selected methods of water analysis

8/7/2019 Selected Methods of Water Analysis

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Selected Methods of Water Analysis

Brenda Mottle

Earth Science ProgramUniversity of Calgary

2007


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Disclaimer

The contents of this manual were prepared as a guide for educational purposes. The

author assumes no liability for the use or application of any method, process, equipment

or information contained in this document.

While every effort was made to assure accuracy, the author assumes no responsibility for

errors either typographical or in content.

The methods in this manual involve the use of hazardous material, methods and

equipment, however no attempt was made to mitigate any risk. The user is responsible

for knowing, understanding and following standard laboratory safe practices.

Suggested citation:

Mottle, B.J. 2007. Selected Methods of Water Analysis. University of Calgary,unpublished lab manual. 28pp.


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Selected Water Methods

Table of Contents

1.0 TAKING A WATER SAMPLE........................................................................21.1BEFORE YOU LEAVE FOR THE FIELD .................................................................21.2BOTTLE PREPARATION ...................................................................................21.3BOTTLE WASHING..........................................................................................21.4 LABELLING AND FIELD SHEETS .......................................................................21.5TAKING A SAMPLE WHILE WADING ....................................................................31.6 TAKING A SAMPLE USING A KEMMERER SAMPLER .............................................4

2.0 CONDUCTIVITY.............................................................................................5

2.1EQUIPMENT ...................................................................................................52.2PROCEDURE..................................................................................................5

3.0 PH...................................................................................................................7

3.1EQUIPMENT ...................................................................................................73.2PROCEDURE..................................................................................................7

4.0 TOTAL SUSPENDED SOLIDS AND TURBIDITY..........................................9

4.1EQUIPMENT .................................................................................................104.2PROCEDURE................................................................................................104.3CALCULATIONS ............................................................................................104.4REFERENCES...............................................................................................10

5.0 METALS (CA, MG, NA, K, FE, AL AND MN)...............................................11

5.1EQUIPMENT .................................................................................................115.2REAGENTS ..................................................................................................125.3PROCEDURE................................................................................................135.4CALCULATIONS ............................................................................................13

6.0 NUTRIENTS .................................................................................................14

6.1NITRATES....................................................................................................146.1.1 Equipment...........................................................................................146.1.2 Filtering procedure..............................................................................14

6.2AMMONIA ....................................................................................................186.3PHOSPHATES...............................................................................................21

7.0 ALKALINITY.................................................................................................24

7.1EQUIPMENT .................................................................................................247.2REAGENTS ..................................................................................................247.3SAMPLE ANALYSIS .......................................................................................25


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1.0 Taking a Water SamplePlan ahead! The selection of the size of bottles and the preservative methods (ifany) are dependent on the analysis you will require. Some analyses are done inthe field while others are taken back to the lab. Some analyses are time

dependant and hold times (the time you have before the sample degrades to thepoint where analysis can not be done) will vary.

1.1 Before you leave for the field

1. Make sure that you pack everything you might need. Making anequipment list is often the easiest way to remember everything.

2. It is wise to label bottles and make field sheets prior to leaving thelab.

3. Pack empty bottles into coolers and dont forget the ice packs.4. Take extra bottles in case you lose, contaminate or break one of

the bottles.

5. Make sure that all the field equipment is in usable condition andthat it is calibrated before leaving the lab.

1.2 Bottle Preparation

1. Samples are generally collected in polyethylene or glass bottles.Bottle type is parameter dependant.

2. Depending on the analysis you require, some bottles might need apreservative. For example, samples taken for metal analysis wouldneed 2 mL of Nitric acid added to a 1L bottle. This acid is generallyadded to clean bottles in the lab prior to sampling. Transportingthis acid and/or other hazardous goods requires that you are

certified in the Transportation of Dangerous Goods (TDG) and thatyou fill out the specific forms before you leave. If you do not havethis certification or fill out the forms, you may be fined or have yourvehicle confiscated by provincial inspectors who may stop yourvehicle at any time.

1.3 Bottle Washing

1. Most standard operating procedures for bottle preparation dictatethat you acid wash the bottles prior to use. This is particularlynecessary if you are reusing bottles where prior contaminates mightstill adhere to the bottle, even after washing.

