N 2 O Sensor Manual
Contents
1. We recommend the Unisense laboratory stand 1518 and the Unisense micromanipulator MM33 double MM33 2 for laboratory use For in situ use we recommend our in situ stand IS19 and a micromanipulator ELECTRICAL NOISE The signal of the microsensor is very small 10 to 107 ampere Although both the Unisense picoammeter and the Unisense nitrous oxide microsensors are quite resistant to electrical noise from the environment electrical fields may interfere with the sensor signal Therefore we recommend that unnecessary electrical mechanical equipment is switched off and the sensor or wires are not touched during measurements and signal recording 15 INTERFERENCE Exposure to high concentrations of sulfide should be avoided as it can affect the sensitivity of the nitrous oxide microsensor Nitric Oxide NO is interfering the N O sensor signal On suspicion of sensor damage repeat calibration and consult Irouble shooting ADVANCED USE OF THE N O SENSOR Unisense can construct nitrous oxide sensors for customer requested applications at an additional cost Unisense provides several options for customizations e g tip size response time pressure tolerance and stirring sensitivity and adaptations e g mounting in needle or flow through cell making accurate measurements possible for even more applications Please visit our website for more information 17 STORAGE AND MAINTENANCE Always store the sensor in the prote2. PRE ACTIVATION AND POLARIZATION Please see procedure below Pre activation Nitrous oxide sensors have a metal cathode which during normal exposure to oxygen over time will acquire an oxidated surface layer If the sensor is new or has not been used recently this layer must be pre activated in order for the sensor to work This is done by applying a voltage of 1 3 V for a short time prior to the period of polarization which is required for most electrochemical sensors Polarization The electrolyte inside the sensor can contain large amounts of oxygen which must always be removed before the sensor is stable This is done by the guard cathode inside the sensor during the period of polarization for some other sensor types referred to as pre polarization and this process requires some time depending on the dimensions and exact proportions of the individual sensor IMPORTANT WARNING Do not remove the seal and protective plastic tube before these steps and calibration are successfully completed WARNING Incorrect polarization may destroy the sensor If the sensor is new or not recently used follow the procedure for PRE ACTIVATION For recently used N O sensors follow the procedure for POLARIZATION Please read both sections before starting the relevant procedure For directions on adjusting the polarization Microsensor Multimeter Monometer or the PA2000 please consult the relevant manual PRE ACTIVATION PR
3. polarized overnight If the signal does not stabilize or is too high or too low see Trouble shooting CALIBRATION Calibration must be performed after the sensor signal has stabilized Nitrous oxide sensors respond linearly in the range of 0 to 2 596 nitrous oxide and signals can thus be linearly converted to partial pressure Check and repeat calibration at appropriate intervals Shortly after taking a sensor into use the appropriate interval may be 2 hours when the sensor has been used for some time it may be 24 hours To minimize the need for calibrations keep the sensor polarized between measurements unless the time between measurements exceeds several days The membrane permeability of nitrous oxide microsensors changes with time so a change in signal of up to 5096 may occur over months ZERO NITROUS OXIDE READING Place keep the sensor tip in nitrous oxide free water and read the signal This signal is your calibration value for zero nitrous oxide conditions NITROUS OXIDE RESPONSE READING The nitrous oxide sensor in the standard version responds linearly between 0 500 uM N20 0 2 596 N2O This does not apply for high range sensor versions Therefore a two point 12 IMPORTANT Calibration must be performed after pre polarization when the sensor signal has stabilized CALIBRATION As N O micro sensors respond linearly to changes in N O concentra tions a two point calibration is sufficient calibrat
