Hanna Instruments HI4105 User's Manual
Contents
1. Instruction Manual HI 4105 Carbon Dioxide lon Selective Electrode ions With Great instruments ome Great Resul HI 4105 Carbon Dioxide Electrode Introduction The Hanna HI 4105 Carbon Dioxide gas sensing electrode is a combination electrode designed for the measurement of Carbon Dioxide in aqueous solutions such as water soft drinks or wine samples Carbonate and Bicarbonate ions are also measured by conversion to Carbon Dioxide gas upon ISA addition Il Specifications Type CO gas sensing electrode with glass pH internal Ag Ag reference and gas permeable membrane Species detected 00 100 CO CO Measurement Range 0 02 Mto4x10 M 880 to 17 6 ppm Interfering ions 0 S0 H 5 S Operating Temperature 0to40C Operating pH 4 5 pH Dimensions 12 mm 0D X 120 mm insertion 0 47 x4 72 Wetted materials Delrin body and cap with PTFE membrane Connection BNC Ill Theory of Operation The Carbon Dioxide electrode is a complete potentiometric cell that contains both a silver silver chloride Ag AgQ reference and a pH measurement element These elements are housed within a thermoplastic body in a chloride ion containing electrolyte and are isolated from the sample by a PTFE membrane ISA addition changes the pH of the sample to approxi mately 4 7 pH and Bicarbonate HCO and carbonate CO ions in the sample are converted to carbon dioxide C0 The CO in the sa2. The sample is covered and permitted to mix throughly and continueously The mV is then recorded when the sensor has stabilized 2 5ml AV ogo OF 0 1 M Cogo standard is then added to the vessel and is permitted to mix The mV value increases as the concentration increases Note for other concentration samples add a known volume and concentration of standard to produce a 30 mV change or greater 3 The unknown carbon dioxide concentration in the original sample C can then be determined by using the equation provided XV Storage and Care of the HI 4105 sensor The HI 4105 sensor can be stored assembled and ready to use in HI 4005 45 i between measurements After ovemight storage gently pull on the cable to compress the spring mechanism thus permitting electrolyte film between the m required after doing this For longer term storage over a week disassemble the sensor completely an assembly the outer Conditioning solution overnight or to exchange from the bulk to the thin embrane and glass Calibration is p om d rinse off the internal pH referenc body and the membrane cap It aN advised the membrane cap be discarded to prevent pos sible problems associ ated with reuse Cover the glass tip with the protective sh the original shipping follow section IX ipping cap and store parts securely in box When reassembling the sen
3. 0 8 mV 80 6 90 2 A calculated value equal or greater than 160 mV is ac ceptable for ambient temperatures between 20 and 25 C IX Electrode Preparation 1 Remove glass internal from sensor body and perform inner electrode check See section VIII 2 The HI 4105 sensor comes with three easily replace able membrane caps two which are spares Remove a cap from membrane box and screw on to lower threads of outer probe body compressing the o ring seal Avoid touching working area of membrane with your fingers as skin oil will change the membrane properties 3 Using dropper provided add about 2 mL of carbon dioxide internal fill solution HI 4005 40 into outer probe body 4 Insert and position the inner glass reference assem bly into the outer body so that the anti rotation key sits in the cut out on the outer probe body 5 Holding the electrode upright slide spring and elec trode cap down cable and screw cap on outer body until fully engaged Do not invert electrode Do not overtighten 6 Install assembled electrode in gas sensor test vessel or in electrode holder and connect cable connector to pH mV meter X Quick Check of Electrode Slope e Connect BNC connector to pH mV ISE meter Place meter in mV mode Place 100 mL of deionized water into a vessel with stir bar Add 10 mL of ISA Hanna HI 4005 00 Place sensor into prepared sample Add 1 mL of 1000 ppm or 0 1 M Carbon d
4. ab dry with lab wipe or other soft disposable absorbent toweling Check calibration every 1 2 hours Recalibrate if nec essary Position sensors at an angle of approximately 20 to 30 from verticle to reduce possibility of trapping gas bubbles on on the membrane cap Gas bubbles also form from solution out gassing due to temperature change Gently tap body of sensor to dislodge them Close container with plastic wrap or use HI 4000 71 gas sensor test vessel to prevent gas from leaving If electrode was left out in air for a prolonged period gently pulling cable will permit an exchange of fil solution at the membrane surface Re Calibration is required tS VIII Inner Electrode Check Prior to assembling the electrode for the first time or Subsquently reactivating it after extended periods of dry storage the inner electrode assembly should be hydrated and then tested as a pH electrode Prepare pH test solutions HI 4000 47 4 and HI 4000 47 7 by mixing and dissolving each buffer packet in separate containers with 50 mL deionized water These pH solutions contain chloride ions and pH buffers that are used to verify the inner electrode pH internal is operational See Section XVII for replacement accessories and maintenance items For a new sensor Remove the protective shipping cap from the glass inner oa Protective shipping cap P For existing sensor Unscrew th
