pH Measurements in Today’s Lab

Midland Scientific Feb. 19, 2014

Don IvyWestern US and Canada Sales ManagerThermo Scientific – Orion Products

2

What is pH?

• The Theoretical Definition

pH = - log aH

• aH is the hydrogen ion activity. • In solutions that contain other ions, activity and concentration are not

the same. The activity is an effective concentration of hydrogen ions, rather than the true concentration; it accounts for the fact that other ions surrounding the hydrogen ions will shield them and affect their ability to participate in chemical reactions.

• These other ions effectively change the hydrogen ion concentration in any process that involves H+.

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What is pH?

• pH = “Potential Hydrogen” or Power of Hydrogen• The pH of pure water around room temperature is about 7. This is considered

"neutral" because the concentration of hydrogen ions (H+) is exactly equal to the concentration of hydroxide (OH-) ions produced by dissociation of the water.

• Increasing the concentration of H+ in relation to OH- produces a solution with a pH of less than 7, and the solution is considered "acidic".

• Decreasing the concentration H+ in relation to OH- produces a solution with a pH above 7, and the solution is considered "alkaline" or "basic".

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What is pH?

• The pH Scale

• Each pH unit is a factor 10 in [H+]• pH of Cola is about 2.5. This is

10x more acidic than Orange Juice (pH of 3.5).

• Cola is 100x more acidic than Beer!

Substance pH

Hydrochloric Acid, 10M -1.0

Lead-acid battery 0.5

Gastric acid 1.5 – 2.0

Lemon juice 2.4

Cola 2.5

Vinegar 2.9

Orange or apple juice 3.5

Beer 4.5

Acid Rain <5.0

Coffee 5.0

Tea or healthy skin 5.5

Milk 6.5

Pure Water 7.0

Healthy human saliva 6.5 – 7.4

Blood 7.34 – 7.45

Seawater 7.7 – 8.3

Hand soap 9.0 – 10.0

Household ammonia 11.5

Bleach 12.5

Household lye 13.5

Representative pH values

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pH Measurement System

• When two solutions containing different concentrations of H+ ions are separated by a glass membrane, a voltage potential is developed across the membrane. (Sensing electrode)

• A voltage potential is also generated from the reference electrode.• The pH meter measures the voltage potential difference (mV) between the

sensing electrode and the outside sample (reference electrode)

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pH Measurement System

• The pH Meter• Acts as a volt meter• Translates electrode potential (mV) to

pH scale• Meter functions

• Stores calibration curve• Adjusts for temperature changes• Adjusts electrode slope• Signals when reading is stable

• Features• mV and relative mV scales• Autocalibration/autobuffer recognition• Number of calibration points• Display information• RS232 or recorder outputs• Datalogging• GLP/GMP compliant

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pH Measurement System

• The pH Electrode• Combination• Sensing Half-Cell• Reference Half-Cell

• Internal filling solution (Sensing)• Buffer solution

• Outer Filling solution (Reference)• Saturated AgCl, KCl

• Common References• Calomel• Ag/AgCl• ROSS™

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pH Measurement System – Reference Electrode

• In a two electrode system a reference electrode is needed to complete the “circuit”.

• Combination electrode has the reference built in.

• The reference wire or element is typically encased in Saturated AgCl or KCl

• The reference must have a “liquid” connection to the sample in order to generate a voltage potential.

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pH Measurement System – Reference Types

• Calomel Reference (Hg/Hg2Cl2)• Calomel electrodes is very stable and is ideally suited for use with TRIS buffers

and sample solutions containing proteins and other biological media. • Also used where samples contain metal ions, sulfides, or other substances that will

react with Ag or AgCl .• Advantages

• Low Cost, Good Precision (±0.02 pH)• Disadvantages

• Limited body styles, Temperature Hysteresis, Contains Mercury!

