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Agricultural Service Laboratory
Irrigation Water Analysis Procedures
September 10, 1999
TABLE OF CONTENTS
Water Sampling
Sample Check In
Alkalinity
Nitrate ISE and Cd Rd
Chloride
pH
Electrical Conductivity
Minerals
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 PROCEDURE
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
Alkalinity, meq/L = (mL acid)(N H2SO4)(1000)/mL sample
Use the phenolphthalein number in the above equation to
calculate the phenolphthalein
alkalinity.
Use the bromcresol-green number in the above equation to
calculate the total
alkalinity.
CONTROL UNIT SETTINGS
Sample mg = 1000
pH = 4.5 for total alkalinity
pH = 8.3 for phenolphthalein alkalinity
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 mode
appears.
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 PROCEDURE - ISE
REAGENTS
1. Boric acid preservation solution - Dissolve 6.2 g boric
acid in 100 mL hot distilled water.
2. 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.
3. 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.
4. 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
1. Orion ionanalyzer
2. Nitrate ion electrode
3. Reference electrode
4. Magnetic stirrer
5. 150 mL beakers, 100 and 1000 mL volumetric flasks.
6. Plastic bottles for solution storage.
7. 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
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 – 6 for water, 5 for soil
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 for STD 1 through std 6 of the Excel spreadsheet enter
(on top of default standard values):
For water:
0, 1, 2, 3, 4, 5
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 PROCEDURE (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 for
end-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
before
titrating 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
ppm Cl- = (mL AgNO3 for sample) x N AgNO3 x 35450 / mL sample
(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 PROCEDURE
Read pH of sample using pH electrode and meter. Use
appropriate buffers for
calibration.
Record value with one decimal.
ELECTRICAL CONDUCTIVITY PROCEDURE
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.
If microS/cm => move decimal 3 places to left.
If mS/cm=> take direct reading.
Record with 2 decimals.
16. Rinse between samples.
17. Leave probe in air.
18. Turn off meter.
19. Cover.
MINERALS
Determine P, K, Ca, Mg, S, Fe, Na, and B by ICP. Record P, K,
Ca, Mg, Fe, and B with
one decimal. Record S and Na with no decimal. For P, K, Ca, Mg, and S, take
readings
directly from ICP printout. |