Fast and High-Resolution LC-MS Separation of PFAS

Petra Lewits, Cory Muraco, Product Manager Liquid Separations, Johanna Simon, Scientist Central Analytics

Merck

Article from Analytix Reporter - Issue 11

Introduction

PFAS (Per- and poly-fluoroalkyl substances) are persistent, man-made organic compounds, widely found in the environment. Recent awareness about their toxicity has led the U.S. Food and Drug Administration (FDA) and the U.S. Environmental Protection Agency (EPA) to initiate actions against PFAS. Hence reliable and fast methods for their determination are needed.

EPA has developed, validated, and published three methods to support the analysis of 29 PFAS in drinking water, Method 533, 537 and 537.1. EPA 8327 covers the analysis of selected per- and polyfluoroalkyl substances (PFAS) in prepared extracts of various matrices (e.g., waters and solids) by liquid chromatography/tandem mass spectrometry (LC-MS/MS) analysis.

As technological advancements continue to progress, mass spectrometers will continue to be improved regarding their level of sensitivity, mass resolution, and scanning speed. This will impact future developments in PFAS analysis, and column performance must be able to handle these advancements. With this in mind, the below method for the separation at maximum speed was developed to test the suitability of the columns for use in these advanced conditions.

The column of choice for PFAS analysis by LC-MS(/MS) is a C18 column. The Ascentis^® Express PFAS columns are based on superficially porous silica particles (SPP) with C18 modification and are specifically tested using a PFAS compound mixture. This ensures the suitability and reliable performance of these columns for an efficient PFAS analysis.

PFAS compounds originating from the HPLC system and materials used for the analysis are a concern. Therefore, it is recommended to place a delay column before the injection port in the system (Figure 1). The Ascentis^® Express PFAS Delay column provides exceptionally high retention of PFAS compounds across the various mobile phase conditions. It efficiently delays the PFAS background contamination that originates from the instrument and therefore prevents co-elution with the PFAS compound present in the sample (Figure 1).

Figure 1. LC-MS instrumental set-up for PFAS analysis & results of perfluorooctanoic acid (PFOA) (MRM 413.0>368.0) using a delay column.

LC-MS Analysis of PFAS - 33 Compounds in 5 minutes

The rapid separation of 33 PFAS compounds found in EPA 537.1, EPA 533, and EPA 8327 demonstrates that the Fused-Core^® technology of Ascentis^® Express PFAS HPLC columns benefits the PFAS analysis for fast, efficient, and rugged separations― paramount to environmental analysis (Figure 2).

Figure 2. 33 PFAS Compounds in 5 min (see conditions below).

Sample Compounds

Peak	Compound	Transition	Retention Time (min)
1	PFBA	213.0000>169.0000	0.755
2	4:2FTS	229.0000>85.0000	1.031
3	PFPeA	263.0000>219.0000	1.762
4	PFBS	299.0000>80.0000	1.979
5	PFHpS	279.0000>85.0000	2.035
6	PFPeS	315.0000>135.0000	2.273
7	PFMPA	327.0000>307.0000	2.454
8	PFHxA	313.0000>269.0000	2.514
9	PFEESA	349.0000>80.0000	2.599
10	HFPO-DA	285.0000>169.0000	2.670
11	PFHxS	399.0000>80.0000	3.013
12	NaDONA	377.0000>251.0000	3.033
13	ADONA	377.0000>250.9	3.034
14	FOSA	427.0000>407.0000	3.299
15	PFOA	413.0000>369.0000	3.316
16	PFMBA	449.0000>80.0000	3.328
17	PFHpA	363.0000>319.0000	3.388
18	PFOS	499.0000>80.0000	3.588
19	9Cl-PF3ONS	530.9>351.0000	3.719
20	8:2FTS	549.0000>80.0	3.816
21	PFNS	527.0000>507.0000	3.820
22	PFDA	513.0000>469.0000	3.822
23	N-MeFOSAA	570.0000>419.0000	3.925
24	PFNA	463.0000>419.0000	3.942
25	NFDHA	599.0000>80.0000	4.015
26	PFUnA	563.0000>519.0000	4.025
27	N-EtFOSAA	584.0000>419.0000	4.029
28	6:2FTS	498.0000>78.0000	4.033
29	11Cl-PF3OUdS	630.7>451.0000	4.110
30	PFTrDA	663.0000>619.0000	4.355
31	PFDoA	613.0000>569.0000	4.496
32	PFTeDA	713.0000>669.0000	4.745
33	PFDS	295.0000>201.0000	4.921

LC Conditions
Analytical Col.:	Ascentis® Express 90Å PFAS, 10 cm x 2.1 mm, 2.7 µm (53559-U)
Delay Col.:	Ascentis® Express 90 Å PFAS Delay, 5 cm x 3 mm, 2.7 µm (53572-U)
Mobile Phase:	[A]10 mM Ammonium acetate; [B] Methanol
Gradient:	Time (min)	%B
	0.0	33.0
	4.0	98.0
	4.1	100.0
	6.0	100.0
	6.1	33.0
	7.5	End
Flow Rate:	0.4 mL/min
Pressure:	485 bar
Temperature:	35 °C
Detection:	ESI (-) MS/MS; ESI LCMS system: Shimadzu LCMS-8040; Spray voltage: -2.0 kV; Nebulizing gas: 2 L/min; Drying gas: 15 L/min; DL temp: 250 ˚C; Heat block: 400 ˚C
Inj. Vol.:	2.0 µL
Sample Solvent:	Methanol (96%), water (4%)

See more for PFAS testing at SigmaAldrich.com/PFAS