User Guide - Fondriest Environmental
Contents
1. 10 C 20 C 30 C Figure 5 Partial Pressure of Oxygen in Air Saturated Water as a Function of Temperature at Standard Barometric Pressure 9708 DO Probe User Guide 13 Concentration Measurements While the probe is in fact measuring the partial pressure of oxygen it can be calibrated in terms of concentration and can be used to read dissolved oxygen levels directly in parts per million To do this several additional factors must be taken into consideration First the solubility of oxygen in water varies strongly as a function of temperature as shown in Table 1 Secondly the solubility also depends on the salinity of the water as shown in Appendix Il Furthermore the calibration of the probe in terms of concentration also requires that the barometric pressure be known as indicated by Figure 6 Even ignoring the influence of barometric pressure and salinity conventional oxygen probes can be calibrated only when the temperature is known so that the proper value for oxygen solubility can be obtained from a nomogram or table The 9708 probe incorporates a special calibration mode based on the variables in Table 1 and a comparison scheme to eliminate the need to measure temperature and look up calibration values Table 1 Partial Pressure of Water and Solubility of Oxygen in Water at 760 mm as a Function of Temperature Temperature C pH O mm Hg O Solubility ppm 10 09 2 11 28 15 12 8 10 07 20 175 09 08 25 23 8 08 262. 30 31 8 07 57 35 42 2 06 98 40 55 3 06 47 820 mm 760 mm 700 mm 9 80 ppm 9 08 0 ppm 8 36 0 ppm 0 Figure 6 Concentration of Dissolved Oxygen in 20 C Air Saturated Water as a Function of Atmospheric Pressure 14 9708 DO Probe User Guide Simplified Calibration The AIR position on the 9708 probe allows the probe to be calibrated in terms of barometric pressure rather than concentration which varies as a function of temperature This is possible because the relationship between oxygen partial pressure and air pressure is completely predictable since air is known to be 20 9 oxygen 0 209 barometric pressure pH20 pO2 The calibration in terms of barometric pressure can be carried out in either airsaturated water or watersaturated air with watersaturated air being easier Once the probe has been calibrated in the AIR position correct concentration values will be obtained in the measurement mode An electronic circuit and temperature sensor built into the probe take into account the factors shown in Table 1 that relate the partial pressure of oxygen to its concentration For example before making a measurement the probe must be calibrated The barometric pressure is 760 mm Hg and the temperature of the room is 20 C The probe is placed in a bottle containing a small amount of water which provides the water saturated air for calibration After setting the ZERO adjustment the probe is set to the AIR position a
3. 4 Turn the mode switch to OFF and set the meter to the pH mode Calibrate the meter to read 7 00 in the pH mode For detailed instructions on calibrating the meter consult your meter user guide 5 Turn the mode switch to BT CK The pH meter reading should be 13 40 or greater 6 Turn the mode switch to ZERO Use the zero calibration control to set the meter to read 0 00 in the pH mode 7 Turn the mode switch to AIR If measurements are being made at sea level use the AIR calibration control to set the pH meter reading to the barometric pressure divided by 100 If the barometric pressure is unknown the elevation is above sea level or the sample has a salinity greater than 2 parts per thousand refer to Appendix I and Il to obtain the correct AIR setting If the sea level barometric pressure is unknown multiply 760 by the elevation correction factor listed in Appendix I If the sea level barometric pressure is known divide the barometric pressure by 100 and multiply the resulting value by the elevation correction factor listed in Appendix I e If the sample salinity is greater than 2 ppt divide the barometric pressure by 100 and multiply the resulting value by both the elevation correction factor listed in Appendix I and the salinity correction factor listed in Appendix Il 8 Turn the mode switch to H20 for sample analysis 8 9708 DO Probe User Guide Sample Analysis 1 Insert the funnel into the sample B
