PASCO Specialty & Mfg. CI-6734 User's Manual
Contents
1. 140 100 10 fold change 60 ae 59 mV electrode 29 potential mV 20 60 m 0 1 1 10 100 1 000 ppm 10 6 10 5 10 4 10 3 10 2 10 1 Na concentration M Figure 3 Typical sodium electrode calibration curve 6 Toaclean dry 150 ml beaker add 100 ml of sample and 2 ml of ISA Place the beaker on the magnetic stirrer and begin stirring After rinsing the electrode tip with electrode rinse solution blot dry and place the electrode tip in the solution When the reading has stabilized record the Voltage reading in the Digits Display Using the calibration curve determine the sample concentration 7 The calibration should be checked every two hours Assuming no change in ambient temperature place the electrode tip in the mid range standard After the reading has stabilized compare it to the original reading recorded in step 3 above A reading difference by more than 0 5 mV or a change in the ambient temperature will necessitate the repetition of steps 2 5 above A new calibration curve should be prepared daily Low Level Sodium Determination This procedure is recommended for solutions with ionic strength less than 1 0x10 M and a sodium concentration less than IxIO M or 1 ppm If the solution is high in ionic strength but low in sodium use the same procedure but prepare a calibration solution with a composition similar to the sample Use plastic lab ware for low sodium measurements 1 Using 20 ml of standard ISA dilute2. The Sodium Ion Selective Electrode is composed of a sodium selective glass membrane bonded to a glass body When the membrane is in contact with a solution containing sodium ions an electrode potential develops across the membrane This electrode potential is measured against a constant reference potential using an ISE Amplifier and a ScienceWorkshop computer interface The level of sodium ions corresponding to the measured potential is described by the Nernst equation E Eo S log X where E measured electrode potential E reference potential a constant _ mV S electrode slope 59 decade X level of sodium ions in solution The activity X represents the effective concentration of free sodium ions in the solution The activity is related to the free ion concentration C P by the activity coefficient yby X 4C Activity coefficients may vary depending on the total ionic strength Z determined as I 1 SCZ where C concentration of ion X Z charge of ion X X sum of all of the types of ions in the solution In the case of high and constant ionic strength relative to the sensed ion concentration the activity coefficient y is constant and the activity X is directly proportional to the concentration PASC Ce screntitrec Sodium Ion Selective Electrode 012 06615A To adjust the background ionic strength to a high and constant value ionic strength adjuster is added to samples and sta
3. Instruction Manual and 012 06615A Experiment Guide for the 9 97 PASCO scientific Model CI1 6734 SODIUM ION SELECTIVE ELECTRODE 1997 PASCO scientific BD A 10101 Foothills Blvd P O Box 619011 Roseville CA 95678 9011 USA sc f teach science ITEM TITLE Phone 916 786 3800 FAX 916 786 8905 web www pasco com Sodium Ion Selective Electrode 012 06615A Always use eye protection and gloves when working with chemicals PASC Oe cl f c 3 012 06615A Sodium Ion Selective Electrode Table of Contents linum rauen 1 heavy 1 QU PHT OME ca dcceessadesstesccpevsicecdsscosnese sides eheaacdaetvauspevasendsvsascsosestucesestoccpiveeddeeiteuctencaouedessioseesesabessuesostaoace 2 MCS M EAE 2 Additional Required oce eerie et een een 2 RREG UPC SOLMPONS I Renner seeha seen Fasten rear sonsusdeoassdessetsusasesucsssssesaisosnntsesoes seesensssevenssessiens 2 General Preparation 5o adii esci anna 4 Electrode Preparation 1 eene riter tinere caro trate oen ieai e tee tes parte sechs 4 Electrode Slope Check Using Science Workshop esses 4 Measurement e 3 Measuring sure 5 Sample Requiremients 4d iere ihe es enee en haee eei nee nalen srl ala 5 Units OF Measurement uio iere Erin E anne s uen d s des be sen Ve Ene ea En 5 Measurement Procedure eeeee erts eee etos etta aeo etapa o ena reo rotsen sao Fe so
