How it Works
Thermo Fisher Scientific
Loading...
Ion Selective Electrodes Ammonium
User Manual
24 pgs329.49 Kb0

Thermo Fisher Scientific Ion Selective Electrodes Ammonium User Manual

Download
Page 1
EUTECH INSTRUMENTS PTE LTD.
AMMONIUM ION ELECTRODE
INSTRUCTION MANUAL
Page 2
Page 3
Page 4
Page 5
TABLE OF CONTENTS
GENERAL INSTRUCTIONS ..........................................................................................................1
GENERAL PREPARATION............................................................................................................2
Electrode Slope Check (with standard pH/mV meter)....................................................................2
Electrode Slope Check (with ion meter).........................................................................................2
MEASUREMENT..............................................................................................................................3
MEASUREMENT PROCEDURE ...................................................................................................4
Direct Measurement of Ammonium (using a standard pH/mV meter)...........................................4
Direct Measurement of Ammonium (using an ion meter)..............................................................5
Low Level Ammonium Determination (using a standard pH/mV meter)......................................6
Low Level Ammonium Determination (using an ion meter)..........................................................7
ELECTRODE CHARACTERISTICS.............................................................................................7
Reproducibility................................................................................................................................7
Interference......................................................................................................................................7
Detection Limit ...............................................................................................................................9
pH Effects......................................................................................................................................10
Electrode Life................................................................................................................................10
ELECTRODE THEORY................................................................................................................10
Electrode Operation ......................................................................................................................10
TROUBLESHOOTING .................................................................................................................. 11
Troubleshooting Guide.................................................................................................................. 11
Meter ............................................................................................................................................. 11
Electrodes......................................................................................................................................11
Standard......................................................................................................................................... 12
Sample........................................................................................................................................... 12
Technique......................................................................................................................................12
TROUBLESHOOTING HINTS.....................................................................................................13
SPECIFICATIONS..........................................................................................................................15
ORDERING INFORMATION.......................................................................................................15
Page 6
Page 7
Instruction Manual Ammonium Electrode
GENERAL INSTRUCTIONS
Eutech Instruments Ammonium Ion Electrode is used to measure ammonium ions in aqueous solutions in a more simple, quick, accurate, and economical manner.
Required Equipment
1. A pH/mV meter or an ion meter, either line operated or portable.
2. Semi-logarithmic 4-cycle graph paper for preparing calibration curves when using the
meter in the mV mode.
3. A magnetic stirrer.
4. Eutech Ammonium Ion Combination Epoxy-body Electrode, Code no. EC-NH4-03.
Required Solutions
1. Deionized or distilled water for solution and standard preparation.
2. Eutech Ionic Strength Adjuster (ISA), 5M NaCl, Code no. EC-ISA-AM1-BT to keep a constant background ionic strength present in the solution. To prepare the 5M NaCl ISA from your own laboratory stock, add 292 grams of reagent-grade sodium chloride (NaCl) to a 1,000 ml volumetric flask about half full of distilled water. Swirl the flask to dissolve the solid and fill to the mark with distilled water. Cap the flask and invert several times to mix the solution. Add 2 ml of ISA to every 100 ml of sample or standard solution for a background ionic strength of 0.10M.
3. Eutech Ammonium Standard, 0.1M NH
Cl, Code no. EC-SCS-AM1-BT. To prepare this
4
standard, add 5.34 grams of reagent-grade ammonium chloride to a 1 liter volumetric flask about half full of distilled water. Swirl the flask to dissolve the solid and fill to the mark with distilled water. Cap the flask and invert several times to mix the solution.
4. Eutech Ammonium Standard, 1,000 ppm NH
+1
, Code no. EC-SCS-AM2-BT. To prepare
4
this standard, add 2.97 grams of reagent-grade ammonium chloride to a 1 liter volumetric flask about half full of distilled water. Swirl the flask to dissolve the solid and fill to the mark with distilled water. Cap the flask and invert several times to mix the solution.