5. after calibrating the meter with the standards The meter is calibrated with two or more freshly made standards that are in the measurem ent range of the unknowns HI 4005 00 ISA is added prior to measurement and the solution is stirred thoroughly and continuously Covering the vessel to prevent gas loss is advised A pH mV meter in mV mode and semi log graph paper may also be used Two or freshly prepared standards that are in the measurement range of the unknowns with ISA added are measured in mV mode on the meter These standards are plotted on semilog graph paper and their points are connected to form a straight line curve When samples are measu a gas loss red their mV values are converted to oncentration by following the mV to the concentration axis on the semi log plot For both direct reading and mV convertion ISA is added prior to measurement the solution stirred thoroughly and continuously and the vessel should be covered to prevent In the lower concentration ranges the electrode calibration becomes less linear many more calibration points are needed and calibration will need to be repeated more frequently Known addition method may also be used in these regions provid been determined Direct Measurement ed the actual slope of the sensor has Procedure 1 Follow section IX to prepare sensor 2 Follow section VI to prepare standards and solutions e Standard
6. dvance notice truments With Great Products Come Great Results www hannainst com DHANNS
7. e upper cap on the top of the electrode and carefully withdraw the internal pH reference assembly For stable readings glass should be covered to the bottom of the long black band Use test tube or Test buffer graduated can be cylinder 8 used as a weighed conditioning Bottom when solution testing or for the conditioning pH internal pH internal e f sensor has been stored or shipped dry it should be conditioned by soaking the pH reference assem bly 1 hour or more in one of the pH test solutions e Avoid touching the pH glass with your fingers e Attention The pH reference assembly is fragile Support the upper portion of the internal cell while immersing the glass and reference assembly A tall narrow container with weighted bottom is best The pH test solution should cover the bottom of the large black band Test Connect the BNC connector on the electrode cable to a pH mV mV or ORP mode meter Carefully immerse the sensor assembly into one of the buffers When the measurment stabilizes record the mV generated Rin sensor tip in deionized water and dab dry between buffers to prevent solution carry over Do not rub the glass Take a measurement in the second buffer and record mV Pay attention to minus sign if present WN D Calculate the difference in mV between the two solutions Example of typical values HI 4000 47 7 90 2 mV HI 4000 47 4 80 66 mV Difference 17
8. ioxide standard to beaker and stir sample Wait approxi mately 5 minutes Record the mV value when stable Add an additional 10 mL of standard to the solution Record the mV when reading has stabilized approxi mately 5 minutes This value should be greater than the previous noted more positive Determine the difference between the two mV values An acceptable value for this slope is 54 4 mV at ambient temperatures between 20 and 25 C n XI Corrective action e Verify standard has been properly added e Verify ISA has been added in the correct ratio to the standard 1 part ISA to 10 parts sample or standard e Verify that the upper cap has been screwed in all the way e Verify electrode is connected properly to meter and the meter is is powered e Verify membrane cap is tightened securely to probe body e Examine the membrane for discoloration or perfora tions or for intemal fill solution that might have eaked through the PTFE membrane Replace mem brane cap if damaged If drift is seen e Verifye ture e Verify electrode has adaquate fill solution e Verify electrode was not left in air for prolonged pe riod far ctrode and standards are at same tempera XII Sample Handling e For optimum results allow samples and standards and the HI 4105 electrode to reach the same tem perature e As CO is volatile measure samples immediately af ter collection e f sa
