1. Electrochemistry in Today’s Lab FUEL ETHANOL LABORATORY CONFERENCE November 12, 2013 Don Ivy Western US and Canada Sales Manager Thermo Scientific – Orion Products

2. 2 What is pH? The Theoretical Definition pH = - log a H a H 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 +.

3. 3 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".

4. 4 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! SubstancepH Hydrochloric AcidHydrochloric Acid, 10M Lead-acid battery0.5 Gastric acid1.5 – 2.0 Lemon juice2.4 Cola2.5 Vinegar2.9 OrangeOrange or apple juiceapple3.5 Beer4.5 Acid Rain<5.0 Coffee5.0 TeaTea or healthy skinskin5.5 Milk6.5 Pure Water7.0 Healthy human salivahumansaliva6.5 – 7.4 Blood7.34 – 7.45 Seawater7.7 – 8.3 Hand soap9.0 – 10.0 Household ammonia11.5 Bleach12.5 Household lye13.5 Representative pH values

5. 5 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)

6. 6 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

7. 7 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™

8. 8 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.

9. 9 pH Measurement System – Reference Types Calomel Reference (Hg/Hg 2 Cl 2 ) 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!

10. 10 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

11. 11 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

12. 12 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

13. 13 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

14. 14 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

15. 15 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

16. 16 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)

17. 17 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

18. 18 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?

19. 19 pH Calibration The Nernst Equation E = E 0 - RT/nF log a H E = measured potential E 0 = reference potential R = Universal Gas Constant T=Temperature (at 25 °C) n = Number of electrons F = Faraday Constant a H = Hydrogen Ion activity Slope = RT/nF = 59.16mv @ 25 °C

20. 20 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%

21. 21 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%

22. 22 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

23. 23 Effects of Temperature – Electrode Effects Temperature Hysteresis AgCl or Hg 2 Cl 2 references drift with temperature changes 0.05 pH unit error with 4 °C difference ROSS™ electrodes stabilize within seconds

24. 24 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

25. 25 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

26. 26 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

27. 27 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

28. 28 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

29. 29 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

30. 30 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

31. 31 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

32. 32 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

33. 33 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

34. 34 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

35. 35 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

36. 36 New Technologies ROSS™ Ultra Electrodes Best of the Best! Superior Performance Fast Response Very Stable 2-Year Replacement Warranty

37. 37 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/waterwww.thermoscientific.com/water WAI Library: www.thermoscientific.com/WAI-Librarywww.thermoscientific.com/WAI-Library

38. 38 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

39. 39 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

40. 40 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

41. 41 What Are ISE’s? Electrodes are devices which detect species in solutions Electrodes consist of a sensing membrane in a rugged, inert body

42. 42 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

43. 43 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

44. Don Ivy Western US and Canada Sales Manager Thermo Scientific – Orion Products Conductivity Measurement

45. 45 Conductivity in Today’s Lab Overview Technology Measurement Calibration Temperature Issues??

46. 46 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

47. 47 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 +  H 2 bubbles Reactions can deplete all ions in the vicinity, changing the number of carriers

48. 48 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

49. 49 Common Units and Symbols Conductivity = d/A x conductance Conductance Units S (Siemens) mS  S Conductivity Units S/cm mS/cm  S/cm

50. 50 Common Units and Symbols Resistivity = A/d x resistance Resistance Units  (Ohm) k  M  Resistivity Units  cm k  cm M  cm

51. 51 Conductivity Theory Conductivity is defined as the reciprocal of the resistance between opposing faces of a 1 cm cube (cm 3 ) at a specific temperature (K = 1.0 cm -1 ) Distance (d = 1 cm) Area (A = 1 cm 2 )

52. 52 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)

53. 53 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

54. 54 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

55. 55 Cell Constants by Application Cell Constant (K)Application K = 0.1 / cmPure Water K = 0.4 to 1.0 / cm Environmental water and industrial solutions K = 10 / cmVery high conductivity samples Cell Constant (K)Range K = 0.10.001 µS/cm to 300 µS/cm K = 0.47510 µS/cm to 1000 mS/cm K = 1.010 µS/cm to 200 mS/cm K = 1010 µS/cm to 2000 mS/cm

56. 56 Conductivity in Solutions Carried by ions and is dependent upon: Concentration (number of carriers) Charge per carrier Mobility of carriers K+ Cl- SO 4 -2 Na+

57. 57 Conductivity in Solutions Conductivity = number of carriers x charge per carrier x mobility of the Carriers

58. 58 Concentration As concentration increases, conductivity generally increases

59. 59 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/cm 1% HCl = 100,000 µS/cm

60. 60 Charge per Carrier In general, divalent ions contribute more to conductivity than monovalent ions Ca +2 Na +1 vs.

61. 61 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

62. 62 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/cm 0.01 M KCl at 25 ºC = 1410 µS/cm

63. 63 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

64. 64 Temperature Coefficients Temperature effects vary by ion type. Some typical temperature coefficients: Sample%/°C (at 25 °C) Salt solution (NaCl)2.12 5% NaOH1.72 Dilute Ammonia Solution1.88 10% HCl1.32 5% Sulfuric Acid0.96 98% Sulfuric Acid2.84 Sugar Syrup5.64

65. 65 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 07.1 106.3 205.5 304.9 503.9 703.1 902.4

66. 66 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 +  H 2 bubbles Reactions can deplete all ions in the vicinity, changing the number of carriers

67. 67 Measuring Conductivity Instead of using a direct current (DC), the conductivity meter uses an alternating current (AC) to overcome these measurement problems

68. 68 Two Electrode Conductivity Cell Electrode Field Effect

69. 69 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

70. 70 4-Electrode Cells Voltage sensed by inner 2 electrodes - a constant current is supplied regardless of any coating on them A V

71. 71 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

72. 72 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

73. 73 Conductivity Measurement Most conductivity measurements are made on natural waters WATERCONDUCTIVITY (  s/cm) Ultrapure 0.0546 Good Distilled 0.5 Good R/O 10 Typical City250 Brackish 10,000

74. 74 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

75. 75 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

76. 76 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.

77. 77 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

78. 78 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

79. 79 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

80. 80 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

81. 81 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

82. 82 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

83. 83 ORION TECHNICAL SUPPORT Unmatched Technical Expertise Available to Your Lab Local Technical Sales Representatives 800 Tech Support Team Tech Support Hot Line 800.225.1480

84. 84 Thank You!