1.4 Labelling and Field Sheets

1. Each bottle should be labeled with a unique identifier. Otherinformation about the site should be written on the field sheets. Donot write directly on the bottle and do not use water soluble pen orpencil. Make sure labels will not come off the bottle if it gets wet.


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2. Fill out appropriate field data sheets with all other site descriptorsincluding bottle number, site name and location, weather conditions(if applicable), date, time, depth of sample and distance from thesteam bank or any other information that is pertinent to yoursample. The design of the field sheet may vary depending on your

employer and/or the project you work on. Here is an example ofone type of field sheet.

Do not lose or misplace your field sheets. They

are the only records that you will have to cross-

reference your sample to the bottle number.

1.5 Taking a sample while wading

1. Wearing waders and a life vest and observing safety protocol, wadeinto the water trying not to disturb bottom sediment. If sampling ina stream, stand facing upstream. Collect the sample on yourupstream side, in front of you.


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2. Remove the cap and hold the bottle near the base while plunging it(opening side down) below the water surface.

3. Collect the water sample 8-12 (20-30 cm) beneath the surface ormid-way between the surface and the bottom if stream is shallow.

4. Turn the bottle under the water into the current and away from you.

5. Tilt the bottle upwards to fill. Hold the bottle at arms length while itfills.6. Rinsing the bottle prior to sampling is not advised particularly if the

bottle already contains preservative. If the bottle was cleanedbefore leaving the lab, it should still be clean. Be careful to avoidtouching the bottle mouth with your fingers or your clothing.

7. Cap the bottle leaving 1 air space so that the sample can beshaken prior to analysis. Note: Leaving air space is notappropriate for some types of analysis (e.g. Dissolved oxygen )

8. Place samples in a cooler with ice packs and transport to lab or setup to measure your field parameters.

ReferencesEnvironment Canada. 2005. Northern Waters: A guide to Designingand Conducting Water Quality Monitoring in Northern Canada.Northern Ecological Monitoring and Assessment Network (EMAN-North).http://www.emannorth.ca/reports/EN_WQManual_Full_TOC.pdf

1.6 Taking a sample using a Kemmerer sampler

1. When deeper samples are needed, a Kemmerer sampler may beused. This is a device that consists of a plastic hollow cylinder withremotely activated stoppers at either end. The sampler is loweredto a desired depth with a graduated line. Once the desired depth isreached, a heavy metal slug or messenger, attached to the line, isreleased. This triggers the release mechanism, pulling the stoppertight against the ends, trapping the water sample inside.

2. When the sampler is pulled up, the sample is put into a bottlethrough a spigot.

A note about significant figures..When measurements are added or subtracted, multiplied or divided,the answer can contain no more significant figures than the leastaccurate measurement.When you report a measurement, that number can not appear to bemore accurate than the equipment used to make themeasurement allows.
http://www.emannorth.ca/reports/EN_WQManual_Full_TOC.pdfhttp://www.emannorth.ca/reports/EN_WQManual_Full_TOC.pdf


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2.0 ConductivityConductivity is the measure of the ability of the water to conduct an electricalcurrent. Conductivity in water is affected by the presence of inorganic dissolvedsolids such as chloride, nitrate, sulfate (cations) or sodium, magnesium, calcium

(anions). Conductivity is affected by temperature (the warmer the water, thehigher the conductivity). For this reason, all measurements are reported asconductivity at 25C. Conductivity is measured in microSiemens per centimeter(uS/cm) or micromhos per centimeter (umhos/cm).

Conductivity in streams and rivers is primarily affected by the geology of the areathrough which the water flows. For example, streams that run through areas thatare composed of granite have lower conductivity because granite is more inertand does not dissolve into ionic components. Streams and rivers that runthrough limestone have higher conductivity.Discharges to streams and rivers can also affect the conductivity. A leaking

sewage system would raise the conductivity because of the presence of nitrates,phosphates and chlorides. An oil spill will lower the conductivity because organiccompounds do not conduct electrical current very well.

Conductivity is a useful measure of water quality. Every body of water tends tohave a fairly constant range of conductivity, that, once established, can be auseful comparison for measurements. Significant changes could indicate that adischarge or some other source of pollution has entered the system.

2.1 Equipment

1. Conductivity meter Accumet AP 502. Conductivity probe3. Conductivity standard4. 50 mL nalgene beakers5. Deionized water6. Wash bottles

2.2 Procedure

1. Install batteries in meter.2. Attach the conductivity probe to the meter using the BNC

connector. This probe is temperature compensating and all

conductivity measurements are reported to 25C. Remove theprotective cover from the probe.

