Page 29 - 5_TOC in daily practice

SCA-130-515

The example above describes the oxidation ■ Methanol
of carbon with oxygen. For organic Oxidation of methanol:
substances the ratio between carbon atoms
and oxygen atoms is different, which is of 2 �� �� � 3 � � 2 �� � 4 � �
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direct influence on the conversion factors
from TOC to COD. 2 Carbons react with 3 oxygen molecules.
The calculation is as follows:
Here are a few examples.
for C: 1000 �� ∶ �2 ∗ 12 � � � 41.67 ����
■ Oxalic acid � ��� �
Oxidation of oxalic acid proceeds as follows:
�� � ����
for O 2: 1000 � ∶ �3 ∗ 32 ��� � � 10.42 �
2 � � � �� � 4 �� � 2 � �
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���� ���� � 4.000
4 carbons react with an oxygen molecule. 41.67 � ∶ 10.42 �
This is the calculation:
■ Real water samples
�� � ���� These examples show how the COD factor
for C: 1000 ∶ �4 ∗ 12 � � 20.83
� ��� � can be calculated. They also illustrate why,
due to the composition of a sample, the COD
�� � ����
for O 2: 1000 ∶ �1 ∗ 32 � 31.25 factor may vary so much.
� ��� �

In addition, real water samples usually
���� ����
20.83 ∶ 31.25 � 0.667 contain a large number of different organic
� �
substances. This is why the bandwidth of the
■ Benzene conversion factors ranges from < 1 to > 5,
The way oxidation of benzene proceeds: depending on the amount of oxygen that is
already bound in the organic compounds.
2 � � � 15 � � 12 �� � 6 � �
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Furthermore, COD determination also
12 Carbons react with 15 oxygen molecules. measures oxidizable inorganic compounds,
The calculation is as follows: such as nitrites, bromides, iodides, metal ions
and sulfur compounds and this may influence
�� � ���� the conversion factor.
for C: 1000 ∶ �12 ∗ 12 �� 6.94
� ��� �

The instrument software of Shimadzu TOC
�� � ����
for O 2: 1000 ∶ �15 ∗ 32 �� 2.08 systems (TOC-L standalone, TOC-Control L,
� ��� �
TOC-4200 standalone) enables the automatic
���� ���� conversion of measured TOC values into
6.94 ∶ 2.08 � 3.34
� � COD value (if the correlation is known).