User manual EUTECH INSTRUMENTS AMMONIA GAS

[. . . ] Instruction Manual Ammonia Gas-sensing Electrode EUTECH INSTRUMENTS PTE LTD. AMMONIA GAS-SENSING ELECTRODE INSTRUCTION MANUAL GENERAL INSTRUCTIONS Introduction Eutech Instruments Ammonia Gas-Sensing Electrode is used to quickly, simply, accurately, and economically measure dissolved ammonia in aqueous solutions. It can also be used to measure the ammonium ion after conversion to ammonia or organic nitrogen from Kjeldahl digestion of the sample. The measurement is not affected by sample color or turbidity and samples do not need to be distilled. Interference from anions, cations, and dissolved species, other than volatile amines, do not occur. [. . . ] Adjust the meter to the concentration of the ammonia standard and fix the value in the memory according to the meter manufacturer's instructions after stabilization of the reading. For low level measurements, place the rinsed, dried electrodes into a solution containing 100 ml of distilled water and 1 ml of ISA. After stabilization, fix the blank value in the meter according to the meter manufacturer's instructions. When the reading has stabilized, read the concentration directly from the meter display. 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 of steps 28 above. 6. 7. 8. 9. 10. 11. Low Level Ammonia Determination (using a pH/mV meter) As the concentration of ammonia decreases, the rate of ammonia diffusion through the membrane is slow, the rate of equilibrium between the ammonium in the internal filling solution and ammonia is slow, and thus the response time increases. If the internal filling solution is diluted with ammoniafree distilled water (1:10), response at low levels can improve. Measurements can be speeded up by first placing the electrode tip in an ammonia-free pH 4 buffer, then into the sample. Work with large solution volumes to minimize surface-area-tovolume ratio, thereby avoiding ammonia absorption from air. Allow 5-10 minutes for a stable reading in the pH 4 buffer or a low-level solution. Use the following low level ammonia measurement procedure in the non-linear portion of the calibration curve. (See Figure 1. ) This procedure is used for ammonia samples containing less than 1. 0x10-5M ammonia. 7 Instruction Manual Ammonia Gas-sensing Electrode 1. Measure out 100 ml of a pH 4 buffer solution, add it to a 150 ml beaker, place the beaker on the magnetic stirrer, and begin stirring. By serial dilution, prepare a 10-2M or 100 ppm ammonia standard by diluting the 0. 1M or 1, 000 ppm standard solution. To a 2500 ml erlenmeyer flask, add 1, 000 ml of distilled water and 10 ml of 10M NaOH. After rinsing the electrode, place the tip in this calibration solution. Using a 1 ml graduated pipet (A) and a 2 ml pipet (B), add increments of the 10-2M or 100 ppm dilution to the calibration solution using the steps outlined in Table 2. Allow the reading to reach equilibrium and record the electrode potential after each step. the electrode potential (linear axis) on semi-logarithmic paper to obtain the calibration curve. After rinsing the electrode, immerse the electrode tip in pH 4 buffer for 3 minutes. 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. [. . . ] Be sure to wash the glassware well with a mild detergent and rinse very well with distilled or deionized water. Clean glassware will drain without leaving water droplets behind. Electrodes The electrodes may be checked by using the procedure found in the section entitled Electrode Slope Check. 1. Be sure to use either distilled or deionized water when following the procedures given in Electrode Slope Check. 2. 3. If electrode fails to response as expected, see the sections entitled Electrode Assembly and Checking Membrane. If the electrode still does not perform as described, determine whether the ammonia electrode inner body is working properly as directed in Checking the Electrode Inner Body. 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. ) Before replacing a "faulty" electrode, review the instruction manual and be sure to: - Clean and rinse the electrode thoroughly. [. . . ]