1
Page 8
Ammonium Electrode Instruction Manual
GENERAL PREPARATION
Electrode Preparation
Remove any rubber cap(s) covering the electrode tip(s) and the rubber inserts covering the filling holes of the reference electrode. Fill the combination electrode or the reference electrode with the filling solution shipped with the electrode to a level just below the fill hole. No preparation is required for a sealed reference electrode. Gently shake the electrode downward in the same manner as a clinical thermometer to remove any air bubbles that might be trapped behind the ammonium membrane. Prior to first usage, or after long term storage, immerse the ammonium electrode in ammonium standard for thirty minutes. The electrode is now ready for use. Connect the electrode(s) to the proper terminal(s) as recommended by the meter manufacturer.
Electrode Slope Check (with standard pH/mV meter)
(Check electrodes each day)
To a 150 ml 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. After assuring that the meter is in the mV mode, lower the electrode tip(s) into the solution.
Using a pipet, add 1 ml of 0.1M or 1,000 ppm ammonium standard to the beaker. When the reading is stable, record the millivolt reading. Using a pipet, add 10 ml of the standard used above to the beaker. When the reading has stabilized, record the millivolt reading.
Determine the difference between the two readings. A difference of 56±2 mV indicates correct electrode operation, assuming the solution temperature is between 20o and 25oC. See the
TROUBLESHOOTING section if the potential change is not within this range.
is defined as the change in potential observed when the concentration changes by a factor of
Slope
10.
Electrode Slope Check (with ion meter)
(Check electrodes each day)
Prepare standard ammonium solutions whose concentrations vary by tenfold. Use either the 0.1M
+1
or the 1,000 ppm NH
NH
4
+1
standard stock solutions. Use the serial dilution method for this
4
preparation.
To a 150 ml beaker, add 100 ml of the lower value standard and 2 ml of ISA. Place the beaker on the magnetic stirrer and begin stirring at a constant rate. Lower the electrode tip(s) into the solution.
Assure that the meter is in the concentration mode. Adjust the meter to the concentration of the standard and fix the value in the memory according to the meter manufacturer's instructions.
Rinse the electrode(s) with distilled water and blot dry. To a 150 ml beaker, add 100 ml of the higher value standard and 2 ml of ISA. Place the beaker on the magnetic stirrer and begin stirring at a constant rate. Lower the electrode tip(s) into the solution.
Adjust the meter to the concentration of the standard and fix the value in the memory. Read the electrode slope according to the meter manufacturer's instructions. Correct electrode operation is
2
Page 9
Instruction Manual Ammonium Electrode
indicated by a slope of 90-100%. See the TROUBLESHOOTING section if the slope is not within this range.
MEASUREMENT
Measuring Hints
The sensing membrane is normally subject to water uptake and might appear milky. This has no effect on performance. All samples and standards should be at the same temperature for precise measurement, preferably ambient temperature.
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 material, such as styrofoam sheet or asbestos sheet, between the stirrer and beaker.
Always rinse the electrode tip(s) with distilled water and blot dry with a fresh tissue between readings to prevent solution carryover.
Check the electrode for air bubbles adhering to the membrane surface after immersion in solution. Agitate the electrode gently to remove the air bubbles.
A slow or sluggish electrode response may indicate surface contamination of the ammonium electrode membrane. Soak the electrode tip in distilled water for about 5 minutes to clean the membrane. Rinse the membrane and soak in diluted standard solution for about 5 minutes to restore performance.
When measuring samples with high ionic strength, prepare standards with compositions similar to that of the sample.
Dilute concentrated samples (over 0.1M) before measurement. Recalibrate every few hours for routine measurement.
Sample Requirements
Make sure that the samples and standards are at the same temperature. About a 2% error will be introduced for a 1oC difference in temperature. Temperature should normally be less than 40oC with intermittent measurements allowed to 50oC. All samples and standards must be aqueous. They must not contain organic solvents.
