CH2MHILL GILROY/MORGAN HILL LABORATORY LABORATORY STANDARD OPERATING PROCEDURE NO TOTAL KJELDAHL NITROGEN - TKN SM 4500-N org.

Transcription

1 CH2MHILL GILROY/MORGAN HILL LABORATORY LABORATORY STANDARD OPERATING PROCEDURE NO. 709 TOTAL KJELDAHL NITROGEN - TKN SM 4500-N org. B I. SCOPE AND APPLICATIONS A. The kjeldahl method determines nitrogen in the tri-negative state. If ammonia nitrogen is not removed in the initial phase of the procedure, the term "kjeldahl nitrogen" is applied to the result. Should kjeldahl and ammonia nitrogen be determined individually "organic nitrogen" can be obtained from the difference. II. DETECTION AND REPORTING LIMITS A. See Reference table for detection and reporting limits. III. PRECISION AND BIAS A. Three synthetic samples containing various organic nitrogen concentrations and other constituents were analyzed by three procedural modifications of the macro-kjeldahl method. The results obtained by participating laboratories are summarized. Thirty-one laboratories running a sample of 800 ug./l had a 44.8 % relative standard deviation and 3.7 % relative error. IV. WORKING RANGE A. The titrimetric and selective electrode methods of measuring ammonia in the distillate are suitable for determining a wide range of organic nitrogen concentrations. V. SUMMARY OF METHOD A. In the presence of H2SO4, potassium sulfate and Cupric sulfate catalyst, amino nitrogen of many organic materials is converted to ammonium. Free ammonia is converted to ammonium. After addition of base, the ammonia is distilled from alkaline medium and absorbed in boric or sulfuric acid, the ammonia is determined by titration with a standard mineral acid. Or by ammonia-selective electrode. VI. SAMPLE COLLECTION, PRESERVATION AND HOLDING TIMES A. See Reference table for collection, preservation and holding times. B. The most reliable results are obtained on fresh samples. If and immediate

2 analysis is not possible, preserve samples by acidifying to a ph <2 with 1:1 H2SO4 and storing at 4 deg. C. Not to exceed 28 days. VII. HELPFUL COMMENTS A. Occasionally a digesting flask will "burp" up, if this happens start digestion over. B. Warm up heaters before placing samples on them for digesting. C. Have the next set of samples ready to place on still. VIII.SAFETY ISSUES A. All samples for TKN represent a biohazard. Wear all required lab protective equipment. B. TKN Digestion reagent is very deadly. Do not breathe fumes or ingest. Also use caution when handling NaOH reagent. C. When digesting TKN s leave fume hood closed, and do not open. D. When removing flask from distillation apparatus, point flask away from you at all times. Wear goggles or face shield if possible. IX. INSTRUMENT/EQUIPMENT A. Make sure cooling water is running trough still. X. REAGENTS, STANDARDS, AND SUPPLIES A. Digestion Reagent: dissolve 134 g. Potassium Sulfate and 7.3 g CuSO4 in about 800 ml distilled water. Carefully add 200 ml concentrated H2SO4. Cool to room temperature and dilute the combined solution to 1 liter with water. KEEP AT A TEMPERATURE CLOSE TO 20 DEG. C. TO PREVENT CRYSTALLIZATION. B. Potassium sulfate is ordered through VWR (CATALOG # EM-PX1595-1) 500 g. at a time. C. Copper Sulfate: Order through VWR (CATALOG # VW )500 G. at a time. D. Sodium Hydroxide-Sodium Thiosulfate reagent: Dissolve 500g NaOH and 25 g. Na2S2O3.5H20 in water and dilute to 1000 ml. Order through VWR (CATALOG # JT ) NaOH 2.5 kg. at a time. Na2S2O3.5H20 (CATALOG # EM-SX0815-1) 500 g. at a time.

