Online chloride and residual chlorine analyzerChloride is almost present in all water and wastewater. The chloride ion content in natural freshwater is relatively low, about a few milligrams per liter, and its main source is brought in by water sources flowing through chloride containing formations; The content of chloride ions in seawater, salt lakes, and some groundwater can reach tens of grams per liter; Domestic sewage and industrial wastewater also contain a large amount of chloride ions.
Chlorination is a reliable method for disinfecting drinking water, killing pathogenic bacteria in the water, and preventing the spread of waterborne diseases. Due to its strong ability to kill bacteria and algae, easy operation, and low price, it is still the main method of disinfecting drinking water in the world

Online chloride and residual chlorine analyzerIodometric method
Under acidic conditions, residual chlorine reacts with potassium iodide to release free elemental iodine, resulting in a brownish yellow color of the water sample. Standard sodium thiosulfate is used
Titrate the solution to a light yellow color, add starch indicator and continue titration until the blue color disappears. The reaction equation is:
　　
Calculate the residual chlorine content based on the amount of sodium thiosulfate consumed, using the following method:
Total residual chlorine (Cl₂， mg/L）＝
In the formula: c - concentration of standard solution, mol/L；
——The volume of consumed standard solution, mL；
V - volume of water sample, mL；
35.45- molar mass of chlorine, g/mol
This method is applicable for determining total residual chlorine (as Cl)₂Water samples with a concentration (mg/L) greater than 1mg/L.
（2） N, N-Diethyl p-phenylenediamine (DPD)-Ammonium ferrous sulfate titration method
Under pH conditions of 6.2-6.5, when there are no iodine ions present in water, free residual chlorine reacts with DPD to form a red compound,
Titrate with ammonium ferrous sulfate solution until the red color disappears, and record the titration volume as V₁（ml）。 The content of free chlorine is:

In the formula: C - concentration of free chlorine, mg/L；
C₁——The concentration of ammonium ferrous sulfate standard solution, mg/L；
V₀——The volume of the water sample, ml。
If 1g of potassium iodide is added after adding DPD, then monochloramine (NH)₂Cl）、 Dichloroamine (NHCl)₂）And nitrogen trichloride (NCl)₃）Both react with DPD to produce a red compound. This reaction occurs simultaneously with the determination of free chlorine, and the result obtained is the total chlorine content, which can be calculated by the following formula:

In the formula: C₂——The volume of ammonium ferrous sulfate standard solution consumed for titration after iodine addition, ml。
If a conical flask containing buffer solution and DPD test solution is added to the sample, and a small amount of potassium iodide is added, the reaction will be limited to monochloramine in free chlorine and compound chlorine; Add a small amount of potassium iodide to the sample before adding buffering value and DPD. At this point, half of the free chlorine and compound chlorine react with monochloramine and nitrogen trichloride; Dichloroamine does not react in either of the above situations. Therefore, the concentrations of monochloramine, dichloroamine, and nitrogen trichloride in the compound chlorine can be calculated separately according to different reaction conditions.
This method is applicable to 0.0004-0.07mmol/L (0.03-5mg/L) free chlorine or total chlorine (as Cl)₂Measurement of measurement. When the following oxides are present in the water sample, this method cannot be used for determination: bromine, iodine, bromoamine, iodoanine, ozone, hydrogen peroxide, chromate, manganese oxide, nitrite, copper ions, and iron ions. The interference of copper ions<8mg/L and iron ions<20mg/L can be masked by disodium EDTA.
（3） N, N-Ethylphenylenediamine (DPD) Colorimetric Method
The principle of this method is basically the same as Method 2, but it does not use ferrous ammonium sulfate solution titration for quantification. Instead, DPD and chlorine are formed into a red compound and compared in a spectrophotometer at a wavelength of 515nm for quantitative analysis based on a standard curve.
This method is applicable to 0.0004-0.07mmol/L (0.03-5mg/L) free chlorine or total chlorine (as Cl)₂Measurement of measurement. This method is applicable in the absence of the following oxidants: bromine, iodine, bromamine, iodolamine, ozone, hydrogen peroxide, chromate, manganese oxide, nitrite, copper ions, and iron ions. The interference of copper ions<8mg/L and iron ions<20mg/L can be masked by disodium EDTA.