4. constant stir rate The speed of many conventional stir plates can be stabilized by placing an aluminum plate on top of the stir plate BOD bottles Distilled or deionized water 9708 DO Probe User Guide DO Probe Preparation Battery Installation 1 Use a small screwdriver or coin to unscrew the cover from the battery compartment of the probe Remove the batteries from the storage box Each battery has a flat positive end and a smaller negative end Grasp the outside edge of each battery as close as possible to the flat positive end and avoid touching the negative end with your fingertips Sweat from the fingers can bridge the insulation between the battery terminals which causes a significant loss in battery life Drop the batteries into the battery compartment with the negative ends down See Figure 1 Replace the battery cover contact batteries battery component Figure 1 Battery Installation 9708 DO Probe User Guide Membrane Module Installation The membrane module is pre filled with a gel electrolyte 1 Remove the protective shipping cap from the end of the probe Remove the membrane module from the foil patch The module is pre filled with a liquid gel electrolyte Do not spill or remove the gel electrolyte Do not touch the anode cathode assembly with your fingers See Figure 2 Unscrew the red plug from the membrane module Hold the module upright and slowly push the anode ca
5. 800 225 1480 and outside the United States call 978 232 6000 or fax 978 232 6031 In Europe the Middle East and Africa contact your local authorized dealer For the most current contact information visit www thermo com water Warranty For the most current warranty information visit www thermo com water 9708 DO Probe User Guide 19 Ordering Information Cat No 970899WP 970800 970801 970802 970803 Description 9708 dissolved oxygen probe with BOD adapter overflow funnel and stir bar membrane module batteries and waterproof BNC connector 9708 dissolved oxygen probe with BOD adapter overflow funnel and stir bar membrane module batteries and U S standard connector Membrane module BOD adapter overflow funnel and stir bar Batteries pack of 2 For optimum performance the 9708 DO probe has been supplied with the Eveready 303 batteries Duracell 357 batteries may also be used Do not substitute batteries with other models or by other manufacturers 20 9708 DO Probe User Guide Thermo Fisher Scientific Environmental Instruments Water Analysis Instruments 166 Cummings Center Beverly MA 01915 USA Tel 978 232 6000 Toll Free 800 225 1480 Dom Fax 978 232 6015 Int l Fax 978 232 6031 254780 001 Rev A 0807 www thermo com water
6. OD bottle and make sure that the funnel fits tightly with the bottle Slowly immerse the probe into the funnel Any sample solution that is displaced by the probe will collect in the funnel Place the BOD bottle on a magnetic stir plate and gently stir the sample Turn the mode switch to H20 and set the meter to the pH mode Wait for a stable dissolved oxygen reading and then record the value The reading is displayed as parts per million ppm of oxygen Slowly remove the probe from the funnel and then remove the funnel from the bottle Insert a stopper into the bottle Rinse the probe and funnel with distilled water Dry the probe and gently blot the membrane Place the funnel and probe in a storage bottle DO Probe Operation Check 1 Calibrate the probe See the DO Probe Calibration section Prepare a sodium sulfite solution by dissolving about 15 0 g Na SO in 250 mL distilled water Transfer the solution to a BOD bottle Insert the funnel into the BOD bottle and then insert the probe into the funnel Make sure that the funnel fits tightly with the bottle Place the bottle on a magnetic stir plate and gently stir the solution Turn the mode switch to H20 After 2 5 minutes the reading should be 0 3 ppm or less Slowly remove the probe from the funnel and then remove the funnel from the bottle Thoroughly rinse the probe and funnel separately under running water to remove the sulfite Place the probe in the storage
7. User Guide 9708 Dissolved Oxygen Probes ROSS and the COIL trade dress are trademarks of Thermo Fisher Scientific Inc AQUAfast Cahn ionplus KNIpHE No Cal ORION perpHect PerpHecT PerpHecTion pHISA pHuture Pure Water Sage Sensing the Future SensorLink ROSS ROSS Ultra Sure Flow Titrator PLUS and TURBO2 are registered trademarks of Thermo Fisher 1 888 pHAX ION A All in One Aplus AQUAsnap AssuredAccuracy AUTO BAR AUTO CAL AUTO DISPENSER Auto ID AUTO LOG AUTO READ AUTO STIR Auto Test BOD AutoEZ Cable Free CERTI CAL CISA DataCOLLECT DataPLUS digital LogR DirectCal DuraProbe Environmental Product Authority Extra Easy Extra Value FAST QC GAP GLPcal GLPcheck GLPdoc ISEasy KAP LabConnect LogR Low Maintenance Triode Minimum Stir Requirement MSR NISS One Touch One Touch Calibration One Touch Measurement Optimum Results Orion Star Pentrode pHuture MMS pHuture Pentrode pHuture Quatrode pHuture Triode Quatrode QuikcheK rf link ROSS Resolution SAOB SMART AVERAGING Smart CheK SMART STABILITY Stacked Star Navigator 21 Stat Face The Enhanced Lab ThermaSense riode TRIUMpH Unbreakable pH Universal Access are trademarks of hermo Fisher Guaranteed Success and The Technical Edge are service marks of Thermo Fisher PerpHecT meters are protected by U S patent 6 168 707 PerpHecT ROSS are protected by U S patent 6 168 707 ORION Series A meters and 900A printer are protect