3. Press on/off.4. Press modeand select conductivityand press enter.5. Press std and press 1 (enter a standard). Enter the value of

standard and follow the prompts.6. Pour about 25 mL of the conductivity standard into one of the

beakers


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7. Rinse the probe with deionized water. Immerse the probe in thebuffer and stir moderately. Remove bubbles trapped in the probeby gently moving the probe up and down.

8. The meter is now standardized. This procedure is only done on aweekly basis.

9. The meter is now ready to measure your sample10. Shake the bottle containing the sample. Rinse a 50 mL beaker witha small portion of the sample and discard. Repeat 3 times.

11. Pour sample into the container until about full.12. Place probe into the sample and wait for the conductivity to

stabilize.13. Record the conductivity for each sample.14. Turn the meter off and detach the probe. Remember to replace the

protective cover.


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3.0 pHpH is a measure of acidity or alkalinity of water ranked on a scale of 0 14.Acidity increases as the pH gets lower and alkalinity increases as the pH getshigher. A pH of 7.0 is said to be neutral. The pH scale is logarithmic so, for

example, an increase from pH 8.0 to pH 9.0 increases the alkalinity 10- fold. ThepH scale is unitless.

pH affects many chemical and biological processes in water. For example, mostaquatic animals prefer water with a pH range between 6.5 and 8.5. Low pHvalues can allow toxic elements and compounds to become available for uptakeby aquatic plants and animals.

Changes in acidity can be caused by atmospheric deposition (acid rain), acid andalkaline effluents from industries such as mining or from natural sources such aslimestone or organic acids produced by vegetative decomposition.

3.1 Equipment

1. pH meter Accumet AP 502. pH electrode3. pH buffers (4, 7 and 10)4. 50 mL nalgene beakers5. Deionized water6. Wash bottles

3.2 Procedure

1. Install batteries in meter.2. Attach the pH electrode to the pH meter using the BNC connector.

Attach the temperature probe to the meter by lining up the whitearrow and the line on the electrodes Twist-Lock connector andpushing into place. Remove the electrode from the pH 4 soakingsolution.

3. Press on/off.4. Press modeand select 1-pHand press enter.5. Press std and press 1 (enter a buffer)6. Pour about 25 mL of pH buffer 7 into one of the beakers7. Rinse the electrode with deionized water. Immerse the electrode in

the buffer and stir moderately Follow the prompts on the display.8. The meter automatically recognizes the buffer and waits for a

stable signal (denoted by S). Discard the buffer in the wastecontainer provided.

9. Repeat steps e-h above for buffer 4 and buffer 10.10.The meter is now standardized. This procedure is only done daily

or between sample sites.11. The meter is now ready to measure your sample


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12. Shake the bottle containing the sample. Rinse a 50 mL beaker witha small portion of the sample and discard. Repeat 3 times.

13. Pour sample into the container until about full.14. Place electrode into the sample and wait for the pH to stabilize.15. Record the pH for each sample. You may notice that the probe also

measures the temperature of the sample. This pH meter istemperature compensating and will report the pH as if the samplewere at 25C. Discard the sample and rinse the container with DIwater before repeating steps k through m for each sample.

16. Turn the meter off and detach the pH electrode. Return theelectrode to the pH 4 soaking solution.


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4.0 Total Suspended Solids and Turbidity

Turbidity is a measure of how water scatters light. Water with many smallparticles scatter much of the light making the water appear cloudy or murky.

Total suspended solids (TSS) are the solids in water that can be trapped by afilter (GFC grade, 1.3um pore size). These solids are some of the same particlesthat contribute to turbidity, however, turbidity also includes the very fine particlesthat are not trapped by the GFC filter. In certain circumstances, turbidity mightbe high but TSS low because of these small colloidal particles. Suspendedmaterials include soil particles, algae, plankton, microbes or other substances.Turbidity can also affect the colour of the water.

High levels of turbidity and total suspended solids may be associated with:1. Soil erosion from agricultural practices and construction2. Domestic and industrial wastewater discharge

3. Urban runoff from parking lots or roads, etc.4. Flooding5. Eutrophication (algae growth from nutrient enrichment)6. Dredging operations7. Removal of riparian vegetation leading to stream bank erosion8. Large numbers of bottom feeding fish (such as Carp) that stir up

bottom sediments.

