We are very pleased to announce the availability of the EPA’s newest PFAS method EPA 1621 Draft: Screening Method for the Determination of Adsorbable Organic Fluorine (AOF) in Aqueous Matrices by Combustion Ion Chromatography (CIC). Our work on Method 1621 continues our long tradition of PFAS excellence and our commitment to helping people measure PFAS at the highest levels of quality.

What is Method 1621?

EPA Draft Method 1621 is a method for the determination of Adsorbable Organic Fluorine (AOF) in aqueous samples. The method. estimates an aggregate concentration of organofluorine compounds in the sample that are retained on an activated carbon sorbent. Results are reported as the concentration of fluoride in the sample.

Why use Method 1621?

With the number of PFAS in the environment exceeding 6000+, there is a compelling need to understand the “total” PFAS load in a sample. All previous EPA methods for PFAS such as 537.1, 533 and 1633 only report the concentrations of specific PFAS such as PFOS and PFOA and lists of up to 40 PFAS. EPA 1621 provides methods for one such “total” proxy estimate: Adsorbable Organic Fluorine or AOF where organic compounds are adsorbed on a carbon cartridge and combusted, with the fluorine from the combustion being reported as a screening level estimate of “total” PFAS. The EPA expects that in addition to monitoring specific PFAS of interest, there will also be a need to measure at a screening level, the organic fluorine presence in a sample in order to understand the extent of PFAS presence and to inform characterization, remediation and water purification decisions. .

What you need to know

• The EPA defines AOF by 1621 as a “method defined parameter”. An MDP is a parameter defined solely by the method used to determine the analyte. In other words, 1621 needs to be performed as written for the results to be compliant with 1621.
• Adsorbable Organic Fluorine as a proxy for total PFAS comes with a few caveats.
  1. Firstly, not all PFAS are adsorbed to the same extent on carbon. Shorter chain (C4 and below) PFAS have lower capture efficiencies and longer chain PFAS are subjective to wall/container losses.
  2. 1621’s AOF estimate will include all organic compounds containing fluorine. Several pharmaceuticals and some pesticides/other chemicals contain fluorine, but do not meet the EPA’s definition of PFAS.
• Unlike other PFAS methods, 1621 produces a blank-subtracted estimate, as background fluorine is very hard to eliminate completely.
• AOF is only one estimation method for PFAS by CIC. For example, PFAS can also be adsorbed on a weak anion cartridge prior to elution and combustion. This provides an estimate known as Extractable Organic Fluorine (EOF). This method can be applied to solid and tissue matrices in addition to aqueous matrices.

Method Details

Parameter	Details	Remarks
Matrices	Water, wastewater, other aqueous
Sample size	100 mL
Sample details	3 bottles per sample, 120 mL HDPE or Polypropylene wih linerless lids.	One bottle for analysis, one for TOC, TSS and other screening test, and one for repeats. Additional needed for MS/MSD
Sample hold time	90 days
Sample storage	0 to 6  ͦC in the dark
Batch size	10 samples + QCs
Reporting limit	1.5 ug/L.	Based on MDL, blank subtracted
QCs	2 blanks, LCS (OPR), MS/MSD
Sample limitations	TSS < 100 mg L, up to 140 mg/L with a quartz wool pre-filter, TOX < 140 mg/L, total fluoride < 8 mg/L, total chloride < 500 mg/L, no residual chlorine and pH > 5.	For all deviations other than pH and residual chlorine, only recourse is a reduced sample size. For pH, adjust with KOH, and quench residual chlorine with thiosulfate.

Method Summary

AOF analysis is performed on aqueous samples by passing them through two activated carbon cartridges connected in series.  Each cartridge is then rinsed to remove inorganic fluoride. The contents of each cartridge are transferred to a ceramic boat which is combusted to mineralize organic compounds. The organic fluorine is converted into Hydrogen fluoride (HF).  The produced HF is adsorbed into solution which is then analyzed for fluoride by ion chromatography. The ion chromatograph is calibrated with inorganic fluoride solutions which are also combusted. Batches include multiple blanks, lab control spikes and matrix spike/duplicates (MS/MSD) that use perfluorohexane sulfonate (PFHxS) as the model spiking PFAS. AOF is reported as the blank corrected sum of the AOF on the first and second carbon cartridges. There is a background fluorine signature from the carbon columns and the combustion/adsorption system so blank detects are expected and corrected for.