Oceanic Trace Gas Measurements

The Hiden HPR-40 DSA is a proven, versatile, and effective product that offers extremely low-level detection of trace gases, making it ideal for various applications, including measuring dissolved species. This device has been used to detect fluctuations in the concentration of Dimethylsulphide (DMS) in seawater, which is a naturally produced trace substance evolved from certain marine micro-organisms such as plankton. In this article, we will discuss the procedure for measuring DMS concentration using the Hiden HPR-40 DSA.

Detection of Fluctuations in DMS Concentration:
The Hiden HPR-40 DSA offers unparalleled sensitivity in the detection of trace gases such as DMS. To measure DMS concentration, successive dilution was used to reduce the concentration of DMS in the sample. The strongest peak at 62 amu was used for the measurements. Correlating this DMS peak signal intensity with the DMS concentration level provides quantitative information on the DMS detection levels. The linear relationship between DMS concentration and peak signal intensity gives a high degree of confidence regarding the detection levels, as shown in Figure 1. Further experiments could extend this detection level down to lower partial pressures. The detection limit of the spectrometer is 5 x 10-15 Torr.

Figure 1 (a & b): Mass scan of dilute concentration levels of DMS and the concentration levels (ppt) derived from DMS partial pressure at 62 amu.

Procedure:
Current research in this area has been performed using a Hiden HPR-40 DSA system. The DMS aqueous solution is circulated around the system to allow continuous monitoring of the DMS concentrations over time. To maintain consistency with seawater conditions, the samples are kept at 10°C using a chiller system. The dilutions of the DMS solution were prepared to produce the desired DMS concentrations relative to water. The samples are then pumped across the membrane inlet pre-configured to reduce the possibility of air bubble contamination.