Interference found in Table 3 should be absent.
Units of Measurement
Ammonium concentrations are measured in units of parts per million as ammonium, parts per million as N, moles per liter, or any other convenient concentration unit. Table 1 indicates some of the concentration units.
3
Page 10
Ammonium Electrode Instruction Manual
TABLE 1: Concentration Unit Conversion Factors
ppm NH
1.80 1.40 1x10
18.00 14.00 1x10
180.00 140.00 1x10
+
ppm N moles/liter NH
4
+
4
-4
-3
-2
Measurement Procedure
Direct Measurement
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 ammonium samples. The temperature of both sample solution and of standard solutions should be the same.
Direct Measurement of Ammonium (using a standard pH/mV meter)
1. Prepare 10
-
2
, 10
3
-
, and 10
4
-
M or 100, 10, and 1 ppm standards by serial dilution of the
0.1M or 1,000 ppm standard. Add 2 ml of ISA per 100 ml of standard.
2. Place the most dilute solution (10
4
-
M or 1 ppm) on the magnetic stirrer and begin stirring at a constant rate. After assuring that the meter is in the mV mode, lower the electrode tip(s) into the solution. When the reading has stabilized, record the mV reading.
3. Place th e midrange solution (10
3
-
M or 10 ppm) on the magnetic stirrer and begin stirring. After rinsing the electrode(s) with distilled water and blotting dry, immerse the electrode tip(s) in the solution. When the reading has stabilized, record the mV reading.
4. Place the most concentrated solution (10
2
-
M or 100 ppm) on the magnetic stirrer and begin stirring. After rinsing the electrode(s) with distilled water and blotting dry, immerse the electrode tip(s) in the solution. When the reading has stabilized, record the mV reading.
5. Using the semi-logarithmic graph paper, plot the mV reading (linear axis) against the concentration (log axis). A typical calibration curve can be found in Figure 1.
4
Page 11
Instruction Manual Ammonium Electrode
A calibration curve is constructed on semi-logarithmic paper when using a pH/mV meter in the direct measurement procedure. The measured electrode potential in mV (linear axis) is plotted against the standard concentration (log axis). In the linear region of the curve, only three standards are necessary to determine a calibration curve. In the non-linear region, additional points must be measured. The direct measurement procedures given are for the linear portion of the curve. The non-linear portion of the curve requires the use of low level procedures. Extrapolate the curve down to about 1x10
5
-
M or 0.2 ppm.
6. To a clean, dry 150 ml beaker, add 100 ml of sample and 2 ml of ISA. Place the beaker on the magnetic stirrer and begin stirring. Place the electrode tip(s) in the solution. When the reading has stabilized, record the millivolt reading. Determine the concentration directly from the calibration curve.
7. The electrode(s) should be re-calibrated every 1-2 hours. Simply repeat Steps 2-5 above.
Direct Measurement of Ammonium (using an ion meter)
1. By serial dilution of the 0.1M or 1,000 ppm ammonium standard, prepare two ammonium
standards whose concentration is near the expected sample concentration. Measure out 100 ml of each standard into individual 150 ml beakers and add 2 ml of ISA to each.
2. Place the more dilute solution on the magnetic stirrer and begin stirring at a constant rate.
Assure that the meter is in the concentration mode.
3. Lower the electrode tip(s) into the solution.
4. Adjust the meter to the concentration of the ammonium standard and fix the value in the
memory according to the meter manufacturer's instructions after stabilization of the reading.
5. Rinse the electrode tip(s) with distilled water and blot dry.
6. Place the more concentrated solution on the magnetic stirrer and begin stirring at a
constant rate.
7. Lower the electrode tip(s) into the solution.
8. Adjust the meter to the concentration of the ammonium standard and fix the value in the
memory according to the meter manufacturer's instructions after stabilization of the reading.
