250 mL
sample water with 1.25 g Trizma
Add surrogates
Figure 1. U.S. EPA Method 537.1 procedure workflow Table 1. Standard calibration solutions
Target PFAS conc. (µg/L)
100 50 20 10 5 2 1
0.5 0.2 0.1
Stock solution conc. (µg/L)
2000 100 100 100 10 10 10 10 10 10
Volume of stock solution (µL)
50
500 200 100 500 200 100 50 20 10
Table 2. Preparation of the fortified samples for the LCMRL test Fortified conc. (ng/L)
DI water with Trizma (mL)
32 8 4 2
0.8 0.4 0.2
Create extraction/cleanup methods in AutoTrace SPE workstation software
250 250 250 250 250 250 250
96% MeOH (µL)
950 500 800 900 500 800 900 950 980 990
Analyte stock conc. (µg/L)
100 100 100 10 10 10 10
Load/transfer methods to AutoTrace 280 instrument
Figure 2. General guideline for AutoTrace 280 sample extraction 8.0e4
9,10 15,16 17,18 20,21 5.0e4 2,3 2.5e4 6 7,8 22 19 11,12,13 14 23 24 25
Surrogate standard PDS (µL)
10 10 10 10 10 10 10 10 10 10
Volume stock solution (µL)
80 20 10 50 20 10 5
Perform extraction/cleanup from AutoTrace 280 front panel
Internal standard PDS (µL)
10 10 10 10 10 10 10 10 10 10
Surrogate standard. PDS (µL)
10 10 10 10 10 10 10
concentrations in the blank test.
The AutoTrace 280 system was modified to reduce Teflon components and replace them with alternative inert materials. The LC solvent lines were modified similarly, and an isolate column was installed prior to the injection to minimize the PFAS contamination. The Sample Path Cleaning method with methanol and water should be run after each sample in the extraction process. The Sample Path Cleaning method with methanol and water should be run whenever the system has been idle for more than 24 h. The Sample Path Cleaning method can be run a second time if needed to achieve a low background.
Calibration and quantification
For the calibration curves, nine concentrations (0.1, 0.2, 0.5, 1.0, 2.0, 5.0, 10, 50, and 100 µg/L) of standards were prepared and run. Calibration curves were created by plotting concentrations versus peak area ratios of analyte to internal standard. A linear regression or quadratic calibration curve was processed for each of the analytes with forced through zero setting as specified in U.S. EPA Method 537.1. Good fitting with the chosen model was obtained over the calibration range for all the method analytes. Figure 4 shows three typical calibration curves representing early, middle and late eluting PFAS.
The LCMRL and MDL
LCMRL is the lowest true concentration for which the future recovery is predicted to fall between 50% and 150% recovery with high confidence (99%). Detection limit (DL) is the minimum concentration of an analyte that can be identified, measured, and reported with 99% confidence that the analyte concentration is greater than zero. The calculated LCMRLs and DLs for each method analyte are presented in Table 4. The calculated LCMRLs ranged from 0.20 to 3.5 ng/L and the MDLs ranged from 0.30 to 2.5 ng/L.
Method precision and accuracy
Precision and accuracy were evaluated to determine the method’s extraction efficiency for PFAS determinations in drinking water samples. Two fortified concentration levels (16.0 ng/L and 80.0 ng/L) were analyzed to measure recovery and evaluate accuracy. At each concentration level, six replicate fortified samples were preserved, prepared, extracted, evaporated and reconstituted, and analyzed by the method.
1 0 3.75 5.0 7.5 Figure 3. LC-MS/MS chromatograms of PFAS at 4 µg/L standard solution
installed after the LC pump and prior to the injection valve to offset background contaminants from the LC pump, degasser, and mobile phases. To minimize the background PFAS peaks and to keep background levels constant, the time the LC column sits at initial conditions must be kept constant and as short as possible (while ensuring reproducible retention times). In addition, prior to daily use, flush the column with 100% methanol for at least 20 min before initiating a sequence. It may be necessary on some systems to flush other LC components such as wash syringes and sample needles before daily use.
* For information on LC conditions, please refer to reference 5.
Results and discussion LC-MS/MS chromatograms
Figure 3 shows the chromatograms of 4 µg/L PFAS standards. The peak identification information along with the peak asymmetry
10.0 Minutes 12.5 15.0 Conclusions
factors, retention times, and internal standards are listed in Table 3. All the analytes are detected in 15 minutes and peak asymmetry factors are within 0.8– 1.2, meeting the U.S. EPA Method 537.1 requirement.
Demonstration of low system background
To ensure that no potential background contaminants interfere with the identification or quantitation of method analytes, a low system background needs to be demonstrated before running the samples. The minimum reporting level (MRL) of U.S. EPA Method 537.1 for the 18 PFAS is 0.53–6.3 ng/L. The interference from solvents, reagents, containers, and SPE instrument needs to be maintained below 1/3 of the MRL value. Interference can come from contaminants of similar properties and also from the analytes that are present in many common laboratory supplies and SPE devices. The EPA method emphasizes that care must be taken with automated SPE systems to ensure that PFAS safe material used in these systems does not contribute to unacceptable analyte
The results demonstrated that the method described can be used for the extraction and determination of 18 PFAS in drinking water with a PFAS-safe AutoTrace 280 extraction system and LC-MS/MS. The modified AutoTrace 280 extraction system ensures inertness and prevents PFAS from leaching into sample during extraction, while at same time delivering consistent and reliable performance. Both sample path cleaning in SPE and separation method precaution for the LC system maintained a low system background, meeting the EPA method requirement. The calculated LCMRLs ranged from 0.20 to 3.5 ng/L and the MDLs ranged from 0.30 to 2.5 ng/L, which were below or comparable to those values reported in U.S. EPA Method 537.1. At both 16.0 ng/L and 80.0 ng/L fortified concentration levels, all the recoveries were within the acceptable range of 70–130%. The calculated RSDs were all less than 10%, suggesting good precision. Thermo Scientific LC-MS/MS with the automatic extraction AutoTrace 280 system demonstrated an efficient, reliable, and sensitive method to fulfill the requirements of U.S. EPA Method 537.1.
4,5
The precision and accuracy results of the method are presented in Table 5. At both 16.0 ng/L and 80.0 ng/L fortified concentration levels, all recoveries were within the acceptable range of 70–130% according to U.S. EPA Method 537.1, ranging from 84.1% to 123%. The calculated relative standard deviations (RSD) were all less than 10%, suggesting good precision.
Extract with AutoTrace 280
Evaporate to dryness and reconstitute in 96% MeOH
Add internal standards
Analyze by LC-MS/MS
WWW.ENVIROTECH-ONLINE.COM AET ANNUAL BUYERS’ GUIDE 2020
Counts
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 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76
