The chromatographic parameters used in the method resulted in good separation of the 80 VOC compounds in less than 7 minutes, as shown in Figure 2. Initial calibration (ICAL) with scan data The operating parameters are listed in Table 1. Agilent MassHunter Workstation software was used for data acquisition and processing.įigure 1 shows the system configuration used here. The ISTD/surrogate mix was added to each calibration stock solution at a level to give 5 µg/mL of each compound in the water. The spiking stock solutions were prepared in methanol using an Agilent 73-compound standard (DWM-525-1), an Agilent six-compound gas standard (DWM-544-1), and an Agilent three-compound ISTD mix (STM-320N-1), containing fluorobenzene (internal standard), 1,2-dichlorobenzene-d4 (surrogate), and BFB (surrogate). After capping, each vial was vortexed vigorously for 20 seconds, before placement in the headspace sampler. Five grams of anhydrous sodium sulphate were weighed into each vial before the addition of water and spiking solution. A pulsed split injection was used with the split ratio set to 21:1.Įight calibration levels ranging from 0.05 to 25 µg/L were prepared in water by spiking 5 µL of a corresponding stock solution (which also included the ISTD) into 10.0 mL of water in a 20 mL headspace vial. The Headspace Sampler was connected to the GC carrier gas inlet line between the GC control pneumatics and the GC injection port. The analytical method used an Agilent Ultra Inert straight-through 1.0 mm GC inlet liner and a DB 624 UI column, 20 m × 0.18 mm, 1 µm. A HydroInert source (G7078-60930 for the fully assembled source with 9 mm lens) was used in the MSD, and autotuned using the etune tuning algorithm. The Agilent 5977C Inert Plus MSD was coupled to the Agilent 8890 GC equipped with a multimode inlet (MMI) and an Agilent 8697 headspace sampler. SIM has a substantial advantage in the signal-to-noise ratio and is preferred where quantitation to low levels is required. It can also be used retrospectively to search for compounds that may become of interest in the future. Scan is useful for confirming the identity of found targets, and for identifying nontarget compounds. This method uses a system configured to perform static headspace/GC/MS analysis of VOCs in drinking water, optimised for using hydrogen as the carrier gas.īoth scan and SIM modes of data acquisition were evaluated. Purge and trap and static headspace are two commonly used automated sampling techniques that extract the VOC analytes from water samples and inject them into the GC/MS. GC/MS offers both the sensitivity and selectivity required to identify and quantify VOCs. Due to the large number of potential contaminants, and the need to measure them at such low levels, GC/MS systems are commonly used. Regulations governing the allowable concentration of VOCs in drinking water vary by country and region but are typically in the low µg/L (ppb) range. Another common source is when VOCs are formed by the addition of chlorine (used to disinfect the water) and react with natural organic matter in the source water. These compounds can appear in drinking water by contamination from numerous sources, including industrial and commercial operations. One of the analyses commonly used to ensure that the quality of drinking water is the measurement of volatile organic compounds (VOCs). As demonstrated in this note, the system gives excellent results for the analysis of VOCs in drinking water. In both modes, quantitative calibration was performed for the 80 compounds over the range of 0.05 to 25 µg/L. For the scan data, spectra were deconvoluted with MassHunter Unknowns Analysis software and searched against NIST 20 to assess the spectral fidelity. Standards and samples were analysed in both scan and SIM data acquisition modes. In addition to the new source, the chromatographic conditions were optimised to provide separation of 80 volatile compounds in 7 minutes. The new source, named HydroInert, was used in the system evaluated here to test volatile organic compounds (VOCs) in drinking water. Therefore, a new EI source for GC/MS and GC/MS/MS was developed and optimised for use with hydrogen carrier gas. This can lead to disturbed ion ratios in the mass spectrum, spectral infidelity, peak tailing, and nonlinear calibration for some analytes. However, hydrogen is not an inert gas, and may cause chemical reactions in the mass spectrometer electron ionisation (EI) source. For GC/MS, hydrogen is the best alternative to helium, and offers potential advantages in terms of chromatographic speed and resolution. Recent concerns with the price and availability of helium have led laboratories to look for alternative carrier gases for their gas chromatography mass spectrometry (GC/MS) methods.
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