氨氮蒸馏

Nitrogen–Ammonia Distillation1 21 For Use with Nessler and Salicylate Methods in colorimetric testing 1Adapted from Standard Methods for the Examination of Water and Wastewater. 1. Measure 250 mL of water sample into a clean 250-mL graduated cylinder. Pour into a 400-mL beaker. Note: For Proof of Accuracy, use a 1.0 mg/L Ammonia Nitrogen Standard Solution (listed in Optional Reagents) in place of sample. Note: If necessary, destroy residual chlorine by adding 2 drops of Sodium Arsenite Solution or 1.0 mL of Sodium Thiosulfate Solution for every mg/L of Cl2. Note: To prepare Sodium Thiosulfate Solution, dissolve 3.5 g of sodium thiosulfate pentahydrate, in 1.0 liter of demineralized water. Prepare fresh weekly.Cl2. 2. TMeasure 25 mL of Borate Buffer Solution in a 25-mL graduated cylinder. Add it to the beaker and mix. 3. Measure the pH of the solution with a pH meter. Using a dropper, add 1 N Sodium Hydroxide Standard Solution drop-wise until the pH is about 9.5. 4. Set up the distillation apparatus by assembling the general purpose accessories as shown in Figure 2 in the Assembly section. Place a stir bar in the distillation flask. Nitrogen–Ammonia Distillation 5. Pour the solution into the distillation flask. Cap the distillation flask. 6. Nessler Method: Using a 25-mL graduated cylinder, pour 25 mL of demineralized water into a clean, 300-mL erlenmeyer flask. Proceed to step Salicylate method: Add 25 mL of 0.04 N Sulfuric Acid Solution to a 300 mL erlenmeyer flask. Proceed to step 8. See Preparing 0.04 N Sulfuric Acid Solution. 7. Add the contents of one Boric Acid Powder Pillow to the erlenmeyer flask. Mix thoroughly by swirling. 8. Place the flask under drip tube. Elevate the flask so the end of the drip tube extends below the level of solution in the flask. This may require the use of a laboratory jack. 9. Turn on the stirrer power switch. Set the stir control to 5. Set the heater control to 10. Turn on the water and adjust it so a constant flow is maintained through the condenser. 10. Collect 150 mL of distillate, then turn the heater off. Immediately remove the erlenmeyer flask. Using a 250-mL graduated cylinder, measure the distillate to be sure that 150 mL has been collected (total volume should be 175 mL). Note: The flask is removed immediately so the distillate is not drawn back into the distillation flask by vacuum. Or, remove the small glass stopper in the thermometer well to break the vacuum. 11. Return the distillate to the erlenmeyer flask. Adjust the pH of the distillate to about 7 by adding 1N Sodium Hydroxide Standard Solution drop-wise. Measure the pH with a pH meter. 12. Pour the distillate into a 250-mL volumetric flask. Rinse the erlenmeyer flask with demineralized water and add the rinsings to the volumetric flask. Dilute to the mark. Stopper and mix thoroughly by inversion. The distillate is ready for analysis. If albuminoid nitrogen is not being determined, the remainder of the solution in the distillation flask may be discarded. If albuminoid nitrogen is being measured, continue with Step 13. 22