AN AUTOMATED APPROACH FOR THE DETERMINATION OF GASOLINE RANGE ORGANICS (GRO) IN WATER BY GAS CHROMATOGRAPHY COUPLED WITH STATIC HEADSPACE SAMPLING


Goal The aim of this application note is to demonstrate the quantitative performance of the Thermo Scientifi c™


TriPlus™ determination of gasoline range organics in water.


Introduction Gasoline range organics (GRO) refer to hydrocarbons with a


carbon range from C6 to C10 that have boiling points ranging from 60 °C to 170 °C. These chemicals are often present in the environment, especially in ground water and soil, mainly as a consequence of contamination incidents. The source of contamination can be human errors and accidents (such as oil spills) that occur when handling, storing, or transporting oil and oil products. If GRO are detected, the level of contamination needs to be determined by using quantitative analytical methods; therefore, this represents a routine application for environmental analysis laboratories. GRO are highly volatile compounds that can be easily extracted from the matrix without the need for time-consuming sample preparation. Therefore, the analytical technique of choice for this application is headspace sampling coupled to gas chromatography and mass spectrometry and/or fl ame ionization detection. In this work, the headspace sampling technique coupled with gas chromatography-FID detection was employed to assess method sensitivity, precision, robustness, and linearity for quantitative assessment of GRO in water.


Experimental In all experiments, a TriPlus 500 HS autosampler was directly


interfaced (without the need for an external transfer line) to a Thermo Scientifi c™


TRACE™ 1310 Gas Chromatograph equipped with a Thermo Scientifi c™ Instant Connect split/ splitless SSL Injector and a Thermo Scientifi c™ Instant Connect


Flame Ionization Detector (FID). Chromatographic separation was achieved on a Thermo Scientifi c™


TraceGOLD™ TG-1MS


GC column, 30 m × 0.32 mm × 3.0 µm (P/N 26099-4840). Additional HS-GC-FID parameters are detailed in Table 1. The GC oven temperature program was optimized to reduce the analysis time and improve sample throughput; all peaks of interest elute in <13 minutes and the autosampler overlapping capability allows for long unattended sequences with automatic cycle time optimization.


Data acquisition, processing,


and reporting Data was acquired, processed, and reported using the Thermo Scientifi c™


Chromeleon™ Chromatography Data System


(CDS) software, version 7.2. Integrated instrument control ensures full automation from instrument set-up to raw data processing, reporting, and storage. Simplifi ed e-workfl ows deliver effective data management ensuring ease of use, sample integrity, and traceability.


Standard and sample preparation GRO standard mix at 1000 µg/mL was purchased from Restek (P/N 30095) and serially diluted using tap water to obtain seven stock solutions ranging from 6.25 µg/L to 10,000 µg/L (ppb). An


AET October / November 2019 www.envirotech-online.com


amount of these standard stock solutions (5 mL) was transferred into a 10 mL crimp cap headspace vial (vials P/N 10CV, caps P/N 20-MCBC-ST3) and used to assess method linearity, sensitivity, recovery, and repeatability.


Sample preparation Unleaded petroleum was diluted with reagent water to produce a sample stock solution at 5% and kept refrigerated at 4 °C. The sample stock was used to evaluate the matrix recovery and the quantitative accuracy and precision.


Results and discussion


Method linearity Linearity was evaluated by injecting seven calibration levels at 6.25, 12.5, 25, 50, 1000, 2500, and 10,000 µg/L (ppb). A list of target compounds is reported in Table 2. Each concentration level was prepared and analyzed in triplicate (n = 3). The calculated correlation coeffi cients (R2


) were 1.000 for all the investigated


gasoline organics. Moreover, the residual values (measured as % RSD of average response factors) were <6.5%, confi rming an excellent linearity (Figure 1).


Detection limit and accuracy


assessment (recovery) The method detection limit is defi ned as the minimum


500 Gas Chromatography Headspace (HS) Autosampler for the


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