The main reason for using the blank sample is to control the volume of organic material in the sample. COD was carried out to measure the oxygen demand of organic compounds in a sample of water, and we have to ensure there were no accidentally outside organic materials added to the sample to be measured.
What is a blank in an experiment?
A blank is a sample that contains everything except for the analyte of interest. For example, if you are doing a UV-vis experiment to measure concentrations of Green Fluorescent Protein, the protein has to be dissolved in a solvent.
What is the most common interference in COD experiment?
The most common interference, however, comes from chloride, as it can contribute to false high results when testing COD levels. Are any test methods available for desalination plants or other laboratories needing to test seawater, brackish, or polluted waters with high chloride levels?
Which indicator is used for the estimation of COD?
Using potassium dichromate
. Most commonly, a 0.25 N solution of potassium dichromate is used for COD determination, although for samples with COD below 50 mg/L, a lower concentration of potassium dichromate is preferred.
What is the function of HgSO4 in the COD determination experiment?
In the standard COD test, mercuric sulphate (HgSO4) is added as a complexing agent for minimizing the chloride interference. Other than having an undesirable effect on the environment, HgSO4 does not exhibit a satisfactory result in minimizing the bromide interference.
What is the purpose of a sample blank?
A sample blank refers to using the sample for zeroing an instrument during a test procedure. A sample blank can correct for potential error from existing color or turbidity in the sample before reagents are added.
Why is a reagent blank used?
Reagent blanks are often used with techniques such as spectrophotometry to zero the instrument before measuring test samples and other blanks. A reagent blank should also be included when a reaction (derivatization, complexation etc.) with the analyte in the test samples is required before analysis.
Why Sulphuric acid is used in COD?
Chemical Oxygen Demand (COD) 1% Silver Sulphate in Sulphuric Acid (conc.) provides the primary and secondary digestion catalysts for oxidation of carbon during chemical oxidation.
Why potassium dichromate is used in COD?
Currently, most COD tests use potassium dichromate as the oxidant. Potassium dichromate is a hexavalent chromium salt that is bright orange in color and is a very strong oxidant. Between 95-100% of organic material can be oxidized by dichromate.
What do we use to remove interferences in COD?
If the COD exceeds 1500 mg/L, the sample should be diluted to bring the results in range. Chloride is the primary interference. Vials with mercuric sulfate can be used to eliminate chloride interference up to 2000 mg/L Cl–.
Which catalyst is used in COD experiment?
Abstract. In this study, 10% CuO/Al2O3 catalyst was used in a catalytic wet-air oxidation process to remove chemical oxygen demand (COD) and color from experimentally designed wastewater containing lignin.
Why mercury sulphate is used in COD?
The most general COD determination uses potassium dichromate (K2Cr2O7) in excess in an acidic medium with the aid of silver sulfate (Ag2SO4) as a catalyst, and mercuric sulfate (HgSO4) added to remove interference of chlorides.
What is the principle of COD test?
The principle behind the COD testing method is that, under acidic conditions, a strong oxidising agent will oxidise almost any organic compound to carbon dioxide. COD analysis will measure the equivalent amount of oxygen that is required to chemically oxidise organic compounds in water.
What are the steps involved in COD test?
Method procedure
- Collect your sample in the appropriate size container and preserve with the appropriate volume of sulfuric acid.
- Properly label enough prepared COD vials (without mercury for non-regulatory samples) for all samples and standards to be digested.
- Turn on your COD reactor and ensure it is set to 150°C.
How do you determine COD in water samples?
The COD test uses a chemical (potassium dichromate in a 50% sulfuric acid solution) that “oxidizes” both organic (predominate) and inorganic substances in a wastewater sample, which results in a higher COD concentration than BOD concentration for the same wastewater sample since only organic compounds are consumed
How do you determine BOD and COD?
Testing for BOD involves incubating a sealed water sample at 20C for five days, followed by measuring the difference in oxygen content before and after incubation. COD measures how much DO is consumed by the oxidation of organic matter and inorganic compounds such as ammonia or nitrite under controlled conditions.
What is the use of blank in colorimetric estimation?
Blank solution contains all of the components of the solution to be analyzed except for the one compound we are testing for. so that the instrument can zero out these background reading and only report values for the compound of interest.
What is the blank method?
A method blank (MB) is an analyte-free matrix such as DI Water for liquids or cleaned sand for solids and/or soils that is processed in exactly the same manner as the samples. The main function of the MB is to document contamination resulting from the analytical process.
Why do we use a reagent blank instead of distilled water?
Why do we use a reagent blank instead of distilled water? A reagent blank is not a transparent as distilled water, so if distilled water is used to zero the spectrometer, there would be error since the absorption of the reagent blank is different.
Why is it necessary to use a blank when using the spectrophotometer?
It is important to “blank” the spectrophotometer before taking an absorption measurement of a sample at each new wavelength, because the water and cuvette also absorb light, so the spectrophotometer won’t measure the absorption of water and cuvette.
What is blank in chemical analysis?
7.3. 1 Blanks. A blank or blank determination is an analysis of a sample without the analyte or attribute, or an analysis without a sample, i.e. going through all steps of the procedure with the reagents only.
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