WPI OMEGA-TIP Z, Инструкция по эксплуатации

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4 World Precision Instruments
At electrode resistance readings much above 300 to 400 megohms, line frequency
interference may cause some instability in the digital display. Grounded aluminum foil
or metal screening around the measuring probe and electrode will often improve the
stability of the resistance reading.
Impedance Measurement of Metal Microelectrodes
Measuring metal microelectrode tip impedance is similar to that of measuring
micropipette resistance described above. WPI part number 5468 is an adapter with
which to hold metal wire electrodes on the probe tip of the instrument. Note that
there is only one impedance range, i.e. 20 MΩ . Set the Function and Mode slide
switches to Metal Tip and Ω, respectively. Immerse the metal tip of the electrode into
a saline electrolyte containing the reference electrode. Most metal microelectrodes’
impedances. Most of the metal microelectrodes sold by WPI fall into the 0.5 to 2 MΩ
range. In the Metal Tip mode, the measuring current is 10 nA and the frequency is 500
Hz, providing a range of 20 MΩ.
WPI metal microelectrodes are calibrated at 1000 Hz and the measured impedance
is noted on the box. The user should re-measure the metal microelectrodes with the
Ω mega-Tip-Z to establish a 500 Hz baseline impedance.
Electrolytic “Cleaning” of Metal Microelectrodes
If the electrodes are to be reused, or if you cannot obtain low impedance, or if the
electrodes have been sterilized or stored for very long periods, electrolytic cleaning
will often renew the electrode surface. Connect the cable assembly provided to the
electrolysis jack at the foot of the instrument. Connect the black clip to the electrode
shank and the other clip to a reference electrode. Immerse the electrode pair in
saline. When the push button next to the jack is pushed, approximately -3 volts
(through an internal resistance) will be applied to the metal electrode and it should
exhibit bubbles issuing from the electrode tip. A short one-minute treatment should
suffice.
Voltage Measurement
Tip and fluid junction potential can be measured with the Mode switch in the V
position. This can be a useful feature. Users of ion-selective electrodes can use
electrode potential as an index of bevelling. It has been observed that cation selective
electrodes (Na+, K+, etc.) will increase potential in the + direction when a little tip
bevelling is done. Anion electrodes will move in the opposite direction.
First, micropipettes are pulled and the tips filled with liquid ion exchange material.
The electrode shank is back-filled with an appropriate chloride solution and the bath
concentration of the chosen cation is selected to be one-tenth of the filling solution.
Since resistances of ion-selective micropipette electrodes can be in the gigaohm
range, careful electrical shielding will be necessary (see paragraph above).