4. Resistance lt 200 mohm Reproducibility 2 Storage store in 5 M NaCl with added ISA Size length 110 mm diameter 12 mm cable length 1 m Troubleshooting Guide The goal of troubleshooting is the isolation of a problem through checking each of the system components in turn 12 the meter the glassware the electrodes the standards and reagents the sample and the technique Glassware Plastic ware Clean glassware is essential for good measurement Be sure to wash the glassware plastic ware well with a mild detergent and rinse very well with distilled or deionized water Clean glassware will drain without leaving water droplets behind Electrode The electrodes may be checked by using the procedure found in the sections entitled Electrode Slope Check I Be sure to use distilled or deionized water when following the procedures given in Electrode Slope Check Ifthe electrode fails to respond as expected see the sections Measuring Hints and Electrode Response Repeat the slope check If the electrode still fails to respond as expected substitute another Sodium Ion Selective Electrode if available that is known to be in good working order for the questionable electrode If the problem persists the reagent may be of poor quality interferences in the sample may be present or the technique may be faulty See Standards amp Reagents Sample and Technique sections below If another electrode is not a
5. 4 76 4 8 X 10 Solutions additions of 100 ppm or 1 0 X 10 M standard to 100 ml of solution prepared in step 3 above 8 On semilogarithmic graph paper plot the millivolt reading linear axis against the concentration log axis as in Figure 3 9 Rinse the electrodes with electrode rinse solution and blot dry 10 To a 150 ml plastic beaker add 100 ml of sample and 1 ml of low level ISA Place the beaker on the magnetic stirrer and begin stirring Adjust the pH if necessary to above 9 Lower the electrode tip into the solution After the reading has stabilized record the Voltage reading in the Digits Display and determine the concentration from the low level calibration curve 11 Prepareanew low level calibration curve daily Check the calibration curve every two hours by repeating steps 3 8 Electrode Characteristics Reproducibility Electrode measurements reproducible to 2 can be obtained if the electrode is calibrated every hour Factors such as temperature fluctuations drift and noise limit reproducibility Reproducibility is independent of concentration within the electrode s operating range Interferences Table 3 lists some common cations that if present in high enough levels will cause electrode interferences and measurement errors or electrode drift when using the sodium ion electrodes Mostsamples do notcontain or contain very little of the cations shown in Table 3 The ammonium ion NH 2 found in
6. indicated in the Digits display Using a pipette add 10 ml of the same sodium standard used above to the beaker When the reading has stabilized record the voltage reading indicated in the Digits display Determine the difference between the two readings A difference of 59 4mV indicates correct electrode operation assuming the solution temperature is between 20 C and 25 C See the Troubleshooting sections if the potential change is not within this range Insert DIN connector into analog channel AorB Rotate ring s one quarter Ki P turn to secure M L2 IV c ISE Amplifier electrode connector Figure 2 Equipment Setup a filling the electrode with filling solution b amp c connecting the electrode to the ISE Amplifier and to the computer interface gt Note Slope is defined as the change in potential observed when the concentration changes by a factor of 10 012 06615A Sodium Ion Selective Electrode Measurement Measuring Hints Allsamples and standards should be at the same temperature for precise measurement preferably ambient temperature A difference of C in temperature will result in about a2 measurement error The electrodes should not be used above 70 C Constant but not violent stirring is necessary for accurate measurement Magnetic stirrers can generate sufficient heat to change the solution temperature To counteract this effect place a piece of insulating
7. problem is with the PASCO apparatus note Title and model number usually listed on the label Approximate age of apparatus A detailed description of the problem sequence of events in case you can t call PASCO right away you won t lose valuable data If possible have the apparatus within reach when calling to facilitate description of individual parts gt If your problem relates to the instruction manual note Part number and revision listed by month and year on the front cover Have the manual at hand to discuss your questions