TSS is a primary water quality indicator because:1. Suspended solids limit the quality of recreation and drinking water2. Turbidity and TSS are significant to all aquatic life. Aquatic plants

need light to carry out photosynthesis. Turbidity causes gilldamage in fish, makes it difficult for them to forage for food andreduces their resistance to disease.

3. Reduced rates of photosynthesis cause less dissolved oxygen tobe released into the water. This in turn can lead to fish kills.

4. High turbidity can cause an increase in surface water temperaturebecause suspended particles absorb heat for the sunlight. This cancause dissolved oxygen levels to fall even further because warmwater can hold less dissolved oxygen.

5. High turbidity can often mean higher concentrations of bacteria,nutrients, pesticides and metals.

6. High turbidity can cause problems for industrial users becausesolids may clog pipes or machinery.

Samples may be taken in glass or plastic bottles. The volume necessarydepends upon the amount of solids present, however, 1L is sufficient in mostcases.


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4.1 Equipment

1. GFC glass fiber filters, 5,5 cm2. Buchner Funnels and adapters3. 1L filter flask4. 100 mL graduated cylinder

5. Constant temperature oven6. Aluminum weighing dish7. Analytical balance (4 decimal places)8. Desiccator

4.2 Procedure

1. With forceps, transfer a glass fiber filter paper (GFC) to analuminum weighing dish. Dry in oven at 103-105 C for 24 hours

2. Cool in a desiccator and weigh to 4 decimals. Record this weight.Choose a sample volume to yield between 2.5 and 200 mg dried

residue. If complete filtration takes more than 10 minutes,decrease sample volume.

3. Assemble filtering apparatus with a preweighed filter. Turn on thevacuum and filter a small volume of water to seat the filter paper.Shake the water sample vigorously and pour a subsample into agraduated cylinder before filtering. You must record the volume ofwater that you filter. Continue measuring subsamples of water untilyou achieve the appropriate yield.

4. Wash filter with 3 10mL portions of deionized water and continuesuction for about 3 minutes prior to removing the filter from the filterapparatus.

5. Return the filter paper to the aluminum weighing dish and dry inoven at 103-105 C for 24 hours.

4.3 Calculations

mg total suspended solids/L = (A-B) x 1000sample volume, mL

where:A = weight of filter + dried residue, mgB = with of filter, mg

4.4 References

Clesceri, Lenore S., A.E. Greenberg and A.D. Eaton, Ed. 1998. StandardMethods for the Examination of Water and Wastewater. United BookPress Inc. Baltimore, Maryland, USA. , Part 2540, pp 2-57.


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5.0 Metals (Ca, Mg, Na, K, Fe, AL and Mn)

Metals occur naturally in both surface and groundwater but may also be present

as a consequence of mans activities. The effects may range from beneficial tohighly toxic depending on the concentration.

Metal ions are dissolved in water when the water comes in contact with rock orsoil containing metals. Metals can also enter the water through discharges fromsewage treatment plants, industrial plants or from processes such as mining.

The natural concentration of metals in water varies with the concentration ofmetals in the soil, the underlying geological structures, the acidity of the water,the concentration of organic matter and the amount of particulate matter.

Before collecting a sample, determine what fraction is to be analyzed (dissolved,suspended or acid-extractable). Samples may be collected in glass orpolyethylene bottles. All bottles should be acid rinsed. Samples that have beenacidified and stored at 4C are stable for up to 6 months.

Dissolved: Samples used for analysis should be free of turbidity or filteredthrough a 0.45um filter which has been previously washed with dilute HNO3.Filter the sample at time of collection and acidify to pH


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8. 125 mL nalgene bottles with lids

5.2 Reagents

1. Purchased stock standards (1000 ppm) for metals

2. Interference agents(a) Lanthanum solution (1% La, 10% spike = 0.1% La in eachsample)

11.7 g La2O3 dissolved in 500 mL of dH2O with 40 mL HCladded and diluted to 1000 mL with H2O

3. Intermediate stock solution (100 ppm in Mn, Mg, Ca, K, Na, Fe)Pipette 10 mL of each stock (1000 ppm) into one 100 mL

volumetric flask. Dilute to the mark with dH2O.4. Working standards

Pipette appropriate amount of intermediate stock standard(100ppm) into 100 mL volumetric flasks and dilute to the mark with

extraction solution

mL IntermediateStandard in 100 mL

volumetric flask

final conc. (ppm)

0.1 0.10.3 0.30.5 0.51.0 1.02.0 2.03.0 3.0

4.0 4.05.0 5.0

Working Standards

5. Before diluting to the mark also add 1.0, 5,0 and 10.0 mL of 1000ppm Al to 3 of the above standards to give 10, 50 and 100 ppm Al.Pour standards into 125 mL nalgene bottles and add 10 mL (10%)of Lanthanum solution to each standard.