4. CONTACT INFORMATION The Unisense nitrous oxide microsensor is a miniaturized Clark type nitrous oxide sensor with a guard cathode designed for research applications within environmental sciences If you wish to order additional products or if you encounter any problems and need scientific technical assistance please do not hesitate to contact our sales and support team We will respond to your inquiry within one working day E mail saleseunisense com Unisense A S Tueager 1 DK 8200 Aarhus N Denmark Tel 45 8944 9500 Fax 45 8944 9549 Further documentation and support is available at our website www unisense com REPLACEMENT OF SENSORS Unisense will replace sensors that have been damaged during shipment provided that The sensors were tested immediately upon receipt in accordance with the delivery note and the manual The seal is still intact The sensors are returned to Unisense for inspection within two weeks The sensors are correctly packed for return to Unisense in accordance with the note included in the sensor box RECOMMENDED AMPLIFIERS One channel amplifier Microsensor Monometer or Microsensor In Situ Amplifier Box Multi channel amplifiers Microsensor Multimeter OVERVIEW This manual covers all the Unisense N O sensors With its minute tip size excellent response time and insignificant stirring sensitivity the Unisense nitrous oxide sensor makes it possible to make reliable and fast measure
5. OCEDURE 1 Secure the nitrous oxide sensor with its tip immersed in nitrous oxide free water It does not harm the sensor to be in air instead but pre activation polarization and calibration might as well be made with the same set up 2 Using a Microsensor Multimeter or Monometer Connect the sensor to the amplifier Turn the polarization to 1 3V and leave for approximately 30 minutes Using a PA2000 amplifier Connect ONLY the BNC connection of the sensor and turn the polarization voltage to 1 3 V On the computer screen or display you will see a very high signal Wait for five minutes POLARIZATION 1 Using a Microsensor Multimeter Turn the polarization voltage to 0 8 V Using a PA2000 amplifier Turn the polarization voltage to 0 8 V Connect the yellow guard wire to the yellow connection on the meter 2 Onthe computer screen you will see a sharp decrease followed by a rapid increase in the signal After this the signal will stabilize with an initial rapid and then a more slow decrease Wait until the signal is below 20 mV and stable This may take many hours e g 12 hours see below If the sensor signal does not reach this value please go to the Troubleshooting section In general you should polarize for as long as possible before calibration and measurements to get maximum stability Unisense recommends that you perform the pre activation the day before measurements and then leave the sensor to be
6. TY AND LIABILITY The Nitrous Oxide sensor is covered by a 60 days limited warranty Microsensors are a consumable Unisense will only replace dysfunctional sensors if they have been tested according with the instructions in the manual within 14 days of receipt of the sensor s The warranty does not include repair or replacement necessitated by accident neglect misuse unauthorized repair or modification of the product In no event will Unisense A S be liable for any direct indirect consequential or incidental damages including lost profits or for any claim by any third party arising out of the use the results of use or the inability to use this product Unisense mechanical and electronic laboratory instruments must only be used under normal laboratory conditions in a dry and clean environment Unisense assumes no liability for damages on laboratory instruments due to unintended field use or exposure to dust humidity or corrosive environments REPAIR OR ADJUSTMENT Sensors and electrodes cannot be repaired Equipment that is not covered by the warranty will if possible be repaired by Unisense A S with appropriate charges paid by the customer In case of return of equipment please contact us for return authorization For further information please see the documents General Terms of Sale and Delivery of Unisense A S as well as the manuals for the respective products CONGRATULATIONS WITH YOUR NEW PRODUCT SUPPORT ORDERING AND
7. VA UNISENSE NITROUS OXIDE SENSOR USER MANUAL NITROUS OXIDE SENSOR MANUAL Copyright 2015 Unisense A S Version July 2015 NITROUS OXIDE SENSOR MANUAL UNISENSE A S TABLE OF CONTENTS WARRANTY AND LIABILITY 44444 HII 6 CONGRATULATIONS WITH YOUR NEW PRODUCTI 7 SUPPORT ORDERING AND CONTACT INFORMATION 7 OVERVIEW odd E OR SN EM RPM NEIN NECEM ON 9 GETTINGISTAREED si x ee een ea 10 UNPACKING AND CONNECTING A NEW SENSOR 10 PRE ACTIVATION AND POLARIZATION 10 Pre activation procedure 11 Polarization 11 CALIBRATION 12 Zero nitrous oxide reading 12 Nitrous oxide response reading 12 MEASUREMENTS onere ea e e ne ERA TRA TQ EHE SAU UII 15 MOUNTING THE SENSORS 15 ELECTRICAL NOISE 15 INTERFERENCE 16 ADVANCED USE OF THE N O SENSOR 17 STORAGE AND MAINTENANCE 000 cece III nne 18 CLEANING THE SENSOR 18 REFERENCES susi airada talle edes 19 TROUBLE SHOOTING second tab 20 APPENDIX EQUILIBRIUM N O CONCENTRATIONS 22 WARRANTY AND LIABILITY NOTICE TO PURCHASER This product is for research use only Not for use in human diagnostic or therapeutic procedures WARNING Microsensors have very pointed tips and must be handled with care to avoid personal injury and only by trained personnel Unisense A S recommends users to attend instruction courses to ensure proper use of the products WARRAN