8. sa CE e ren OE Re so eher 6 Direct Measurement of Sodium sssrinin ie entente enne ATE rentre trennen 6 Low Level Sodium Determination essent reete nennen trennen 7 El ctrode C haracteristics cc RR RER 8 Reproducibility su M M 8 Tinterferen Ces m 8 Temperature Inf etices iden reete dee drca eed ngo eeu reo Ea Ea 9 Electrode Response cde iret tee det erre e erp ree Peter ee ere tu E EA EARE 10 Limits Of Det UE S M 10 PH Effects 10 Eleetr de T 11 Mameta c 11 Electrode Storage ree ect ett er EIS ERR anne ren 11 SPE CHICA ONS ke ET 12 Troubleshooting Guide scssccssccssesscsssscssscssscssscssssnssesssessesscscssssssessesssssssesescssssncssossessnsseceseoes 12 Glassware Plastic Ware oerte keines horse 12 Flectrode 12 Standards amp Reagents 2 eder teer reed a pies ne EEA EE EEE EE e cbr eee S 13 Sample e A EIE ET TEE NE T ENE E EE 13 Techniques E E E 13 Troubleshooting Fils esssissssssccsecisceessstsessssdinesosiseasarsececoteticeses svscesschscccosdscossusciecsesbscsvieseccvostesseiesdeests 13 iEzdanDelblqgii E 17 PASC Ce i scientific Copyright Warranty and E
9. use recommended ISA prepare fresh standards use ISA soak overnight in electrode storage solution adjust pH with ISA remove bubble by re dipping probe 012 06615A Sodium Ion Selective Electrode Symptom Possible Causes Next Step Incorrect Answer incorrect scaling of semilog paper plot voltage potential on the linear axis but calibration curve On the log axis be sure concentration is good numbers within each decade are increasing with increasing concentration incorrect sign be sure to note sign of millivolt reading correctly incorrect standards prepare fresh standards wrong units used apply correct conversion factor 1 0X10 M 23 0 ppm as Na sample pH too acidic adjust pH with ISA PASC scientific Sodium Ion Selective Electrode 012 06615A 16 Technical Support Feedback If you have any comments about the product or manual please let us know If you have any suggestions on alternate experiments or finda problem in the manual please tell us PASCO appreciates any customer feedback Your input helps us evaluate and improve our product To Reach PASCO For technical support call us at 1 800 772 8700 toll free within the U S or 916 786 3800 fax 916 786 3292 e mail techsupp pasco com web www pasco com Contacting Technical Support Before you call the PASCO Technical Support staff it would be helpful to prepare the following information gt If your
10. ASCO scientific Credits Author Peter Boyle Editor Steve Miller ii Equipment Return Should the product have to be returned to PASCO scientific for any reason notify PASCO scientific by letter phone or fax BEFORE returning the product Upon notification the return authorization and shipping instructions will be promptly issued gt NOTE NO EQUIPMENT WILL BE ACCEPTED FOR RETURN WITHOUT AN AUTHORIZATION FROM PASCO When returning equipment for repair the units must be packed properly Carriers will not accept responsibility for damage caused by improper packing To be certain the unit will not be damaged in shipment observe the following rules The packing carton must be strong enough for the item shipped Make certain there are at least two inches of packing material between any point on the apparatus and the inside walls of the carton Make certain that the packing material cannot shift in the box or become compressed allowing the instrument come in contact with the packing carton Address PASCO scientific 10101 Foothills Blvd P O Box 619011 Roseville CA 95678 9011 Phone 916 786 3800 FAX 916 786 3292 email techsupp pasco com web www pasco com 012 06615A Sodium Ion Selective Electrode Introduction The PASCO scientific Sodium Ion Selective Electrode is used to quickly simply accurately and economically measure sodium ions in aqueous solutions Theory
11. ature Provided that temperature equilibria has occurred the sodium ion electrodes can be used at temperatures from 5 to 70 C Room temperature measurements are recommended since measurements at temperatures markedly different from room temperature may require equilibrium times up to one hour The electrode should not be used at temperatures above 70 C since damage to the membrane may result TABLE 4 Temperature vs Values for the Electrode Slope Temperature C Ss 0 54 20 10 56 18 20 58 16 25 59 16 30 60 15 40 62 13 50 64 11 PASC Ce 9 screntitrc Sodium Ion Selective Electrode 012 06615A Electrode Response Plotting the electrode potential against the sodium concentration on semilogarithmic paper results in a straight line with a slope of about 59 mV per decade Refer to Figure 1 The time needed to reach 99 of the stable electrode potential reading the electrode response time varies from one minute or less for sodium concentrations above 1 0X10 M to several minutes near the detection limit Refer to Figure 4 125 3 2 TT 103 M to 102M NaCl 75 50 electrode 25 N 103M to 104M NaCl potential mV i 25 10 M to 105 M NaCl 50 103M to 10 M NaCl 75 1 2 3 i time minutes Figure 4 Typical sodium electrode time response to step changes in NaCl Limits of Detection The upper limit of detection in pure sodium solutions is 1 M In the presence of other ions t
