Hanna Instruments HI 904 - Manual (Page 120)

9-8
METHODS OPTIMIZATION
9.2.4 Liquid Samples
The water contained in liquid samples must be available to react with the KF reagent. It is
important to select a reagent or co-solvent with which the sample is miscible.
Liquids are typically added through the septum in the sample port via a syringe and needle
using the following steps:
1. Attach a long needle (approximately 6” long, 21-gauge) to a syringe large enough
to hold at least one complete sample volume.
2. Rinse the syringe and needle with sample several times by drawing in a small
portion of sample, fully extending the plunger, shaking to coat the syringe interior
and expelling the sample into a waste collection container.
3. Draw enough sample into the syringe for at least one titration.
4. Dry the outside of the needle with a lint free wipe or tissue.
5. Determine the mass of the syringe and sample.
6. Initiate a titration from standby mode by pressing the ‘start analysis’ option key.
7. Insert the needle through the septum in the sample port. Push the syringe through
the septum until the end of the needle is approximately 1 cm from the surface of
the solvent.
8. Steadily dispense the contents of the syringe ensuring that the sample is introduced
directly into the solvent and does not splash or spatter onto the wall of the titration
vessel electrode or dispensing tip.
9. Draw a small amount of air from inside the cell into the syringe to ensure that no
sample drops remain on the tip of the needle.
10. Remove the syringe and needle from the septum taking care to not touch the
needle to the solvent or other internal cell components.
11. Determine the mass of the syringe and needle.
12. Calculate the mass of the sample added to the titration cell (subtract the mass of
the syringe after the sample has been added from the mass of the syringe before
sample addition).
13. Enter the calculated mass of the sample into the HI 904.
14. Start titration using the option key ‘start analysis’ from the add sample screen.
As indicated above, when adding a liquid sample with a needle and syringe, it is important
that the sample is introduced directly into the solvent. Sample that is deposited on the sides
of the vessel or other internal components of the cell may not be titrated with the rest of the sample.
It is equally important that no drops remain on the tip of the needle. ‘Hanging drops’ will end
up on the bottom of the septum. This will result in false low results for the determination.
Liquid samples with high viscosity may be careful warmed to improve the flow through the
needle.
In some cases liquid samples may require one of the additional preparatory steps listed in
the sections that follow. Specific sample preparation instructions are included with each
standard method.