8. blem Possible cause Solution Problem Possible cause Solution A slow response Insoluble compounds deposited at the sensor tip Rinse with 9696 ethanol rinse with 0 01M HCI and rinse with water An unstable signal or the signal fluctates if the setup is touched or equipmen is introduced in the medium you are measuring in Electrical disturbance of the sensor through the tip membrane Ground the set up using the blue grounding cable supplied with the picoammeter Connect the reference plug on the picoam meter blue plug with the medium you are measuring in High and drifting signal The sensor tip is broken Replace the microsensor A high signal Possible oxygen interference if the oxygen front guard is damaged Replace the microsensor A high signal 2 Air is trapped in the tip Degas water by boiling and subsequent cooling or by 10 min of vacuum treatment Immerse the sensor tip for 20 min in the degassed water Repeated or prolonged treatment may be necessary Problem The signal is very low Possible cause Contamination of the cathode surface e g by sulfide or loss of the cathode material due to excessive vibration Solution Replace the microsensor If you encounter other problems and need scientific technical assistance please contact sales unisense com for online support we will answer you within one workday 21 APPENDIX EQUILIBRIUM N O CONCENTRATIONS Equilibrium nitrous oxide concentrations mmo
9. ctive plastic tube used for shipping The nitrous oxide microsensor can be stored with the tip exposed to water or air The room in which the microsensor is stored should be dry and not too hot 10 30 If the sensor is used regularly it can be stored polarized CLEANING THE SENSOR Depending on which substance is present on the sensor tip or membrane the sensor can be cleaned with different solutes The standard method is to rinse with 9696 ethanol then rinse with 0 01 M HCl and rinse with water This will remove most substances Alternatively it is possible to rinse with 0 1M NaOH isopropanol or other detergent REFERENCES Andersen K T Kjaer and N P Revsbech 2001 An oxygen insensitive microsensor for nitrous oxide Sensors and Actuators B Chemical 81 1 42 48 Elberling B Christiansen H H and Hansen B U 2010 High nitrous oxide production from thawing permafrost Nature geoscience 3 332 335 Abstract Horn M A Schramm and H L Drake 2003 The earthworm gut an ideal habitat for ingested N2O producing microorganisms Appl Environ Microbiol 69 1662 1669 Revsbech N P and B B Jorgensen 1986 Microelectrodes Their Use in Microbial Ecology p 293 352 In C Marshall ed Advances in Microbial Ecology vol 9 Plenum New York 19 TROUBLE SHOOTING 20 Problem Possible cause Solution Problem Possible cause Solution Problem Possible cause Solution Pro
10. ion is sufficient Prepare water with a defined nitrous WARNING oxide concentration partial pressure which is slightly above the Never expose the maximum expected nitrous oxide concentration partial pressure sensor to concen in the samples Never expose the sensor to concentrations more trations more than than the specified linear range it may cause irreversible damage 500 micromolar to the sensor N20 it may A defined nitrous oxide concentration can be obtained by two cause irreversible different procedures damage to the sensor a Use a gas mixture controller to obtain a defined mixture of nitrous oxide and nitrous oxide free inert bulk carrier gas from a gas tank e g N2 For instance to obtain a nitrous oxide concentration of 100 uM in the calibration chamber at 20 bubble the water in the calibration chamber with a gas mixture containing 1 atm 2 and 0 003679 atm N20 nitrous oxide partial pressure 0 003679 atm solubility 27 05 10 3 mol liter atm WARNING Bubbling of water with any gas may cause the water to 100 umol liter see Table 1 For a Unisense 300 ml calibration cool pnis chamber CAL300 5 minutes of bubbling at a rate of 5 L per Ontor PR a pus temperature to find minute is sufficient time to achieve 99 of the concentration a suitable bubbling If the equipment gas mixture controller is available this method can be convenient because it is possible to switch between different nitrou