3 E. Sodium Hydroxide 6N: Dissolve 240 g. NaOH in distilled water and dilute to one liter. F. Sodium Sulfite solution: dissolve 0.9 g. Na2SO3 in water and dilute to 1 liter. Prepare fresh daily. Order through VWR (CATALOG # JT ) 500 g. at one time. Use one ml of Na2SO3 Solution to remove 1 mg/l of residual chlorine. G. Boric acid: dissolve 20 g. boric acid in 1000 ml distilled water Order through VWR (CATALOG # JT ) order 500 g. at a time. H. Mixed indicator solution: Dissolve 200 mg methyl red indicator(hcl) in 100ml 95% ethyl or isopropyl alcohol. Dissolve 100 mg methylene blue in 50 ml 95% ethyl or isopropyl alcohol. Combine solutions. Prepare monthly. Order through VWR (CATALOG # JT )30g at a time. For methylene Blue (CATALOG # EM-MX0975-3)125g at a time. I. Borate Buffer solution: Add 88 ml 0.1N NaOH solution to 500 ml approximately M Sodium Tetraborate (Na2B4O7) solutions (9.5 g NaB4O7.10H2O/L) and dilute to 1 liter. XI. QA/QC REQUIREMENTS A. Run a standard and LCS through the procedure above every time a sample is set up. Plot the accuracy in the QA/QC graphs for that particular parameter daily. B. Run a duplicate on 10 % of all samples run or one sample per week. Plot points on the Precision graph for that particular parameter daily. C. Unknown samples are supplied to the lab through ERA and run once a year. XII. TEST PROCEDURE A. DIGESTION B. In special testing workbook under section on TKN write sample description such as Muni Eff for sample ID.- for Blank run one flask exactly as below but use 400 ml of distilled water as sample. Measure out appropriate amount of sample. IF SAMPLE CONTAIN CHLORINE - DECHLORINATE. C. Pour into kjeldahl flask and record No. of flask as sample No. on worksheet. D. Record ml measured in B. as ml of sample used. E. If sample volume is less than 400 ml add distilled water to bring up to 400 ml

4 and record amount of water added. F. Warm up heaters at least ½ hour G. Add 5 boiling beads. H. Add 50 ml of Digestion reagent. I. Turn on hood to high power and place flask on heaters under hood. J. When contents evaporates to very small volume, about 25 ml watch for large amounts of white fumes. When white fumes appear boil 30 minutes longer. Then turn heaters off and unplug allow flask and heater to cool to room temperature 20min do not go longer than 23 min or you sample will crystallize. K. DISTILLATION: L. Prepare still as follows. Take a kjeldahl flask and add 300 ml. distilled water, 25 ml borate buffer solution and 1ml NaOH 6N add 5 boiling beads,place in position one of still, start water through still cooling jacket and turn on still heater repeat process for position 2. allow flask to come to a full boil and boil for 15 minutes. After 15 minutes turn off still but leave flask hooked up until ready to distill samples, but you must remove collection beakers to avoid the purge from siphoning back up the still, let cooling water continue to run. Note: This step is to be done first. This allows to have the distill ready for your samples. M. Obtain ml Erlenmeyer flasks and measure out 50 ml of Boric Acid into each for the titrimetric method and 50ml of H2SO4 0.4 N for the Ion Selective Electrode Method. N. Remove cooled TKN flask from heater and place in the flask holder to hold up right. Add 300 ml distilled water and swirl to dissolve white precipitate, and then allow contents to come to rest. {NO TURBULENCE}. O. Measure 50 ml of NaOH/Na2S2O3 into each TKN flask. P. Place one beaker of Boric acid or H2SO4 on platform of still and be sure the discharge tube is below the surface of the acid. Q. Take TKN flask with sample and with flask slightly tipped pour 50 ml NaOH/Na2s2o3 slowly down inner side of flask since, reagent is heavy, it will form an alkaline layer on the bottom noticeable because of black precipitate. DO NOT MIX LAYERS { NOTE: CLEAR ACID LAYER PROTECTS AGAINST LOSS OF NITROGEN TO ATMOSPHERE.} Immediately place flask in position one of still and turn on heater.

5 R. Repeat steps N. thru Q for the next sample and place into position 2 of still. S. After still has increased the volume in beaker to 200 ml remove beakers from platform set up next distillation and proceed immediately to titration. { NOTE: NEVER SIMPLY TURN OFF HEATER ON STILL BECAUSE VACUUM DEVELOPS AND DRAWS SAMPLE OUT OF BEAKER AND INTO STILL. } T. NOTE: The refractory on the still heater requires a great deal of energy to heat therefore distillation of many samples will proceed more quickly if the next sample to distill is ready to immediately add NaOH/Na2S2O3 to and be placed on still. U. Titrate ammonia in distillate with standard 0.02N H2SO4 titrant until indicator turns a pale lavender. V. For the Ion selective electrode method. Use the ammonia procedure for reading the samples after distillation. NOTE: THIS IS THE METHOD THAT WE USE. XIII.CALCULATIONS A. For Titration Method: A-B*280 / SAMPLE VOLUME Where: A = volume of H2SO4 titrated for the sample, ml B = volume of H2SO4 titrated for blank. ml B. For the Ion Selective Electrode Method: The results will be read of the meter. C. Report results in two significant figures. D. Report results in mg/l. E. Report results below detection limits as <0.1 mg/l F. Results are validated by the Laboratory Analyst and transmitted to the Project Manager. XIV. SOURCE OF METHOD AND REFERENCES A. STANDARD METHODS FOR THE EXAMINATION OF WATER AND WASTEWATER 18 TH EDITION. Revised 8/6/2012