Element Upper Linear Range(mg/L)

Mn 2.0Mg 0.5K 2.0Fe 5.0Ca 5.0Al 100.0Na 1.0


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6. Use the appropriate standard range for each element knowing thateach element has a different linear range.

5.3 Procedure

1. Set the spectrophotometer to appropriate settings for a particularelement. See instrument instruction manual.

2. Calibrate for the standards according to instrument instructions.3. Read the concentration of the samples and the sample blank.

The sample blank is a sample consisting of the extractant solutionand the interference agent.

4. Check calibration every 10th sample. Analyze one of thestandards as a sample and if the concentration is not close to theknown value then recalibrate.

5. Run duplicate samples every 20 samples.6. Check recovery with sample spike. Add a known concentration ofstandard to a known sample and measure the concentration ofthe spike. The recovery is the measured concentration divided bythe estimated value. For example, if the sample concentrationmeasured 8 ppm and the spike was a 1:1 (vol:vol) mix of the 10ppm standard and this sample, the estimated concentration of thespike would be (8+10)/2 = 9 ppm. If, upon measuring theconcentration of this spike your reading was 9.2 ppm, then therecovery is 9.2/9.0 x 100 = 102.2%.

5.4 Calculations

ppm (ug/g) = ( sample- blk) x vol (L) x 1 x 1000 ug/mg x DFwt (g)

where vol= volume of extractant solution used in litreswt = dry weight equivalent of soil in gramsDF = dilution factor if usedblk = blank value


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6.0 Nutrients

6.1 Nitrates

Analyze as soon as possible after collection. Maximum storage timerecommended is 48 hours. Refrigerate at 4 C. For longer storage of

unchlorinated samples, preserve with 2 mL of conc. Sulfuric acid (per literof sample) and store at 4 C for up to 28 days. If water samples havebeen acidified, the pH must be adjusted to between 5 and 9 using SodiumHydroxide or Ammonium hydroxide prior to analysis. To eliminateadjustment of samples individually, the ammonium chloride reagent canbe made up to include 11.5 mL of 10% w/v Sodium hydroxide per liter ofsolution.

6.1.1 Equipment

a. 0.45um cellulose acetate filters, 4.7 cmb. Membrane filter apparatusc. Small bottles (25-50 mL polyethylene), with lids, acid

washedd. Technicon Autoanalyzer with Nitrate modulee. Reagents as stipulatedf. 4 mL sample cups

6.1.2 Filtering procedure

a. Assemble the membrane filter apparatus with a celluloseacetate filter paper in place. Use forceps to handle the filterpaper and do not touch it with your hands

b. Turn on the vacuum.c. Filter 3 20 mL portions of deionized water through the filter.d. Turn off the vacuum and discard the water in the filter flask.

Reassemble the filtration apparatus and turn on the vacuum.e. Shake your sample well and pour about 50 mL in the filter

funnel.f. Collect the filtrate and pour into labeled, acid washed bottles.


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6.2 Ammonia

The most reliable results for ammonia are obtained on fresh samples. Samples

that cannot be analyzed with 24 hours should be frozen unpreserved at -20Cand analyzed within 28 days. Since turbidity interferes with the analysis,samples must be filtered. Use the same filters and filtering procedure asindicated for nitrates. Samples may be collected in glass or plastic bottles.


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6.3 Phosphates

Samples analyzed for phosphates should be filtered immediately with 0.45 ummembrane filters using the same method as specified for nitrates. Samples maybe collected in plastic or glass bottles. Samples should be kept at 4C andanalyzed with 24 hours or preserved by freeing below -10C.