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pH Measurement System – Reference Types

• Single Junction Silver/Silver Chloride Reference (Ag/AgCl)• Recommended for all applications except those involving TRIS buffer, proteins,

metal ions, sulfides or other substances that will react with either Ag or AgCl. • Advantages

• Mid-range cost, Variety of body styles, Refillable or gel-filled, Good Precision (±0.02 pH)

• Disadvantages• Temperature Hysteresis, complexation in samples such as: TRIS, proteins, sulfides

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pH Measurement System – Reference Types

• Double Junction Silver/Silver Chloride Reference (Ag/AgCl)• The double junction Ag/AgCl reference isolates the reference, making it

ideally suited for all types of samples. • Advantages

• Mid-range cost, Variety of body styles, Refillable or gel-filled, Good Precision (±0.02 pH)

• Disadvantages• Temperature Hysteresis

• Mercury Free alternative to the Calomel Reference

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pH Measurement System – Reference Types

• ROSS™ Reference• Double Junction Iodine/Iodide redox couple• The ROSS™ reference is ideally suited for all sample types and all

temperature ranges. • Advantages

• Variety of body styles, Unmatched Precision (±0.01 pH), Fast response, Stable to 0.01 pH in 30 seconds over 50 °C temperature change, Drift less than 0.002 pH units/day

• Disadvantages• Cost

• Mercury Free alternative to the Calomel Reference

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pH Measurement System - Junctions

• The electrode junction is where the Outer fill solution (reference) passes from inside the electrode body to the sample completing the “circuit”.

• The type of junction is a good indicator of how the electrode will perform in different samples.

• Three basic types of junctions• Wick• Ceramic• Open

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pH Measurement System - Junctions

• The Wick Junction• Glass fiber, fiber optic bundles,

Dacron, etc.• Advantages

• Used in rugged epoxy bodies• Good for aqueous samples

• Disadvantages• Will clog if sample is “dirty” or

viscous• Not as “fast” as other junctions

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pH Measurement System - Junctions

• The Ceramic Junction• Porous ceramics, wooden plugs,

porous Teflon, etc.• Advantages

• Good all-purpose junction• Ideally suited for most lab

applications • Disadvantages

• Will clog if sample is “dirty” or viscous

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pH Measurement System - Junctions

• The Open Junction• Sure-Flow, Laser Drilled Hole,

Ground Glass Sleeve, etc.• Advantages

• Junction will never clog• Can be used in all sample types• Ideal choice for “dirty” or viscous

samples• Can be used in non-aqueous

samples• Disadvantages

• Sure-Flow Junction has a high flow rate of fill solution (2 ml/day)

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pH Measurement System – Electrode Types

• Refillable or Low Maintenance Gel?• Low Maintenance Gel Electrodes

• Easy to use• Rugged epoxy body• 0.05-0.1 pH precision• Slower response rate• 6 month average life• Gel memory effects at junction

• Refillable Electrodes• Fill/drain electrode• Wide applicability• Glass or epoxy body• 0.02 pH precision• Faster response rate• 1 year minimum life• Replaceable fill solution

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pH Measurement System – Electrode Types

• Polymer or Low Maintenance Gel?• Low Maintenance Gel Electrodes

• Easy to use• Rugged epoxy body• 0.05-0.1 pH precision• Slower response rate• 6 month average life• Gel memory effects at junction

• Polymer Electrodes• Low maintenance• Easy to use• Glass or epoxy body• 0.02 pH precision• Faster response rate• 1 year minimum life• Double junction design

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pH Measurement System - Electrode Selection

• Select proper reference for application• ROSS™, Single or Double Junction Ag/AgCl• Remember that Calomel contains Mercury!

• Select proper junction for application• Wick, Ceramic, Open, Sure-Flow, etc.

• Select appropriate body style• Standard, semi-micro, micro, rugged bulb, spear tip, flat surface

• Select appropriate body type• Glass body, epoxy body

• Other considerations• Refillable, Gel, or Polymer?• Built in Temperature Probe?

