Comparison of Three Solid Phase Materials for the Extraction of Carboxylic Acids from River Water Followed by 2D GC × GC-TOFMS Determination

Table 1

Characteristic NOM fractions of surface water described by the LC-OCD technique [4, 17].

Fraction	Molecular mass	Characteristics
Biopolymers	>50,000–2,000,000 g/mol	Mostly polysaccharides; not UV-absorbing; may be associated with amino acids and protein
Humic substances	100–10,000 g/mol	Consisting of humic acids (nonsoluble in acids, soluble in basis) and fulvic acids (soluble in acids and basis) in varying amounts
Building blocks	350–500 g/mol	Intermediates in degradation process fulvic acids
Low molecular weight organic acids (LMWAs)	>1 μm	Final degradation products of organics, but also released by algae and bacteria
Low molecular mass neutrals and (LMWN) amphilics	>1 μm	Slightly hydrophobic substances, such as alcohols, aldehydes, ketones, and amino acids
Hydrophobic compounds (HOC)	>1 μm	Difference between TOC and summarised chromatographic fractions; not detectable by chromatography; consisting probably of natural lipids, lipoids, and hopanoids