8. bottle 9708 DO Probe User Guide 9 DO Probe Storage Store the probe in the BOD bottle used for calibration between measurements and when not in use Probe Characteristics Probe Response The probe exhibits a time response of 96 of the final reading in less than 30 seconds when going from oxygen free to air saturated water A response time of up to 1 5 minutes may be required if the sample temperature is 5 to 10 C different than the air temperature Temperature Effects Changes in temperature affect both the permeability of the membrane to oxygen and the solubility of oxygen in water A dual scheme of thermocompensation is incorporated into the probe and automatically corrects for both of these effects Reproducibility With one calibration performed per hour probe measurements are reproducible to 0 05 ppm or 2 of reading whichever is greater if the solution temperature is between 15 C and 35 C and the temperature of the water saturated air used for calibration is within 10 C of the sample temperature Stirring Effect The probe uses a membrane with low oxygen permeability which reduces the consumption of oxygen from the sample and results in minimum errors due to changes in stirring rate If the magnetic stir plate setting is sufficient for continuous movement of the captive stir bar in the funnel changing the stirring speed will have negligible 0 05 ppm maximum effect on the oxygen reading Module Lifet
9. ed by U S patents 5 198 093 D334 208 and D346 753 ionplus electrodes and Optimum Results solutions are protected by US Patent 5 830 338 ROSS Ultra electrodes are protected by US patents 6 793 787 Orion ORP Standard is protected by US Patent 6 350 367 Orion NoCal electrodes with stabilized potential patent pending 2007 Thermo Fisher Scientific Inc All rights reserved All trademarks are the property of Thermo Fisher Scientific Inc and its subsidiaries The specifications descriptions drawings ordering information and part numbers within this document are subject to change without notice This publication supersedes all previous publications on this subject Introduction The Thermo Scientific Orion 9708 dissolved oxygen probe simplifies measurements of dissolved oxygen particularly Biochemical Oxygen Demand BOD The probe allows the dissolved oxygen concentration to be read directly in parts per million on any pH meter which eliminates the need for a dedicated dissolved oxygen meter Calibration of the probe is performed in water saturated air rather than air saturated water An zero position on the probe allows the probe to be calibrated without a sodium sulfite solution An oxygen sensor thermocompensator battery operated electronic circuits and operating controls are all included in one probe The electronic portion of the probe uses extremely low drain circuits so the battery life during normal use is mini
10. ime In normal laboratory use the lifetime of the membrane module is approximately three months 10 9708 DO Probe User Guide Theory Of Operation Sensor The 9708 DO probe is a polarographic sensor It consists of a pair of polarized silver electrodes and an electrolyte separated from the sample by a gas permeable membrane Oxygen diffuses across the membrane and is reduced to hydroxyl ions at the silver cathode according to the reaction 1 02 2H20 4e gt 40H The electrons necessary for this process are provided by a reaction at the silver anode Because the electrolyte contains chloride ions this reaction occurs as 2 Ag Ck gt AgCl e At any given temperature the current that flows between cathode and anode is directly proportional to the level of oxygen outside of the membrane Electronics Package Four distinct functions are performed by the circuitry located in the probe s electronic section First the current produced by the reduction of oxygen is converted to a voltage so that the output signal of the probe can be used with a pH meter to provide a direct readout of parts per million ppm of oxygen on the pH scale Second an offset potential allows the meter reading to be electronically set to 0 00 ppm oxygen when the mode switch is set to ZERO Third a temperature compensation circuit corrects for changes in the oxygen permeability of the membrane with temperature This compensation is applied