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pH Calibration

• The Nernst Equation

E = E0 - RT/nF log aH

E = measured potentialE0 = reference potentialR = Universal Gas ConstantT= Temperature (at 25 °C)n = Number of electronsF = Faraday ConstantaH = Hydrogen Ion activity

Slope = RT/nF = 59.16mv @ 25 °C

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pH Calibration

• When you are calibrating, you are determining the electrodes slope as it relates to the theoretical slope defined by the Nernst Equation

• Newer meters automatically calculate slope• Check slope manually by reading mV in buffers and comparing to

Nernstian response (59.2 mV/pH unit)• Example:

• pH 7 = -10 mV• pH 4 = +150 mV• Slope = 160 mV/177.6 mV = 90.1%

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pH Calibration - Guidelines

• Always calibrate with at least 2 buffers• Check calibration drift with 1 buffer• Always calibrate with buffers that bracket the expected measurement

range• Calibrate with buffers that are no more than 3 pH units apart• Track calibration slope on a daily basis• Calibration frequency

• Electrode type• Sample type• Number of samples

• Electrode slope guidelines• Ideal range: 95% - 102%

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Effects of Temperature

• Temperature can have a significant effect on pH measurements

• Electrode• Calibration• Buffers• Samples

• Temperature Compensation Techniques

• Calibrate and measure at same temperature

• Manually temperature compensate using temperature control on meter

• Use automatic temperature compensator (ATC) or 3-in-1 Triode electrode

• Use LogR temperature compensation

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Effects of Temperature – Electrode Effects

• Temperature Hysteresis• AgCl or Hg2Cl2 references drift

with temperature changes• 0.05 pH unit error with 4 °C

difference• ROSS™ electrodes stabilize

within seconds

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Effects of Temperature – Calibration Effects

• Calibration Effects• Theoretical slope of electrode is

59.16mv at 25 °C• Temperature changes the

calibration slope• Temperature compensation

adjusts the calibration slope for temperature effects

• The point at which temperature has no effect on mV is referred to as the isopotential point

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Effects of Temperature – Buffer Effects

• Buffer Effects• Buffers have different pH values at different temperatures• Use the value of the buffer at the calibration temperature• New meters have NIST calibration tables pre-programmed• NIST Certified Values only at 25°C

25 C 0 C 5 C 10 C 20 C 30C 40 C 50 C 60 C 70 C 80 C 90 C 1.68 1.67 1.67 1.67 1.67 1.68 1.69 1.71 1.72 1.74 1.77 1.79 3.78 3.86 3.84 3.82 3.79 3.77 3.75 3.75 4.01 4.00 4.00 4.00 4.00 4.02 4.03 4.06 4.08 4.13 4.16 4.21 6.86 6.98 6.95 6.92 6.87 6.85 6.84 6.83 6.84 6.85 6.86 6.88

7.00* 7.11 7.08 7.06 7.01 6.98 6.97 6.97 7.41 7.53 7.50 7.47 7.43 7.40 7.38 7.37 9.18 9.46 9.40 9.33 9.23 9.14 9.07 9.01 8.96 8.92 8.89 8.85

10.01 10.32 10.25 10.18 10.06 9.97 9.89 9.83 12.46 13.42 13.21 13.01 12.64 12.30 11.99 11.71 *Non-NIST Phosphate Buffer

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Effects of Temperature – Sample Effects

• Sample effects• Temperature compensation corrects for changes in electrode slope not

sample pH• It is not possible to normalize pH readings to a specific temperature• pH of samples will change with temperature changes • Record temperature with pH readings

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Electrode Care and Maintenance

• Electrode Storage• Short-term storage

• Use electrode storage solution• Alternatively, soak in 100 ml pH 7 buffer with 0.5 g KCl

• Long-term storage• Fill electrode, close fill hole, store with storage solution in protective cap

• Cleaning Solutions• Soak electrode in solvent that will remove deposits

• Example: 0.1 M HCl for general cleaning• Example: 1% pepsin in HCl for proteins• Example: Bleach for disinfecting• Example: detergent for grease & oil