12. dissolve the solid and allow to cool Fill the Included Equipment flask to the mark with distilled water cap and upend several times to mix the solution Sodium Electrode Storage Solution 5 M NaCl To prepare this solution add 29 2 grams of reagent grade sodium chloride NaCl to 100 ml of distilled water To each 100 ml storage solution add 2 ml of ISA 2 PASCOE ent f c 012 06615A Sodium Ion Selective Electrode Note Electrodes must not be stored in distilled water or air Do not rinse with distilled water Dilute Electrode Rinse Solution To prepare this solution from your own laboratory stock add 20 ml of ISA to a one liter volumetric flask and fill to the mark with distilled water Use this solution to rinse the electrode between measurements Sodium Standard 0 1 M NaCl To prepare this solution half fill a one liter volumetric flask with distilled water and add 5 84 grams of reagent grade NaCl Swirl the flask gently to dissolve the solid Fill the flask to the mark with distilled water cap and upend several times to mix the solution Sodium Standard 1 000 ppm Na To prepare this solution half fill a one liter volumetric flask with distilled water and add 2 542 grams of reagent grade NaCl Swirl the flask gently to dissolve the solid Fill the flask to the mark with distilled water cap and upend several times to mix the solution Sodium Standard 100 ppm Na To prepare this solution half fil
13. e The pH should be adjusted to a pH greater than 9 by the addition of ISA to all standards and samples for optimal results over the entire concentration range of sodium Additional ammonium hydroxide may be necessary to adjust the pH to the desired level in some cases Electrode Life The sodium electrode will last six months in normal laboratory use On line measurements might shorten operational lifetime to several months In time the response time will increase end the calibration slope will decrease to the point calibration is difficult and electrode replacement is required Maintenance Electrode Storage The Sodium Ion Selective Electrode should be stored in the sodium electrode storage solution never in air or in distilled water A more dilute sodium chloride solution with pH adjusted through the use of ISA may be used for storage before low level measurements For longer storage longer than two weeks rinse and dry the sensing glass and cover the glass tip with any protective cap shipped with the electrode The reference portion of the combination electrode or the outer chamber of the reference electrode should be drained of filling solution if refillable and the rubber insert placed over the filling hole PASC Ca M Screntrtre Sodium Ion Selective Electrode 012 06615A Specifications Concentration Range Saturated to 1 0X10 M 0 02 ppm pH Range 5 to 12 depending on pH level Temperature Range 5 C 70 C
14. he upper limit of detection is above 10 M sodium but two factors influence this upper limit Both the possibility of a liquid junction potential developing at the reference electrode and the salt extraction effect influence this upper limit Some salts may extract into the electrode membrane at high salt concentrations causing deviation from the theoretical response Either dilute samples between 1 M and 10 M or calibrate the electrode at 4 or 5 intermediate points Free sodiumion concentration downto l OXIO M or 0 1 ppmcan be measured in basic solutions For measurements below 10 M or 1 ppm use plastic lab ware and low level procedures since a significant pickup of sodium may occur from glassware due to removal from container walls pH Effects The electrode response to sodium ions is greatly influenced by the pH of the solution Hydrogen ion interferes with measurements of low level sodium ion measurements although the electrode can be used over a wide pH range See Figure 5 10 PASC Ch 012 06615A Sodium Ion Selective Electrode 107 M Na 180 160 140 120 electrode potential 100 mV 80 60 40 20 Figure 5 Electrode potential behavior vs solution pH in pure NaCl solution at 25 The edge of the shaded area the straight line shown in Figure 5 indicates a minimum pH at which dilute sodium measurements can be made with less than 10 hydrogen ion interferenc
