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2 Photometric TestKits
2.2.7 Shelf-life of the Reagents
The Spectroquant
®
test kits are in most cases stable for 3 years when
stored in a cool, dry place. A few test kits have a lower shelf-life of 18 or
24 months or must else be stored in a refrigerator.
COD Cell Tests must be stored protected from light.
The expiry date of the package unit is printed on the outer label. The shelf-
life may become reduced when the reagent bottles are not reclosed tightly
after use or when the test kit is stored at temperatures higher than those
specified.
3 Sample Preparation
Sample preparation covers all the steps necessary before the actual ana-
lysis can be performed.
3.1 Taking Samples
The taking of samples is the first and most impor tant step on the way to
obtaining the correct ana lysis result. Not even the most exact method of
analysis can correct any mistakes made in the taking of the sample. The
objective of the sampling proce dure is to gain a sample with a represen-
tative com position. The most important pre condition for gain ing a re-
presentative sample is the identification of the suitable sampling site.
Here it must be borne in mind that the solution to be investigated can dis-
play varying con centrations in different places at different times.
In sampling, a distinction is made between manual and automatic
methods. In many cases a true picture of the average composition of the
sample can be obtained only once several individual samples have been
collected; this can be done manually or with an automatic sampler.
Clean plastic containers with a volume of 500 or 1000 ml are suitable for
collecting samples. They should be rinsed several times, under vigorously
shaken, with the water to be investigated, and then filled free of air bub-
bles and immediately closed tightly. The containers must be protected
against the effects of air and heat and then be forward ed for the further
analytical steps as soon as possible. In ex ceptional cases, preserva tion
measures in the form of short-term refrigeration at +2 to +5 °C and
chemical conservation can be taken.
Parameter
COD
N compounds:
NH
-N, NO
-N, NO
-N
4
3
2
P compounds:
PO
-P, P total
4
Heavy metals
Release 01/2009
Preservation
+ 2 to + 5 °C max. 24 h or
–18 °C max. 14 days
analyze immediately, only in exceptional case
+ 2 to + 5 °C max. 6 h
short-term storage, no preservation;
with nitric acid to pH 1, max. 4 weeks
short-term storage, no preservation;
with nitric acid to pH 1, max. 4 weeks
photoLab
®
Series
9
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