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Electrode Care and Maintenance

• When do you need to clean your electrode?• Check slope range

• Ideal range: 95% - 102%• Cleaning range: 92% - 95%• Replacement range: below 92%

• Check response times in buffers• Electrode stability within 30 seconds

• Check precision of electrode by reading buffers as samples• Check for any drift of electrode in pH buffer

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Electrode Care and Maintenance

• General electrode bulb cleaning• Soak in Cleaning Solution for 30 minutes• Replace electrode fill solution• Soak in storage solution for at least 2 hours

• Electrode junction cleaning• Soak in 0.1M KCl for 15 minutes at 70 °C• Replace electrode fill solution when needed• Soak in electrode storage solution for 2 hours

• Check junction by suspending in air for ten minutes• Observe KCl crystal formation

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Keys to Accuracy

• Always use fresh buffers• Check bottle expiration and date

opened• pH 4 and pH 7 buffers expire within 3

months of being opened• pH 10 buffer expires within 1 month of

being opened• Fresh buffer for each calibration

• Calibrate only once in buffer… don’t re-use buffer

• Replace the fill solution in the electrode every week

• Fill solution concentration is maintained

• KCl crystallization is prevented• Make sure to use the correct fill

solution• Ross electrodes cannot use silver fill

solutions

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Keys to Accuracy

• Make sure level of fill solution is high

• Gently stir buffers and samples• Shake any air bubbles out of the

electrode• Use insulation between stir plate

and sample container to minimize heat transfer

• Blot electrodes between samples• Uncover fill hole during

measurement

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Troubleshooting pH Problems

• Common measurement problems• Readings not reproducible• Slow response• Noisy response• Drifty response• Inaccurate

• Troubleshooting Sequence• Meter• Buffers• Reference electrode• pH electrode• Sample• Technique

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Troubleshooting pH Problems

• Troubleshooting pH Meters• Use meter shorting strap• Reading should be 0 mV +/- 0.2

mV• Use meter self-test procedure

• Troubleshooting Buffers• Use Fresh Buffers for calibration• Verify expiration date• Stir buffers during calibration

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Troubleshooting pH Problems

• Troubleshooting pH Electrodes• Clean bulb, junctions• Replace Fill solution• Uncover fill hole• Check for scratches on sensing

bulb• Troubleshooting Samples

• Proper sample preparation• Stir samples

• Troubleshooting Technique• Treat samples and buffers the

same• Clean and blot electrode

between samples

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New Technologies

• LogR Temperature Compensation• Meter reads the resistance (R) from the bulb of any pH electrode• Resistance measurement is inverse to temperature: LogR = 1/T• Calibrate pH electrode for temperature• Direct temperature compensation without using ATC• Use PerpHect Electrodes for ideal Temperature response and improved

accuracy and precision

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Thermo Scientific – Orion Products

• Contact us for any technical questions!• Technical Service: (800) 225-1480• Technical Service fax: (978) 232-6015• Web site: www.thermoscientific.com/water• WAI Library: www.thermoscientific.com/WAI-Library

New Products

Don IvyWestern US and Canada Sales ManagerThermo Scientific – Orion Products

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• Star A111 pH Meter• Star A112 Conductivity Meter• Star A113 DO Meter• Star A211 pH Meter• Star A212 Conductivity Meter• Star A213 RDO/DO Meter• Star A214 pH/ISE Meter• Star A215 pH/Conductivity Meter• Star A216 pH/RDO/DO Meter• VERSA STAR Modular Meters

• Select up to 4 modules per meter• pH Module• ISE Module• LogR pH Module• Conductivity Module• RDO/DO Module

Orion Star A and VERSA STAR Benchtop Meters

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Orion Star A Portable Meters