15. l a one liter volumetric flask with distilled water and add 0 254 grams of reagent grade NaCl Swirl the flask to dissolve the solid Fill the flask to the mark with distilled water cap and upend several times to mix the solution PASC Ce 3 scientific Sodium Ion Selective Electrode 012 06615A General Preparation Electrode Preparation 1 Electrode Slope Check Using ScienceWorkshop Remove the rubber cap covering the electrode tip and the rubber insert covering the filling hole of the Sodium Ion Selective Electrode Fill the electrode with the included filling solution to a level just below the fill hole No preparation is required with a sealed reference electrode Connect the Sodium Ion Selective Electrode to the ISE Amplifier and insert the DIN connector of the ISE Amplifier into analog channel A or B on a PASCO Computer Interface Figures 2b and 2c check electrodes each day 1 To a 150 ml glass beaker add 100 ml of distilled water and 2 ml of ISA Place the beaker on a magnetic stirrer and begin stirring at a constant rate Start the ScienceWorkshop software select the Ion Selective Electrode sensor open a Digital display change the number of digits to the right of the decimal from 1 to 3 and begin monitoring data Lower the electrode tip into the solution Using apipette add 1 ml of 0 1 Mor 1 000 ppm sodium standard to the beaker When the reading has stabilized record the voltage reading
16. material such as a styrofoam sheet between the stirrer and the beaker Alwaysrinse the electrodes with electrode rinse solution from a wash bottle between measurements Use a clean dry tissue to prevent cross contamination Never use distilled water Store the electrodes in electrode storage solution between measurements Do not store in air or distilled water Always soak new electrodes overnight in electrode storage solution prior to first use When making low level sodium measurements use a dilute sodium chloride storage solution Add 1 ml of ISA to 100 ml of dilute storage solution Plastic lab ware should be used for low level measurements 1 ppm All measurements should be made in basic solution All samples and standards should be adjusted to a pH 9 with ISA For samples with high ionic strength prepare standards whose composition is similar to the sample Always check to see that the membrane is free from air bubbles after immersion into standard or sample Sample Requirements The sample measuring range is pH 9 12 Use the ISA recommended to adjust the pH for best accuracy Make sure that the samples and standards are at the same temperature The glass electrode sensing bulb will not be attacked by most organic solvents Units of Measurement Sodium concentrations are measured in units of parts per million equivalents per liter soles per liter or any other convenient concentration unit Table 1 indicate
17. ndards The recommended ISA for sodium is an ammonium chloride ammonium hydroxide buffer Solutions other than this may be used as ionic strength adjusters as long as ions that they contain do not interfere with the electrode s response to sodium ions Equipment Included Additional Required Sodium Ion Selective Required Equipment Electrode PASCO CI 6738 ISE Ion Selective Electrode Amplifier Science Workshop 2 2 5 or higher PASCO Science Workshop Computer Interface Sodium Ion Selective Electrode fill solution pipette for fill solution e Semilogarithmic 4 cycle graph paper for preparing calibration curves magnetic stir plate Lab ware made of plastic not glass for all low level measurements to ISE Sodium lon Selective Amplifier Electrode Required Solutions The stock solutions described in this section may be created as describedin thetextor ordered directly from PASCO The solutions available for order and their respective prices are listed on the ISE Working Solution Price List Deionized or distilled water for solution and standard preparation e Tonic Strength Adjuster ISA 4 M NH Cl 4 M NH OH To prepare this solution half fill a 1000 ml volumetric flask with distilled water and add 214 grams of reagent grade ammonium chloride NH 4Cl Under a hood add 270 ml of I BE filling vi s a pa m concentrated ammonium hydroxide NH OH swirl the Figure 1 flask gently to
