Nitrate Procedure - ISE
- Boric acid preservation solution - Dissolve 6.2 g boric acid in 100 mL hot distilled water.
- Stock nitrate solution - To make 1000 ppm N stock solution, dissolve 0.7218 g KNO3 (dry) in deionized water. Add 1 mL preservation solution then dilute to 100 mL.
- Standard nitrate solutions - Dilute 0.1, 1, and 10 mL respectively of the stock nitrate solution to 100 mL with deionized water to obtain standard solutions of 1, 10, and 100 ppm, respectively.
- Buffer solution - Dissolve 6.66 g Al2(SO4)3.18H2O, 3.12 g Ag2SO4, 1.24 g H3BO3, and 1.94 g sulfamic acid (H2NSO3H), in about 400 mL water. Adjust to pH 3.0 by slowly adding concentrated NaOH. Dilute to 1000 mL.
- Orion ion analyzer
- Nitrate ion electrode
- Reference electrode
- Magnetic stirrer
- 150 mL beakers, 100 and 1000 mL volumetric flasks.
- Plastic bottles for solution storage.
- Repipeter and tips.
- Transfer 20 mL of 1, 10, 100 ppm standards to three 100 mL beakers. Add 20 mL buffer to each standard.
- Transfer 20 mL of sample to a 100 mL beaker. Add 20 mL buffer to sample.
- Check levels of inner and outer filling solutions in reference electrode (see reference electrode manual for specifications).
- Follow instructions for setting up meter to standardize with the three standards. Insure that the slope is appropriate.
- Rinse electrodes and place into sample. Record reading directly in ppm with no decimal.
- Recheck standards frequently.
- When finished place meter in standby mode and submerge electrodes in appropriate solutions.
Standard Methods for the Examination of Water and Wastewater, 1985, 16th Edition, p. 393.
Nitrate-Nitrogen Flow Injection/Cadmium Reduction FIALab Nitrate Analyzer
Carrier Water: water
Standards: 1, 2, 3, 4 ppm NO3-N solutions: Make 1:1000, 2:1000, 3:1000, and 4:1000 solutions from the 1000 ppm stock.
Reagent 1: 1.6 M Ammonium Chloride Buffer
- 43 g ammonium chloride (53.49 FW)
- 0.50 g disodium eththylenediamine tetraacetic acid (EDTA)
- 4 grams sodium hydroxide pellets
- 500 mL DI water
- 6 drops of Joy soap
Place 400 mL DI water into a 500 mL volumetric flask. Weigh 43 grams ammonium chloride and 0.50 grams EDTA into the 500 mL volumetric flask. Mix until dissolved. Adjust the pH of this solution to about 8.5 using sodium hydroxide pellets. Add DI water to fill flask to 500 mL. Add 6 drops of Joy soap. CAUTION: ASC grade of ammonium chloride sometimes may contain significant amounts of nitrate.
Reagent 2: Colorimetric Sulfanilamide Solution Purchased from LabChem (412)-826-5230. Catalog number LC132802 (1L) Dilute the concentrate by adding 50 mL concentrate to 400 mL DI water. To Prepare:
- 20 grams sulfanilamide (172.21 FW)
- 50 mL 85% conc. Phosphoric acid (H3PO4)
- 0.50 grams N-1-naphthylethylenediamine dihydrochloride (259.18 FW)
- 500 mL DI water
Place 300 DI water into a 500 mL volumetric flask. Pipette 40 mL phosphoric acid into the 500 mL volumetric flask and mix well. Weigh 20 grams sulfanilamide and 0.50 grams N-1-naphthylethylenediamine into the 500 mL volumetric flask. Mix until dissolved. Add DI water to dilute to 500 mL and store in the refrigerator. CAUTION: Reagent grade of phosphoric acid may contain a few ppm concentration of nitrate.
Instrument Set Up
- Turn Computer on
- Open FIALab for Windows 5.0
- Tighten screw on peristaltic pump
- Wearing Gloves – get reagent 2 out of the refrigerator. Put pump tubing in appropriate bottles: Carrier (water or soil), Reagent 1, and Reagent 2)
- Select appropriate standards and remove caps.
- Click on Autosampler
- Click on Create/Select Sample Definition File
- Enter # Standards including Blank
- Enter # Samples
- Feq. Of QC/Driftcor Sampling should be 20
- Pos. of QC/Driftcor Sample should be 3
- Click Create New File
- Select Nitrate – enter OPEN (this is a .csv file)
- Click Yes
- In column D starting with STD 1 of the Excel spreadsheet enter (on top of default standard values): For water: 0, 1, 2, 3, 4
- In column C enter sample numbers (on top of unknowns)
- Click X at tippy top, Click YES, Click SAVE, Click YES, Click YES
- Click Refresh and make sure standards and sample ID’s are correct.
- Click EXIT, Click EXIT
- Click Program, Click Start
- There will be a 40 sec flush time. Make sure all bubbles are gone from cell at the end of the flush time.
- Click EXIT when run is complete – click EXIT again
- Click Analysis
- Check plots, Click calibration and check calibration curve (should be 2nd order polynomial curve going through zero.)
- Click Summary
- Click Report, SAVE, File Print (use only Channel 1 results)
- Click X, Click EXIT
- Click Autosampler, Click Down, SEND, EXIT
- Click FIALab
- With Gloves, put all three tubes in soap rinse
- Click on peristaltic pump (on screen) and let pump for 3 minutes
- Click pump again to stop
- Click EXIT
- Click Autosampler, UP, SEND, EXIT
- Click EXIT, Click OK
- Loosen screw on pump tubing
- Put Reagent 2 in refrigerator
- Using Gloves - Empty waste container when full in pH sink
- Shut down computer
- Cap up standards