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7.0 Alkalinity

Alkalinity is a measure of the capacity of a water to absorb H+ ions without asignificant drop in the pH. The principal ions contributing to alkalinity arehydroxide (OH-), carbonate (CO3

2-) and bicarbonate (HCO3-). Alkalinity is

reported in units of mg/L CaCO3. Water samples must not be filtered, diluted oraltered in any way. Samples should be collected in glass or polyethylene bottlesand kept at 4C. Bottles must be completely filled (no head space) and tightlycapped. Avoid sample agitation and prolonged exposure to air. Samples shouldbe analyzed within 14 days of sampling.

7.1 Equipment

1. Graduated cylinder2. 1L volumetric flask3. 50 mL volumetric flask

4. 10 mL pipet5. 150 mL beaker6. 50 mL pipet7. 250 mL beaker8. Analytical balance9. Constant temperature oven10. Buret11. pH meter with pH buffers for standardizing12. Magnetic stirrer and stirring bar

7.2 Reagents0.2 N H2SO4

1. Using a graduated cylinder, measure out approximately 5.55 mLof concentrated H2SO4.

2. Fill a 1 L volumetric flask with 500 mL of DI water and slowlypour the acid into the water.

3. Fill the volumetric to volume with DI water.4. The concentration of this acid is approximately 0.2 N

0.01 N H2SO41. Measure out 50 mL of 0.2 N H2SO4 with a 50 mL volumetric

flask.2. Fill a 1L volumetric flask with about 500 mL of DI water and

carefully pour the acid into the water.3. Fill the 1L volumetric to volume with DI water.4. The concentration of this acid is approximately 0.01N


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0.02N Na2CO31. Weight out 1.060 g of Na2CO3 which has been dried in an oven

at 105C for 24 hours. The weight just needs to be around thisamount but you must know what it is exactly.

2. Fill a 1L volumetric flask with about 500 mL of DI water and pour

the Na2CO3 into the water. Use a wash bottle to wash all thecrystals into the volumetric flask.3. Fill the volumetric to volume with DI water.4. Calculate the exact concentration of this solution by the

following formula:Normality (N) = wt of Na2CO3 (g) x 1 equivalent

Volume (L) 53g Na2CO35. This number should be close to 0.02.

Standardizing the H2SO41. Pipet 10.0 mL of Na2CO3 solution into a 150 mL beaker. Make

3 replicates.2. Fill the buret with 0.01N H2SO4 and note the start volume.3. Place a stir bar in the beaker and place on a magnetic stirrer.

Slowly turn on so that the solution stirs gently.4. Place a pH electrode into the beaker in such a way that it does

not interfere with the stir bar.5. Open the buret stopcock and slowly introduce H2SO4 to the

beaker until the pH reaches 4.5.6. Note the end volume of H2SO4.7. Repeat for all 3 reps, rinsing the pH probe between samples.8. Calculate the concentration (Normality) of H2SO4 as follows:

N = V1 x NV2

Where V1 = volume of Na2CO3 aliquot in Litres (i.e. 0.01L)N = normalilty of Na2CO3 (i.e 0.02N)V2 = volume of H2SO4 used in titration in Litres

Average the 3 reps

7.3 Sample Analysis

1. Using the 50 mL pipet, measure 100 mL of your sample into a250 mL beaker.

2. Add the stir bar and immerse the pH electrode.3. Fill the buret with standardized H2SO4 solution and note thestart volume.

4. Note the initial pH.5. If the initial sample pH is between 8.3 and 6.2, add acid until pH

4.5 is reached.


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6. If you find that total alkalinity measures less than 20 mg/L, youshould not only measure the volume to pH 4.5 but also to pH4.2.

Calculations for Total Alkalinity > 20 mg/L

Total Alkalinity (mg/L CaCO3) = VB x N H2SO4 x 50000 mg CaCO3VS equivalent

Where VB = volume of H2SO4 to reach equivalence point pH 4.5 (L)VS = volume of sample (L)N H2SO4 = Normality of titrating acid

Calculation for Total Alkalinity < 20 mg/L

Total Alkalinity (mg/L CaCO3) =(2 VB VC) x N H2SO4 x 50000 mg CaCO3VS equivalent

Where VB = volume of H2SO4 to reach equivalence point pH 4.5 (L)VC = volume of H2SO4 to reach equivalence point pH 4.2 (L)VS = volume of sample (L)N H2SO4 = Normality of titrating acid

selected methods of water analysis

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