YSI pHotoFlex Series - Manual (Page 12)

Practical part pHotoFlex
®
Series
12 ba76126e01 03/2013
1.6.3 Influence of turbidity
With samples that are visibly turbid, measured values can be oscillating
or too high or too low during photometrical determination.
Compensating for
turbidity
Depending on the type of sample or substance to be determined, the
influence of turbidity can be compensated for in different ways:
 If you are positive that the substance to be determined is exclusively
in the dissolved part, the sample can be filtrated before carrying out
determination. For filtrating, simple common laboratory paper filters
or membrane filters (recommended pore size 0.45 µm) can be used.
 If you assume that a considerable part of the substance to be deter-
mined is bound in the solid part of the sample, the substance has to
be brought into an analysable form before carrying out the photo-
metric determination. This is done in a chemical digestion proce-
dure. Suitable digestion reagents can be found in the YSI catalog.
With some procedures, the critical solid substance part is digested
during the determination itself (e. g. COD measurement in aqueous
samples with suspended matter with parts of organic compounds).
Here it is important for an exact determination that the part of sus-
pended matter be representative for the sample. For this the sample
has to be homogenized, e.g. with a disperser.
1.6.4 Influence of complexing agents
Complexing agents can disturb the determination of metals by forming
very stable compounds with them. In this form the metals cannot be an-
alyzed. Here, a digestion has to be carried out prior to photometric de-
termination. Suitable digestion reagents can be found in the YSI
catalog.