11. in the bottle used for calibration between measurements Keep the probe away from any sharp objects that may puncture the membrane After installing a new membrane leave the probe in a BOD bottle with about 50 mL of distilled water for 30 minutes before calibrating The probe must be in a BOD bottle and stir rate must be constant for accurate measurements Oxygen consumption by the probe can cause a lowered oxygen concentration at the boundary layer between the solution and the probe membrane For this reason sample stirring is required Probe Polarization The probe must be polarized before use To polarize a new probe insert the batteries into the probe insert the probe in a BOD bottle with about 50 mL of distilled water and wait 30 minutes The probe is continuously polarized when the batteries are in the probe so this process does not need to be repeated unless a new membrane module is installed the batteries are removed or the battery check gives a low reading 9708 DO Probe User Guide DO Probe Calibration When a new membrane module is installed wait 30 minutes before calibrating 1 Connect the probe to the meter 2 Prepare a BOD bottle by filling the bottle with about 50 mL of distilled water 3 Insert the funnel into the BOD bottle and then insert the probe into the funnel Make sure that the probe is suspended about half an inch above the water and there is no water on the surface of the probe membrane
12. is pO 760 x 0 209 159 mm Hg Water vapor is also a gas The maximum amount of water vapor in air expressed as a partial pressure varies with temperature as shown in Figure 5 As the air temperature increases the water vapor in watersaturated air air at 100 relative humidity reduces the partial pressures of the other gases that make up air For example at 20 C and standard pressure the partial pressure of oxygen in water saturated air is pO 760 17 5 x 0 209 155 mm where 17 5 mm is the water vapor pressure at 20 C 12 9708 DO Probe User Guide It is important to note that at any given temperature the partial pressure of oxygen in water saturated air is exactly the same in airsaturated water This means that a probe that is calibrated in terms of partial pressure in watersaturated air will correctly read the partial pressure of the dissolved oxygen in a water sample Proper calibration requires taking into account the barometric pressure Therefore if the barometric pressure is 740 mm the pO of air saturated water at 25 C is pO 740 23 8 x 0 209 150 mm where 23 8 mm is the water vapor pressure at 25 C Therefore it is easy to calibrate the probe in terms of partial pressure since only two factors need to be taken into consideration barometric pressure and the partial pressure of water as a function of temperature 760 mm A 760 mm 9 2mm 760 mm E all other gases 175mm ae water vapor
13. mal The probe includes a BOD adapter with an overflow funnel and built in magnetic stirring bar The 9708 DO probe has a concentration range of 0 to 14 ppm and a temperature range of 0 to 45 C With one calibration performed per hour probe measurements are reproducible to 0 05 ppm or 2 of reading whichever is greater if the solution temperature is between 15 C and 35 C and the temperature of the water saturated air used for calibration is within 10 C of the sample temperature The probe consumes approximately 0 1 microgram hour of oxygen The battery life is one year based on four hours per day operation 9708 DO Probe User Guide Required Equipment 1 pH meter with a BNC or U S standard connection The 9708 DO probe can be used on any pH meter with a BNC or U S standard connection Thermo Scientific Orion pH meters are recommended such as the 3 Star pH meter 4 Star pH ISE meter 4 Star pH DO meter 4 Star pH conductivity meter or 5 Star pH ISE DO conductivity meter Thermo Scientific Orion 9708 DO Probe Cat No 970899WP has a waterproof BNC connector that is compatible with any pH meter with a BNC connection Cat No 970800 has a U S standard connector that is compatible with any pH meter with a U S standard connection Membrane modules Cat No 970801 Batteries Cat No 970803 Magnetic stir plate required to operate the built in stir bar on the BOD adapter Use a stir plate that will maintain a