9. mple must be stored Completely fill collection bottle with dilute samples and tightly cap container to prevent carbon dioxide loss or contamination from other sources e f sample must be stored For acetic samples add sodium hydroxide 10N to raise pH to 8 9 for stor age Tightly close collection bottle e f sample must be stored keep sample at a lower temperature than it was collected at until time of measurement e Add Hanna HI 4005 00 ISA just prior to measure ment to adjust standards and samples to a pH between 4 2 5 2 for measurement ISA must mix thoroughly with solutions and time allowed to convert carbonate and bicarbonate species to CO dissolved e Covering sample and standards after adding ISA will minimize carbon dioxide loss from the solution e Calibration standards and samples must be the same ionic strength The concentration for all dissolved spe Cies in a sample should not exceed 1M Samples that exceed this should be diluted with CO free deion ized water Do not reduce CO below 10 M Multiply the final result by the corresponding dilution factor XIII Direct Calibration and Measurement The direct measurement method is best used in the linear working regions of th e sensor See figure for typical sensor response and can be used when measuring many samples A direct reading ISE meter HI 4222 or equivalent deter mines concentration of the unknown by a direct reading
10. mple solution diffuses through the PTFE membrane where it dissolves into the thin film of fill solution found between the membrane and the internal pH membrane Here it converts back into bicarbonate and hydrogen ions The pH changes proportionally with the concentration of dissolved gas in the sample solution Dif fusion of CO continues until the partial pressures of the gas in the sample and thin film are equal The Nernst expression for an Carbon Dioxide sensor is ex pressed in the equation below Note that the potential is a function of the Carbon Dioxide gas which in turn is related to the hydrogen ion concentration The glass internal Ag AgQ reference equilibrium constant and Henry s law constant are rolled into the E and E terms The Nemst equation for the sensor becomes the equation noted below E E 2 3RT nF log C0 0 059 log H E observed potential E Reference and fixed intemal voltages R gas constant 8 314 J K Mol n Charge on ion equivalents mol T absolute temperature in K F Faraday constant 9 648 x 10 C equivalent The mV should increase in a Nernstian manner as the carbon dioxide partial pressure increases in the sample 4 IV Design Elements The Hanna HI 4105 Carbon Dioxide gas sensor has 3 main parts These are the membrane membrane cap outer probe body with antirotation key and the pH reference assembly which includes the outer electrode cap
11. ndard and sample are measured within minutes of one another The tech ri the temperature of measurement should be determined nd used if possible This will improve accuracy The volume of the unknown sample V oxide because changes in the sensor calibration are cor que can use an ideal sensor slope but actual slopes at Pe IS mea sured accurately and placed into the closed sample vessel The sensor is secured in the vessel and then the vessel is placed on a stirrer ISA is added at 1 part per 10 parts sample When the measurement is stable the mV value is noted A known amount volume Vni and concentration Canar Of CO Standard is then added to the sample mV values are again noted when the measurement is stable The mV change is then calculated AE Using the measured and calculated values the sample concentration C e Can be determined ample 2 C C ample deanna Vei V V 1 OARS 7 V5 V ample Vanat V nanat Vsa Vi V Visa Vs sample 7 The procedure can be repeated with a second standard addition to verify slope and operation of the method Note This method is preprogrammed in the Hanna HI 4222pH SE mV meter which simplifies the method greatly and permits repeated determinations easily Example Carbon Dioxide determination with known addition 1 A50 mL sample of unknown V yp is placed in an clean vessel with an electrode 5 mL of ISA is added to the sample
12. s should bracket the measurement range of interest and differ from each other by a factor of 10 in the linear regions Standards and solutions should be at the same tem perature 10 mL of ISA is added to each 100 mL of sample and standard Protect these solutions from loss of dissolved gas by covering and using promptly Follow section VII General Guidelines to optimize test set up During calibration it is best to start with lower concen tration samples first Wait for a stable reading before reading recording values approximately 5 minutes To prevent carry over and contamination of samples rinse sensors with deionized water and dab dry be tween samples Between measurements suspend sensor tip in a small sample of CO Conditioning solution HI 4005 45 Rinse body with deionized water and dab dry before placing in next sample Check HI 4105 electrode calibration every 2 hours by verification of at least one calibration point Typical calibration curve for HI 4105 Carbon Dioxide ISE Typical response for H 4105 Carbon Dioxide sensor XIV Other Measurement Techniques Known Addition An unknown concentration of carbon dioxide can be deter me DW mined by adding a known amount volume and concen tration of carbon dioxide standard to a known volume of the sample This technique is extremely useful for carbon j rected for continuously because the sta