9. For low level measurements, place the rinsed, dried electrode(s) into a solution containing
100 ml of distilled water and 2 ml of ISA. After stabilization, fix the blank value in the meter according to the meter manufacturer's instructions.
10. Place 100 ml of the sample and 2 ml of ISA in a 150 ml beaker, place it on the magnetic
stirrer, and begin stirring.
5
Page 12
Ammonium Electrode Instruction Manual
11. Immerse the electrode tip(s) in the solution and wait for the reading to stabilize. Read the
concentration directly from the meter display.
12. The electrodes should be re-calibrated every 1-2 hours. Simply repeat Steps 2-8 (2-9)
above.
Low Level Ammonium Determination (using a standard pH/mV meter)
This procedure is recommended for solutions with ionic strengths less than 1.0 x 10
2
-
M. If the solution is high in ionic strength, but low in ammonium, use the same procedure, but prepare a calibration solution with a composition similar to the sample.
1. Using 20 ml of stock ISA, dilute to 100 ml with distilled water.
2. Dilute 1 ml of the 0.1M standard to 100 ml to prepare a 1.0x10
3
-
M standard solution for measurements in moles per liter. Dilute 10 ml of the 1,000 ppm standard to 100 ml to prepare a 100 ppm standard solution for measurements in ppm.
3. To a 150 ml beaker, add 100 ml of distilled water and 1 ml of low level ISA. Place the
beaker on the magnetic stirrer and begin stirring at a constant rate.
4. Place the electrode tip(s) in the solution. Assure that the meter is in the mV mode.
5. Add increments of the 1.0x10
3
-
M or 100 ppm standard as given in Table 2 below.
6. After the reading has stabilized, record the mV reading after each addition.
TABLE 2
: Stepwise Calibration for Low Level Ammonium Measurements
Added
Pipet Volume (ml) M ppm
Step 1 A 0.1 1.0X10 2 A 0.1 2.0X10 3 A 0.2 4.0X10 4 A 0.2 6.0X10 5 A 0.4 9.9X10 6 B 2 2.9X10 7 B 2 4.8X10
Concentration
6
-
0.1
6
-
0.2
6
-
0.4
6
-
0.6
6
-
1.0
5
-
2.9
5
-
4.8
Pipet A = 1 ml graduated pipet Pipet B = 2 ml pipet
7. On semi-logarithmic graph paper, plot the mV reading (linear axis) against the concentration (log axis) as in Figure 1.
8. Rinse the electrode(s) in distilled water and blot dry.
6
Page 13
Instruction Manual Ammonium Electrode
9. Measure out 100 ml of the sample into a 150 ml beaker, add 1 ml of low level ISA, and place the beaker on the magnetic stirrer. Begin stirring. Lower the electrode tip(s) into the solution.
10. After the reading has stabilized, record the mV reading and determine the concentration from the low level calibration curve.
11. Prepare a new low level calibration curve daily. Check the calibration curve every 1-2 hours by repeating Steps 3-7 above.
Low Level Ammonium Determination (using an ion meter)
Follow the procedure given for normal ammonium determinations using an ion meter and the blank correction procedure.
ELECTRODE CHARACTERISTICS
Reproducibility
Direct 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.
Interference
Table 3 lists some common cations that, if present in high enough levels, will cause electrode interference and measurement errors or electrode drift when using the ammonium ion electrodes.
Electrode drift and slow response could indicate the presence of high interference from the ions listed. Soak the electrode(s) in distilled water for an hour, then for two hours in ammonium standard solution to restore proper response.
TABLE 3 Levels of NH
: Concentration of Possible Interference Causing a 10% Error at Various
Cl; Background Ionic Strength is 0.12M NaCl.