14. nd the AIR calibration control is turned to obtain a reading of 760 barometric pressure divided by 100 Then the probe is set to the H20 position A reading of 9 08 ppm is obtained which is the solubility of oxygen in ppm at 20 C One hour later the room temperature warms to 25 C The probe is set to the H O position and the probe reading changes to 8 26 ppm the solubility of oxygen at 25 C When the probe is set to the AIR position the reading is 7 60 Then the probe is removed from the bottle The probe is set to the AIR position and the reading rises slightly to 770 or 7 75 This is because the vapor pressure of water is lower in the room air than in the bottle depending on the relative humidity of the room air and the partial pressure of oxygen is slighter higher When the probe is placed in a water sample with a temperature of 30 C and the probe is set to the H20 position the value obtained for the oxygen concentration is correct even though calibration was performed at 20 C Failure to calibrate in air that is saturated with water will give rise to about a 2 error 9708 DO Probe User Guide 15 Appendix l Correction for Elevation This table is used to determine the correct calibration value as a function of elevation If the sea level barometric pressure is known it is multiplied by the factor shown in the second column that corresponds to the elevation If the sea level barometric pressure is not known it is a
15. probe Technique Check that the method of analysis is compatible with the sample Interfering Substances Substances such as ozone sulfides sulfur dioxide nitrous oxide and carbon monoxide may interfere with dissolved oxygen measurements If the measurements are unstable and other troubleshooting procedures do not correct the problem there may be interfering substances present in the solution 18 9708 DO Probe User Guide Troubleshooting Chart Issue Recommended Action Unable to Check the zero setting and adjusted if calibrate needed Verify that no water is on the membrane Check the batteries and replace if needed Replace the membrane module Drift or slow Check that the solution is being stirred and response the stir rate is sufficient Check the solution temperature Measurements may take longer if the solution temperature is unstable Ensure that the probe is fully polarized Check the batteries and replace if needed Unscrew the membrane module and slowly screw the module back onto the probe Check the sample composition An interfering substance may be present Replace the membrane module Measured Salt may be present in the sample Use value low Appendix Il to calculate the AIR setting Check that the solution is being stirred and the stir rate is sufficient Assistance After troubleshooting all components of your measurement system contact Technical Support Within the United States call 1
16. ssumed to be 760 mm and the setting in the last column should be used Elevation feet Elevation Correction Factor AIR Setting CF x 7 60 0 sea level 1 000 760 500 0 982 746 1 000 0 965 133 1 500 0 948 7 20 2 000 0 931 7 08 2 500 0 915 6 95 3 000 0 899 6 83 3 500 0 883 6 71 4 000 0 867 6 59 4 500 0 851 6 47 5 000 0 836 6 35 5 500 0 821 6 24 6 000 0 806 6 13 6 500 0 791 6 01 7 000 0 777 5 90 7 500 0 762 5 79 8 000 0 748 5 68 8 500 0 735 5 59 9 000 0 721 5 48 9 500 0 708 5 38 10 000 0 694 5 27 10 500 0 680 5 17 11 000 0 666 5 06 Elevation meters Elevation Correction Factor AIR Setting CF x 7 60 0 sea level 1 000 7 60 250 0 970 737 500 0 942 7 16 750 0 914 6 95 1 000 0 887 6 75 1 250 0 861 6 54 1 500 0 835 6 35 1 750 0 809 6 15 2 000 0 784 5 96 2 250 0 760 5 78 2 500 0 737 5 60 3 000 0 692 5 26 3 250 0 670 5 09 3 500 0 649 4 93 16 9708 DO Probe User Guide Appendix Il Salinity Correction This table is used to determine the correct calibration value when brines seawater or brackish samples are being measured The salinity of the final diluted sample should be used to obtain the correction factor If samples are measured above sea level the corrected AIR setting obtained from Appendix I should be multiplied by the salinity factor below Example A brackish sample having 6 ppt salinity is to be meas
17. thode assembly into it Slowly screw the module onto the probe until it is finger tight anode cathode assembly gt membrane electrolyte module _ Figure 2 Membrane Module Installation 9708 DO Probe User Guide Operating Controls The mode switch is used to select the operation mode of the probe The five positions of the mode switch are OFF BT CK ZERO AIR and H O The OFF position is used when the probe is not in operation In the OFF position the electronic amplifiers are not operating but the polarizing voltage is maintained so stable readings will be obtained when the probe is switched to the calibration and operating modes e The BT CK position is used to check the battery power Good battery power is indicated by a reading of 13 4 or greater on the pH meter display e The ZERO position is used to electronically zero the probe Probe calibration is simplified by electronically simulating the output of the probe in the presence of zero oxygen e The AIR position is used to calibrate the probe in a watersaturated air solution e The H20 position is used for sample analysis The zero calibration control is used to adjust the pH meter reading to zero when the ZERO position is selected on the mode switch The air calibration control is used to set the barometric pressure on the pH meter display battery compartment eo zero air calibration calibra
