990
Regulator
Check Valve
—S-
^Combustion Tube
Flow
Meter
&J
Needle
Valve
Temperature should
be maintained at
=0^   900°C-I000°C
Condenser
Transformer
( Flow rate effect on peak height
is minimal between 60-150 ml/min)
Oxygen
Source
Filter
r \
:;:i. o
Recorder
Amplifier
Infrarea Analyzer
Figure 1 ■ Flow diagram of carbon analyzer.
a calibration curve and the value determined. This value includes carbon in the
form of carbonates or bicarbonates which may have been present; and, in order to
measure only organic carbon, all inorganic carbon must first be removed from the
sample. This is accomplished by acidifying the sample and purging with nitrogen
gas prior to injection. The sample is measured for carbon before and after the
acidification-purging step with any reduction being attributed to the loss of inorganic carbon and volatile organic compounds. The volatile organic fraction, if
present, must be measured independently, and this is accomplished by using a
closed system diffusion cell method (3,4).
A modified carbon analyzer has facilitated the measurement of total organic
carbon. The flow diagram of this analyzer is shown in Figure 2. A dual combustion tube system allows direct differentiation between organic and inorganic
carbon, making the preliminary acidification and scrubbing step unnecessary. A
micro-sample is first injected into the high temperature combustion tube and the
total carbon concentration is determined by the same mechanism illustrated in
Figure 1. An identical volume of sample is then injected into the low temperature combustion tube which contains quartz chips wetted with phosphoric acid.
The operating temperature of 150 C is below the value at which organic matter is
oxidized, but in the acid environment all carbonates are removed in the form of
carbon dioxide. This gas then flows through the infrared analyzer and measured
as inorganic carbon. The total organic carbon concentration is taken as the difference between the total carbon and total inorganic carbon values. An optional
air purification unit to provide the carrier gas is available should a bottled source
not be desirable.
There is possibly some interference in the infrared energy absorption pattern
if anions such as
NO,
CI", SO*
and POA
are present in excess of 10, 000 mg/l. Industrial wastewaters containing such concentrations should therefore be diluted with carbon dixoide - free water prior to
analysis.