Spotlight on PFAS - Environmental Laboratory 21


a. Instrument calibration range is the actual concentration range of calibration standards used to determine calibration curves. b. Method calibration range is determined by multiplying the instrument calibration range by 1/250 to account for the SPE sample preparation/concentration.


c. R2 values are the average of triplicate calibration curves. Table 1. Instrument and method calibration ranges and linearity (R2) for eight-point calibration curves of all EPA Method 537.1 analytes and surrogates. Example: Validation study Compound PFBS PFHxA 13C2 13C3 -PFHxA -HFPO-DA


HFPO-DA PFHpA PFHxS ADONA PFOA PFOS PFNA


9Cl-PF3ONS PFDA


13C2 -PFDA


NMeFOSAA PFUnA


NEtFOSAA


d5-NEtFOSAA 11Cl-PF3OUdS PFDoA PFTrDA PFTA


Instrument Calibration Range (ng/L)a


16.4 - 26287 5.5 - 29703 4.6 - 24752 67.5 - 24752 18.5 - 29703 5.5 - 29703 5.2 - 28218 5.2 - 28218 5.5 - 29703 5.3 - 28515 18.5 - 29703 5.1 - 27772 81.0 - 29703 4.6 - 24752 5.5 - 29703 18.5 - 29703 5.5 - 29703 18.3 - 99010 5.2 - 28069 18.5 - 29703 5.5 - 29703 5.5 - 29703


Method Calibration Range (ng/L)b


0.07 - 105.1 0.02 - 118.8 0.02 - 99.0 0.27 - 99.0 0.07 - 118.8 0.02 - 118.8 0.02 - 112.9 0.02 - 112.9 0.02 - 118.8 0.02 - 114.1 0.07 - 118.8 0.02 - 111.1 0.32 - 118.8 0.02 - 99.0 0.02 - 118.8 0.07 - 118.8 0.02 - 118.8 0.07 - 396.0 0.02 - 112.3 0.07 - 118.8 0.02 - 118.8 0.02 - 118.8


R2 c


0.9994 0.9987 0.9989 0.9992 0.9985 0.9984 0.9998 0.9990 0.9998 0.9974 0.9993 0.9998 0.9990 0.9988 0.9998 0.9968 0.9968 0.9962 0.9997 0.9963 0.9959 0.9967


using EPA 537.1 A recent study validated PerkinElmer’s PFAS mitigative steps by employing EPA Method 533 9 a QSight®


and EPA Method 537.1 on 220 LC/MS/MS system (Figure 2). The method


involved fortifi cation with surrogates to monitor the extraction effi ciency.


250 mL drinking water sample was collected in a polyethylene bottle. The sample was concentrated by SPE using a polystyrenedivinylbenzene (SDVB) stationary phase. In this step, the sample was loaded onto the SPE tube and eluted with methanol. The extract was evaporated to dryness under nitrogen and reconstituted in 1 mL of 96% methanol. This concentrated the sample by a factor of 250, thereby enabling quantifi cation of the low levels necessary for the analysis. Internal standards were added after reconstitution of the sample.


Subsequently, 10 μL of sample was injected onto a C18 column in the LC/MS/MS instrument. The mass spectrometer was used in Multiple Reaction Monitoring (MRM) mode. Retention times for the calibration standards enabled identifi cation of the compounds and the MRM transitions, for both quantifi er and qualifi er ions.


Separation


EPA Method 537.1 describes a chromatographic technique that takes approximately 37 minutes to separate the 18 analytes, surrogates, and internal- standards. However, improvements to the chromatographic method made by PerkinElmer scientists achieved a run time of about 10 minutes. This represented signifi cant time savings while maintaining excellent chromatographic resolution, and excellent separation of the linear and branched isomers. An example of their separation is shown in Figure 3.


Calibration


a. Instrument LOD/LOQ was determined using the signal-to-noise ratio (S/N) of the peak from the lowest detectable calibration standard (5-18 ng/L) and extrapolating to the concentration at which the S/N = 3 or 10 for LOD or LOQ, respectively. This is an estimate to demonstrate expected LOD/LOQ and can vary from lab to lab.


b. Method LOD/LOQ is calculated by multiplying the Instrument LOD/LOQ by 1/250 to account for the 250 to 1 sample concentration from the SPE extraction. LOD/LOQ cannot be used as MRLs but provide an estimate of instrument sensitivity.


Table 2. Instrument sensitivity (LOQ & LOD) for all target analytes in EPA Method 537.1. Instrument (ng/L)a Analyte PFBS PFHxA


HFPO-DA PFHpA PFHxS ADONA PFOA PFOS PFNA


9Cl-PF3ONS PFDA


NMeFOSAA PFUnA


NEtFOSAA


11Cl-PF3OUdS PFDoA PFTrDA PFTA


LOD 2.00 2.31 6.70 2.10 0.38 0.24 2.57 0.92 2.52 0.60 2.17 0.29 3.50 0.25 0.44 2.02 1.55 4.29


LOQ 6.68 7.70


22.35 6.99 1.28 0.79 8.56 3.07 8.40 2.00 7.24 0.96


11.67 0.85 1.48 6.73 5.16


14.30 LOD


0.008 0.009 0.027 0.008 0.002 0.001 0.010 0.004 0.010 0.002 0.009 0.001 0.014 0.001 0.002 0.008 0.006 0.017


LOQ


0.027 0.031 0.089 0.028 0.005 0.003 0.034 0.012 0.034 0.008 0.029 0.004 0.047 0.003 0.006 0.027 0.021 0.057


Method (ng/L)b


Calibration curves were run for all 18 analytes and the surrogate standards, encompassing the range necessary to include the lower limits of detection (LOD) from EPA regulations. The full method ranged from 0.02 ppt to 120 ppt. As demonstrated in Table 1, excellent linearity was observed, with all correlation coeffi cient (R2 curves of 0.99 or better.


) values for the calibration Sensitivity


In terms of instrument sensitivity, the limits of quantitation (LOQ) and limits of detection (LOD) were estimated based on signal-to-noise ratios. Data reported in Table 2 confi rm that the QSight®


220 LC/MS/MS system is highly capable


of performing the method successfully. With the 250-to-1 sample concentration from the SPE extraction step, the limits were well below the current requirements for all compounds, even those at extremely low levels.


Experiments were conducted to defi ne the method detection limits of all target analytes for EPA Method 537.1. The lowest concentration minimum reporting limits (LCMRLs) as well as the experimental minimum reporting limits (MRLs) were also determined. Results are tabulated in Table 3. Experimental MRLs are at acceptable levels to meet the current requirements for all the targeted PFAS compounds.


Recovery


Recovery studies were completed for all 18 analytes by spiking fortifi ed laboratory fi eld blanks at four different levels, ranging from 0.3 ppt up to 80 ppt. Figure 4 shows the recoveries for each analyte at each of the four concentrations. EPA Method 537.1 requires recoveries between 70% to 130% of the known spiking level. The developed method using the QSight®


220 LC/MS/MS met requirements for recovery across all four concentrations evaluated. CONCLUSION


LC/MS/MS analysis of PFAS at ultra-trace levels requires mitigation to both liquid chromatograph and mass


may be constructed of PTFE; substitution with polyethylene stopcocks is recommended. Finally, sample collection during SPE extraction should employ polyethylene centrifuge tubes.


WWW.ENVIROTECH-ONLINE.COM


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44