Metrohm 851 Titrando Bedienungsanleitung PDF herunterladen (Seite 48)

4.4 Optimum working conditions

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851 Titrando

4.4 Optimum working conditions

4.4.1 General

When a coulometer cell that has been well dried-out beforehand is put

into operation with a generator electrode without diaphragm, the basic

drift will be reached within approx. 30 minutes. It is recommended that

the coulometer cell be repeatedly and carefully shaken during this time.

For generator electrodes with diaphragm, you should expect a preparation

time of approx. 2 hours.

To obtain precise determinations of amounts of water smaller than

100 µg, it may also be of advantage to condition the coulometer cell over-

night before using it.

If the Titrando is switched off for extended periods with the coulometer

cell filled, it will take some time for it to become conditioned again after it

is switched back on.

With continuous use, the Titrando should not be switched off overnight.

4.4.2 Drift

A constant drift in the range of ≤ 4 µg/min is all right. Lower values, how-

ever, are quite possible. Higher but stable values will still produce good

results, because the drift can be compensated.

A constantly high drift can be caused by water-containing deposits in

inaccessible parts of the coulometer cell. In these cases, shaking the cell

can reduce the value. Ensure that there are no drops above the liquid level

in the coulometer cell.

If you are working with a generator electrode with diaphragm, shake the

cell only hard enough that the catholyte and anolyte do not mix with one

another. If the drift remains too high for a prolonged time, even after

shaking the cell, then the electrolyte solutions should be replaced. The

catholyte should be replaced once per week.

A wet catholyte can be another reason for the excessively high drift. The

wet catholyte can be dried with a KF single-component reagent.

When you work with a Karl Fischer oven, a drift ≤ of 10 µg/min is all right.

The drift depends on the gas flow (the smaller the gas flow, the lower the

drift) and on the humidity of the surroundings.

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Metrohm 851 Titrando Bedienungsanleitung Seite 48