Chinese Journal of Oceanology and Limnology Vol. 31 No. 4, P. 860-866, 2013 http://dx.doi.org/10.1007/s00343-013-2212-1 Henry’s Law constant for phosphine in seawater: determi- nation and assessment of influencing factors* FU Mei (付梅) 1, 2 , YU Zhiming (俞志明) 1 , LU Guangyuan (卢光远) 1, 2 , SONG Xiuxian (宋秀贤) 1, ** 1 Key Laboratory of Marine Ecology and Environmental Sciences, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China 2 University of Chinese Academy of Sciences, Beijing 100049, China Received Sep. 3, 2012; accepted in principle Nov. 10, 2012; accepted for publication Dec. 11, 2012 © Chinese Society for Oceanology and Limnology, Science Press, and Springer-Verlag Berlin Heidelberg 2013 Abstract The Henry’s Law constant ( k) for phosphine in seawater was determined by multiple phase equilibration combined with headspace gas chromatography. The effects of pH, temperature, and salinity on k were studied. The k value for phosphine in natural seawater was 6.415 at room temperature (approximately 23°C). This value increases with increases in temperature and salinity, but no obvious change was observed at different pH levels. At the same temperature, there was no significant difference between the k for phosphine in natural seawater and that in artificial seawater. This implies that temperature and salinity are major determining factors for k in marine environment. Double linear regression with Henry’s Law constants for phosphine as a function of temperature and salinity confirmed our observations. These results provide a basis for the measurement of trace phosphine concentrations in seawater, and will be helpful for future research on the status of phosphine in the oceanic biogeochemical cycle of phosphorus. Keyword: phosphine; Henry’s Law constant; seawater; influencing factors; multiple phase equilibration 1 INTRODUCTION Phosphine (PH 3 ), as a gaseous form of phosphorus, has been confirmed as a trace component in the atmosphere (Devai and Delaune, 1995; Gassmann et al., 1996; Glindemann et al., 1996; Liu et al., 1999; Glindemann et al., 2003; Roels and Verstraete, 2004; Zhu et al., 2006; Zhu et al., 2007), the hydrosphere (Devai et al., 1988; Gassmann, 1994; Devai et al., 1999; Niu et al., 2004; Geng et al., 2010), and in sediments (Devai and Delaune, 1995; Yu and Song, 2003; Feng et al., 2008a, b; Song et al., 2011). It is generally accepted that phosphine is easily transformed to phosphate after a complicated oxidation reaction via hypophosphite and phosphite (Frank and Rippen, 1987; Geng et al., 2010); however, the specific mechanism of the transformation has not been clarified because of the limited analytical techniques available for phosphine detection in water. Evidence exists that organisms can use the reduced form of phosphorus, so phosphine is an important source of phosphorus and could be important in the overall phosphorus cycle (Devai et al., 1988; Glindemann et al., 1998; Hanrahan et al., 2005). In recent years, many scholars have investigated the distribution, release, and possible environmental controls of phosphine in marine sediments (Feng et al., 2008a, b; Niu et al., 2004; Song et al., 2011). Unfortunately, there is no method that can accurately detect phosphine in seawater. This limits the understanding of the role of phosphine in the marine environment. The detection method for phosphine in gases is very sensitive (Niu et al., 2004; Li et al., 2009). If the Henry’s Law constant ( k) for phosphine is known, the concentration of phosphine in seawater can be quantified from the equilibrated concentration in the gas phase. Henry’s Law constant, k H , is defined as: * Supported by the National Natural Science Foundation of China (Nos. 30970522, 40576058) and the National Natural Science Foundation of China for Creative Research Groups (No. 41121064) ** Corresponding author: songxx@qdio.ac.cn