13. sor XVI Conversion Tables For CO Multiply by Moles L M CO to ppm CO mg L 4 4 X10 ppm CO mg L to M Moles L 2 273 X10 For CaCO ppm Multiply by Moles L M CO to ppm CaCO mg L 1 00 X10 XVII HI 4105 Accessories and Replacement Parts For Calibration Code HI 4005 00 lonic Strength Adjuster 500 mL HI 4005 01 Hanna 0 1 M CO Standard 500 mL HI 4005 03 Hanna 1000 ppm CO Standard 500 mL Please Note This calibration standard is ppm as CaCO For Maintenance HI 4005 40 Hanna Carbon Dioxide Fill Solution 4 X30 mL HI 4005 45 Hanna Carbon Dioxide Conditioning Solution 500 mL HI 4000 47 Bulk package of 10 each HI 4000 47 4 and HI 4000 47 7 Buffer Packets HI 4005 53 Replacement Membranes Caps 3 Membrane Caps HI 4000 54 Replacement pH reference Electrode Assembly for CO HI 4000 71 Gas Sensor test vessel HI 740155P Capillary Pipettes 20 piece IMAN4IO5 OOSA WARRANTY Hanna Instruments lon Selective Electrodes are warranted to be free of defects in material and workmanship for 6 months from date of purchase when used for their intended purpose and maintained according to instructions If they fail to work when first used contact your dealer immediately Damage due to accidents misuse misapplication tampering or lack of prescribed maintenance is not covered Hanna Instruments reserves the right to modify the design construction or appearance of its products without a
14. spring inner cap and pH reference electrode assembly pH reference electrode assembly cable outer electrode cap spring antirotation key inner cap Outer probe body Reference electrode pH sensitive LJ membrane a Membrane membrane cap 5 V Equipment Required e Hanna HI 4222 pH ISE mV meter or other suitable ion or pH mV meter Note log linear graph paper is useful if an ISE meter is not available e Hanna HI 180 magnetic stirrer or equivalent with stirring bars Note Isolate beakers from stirrer motor heat by placing insulating material such as foam or cork between them e Hanna HI 4000 71 gas sensor test vessel or Hanna HI 76404 electrode holder or equivalent with Beakers or other suitable measurement vessel with plastic sealing film or wrap VI Solutions Required for Calibration lonic Strength Adjuster ISA 500 mL HI 4005 00 Hanna 0 1 M standard 500 mL HI 4005 01 Hanna 1000 ppm CO standard 500 mL HI 4005 03 Please Note This calibration standards is ppm as Ca00 See Section XVII for additional solutions and accessories used for maintenance Using volumetric pipettes and glassware prepare serial dilutions of the standard Select concentrations that will approximately bracket the concentration of the samples to be measured Standards with concentrations less than 103M should be prepared fresh daily Store solution in a tightly sealed bottle witho
15. ut ISA added 10 mL of HI 4005 00 ISA should be added to each 100 mL sample of stan dard and samples just prior to measurement ISA adjusts the pH of the sample or standard to about pH 4 7 thus converting carbonate and bicarbonate ion to carbon diox ide It also provides samples and standards a constant ionic strength background that stabilizes the solutions ac tivity coefficient and permits concentration to be measured directly VII General Guidelines Calibration standards and sample solutions should have the same ionic strength ISA should be added to both samples and standards immediately before tak ing measurements Calibration standards and sample solutions should be stirred at the same rate using identical sized stir bars Stir thoroughly and continuously Calibration standards and sample solutions should be at the same temperature Thermally insulate solution vessel from magnetic stirrer with cork or other insulat ing medium Wait until sensor value has stabilized before taking reading at least 5 minutes when going from more dilute to more concentrated samples longer when the order is reversed Surface coating on the PTFE membrane will effect the esponse Inspect sensor before using Wash off with a et of deionized water or mild detergent to remove film Replace PTFE membrane if damage is evident or a droplet of internal electrolyte is seen Rinse electrode with distilled or deionized water be tween samples and d
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