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Electrochemistry in Today’s Lab. FUEL ETHANOL LABORATORY CONFERENCE November 12, 2013 Don Ivy Western US and Canada Sales Manager Thermo Scientific – Orion Products. What is pH?. The Theoretical Definition pH = - log a H a H is the hydrogen ion activity .

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Electrochemistry in today s lab

Electrochemistry in Today’s Lab


November 12, 2013

Don Ivy

Western US and Canada Sales Manager

Thermo Scientific – Orion Products

What is ph
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+.

What is ph1
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".

What is ph2
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!

Ph measurement system
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)

Ph measurement system1
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

Ph measurement system2
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™

Ph measurement system reference electrode
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.

Ph measurement system reference types
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!

Ph measurement system reference types1
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

Ph measurement system reference types2
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

Ph measurement system reference types3
pH Measurement System – Reference Types

  • ROSS™ Reference

  • Double Junction Iodine/Iodide redox couple

  • The ROSS™ referenceis 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

Ph measurement system junctions
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

Ph measurement system junctions1
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

Ph measurement system junctions2
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

Ph measurement system junctions3
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)

Ph measurement system electrode types
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

Ph measurement system electrode selection
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?

Ph calibration
pH Calibration

  • The Nernst Equation

    E = E0 - RT/nF log aH

    E = measured potential

    E0 = reference potential

    R = Universal Gas Constant

    T = Temperature (at 25 °C)

    n = Number of electrons

    F = Faraday Constant

    aH = Hydrogen Ion activity

    Slope = RT/nF = 59.16mv @ 25 °C

Ph calibration1
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%

Ph calibration guidelines
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%

Effects of temperature
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

Effects of temperature electrode effects
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

Effects of temperature calibration effects
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

Effects of temperature buffer effects
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

Effects of temperature sample effects
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

Electrode care and maintenance
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

Electrode care and maintenance1
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

Electrode care and maintenance2
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

    • Soak in electrode storage solution for 2 hours

  • Check junction by suspending in air for ten minutes

    • Observe KCl crystal formation

Keys to accuracy
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 day/shift

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

  • Replace the fill solution in the electrode every week as needed

    • Fill solution concentration is maintained

    • KCl crystallization is prevented

  • Make sure to use the correct fill solution

    • Ross electrodes cannot use silver fill solutions

Keys to accuracy1
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

Troubleshooting ph problems
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

Troubleshooting ph problems1
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

Troubleshooting ph problems2
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

New technologies
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

New technologies1
New Technologies

  • ROSS™ Ultra Electrodes

    • Best of the Best!

      • Superior Performance

      • Fast Response

      • Very Stable

    • 2-Year Replacement Warranty

Thermo scientific orion products
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

Ise analysis in today s lab
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

Why use ise s
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

Why use ise s1

EPA approved methods






Residual Chlorine



Total Kjeldahl Nitrogen (TKN)


Dissolved Oxygen/BOD



Why Use ISE’s?

What are ise s
What Are ISE’s?

  • Electrodes are devices which detect species in solutions

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

How do ise s work
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

Ise meters
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

Conductivity measurement

Conductivity Measurement

Don Ivy

Western US and Canada Sales Manager

Thermo Scientific – Orion Products

Conductivity in today s lab
Conductivity in Today’s Lab

  • Overview

    • Technology

    • Measurement

    • Calibration

    • Temperature

    • Issues??

Properties of conductivity
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 Siemens

    1 Siemen = 1/ohm = 1 mho =1000 mS = 1,000,000 µS

Measuring conductivity
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

Properties of conductivity1
Properties of Conductivity

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


Conductance and Resistance depend on both material and geometry

Common units and symbols
Common Units and Symbols

  • Conductivity = d/A x conductance

  • Conductance Units

    • S (Siemens)

    • mS

    • S

  • Conductivity Units

    • S/cm

    • mS/cm

    • S/cm

Common units and symbols1
Common Units and Symbols

  • Resistivity = A/d x resistance

  • Resistance Units

    •  (Ohm)

    • k

    • M

  • Resistivity Units

    • cm

    • kcm

    • Mcm

Conductivity theory
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)

Cell constant
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)

Cell constant1
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

Cell constant k in cm 1
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

Conductivity in solutions
Conductivity in Solutions

Carried by ions and is dependent upon:

Concentration (number of carriers)

Charge per carrier

Mobility of carriers





Conductivity in solutions1
Conductivity in Solutions

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


  • As concentration increases, conductivity generally increases


  • 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


1% Acetic Acid = 640 µS/cm

1% HCl = 100,000 µS/cm

Charge per carrier
Charge per Carrier

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





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

Mobility according to temperature
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


0.01 M KCl at 0 ºC = 775 µS/cm

0.01 M KCl at 25 ºC = 1410 µS/cm

Temperature coefficients
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

Temperature coefficients1
Temperature Coefficients

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

Sample %/°C (at 25 °C)

Salt solution (NaCl) 2.12

5% NaOH 1.72

Dilute Ammonia Solution 1.88

10% HCl 1.32

5% Sulfuric Acid 0.96

98% Sulfuric Acid 2.84

Sugar Syrup 5.64

Non linear temperature coefficients
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 °C

0 7.1

10 6.3

20 5.5

30 4.9

50 3.9

70 3.1

90 2.4

Measuring conductivity1
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

Measuring conductivity2
Measuring Conductivity

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

Two electrode conductivity cell
Two Electrode Conductivity Cell




2 electrode cells
2-Electrode Cells

Uses two electrodes for measuring current

Benefits Include:

  • Lower cost than four electrode cells

  • Limited operating range with cell constants geared toward specific applications

    Drawbacks Include:

  • Resistance increases due to polarization

  • Fouling of the electrode surfaces

  • Unable to correct for surface area changes

  • Longer cable lengths increase resistance

4 electrode cells
4-Electrode Cells

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



4 electrode cells1
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

Advantages of 4 electrode cells
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

Conductivity measurement1
Conductivity Measurement

  • Most conductivity measurements are made on natural waters


Ultrapure 0.0546

Good Distilled 0.5

Good R/O 10

Typical City 250

Brackish 10,000

Conductivity measurement2
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

Total dissolved solids
Total Dissolved Solids

  • Comparison of conductivity to TDS


0.1 0.0210

1.0 0.44

10.0 4.6

100 47

200 91

1000 495

Other measurement capabilities
Other Measurement Capabilities

  • Salinityis 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.

Other measurement capabilities1
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

Applications for conductivity cells
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

Conductivity applications
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

Conductivity applications1
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

Conductivity applications2
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

Usp 645
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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