132
Exercise 9
shake out the broken glass into a waste beaker, and repeat the process with the next
ampoule.
to. Measure the peak height of the curve recorded from the IR analyzer or integrate
the area under the curve. The values of the glucose carbon standards and blanks
(reagents only in organic-free water) should be determined similarly. The IR
analyzer can be calibrated further by injecting a measured amount of CO2 (e.g.,
to Ill) with a gas-tight syringe into the flow system through the silicone tubing.
With appropriate adjustments, a similar system could be used with a gas
chromatograph [e.g., Stainton (1973)]. It should be noted that DOC determined by
this method is potentially an underestimate. Recent evidence with combustion at
650°C recovers greater amounts of DOC that the per sulfate oxidation (Suzuki et aI.
1990).
Calculations
Plot a calibration curve of CO 2 peak heights or curve areas for all standards minus
blank corrections. The calibration curve should be linear for the lower concentrations
and slightly curvilinear for the higher concentrations. Blank corrections should not
exceed 0.5 mg CII. Determine the concentrations of the water samples from this
calibration curve.
When samples require dilution, their concentration is given by (Stainton et aI.,
1977):
C 1 = (C 2 X D) - [C 3 - (D - 1)]
where C 1 = concentration of DOC in sample, C 2 = concentration of DOC in diluted
sample, C 3 = concentration of DOC in dilution water, and D = dilution factor.
The smallest amount of DOC that can be detected with certainty is about 0.09 mg Cjl
within a range of 0.09 to 6.0mg Cjl (ca. 10 to 800llmol Cjl). Precision at the 1.0-mg CII
level lies in the range of: Mean of n determinations ± 0.06nl/2 mg Cjl (standard
deviation of ca. ± 10 Ilmol C/I).
PARTICULATE ORGANIC CARBON
A number of techniques have been developed to determine the organic carbon content
of particulate organic matter [cf., Strickland and Parsons (1972), Golterman and
Clymo (1969), and Stainton et aI. (1977)]. Many methods involve dry oxidation under
an oxygen atmosphere and measurement of the CO 2 liberated by infrared CO2
spectrometry or gas chromatography. Other techniques utilize wet oxidation where the
amount of dichromate reacting with organic matter in a strongly acidic solution is
determined by titration (Maciolek, 1962). The latter methods have been used for both
POC and DOC, although they are much more tedious and subject to error for the
analysis of DOC than is the method outlined above.
The wet oxidation procedure discussed here is simple and allows a large number of
samples to be assayed without complex or specialized equipment. The method may
give results slightly higher than carbon measured by dry oxidation and measurement of
CO 2 , Results are expressed in terms of glucose carbon (Strickland and Parsons, 1972).
The true carbon content of particulate organic material would approach this value only
if all the carbon were present as carbohydrate. The average composition of
phytoplankton and particulate detritus is such that the true carbon content is within 10
Exercise 9
shake out the broken glass into a waste beaker, and repeat the process with the next
ampoule.
to. Measure the peak height of the curve recorded from the IR analyzer or integrate
the area under the curve. The values of the glucose carbon standards and blanks
(reagents only in organic-free water) should be determined similarly. The IR
analyzer can be calibrated further by injecting a measured amount of CO2 (e.g.,
to Ill) with a gas-tight syringe into the flow system through the silicone tubing.
With appropriate adjustments, a similar system could be used with a gas
chromatograph [e.g., Stainton (1973)]. It should be noted that DOC determined by
this method is potentially an underestimate. Recent evidence with combustion at
650°C recovers greater amounts of DOC that the per sulfate oxidation (Suzuki et aI.
1990).
Calculations
Plot a calibration curve of CO 2 peak heights or curve areas for all standards minus
blank corrections. The calibration curve should be linear for the lower concentrations
and slightly curvilinear for the higher concentrations. Blank corrections should not
exceed 0.5 mg CII. Determine the concentrations of the water samples from this
calibration curve.
When samples require dilution, their concentration is given by (Stainton et aI.,
1977):
C 1 = (C 2 X D) - [C 3 - (D - 1)]
where C 1 = concentration of DOC in sample, C 2 = concentration of DOC in diluted
sample, C 3 = concentration of DOC in dilution water, and D = dilution factor.
The smallest amount of DOC that can be detected with certainty is about 0.09 mg Cjl
within a range of 0.09 to 6.0mg Cjl (ca. 10 to 800llmol Cjl). Precision at the 1.0-mg CII
level lies in the range of: Mean of n determinations ± 0.06nl/2 mg Cjl (standard
deviation of ca. ± 10 Ilmol C/I).
PARTICULATE ORGANIC CARBON
A number of techniques have been developed to determine the organic carbon content
of particulate organic matter [cf., Strickland and Parsons (1972), Golterman and
Clymo (1969), and Stainton et aI. (1977)]. Many methods involve dry oxidation under
an oxygen atmosphere and measurement of the CO 2 liberated by infrared CO2
spectrometry or gas chromatography. Other techniques utilize wet oxidation where the
amount of dichromate reacting with organic matter in a strongly acidic solution is
determined by titration (Maciolek, 1962). The latter methods have been used for both
POC and DOC, although they are much more tedious and subject to error for the
analysis of DOC than is the method outlined above.
The wet oxidation procedure discussed here is simple and allows a large number of
samples to be assayed without complex or specialized equipment. The method may
give results slightly higher than carbon measured by dry oxidation and measurement of
CO 2 , Results are expressed in terms of glucose carbon (Strickland and Parsons, 1972).
The true carbon content of particulate organic material would approach this value only
if all the carbon were present as carbohydrate. The average composition of
phytoplankton and particulate detritus is such that the true carbon content is within 10