especially below 40 NTU, where standards must be used immediately due to rapid degradation.
Innovation Solution
A stabilised formazin composition is developed with a pH buffer system maintaining a range of 8.4 to 10, reducing hexamine concentration to prevent refractive index changes, and eliminating sulfate salts, which provides long-term stability down to 0.05 NTU for at least 12 to 18 months, ensuring accurate and repeatable turbidity measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If formazin is diluted to low turbidity values (below 40 NTU), then the turbidity measurement range is extended to lower values, but the stability of the standard degrades rapidly (within a day or less)
Solution Approach 1:
The patent changes the chemical composition parameters of the diluent by incorporating residual reactants (hexamethylenetetramine and sulfate salts) at specific concentration ranges. This parameter modification stabilizes the polymer matrix of formazin during dilution, preventing rapid degradation while maintaining low turbidity values for extended measurement ranges.
Solution Approach 2:
The patent introduces an intermediary diluent composition that contains residual reactants acting as stabilizing agents. These intermediaries (hexamethylenetetramine and sulfate salts) protect the formazin polymer structure during dilution, enabling low turbidity standards to remain stable for months rather than degrading within a day.
2Stability of the object's composition
If hexamine concentration is increased to stabilize formazin, then the stability of low turbidity standards is improved, but refractive index changes occur leading to irregular turbidity readings
Solution Approach 1:
The patent optimizes the hexamine concentration parameter within a specific range (50-200 g/l) to achieve the optimal balance between stability and measurement accuracy. This parameter optimization ensures sufficient stabilization of the formazin polymer while minimizing refractive index changes that would interfere with turbidity readings.
Solution Approach 2:
The patent applies partial action by using a moderate concentration of hexamine (50-200 g/l) rather than excessive amounts. This partial stabilization approach provides sufficient protection against degradation while avoiding the harmful side effects of high hexamine concentrations, specifically refractive index changes.
3Stability of the object's composition
If formazin stock solution is stored at high concentration (4000 NTU), then the standard maintains stability for one year, but dilution to working concentrations is required for practical use
Solution Approach 1:
The patent applies preliminary action by pre-stabilizing the formazin polymer matrix in the stock solution through controlled dilution with a diluent containing residual reactants. This preliminary stabilization ensures that when the solution is further diluted to working concentrations, it maintains stability without requiring immediate use, thus preparing the standard in advance for long-term storage and later use.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The stabilised formazin composition maintains turbidity stability within 5% of the original reading for over a year, eliminating the need for immediate use and reducing toxicity, while maintaining accuracy and repeatability of traditional formazin standards.
Implementation Method 1
a buffer composition, wherein the buffer composition is adjusted to maintain a pH of the formazin composition in a range from 8.4 to 10
Implementation Method 2
Formazin is an aqueous suspension of an insoluble white polymer formed by the condensation reaction between hydrazine sulfate and hexamethylenetetramine
Implementation Method 3
Turbidity measurement plays an important role as an indicator of water quality... formazin as the primary standard for turbidity
Data Source
AI summary
A stabilised aqueous formazin composition comprises 100 parts by weight water; up to 0.03 parts by weight formazin polymer; 0.4 to 5 parts by weight hexamethylenetetramine; and a buffer composition, wherein the buffer composition is adjusted to maintain a pH of the formazin solution in a range between 8.4 and 10. The stabilised formazin composition has a turbidity of 400 NTU or less. A diluent for preparing the stabilised formazin composition from a formazin stock composition is provided, wherein the diluent comprises hexamethylenetetramine in a concentration of between 4 and 50 g/l and a buffer composition adjusted to a pH of the diluent in a range of from 8.4 to 10.