In-situ measurement of trace isoprene and dimethyl sulfide in seawater and oceanic atmosphere based on room temperature adsorption-thermal desorption

摘要

Aqueous biogenic gases play an important role in the global environment. Here, we describe a novel method developed to determine trace levels of biogenic gases (isoprene and dimethyl sulfide, DMS) in situ, based on room temperature enrichment-thermal desorption. The two gases from seawater (isoprene: 630 mL; DMS: 20 mL) and the marine atmosphere (1 L) were adsorbed into a funnel-shaped quartz tube at room temperature, then thermally desorbed (358 degrees C) and introduced into a gas chromatograph-flame ionization detector (GC-FID) using a portable curie-point injector. A suitable adsorbent material (Carbopack X) was added to the adsorption tube to trap two the target compounds in a gas stream for the first time. Good reproducibility ( 3%; 1%), linearity (R-2 = 0.999; R-2 = 0.997), and low detection limits (0.5 pmol L-1; 0.07 nmol L-1) were obtained for isoprene and DMS, respectively. In addition, this method can be used for atmospheric isoprene and DMS quantization and involves an easier procedure than previous extraction techniques. The method was also applied for in situ seawater analysis off the coast of Hokkaido, Japan (isoprene: 27.54 +/- 0.46 pmol L-1), in the continental shelf area of the Bering Sea (isoprene: 42.55 +/- 16.24 pmol L-1; DMS: 5.20 +/- 3.29 nmol L-1), and for marine atmospheric analysis (average isoprene and DMS: 59 and 219 pptv, respectively) in the North Pacific. The results suggest that the method can be used successfully at room temperature, in place of traditional cryo-trapping techniques used to determine isoprene and DMS levels in seawater and the atmosphere.