manualshive.com logo in svg

EUTECH INSTRUMENTS AMMONIA GAS, Инструкция по эксплуатации, Страница: 9 / 21

Поделиться
Скачать
EUTECH INSTRUMENTS AMMONIA GAS Скачать руководство пользователя страница 9

Instruction Manual 

 

Ammonia Gas-sensing Electrode

 

 

9

Since water vapor reacts with ammonia in the gas phase, placing the ammonia electrode in a closed 
system containing water vapor will allow measurements of solutions above 10-

3

M (14 ppm) to be 

taken. 
 
Ammonia in samples containing non-aqueous solutions or surfactants can be measured by adjusting 
the sample pH to 11 to 13 with 10M NaOH. After measuring the sample, transfer it to an 
erlenmeyer flask large enough to contain approximately 2/3 volume of air after sample addition. 
Place a magnetic stir bar in the flask, fit the flask with a one-hole rubber stopper (opening large 
enough to insert the electrode snugly), and insert the electrode until it is just above the level of 
liquid in the flask. The closed flask now forms an air-tight closed system with the gas phase 
saturated with water vapor. The partial pressure of ammonia is in equilibrium with the solution. 
 
For gas phase measurements, calibrate the electrode in a closed flask using standards. The response 
time for the ammonia electrode will be longer in the gas phase than if it were actually immersed in a 
surfactant-free, aqueous solution. 
 

ELECTRODE CHARACTERISTICS 

 

Reproducibility 

 
Electrode measurements reproducible to ±2% can be obtained if the electrode is calibrated every 
hour. Factors such as temperature fluctuation, drift, and noise limit reproducibility. Reproducibility 
is independent of concentration within the operating range of the electrode. 
 

Interference 

 
Volatile amines interfere with the operation of the ammonia electrode. Most gases, since they are 
converted to the ionic form in basic solutions, do not interfere with ammonia electrode 
measurement. The level of ions in solution can change the solubility of ammonia, though ionic 
species cannot cross the gas-permeable membrane and are not considered direct electrode 
interference.  The level of ions in sample solution and standards do not interfere, given that they are 
equal. The same holds true for dissolved species. Low results can occur in direct measurements, due 
to the presence of some metallic ions and their complexation effect on ammonia. 
 

Effect of Dissolved Species 

 
One common substance that is a potential electrode interference is water vapor. The concentration 
of the internal filling solution under the membrane is changed when water, in the form of water 
vapor, moves across the electrode membrane. These changes will be seen as electrode drift. If the 
total level of dissolved species in solution, the osmotic strength, is below 1M and the sample and 
electrode temperatures are the same, water vapor transport is not a problem. 
 
Samples of low osmotic strength are automatically adjusted to the correct level through addition of 
10M NaOH. If samples have osmotic strengths greater than 1M, they should be diluted before 
measurement. However, this dilution should not reduce the ammonia level below 10-

5

M. If dilution 

is not possible, for the reason mentioned, the sample can be measured by adjusting the osmotic 
strength of the electrode filling solution. The total level of dissolved species in the electrode filling 
solution may be adjusted by adding 0.425 grams of reagent-grade sodium nitrate (NaNO

3

) to 10 ml 

of the electrode filling solution. 
 

Содержание AMMONIA GAS

Страница 1: ... No EC NH3 01 Required Solutions 1 Deionized or distilled water for solution preparation 2 Eutech Ammonia Standard 0 1M NH4Cl Code No EC SCS AA1 BT To prepare this solution from your own laboratory stock half fill a one liter volumetric flask with distilled water and add 5 35 grams of reagent grade NH4Cl Swirl the flask gently to dissolve the solid Fill the flask to the mark with distilled water c...

Страница 2: ...de is shipped dry Before using unscrew the large cap See Figure 5 and remove the inner glass electrode from the outer body Fill the outer body with 2 to 3 ml of internal filling solution Place the inner glass electrode into the outer body and screw on the large cap until finger tight Place the assembled electrode in an electrode holder with a 20o angle from the vertical to avoid trapping air bubbl...

Страница 3: ... 100 ml of distilled water and 1 ml of ISA Place the beaker on a magnetic stirrer and begin stirring at a constant rate After assuring that the meter is in the millivolt mode lower the electrode tip into the solution Remove air bubbles by redipping probe 2 Using a pipet add 1 ml of 0 1M or 1 000 ppm standard into the solution When the reading has stabilized record the mV value 3 Using a pipet add ...

Страница 4: ...ld be added just before measurement All samples and standards should be at the same temperature for precise measurement A difference of 1o C in temperature will result in approximately a 2 error All samples must be aqueous Always rinse the electrode with distilled water and blot dry between measurements Use a clean dry tissue to prevent cross contamination Constant but not violent stirring is nece...

Страница 5: ... ISA for all ammonia solutions The temperature of both sample solutions and standard solutions should be the same Direct Measurement of Ammonia using a pH mV meter 1 By serial dilution prepare three standard solutions from the 0 1M or 1 000 ppm stock standard The resultant concentrations should be 10 2 M 10 3 M and 10 4 M or 1 000 100 and 10 ppm ammonia standards Add 1 ml of ISA per 100 ml of stan...

Страница 6: ...o a clean dry 150 ml beaker add 100 ml of sample and 1 ml of ISA Place the beaker on the magnetic stirrer and begin stirring at a constant rate Rinse the electrodes with distilled water blot dry and lower the electrode tip into the solution When the reading has stabilized record mV reading Using the calibration curve determine sample concentration 7 The calibration should be checked every two hour...