18. nual again Reread General Preparation and Electrode Characteristics If trouble still persists call PASCO Technical Support Troubleshooting Hints Symptom Possible Causes Next Step Out of Range Reading defective electrode check electrode operation electrodes not plugged in unplug electrodes and reseat electrodes properly reference electrode not filled replenish reference filling solution electrodes not in solution put electrodes in solution air bubble on membrane remove bubble by re dipping electrode PASC screntitrec Sodium Ion Selective Electrode 012 06615A Symptom Noisy or Unstable Readings readings continuously or rapidly changing Drift reading slowly changing in one direction Low Slope or No Slope 14 Possible Causes electrode exposed to interferences defective electrode ISA not used stirrer not grounded samples and standards at different temperatures electrode exposed to interferences incorrect reference filling solution PH too acidic ISA not used standards contaminated or incorrectly made standard used as ISA electrode exposed to interferences PH too acidic air bubble on membrane Next Step soak overnight in electrode storage solution replace electrode use recommended ISA ground stirrer allow solutions to come to room temperature before measurement soak overnight in electrode storage solution use recommended filling solution adjust pH with ISA
19. position similar to the samples if the samples have an ionic strength above 0 M 2 Place the most dilute solution 10 M or 10 ppm in a beaker Place the beaker on the magnetic stirrer and begin stirring at a constant rate After assuring that ScienceWorkshop is operating lower the electrode tip into the solution When the reading has stabilized record the voltage reading indicated in the Digits display 3 Place the mid range solution 10 M or 100 ppm in a beaker Place the beaker on the magnetic stirrer and begin stirring After rinsing the electrodes with electrode rinse solution blot dry and immerse the electrode tip in the solution When the reading has stabilized record the voltage reading indicated in the Digits display 4 Place the most concentrated solution 10 M or 1 000 ppm in a beaker Place the beaker on the magnetic stirrer and begin stirring After rinsing the electrodes with electrode rinse solution blot dry and immerse the electrode tip in the solution When the reading has stabilized record the voltage reading indicated in the Digits display 5 Using the semilogarithmic graph paper plot the voltage reading linear axis against the concentration log axis Extrapolate the curve down to about 5 0XI0 M For measurements below this level follow the instructions for low level measurement A typical calibration curve can be found in Figure 3 012 06615A Sodium Ion Selective Electrode
20. quipment Return Please Feel free to duplicate this manual subject to the copyright restrictions below Copyright Notice The PASCO scientific 012 06615 A manual is copyrighted and all rights reserved However permission is granted to non profit educational institutions for reproduction of any part ofthe Sodium Ion Selective Electrode manual providing the reproductions are used only for their laboratories and are not sold for profit Reproduction under any other circumstances without the written consent of PASCO scientific is prohibited Limited Warranty PASCO scientific warrants the product to be free from defects in materials and workmanship for a period of one year from the date of shipment to the customer PASCO will repair or replace at its option any part of the product which is deemed to be defective in material or workmanship The warranty does not cover damage to the product caused by abuse or improper use Determination of whether a product failure is the result of a manufacturing defect or improper use by the customer shall be made solely by PASCO scientific Responsibility for the return of equipment for warranty repair belongs to the customer Equipment must be properly packed to prevent damage and shipped postage or freight prepaid Damage caused by improper packing of the equipment for return shipment will not be covered by the warranty Shipping costs for returning the equipment after repair will be paid by P
21. s some of the concentration unit conversion factors TABLE 1 Concentration Unit Conversion Factors ppm Na moles liter Na 229 90 50x 10 22 99 l10x1 2 30 1 0 X 107 PASC Ce 5 Screntrtre Sodium Ion Selective Electrode 012 06615A Measurement Procedure Direct Measurement Direct measurement is a simple procedure for measuring a large number of samples A single meter reading is all that is required for each sample The ionic strength of samples and standards should be made the same by adjustment with ISA for all sodium solutions The temperature of both sample solution and of standard solutions should be the same Direct Measurement of Sodium gt Note A calibration curve is constructed on semilogarithmic paper The measured electrode potential linear axis is plotted against the standard concentration log axis In the linear region of the curve only two standards are necessary to determine a calibration curve Calibration solutions close to the anticipated value of the unknown should be chosen In the nonlinear region additional points must be measured The direct measurement procedures given are for the linear portion of the curve The nonlinear portion of the curve requires the use of low level procedures 1 By serial dilution of the 0 1 M or 1 000 ppm standards prepare 100 ml of 10 M 10 M and 10 M or 100 and 10 ppm sodium standards Add 2 ml of ISA per 100 ml of standard Prepare standards with a com
