Concentrating a suite of semi-volatile compounds from EPA method 625 using TurboVap® II

Introduction

There are a wide range of volatile and semi-volatile contaminants finding their way into both terrestrial bodies and water sources worldwide. In the United States (US), the contaminants are analysed according to stipulated US-EPA methods. In the European Union (EU), a large number of these same compounds are tested according to the European Water Framework Directive. Though these analytes are approached differently from a regulatory perspective, it is clear that background monitoring occurs on a global basis. Initial extraction of these analytes depends on the matrix being analysed and is often a multifaceted process, but ultimately analysts are presented with some form of extraction/organic solvent they must concentrate to achieve instrumental limits of quantification. Presented within this application note are the results of such an evaporative process using the new Biotage TurboVap® II.

The new TurboVap® II is built on the solid foundations of reliability and performance that made it the market leader for solvent evaporation. The modern design incorporates many new customer driven features for easier use and expanded functionality. TurboVap II still utilizes the highly efficient patented gas vortex shearing technology, which is synonymous with the TurboVap brand.

This modern design features many new enhancements, including a well-lit glass tank for much greater visibility of the samples, improved sensors with automatic end-point detection, user replaceable nozzles, easy access drain port, and a colour, menu driven touchscreen for simple operation and monitoring. The system can be vented from the bench or placed in the fume hood. Because the footprint is noticeably smaller on this modern unit, less space is required.

Experimental

A TurboVap® II evaporation system (P/N 415001) was operated with a TurboVap II Rack with End-Point Sensors 6 Positions, 200 mL Tubes (P/N 415100) using 1 mL end-point evaporation tubes (P/N C128506).

Dichloromethane (DCM), a mixed analyte standard P/N 506559 and p-Terphenyl were all purchased from Sigma-Aldrich.

180 mL of DCM was added into six 200 mL, 1 mL end-point evaporation tubes and spiked with 20 µg of each analyte to provide a concentration of ~111 ng/mL. The system was initially operated using the parameters documented in table 1.

Evaporation was automatically halted once the end-point sensors detected the solvent had reached the cut off volume (~ 0.7 mL). p-Terphenyl was added at a concentration of
20 µg/mL to each of the six tubes to act as an external standard and enable response factor (Response Factor) generation. Using a pipette, the concentrated extract was transferred to a screw capped autosampler vial and the inner walls of the evaporator tube rinsed with DCM ensuring a final volume of 1 mL.

The experimental procedure was repeated a second time but in place of a constant 2.8 L/min gas flow, a ramped gradient flow was applied as detailed in table 2.

Analysis

Gas chromatography-mass spectrometry (GC-MS) was used for the quantitative determination of each analyte following evaporation. GC separation was carried out on an Agilent 7890A equipped with QuickSwap. Separation of target analytes was achieved using an Agilent J&W DB-5ms, 30 m x 0.25 mm ID x 0.25 μm cartridge. Oven parameters were as follows; initial temperature of 40 °C with a 2 minute isocratic hold. Ramp conditions were 20 °C/min to 290 °C and a hold for 1.5 minutes, followed by a second ramp 100 °C/min to 325 °C held for 4.6 minutes providing a total run time of 20.95 minutes. Post run the cartridge was back flushed for 2.4 minutes (approximately
3 void volumes).

Injection volume was set at 2 µL, whilst using helium at a flow rate of 1 mL/min (constant flow) as the carrier gas. The inlet was set to operate in split-less mode and inlet temperature was maintained at 300 °C with a purge flow of 50 mL/min at
0.8 minutes.

The GC system was coupled directly to an Agilent 5975C mass spectrometer, with the transfer line temperature set at 300 °C. The MS was operated in electron impact ionization (EI), acquiring data in full scan mode between 40 and 285 m/z. Source and quadrupole temperature were maintained at 230 and 150 °C respectively, whilst a 4 minute solvent delay was maintained.

Results

Table 3 shows the results of the evaporation and instrumental analysis. A total of n=6 replicates for each of the two evaporation methods were analysed and the averages are presented. Recovery and RSD values were calculated by comparing the peak area response of p-Terphenyl in a standard and the processed samples and generating a RF. This RF was then used to volumetrically normalize the results for the processed samples when compared to the standard.

Conclusion

The new TurboVap® II evaporation system provides excellent recoveries and RSDs for a wide range of semi-volatile compounds. With two options available for tube sizes 50 or 200 mL and either 0.5 or 1.0 mL end-point the system can be used with solvent extracts derived from a wide range of
extraction methodologies, including Solid Phase Extraction, Supported Liquid Extraction, Liquid-Liquid Extraction, Continuous Liquid-Liquid Extraction, TLCP Extracts, Pressurized Fluid Extraction, and Ultrasonic Extraction.

Ordering information

Literature number: AN879