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Agricultural Service Laboratory

Procedures

Water Sampling

General Guidelines

Sample carefully to insure that your analytical results will present the actual sample composition.

Distribution Systems

Flush lines sufficiently to insure that the sample is representative of the supply.

Wells

Pump well sufficiently to insure the sample represents the ground water source.

River or Stream

If equipment is available, take an integrated sample from top to bottom in the middle of the stream in such a way that the sample is composited according to flow. If only a grab sample can be collected, take it in the middle of the stream at mid-depth.

Lakes and Reservoirs

Choose location, depth, and frequency of sampling depending on local conditions and the purpose of the investigation. Avoid surface scum.

Use 1

liter polyethylene bottle for collecting water samples. Before filling, rinse sample bottle out two or three times with the water being collected. Fill bottles completely and cap tightly. Avoid sample agitation and prolonged exposure to air. Have samples analyzed without delay,preferably within 1 day. To aid preservation, keep samples under refrigeration. Identify every bottle by attaching an appropriately inscribed label. Complete record form.

Types of Samples

Grab Samples

A sample collected at a particular time and place representing only the composition of the source at that time and place. If the source is known to be fairly constant in composition, then the sample may represent a longer time period or larger volume than the point at which it was collected. If the source is known to vary with time, grab samples collected at suitable intervals can document these variations. If the source varies in space rather than time, collect samples from appropriate locations.

Integrated Samples

A mixture of grab samples collected from different points simultaneously, or as nearly so as possible.

Sample Check In

  1. Laboratory numbers are assigned to the sample submission form and data sheet. The lab numbers are written on the bottles with a sharpie. The first digit of the lab number is a 0. The next two digits are the month. The last four are the sample number for the year.
  2. Samples may be disposed of after two weeks.

Alkalinity

Reagents

  1. Standardized sulfuric acid (0.1142 N H2SO4)
  2. Bromcresol green indicator solution - Dissolve 100 mg bromcresol green in 100 mL of about a 1:1 ethanol/deionized H2O solution.
  3. Phenolphthalein indicator solution - Dissolve 0.5 g phenolphthalein in 85 mL 95% ethanol and dilute to 100 mL with deionized water.

Apparatus

  1. Automatic titrator
  2. 150 mL beakers

Procedure

  1. Pour 100 mL of the sample into a 150 mL beaker.
  2. If free residual chlorine is present, add 1 drop of 1 M Na2S2O3.
  3. Measure and record pH of solution.
  4. Place beaker under electrode, stirrer and titration probe.
  5. If the pH is greater than 8.3 go to step 6.
    • If the pH is less than or equal to 8.3, go to step 9.
    • (If the pH is 4.5 or less, the alkalinity equals zero.)
  6. Put 3 drops of the phenolphthalein indicator into the sample. Solution will turn pink.
  7. Titrate to almost clear. (For set-up of control unit see next page.)
  8. Control unit will calculate % phenolphthalein alkalinity. Record on record sheet with one decimal.
  9. Put 5 drops of the bromcresol-green indicator into another 100 mL sample.
    • (Solution will turn blue.)
  10. Titrate to a clear green (no blue or yellow tints).
  11. Control unit will calculate % total alkalinity. Record on record sheet with one decimal.
  12. When finished cover electrode hole and turn control unit off.

Calculations

  1. Alkalinity, meq/L = (mL acid)(N H2SO4)(1000)/mL sample
  2. Use the phenolphthalein number in the above equation to calculate the phenolphthalein alkalinity.
  3. Use the bromcresol-green number in the above equation to calculate the total alkalinity.

