COD Cuvette Reagent for High-Chloride Water Analysis
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Solution Overview
Problem
Current photometric methods for determining chemical oxygen demand (COD) in water samples are limited by high chloride content, as they cannot accurately measure samples with chloride levels above 5000 mg/l, necessitating complex titration methods and pre-dilution procedures that dilute the COD, making it unsuitable for industrial wastewater and seawater samples.
Innovation Solution
A cuvette test reagent solution comprising potassium dichromate, silver sulfate, and sulfuric acid, with a sulfuric acid content between 20-50% (w/w), allows for the photometric determination of COD in chloride-depleted samples, enabling measurement of samples with high chloride content without the need for mercury(II) sulfate, using a reversible cuvette for incubation and photometric analysis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If photometric methods are used for COD determination, then ease of operation and productivity are improved, but measurement precision deteriorates for samples with chloride content above 5000 mg/l
Solution Approach 1:
The invention changes the chemical parameters of the reagent solution by specifying a sulfuric acid content between 20-50% (w/w) and particular concentration ranges for potassium dichromate (0.05-2.5% w/w) and silver sulfate (0.05-2% w/w). This parameter optimization enables the photometric method to accurately measure COD in samples with chloride content above 5000 mg/l, resolving the measurement precision issue while maintaining ease of operation
Solution Approach 2:
Silver sulfate acts as an intermediary substance that precipitates chloride ions as silver chloride, preventing chloride interference in the photometric COD determination. This mediator enables accurate measurement of high-chloride samples using the simple photometric method rather than complex titration procedures
2Measurement precision
If complex titration methods are used for high chloride samples, then measurement precision is improved, but device complexity and time consumption increase
Solution Approach 1:
The invention extracts the chloride interference problem by using silver sulfate to precipitate chloride ions before the COD determination. This separation allows the use of simple photometric equipment instead of complex titration apparatus, maintaining measurement precision while reducing device complexity
Solution Approach 2:
The reagent solution is prepared in advance with optimized concentrations of potassium dichromate, silver sulfate, and sulfuric acid. This preliminary preparation of the reagent mixture eliminates the need for complex step-by-step titration procedures during actual measurement, reducing both device complexity and operation time while maintaining precision
3Object-affected harmful factors
If pre-dilution of samples is performed to reduce chloride content, then chloride interference is reduced, but COD content is diluted making measurement unsuitable for low COD samples
Solution Approach 1:
Instead of diluting the sample, the invention changes the parameters of the reagent solution by optimizing the sulfuric acid content (20-50% w/w) and the concentrations of potassium dichromate and silver sulfate. This allows direct measurement of undiluted high-chloride samples, preserving the original COD content while eliminating chloride interference through the chemical action of silver sulfate
4Measurement precision
If mercury(II) sulfate is used in reagents to increase chloride tolerance, then measurement precision for high chloride samples is improved, but environmental harm and toxicity increase
Solution Approach 1:
The invention replaces toxic mercury(II) sulfate with silver sulfate, which forms insoluble silver chloride precipitate that can be easily removed. This substitution eliminates the environmental and health hazards of mercury while maintaining the ability to accurately measure high-chloride samples, and the reagent can be disposed of as ordinary chemical waste rather than hazardous waste
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
This method enables reliable photometric determination of COD in samples with high chloride content, reducing the need for complex titration and mercury-based reagents, providing accurate and reproducible results comparable to standard DIN methods while avoiding environmental hazards.
Implementation Method 1
a water sample is strongly acidified with sulfuric acid and heated with a specified exact amount of the strong oxidizing agent potassium dichromate (K 2 Cr 2 O 7 )
Implementation Method 2
with the addition of silver sulfate as a catalyst
Implementation Method 3
the determination of dichromate consumption is not titrimetric but photometric
Implementation Method 4
20 ml of the sample are mixed with 25 ml of concentrated sulfuric acid and stirred for several hours. The chloride is thus driven off as hydrogen chloride
Data Source
AI summary
The invention relates to a means and a method for photometrically determining the chemical oxygen demand of chloride-containing samples.