4
Interference (moles/liter) Cs
K
Tl
H
Ag
+Tris
10
+1
3.0X10
+1
1.0X10
+1
6.0X10
+1
1.0X10
+1
1.0X101 1.0 1.0X10
+1
1.0X101 1.0 1.0X10
2
-
M NH
+1
10
4
3
-
3.0X10
2
-
1.0X10
2
-
6.0X10
1
-
1.0X10
3
-
M NH
+1
4
4
-
3.0X10
3
-
1.0X10
3
-
6.0X10
2
-
1.0X10
10
4
-
M NH
+1
4
5
-
4
-
4
-
3
-
1
-
1
-
7
Page 14
Ammonium Electrode Instruction Manual
1
Li+1 2.0X101 2.0 2.0X10
Na
+1
+Tris
is the cation of tris(hydroxymethyl)aminomethane
+1
2.0X101 2.0 2.0X10
-
1
-
Interference (ppm)
Cs
K
Tl
H
Ag
+1
1.0X102 1.0X101 1.0
+1
2.7X102 2.7X101 2.7
4
+1
3.1X103 3.1X102 3.1X101
+1
1.6 pH 2.6 pH 3.6 pH
+1
2.7X105 2.7X104 2.7X103
+Tris
Li
Na
Temperature Influences
+1
3.5X104 3.5X103 3.5X102
+1
1.1X105 1.1X104 1.1X103
100 ppm NH
+1
3.1X105 3.1X104 3.1X103
+
10 ppm NH
4
+
1 ppm NH
4
+
4
Samples and standards should be at the same temperature, since electrode potentials are influenced by changes in temperature. A 1oC difference in temperature results in a 2% error at the 1.0X10
3
-
M
level.
Provided that temperature equilibrium has occurred, the ammonium ion electrodes can be used at temperatures from 0o-50oC continuously and 40o-50oC intermittently. Room temperature measurements are recommended, since measurements at temperatures markedly different from room temperature may require equilibrium times up to one hour. Table 4 indicates the variation of theoretical slope with temperature.
TABLE 4
: Temperature vs Value for the Electrode Slope
Temp (oC)
S"(slope) 0 54.20 10 56.18 20 58.16 25 59.16 30 60.15 40 62.13 50 64.11
8
Page 15
Instruction Manual Ammonium Electrode
Electrode Response
Plotting the electrode mV potential against the ammonium concentration on semi-logarithmic paper results in a straight line with a slope of about 56 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 ammonium concentration above 1.0X10
5
-
M to several minutes
near the detection limit. Refer to Figure 2.
Electrode Storage
The ammonium ion electrode may be stored in 1.0X10
2
-
M ammonium standard for short periods of time. For storage over 3 weeks, rinse and dry the ammonium membrane electrode and cover the tip with any protective cap shipped with the electrode(s). 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.
Detection Limit
The upper limit of detection is 1M in pure ammonium chloride solutions. The upper limit of detection is above 1.0X10
1
-
M when other ions are present, but the possibility of a liquid junction potential developing at the reference electrode and the "salt extraction effect" are two limiting factors. Some salts may be extracted into the electrode membrane at high salt concentrations causing deviation from theoretical response. Calibrate the electrode at four or five intermediate points, or dilute the sample, to measure samples between 1.0X10
1
-
M and 1M.
The slight water solubility of the ion exchanger in the sensing module, which causes deviation from theoretical response, determines the lower limit of detection. The theoretical response at low levels of ammonium chloride compared to actual response is shown in Figure 1. A low level measurement is recommended if ammonium measurements are made below 1.0X10
5
-
M (0.18 ppm as
ammonium).
9
Page 16
Ammonium Electrode Instruction Manual
pH Effects
Hydrogen ion interferes with measurements of low levels of ammonium ion although the electrode can be used over a wide pH range. Table 3 should be used to determine the minimum pH at which low level ammonium measurements can be made without more than a 10% error due to hydrogen ion interference.
Electrode Life
An ammonium ion electrode will last six months in normal laboratory use. On-line measurement might shorten operational lifetime to several months. In time, the response time will increase and the calibration slope will decrease to the point calibration is difficult and electrode replacement is required.