18. tion control sick na control OFF A fe A mode switch Figure 3 Operating Controls 9708 DO Probe User Guide 5 Overflow Funnel and Stir Bar The BOD adapter includes an overflow funnel and stir bar The built in stir bar eliminates the need to retrieve a separate magnetic stir bar from each sample BOD bottle The funnel provides an overflow reservoir that holds displaced sample solution when the probe is inserted into a BOD bottle This allows measurements to be made without spilling the sample After the probe is removed from the bottle the displaced solution drains back into the bottle The funnel is designed to act as an probe holder when the probe is inserted into a BOD bottle sample solution displaced by electrode funnel with built in stirring bar BOD bottle captive magnetic stirring bar magnetic stirrer Figure 4 Overflow Funnel and Stir Bar 6 9708 DO Probe User Guide Measuring Hints To avoid spilling the sample solution always remove the probe from the funnel before removing the funnel from the BOD bottle Do not touch the anode cathode assembly with bare fingers when removing the membrane module from the probe Slowly insert and remove the probe from the funnel Rapidly inserting or removing the probe may change the calibration values of the probe Thoroughly rinse the probe and funnel separately under running water after exposure to sodium sulfite solutions Store the probe
19. ured at an elevation of 1000 M and a sea level barometric pressure of 740 mm What is the correct AIR setting 1 From Appendix I the conversion factor for 1000 M is 0 887 so the corrected sea level barometric pressure is Corrected Pressure 740 x 0 887 656 mm 2 The salinity correction factor from the table below is 0 94 for 6 ppt Therefore Air Setting 656 x 0 94 617 mm 6 17 on the pH meter Salinity parts per thousand Salinity Correction Factor 0 1 00 2 0 98 4 0 96 6 0 94 8 0 92 10 0 90 12 0 88 14 0 86 16 0 85 18 0 83 20 0 81 22 0 80 24 0 78 26 0 76 28 0 75 30 0 73 35 0 70 40 0 66 45 0 63 50 0 60 Salinity is calculated as ppt chloride 9708 DO Probe User Guide 17 Troubleshooting The most important principle in troubleshooting is to isolate the components of the system and check each in turn Meter The meter is the easiest component to eliminate as a possible cause of error Thermo Scientific Orion meters include an instrument checkout procedure in the meter user guide Consult the manual for complete instructions and verify that the instrument operates as indicated and is stable in all steps Probe Rinse the probe thoroughly with distilled water If readings continue to be unstable replace the membrane module Sample If the probe works properly in standards but not in the sample look for possible interferences or substances that could alter probe response or physically damage the
20. when the mode switch is set to AIR and H320 Finally a second temperature compensation circuit is used when the mode switch is set to H O to correct for changes in oxygen concentration as a function of temperature 9708 DO Probe User Guide 11 Theory Of Measurement Partial Pressure To measure the biochemical oxygen demand BOD of a water sample it is necessary to measure the concentration of dissolved oxygen in the sample However oxygen probes do not directly measure the oxygen concentration but rather they measure the partial pressure of oxygen Fortunately the conversion of oxygen concentration to partial pressure can be easily done electronically due to the constant and predictable relationship between oxygen solubility and temperature and total atmospheric pressure Also under equilibrium conditions the partial pressure or activity of oxygen in air saturated water is equal to that of the oxygen in the humidified air above the water The partial pressure of any gaseous component in air is the fraction of the total pressure exerted by that component generally taken to be the total pressure multiplied by the volumetric fraction of that component in air Air is a mixture of oxygen nitrogen and other gases Dry air contains about 20 9 oxygen The partial pressure of oxygen p02 in dry air varies with the barometric pressure thus pO barometric pressure x O fraction Therefore as standard pressure the pQ in air
Download Pdf Manuals
Related Search