11. l liter at ambient partial pressure of 1 atm in water as a function of temperature and salinity Source Weiss R F Price B A Marine Chemistry 1980 8 347 359 22 UNISENSE UNISENSE DENMARK www unisense com infogunisense com
12. ments with a high spatial resolution The Unisense nitrous oxide microsensor is a miniaturized Clark type sensor with an internal reference and a guard cathode In addition the sensor is equipped with an oxygen front guard which prevents oxygen from interfering with the nitrous oxide measurements The sensor is connected to a high sensitivity picoammeter and the cathode is polarized against the internal reference Driven by the external partial pressure nitrous oxide from the environment will penetrate through the sensor tip membrane and be reduced at the metal cathode surface The picoammeter converts the resulting reduction current to a signal The internal guard cathode is also polarized and scavenges oxygen in the electrolyte thus minimizing zero current and polarization time AVAILABLE N O SENSORS N 025 tip diameter 20 50 um N 0100 tip diameter 70 120 um N O spec customer specified WARNING Unisense sensors are neither intended nor approved for use on humans 5089101 GETTING STARTED UNPACKING AND CONNECTING A NEW SENSOR When receiving a new microsensor first remove the shock absorbing grey plastic net Then secure the sensor in a safe position e g micromanipulator or calibration chamber before connecting it to the measuring meter The signal from the nitrous oxide sensor is generated in picoamperes Therefore the nitrous oxide sensor must be connected to a picoammeter amplifier unit during measurements
13. s oxide conditions without changing the water Use the solubility table Table 1 to find the correct mixture at temperatures other than 20 For obtaining correct concentrations it is important that the headspace above the rate which does not cool the water significantly water in the calibration chamber is closed except for one hole which should be only slightly larger than the microsensor shaft This effectively prevents ambient air from entering the vessel We recommend the Unisense Calibration chamber CAL300 and rubber stoppers for calibrations b Add a defined volume of nitrous oxide saturated water to a defined volume of water in a calibration chamber For instance adding 3 679 ml of nitrous oxide saturated to 996 32 ml water gives a concentration of 100 uM at 20 C see Table 1 as 3 679 ml of nitrous oxide saturated water contains Calibration chamber CAL300 Do not apply for high range sensor versions 13 100 umol nitrous oxide Using a calibration chamber containing 200 ml reduce the volume of added nitrous oxide saturated water by a factor of 5 for obtaining 100 uM and so on After adding nitrous oxide saturated water to the calibration chamber mix it thoroughly for a few seconds and read the signal when it is stable Do not stir bubbles into the water and do not mix by bubbling as this will flush nitrous oxide from the water A magnetic stirrer is also not recommended as a mixing tool because it can introd
14. uce electrical noise to the signal The nitrous oxide in the water will slowly escape to the atmosphere and the concentration can only be considered constant for a few minutes If the sensor functions according to the above description carefully remove the seal and the protective tube before making measurements MEASUREMENTS Nitrous oxide sensors can be used for a wide variety of TEMPERATURE measurements please see our web page www unisense com for Closely monitor further information They are most commonly used for making the temperature profiles in e g sediments or tissues where a high spatial resolution The temperature is required or for nitrous oxide measurements in water samples coefficient varies from sensor to MOUNTING THE SENSORS sensor but is approximately Although the Unisense microsensors are made of glass the tip is flexible and can adjust slightly around physical obstacles The sensor is thus rather sturdy in the longitudinal direction However 2 396 per C large obstacles like stones or lateral movements of the sensor when the tip is in contact with a solid substrate may cause the tip to break Furthermore due to the small size of the microsensor tip and to the steepness of gradients in many environments a displacement of the sensor tip of only a few microns may change its environment Therefore we recommend that measurements be performed only in a stabilized set up free of moving or vibrating devices
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