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【求助】“湖相沉积C14测年采样、送样要求”
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哪位知道湖相淤泥沉积C14测年的采样、送样要求？ [ Last edited by ewigkeit on 2009-2-19 at 14:07 ] |
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Sampling for AMS: Considering the rather involved procedure to strip sufficient DIC from groundwater for conventional analysis, it is of little wonder that accelerator mass spectrometry (AMS) has gained so much interest. For AMS, only about 5 mg carbon is required. This reduces the sample volume for typical groundwaters from up to 100 L for LSC to <500 mL for AMS. This tremendous advantage in sample size allows extraction in the laboratory by the same method as that for d13CDIC (see above). It also minimizes contamination by reducing the amount of sample "handling" in the field. We can also consider analysing samples that are not accessible by conventional methods, such as brines with <10 mg/L HCO3–, and high sulphate discharging at low flow rates from deep geologic settings, or porewaters in low-permeability sediments. SAMPLING SYNOPSIS: DIC-14C for Accelerator Mass Spectrometry (AMS) VOLUME: About 5 mg C are required for standard analysis. EQUIPMENT: · Same as for 13CDIC extraction. · Container: acid- and deionized water- rinsed glass bottle (dried) with a silicon septum in cap (250 mL to 1 L), heavy-wall plastic or glass bottle, double-valve steel or glass cylinder. · NaN2 for waters with >1 to 2 mg-C/L DOC. TECHNIQUE: · Samples must be collected without air contact and kept dark and cool. · If DOC is present in significant quantities, biological activity should be killed with NaN2. ANALYSIS DIC is extracted from solution by acidification under vacuum, in the same manner as for d13C (above). The purified CO2 is sealed in a glass breakseal for conversion to black (elemental) carbon at the AMS facility. Accelerator mass spectrometry is basically an atom counting method. The carbon, mounted on Fe-filaments in the source of the mass spectrometer, is ionized and accelerated through a magnetic field to separate the three main isotopes. Accuracy is slight less than for high-precision gas counting, yet is more than adequate for hydrogeological purposes. 转载自：www.gochemist.cn |
11楼2009-07-27 00:05:30
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5楼2009-06-09 14:06:41
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6楼2009-06-09 14:26:53
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