CHROMATOGRAPHIC QUALIFICATIONS AND THEIR EFFECTS ON RELIABILITY OF LOW-LATITUDE TRACE LONG-CHAIN ALKENONE AS A TEMPERATURE INDICATOR

Two main chromatographic qualifications, programmed temperature mode and carrier gas flow rate, were investigated for the analysis of trace alkenone from low-latitude continental shelf samples. The separability, test precision and repeatability under various gas chromatographic (GC) analytical circumstances were discussed. Our results show that chromatographic qualifications have great impacts on the analysis of those trace alkenone. Traditional high GC programmed temperature ramps (PTR), which are adequate for ocean sediment samples, were confirmed no longer applicable for the analysis of the shelf samples highly diluted by terrigenous debris. Excellent separabilities for C_37:x (C_37:2 & C_37:3) and the homolog compounds were obtained under Low PTR condition (1.3℃/min at high temperature stage), even for the samples in which the C_37:3 alkenone content is extremely low (1ng/g dry sediment, calculated sea surface temperature is near to 27℃). Furthermore, the test precision and repeatability are much better under low PTR. Our results also indicate that perfect separabilities and test precision are likely to be obtained under low carrier gas flow rate for those shelf sediment samples with low trace alkenone content.