Verifying Aquatest Accuracy

AQUATESTS require no calibration, as it is known in general analytical chemistry. The instrument is based upon the use of FARADAY’S LAW which states that one coulomb of electricity is required to electrolyze one mole of material – which for the AQUATEST would be one mole of water. The user of an AQUATEST is not required to or able to make any adjustments in the electrical circuits of the instrument that would invalidate this law. The user is able to and required to assess the state of the instrument, before making any analyses, by the use of either a primary standard (water) or a secondary standard (usually water in hydrophobic solvents).

abstract:

1. Water* can be used to check the accuracy of the AQUATESTS. It is important to use the proper equipment, appropriate sample volumes and good injection technique. If using the PHOTOVOLT WATER STANDARD (PN 2712803) refer to the TECHNICAL NOTE packed with the standard. General syringe techniques outlined here apply for that application with the exception of the volume injected.

apparatus:

2. Either a 1 or 2 mm³ (µL) HAMILTON DIGITAL SYRINGE (traceable to NIST*) or a 5 mm³ (µL) HAMILTON SYRINGE with a Chaney adapter (Photovolt PN 2612255) may be used. *The HAMILTON DIGITAL SYRINGE allows one to trace the operation of an AQUATEST back to NIST. This is analogous to using a set of NIST weights to verify the accuracy of a balance.

procedure:

3-1. Set the delivery volume on the syringe to 2mm³ (µL) according to the manufacturer’s instructions. Be sure that the locking screws on the adapter are tight before injecting samples.
3-2. Clean and wet the syringe by placing the tip into a container of water and pumping the plunger several times. Make sure that the water is pulled up and completely expelled each time.
3-3. Insert the needle into a fresh container of water. Fill and expel the water several times.
3-4. Pump the plunger a few times with the needle in the water. (Water is in needle, not in barrel).
3-5. Remove syringe from the water, press the spring loaded button stop on the lower part of the Chaney adapter and then depress the plunger until it hits the stop.
3-6. Wipe the full length of the needle with a clean, dry tissue. To avoid wicking the sample out of the needle, do not wipe across the tip.
3-7. Press the start key on the AQUATEST and inject the sample. Keep the tip of the needle well below the liquid level when injecting. Occasionally lift the titration vessel off the stand and gently swirl the contents to wash down any condensed moisture from the vessel walls.
3-8. Following the above procedure with the injection of 2 µL of water, a response of 2000 µg ± 100 µg must be observed on the instrument display. This gives an allowable ± 5% deviation in recovery and ensures that the titrator is operating properly.

* NOTE: Any grade of water is acceptable for this test. This would include water described in ASTM D 1193, which lists four grades of reagent water to ordinary drinking (or tap) water.

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