Separation and Fractionation of Sediments from Seawater
83
Both membranes and fibres retained material well below the expected molecular
weight cut-off.
These techniques are only just coming into use in marine organic chemistry. The
apparatus is now available for processing large quantities of sea water at pilot plant
levels, to yield gram quantities of dissolved organic materials in specified molecular
size classes. This should be one of the most fruitful methods for accumulation,
separation and rough fractionation of dissolved organic materials.
4.7.4
Fractionation by Column Chromatography
Separation into molecular size classes by ultrafIltration is necessarily discontinuous;
the fractions resulting are composed of mixtures of compounds within a given band
of molecular sizes. We would often prefer a continuous separation by molecular size,
particularly if it is suspected that the material in question might naturally fall into
only a few fractions, each consisting of a tight grouping of molecular size or weights.
This kind of fractionation is best carried out by some form of column chromatography. If molecular size is to be the criterion for separation, then materials such as
Sephadex can be used as column packing. Sephadex separates compounds by exclusion, holding the smaller molecules within the particles and rejecting those which will
not fit within the pores of the resin. Thus, with a Sephadex column, the large
components come off the column first. The system is not perfect; some charged
compounds, such as phenols, can be bound irreversibly to some of the resinsomitt
(Gjessing and Lee [712], Sirotkina et al. [713]).
XAD resins have been used to collect and concentrate organic materials from sea
water. They can also be used as packings for fractionation by column chromatography. While they have been used in simple gravity flow column chromatography, high
pressure liquid chromatography has also used them (Pietrzyk and Chu [714,715]).
This technique in marine chemistry offers many possibilities and a few major drawbacks. The first drawback is the lack of sensitivity of the detectors. If the compounds
sought happen to be fluorescent, or can be made into fluorescent derivatives, the
inherent sensitivity of fluorescence can be used. Otherwise, the technique is limited to
the much less sensitive refractive index and ultraviolet absorbance detectors.
There is also the possibility of combining liquid chromatography with mass spectrometry as a standard technique for identification of at least the compounds oflower
molecular weight.
Workers who have examined the applicability of high performance liquid chromatography to water analysis include Waggot [716], Scott and Kucera [717], Snyder
[718], and Engelhardt [719].
Reversed phase chromatography is a variant of high performance liquid chromatography where a non-polar organic phase is immobilized and a polar solvent is used as
eluent. This variant may also be applied when non-polar compounds are to be sorbed
from a polar solvent. This very situation is encountered in the attempt to accumulate
non-polar organic substances from sea water by liquid-solid adsorption.
Activated charcoal was one of the first adsorb ants used to accumulate dissolved
organic material from water (Braus et al. [720], Eichelberger and Lichtenberg [721]).
83
Both membranes and fibres retained material well below the expected molecular
weight cut-off.
These techniques are only just coming into use in marine organic chemistry. The
apparatus is now available for processing large quantities of sea water at pilot plant
levels, to yield gram quantities of dissolved organic materials in specified molecular
size classes. This should be one of the most fruitful methods for accumulation,
separation and rough fractionation of dissolved organic materials.
4.7.4
Fractionation by Column Chromatography
Separation into molecular size classes by ultrafIltration is necessarily discontinuous;
the fractions resulting are composed of mixtures of compounds within a given band
of molecular sizes. We would often prefer a continuous separation by molecular size,
particularly if it is suspected that the material in question might naturally fall into
only a few fractions, each consisting of a tight grouping of molecular size or weights.
This kind of fractionation is best carried out by some form of column chromatography. If molecular size is to be the criterion for separation, then materials such as
Sephadex can be used as column packing. Sephadex separates compounds by exclusion, holding the smaller molecules within the particles and rejecting those which will
not fit within the pores of the resin. Thus, with a Sephadex column, the large
components come off the column first. The system is not perfect; some charged
compounds, such as phenols, can be bound irreversibly to some of the resinsomitt
(Gjessing and Lee [712], Sirotkina et al. [713]).
XAD resins have been used to collect and concentrate organic materials from sea
water. They can also be used as packings for fractionation by column chromatography. While they have been used in simple gravity flow column chromatography, high
pressure liquid chromatography has also used them (Pietrzyk and Chu [714,715]).
This technique in marine chemistry offers many possibilities and a few major drawbacks. The first drawback is the lack of sensitivity of the detectors. If the compounds
sought happen to be fluorescent, or can be made into fluorescent derivatives, the
inherent sensitivity of fluorescence can be used. Otherwise, the technique is limited to
the much less sensitive refractive index and ultraviolet absorbance detectors.
There is also the possibility of combining liquid chromatography with mass spectrometry as a standard technique for identification of at least the compounds oflower
molecular weight.
Workers who have examined the applicability of high performance liquid chromatography to water analysis include Waggot [716], Scott and Kucera [717], Snyder
[718], and Engelhardt [719].
Reversed phase chromatography is a variant of high performance liquid chromatography where a non-polar organic phase is immobilized and a polar solvent is used as
eluent. This variant may also be applied when non-polar compounds are to be sorbed
from a polar solvent. This very situation is encountered in the attempt to accumulate
non-polar organic substances from sea water by liquid-solid adsorption.
Activated charcoal was one of the first adsorb ants used to accumulate dissolved
organic material from water (Braus et al. [720], Eichelberger and Lichtenberg [721]).