When the chloride coating of an Ag/AgCl electrode is broken, scratched or sulphides/oxides are forming this may cause noise in recordings with this electrodes. Hence, the electrodes should be re-chlorided at regular intervals. Note that silver chloride is water-insoluble and cannot be cleaned in rinse water. Before first use rinse new electrodes in hot water and soak them in a salt-solution (NaCl) over night. Storing unused electrodes in a salt solution will help to keep the chloride surface in good shape.

Step 1

Thoroughly clean the silver surface celectrodes of tarnish and dirt. Scouring powder or silver cleaner will do.

Step 2

Place the electrode in an opaque non-metallic container with 5% NaCl solution (figure 1).

	figure 1

Step 3

Connect electrode to be chlorided to the (+) positive terminal of a 1.5V battery and the other electrode to the (-) negative terminal. Use a 100 Ohm resistor in series with the electrode. Apply current for approximately 1 minute.

Step 4

The chloriding electrode darkens, while the other bubbles. Continue until the darkened surface is evenly coated.

Step 1

In order to properly mount the g.EEGcap measure (i) the distance between the nasion and inion and (ii) the distance between the left and right preauricular points of the subject (see figure 1). The position at the half of both distances is the vertex position Cz. Align this measured position with the position Cz of the electrode cap. Now the electrode cap is in the correct position. g.EEGcap is available in standard sizes (S,M,L). The electrode positions are defined by the extended 10/20 system.

figure 1

Step 2

Fix the cap with the chest belt to ensure the cap's position (figure 2).

figure 2

Step 3

Choose now the preferred recording positions according to the extended 10/20 system on the cap.

figure 3

Step 4

Clean carefully the visible areas within the electrode rings using an abrasive gel This will ensure low impedances for the recordings.

figure 4

Step 5

Fill the electrode with electrode gel (figure 5) and prevent air inclusions. Attach now the screwable gold or Ag/AgCl electrodes. NOTE: Dirty or scratched surfaces will result in low quality EEG recordings!

figure 5

Step 6

Plug the electrode at the desired position into the electrode ring. Lift the ring and turn the electrode for 90 degrees. The electrode is now fixed.

figure 6

Step 7

Check the impedances of the electrodes agains a reference electrode using g.Zcheck. The impedances should be lower than 10 kOhm. Impedances around 5 kOhms are optimal for your recordings. If the impedance of an electrode is > 20 kOhms you repeat steps 4 to 7. Connect now the electrodes to the biosignal amplifier e.g. g.BSamp. Avoid long distances between the electrode cables to minimize inductive and capacitive interferences.

figure 7