APPLICATION OF CAPILLARY GAS CHROMATOGRAPHY TO THE DETERMINATION OF THE COMPOSITION OF POLYSACCHARIDES IN MARINE SEDIMENTS

Carbohydrates, mostly occurring as polysaccharides, represent a major component of marine organic matter. The composition of carbohydrates at a molecular level is applicable to distinguish marine- from terrestrially-derived organic matter and to understand their role in the carbon biogeochemical cycle.We developed a gas chromatographic method to determine the composition of polysaccharides in marine sediments. Polysaccharides in sediments were hydrolyzed into monosaccharides with 2.0mol/L trifluoroacetic acid (TFA) at 80℃ for 8 hours. The hydrolysate was centrifuged and the supernatant was collected. The solution was then evaporated to remove TFA in a water bath at 60℃. The dried sample was dissolved in approximately 2ml Milli-Q water, and then run through a 20ml column packed with mixed cation and anion exchange resins (1∶1 mixture) at a flow rate of 0.8-1.0ml/min. The column is then rinsed with at least three beds volume of Milli-Q water. The deionized hydrolysate was evaporated to dryness, upon which 0.2% (W/V) lithlum perchlorade was used to catalytically equilibrate sugar isomer mixture in pyridine at 60℃ for 48 hours. Regisil (bis(trimethylsilyl) trifluoroacetamide +1% trimethylchorosilane) was then added to form trimethylsilyl ether derivatives of sugar. Each monosaccharide was identified by its relative retention time, and quantified by an internal standard method. Quantification on the basis of single clearly resolved peak for each sugar is made possible by this equilibration step. Analysis was carried out using a HP5890 gas chromatography equipped with a 30 m by 0.32mm i.d. fused-silica capillary column (HP-5) and with a flame ionization detector (FID). Both the injection port and the FID are maintained at a constant temperature of 300℃. The injection was splitless with a constant column flow of 2.0ml/min of N 2. Column temperature was programmed from 140℃ increasing at 2℃/min after an initial delay of 4min. Under this condition, seven major neutral monosaccharides in the sediment samples taken from Xiamen Harbour, China were identified and quantified. The method showed a spiked recovery (sample + spike) of 77%-115% with a relative standard deviation (RSD) of 1.8%-11%, and a standard recovery (blank + spike) of 94%-113% with a RSD of 1.6%-9.5%. The detection limit of the monosaccharides ranged from 0.02-0.06mg/L with a signal to noise ratio of 3. The recovery of an internal standard, adonitol, was 79.8% (n=6, RSD=5.2%) throughout the sample processing procedure.