Pipetting System - wtw PhotoLab S12-A Operating Instructions Manual

photoLab ® Series
3 Sample Preparation

4 Pipetting System

14
In the event that the sample to be analyzed is a highly contaminated ma-
terial (high proportion of organic substances) or water-insoluble samples,
decomposition using concentrated acids and other agents is in dispensible.
Corresponding examples from the collection of applications for real
samples are available on request.
The necessity for decomposition can be checked according to the follo-
wing diagram:
Decomposition
Procedure
Measurement
Result A
Decomposition
necessary
For wastewater with a consistent composition, this check as a rule need
be carried out only once. It is, however, advisable to check the result peri-
odically.
Positive-displacement pipettes permit
•
an exact dosage of the sample volume
•
a precise measurement of sample and reagent volumes and of the
volumes of water for dilution purposes.
Pipettes of varying volumes and also ones with a fixed volume are available.
Sources of error and hints on how to avoid them:
•
Closely follow the instructions for use contained with the pipette in
question.
•
Check the pipetted volumes
a) by weighing using analytical scales (weighing ac cu racy ±1 mg),
1 ml of water at 20 °C = 1.000 g ±1 mg
b) using Spectroquant
this is a pho tometric check of the pipette, and scales are not
necessary (see section "AQA").
•
Avoidance of spread effects by rinsing the pipette several times with
the solution to be pipetted.
•
Always exchange the pipette tip.
•
Draw up the liquid slowly and depress piston completely to discharge
the liquid.
No Yes
A and B
idential?
®
PipeCheck;
Procedure
Measurement
Result B
No decomposition
necessary
Release 01/2009