Control Unit Settings

  1. Sample mg = 1000
  2. pH = 4.5 for total alkalinity
  3. pH = 8.3 for phenolphthalein alkalinity
  4. titrant normality = 0.815

Set-Up of Control Unit

  1. Turn power on. Let unit set-up.
  2. When ENTER DATE APPEARS press next step. Continue pressing next step until modeappears.
  3. Enter 1 for mode. Then continue pressing next step until pH calibr.
  4. Enter Y. Then press next step until Buffer 1 appears.
  5. Uncover electrode hole. Place electrode in yellow pH 7 solution. Press next step.
    • Wait until Buffer 2 appears.
  6. Rinse electrodes and place in pink pH 4 solution. Press next step.
  7. When calibrated, rinse electrodes and prepare to run samples.
  8. Press BALANCE PROGRAM.
  9. Press Y, then continue pressing next step until SAMPLE 1 MG appears.
  10. Type in 1000 - next step for each sample. When finished press BALANCE PROGRAM.
  11. Place sample 1 under electrode and press START.

References

  1. Jenkins, S.R., Moore, R. C. January, 1977. A Proposed Modification to the Classical Method of Calculating Alkalinity in Natural Waters. Journal AWWA.P 56.
  2. Larson, T. E., Henley, L. 1955. Determination of Low Alkalinity or Acidity in Water. Anal. Chem. 27:851.
  3. American Society for Testing and Materials. Manual of Water. 1969. 3rd Edition.P 210.

Nitrate ISE & CD Rd

Nitrate Procedure - ISE

Reagents

  • 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.

Apparatus

  • 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.

Procedure

  1. Transfer 20 mL of 1, 10, 100 ppm standards to three 100 mL beakers. Add 20 mL buffer to each standard.
  2. Transfer 20 mL of sample to a 100 mL beaker. Add 20 mL buffer to sample.
  3. Check levels of inner and outer filling solutions in reference electrode (see reference electrode manual for specifications).
  4. Follow instructions for setting up meter to standardize with the three standards. Insure that the slope is appropriate.
  5. Rinse electrodes and place into sample. Record reading directly in ppm with no decimal.
  6. Recheck standards frequently.
  7. When finished place meter in standby mode and submerge electrodes in appropriate solutions.

Reference

Standard Methods for the Examination of Water and Wastewater, 1985, 16th Edition, p. 393.

 

Nitrate-Nitrogen Flow Injection/Cadmium Reduction FIALab Nitrate Analyzer

Reagents 

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 

  1. Turn Computer on
  2. Open FIALab for Windows 5.0
  3. Tighten screw on peristaltic pump
  4. Wearing Gloves – get reagent 2 out of the refrigerator.  Put pump tubing in appropriate bottles:  Carrier (water or soil), Reagent 1, and Reagent 2)
  5. Select appropriate standards and remove caps.
  6. Click on Autosampler
  7. Click on Create/Select Sample Definition File
  8. Enter # Standards including Blank
  9. Enter # Samples
  10. Feq. Of QC/Driftcor Sampling should be 20
  11. Pos. of QC/Driftcor Sample should be 3
  12. Click Create New File
  13. Select Nitrate – enter OPEN (this is a .csv file)
  14. Click Yes
  15. 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
  16. In column C enter sample numbers (on top of unknowns)
  17. Click X at tippy top, Click YES, Click SAVE, Click YES, Click YES
  18. Click Refresh and make sure standards and sample ID’s are correct.
  19. Click EXIT, Click EXIT
  20. Click Program, Click Start
  21. There will be a 40 sec flush time.  Make sure all bubbles are gone from cell at the end of the flush time.

Collect Data

  1. Click EXIT when run is complete – click EXIT again
  2. Click Analysis
  3. Check plots, Click calibration and check calibration curve (should be 2nd order polynomial curve going through zero.)
  4. Click Summary
  5. Click Report, SAVE, File Print (use only Channel 1 results)
  6. Click X, Click EXIT

Shut Down

  1. Click Autosampler, Click Down, SEND, EXIT
  2. Click FIALab
  3. With Gloves, put all three tubes in soap rinse
  4. Click on peristaltic pump (on screen) and let pump for 3 minutes
  5. Click pump again to stop
  6. Click EXIT
  7. Click Autosampler, UP, SEND, EXIT
  8. Click EXIT, Click OK
  9. Loosen screw on pump tubing
  10. Put Reagent 2 in refrigerator
  11. Using Gloves - Empty waste container when full in pH sink
  12. Shut down computer
  13. Cap up standards