ELECTRODE THEORY
Electrode Operation
An ammonium ion electrode consists of an electrode body containing an ion exchanger in a sensing module. This sensing module contains a liquid internal filling solution in contact with a gelled organophilic membrane containing an ammonium selective ion exchanger.
An electrode potential develops across the membrane when the membrane is in contact with an ammonium solution. Measurement of this potential against a constant reference potential with a digital pH/mV meter or with a specific ion meter depends on the level of free ammonium ion in solution. The level of ammonium ions, corresponding to the measured potential, is described by the Nernst equation:
E = Eo + S log X where: E = measured electrode potential Eo= reference potential (a constant) S = electrode slope (~ 56 mV/decade) X = level of ammonium ions in solution
The activity, X, represents the effective concentration of the ions in solution. Total ammonium concentration, Ct, includes free ammonium ions, Cf, plus bound or complexed ammonium ions, Cb. Since the ammonium electrodes only respond to free ion, the free ion concentration is:
C
= Ct - Cb
f
The activity is related to the free ion concentration, Cf, by the activity coefficient, γ ,by: X = γ Cf
Activity coefficients vary, depending on total ionic strength, I, defined as:
2
I = ½ Σ CxZ
x
where: Cx = concentration of ion X Zx = charge of ion X Σ = sum of all of the types of ions in the solution.
10
Page 17
Instruction Manual Ammonium Electrode
In the case of high and constant ionic strength relative to the sensed ion concentration, the activity coefficient, γ , is constant and the activity, X, is directly proportional to the concentration.
To adjust the background ionic strength to a high and constant value, ionic strength adjuster (ISA) is added to samples and standards. The recommended ISA for ammonium is sodium chloride, NaCl. Solutions other than this may be used as long as ions that they contain do not interfere with the electrode's response to ammonium ions.
The reference electrode must also be considered. When two solutions of different composition are brought into contact with one another, liquid junction potentials arise. Millivolt potentials occur from the interdiffusion of ions into the two solutions. Electrode charge will be carried unequally across the solution boundary resulting in a potential difference between the two solutions, since ions diffuse at different rates. When making measurements, it is important to remember that this potential be the same when the reference is in the standardizing solution as well as in the sample solution or the change in liquid junction potential will appear as an error in the measured electrode potential.
The composition of the liquid junction filling solution in the reference electrode is most important. The speed with which the positive and negative ions in the filling solution diffuse into the s ample should be as nearly equal as possible, that is, the filling solution should be equitransferant. No junction potential can result if the rate at which positive and negative charge carried into the sample is equal.
Strongly acidic (pH = 0-2) and strongly basic (pH = 12-14) solutions are particularly troublesome to measure. The high mobility of hydrogen and hydroxide ions in samples make it impossible to mask their effect on the junction potential with any concentration of an equitransferant salt. One must either calibrate the electrode(s) in the same pH range as the samples or use a known increment method for ion measurement.
TROUBLESHOOTING
Troubleshooting Guide
The most important principal in troubleshooting is to isolate the components of the system and check each in turn. The components of the system are: 1) Meter, 2) Electrodes, 3) Standard, 4) Sample, and 5) Technique.
Meter
The meter is the easiest component to eliminate as a possible cause of error. Most meter are provided with an instrument check-out procedure in the instruction manual and a shorting strap for convenience in troubleshooting. Consult the manual for complete instructions and verify that the instrument operates as indicated.
Electrodes
1. Rinse electrode(s) thoroughly with distilled water.
2. Perform Electrode Slope Check.
11
Page 18
Ammonium Electrode Instruction Manual
3. If electrode(s) fail this procedure, see the section on
Measuring Hints.
4. If the stability and the slope check out properly, but measurement problems persist, the
standards may be of poor quality, the sample may contain interference or complexing agents, or the technique may be in error. See
Standard, Sample, and Technique 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, ISA, and standards measure correctly review
TROUBLESHOOTING HINTS.