•Star A121 pH Meter•Star A122 Conductivity Meter•Star A123 DO Meter•Star A221 pH Meter•Star A222 Conductivity Meter•Star A223 RDO/DO Meter•Star A321 pH Meter•Star A322 Conductivity Meter•Star A323 RDO/DO Meter•Star A324 pH/ISE Meter•Star A325 pH/Conductivity Meter•Star A326 pH/RDO/DO Meter•Star A329 pH/ISE/Conductivity/RDO/DO Meter

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Orion High Performance Ammonia ISE

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Orion Dual Star pH/ISE Meter

The interface of the 720/920A on a Star Meter—

• Simultaneously two channel measurements

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Available in Q2

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ROSS Triode Electrode

The convenience of a Triode with the accuracy of a ROSS—

• Accurately measure pH and temperature with one electrode

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1 year

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ISE Analysis in Today’s Lab

• Consider Electrode Advancements• New probes-Ammonia and Sure-Flow Ion Plus

• Consider Automation Capabilities• Autosampler capabilities• New Techniques Using MKA and Serial Calibrations

• Consider Broad Applications and Accurate Performance• Take Advantage of Ease of Use and Relative Low Cost

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Why Use ISE’s?

• Responsive over a wide concentration range

• Not affected by color or turbidity of sample

• Rugged and durable

• Rapid response time

• Real time measurements

• Low cost to purchase and operate

• Easy to use

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Why Use ISE’s?

• EPA approved methods• Acidity• Alkalinity• Ammonia• Bromide• Chloride• Residual Chlorine• Cyanide

• Fluoride• Total Kjeldahl Nitrogen (TKN)• Nitrate• Dissolved Oxygen/BOD• pH• Sulfide

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What Are ISE’s?

• Electrodes are devices which detect species in solutions

• Electrodes consist of a sensing membrane in a rugged, inert body

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How Do ISE’s Work?

• The reference electrode completes the circuit to the sensing electrode (ISE)

• Reference electrodes have a small leak to establish contact with the sample

• The reference solution (usually KCl) in contact with the reference keeps the reference potential constant

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ISE Meters

• ISE meters report concentrations• No manual calibration curves are required

• ISE meters generate sophisticated curves which are held in the meter’s memory

• Run standards• Run unknowns• Read results

Don IvyWestern US and Canada Sales ManagerThermo Scientific – Orion Products

Conductivity Measurement

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Conductivity in Today’s Lab

• Overview• Technology• Measurement• Calibration• Temperature• Issues??

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Properties of Conductivity

In a metal, current is carried by electrons• Measures the Resistance to the flow of electrons • A wire with 1 ohm resistance allows a current of

1 amp when 1 volt is applied• Resistance = Voltage/Current• Units of resistance are measured in ohms

• Conductance is the reciprocal of resistance• Conductance = Current/Voltage• Units of conductance are measured in Siemens1 Siemen = 1/ohm = 1 mho =1000 mS = 1,000,000 µS

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Measuring Conductivity

• A meter applies a current to the electrodes in the conductivity cell

• Reactions can coat the electrode, changing its surface area• 2 H+ H2 bubbles

• Reactions can deplete all ions in the vicinity, changing the number of carriers

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Properties of Conductivity

Conductivity and Resistivity are inherent properties of a materials ability to transport electrons

While

Conductance and Resistance depend on both material and geometry

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Common Units and Symbols

• Conductivity = d/A x conductance• Conductance Units

• S (Siemens)• mS• S

• Conductivity Units• S/cm• mS/cm• S/cm

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Common Units and Symbols

• Resistivity = A/d x resistance• Resistance Units

• (Ohm)• k• M

• Resistivity Units• cm• kcm• Mcm

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Conductivity Theory

Conductivity is defined as the reciprocal of the resistance between opposing faces of a 1 cm cube (cm3) at a specific temperature (K = 1.0 cm-1)

Distance (d = 1 cm)

Area (A = 1 cm2)

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Cell Constant

• The cell constant (K) is defined as the ratio of the distance between the electrodes, (d) to the electrode area (A). Fringe-field effects the electrode area by the amount AR.

