The influence of different pretreatment methods on theδ13C value of dissolved inorganic carbon in water

In order to research the influence of different sample preparation methods on the dissolved inorganic carbon isotope in water samples, and to establish the best sample preparation method, this paper systematically study the sample collection (headspace vial and polyethylene bottle) methods, storage temperature, saturation mercuric chloride and storage duration which affect the dissolved inorganic carbon isotope value in different types of water samples. The results show that δ13CDIC headspace vial collection method is more stable than the polyethylene bottle collection method for the same water type. Using polyethylene bottle collection method and adding saturated mercury chloride may inhibit the growth of microorganisms. The δ13CDIC value irregularly varies in a big range in case of no saturated mercury chloride added. In contrast, the δ13CDIC value roughly stabilizes at its initial value. The value increased in the case of the relative high temperature or long duration, which is mainly attributed to the release of CO2 in this condition of sample preservation. Different types of water samples without saturated mercuric chloride and with prolonged preservation, the karst water δ13CDIC was more positive than the original value, and the mixed water and non- karst water was negative than the original value. The experiment results show, the maximum difference of δ13C value was merely 0.42‰ after 100 days of storage by using headspace vial sample collection, which is proved to be the best way of sample collection and preservation. In the meantime, the water sampled by polyethylene bottle collection method and stored in a 5 ℃ condition can last a short time to maintain the reliable δ13CDIC value.