Standard
The quality or results depends greatly upon the quality of the standards. ALWAYS prepare fresh standard when problems arise. It could save hours of frustrating troubleshooting! Error may result from contamination of prepared standards, accuracy of dilution, quality of distilled water, or a mathematical error in calculating the standard concentrations.
Sample
If the electrode works properly in standard but not in sample, look for possible interference, complexing agents, or substances which could affect response or physically damage the sensing electrode or the reference electrode. See
Sample Requirements and Interference. Try to determine
the composition of the samples prior to testing to eliminate a problem before it starts.
Technique
Check the method of analysis for compatibility with your sample. Direct measurement may not always be the method of choice. Also be sure that the expected concentration of the ion of interest is within the electrode's limits of detection. If problems persist, review operational procedures and the instruction manual to be sure that proper technique has been followed. Call Eutech Instruments Pte Ltd. at (65) 6778-6876 and ask for the Customer Services Department to answer any questions.
12
Page 19
Instruction Manual Ammonium Electrode
TROUBLESHOOTING HINTS
Symptom Possible Causes Next Step Out of Range defective meter check meter with Reading shorting strap (see meter instruction manual)
electrode(s) unplug electrode(s) not plugged in and reset properly
reference electrode be sure reference not filled electrode is filled
air bubbles on remove bubble by membrane redipping electrode
electrodes not put electrode(s) in solution in solution
"Incorrect incorrect scaling plot millivolts on the linear Answer" of semi-log paper axis. On the log axis, be sure curve is good) concentration numbers within (but calibration each decade are increasing with increasing concentration
incorrect sign be sure to note sign of millivolt number correctly
incorrect standards prepare fresh standards
wrong units used apply correct conversion factor: 10
3
-
M = 18 ppm NH
+
=
4
14 ppm as N
sample carryover rinse electrodes thoroughly between samples
Drift (reading samples and standards allow solutions slowly changing at different to come to room in one direction) temperatures temperature before measurement
electrode exposed soak electrode to interference in ammonium standard
incorrect reference use recommended filling solution filling solution
13
Page 20
Ammonium Electrode Instruction Manual
Low Slope or standards contaminated prepare fresh No Slope or incorrectly made standards
ISA not used use recommended ISA
standard used as ISA use ISA
defective electrode check electrode operation
electrode exposed soak electrode to interference in ammonium standard
air bubble on membrane remove bubble by redipping probe
Noisy or Unstable defective meter check meter with Readings (readings shorting strap continuously or randomly changing) air bubble on remove bubble by membrane redipping electrode
defective electrode replace electrode
electrode exposed soak electrode to interference in ammonium standard
meter or stirrer ground meter or not grounded stirrer
outer filling solution fill electrode level too low to level just below fill hole
14
Page 21
Instruction Manual Ammonium Electrode
SPECIFICATIONS
Concentration Range: 1M to 5X10
6
-
M (18,000 ppm to 0.01 ppm)
pH Range: 4 to 10
Temperature Range: 0o to 40oC (continuous) 40o to 50oC (intermittent)
Resistance: 100 megaohms
Reproducibility: ±2%
Samples: Aqueous solutions only; no organic solvents
Size: 110 mm length; 12 mm diameter; 1 m cable length
Storage: Electrode should be stored in dilute ammonium standard
ORDERING INFORMATION
CODE NO. DESCRIPTION
EC-NH4-03 Ammonium Ion Combination Electrode, epoxy body
EC-SCS-AM1-BT Ammonium Standard, 0.1 M NH
EC-SCS-AM2-BT Ammonium Standard, 1,000 ppm NH
EC-SCS-AM2-BT Ammonium Standard, 100 ppm NH
4
Cl
+
4
+
4
EC-ISA-AM1-BT Ammonium ISA (Ionic Strength Adjuster), 5 M NaCl
15
Page 22
Page 23
Page 24
Loading...
Buy Points How it Works FAQ Contact Us Questions and Suggestions Privacy Policy Cookie Policy Terms of Use