Liquid chromatography-organic carbon detection

These effects were further investigated by size exclusion analysis (SEC) of the fractions (see section 6.4.8) and by liquid chromatography — organic carbon detection (LC-OCD) (see section 6.4.9). 

The radical "OH in surface waters is quickly consumed by organic compounds, bicarbonate, carbonate, and nitrite. It has a typically low steady-state concentration of around 10"16 M. For this reason it cannot be directly detected, and quantification in laboratory experiments is usually carried out by means of reactions of known kinetics. The formation of phenol from benzene, of 4-hydroxybenzoic from benzoic acid, and the disappearance of nitrobenzene are suitable systems if intermediate monitoring is carried out by liquid chromatography, while the disappearance kinetics of butyl chloride is suitable for headspace sampling and gas-chromato-graphic analysis [64]. 

High performance liquid chromatography (HPLC) has been widely used for many years in industrial laboratories but its use in environmental laboratories has usually been restricted to analyses such as the determination of polyaromatic hydrocarbons and linear alkylbenzene sulphonates. Traditionally gas chromatography (GC) has been the first choice technique and HPLC only used when GC has proved unsuitable, due to thermal lability or other reasons. This reliance on GC is despite the fact it has been reported that 80-90% of the total organic carbon content in waters is non-volatile and not amenable to GC. Probably the reason for the lack of use of HPLC lies in the poor sensitivity of its most common detector (UV spectrophotometric) compared with GC detectors and the often demanding limits of detection required for environmental analysis, where sub-pg 1 limits of detection are the norm. 

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