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Method for determining the concentration of COPPER (Cu++)
in Aqueous Solutions


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

Apparatus Required:

Ion-Selective Electrode for cupric ion (ELIT 8227 crystal membrane)

Reference electrode: double junction Lithium Acetate (ELIT 003n).

Dual electrode head (ELIT 201)

Standard solution: 1000 ppm Cu as CuSO4

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, and 1 ppm Cu. If the approximate range of concentrations of the samples is known, and this is within the linear range of the ISE, then it is only necessary to make two solutions (preferably a decade apart) which span this range.

NB: The Cu electrode works most reliably when samples and standards are mixed with ISAB to give a background matrix of around 0.1 Molar NaNO3. Thus 2 ml of buffer solution should be added to each 100ml standard (and sample) solution and mixed thoroughly before measurement.

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

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. Since buffer solution has been added equally to standards and samples, these figures will not need adjusting for this extra dilution factor.



Technical Specifications
for the Cupric Ion-Selective Electrode
(ELIT 8227)

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

Introduction
The Cupric Ion-Selective Electrode has a solid-state crystal membrane. The electrode is designed for the detection of cupric ions (Cu+2 ) in aqueous solutions and is suitable for use in both field and laboratory applications.
The Cupric Ion is a divalent cation .
One mole of ( Cu+2) has a mass of 63.546 grams; 1000 ppm is 0.016M
Dissolve 3.929g copper sulphate penta hydrate (CuSO4.5H2O) 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 25 C < 2.5 MOhm
Minimum feasible sample volume = 5 ml

Chemical / Operational Specifications
Preconditioning / Standard solution : Normally 1000 ppm Cu +2 as CuSO4
(But see General Operating Instructions)
Preconditioning time : 5 minutes
Optimum pH range : pH 2 to pH 7
Temperature range : 0 to 80C
Recommended ISAB : 5M NaNO3 (Add 2% v/v)
NB:For best results ISAB should always be added to all standards and samples.
Recommended reference electrode : Double junction (ELIT 003)
Reference electrode outer filling solution : 0.1M CH3COOLi
Electrode slope at 25C : 263 mV/decade
Concentration range : 0.006 to 6,400 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:
NB: All poly-crystalline membranes contain Silver Sulphide and thus will not give reliable readings if Ag or S ions are present in the solution. Mercury ions also have very high interference and can only be tolerated in very low concentrations compared to the Cu.

Bromide and Chloride ions both have selectivity coefficients of >1 and will cause a significant negative error it they are present in concentrations greater than one tenth of that of the Copper.



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