Environmental Engineering Reference
In-Depth Information
fulvic acid, it is suggested to denote the first and the second fluorescent component
as 'autochthonous fulvic acid (key component)' and 'autochthonous fulvic acid
(minor component)', respectively. These names could be useful to denote the two
fluorescent components originated from algae or phytoplankton in fresh- and marine
waters in future research studies. The differences between autochthonous fulvic
acids and allocthonous fulvic acids and their identification are extensively discussed
in the next chapter, 'Fluorescent dissolved Organic Matter in Natural Waters'.
5 Measurement, Distribution and Sources of DOM
in Natural Waters
Measurement of DOM
DOM is generally determined as dissolved organic carbon (DOC) concentration,
because of the predominant presence of organic carbon in all dissolved organic
substances included in bulk DOM. The amount of DOC in natural waters is deter-
mined using a high-temperature catalytic oxidation (HTCO) method developed
by Sugimura and Suzuki (Sugimura and Suzuki
1988
). This technique is very
precise and rapid for the determination of non-volatile DOM in concentrations
between 0 and 2000
μ
M, compared to conventional wet chemical oxidation meth-
ods (Menzel and Vaccaro
1964
; Jonathan
1973
). In the HTCO method (Sugimura
and Suzuki
1988
), the oxidation of DOM in water is carried out on a platinum
catalyst at 680 °C under an oxygen atmosphere after the sample has been freed
of inorganic carbon. The concentration of CO
2
generated is measured with a non-
dispersive IR gas analyzer. The determination can be carried out with a precision
of
±
2 % using a sample volume of 100-200
μ
l.
Methodology for HTCO
(Sugimura and Suzuki
1988
): After collection of
water samples using polycarbonate bottles, water is filtered with precombusted
(450 °C) glass-fiber or any other filters (0.1-0.7
μ
m size). Triplicate samples
(15 ml) are stored in brown glass bottles (30 ml in volume). 25
μ
l of 6 N HCl
solution is added to remove dissolved inorganic carbon (DIC). These bottles are
sealed with Teflon-coated butyl-rubber stoppers and aluminum caps and stored in
a freezer (
−
40 °C). There is need to analyze the samples as soon as possible. For
sample measurement, DIC is firstly removed by bubbling the brown bottles with
pure air for approximately 15 min. After removing DIC, 200
μ
l of the water sam-
ple is injected into a TOC analyzer (e.g. TOC-5000A, Shimadzu, Kyoto, Japan).
Note that analytical blanks for the DOC measurement originating from the instru-
ment (system blank) and from pure water (e.g. Milli Q TOC, Millipore) are on
average in the range of 2-4
μ
M C and 6
μ
M C, respectively (Yoshioka et al.
2002a
). The system blank is determined during sample measurement according to
the instrument software of the TOC 5000A. The system blank is generally used for
the correction of DOC concentration for samples. Potassium hydrogen phthalate is
generally used as a standard for calibration.
