Introduction
This video guide walks you through the complete setup of the MME Pro electrode for use with the 884 Professional VA. The accompanying video demonstrates each step of the process, including installing the needle and capillary, filling the electrode with mercury, adjusting the needle valve, and verifying proper electrode operation.
Before beginning, ensure you have all required components and accessories available. Follow each video in sequence to properly prepare the electrode for operation.
Video
Topics covered
-
Inserting the needle (0:08)
- Turn the needle holder counterclockwise until it can no longer be turned out, and then carefully pull it out using the grey mounting ring.
- Cut open the plastic packaging of the new needle with scissors. Insert the needle into the hole in the membrane and push it in until the white mark is reached.
- Insert the needle holder with the new needle into the MME pro and turn it clockwise until the black sealing ring is just visible. This prevents mercury from leaking out. Do not turn the needle holder in too far. The needle valve will be adjusted later, on the measuring stand.
-
Installing the capillary (1:01)
- To prepare, unscrew the retaining screw for the capillary, loosely reinsert it into the thread but do not tighten it.
- Do not touch the needle with your bare fingers during this process.
- Insert the capillary into the MME pro and, using gentle twisting motions, push it down through the seal until it stops. Then, loosely tighten the retaining screw by hand. To secure the capillary, place the key on top and use one finger to turn the retaining screw clockwise until the key falls off. Do not re-engage the key. The application areas of the standard capillary (6.1226.030) and the silanized capillary (6.1226.050) can be found in the corresponding data sheet for the capillaries.
-
Filling the electrode with mercury (2:27)
- The following tasks must be carried out over the plastic tray!
- In addition to the MME pro, the following are required for filling the mercury: collection tray, electrode stand, mercury, syringe with needle, the key for the MME, and the mercury catcher for collecting any spilled mercury droplets.
- Slowly pour mercury into the electrode. It should be filled to the "max. fill" mark (max. 6 mL) at most.
- Using the key, tighten the screw cap until it stops. The opening of the mercury reservoir will then be securely closed.
- Small amounts of spilled mercury can be collected using the mercury catcher (part number 6.2406.000).
-
Adjusting the needle valve (04:22)
- The needle valve is adjusted in the measuring station.
- Before inserting an electrode with a new capillary, be sure to empty the measuring vessel (any solution entering the vessel can render the capillary unusable)!
- Pressurize the electrode (required pressure 1.0 to 1.2 bar).
- In the "Manual control" window, select the 884 Professional VA and switch to the "Electrodes" tab. Then click the "Open" button under "Valves / Main valve" to open the main valve. Once a large mercury droplet has formed, add approximately 20 mL of water and a few drops of KCl solution to the measuring vessel.
- Coarse adjustment: Turn the needle holder clockwise until no more mercury flows out. It has proven useful to check after each half turn, by observing the formation of new drops, whether the capillary is already sealed by the needle.
- Fine adjustment: Slowly rotate the needle holder counterclockwise until a new droplet forms. Close the capillary again with a small clockwise turn (approx. 10°).
- Rotate the needle holder another 90–100° clockwise. The electrode is now ready for use. Droplet formation can be controlled by the software.
-
Verifying electrode function in DME, SMDE, and HMDE operating modes (08:24)
- DME – Dropping Mercury Electrode. The classic dropping mercury electrode.
- To check the DME function, select the DME operating mode on the "Electrodes" tab in the "Manual control" window and start drop formation by clicking "Start".
- Drop formation is correct if the drop falls from the capillary at regular intervals.
- SMDE – Static Mercury Drop Electrode. A dripping mercury electrode, like the DME, but with a static surface, like the HMDE.
- With the SMDE electrode type, the needle valve opens for only a few milliseconds. During this time, mercury flows through the capillary, forming a droplet with a defined surface area. After a short time, this droplet is removed from the capillary by the knock-off mechanism. A new droplet then forms and is knocked off again after a short time. This process is repeated throughout the entire measurement cycle.
- To check the SMDE function, select the SMDE operating mode in the "Manual control" window on the "Electrodes" tab and start drop formation by clicking "Start".
- Drop formation is correct if each strike of the knock-off mechanism removes an equally sized droplet from the capillary.
- HMDE – Hanging Mercury Drop Electrode. The hanging mercury drop electrode; a single hanging drop of mercury serves as the electrode.
- When the HMDE electrode type is switched on, any existing mercury droplet is first removed by the knock-off mechanism. The needle valve then opens for a few milliseconds. During this time, mercury flows through the capillary, forming a droplet with a defined surface area, which serves as the electrode for the entire measurement cycle. Only when the electrode is switched on again does a new droplet form.
- To check the function of the HMDE, select the HMDE operating mode in the "Manual control" window on the "Electrodes" tab and start droplet formation by clicking "Start".
- Droplet formation is correct when the old droplet is broken off and a new one is formed. The droplet should not increase in size over time. Switching the electrode on again will produce a new droplet.
Additional Support
If you encounter any issues or need additional help, please submit a support ticket through Metrohm Technical Support.
For more detailed training on any of these topics, explore our Metrohm Custom Training options.