K = d (A + AR)

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Cell Constant

• The cell constant can be determined by placing the cell in a solution of known conductivity at a known temperature and adjusting the meter to read the correct value

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Cell Constant (K) in cm-1

• Cell constant is the value by which you have to multiply the conductance to calculate conductivity. This converts conductance to conductivity.

• Conductance = the measured value relative to the specific geometry of the cell (actual meter reading) Conductivity = the inherent property of the solution being tested

• Conductance x K = Conductivity

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Cell Constants by Application

Cell Constant (K) Application

K = 0.1 / cm Pure Water

K = 0.4 to 1.0 / cm Environmental water and industrial solutions

K = 10 / cm Very high conductivity samples

Cell Constant (K) Range

K = 0.1 0.001 µS/cm to 300 µS/cm

K = 0.475 10 µS/cm to 1000 mS/cm

K = 1.0 10 µS/cm to 200 mS/cm

K = 10 10 µS/cm to 2000 mS/cm

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Conductivity in Solutions

Carried by ions and is dependent upon:• Concentration (number of carriers)• Charge per carrier • Mobility of carriers

K+Cl-

SO4-2

Na+

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Conductivity in Solutions

• Conductivity = number of carriers x charge per carrier x mobility of the Carriers

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Concentration

• As concentration increases, conductivity generally increases

KCl Sample at 25 C Conductivity, uS/cm0.0 M/L 00.0005 M/L 73.90.001 M/L 1470.005 M/L 7180.01 M/L 1,4130.05 M/L 6,6670.1 M/L 12,9000.5 M/L 8,6701.0 M/L 111,900

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Concentration

• The tendency of a salt, acid or base’s to dissociate in water provides more carriers in the form of ions

• More highly ionized species provide more carriers

Example:1% Acetic Acid = 640 µS/cm1% HCl = 100,000 µS/cm

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Charge per Carrier

• In general, divalent ions contribute more to conductivity than monovalent ions

Ca+2 Na+1vs.

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Mobility

• The mobility of each ion is different, so that the conductivity of 0.1M NaCl and 0.1M KCl will not be the same

Ion Relative MobilityH+ 350Na+ 50K=+ 74Ag+ 62OH- 200F- 55Cl- 76HCO3- 45

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Mobility According to Temperature

• Increasing temperature makes water less viscous, increasing the mobility of ions

• Most meters refer temperatures back to 20 ºC or 25 ºC - the correction is approximate: the degree of ionization and activity may also change with temperature

Example:0.01 M KCl at 0 ºC = 775 µS/cm0.01 M KCl at 25 ºC = 1410 µS/cm

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Temperature Coefficients

• Each ionic species has its own temperature coefficient… and these can change with changes in concentration

• The temperature coefficient can be determined experimentally• For any given solution, the temperature coefficient needs to be determined

only one time

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Temperature Coefficients

• Temperature effects vary by ion type. Some typical temperature coefficients:

Sample %/°C (at 25 °C)Salt solution (NaCl) 2.125% NaOH 1.72Dilute Ammonia Solution 1.8810% HCl 1.325% Sulfuric Acid 0.9698% Sulfuric Acid 2.84Sugar Syrup 5.64

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Non-Linear Temperature Coefficients

• Unlike salt solutions, pure water’s temperature coefficient is not linear• Typical temperature coefficients of pure water at different temperatures:

Temp °C % per °C0 7.110 6.320 5.530 4.950 3.970 3.190 2.4

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Measuring Conductivity

• A meter applies a current to the electrodes in the conductivity cell• Reactions can coat the electrode, changing its surface area

• 2 H+ H2 bubbles• Reactions can deplete all ions in the vicinity, changing the number of

carriers

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Measuring Conductivity

• Instead of using a direct current (DC), the conductivity meter uses an alternating current (AC) to overcome these measurement problems

