Metrohm 784 KFP Titrino User Manual

Page 26

2.6 Parameters, key

784 KFP Titrino

The determination of the free water is easily done, as far as the specifications of the

reagent manufacturer regarding the "water capacity" of the reagents are considered.

Problems may occur with specific sample matrices. The relevant literature contains many

precise analysis instructions. Here, we give you some useful hints for the sample

addition.

Sample addition

For sample addition various accessories are available, for example injection syringes,

weighing spoons etc.

It is a good idea to apply the back-weighing technique, except when you are disposing

small amounts of liquids with a micro-syringe. Fill the syringe or the weighing spoon with

your sample just before the titration (e.g. during conditioning) and tare it on a balance

with an appropriate precision, which ideally is connected to the Titrino. Sample size

request should always be switched on (see page 19). Add the sample during the request

for the sample size, and weigh the syringe or weighing spoon again to evaluate the

weight difference. Use the transfer of balance data to enter the correct sample size if

possible. The weight has to be transmitted in gram. If you transfer the sample size from

the balance, the sample size request is confirmed automatically, and the titration is

started at once. Otherwise use the keypad to enter the weight.

If the sample size request is switched off, and preconditioning is set, you are explicitly

prompted to add your sample. For six seconds, the message "add sample" is displayed

after which the titration is started by the Titrino itself. This waiting time can be extended by

pressing .

Solid samples

Use the glass weighing spoon 6.2412.000 and dispose the sample through the opening

for the septum stopper.

Liquid samples

Use a disposable syringe (2...20 mL) or a micro-syringe with a long needle attached.

Puncture the septum and dispose the sample carefully. When using disposable syringes,

add the liquid sample carefully without dipping into the solvent. Draw back the last drop

of sample into the syringe before you redraw the needle. For disposing an exact, small

volume of liquid sample, use a micro-syringe. Proceed as described above, but dip the

needle into the preconditioned solvent and dispose the sample carefully. Here drawing

back of solvent or sample adhering to the needle is not recommended.

Always keep in mind to exchange the septum as soon as it shows any large punctures

impairing the tightness of the titration cell.

Pasty, viscous samples

For samples which cannot be disposed with a needle because of their high viscosity, you

can handle your samples with disposable syringes with a large volume without using a

needle. Dispose your sample through the opening of the septum stopper. Back-weigh the

syringe after addition of the sample. Be sure to wipe off any adhering excess sample

substance of the syringe before taring it.

In any case, pay attention to prevent the penetration of atmospheric moisture into the

titration vessel when you are disposing the sample. If you still have to open the titration

cell for any reason, determine a blank value and take it into account for the calculation of

the titration result (see page 132).