Once sample has been acquired, then the end of the needle is sealed and the needle body is inserted into the hot injector

EPZ5676 order of the gas chromatograph. Water collected with the sample is in this case an advantage as the pressure change associated with its vaporization is used to drive the VOC into the column. Sensitivity can be increased simply by increasing the sample volume, until breakthrough occurs (Trefz et al., 2012). Needle trap methods provide a simple, robust, high sensitivity and low cost alternative to presently used seawater sampling methods (Alonso et al., 2011a, Bagheri et al., 2011 and Risticevic et al., 2009). Here, we exploit the suitability of needle trap devices for the study of VOCs in seawater samples. A sampling method based on purging volatile tracers out of water samples directly onto the needle traps has been developed and evaluated for DMS, isoprene, benzene, toluene, p-xylene,

(+)-α-pinene and (−)-α-pinene. Subsequently the method was applied in a CO2 enrichment field study. Seawater concentrations of dimethyl sulfide (DMS), isoprene and monoterpenes were monitored from May 8 to June 6, 2011. Datasets of DMS and isoprene during this period are presented here. These examples show contrasting responses upon ocean acidification. In the field, additional method validation was achieved for DMS through an inter-laboratory comparison Pirfenidone datasheet between our NTD GC–MS method and an independent purge and trap technique using gas chromatograph–flame photometric analysis (P&T GC–FPD). Commercial side-hole NTDs (needle trap devices) consisting of a 23-gauge, 60 mm long stainless steel needle, packed with 1 mg polydimethyl siloxane (PDMS), 0.4 mg Carbopack X and 0.5 mg Carboxen

1000 (1 cm each), were purchased from PAS Technology, Magdala, Germany (Fig. 1). Gas entering the needle trap was directed over the weaker adsorber first (PDMS). Prior to first use, the NTDs were conditioned in the gas chromatograph injection port at 300 °C for 30 min under a permanent helium flow (1 ml/min) to remove impurities. Gas tight syringes, glass fiber filters (25 mm, Whatman GF/F) and water sampling syringes (10 ml) were purchased from Sigma Aldrich. A commercial ZD1839 in vitro multi-component gas standard mix (Apel-Riemer Environmental Inc.) was used for calibrations (stated accuracy 5 %). Helium 6.0 and synthetic air (20.5 % O2, rest N2, hydrocarbon free) were from Westfalen AG, Germany. A sampling set up (supplied by PAS Technology) comprising of a mass flow controller (5–250 ml/min, calibrated on He), vacuum pump, voltage regulator, temperature regulator, purge tube heating body and a manual water inlet kit was used to extract VOCs from water samples. The set-up is shown schematically in Fig. 2. Glass purging tubes (10 ml sampling volume) including a bottom frit were prepared in the glass workshop of the Max Plank Institute in Mainz.