General pharmaceutical factories only need to detect two indicators, COD and ammonia nitrogen, so please be equipped with a HJ-200 COD meter and a HJ-09N ammonia nitrogen detector, or a HJ-20B COD ammonia nitrogen two-in-one detector. That’s it. Reagents required: Ammonia nitrogen reagent
3-2-1 Preparation of potassium sodium tartrate solution
Weigh 250g potassium sodium tartrate (KNaC4H4O6·4H2O) and dissolve it in 500mL water, heat and boil for 20 minutes To remove ammonia, let cool and adjust the volume to 500ml.
3-2-2. Preparation of Nessler's reagent solution
Weigh 80g of sodium hydroxide, dissolve it in 250mL of water, and fully cool to room temperature. Weigh another 35g of potassium iodide (KI) and 50g of mercury iodide (HgI2) and dissolve it in 250mL of water. Stir until fully dissolved. Then slowly pour this solution into the fully cooled sodium hydroxide solution while stirring, and dilute to 500mL with water. , let it sit for more than 5 hours. Carefully pour out the upper layer and set aside.
3-2-3. Preparation of sodium thiosulfate solution
If the water sample contains residual chlorine, an appropriate amount of 0.35% sodium thiosulfate solution should be added, every 0.5ml can Remove 0.25mg residual chlorine. Weigh 2.5g sodium thiosulfate (Na2S2O3) and dissolve it in 200mL water. Weigh 1.5g disodium ethylenediaminetetraacetate and 2.5g sodium hydroxide (NaOH) and dissolve it in 200mL water. Then mix the two solutions and stir. Dilute to 500mL.
3-2-4. Preparation of ammonia nitrogen standard solution
The appropriate standard solution range should be selected according to the ammonia nitrogen concentration of the on-site water sample, and the standard solution should be prepared with the full-scale value . For example: if the ammonia nitrogen concentration of the water sample is known to be between 5-10mg/L, you can select the calibration range 0-12mg/L and configure the nitrogen standard solution to 12mg/L. In principle, it should be ensured that the ammonia nitrogen concentration of the water sample is within the selected range.
Weigh 3.819g of high-grade pure ammonium chloride (NH4Cl) that has been dried at 100°C and dissolve it in water. Move it into a 1000mL volumetric flask, dilute it with water to the mark and mix well. The concentration of this standard solution is 1000mg/L, and the standard solutions of other concentrations are obtained by diluting the 1000mg/L standard solution in sequence.
3-2-5. Ammonium standard solution: Transfer 5.00ml of ammonium standard stock solution into a 500ml volumetric flask, and dilute with water to the mark. This solution contains 0.010mg ammonia nitrogen per ml. ?COD reagent
Note: Please use sulfuric acid of analytical grade or above. It is a colorless and transparent liquid. Since sulfuric acid is water-absorbent, the reagents should be sealed and stored immediately after preparation, and should not be exposed to the air for a long time.
3-1-1 Preparing reagents:
Before analyzing water samples, they should be pretreated. Only water samples that have been pretreated can be tested on the instrument. During the pretreatment process, please use the two original special reagents.
Both special reagents are packaged and transported in solid form. ***There are two packaging specifications:
Oxidation C1 reagent: C1-200; Catalytic C2 reagent: C2- 200.
C1-200 reagent: Pour the entire bottle of powdered crystal reagent into a beaker, add 200ml of 28.6% sulfuric acid, (Configuration of 28.6% sulfuric acid: Dissolve 60ml of concentrated sulfuric acid in 140ml of distilled water ), stirring constantly until all dissolved.
C2-200 reagent: Dissolve the entire bottle of powdered crystal reagent in 1000mL of analytical grade sulfuric acid, stir continuously or leave it overnight until the reagent is completely dissolved. Note: It takes approximately 1-2 days for the catalyst to completely dissolve.
3-1-2 Preparation of masking agent (for water samples with high chlorine content):
For water samples with high chlorine content, interference can be avoided by adding mercury sulfate masking agent. Under normal circumstances, when the COD value is above 50mg/L and the chloride ion concentration exceeds 2000mg/L, the dilution method can be used to dilute the water sample with distilled water to make the chloride ion content below 2000mg/L before analysis.
Preparation of masking agent: Weigh 20g of analytically pure mercury sulfate into a 100ml small beaker, add about 80ml of distilled water, then add 10ml of concentrated sulfuric acid to dissolve it, shake well, transfer to a 100ml volumetric flask, and use distilled water Dilute to volume.
3-1-3 Prepare standard solution: (It can also be purchased, there are COD standard solutions of different specifications on the market)
Standard solution is also called standard material, which simulates natural fresh water. The ingredient matrix is ??precisely formulated in a specified environment using a special process. Its chemical oxygen demand (COD) concentration is known. Users can purchase it or prepare it themselves according to their requirements. The standard solution mainly has the following uses:
① Calibrate the curve of the chemical oxygen demand meter;
② Test the accuracy of the chemical oxygen demand meter ;
③Confirm and evaluate the operator's analysis process;
④Conduct quality control on the entire measurement process of the instrument.
Standard stock solution: 5000mg/L standard material as the stock solution. When using, use measuring instruments to dilute step by step as needed to obtain standard use solutions of different concentrations, which can be stored and used under specified conditions. Strictly follow the instructions for use and operate with caution.
Standard solution 1: Accurately measure 10mL of standard stock solution, transfer to a 100mL volumetric flask, dilute to the mark with distilled water and mix well. The COD concentration of this solution is 500mg/L. Used for testing and calibrating instruments.
Standard use solution 2: Accurately measure 20mL of standard use solution 1, transfer it to a 100mL volumetric flask, dilute to the mark with distilled water and mix well. The COD concentration of this solution is 100mg/L. Used for testing and calibrating instruments.
The standard solution can also be prepared by yourself according to the following method:
Prepare according to the method specified in "GB 11914-89 Determination of chemical oxygen demand of water quality by dichromate method", Note: The accuracy and uncertainty of the prepared standard solution mainly depend on the errors in each link during the preparation process.
Standard solution preparation method:
Weigh 0.4251g of potassium hydrogen phthalate (HOOCC6H4COOK) that has been dried at 105°C for 2 hours and cooled, and dissolve it in distilled water. Dilute to 1000mL and mix well. The theoretical COD value of this solution is 500mg/L.
Weigh 0.4251g of standard or superior grade pure potassium hydrogen phthalate (HOOCC6H4COOK) that has been dried at 105~110℃ for 2 hours, dissolve it in a small amount of water, transfer it to a 500mL volumetric flask, and dilute with water to Mark the line and shake well. The COD value of this solution is 1000mg/L.