Chloride

Read sample directly on ICP or titrate as follows

Reagents

  1. Potassium chromate indicator solution - Dissolve 5 g K2CrO4 in 100 mL deionized water.
  2. Standard silver nitrate titrant, 0.030 N - Dissolve 5.0964 g AgNO3 in deionized water and carefully dilute to 1 L. To check normality of this solution, titrate against a standard sodium chloride solution. Store silver nitrate solution in a brown bottle. (You don't need to check normality if you weigh out the AgNO3 accurately.)
  3. Standard sodium chloride, 0.015 N - Dissolve 0.4384 g NaCl (dried at 140oC) in deionized water and dilute to 500 mL.

Apparatus

  1. 25 mL refilling buret and stand.
  2. 500 mL volumetric flask.
  3. 150 mL beaker.
  4. Magnetic stirrer.

Procedure

  1. Pour 50 mL of the sample into a 150 mL beaker.
  2. If sulfide, sulfite, or thiosulfate is present, add 1 mL H2O2 (30%) to the sample and stir for 1 minute.
  3. If necessary, adjust sample pH to within the range of 7 - 10 with H2SO4 or NaOH.
  4. Fill refilling buret bottle with silver nitrate titrant.
  5. Adjust solution level to 0.0 mL.
  6. Add 5 drops of the indicator solution to the sample.
  7. Titrate a blank with standard AgNO3 to a persistent light orange-red to use forend-point recognition. (A 50 mL distilled water blank giving a value of 0.2 to 0.3 mL is usual.) If the blank requires more than 0.3mL the solution in the buret may have decomposed. Refill buret and titrate another blank. Make sure blank reads appropriately beforetitrating samples.
  8. Titrate the sample to the same light orange-red color. Calculate ppm Cl and record with one decimal. (Be consistent in end-point recognition.)
  9. Dispose of samples in carboy for pick up by hazardous materials manager.

Calculation

  1. ppm Cl- = (mL AgNO3 for sample) x N AgNO3 x 35450 / mL sample
  2. (mL AgNO3 for blank = 0 if sample was not diluted with distilled water. If sample was diluted, subtract value for amount of distilled water used.)

References

  1. Standard Methods for the Examination of Water and Wastewater. 1985. 16th Edition. P 286.  

pH

  1. Read pH of sample using pH electrode and meter. Use appropriate buffers for calibration.
  2. Record value with one decimal.

Electrical Conductivity

Conductivity Meter 411

  1. Remove cover. Turn meter on.
  2. Make sure mode is microS/cm.
  3. Make sure an A appears in upper left corner by pressing auto read.
  4. Calibrate.
  5. Leave sensor in air. Press CAL. (a 1 appears - lower right.)
  6. Let stabilize. An [/-A] appears in upper left corner.
  7. Place sensor in 1413 solution. Make sure sensor is submerged.
  8. Press CAL. (a 2 appears - lower right.)
  9. Let stabilize. An [/-A] appears.
  10. Rinse sensor thoroughly.
  11. Measure sample.
  12. Place sensor in sample. Make sure sensor is submersed.
  13. Press READ.
  14. Let stabilize. An [/-A] appears.
  15. Take reading.
    1. If microS/cm => move decimal 3 places to left.
    2. If mS/cm=> take direct reading.
    3. Record with 2 decimals.
  16. Rinse between samples.
  17. Leave probe in air.
  18. Turn off meter.
  19. Cover.

Minerals

  1. Determine P, K, Ca, Mg, S, Fe, Na, and B by ICP.
  2. Record P, K, Ca, Mg, Fe, and B with one decimal.
  3. Record S and Na with no decimal.
  4. For P, K, Ca, Mg, and S, take readings directly from ICP printout.