DETERMINATION OF PER- AND POLYFLUORINATED ALKYL SUBSTANCES (PFAS) IN DRINKING WATER USING AUTOMATED SOLID-PHASE EXTRACTION AND LC-MS/MS
GOAL TO DEMONSTRATE AN EFFICIENT AND RELIABLE SOLID-PHASE EXTRACTION METHOD WITH THE THERMO SCIENTIFIC™
DIONEX™ AUTOTRACE™
Per- and polyfl uorinated alkyl substances (PFAS) are a group of man-made chemicals including perfl uorooctanoic acid (PFOA), perfl uorooctanesulfonic acid (PFOS), and GenX chemicals that have been manufactured and used in a variety of industries globally.1,2
POLY-FLUORINATED COMPOUNDS IN DRINKING WATER PER U.S. EPA METHOD 537.1. Introduction
• Thermo Scientifi c™ TSQ Fortis™ triple quadrupole mass spectrometer
• Organomation Associates™ Evaporator
These compounds have a wide range of commercial
product applications including industrial polymers, stain repellents, surfactants, waterproofi ng products, packaging, and aqueous fi lm forming foams used for fi refi ghting. PFAS are highly soluble in water, chemically stable, persistent in the environment, and can accumulate in the human body over time, leading to adverse human health effects.3
PFOA and PFOS are no longer
manufactured in the United States due to their persistence and potential human health risks.
In November 2018, the United States Environmental Protection Agency (U.S. EPA) published Method 537.1 “Determination of selected per- and polyfl uorinated alkyl substances in drinking water by solid phase extraction and LC/MS/MS”.4
12 Position N-EVAP Nitrogen
* For information on reagents, standards and consumables, please refer to reference 5.
Method workfl ow
Figure 1 shows the workfl ow of the method that applies to the test blank, LCMRL, and the precision and accuracy test samples. Trizma (1.25 g) was added to the 250 mL water samples as a preservation reagent to remove free chlorine.
The method uses
an offl ine solid-phase extraction (SPE) with liquid chromatography tandem mass spectrometry (LC-MS/MS) to extract, enrich, and determine 18 PFAS in drinking water.
Currently most testing laboratories perform the sample extraction manually using a vacuum manifold, which is labor-intensive, time- consuming, and the fl ow rate through the cartridge is diffi cult to control. There is a high demand for automation of the SPE procedure.
This article will discuss the development of an analytical method using an automated SPE system, AutoTrace 280, and LC-MS/MS for the determination of 18 PFAS following the guidelines provided by U.S. EPA Method 537.1.
The method discussed in this article demonstrated that the AutoTrace 280 system provides reliable automated SPE for determination of PFAS in large-volume (20 mL–4 L) aqueous samples.
Experimental Instruments • Thermo Scientifi cTM
Ten microliters of the Surrogate Primary Dilution Standard (SUR PDS) were added prior to SPE extraction. After extraction with the AutoTrace 280 system, the extraction eluent was evaporated to dryness under nitrogen gas fl ow at 55–60 °C and reconstituted with 1 mL 96%/4% MeOH/ water. Ten microliters of Internal Standard Primary Dilution Standard (IS PDS) were then added to the extraction eluent. After suffi cient vortexing, the sample was transferred to a PFAS-free vial and was ready for LC-MS/MS analysis.
Sample preparation
Reagent water - Water that does not contain any measurable quantities of method analytes or interfering compounds greater than 1/3 the minimum reporting level (MRL) for each method analyte of interest. For this work, water was obtained from a bench model Millipore water purifi cation system (Millipore Corp, Billerica, MA, Model No. Milli-QR Gradient A10 or equivalent). This water is referred to as deionized water (DI water) in this article.
Standard calibration solution - The PFAS PDS was diluted with 96%/4% MeOH/DI water to produce standard solutions containing different concentration levels of each PFAS. The IS PDS and SUR PDS were added to each calibration standard at a constant concentration. The standard calibration solutions were used to quantify all the samples (Table 1).
DionexTM AutoTraceTM 280 PFAS System
• Thermo Scientifi c™ Vanquish™ Flex Duo UHPLC system, fi tted with Thermo Scientifi c™ PFC free kit
Lowest Concentration Minimum Reporting Level (LCMRL) and Method Detection Limits (MDL) solution - To determine LCMRL, seven replicates of fortifi ed samples prepared at different concentration levels (0.2, 0.4, 0.8, 2.0, 4.0, 8.0, and 32 ng/L,
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280 INSTRUMENT FOR THE DETERMINATION OF PER- AND
preparation details are in Table 2) were processed through the entire method procedure (Figure 1). The LCMRLs were calculated according to the procedure in reference 1.
MDLs were determined by running seven replicate fortifi ed samples at a concentration of 4 ng/L through the entire method procedure.
AutoTrace 280 sample extraction
The AutoTrace 280 system was modifi ed to reduce Tefl on™ components and replace with alternative inert materials. Historically, the solvent side lines of the AutoTrace 280 system were used for the condition, dry, and elute functions and the sample side lines were used for sample loading and rinsing. The line function per the U. S. EPA Method 537.1 requirement was modifi ed in the method discussed. The solvent side lines were used just to condition and dry the cartridges. The sample side lines were used in sample load, rinse, and elute to maximize PFAS recoveries. Thus, both solvent and sample lines need to be fl ushed in the sample path cleaning step. Figure 2 shows a general guideline for AutoTrace 280 sample extraction.
Create methods in the AutoTrace 280 SPE workstation software
The AutoTrace 280 extraction and cleanup methods for PFAS are specifi ed below following U.S. Method EPA 537.1 guidelines and are divided into three parts (methods), cartridge conditioning and sample loading, sample elution, and sample path cleaning. These methods are loaded into the AutoTrace 280 instrument from the software provided with the system and run sequentially.
* For information on the three methods and solvent used, please refer to reference 5.
LC-MS/MS analysis
LC system components, as well as the mobile phase constituents, may contain many of the analytes in this method. Thus, a Thermo Scientifi c™
PFC-free kit which includes PFAS-free tubing, fi ttings,
solvent fi lter inlets, and sample vials is strongly recommended. An isolator column, a Hypersil BDS C18, 2.1 x 50 mm column, was
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