Page 9 - Food&Beverages PFAS_analysis

Sample Preparation and Injection Figure 2: PFAS compounds before

and after vortexing a 50 ng/L standard
Some currently published methods (EPA 537, EPA 537.1) require a step of
allowed to sit for 24 hours
sample pre-concentration by solid phase extraction (SPE). Materials used in
the manufacturing of supplies for preparing the samples by SPE may also BEFORE VORTEX
contain PFAS. To avoid pre-concentrating the background PFAS during this

step of the analysis, all new SPE cartridges, solvents and vials for collecting

samples must be tested for PFAS prior to the first use.

PFAS-free tubing should be used for loading samples into the cartridges.

If automatic sample extractors are employed for this step of the analysis,

checking with the manufacturer is strongly recommended to identify
all components made of PFTE and replace them when feasible.

Once samples are pre-concentrated and ready for injection in the

LC-MS/MS or samples are prepared accordingly to methods that allow
for large volume injection (ASTM D7979), they may sit in the autosampler AFTER VORTEX
tray for extended periods of time. In these situations, some PFAS

compounds may settle, precipitate or adsorb on the surface. It is important

to remember to mix the extract/sample before (re)injection. Vortexing the
solution before injection ensures a homogenous solution and optimum
results. Figure 2 shows the chromatogram of the PFAS compounds before

and after vortexing a 50 ng/L standard allowed to sit for 24 hours. The

recovery of the long-chain PFAS is considerably lower before vortex.

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