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Method for determining the concentration of CYANIDE
(CN-) Method for samples containing cyanide bound in heavy-metal complexes. Apparatus Required: Ion-Selective Electrode for cyanide ion (ELIT 8291 crystal membrane) Reference electrode: double junction Lithium Acetate (ELIT 003n). Dual electrode head (ELIT 201) Standard solution: 1000 ppm CN as KCN Buffer solution (ISAB): 10 Molar NaOH. 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 200, 20, 2, and 0.2ppm CN. 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: 2 ml 10 Molar NaOH buffer solution must be added to each standard and mixed thoroughly to ensure correct pH level for electrode operation and eliminate any possibility of toxic HCN fumes. Follow the instructions in the General Operating Instructions to measure these standard solutions and prepare a calibration graph. Sample Preparation: 2 mls of buffer solution must be added to 100ml of each sample 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. Since 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. Procedure for determining the concentration of CYANIDE CN-) in water containing Heavy Metal Complexes. Any cyanide bound up in complex formation with heavy metals is liberated by displacement with EDTA before analysing for total CN - in the conventional manner. EDTA solution can be made by dissolving 7.44g of ethylene-diamene-tetra-acetic acid in one litre of de-ionised water Standard and Sample Preparation Add 5ml EDTA to 50ml of solution and heat to 50°C in a fume cupboard for 5 mins. Remove from heat and immediately add 50ml of 0.2M NaOH, then cool to room temperature. Results Since buffer and EDTA solutions have been added equally to standards and samples the results will not need adjusting because they will all be affected by the same dilution factor. Technical Specifications Introduction Interference: Note low concentration range (only effective from 0.03 to 260 ppm CN-) and narrow and high pH range (only between pH 11 and 13). WARNING: 10M NaOH buffer is a very caustic solution and should be handled with care. Return to top Last update: CCR 14 August 2015 |