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Two Electrode Conductivity Cell

Electrode

FieldEffect

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2-Electrode Cells

Uses two electrodes for measuring currentBenefits Include:

- Lower cost than four electrode cells- Limited operating range with cell constants geared toward specific

applicationsDrawbacks Include:- Resistance increases due to polarization- Fouling of the electrode surfaces- Unable to correct for surface area changes- Longer cable lengths increase resistance

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4-Electrode Cells

Voltage sensed by inner 2 electrodes - a constant current is supplied regardless of any coating on them

AV

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4-Electrode Cells

• A constant current is sent between two outer electrodes and a separate pair of voltage probes measure the voltage drop across part of the solution

• The voltage sensed by the inner two electrodes is proportional to the conductivity and unaffected by fouling or circuit resistance

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Advantages of 4-Electrode Cells

• Resists fouling• Resistance to polarization errors• Eliminates effects of cable resistance• Very wide operating range which will cover a number of applications • Wastewater testing for Federal or local agencies

• Seawater testing • Freshwater testing for environmental agencies• Beverage testing for manufacturers

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Conductivity Measurement

• Most conductivity measurements are made on natural waters

WATER CONDUCTIVITY (s/cm)Ultrapure 0.0546Good Distilled 0.5Good R/O 10Typical City 250Brackish 10,000

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Conductivity Measurement

• In natural waters, conductivity is often expressed as “dissolved solids”

• The measured conductivity is reported as the concentration of sodium chloride that would have the same conductivity

• Total Dissolved Solids (TDS) assumes all conductivity is due to dissolved NaCl

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Total Dissolved Solids

• Comparison of conductivity to TDS

CONDUCTIVITY (S/cm) DISSOLVED SOLIDS (mg/l) 0.1 0.0210 1.0 0.44 10.0 4.6 100 47 200 91 1000 495

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Other Measurement Capabilities

• Salinity is the measure of the total dissolved salts in a solution and is used to describe seawater, natural and industrial waters. It is based on a relative scale of KCl solution and is measured in parts per thousand (ppt).

• Resistivity is equal to the reciprocal of measured conductivity values. It is generally limited to the measurement of ultrapure water where conductivity values would be very low. Measured in M -cm.

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Other Measurement Capabilities

• Conductivity is an excellent way of measuring concentrations

• It can be used for any solution that has only a single ionic species

• An individual calibration curve must be prepared, but it is a “permanent” calibration curve

• Curves can take various forms

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Applications for Conductivity Cells

• Glass(epoxy)/platinum, platinized - general lab • Glass/platinum, platinized and scintered - pastes, creams etc.• Stainless Steel (K= 0.1cm-1) - ultrapure water• Epoxy/graphite - durable, 4-electrode cell and

2-electrode cells used where glass fears to tread• Weighted, protective sleeves (stainless steel) -for field use, provides

weight and protection for cells

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Conductivity Applications

• Water purity• Boiler/cooling water• Chemical manufacture• Drinking water• Pharmaceutical injection grade water• Biotech

• Education• Used as a tool in teaching analytical chemistry

87

Conductivity Applications

• Environmental• Incursion of seawater into aquifers• Monitor pollution due to industry output

• Industrial• Pulp/paper for bleaching process • Industrial feed water for heating and cooling systems• Refineries

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Conductivity Applications

• USP 645• Specifies the use of conductivity measurements as criteria for qualifying

purified water for injection• Sets performance standards for the conductivity measurement system

• Validation and calibration requirements for the meter and conductivity cell

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USP 645

• The conductivity cell constant must be known within +/- 2% using NIST traceable standards

• Meter calibration is verified using NIST traceable precision resistors (accurate to +/- 0.1% of value)

• The meter must have a minimum resolution of 0.1 S/cm on lowest range• Meter accuracy must be +/- 0.1 S• Conductivity values used in this method are non-temperature compensated• A flow through type cell may function better

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Tech Support Hot Line 800.225.1480

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