Страница 7: ...ized read the concentration directly from the meter display 11 The calibration should be checked every 2 hours Assuming no change in ambient temperature place the electrode tip in the first ammonia standard After the reading has stabilized compare it to the original reading in step 3 above A reading differing by more than 0 5 units or a change in ambient temperature will necessitate the repetition...

Страница 8: ... Be sure to use the magnetic stirrer 6 Place 1 000 ml of the sample into a 1 000 ml beaker add 10 ml of 10M NaOH place the beaker on the magnetic stirrer and begin stirring After rinsing the electrodes immerse the tip in the solution When the reading has stabilized record the mV potential 7 Determine concentration from the calibration curve Prepare a new low level calibration curve on a daily basi...

Страница 9: ...operation of the ammonia electrode Most gases since they are converted to the ionic form in basic solutions do not interfere with ammonia electrode measurement The level of ions in solution can change the solubility of ammonia though ionic species cannot cross the gas permeable membrane and are not considered direct electrode interference The level of ions in sample solution and standards do not i...

Страница 10: ...iation of theoretical response with temperature The electrode response will shift and change slope with change in temperature Standards and samples should be at the same temperature A 2 error results with a 1oC temperature change for a 10 3 M solution Gases are expelled from a solution at a faster rate as the temperature increases TABLE 4 Temperature vs Values for Electrode Slope Temp oC S 0 54 20...

Страница 11: ...lectrode Storage If erratic results are obtained from accidentally leaving the electrode in air the space between the sensing element and the inside of the membrane may be dry To remedy this situation and allow new filling solution to flow into the space withdraw the glass electrode from the membrane by pulling the cable slightly For low level measurements immerse the tip of the electrode in pH 4 ...

Страница 12: ...roxide level E Eo S log OH where S is the slope of the electrode Because the hydroxide concentration is proportional to the ammonia concentration electrode response to ammonia is also Nernstian E Eo 1 S log NH3 Eo 1 represents the reference potential and is partly determined by the internal reference element which responds to the fixed level of chloride in the internal filling solution Ammonia Che...

Страница 13: ...t 25o C and X 0 1 is 9 3 an increase in ionic strength to X 1 0 yields a pH of 9 4 at 25o C TROUBLESHOOTING GUIDE The goal of troubleshooting is the isolation of a problem through checking each of the system components in turn the meter the glassware the electrodes the standard and reagents the sample and the technique Meter The meter is the easiest component to eliminate as a possible cause of er...

Страница 14: ...sections below 5 Before replacing a faulty electrode review the instruction manual and be sure to Clean and rinse the electrode thoroughly Prepare the electrode properly Use proper filling solution buffer and standards Measure correctly and accurately Review TROUBLESHOOTING HINTS Standards The quality of results depends greatly upon the quality of the standards ALWAYS prepare fresh standards when ...

Страница 15: ...exceeded Be sure that the analysis method is clearly understood and is compatible with the sample Refer to the instruction manual again Reread the sections GENERAL PREPARATION and ELECTRODE CHARACTERISTICS If trouble still persists call Eutech Instruments Pte Ltd at 65 6778 6876 and ask for the Customer Services Department ...

Страница 16: ...g solution amount of internal filling solution continuously or randomly changing defective meter perform meter checkout procedure see meter instruction manual bottom cap loose ensure that bottom cap is screwed on tight enough to close gap between bottom cap and body defective inner body refer to Checking the Electrode Inner Body air bubbles on membrane remove bubbles by redipping electrode meter o...

Страница 17: ...tore electrode response Low Slope or standards contaminated prepare fresh standards No Slope or incorrectly made buffer not used use recommended buffer standard used as buffer use buffer electrode exposed hold electrode by outer body and to air for extended period pull on electrode cable internal filling solution will flow under membrane and restore electrode response membrane failure replace memb...

Страница 18: ...onia electrode If the electrode is dry soak the glass tip of the inner body in Eutech Ammonia Electrode Filling Solution Code No EC RE 032 for at least two hours Rinse the electrode thoroughly with distilled water Put 100 ml of pH 7 buffer 0 1M NaCl added in a 150 ml beaker Place the beaker on the magnetic stirrer and begin stirring Immerse the tip of the inner body in the solution so that the ref...

Страница 19: ...ge Store electrodes in 0 1M NH4Cl ORDERING INFORMATION CODE NO DESCRIPTION EC NH3 01 Ammonia Gas Sensing Electrode EC MIS AM Ammonia Membrane Kit bag of 20 membranes and spare o ring EC SCS AA1 BT Ammonia Standard 0 1M NH4Cl EC SCS AA2 BT Nitrogen Standard 1 000 ppm NH3 as N EC SCS AA3 BT Nitrogen Standard 100 ppm NH3 as N EC ISA AA1 BT Ammonia Ionic Strength Adjuster ISA Solution 10 M NaOH EC ISA...

Страница 20: ...Measurement 5 Direct Measurement of Ammonia using a pH mV meter 5 Direct Measurement of Ammonia using an ion meter 6 Low Level Ammonia Determination using a pH mV meter 7 Ammonia Measurements in Membrane Wetting Solutions 8 ELECTRODE CHARACTERISTICS 9 Reproducibility 9 Interference 9 Effect of Dissolved Species 9 Complexation 10 Temperature Influences 10 Electrode Response 10 Limits of Detection 1...

Страница 21: ...Instruction Manual Ammonia Gas sensing Electrode 21 ORDERING INFORMATION 19 ...

Отзывы:

Нет отзывов