22. the recommended ISA will not result in an error if all samples and standards have the same level of ISA present I PASC CH crentifie 012 06615A Sodium Ion Selective Electrode Electrode drift and slow response could indicate the presence of high interference from the ions listed Soak the electrodes in electrode storage solution when this happens to restore proper response See Measuring Hints section TABLE 3 Levels of Interfering lons Resulting in a 10 Error at Specified Levels of Sodium Interference 1 0X10 M 1 0X10 M 1 0X10 M Li 5X10 M 5X10 M 5X10 M K 1X10 M 1IX10 M IM Rb 3XI0 M 3M NH 3X10 M 3M Ag 3X10 M 3X10 M 3X107M TI 5X10 M 5X10 M i Interference 1 ppm 10 ppm 100 ppm Li 1 5 ppm 15 ppm 150 ppm K 17 ppm 170 ppm 1 700 ppm Rb 1 1X10 ppm 1 1X10 ppm NH 1 8X10 ppm 1 8X10 ppm Ag 0 0001 ppm 0 001 ppm 0 01 ppm TI 4 5X10 ppm 4 5X10f ppm Temperature Influences Samples and standards should be at the same temperature since electrode potentials are influenced by changes in temperature Al C difference in temperature results in a2 error at the 10 Mlevel Because of solubility equilibria on which the electrode depends the absolute potential of the reference electrode changes slowly with temperature The slope of the electrode as indicated by the factor S in the Nernst equation also varies with temperature Table 4 indicates the variation of theoretical slope with temper
23. to 100 ml with distilled water 2 Dilute 20 ml of the outer chamber filling solution to 100 ml with distilled water and fill the reference electrode if using a double junction reference electrode 3 Dilute 1 ml of the 0 1 M standard to 100 ml to prepare a 1 0XI0 M standard solution for measurements in moles per liter Dilute 10 ml of the 1000 ppm standard solution to 100 ml to prepare a 100 ppm standard solution for measurements in ppm Add 1 ml of low level ISA toeach 100 ml of standard Standards should be prepared fresh daily 4 Using a 150 ml plastic beaker add 100 ml of distilled water and 1 ml of low level ISA Add NH JOH if necessary to adjust the pH above 9 Place the beaker on the magnetic stirrer and begin stirring at a constant rate 5 Place the electrode tip in the solution Assure that Science Workshop is operating PASC Ce 7 screntifrec Sodium Ion Selective Electrode 012 06615A 6 Add increments of the 1 0x10 M or 100 ppm standard as given in Table 2 below 7 After the reading has stabilized record the Voltage reading in the Digits display after each addition TABLE 2 Step wise Calibration for Low Level Sodium Measurements Added Step Pipette Volume ml 1 A 0 1 2 A 0 1 3 A 0 2 4 A 0 2 5 A 0 4 6 B 2 0 7 B 2 0 Pipette A 1 ml graduated pipette Pipette B 2 ml pipette Concentration ppm M 0 10 1 0 X 10 0 20 2 0 X 105 0 40 4 0 X 10 0 60 6 0 X 10 0 99 9 9 X 10 2 91 2 9 X 10
24. vailable for test purposes or if the electrode in use is suspect review the instruction manual and be sure to Clean and rinse the electrode thoroughly Prepare the electrode s properly Use the proper filling solution Adjust the pH and the ionic strength of the solution by the use of the proper ISA Measure correctly and accurately Review Troubleshooting Hints 012 06615A Sodium Ion Selective Electrode Standards amp Reagents Whenever problems arise with the measuring procedure that has been used successfully in the past be Sure to check the standard and reagent solutions Ifin doubt about the credibility ofany of the solutions prepare them again Errors may result from contamination of the ISA incorrect dilution of standards poor quality distilled deionized water or a simple mathematical miscalculation Sample Look for possible interferences complexing agents or substances which could affect the response or physically damage the sensing electrode or the reference electrode if the electrodes work perfectly in the standard but not in the sample Try to determine the composition of the samples prior to testing to eliminate a problem before it starts See Measuring Hints Sample Requirements and Interferences Technique Be sure that the electrode s limit of detection has not been exceeded Be sure that the analysis method is clearly understood and is compatible with the sample Refer to the instruction ma
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