Effect of blank test value on COD determination and solution

COD reagent in the use of often there will be customers ask why to do blank samples, a blank sample can be reused and other questions about the blank sample, this article is Harvidson in response to everyone's needs, consulted some senior technicians after a simple finish, rough insights, for reference
only.
Why do blanks when measuring COD? In the COD determination, the blank test value is directly related to the final measurement result, which is a basic point of the test, and all rigorous tests must have a blank test, which is used
as a comparison.
The blank comparison during the determination of water quality COD is to prove that the results of the measurement do not have interference from anything other than the reagents required for the measurement, and reduce the error caused by the operation and instrument during the measurement, for example, your distilled water originally contains the substance you want to measure, and this time doing blank experiments can avoid this error
.
The size of the influencing white test value mainly depends on the amount of reagents and reducing impurities in the water, as well as the cleanliness of the glassware
.
Can I reuse the same white space? Multiple experiments using the same experimental vials can be repeated using the
same blank sample.
This blank sample must be kept in a dark place
.
The absorbance of the blank sample is continuously measured over time to check if the results are stable
.
Use bottled deionized water in absorbance mode to zero out the instrument and then detect the absorbance
of the blank sample.
Record the test results, when the absorbance changes beyond 0.
01 absorbance, it is necessary to prepare a new blank sample
.
What is the effect of blank test values on COD determination and its solution? Blank test values have a greater impact on the accuracy of COD determination, especially for water quality analysis with low COD values
.
A large number of tests have proved that the main factors affecting the blank value are the quality of sulfuric acid, test water and reagent concentration
.
1, sulfuric acid quality on the blank value and the solution Through a large number of experiments, it has been confirmed that different origins and different qualities of sulfuric acid have different effects on the blank value, and when the impact is large, it is even several times different
.
The solution to this problem is to analyze pure sulfuric acid with excellent grade pure sulfuric acid or good quality, and the same manufacturer and the same batch of sulfuric acid
should be used in the analysis process.
2, the effect of experimental water on the blank value and the solution Different experimental water has a great impact on the experimental blank value, respectively, with deionized water, redistilled water, sub-boiling water for blank experiments, the results show that deionized water can not be used for blank experiments and the determination of COD, because deionized water often contains trace amounts of resin leachate and exchange of organic matter, which is the main reason for
the high blank value.
In order to reduce the blank value, it is best to choose sub-boiling water or redistilled water (ultrapure water) when using experimental water, rather than deionized water, and the experimental water cannot be retained for too long
.
3.
Effect of reagent concentration on blank value and determination The two concentrations
of K2Cr2O7 and Fe(NH4)2(SO4)2 are specified in the national standard COD determination method.
It has been experimentally proven that the COD blank value measured by the low concentration of reagents is relatively low, so it is especially necessary
to use a low concentration of reagent as much as possible when doing blank experiments or determining COD, especially when determining low COD values.
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.
This system is widely used in the determination of surface water, groundwater, domestic sewage and industrial wastewater, etc.
, not only for field and on-site rapid water quality emergency testing, laboratory water quality analysis, but also for industrial online water quality monitoring
.
The above is Harvidson's sharing of "Do you have to do a blank test when determining COD?" The effect of blank test values on COD determination and solutions" full text, if you have other questions, you can contact our customer service
.