Demonstration of low PFAS background associated with the TurboVap® LV

Environmental laboratories require a system which is clean, reliable, and affordable to evaporate the extracts resulting from the preparation of samples for PFAS testing. This document will outline a protocol that was developed for the TurboVap® LV system to evaporate extracts in methanol to dryness consistent with typical environmental PFAS procedures. It will also show data resulting from this protocol which demon- strates the cleanliness of the system for PFAS compounds using a sample analogue.

Experimental design
 

To simulate a standard PFAS extract which would result from either an automated or a manual solid-phase extraction (SPE) procedure, 15 mL of methanol was added directly to polypropylene centrifuge tubes (VWR p/n 21008-670). The centrifuge tubes were loaded onto the 48-position Multi Rack within a TurboVap® LV and the protocol provided in Table 2 was used to concentrate the samples to dryness. The dry extracts were reconstituted in 1-mL storage vials using 990 μL of 96% methanol/4% water and 10 μL of an internal standard mixture was added. The resulting extracts were analysed on an LC-MS/ MS for the target compounds given in Table 1.

Table 1. PFAS analytes examined as possible contaminants within the evaporation and analysis steps of a standard extraction procedure.

Note: For more in-depth information on the preparation procedure or the materials and equipment used, please refer to application note AN958 entitled “Manual Extraction of PFAS in Drinking Water in Compliance with EPA Method 537.1.

Table 2. TurboVap® LV Concentration Protocol.

*The nozzle position was adjusted such that it was as far to the right as possible to give the user a clear view of the vortex within the tube.

Results

The data shown in Table 3 was generated using a protocol with a Minimum Reporting Level (MRL) of 2 ng/L for all compounds. In the cases where certain compounds were available only in their salt form, the masses of the compounds were adjusted accordingly to correct for the salt content (Table 3). As typical of many environmental methods, for a system to be deemed “clean,” it must demonstrate that any background present is less than one-third of the MRL (1/3 MRL). An examination of the background data collected shows that the highest observed concentrations detected for all analytes are approximately 3.5x lower than the 1/3 MRL limit given by typical environmental methods.

Table 3. Results of PFAS Evaporation Background Study (recoveries in ng/L).

*Analytes were used in their salt form and calculated concentrations were corrected to compensate where needed.

Note: Where “N.D.” is indicative of the inability of the target peak to be separated from the system background.

Figure 1. PFAS Background of the TurboVap® LV.

*Analytes were used in salt form and their calculated concentrations were corrected to compensate.

Discussion

Separating the sample preparation process into its major components and examining them independently allows for the systematic elimination of factors contributing to the background of the overall process. In this document, the extraction process for a typical PFAS environmental sample was eliminated, and the evaporation and analytical processes were examined using a sample analogue. The experiment demonstrates that the TurboVap® LV, along with the other supplies and equipment used, fulfil the requirements for PFAS background levels and are thus acceptable to use in the general production of PFAS data for environmental compliance work.

Ordering information

Literature number: AN961