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Method for determining the concentration of SILVER (Ag+)
in Aqueous Solutions


Electrode Specifications       Links to publications on the WWW     Go to Ion Selective Electrodes page

Apparatus Required:

Ion-Selective Electrode for silver ion (ELIT 8211 crystal membrane)

Reference electrode: double junction lithium acetate (ELIT 003n)

Dual electrode head (ELIT 201)

Standard solution: 1000 ppm Ag as AgNO3

Buffer solution (ISAB): 5 Molar NaNO3.

ELIT Computer Interface/Ion Analyser, or Ion/pH/mV meter.

150 ml polypropylene beakers, 100ml volumetric flask, 1, 2, 5, 10ml pipettes.

Calibration:

Before use, the electrodes must be calibrated by measuring a series of known standard solutions, made by serial dilution of the 1000ppm standard solution. For a full calibration, prepare 100ml of solutions containing 1000, 100, 10, 1, and 0.1ppm Ag. However, this wide calibration is not necessary if the approximate range of concentrations of the samples is known, and this is within the linear range of the ISE. In this case it is only necessary to make two solutions (preferably a decade apart) which span the sample range.

After dilution, the standard solutions should be mixed with buffer solution in the ratio 50:1 and measured whilst stirring.

Follow the instructions in the General Operating Instructions to measure these standard solutions and prepare a calibration graph.

Sample Preparation:

Samples must also be mixed 50:1 with buffer solution and stirred well before measurement.

Sample Measurement:

Follow the instructions in the electrode operating instructions to measure a series of samples and record the results. Briefly, it is important to note that the electrodes must be washed and dried between each sample, to avoid cross contamination, and sufficient time must be allowed (2 or 3 minutes), before taking a reading after immersion, to permit the electrode signal to reach a stable value. For the highest precision, frequent recalibration is recommended (see operating instructions).

Results:

The results will be displayed as ppm and mol/l. If buffer solution has been added equally to standards and samples then these figures will not need adjusting because they will all be affected by the same dilution factor.




Technical Specifications
for the Silver Ion-Selective Electrode
(ELIT 8211)

Click here to download a printer-friendly (pdf) Specification Sheet.

Introduction
The Silver Ion-Selective Electrode has a solid-state Crystal membrane. The electrode is designed for the detection of silver ions (Ag+ ) in aqueous solutions and is suitable for use in both field and laboratory applications.    The Silver Ion is a monovalent cation.
One mole of ( Ag+) has a mass of 107.868 grams; 1000 ppm is 0.009M
Dissolve 1.575g anhydrous silver nitrate (AgNO3) in 1 litre water.

Physical Specifications
Length of body excluding gold contact = 130 mm
Length of body including gold contact = 140 mm
Diameter of body = 8 mm
DC resistance at 25C < 2.5 MOhm
Minimum feasible sample volume = 5 ml

Chemical / Operational Specifications
Preconditioning / Standard solution : Normally 1000 ppm Ag+ as AgNO3
(But see General Operating Instructions)
Preconditioning time : 5 minutes
Optimum pH range : pH 1 to pH 9
Temperature range : 0 to 80C
Recommended ISAB : 5M NaNO3 (Add 2% v/v)
Recommended reference electrode : Double junction lithium acetate (ELIT 003)
Reference outer filling solution: 0.1M CH3COOLi
Electrode slope at 25C : 545 mV/decade
Concentration range : 0.01 to 10,790 ppm  (9x10-8 to 0.1 Molar)
Response time : < 10 seconds
Defined as time to complete 90% of the change in potential after immersion in the new solution.
Time for stable reading after immersion : < 1 to > 5 minutes
Depending on concentration, use of ISAB, nature of sample and stabilisation time of liquid junction potential of reference electrode.
Potential drift (in 1000 ppm) : < 3 mV/day (8 hours)
Measured at constant temperature and with ISE and Reference Electrode continually immersed.

Interference:
S-2 and Hg+2 have very strong interference and can only be tolerated at very low concentrations relative to the Ag.

Procedural Notes:
1) For the most stable and reproducible results it is recommended that all solutions are mixed with ISAB and measured whilst stirring with a magnetic stirrer at approx 100rpm.
2) Silver Nitrate standards should be stored in the dark when not in use.

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