It is easier to analyse what we release to water than what nature releases to its waters. This ”Natural Organic Matter” (NOM) plays a vital role in water usage and we still know almost nothing about it!
Why do we know so little about NOM?
In this situation, what can be done?
Take the water sample as it is,
inject it into a semi-preparative column filled with a hydrophilic polymer containing pores for separation according to speed of diffusion and
use a mild buffer at neutral pH as mobile phase.
Use several detectors for analysis including a DOC-detector for quantification.
Use custom-made intelligent software for data processing.
Have an experienced person for data interpretation.
This approach is called ”LC-OCD” (Liquid Chromatography - Organic Carbon Detection). DOC-Labor Dr. Huber has developed this technique and is currently the only service laboratory offering to research and industry.
The benefit of LC-OCD?
We are still far away from compound identification but we are able to separate NOM into 6 fractions to get meaningful results.
Position of LC-OCD in the family of analytical tools for characterisation of NOM
When we discuss analytical tools for the analysis of unknown organic matter in waters we can choose techniques with a high compound identification potential, like GC-MS, or high mass balancing potential, like TOC (see Fig. below). Many researchers use both strategies and have to realise that a large part of DOC remains unidentified.
LC-OCD was developed to fill this analytical ”gap”, at least to some extent. While mass balancing on the basis of DOC is maintained, a lot of information on the qualitative composition of DOC is obtained. For example, humic substances, which are the most dominating class of compound in natural waters, are quantified and characterised.
The core of the system is the organic carbon detector (OCD) which is also the only OCD commercially available world-wide. Additional detectors include
UV-absorption (UVD), organic and inorganic bound nitrogen (OND), and, optionally, fluorescence (FLU).
Sensitivity of all detectors is in the low ppb range: Even organic impurities in very ”pure” waters such as lab waters can be analysed by direct injection of a sample.
All software for system operation, data acquisition, data processing and data visualisation is ”home-made” with LabVIEW or EXCEL templates.
"Wir sehen nur, was wir kennen."
J. W. v. Goethe
"We only see what we know."
... cannot be concentrated without beeing destroyed.
... is present in very small concentrations only.
... is too hydrophilic to be isolated fully from water.
... has no specific chemical functionalities.